Coastal Sensitivity to
Sea-Level Rise:
A Focus on the
Mid-Atlantic Region
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FEDERAL EXECUTIVE TEAM
Director, Climate Change Science Program: William J. Brennan
Director, Climate Change Science Program Office: Peter A. Schultz
Lead Agency Principal Representative to CCSP,
National Program Director for the Global Change
Research Program, U.S. Environmental Protection Agency: JoelD. Scheraga
Product Lead, Chief, Climate Science and Impacts Branch
U.S. Environmental Protection Agency, Climate Change Division: RonaE. Birnbaum
Chair, Synthesis and Assessment Product Advisory Group
Associate Director, National Center for Environmental
Assessment, U.S. Environmental Protection Agency: Michael W. Slimak
Synthesis and Assessment Product Coordinator,
Climate Change Science Program Office: FabienJ.G. Laurier
EDITORIAL AND PRODUCTION TEAM
Chair James G. Titus, U.S. EPA
Scientific Editor Jessica Blunden, STG, Inc.
Scientific Editor Anne M. Waple, UCAR
Technical Advisor David J. Dokken, USGCRP
Graphic Design Lead Sara W. Veasey, NOAA
Graphic Design Co-Lead Deborah B. Riddle, NOAA
Designer Glenn M. Hyatt, NOAA
Designer Deborah Misch, STG, Inc.
Designer Christian Zamarra, STG, Inc.
Copy Editor Anne Markel, NOAA
Copy Editor Lesley Morgan, STG, Inc.
Copy Editor Susan Osborne, STG, Inc.
Copy Editor Susanne Skok, STG, Inc.
Copy Editor Mara Sprain, STG, Inc.
Technical Support Jesse Enloe, STG, Inc.
Disclaimer: This document, part of the Synthesis and Assessment Products described in the U. S. Climate Change
Science Program (CCSP) Strategic Plan, was prepared in accordance with Section 515 of the Treasury and Gen-
eral Government Appropriations Act for Fiscal Year 2001 (Public Law 106-554) and the information quality act
guidelines issued by the U.S. Environmental Protection Agency pursuant to Section 515. The CCSP Interagency
Committee relies on U.S. Environmental Protection Agency certifications regarding compliance with Section 515
and Agency guidelines as the basis for determining that this product conforms with Section 515. For purposes of
compliance with Section 515, this CCSP Synthesis and Assessment Product is an "interpreted product" as that
term is used in U.S. Environmental Protection Agency guidelines and is classified as "highly influential". This
document does not express any regulatory policies of the United States or any of its agencies, or provide recom-
mendations for regulatory action.
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Coastal Sensitivity to
Sea-Level Rise:
A Focus on the
Mid-Atlantic Region
Synthesis and Assessment Product 4.1
Report by the U.S. Climate Change Science Program
and the Subcommittee on Global Change Research
Coordinating Lead Author:
James G.Titus
Lead Authors:
K. Eric Anderson, Donald R. Cahoon, Dean B. Gesch, Stephen K. Gill,
Benjamin T. Gutierrez, E. Robert Thieler, and S. Jeffress Williams
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January, 2009
Members of Congress:
On behalf of the National Science and Technology Council, the U.S. Climate Change Science Program
(CCSP) is pleased to transmit to the President and the Congress this Synthesis and Assessment Product
(SAP) Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region. This is part of a series
of 21 SAPs produced by the CCSP aimed at providing current assessments of climate change science to
inform public debate, policy, and operational decisions. These reports are also intended to help the CCSP
develop future program research priorities.
The CCSP's guiding vision is to provide the Nation and the global community with the science-based
knowledge needed to manage the risks and capture the opportunities associated with climate and related
environmental changes. The SAPs are important steps toward achieving that vision and help to translate
the CCSP's extensive observational and research database into informational tools that directly address
key questions being asked of the research community.
This SAP assesses the effects of sea-level rise on coastal environments and presents some of the chal-
lenges that will need to be addressed to adapt to sea-level rise. It was developed in accordance with the
Guidelines for Producing CCSP SAPs, the Information Quality Act (Section 515 of the Treasury and
General Government Appropriations Act for Fiscal Year 2001 (Public Law 106-554)), and the guidelines
issued by the U.S. Environmental Protection Agency pursuant to Section 515.
We commend the report's authors for both the thorough nature of their work and their adherence to an
inclusive review process.
Sincerely,
Carlos M. Gutierrez
Secretary of Commerce
Chair, Committee on Climate Change
Science and Technology Integration
Samuel W. Bodman
Secretary of Energy
Vice Chair, Committee on Climate
Change Science and Technology
Integration
John H. Marburger III
Director, Office of Science and
Technology Policy
Executive Director, Committee
on Climate Change Science and
Technology Integration
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Abstract IX
Preface/Motivation for Report XIII
Executive Summary 1
PART I: THE PHYSICAL ENVIRONMENT
Overview...
II
Sea-Level Rise and Its Effects on the Coast
Coastal Elevations
3
Ocean Coasts
.25
.43
.57
Coastal Wetland Sustainability
5 73
Vulnerable Species: The Effects of Sea-Level Rise on Coastal Habitats
PART II: SOCIETAL IMPACTS AND IMPLICATIONS
Overview... ...85
• 6
Shore Protection and Retreat
.87
.105
Population, Land Use, and Infrastructure
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8
Public Access
117
9 123
Coastal Flooding, Floodplains, and Coastal Zone Management Issues
PART III: PREPARING FOR SEA-LEVEL RISE
Overview...,
,139
141
,157
10
Implications for Decisions
I I
Ongoing Adaptation
12
Institutional Barriers
PART IV: NATIONAL IMPLICATIONS AND A SCIENCE
STRATEGY FOR MOVING FORWARD
Overview... ...177
,163
13
179
Implications of Sea-Level Rise to the Nation
14 ,85
A Science Strategy for Improving the Understanding of Sea-Level Rise
and Its Impacts on U.S. Coasts
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O
u
o
Appendix I 193
State and Local Information on Vulnerable Species and Coastal Policies
Appendix 2 239
Basic Approaches for Shoreline Change Projections
Glossary 243
Acronyms and Abbreviations 251
Scientific Names 253
References... ..255
MI
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Preface
Executive Summary
Part 1 Overview
Chapter 1
Chapter 2
Chapter 3
Chapter 4
Chapter 5
Part II Overview
Chapter 6
Chapter 7
Chapter 8
Chapter 9
Part III Overview
AUTHOR TEAM FOR THIS REPORT
Authors*: K. Eric Anderson, USGS; Donald R. Cahoon, USGS;
Stephen K. Gill, NOAA; Benjamin T. Gutierrez, USGS; E. Robert Thieler,
USGS; James G. Titus, U.S. EPA; S. Jeffress Williams, USGS
Authors*: K. Eric Anderson, USGS; Donald R. Cahoon, USGS;
Stephen K. Gill, NOAA; Benjamin T. Gutierrez, USGS; E. Robert Thieler,
USGS; James G. Titus, U.S. EPA; S. Jeffress Williams, USGS
Authors: Donald R. Cahoon, USGS; S. Jeffress Williams, USGS;
Benjamin T. Gutierrez, USGS; K. Eric Anderson, USGS; E. Robert Thieler,
USGS; DeanB. Gesch, USGS
Lead Authors: S. Jeffress Williams, USGS; Benjamin T. Gutierrez, USGS;
James G. Titus, U.S. EPA; Stephen K. Gill, NOAA; Donald R. Cahoon, USGS;
E. Robert Thieler, USGS; K. Eric Anderson, USGS
Contributing Authors: Duncan FitzGerald, Boston Univ.; Virginia Burkett,
USGS; Jason Samenow, U.S. EPA
Lead Author: DeanB. Gesch, USGS
Contributing Authors: Benjamin T. Gutierrez, USGS; Stephen K. Gill, NOAA
Authors: Benjamin T. Gutierrez, USGS; S. Jeffress Williams, USGS; E. Robert
Thieler, USGS
Lead Authors: Donald R. Cahoon, USGS; Denise J. Reed, Univ. of New
Orleans; Alexander S. Kolker, Louisiana Universities Marine Consortium; Mark
M. Brinson, East Carolina Univ.
Contributing Authors: J. Court Stevenson, Univ. of Maryland; Stanley Riggs,
East Carolina Univ.; Robert Christian, East Carolina Univ.; Enrique Reyes,
East Carolina Univ.; Christine Voss, East Carolina Univ.; David Kunz, East
Carolina Univ.
Authors: Ann Shellenbarger Jones, Industrial Economics, Inc.; Christina Bosch,
Industrial Economics, Inc.; Elizabeth Strange, Stratus Consulting, Inc.
Authors: James G. Titus, U.S. EPA; Stephen K. Gill, NOAA
Authors: James G. Titus, U.S. EPA; Michael Craghan, Middle Atlantic Center
for Geography and Environmental Studies
Lead Authors: Stephen K. Gill, NOAA; Robb Wright, NOAA; James G. Titus,
U.S. EPA
Contributing Authors: Robert Kafalenos, US DOT; Kevin Wright, ICF
International, Inc.
Author: James G. Titus, U.S. EPA
Lead Authors: Stephen K. Gill, NOAA; Doug Marcy, NOAA
Contributing Author: Zoe Johnson, Maryland Dept. of Natural Resources
Author: James G. Titus, U.S. EPA
*A11 authors listed in alphabetical order
IV
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AUTHOR TEAM FOR THIS REPORT
Chapter 10
Chapter 11
Chapter 12
Part IV Overview
Chapter 13
Chapter 14
Appendix 1:
Section A
Section B
Section C
Section D
Section E
Section F
Section G
Appendix 2
Lead Author: James G. Titus, U.S. EPA
Contributing Author: James E. Neumann, Industrial Economics, Inc.
Author: James G. Titus, U.S. EPA
Author: James G. Titus, U.S. EPA
Authors: S. Jeffress Williams, USGS; E. Robert Thieler, USGS; Benjamin T
Gutierrez, USGS; Dean B. Gesch, USGS; Donald R. Cahoon, USGS;
K. Eric Anderson, USGS
Authors: S. Jeffress Williams, USGS; Benjamin T. Gutierrez, USGS; James G.
Titus, U.S. EPA; K. Eric Anderson, USGS; Stephen K. Gill, NOAA; Donald R.
Cahoon, USGS; E. Robert Thieler, USGS
Authors: E. Robert. Thieler, USGS; K. Eric Anderson, USGS; Donald R.
Cahoon, USGS; S. Jeffress Williams, USGS; Benjamin T. Gutierrez, USGS
Lead Authors: Daniel E. Hudgens, Industrial Economics, Inc.; Ann
Shellenbarger Jones, Industrial Economics, Inc.; James G. Titus, U.S. EPA.
Contributing Authors: Elizabeth M. Strange, Stratus Consulting, Inc.;
Joseph J. Tanski, New York Sea Grant; Gaurav Sinha, Univ. of Ohio
Lead Author: Elizabeth M. Strange, Stratus Consulting, Inc.
Contributing Authors: Daniel E. Hudgens, Industrial Economics, Inc.;
Ann Shellenbarger Jones, Industrial Economics, Inc.
Lead Author: James G. Titus, U.S. EPA
Contributing Author: Elizabeth M. Strange, Stratus Consulting, Inc.
Lead Author: James G. Titus, U.S. EPA
Contributing Authors: Christopher J. Linn, Delaware Valley Regional
Planning Commission; Danielle A. Kreeger, Partnership for the Delaware
Estuary, Inc.;Michael Craghan, Middle Atlantic Center for Geography &
Environmental Studies; Michael P. Weinstein, New Jersey Marine Sciences
Consortium and New Jersey Sea Grant College Program
Lead Author: James G. Titus, U.S. EPA
Contributing Author: Elizabeth M. Strange, Stratus Consulting, Inc.
Lead Author: James G. Titus, U.S. EPA
Contributing Authors: Ann Shellenbarger Jones, Industrial Economics, Inc.;
Peter G. Conrad, City of Baltimore; Elizabeth M. Strange, Stratus Consulting,
Inc.; Zoe Johnson, Maryland Dept. of Natural Resources; Michael P. Weinstein,
New Jersey Marine Sciences Consortium and New Jersey Sea Grant College
Program
Lead Authors: Rebecca L. Feldman, NOAA; James G. Titus, U.S. EPA; Ben
Poulter, Potsdam Institute for Climate Impact Research
Contributing Authors: Jeffrey DeBlieu, The Nature Conservancy; Ann
Shellenbarger Jones, Industrial Economics, Inc.
Lead Author: Benjamin T. Gutierrez, USGS
Contributing Authors: S. Jeffress Williams, USGS; E. Robert Thieler, USGS
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ACKNOWLEDGEMENTS
Throughout the process of preparing SAP 4.1, the authors were advisedby aFederal Advisory Committee
chosen for their diverse perspectives and technical expertise. The Coastal Elevations and Sea-Level
Rise Advisory Committee (CESLAC) consisted of: Margaret Davidson (Chairperson), NOAA; Rebecca
Beavers, National Park Service; Alan Belensz, New York State Office of the Attorney General; Mark
Crowell, Federal Emergency Management Agency; Andrew Garcia, U.S. Army Corps of Engineers;
Carl Hershner, Virginia Institute of Marine Science; Julie Hunkins, North Carolina Department
of Transportation; Mark Mauriello, New Jersey Department of Environmental Protection; Mark
Monmonier, Syracuse University; William S. Nechamen, Association of State Floodplain Managers;
SamPearsall, Environmental Defense Fund; Anthony Pratt, Coastal States Organization; Greg Rudolph,
American Shore and Beach Preservation Association; Harvey Ryland, Institute for Business and Home
Safety; Gwynne Schultz, Maryland Department of Natural Resources. Jack Fitzgerald of U.S. EPA was
the Designated Federal Official for the CESLAC, with support provided by Stratus Consulting.
Technical expert review was provided by: Fred Anders, New York Department of State; Mark Davis,
Tulane University; Lesley Ewing, California Coastal Commission; Janet Freedman, Rhode Island
Coastal Resources Council; Vivien Gornitz, NASA; Ellen Hartig, New York City Department of
Parks & Recreation; Maria Honeycutt, AGI Congressional Fellow; Kurt Kalb, New Jersey Department
of Environmental Protection; Stephen Leatherman, Florida International University; Ken Miller,
Maryland Department of Natural Resources; Jim O'Connell, University of Hawaii, Sea Grant; Richard
Osman, Smithsonian Institution; Marc Perry, U.S. Census Bureau; Chris Spaur, U.S. Army Corps of
Engineers; John Teal, Teal Partners; John Thayer, North Carolina Department of Environment and
Natural Resources; Dan Trescott, Southwest Florida Regional Planning Council; John Whitehead,
Appalachian State University; Rob Young, Western Carolina University. An expert review of an early
draft of Chapter 2 was also provided by an interagency geospatial team consisting of Eric Constance,
USGS; Todd Davison, NOAA; Dean Gesch, USGS; and Jerry Johnston, U.S. EPA.
This report relied heavily on stakeholder involvement that was implemented through a series of three
meetings held in the Mid-Atlantic Region (Easton, Maryland; Red Bank, New Jersey; and Plymouth,
North Carolina). Many of the comments received and discussion initiated at these meetings helped to
define some of the issues addressed in this report. Linda Hamalak of NOAA organized these public
meetings and the subsequent author meetings. The author meetings were hosted by the Blackwater
National Wildlife Refuge in Maryland; the NOAA National Marine Fisheries Service in Sandy Hook,
New Jersey; and the Partnership for the Sounds in Columbia, North Carolina.
The authors were also assisted by several of their colleagues at U.S. EPA, NOAA, and USGS. The
interagency management team of Rona Birnbaum, U.S. EPA; Patricia Jellison, USGS; and Michael
Szabados, NOAA, were instrumental in advising the authors during the final stages of the report.
Rebecca Feldman of NOAA provided key logistical support in addition to her contributions as an author.
Karen Scott of U.S. EPA managed the expert review process, supported by Perrin Quarles Associates.
The authors thank several USGS colleagues for their reviews, discussions, and contributions to Chapters
1, 3, 4, 13, and 14, as well as other portions of the report. These include: Mark Brinson, East Carolina
University; Tom Cronin, USGS; Duncan FitzGerald, Boston University; Virginia Burkett, USGS;
Curt Larsen, USGS (retired); Laura Moore, University of Virginia; Elizabeth Pendleton, USGS; Shea
Penland (deceased), University of New Orleans; and Asbury Sallenger, USGS.
Russ Jones of Stratus Consulting coordinated technical and GIS support for several chapters in this
report, with support from Jue Wang, Pyramid Systems Inc.; Richard Streeter and Tom Hodgson, Stratus
Consulting; and John Herter and Gaurav Sinha, Industrial Economics. Christina Thomas (contractor to
Stratus Consulting) edited the expert review draft.
VI
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ACKNOWLEDGEMENTS
Chapter 3 includes results of a panel assessment. The authors of Chapter 3 thank the panelists for their
contributions: Fred Anders, New York State, Dept. of State; K. Eric Anderson, USGS; Mark Byrnes,
Applied Coastal Research and Engineering; Donald R. Cahoon, USGS; Stewart Farrell, Richard
Stockton College; Duncan FitzGerald, Boston University; Paul Gayes, Coastal Carolina University;
Carl Hobbs, Virginia Institute of Marine Science; Randy McBride, George Mason University; Jesse
McNinch, Virginia Institute of Marine Science; Stan Riggs, East Carolina University; Antonio
Rodriguez, University of North Carolina; Jay Tanski, New York Sea Grant; Art Trembanis, University
of Delaware.
Chapter 4 includes results based ona panel assessment. The panel consisted of: Denise Reed, University of
New Orleans; Dana Bishara, USGS; Jeffrey Donnelly, Woods Hole Oceanographic Institution; Michael
Kearney, University of Maryland; Alexander Kolker, Louisiana Universities Marine Consortium; Lynn
Leonard, University of North Carolina-Wilmington; Richard Orson, Orson Environmental Consulting;
J. Court Stevenson, University of Maryland. The panel was conducted under contract to U.S. EPA,
with James G. Titus as the project officer. Jeff DeBlieux of The Nature Conservancy also contributed
to portions of Chapter 4.
The review process for SAP 4.1 included a public review of the Second draft. We thank the individuals
who commented on this draft. The author team carefully considered all comments submitted, and many
resulted in improvements to this Product.
We also thank the team of editors that worked closely with authors to produce this product. This includes
Anne Waple, UCAR; Jessica Blunden, STG, Inc.; and the entire graphics team at the National Climatic
Data Center.
Finally, we are especially grateful to Alan Cohn of U.S. EPA for his management of the day-to-day
process of developing and producing this report, and providing overall coordination for this effort.
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I his Synthesis and Assessment Product (SAP), developed as part of the U.S. Climate Change Science
Program, examines potential effects of sea-level rise from climate change during the twenty-first
century, with a focus on the mid-Atlantic coast of the United States. Using scientific literature and
policy-related documents, the SAP describes the physical environments; potential changes to coastal
environments, wetlands, and vulnerable species; societal impacts and implications of sea-level rise;
decisions that may be sensitive to sea-level rise; opportunities for adaptation; and institutional barriers
to adaptation. The SAP also outlines the policy context in the mid-Atlantic region and describes the
implications of sea-level rise impacts for other regions of the United States. Finally, this SAP discusses
ways natural and social science research can improve understanding and prediction of potential impacts
to aid planning and decision making.
Projections of sea-level rise for the twenty-first century vary widely, ranging from several centimeters
to more than a meter. Rising sea level can inundate low areas and increase flooding, coastal erosion,
wetland loss, and saltwater intrusion into estuaries and freshwater aquifers. Existing elevation data
for the mid-Atlantic United States do not provide the degree of confidence needed for local decision
making. Systematic nationwide collection of high-resolution elevation data would improve the ability
to conduct detailed assessments in support of planning. The coastal zone is dynamic and the response
of coastal areas to sea-level rise is more complex than simple inundation. Much of the United States
consists of coastal environments and landforms such as barrier islands and wetlands that will respond
to sea-level rise by changing shape, size, or position. The combined effects of sea-level rise and other
climate change factors such as storms may cause rapid and irreversible coastal change. All these
changes will affect coastal habitats and species. Increasing population and development in coastal areas
also affects the ability of natural ecosystems to adjust to sea-level rise.
Coastal communities and property owners have responded to coastal hazards by erecting shore
protection structures, elevating land and buildings, or relocating inland. Accelerated sea-level rise
would increase the costs and environmental impacts of these responses. Shoreline armoring can
eliminate the land along the shore to which the public has access; beach nourishment projects often
increase access to the shore.
Preparing for sea-level rise can be justified in many cases, because the cost of preparing now is small
compared to the cost of reacting later. Examples include wetland protection, flood insurance, long-
lived infrastructure, and coastal land-use planning. Nevertheless, preparing for sea-level rise has been
the exception rather than the rule. Most coastal institutions were based on the implicit assumption
that sea level and shorelines are stable. Efforts to plan for sea-level rise can be thwarted by several
institutional biases, including government policies that encourage coastal development, flood insurance
maps that do not consider sea-level rise, federal policies that prefer shoreline armoring over soft shore
protection, and lack of plans delineating which areas would be protected or not as sea level rises.
The prospect of accelerated sea-level rise and increased vulnerability in coastal regions underscores
the immediate need for improving our scientific understanding of and ability to predict the effects of
sea-level rise on natural systems and society. These actions, combined with development of decision
support tools for taking adaptive actions and an effective public education program, can lessen the
economic and environmental impacts of sea-level rise.
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Entire Report:
CCSP, 2009: Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region. A report by the U.S. Climate
Change Science Program and the Subcommittee on Global Change Research. [James G. Titus (Coordinating Lead Author),
K. Eric Anderson, Donald R. Cahoon, Dean B. Gesch, Stephen K. Gill, Benjamin T. Gutierrez, E. Robert Thieler, and S.
Jeffress Williams (Lead Authors)]. U.S. Environmental Protection Agency, Washington D.C., USA, 320 pp.
Preface:
Anderson, K.E, D.R. Cahoon, S.K. Gill, B.T. Gutierrez, E.R. Thieler, J.G. Titus, and S.J. Williams, 2009: Preface: Re-
port Motivation and Guidance for Using this Synthesis/Assessment Report. In: Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region. A report by the U.S. Climate Change Science Program and the Subcommittee on
Global Change Research. [J.G. Titus (coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T.
Gutierrez, E.R. Thieler, and S.J. Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC, pp.
xiii-viv.
E x, e c: u t i ve S u m m a r y:
Anderson, K.E., D.R. Cahoon, S.K. Gill, B.T. Gutierrez, E.R. Thieler, J.G. Titus, and S.J. Williams, 2009: Executive
summary. In: Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region. A report by the U.S. Climate
Change Science Program and the Subcommittee on Global Change Research. [J.G. Titus (coordinating lead author), K.E.
Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R. Thieler, and S.J. Williams (lead authors)]. U.S. En-
vironmental Protection Agency, Washington DC, pp. 1-8.
Part II Overview:
Cahoon, D.R., S.J. Williams, B.T. Gutierrez, K.E. Anderson, E.R. Thieler, and D.B. Gesch, 2009: Part I overview: The
physical environment. In: Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region. A report by the
U.S. Climate Change Science Program and the Subcommittee on Global Change Research. [J.G. Titus (coordinating
lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R. Thieler, and S.J. Williams (lead
authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 9-10.
Williams, S.J., B.T. Gutierrez, J.G. Titus, S.K. Gill, D.R. Cahoon, E.R. Thieler, K.E. Anderson, D. FitzGerald, V. Burkett,
and J. Samenow, 2009: Sea-level rise and its effects on the coast. In: Coastal Sensitivity to Sea-Level Rise: A Focus on
the Mid-Atlantic Region. A report by the U. S. Climate Change Science Program and the Subcommittee on Global Change
Research. [J.G. Titus (coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R.
Thieler, and S.J. Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 11-24.
Chapter 2:
Gesch, D.B., B.T. Gutierrez, and S.K. Gill, 2009: Coastal elevations. In: Coastal Sensitivity to Sea-Level Rise: A Focus on
the Mid-Atlantic Region. A report by the U. S. Climate Change Science Program and the Subcommittee on Global Change
Research. [J.G. Titus (coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R.
Thieler, and S.J. Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 25-42.
Chapter 3:
Gutierrez, B.T, S.J. Williams, and E.R. Thieler, 2009: Ocean coasts. In: Coastal Sensitivity to Sea-Level Rise: A Focus on
the Mid-Atlantic Region. A report by the U. S. Climate Change Science Program and the Subcommittee on Global Change
Research. [J.G. Titus (coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R.
Thieler, and S.J. Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 43-56.
Chapter 4:
Cahoon, D.R., D.J. Reed, A.S. Kolker, M.M. Brinson, J.C. Stevenson, S. Riggs, R. Christian, E. Reyes, C. Voss, and
D. Kunz, 2009: Coastal wetland sustainability. In: Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic
Region. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. [J.G.
Titus (coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R. Thieler, and
S.J. Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 57-72.
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to
A Focus on the Mid-Atlantic Region
5:
Shellenbarger Jones, A., C. Bosch, and E. Strange, 2009: Vulnerable species: the effects of sea-level rise on coastal
habitats. In: Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region. A report by the U.S. Climate
Change Science Program and the Subcommittee on Global Change Research. [J.G. Titus (coordinating lead author),
K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R. Thieler, and S.J. Williams (lead authors)]. U.S.
Environmental Protection Agency, Washington DC, pp. 73-84.
P " III •
Titus, J.G., and S.K. Gill, 2009: Part II overview: Societal impacts and implications. In: Coastal Sensitivity to Sea-Level
Rise: A Focus on the Mid-Atlantic Region. A report by the U.S. Climate Change Science Program and the Subcommittee
on Global Change Research. [J.G. Titus (coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill,
B.T. Gutierrez, E.R. Thieler, and S.J. Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC,
pp. 85-86.
<§,*
Titus, J.G. and M. Craghan, 2009: Shore protection and retreat. In: Coastal Sensitivity to Sea-Level Rise: A Focus on the
Mid-Atlantic Region. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change
Research. [J.G. Titus (coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R.
Thieler, and S.J. Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 87-104.
1:
Gill, S.K., R. Wright, J.G. Titus, R. Kafalenos, and K. Wright, 2009: Population, land use, and infrastructure. In: Coastal
Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region. A report by the U.S. Climate Change Science Program
and the Subcommittee on Global Change Research. [J.G. Titus (coordinating lead author), K.E. Anderson, D.R. Cahoon,
D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R. Thieler, and S.J. Williams (lead authors)]. U.S. Environmental Protection
Agency, Washington DC, pp. 105-116.
8:
Titus, J.G., 2009: Public access. In: Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region. A report by
the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. [J.G. Titus (coordinating
lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R. Thieler, and S.J. Williams (lead
authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 117-122.
9:
Gill, S.K., D. Marcy, and Z. Johnson, 2009: Coastal flooding, floodplains and coastal zone management issues. In: Coastal
Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region. A report by the U.S. Climate Change Science Program
and the Subcommittee on Global Change Research. [J.G. Titus (coordinating lead author), K.E. Anderson, D.R. Cahoon,
D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R. Thieler, and S.J. Williams (lead authors)]. U.S. Environmental Protection
Agency, Washington DC, pp. 123-138.
Part 111
Titus, J.G., 2009: Part III overview: Preparing for sea-level rise. In: Coastal Sensitivity to Sea-Level Rise: A Focus on the
Mid-Atlantic Region. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change
Research. [J.G. Titus (coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R.
Thieler, and S.J. Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 139-140.
10:
Titus, J.G., and J.E. Neumann, 2009: Implications for decisions. In: Coastal Sensitivity to Sea-Level Rise: A Focus on the
Mid-Atlantic Region. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change
Research. [J.G. Titus (coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R.
Thieler, and S.J. Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 141-156.
XI
-------
Chapter IIII:
Titus, J.G., 2009: Ongoing adaptation. In: Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region.
A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. [J.G. Titus
(coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R. Thieler, and S.J.
Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 157-162.
Chapter 1,2:
Titus, J.G., 2009: Institutional barriers. In: Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region.
A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. [J.G. Titus
(coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R. Thieler, and S.J.
Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 163-176.
Part IV Overview:
Williams, S.J., E.R. Thieler, B.T. Gutierrez, D.B. Gesch, D.R. Cahoon, and K.E. Anderson, 2009: Part IV overview:
National implications and a science strategy for moving forward. In: Coastal Sensitivity to Sea-Level Rise: A Focus on
the Mid-Atlantic Region. A report by the U. S. Climate Change Science Program and the Subcommittee on Global Change
Research. [J.G. Titus (coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R.
Thieler, and S.J. Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 177-178.
Chapter 13:
Williams, S.J., B.T. Gutierrez, J.G. Titus, K.E. Anderson, S.K. Gill, D.R. Cahoon, E.R. Thieler, and D.B. Gesch, 2009:
Implications of sea-level rise to the nation. In: Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region.
A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. [J.G. Titus
(coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R. Thieler, and S.J.
Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 179-184.
Chapter 14:
Thieler, E.R., K.E. Anderson, D.R. Cahoon, S.J. Williams, and B.T. Gutierrez, 2009: A science strategy for improving
the understanding of sea-level rise and its impacts on U.S. coasts. In: Coastal Sensitivity to Sea-Level Rise: A Focus on
the Mid-Atlantic Region. A report by the U. S. Climate Change Science Program and the Subcommittee on Global Change
Research. [J.G. Titus (coordinating lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R.
Thieler, and S.J. Williams (lead authors)]. U.S. Environmental Protection Agency, Washington DC, pp. 185-192.
Appendix II:
To cite regional sections, refer to the authors, section title, and pagination information on pages 193-194 (Appendix 1)
following this format:
Section authors, 2009: Section title. In: Appendix 1: State and local information on vulnerable species and coastal policies
in the Mid-Atlantic. In: Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region. A report by the
U.S. Climate Change Science Program and the Subcommittee on Global Change Research. [J.G. Titus (coordinating
lead author), K.E. Anderson, D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R. Thieler, and S.J. Williams (lead
authors)]. U.S. Environmental Protection Agency, Washington DC, pp. - .
Gutierrez, B.T, S.J. Williams, and E.R. Thieler, 2009: Appendix 2: Basic approaches for shoreline change projections. In:
Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region. A report by the U.S. Climate Change Science
Program and the Subcommittee on Global Change Research. [J.G. Titus (coordinating lead author), K.E. Anderson,
D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, E.R. Thieler, and S.J. Williams (lead authors)]. U.S. Environmental
Protection Agency, Washington DC, pp. 239-242.
XII
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U
<
(XL
Q_
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Reg/on
Report Motivation and Guidance for Using
this Synthesis/Assessment Report
Authors*: K. Eric Anderson, USGS; Donald R. Cahoon, USGS; Stephen K. Gill, NOAA;
Benjamin T. Gutierrez, USGS; E. Robert Thieler, USGS; James G. Titus, U.S. EPA;
S.Jeffress Williams, USGS
*AII authors listed in alphabetical order.
The U.S. Climate Change Science Program (CCSP)
was launched in February 2002 as a collaborative
federal interagency program, under a new cabinet-level
organization designed to improve the government-wide
management and dissemination of climate change sci-
ence and related technology development. The mission
of the CCSP is to "facilitate the creation and applica-
tion of knowledge of the Earth's global environment
through research, observations, decision support, and
communication". This Product is one of 21 synthesis
and assessment products (SAPs) identified in the 2003
Strategic Plan for the U.S. Climate Change Science
Program, written to help achieve this mission. The
SAPs are intended to support informed discussion
and decisions by policymakers, resource managers,
stakeholders, the media, and the general public. The
products help meet the requirements of the Global
Change Research Act of 1990, which directs agencies
to "produce information readily usable by policymak-
ers attempting to formulate effective strategies for
preventing, mitigating, and adapting to the effects of
global change" and to undertake periodic scientific
assessments.
One of the major goals within the mission is to un-
derstand the sensitivity and adaptability of different
natural and managed ecosystems and human systems
to climate and related global changes. This SAP (4.1),
Coastal Sensitivity to Sea-Level Rise: A Focus on the
Mid-Atlantic Region, addresses this goal by providing
a detailed assessment of the effects of sea-level rise
on coastal environments and presenting some of the
challenges that need to be addressed in order to adapt
to sea-level rise while protecting environmental re-
sources and sustaining economic growth. It is intended
to provide the most current knowledge regarding the
implications of rising sea level and possible adaptive
responses, particularly in the mid-Atlantic region of
the United States.
P.I SCOPE AND APPROACH OF THIS
PRODUCT
The focus of this Product is to identify and review the
potential impacts of future sea-level rise based on present
scientific understanding. To do so, this Product evaluates
several aspects of sea-level rise impacts to the natural en-
vironment and examines the impact to human land devel-
opment along the coast. In addition, the Product addresses
the connection between sea-level rise impacts and current
adaptation strategies, and assesses the role of the existing
coastal management policies in identifying and responding
to potential challenges.
As with other SAPs, the first step in the process of prepar-
ing this Product was to publish a draft prospectus listing
the questions that the Product would seek to answer at the
local and mid-Atlantic scale. After public comment, the
final prospectus listed 10 questions. This Product addresses
those 10 questions, and answers most of them with speci-
ficity. Nevertheless, development of this Product has also
highlighted current data and analytical capacity limitations.
The analytical presentation in this Product focuses on what
characterizations can be provided with sufficient accuracy
to be meaningful. For a few questions, the published lit-
erature was insufficient to answer the question with great
specificity. Nevertheless, the effort to answer the question
has identified what information is needed or desirable, and
current limitations with regard to available data and tools.
This Product focuses on the U.S. mid-Atlantic coast, which
includes the eight states from New York to North Carolina.
The Mid-Atlantic is a region where high population density
and extensive coastal development is likely to be at increased
risk due to sea-level rise. Other coastal regions in the United
States, such as the Gulf of Mexico and the Florida coast, are
potentially more vulnerable to sea-level rise and have been
the focus of other research and assessments, but are outside
the scope of this Product.
XIII
-------
The U.S. Climate Change Science Program
Preface
During the preparation of this Product, three regional meet-
ings were held between the author team and representatives
from relevant local, county, state, and federal agencies, as
well as non-governmental organizations. Many of the ques-
tions posed in the prospectus for SAP 4.1 were discussed
in detail and the feedback has been incorporated into the
Product. However, the available data are insufficient to
answer all of the questions at both the local and regional
scale. Therefore, the results of this Product are best used as
a "starting point" for audiences seeking information about
sensitivity to and implications of sea-level rise.
Many of the findings included in this Product are expressed
using common terms of likelihood (e.g., very likely, un-
likely), similar to those used in the 2007 Intergovernmental
Panel on Climate Change (IPCC) Fourth Assessment Report,
Climate Change 2007: The Physical Science Basis. The
likelihood determinations used in this Product were estab-
lished by the authors and modeled after other CCSP SAPs
such as CCSP SAP 1.1, Temperature Trends in the Lower
Atmosphere: Steps for Understanding and Reconciling Dif-
ferences. However, characterizations of likelihood in this
Product are largely based on the judgment of the authors
and uncertainties from published peer-reviewed literature
(Figure P.I). Data on how coastal ecosystems and specific
species may respond to climate change is limited to a small
number of site-specific studies, often carried out for pur-
poses unrelated to efforts to evaluate the potential impact
of sea-level rise. Nevertheless, being able to characterize
current understanding—and the uncertainty associated
with that information—is important. In the main body of
this Product, any use of the terms in Figure P.I reflects
qualitative assessment of potential changes based on the
authors' review and understanding of available published
coastal science literature and of governmental policies (the
appendices do not contain findings). Statements that do not
use these likelihood terms either have an insufficient basis
for assessing likelihood or present information provided
in the referenced literature which was not accompanied by
assessments of likelihood.
The International System of Units (SI) has been used in this
Product with English units often provided in parentheses.
Where conversions are not provided, some readers may wish
to convert from SI to English units using Table P.I.
P.2 FUTURE SEA-LEVEL SCENARIOS
ADDRESSED IN THIS PRODUCT
In this Product, the term "sea level" refers to mean sea level
or the average level of tidal waters, generally measured over
a 20-year period. These measurements generally indicate the
water level relative to the land, and thus incorporate changes
in the elevation of the land (i.e., subsidence or uplift) as well
as absolute changes in sea level (i.e., rise in sea level caused
by increasing its volume or adding water). For clarity, sci-
entists often use two different terms:
Table P.I Conversion from the International System of Units (SI) to
English Units
centimeter (cm)
millimeter (mm)
meter (m)
kilometer (km)
meter (m)
square meter (sq m)
hectare (ha)
square kilometer (sq km)
square meter (sq m)
hectare (ha)
square kilometer (sq km)
meters per year (m per year)
millimeters per year (mm per year)
meters per second (m per sec)
0.3937
0.0394
3.2808
0.6214
1.0936
0.000247
2.47
247
10.7639
0.00386
0.3861
3.28084
0.03937
1.943
K^Z
inch (in)
inch (in)
foot (ft)
mile (mi)
yard (yd)
acres (ac)
acres (ac)
acres (ac)
square foot (sq ft)
square mile (sq mi)
square mile (sq mi)
foot per year (ft per year)
inch per year (in per year)
knots
XIV
-------
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Reg/on
| virtually certain
very likely
likely
about as likely as nol
unlikely
very unlikely
virtually impossible
10
20
30
I
40
50 60
Likelihood (percent)
i
70
80
90
100
Figure P.I Likelihood terms and related probabilities used for this Product (with the exception of Appendix I).
"Global sea-level rise" is the average increase in the
level of the world's oceans that occurs due to a variety
of factors, the most significant being thermal expansion
of the oceans and the addition of water by melting of
land-based ice sheets, ice caps, and glaciers.
"Relative sea-level rise" refers to the change in sea level
relative to the elevation of the adjacent land, which can
also subside or rise due to natural and human-induced
factors. Relative sea-level changes include both global
sea-level rise and changes in the vertical elevation of
the land surface.
In this Product, both terms are used. Global sea-level rise
is used when referring to the worldwide average increase
in sea level. Relative sea-level rise, or simply sea-level rise,
is used when referring to the scenarios used in this Product
and effects on the coast.
This Product does not provide a forecast of future rates of
sea-level rise. Rather, it evaluates the implications of three
relative sea-level rise scenarios over the next century devel-
oped from a combination of the twentieth century relative
sea-level rise rate and either a 2 or 7 millimeter per year
increase in global sea level:
Scenario 1: the twentieth century rate, which is gener-
ally 3 to 4 millimeters per year in the mid-Atlantic
region (30 to 40 centimeters total by the year 2100);
Scenario 2: the twentieth century rate plus 2 millime-
ters per year acceleration (50 to 60 centimeters total
by 2100);
Scenario 3: the twentieth century rate plus 7 millimeters
per year acceleration (100 to 110 centimeters total by
2100).
The twentieth century rate of sea-level rise refers to the local
long-term rate of relative sea-level rise that has been ob-
served at NOAA National Ocean Service (NOS) tide gauges
in the mid-Atlantic study region. Scenario 1 assesses the
impacts if future sea-level rise occurs at the same rate as was
observed over the twentieth century at a particular location.
Scenarios 1 and 2 are within the range of those reported in
the recent IPCC Report Climate Change 2007: The Physical
Science Basis, specifically in the chapter Observations: Oce-
anic Climate Change and Sea Level. Scenario 3 is consistent
with higher estimates suggested by recent publications.
P.3 PRODUCT ORGANIZATION
This Product is divided into four parts:
Part I first provides context and addresses the effects of sea-
level rise on the physical environment. Chapter 1 provides the
context for sea-level rise and its effects. Chapter 2 discusses
the current knowledge and limitations in coastal elevation
mapping. Chapter 3 describes the physical changes at the coast
that will result in changes to coastal landforms (e.g., barrier
islands) and shoreline position in response to sea-level rise.
Chapter 4 considers the ability of wetlands to accumulate
sediments and survive in response to rising sea level. Chapter
5 examines the habitats and species that will be vulnerable to
sea-level rise related impacts.
Part II describes the societal impacts and implications of
sea-level rise. Chapter 6 provides a framework for assessing
shoreline protection options in response to sea-level rise.
Chapter 7 discusses the extent of vulnerable population and
infrastructure, and Chapter 8 addresses the implications for
public access to the shore. Chapter 9 reviews the impact of
sea-level rise to flood hazards.
Part III examines strategies for coping with sea-level rise.
Chapter 10 outlines key considerations when making decisions
to reduce vulnerability. Chapter 11 discusses what organiza-
tions are currently doing to adapt to sea-level rise, and Chapter
12 examines possible institutional barriers to adaptation.
Part IV examines national implications and a science strategy
for moving forward. Chapter 13 discusses sea-level rise im-
pacts and implications at a national scale and highlights how
coasts in other parts of the United States are vulnerable to sea-
level rise. Chapter 14 presents opportunities for future efforts
to reduce uncertainty and close gaps in scientific knowledge
and understanding.
XV
-------
Finally, this Product also includes two appendices: Appendix
1 discusses many of the species that depend on potentially
vulnerable habitat in specific estuaries, providing local
elaboration of the general issues examined in Chapter 5. The
Appendix also describes key statutes, regulations, and other
policies that currently define how state and local govern-
ments are responding to sea-level rise, providing support for
some of the observations made in Part III. This Appendix is
provided as background information and does not include
findings or an independent assessment of likelihood.
Appendix 2 reviews some of the basic approaches that
have been used to conduct shoreline change or land loss
assessments in the context of sea-level rise and some of the
difficulties that arise in using these methods.
Technical and scientific terms are used throughout this
Product. To aid readers with these terms, a Glossary and a
list of Acronyms and Abbreviations are included at the end
of the Product.
XVI
-------
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Reg/on
Global sea level is rising, and there is evidence that
the rate is accelerating. Increasing atmospheric
concentrations of greenhouse gases, primarily
from human contributions, are very likely warming
the atmosphere and oceans. The warmer
temperatures raise sea level by expanding ocean
water, melting glaciers, and possibly increasing the
rate at which ice sheets discharge ice and water
into the oceans. Rising sea level and the potential for stronger storms pose an increasing
threat to coastal cities, residential communities, infrastructure, beaches, wetlands, and
ecosystems. The potential impacts to the United States extend across the entire country:
ports provide gateways for transport of goods domestically and abroad; coastal resorts
and beaches are central to the U.S. economy; wetlands provide valuable ecosystem
services such as water filtering and spawning grounds for commercially important
fisheries. How people respond to sea-level rise in the coastal zone will have potentially
large economic and environmental costs.
This Synthesis and Assessment Product examines the implications of rising sea level, with
a focus on the mid-Atlantic region of the United States, where rates of sea-level rise
are moderately high, storm impacts occur, and there is a large extent of critical habitat
(marshes), high population densities, and infrastructure in low-lying areas. Although
these issues apply to coastal regions across the country, the mid-Atlantic region was
selected as a focus area to explore how addressing both sensitive ecosystems and
impacts to humans will be a challenge. Using current scientific literature and expert panel
assessments, this Product examines potential risks, possible responses, and decisions
that may be sensitive to sea-level rise.
The information, data, and tools needed to inform decision making with regard to sea-
level rise are evolving, but insufficient to assess the implications at scales of interest to
all stakeholders. Accordingly, this Product can only provide a starting point to discuss
impacts and examine possible responses at the regional scale. The Product briefly
summarizes national scale implications and outlines the steps involved in providing
information at multiple scales (e.g., local, regional).
-------
Executive Summary
During periods of climate warming, two major
processes cause global mean sea-level rise: (1)
as the ocean warms, the water expands and
increases its volume and (2) land reservoirs of
ice and water, including glaciers and ice sheets,
contribute water to the oceans. In addition,
the land in many coastal regions is subsiding,
adding to the vulnerability to the effects of
sea-level rise.
Recent U.S. and international assessments of
climate change show that global average sea
level rose approximately 1.7 millimeters per
year through the twentieth century, after a
period of little change during the previous two
thousand years. Observations suggest that the
rate of global sea-level rise may be accelerating.
In 2007, the Intergovernmental Panel on Climate
Change (IPCC) projected that global sea level
will likely rise between 19 and 59 centimeters (7
and 23 inches) by the end of the century (2090
to 2099), relative to the base period (1980 to
1999), excluding any rapid changes in ice flow
from Greenland and Antarctica. According to
the IPCC, the average rate of global sea-level
rise during the twenty-first century is very
likely to exceed the average rate over the last
four decades. Recently observed accelerated
ice flow and melting in some Greenland outlet
glaciers and West Antarctic ice streams could
substantially increase the contribution from
the ice sheets to rates of global sea-level rise.
Understanding of the magnitude and timing
of these processes is limited and, thus, there
is currently no consensus on the upper bound
of global sea-level rise. Recent studies suggest
the potential for a meter or more of global sea-
level rise by the year 2100, and possibly several
meters within the next several centuries.
In the mid-Atlantic region from New York to
North Carolina, tide-gauge observations indicate
that relative sea-level rise (the combination of
global sea-level rise and land subsidence) rates
were higher than the global mean and generally
ranged between 2.4 and 4.4 millimeters per
year, or about 0.3 meters (1 foot) over the
twentieth century.
Coastal environments such as beaches, barrier
islands, wetlands, and estuarine systems are
closely linked to sea level. Many of these
environments adjust to increasing water level
by growing vertically, migrating inland, or
expanding laterally. If the rate of sea-level rise
accelerates significantly, coastal environments
and human populations will be affected. In
some cases, the effects will be limited in scope
and similar to those observed during the last
century. In other cases, thresholds may be
crossed, beyond which the impacts would be
much greater. If the sea rises more rapidly than
the rate with which a particular coastal system
can keep pace, it could fundamentally change
the state of the coast. For example, rapid sea-
level rise can cause rapid landward migration
or segmentation of some barrier islands, or
disintegration of wetlands.
Today, rising sea levels are submerging low-
lying lands, eroding beaches, converting
wetlands to open water, exacerbating coastal
flooding, and increasing the salinity of estuaries
and freshwater aquifers. Other impacts of
climate change, coastal development, and
natural coastal processes also contribute
to these impacts. In undeveloped or less-
developed coastal areas where human influence
is minimal, ecosystems and geological
systems can sometimes shift upward and
landward with the rising water levels. Coastal
development, including buildings, roads, and
other infrastructure, are less mobile and more
vulnerable. Vulnerability to an accelerating
rate of sea-level rise is compounded by the
high population density along the coast, the
possibility of other effects of climate change,
and the susceptibility of coastal regions to
storms and environmental stressors, such as
drought or invasive species.
-------
ES.2.1 Sea-Level Rise and
the Physical Environment
The coastal zone is dynamic and
the response of coastal areas to
sea-level rise is more complex
than simple inundation. Erosion
is a natural process from waves
and currents and can cause land
to be lost even with a stable sea
level. Sea-level rise can exacer-
bate coastal change due to ero-
sion and accretion. While some
wetlands can keep pace with sea-
level rise due to sediment inputs,
those that cannot keep pace will
gradually degrade and become
submerged. Shore protection and
engineering efforts also affect
how coasts are able to respond
to sea-level rise.
For coastal areas that are vulner-
able to inundation by sea-level
rise, elevation is generally the
most critical factor in assessing
potential impacts. The extent of
inundation is controlled largely
by the slope of the land, with a
greater area of inundation oc-
curring in locations with more
gentle gradients. Most of the
currently available elevation
data do not provide the degree
of confidence that is needed for
making quantitative assessments
of the effects of sea-level rise
for local planning and decision
making. However, systematic
collection of high-quality eleva-
tion data (i.e., lidar) will improve
the ability to conduct detailed
assessments (Chapter 2).
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Reg/on
Potential Mid-Atlantic Landform Responses to Sea-Level Rise
41' •
39* -
Atlantic Ocean
j
50
100
150 200 Kilometers
EXPLANATION
SLR Scenario
CD
en
en
n
•
MKhC.nL 25th C»n4.
RJI»* »lmnVyf
BUE BUE
OEIB OEI8
OEIB OEIB
OEIB T?
T? T
ZWhC.nl
+7inm/yr
BUE
OEIB
T?
T
T
SUE = Bluff and Upland Erosion
OEIB = Overwash. Erosion, Island Breaching
? = Indicates that (he condition could be marginal
T • Threshold Condition
ze*
74°
72"
Figure ES. I Potential mid-Atlantic coastal landform responses to three sea-level rise scenarios
(in millimeters [mm] per year [yr]). Most coastal areas are currently experiencing erosion, which
is expected to increase with future sea-level rise. In addition to undergoing erosion, coastal
segments denoted with a "T" may also cross a threshold where rapid barrier island migration
or segmentation will occur.
Nationally, coastal erosion will probably
increase as sea level rises at rates higher than
those that have been observed over the past
century. The exact manner and rates at which
these changes are likely to occur will depend on
the character of coastal landforms (e.g., barrier
islands, cliffs) and physical processes (Part I).
Particularly in sandy shore environments which
comprise the entire mid-Atlantic ocean coast
(Figure ES.l), it is virtually certain that coastal
headlands, spits, and barrier islands will erode
at a faster pace in response to future sea-level
rise. For accelerations in the rate of sea-level rise
by 2 and 7 millimeters per year, it is likely that
some barrier islands in this region will cross a
threshold where rapid barrier island migration
or segmentation will occur (Chapter 3).
Tidal wetlands in the United States, such as the
Mississippi River Delta in Louisiana and Black-
The coastal zone
is dynamic and the
response of coastal
areas to sea-level rise
is more complex than
simple inundation.
Nationally, coastal
erosion rates will
probably increase in
response to higher
rates of sea-level rise.
-------
The U.S. Climate Change Science Program
Executive Summary
Potential Mid-Atlantic Wetland Survival
r' " • I ,'.,',• .'
Pennsylvania
Jersey
Maryland /";
Atlantic
Ocean
100 150
Kilometers
WIN Wetlands Be Converted to Opm Wal»r?
Cumnl + 2 mm/yr
Cufrsnl*7mm/yf
Y»»? - *»U«K! «wld 0» iBngiiua« h»t
re* 74-
Figure ES.2 Areas where wetlands would be marginal or lost (i.e., converted to open water) under
three sea-level rise scenarios (in millimeters [mm] per year [yr]).
For the mid-
Atlantic region,
acceleration in
sea-level rise by
2 millimeters per
year will cause
many wetlands to
become stressed;
it is likely that most
wetlands will not
survive acceleration
in sea-level rise by 7
millimeters per year.
water River marshes in Maryland, are already
experiencing submergence by relative sea-level
rise and associated high rates of wetland loss.
For the mid-Atlantic region (Figure ES.2), ac-
celeration in sea-level rise by 2 millimeters
per year will cause many wetlands to become
stressed; it is likely that most wetlands will
not survive acceleration in sea-level rise by 7
millimeters per year. Wetlands may expand
inland where low-lying land is available but, if
existing wetlands cannot keep pace with sea-
level rise, the result will be an overall loss of
wetland area in the Mid-Atlantic. The loss of
associated wetland ecosystem functions (e.g.,
providing flood control, acting as a storm surge
buffer, protecting water quality, and serving as a
nursery area) can have important societal conse-
quences, such as was seen with the storm surge
impacts associated with Hurricanes Katrina
and Rita in southern Louisiana, including New
Orleans, in 2005. Nationally, tidal wetlands
already experiencing submergence by sea-level
rise and associated land loss (e.g., Mississippi
River Delta in Louisiana, and Blackwater River
marshes in Maryland) will continue to lose
area in response to future accelerated rates of
sea-level rise and changes in other climate and
environmental drivers.
Terrestrial and aquatic plants and animals that
rely on coastal habitat are likely to be stressed
and adversely affected as sea level rises. The
quality, quantity, and spatial distribution of
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coastal habitats will change as a result of
erosion, salinity changes, and wetland loss.
Depending on local conditions, habitat may be
lost or migrate inland in response to sea-level
rise. Loss of tidal marshes would seriously
threaten coastal ecosystems, causing fish and
birds to move or produce fewer off spring. Many
estuarine beaches may also be lost, threatening
numerous species (Chapter 5).
Sea-level rise is just one of many factors affect-
ing coastal habitats: sediment input, nutrient
runoff, fisheries management, and other factors
are also important. Under natural conditions,
habitats are continually shifting, and species
generally have some flexibility to adapt to var-
ied geography and/or habitat type. Future habi-
tat and species loss will be determined by fac-
tors that include rates of wetland submergence,
coastal erosion, and whether coastal landforms
and present-day habitats have space to migrate
inland. As coastal development continues, the
ability for habitats to change and migrate inland
along the rest of the coast will not only be a
function of the attributes of the natural system,
but also of the coastal management policies for
developed and undeveloped areas.
Increasing population, development, and sup-
porting infrastructure in the coastal zone often
compete with the desire to maintain the benefits
that natural ecosystems (e.g., beaches, barrier
islands, and wetlands) provide to humans. In-
creasing sea level will put additional stress on
the ability to manage these competing interests
effectively (Chapter?). In the Mid-Atlantic, for
example, movement to the coast and develop-
ment continues, despite the growing vulner-
ability to coastal hazards.
Rising sea level increases the vulnerability of
development on coastal f loodplains. Higher sea
level provides an elevated base for storm surges
to build upon and diminishes the rate at which
low-lying areas drain, thereby increasing the
risk of flooding from rainstorms. Increases in
shore erosion also contribute to greater flood
damages by removing protective dunes, beach-
es, and wetlands and by leaving some properties
closer to the water's edge (Chapter 9).
At the current rate of sea-level rise, coastal
residents and businesses have been responding
by rebuilding at the same location, relocating,
holding back the sea by coastal engineering, or
some combination of these approaches. With a
substantial acceleration of sea-level rise, tradi-
tional coastal engineering may not be economi-
cally or environmentally sustainable in some
areas (Chapter 6).
Nationally, most current coastal policies do
not accommodate accelerations in sea-level
rise. Floodplain maps, which are used to guide
development and building practices in hazard-
ous areas, are generally based upon recent
observations of topographic elevation and local
mean sea-level. However, these maps often do
not take into account accelerated sea-level rise
or possible changes in storm intensity (Chapter
9). As a result, most shore protection structures
are designed for current sea level, and develop-
ment policies that rely on setting development
back from the coast are designed for current
rates of coastal erosion, not taking into account
sea-level rise.
The prospect of accelerated sea-level rise un-
derscores the need to rigorously assess vulner-
ability and examine the costs and benefits of
taking adaptive actions. Determining whether,
what, and when specific actions are justified
is not simple, due to uncertainty in the timing
and magnitude of impacts, and difficulties in
quantifying projected costs and benefits. Key
opportunities for preparing for sea-level rise
include: provisions for preserving public access
along the shore (Chapter 8); land-use planning
to ensure that wetlands, beaches, and associ-
ated coastal ecosystem services are preserved
(Chapter 10); siting and design decisions such as
retrofitting (e.g., elevating buildings and homes)
(Chapter 10); and examining whether and how
changing risk due to sea-level rise is reflected
in flood insurance rates (Chapter 10).
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Executive Summary
However, the time, and often cultural shift,
required to make changes in federal, state, and
local policies is sometimes a barrier to change.
In the mid-Atlantic coastal zone, for example,
although the management community recog-
nizes sea-level rise as a coastal flooding hazard
and state governments are starting to face the
issue of sea-level rise, only a limited number
of analyses and resulting statewide policy
revisions to address rising sea level have been
undertaken (Chapters 9,11). Current policies in
some areas are now being adapted to include the
effects of sea-level rise on coastal environments
and infrastructure. Responding to sea-level
rise requires careful consideration regarding
whether and how particular areas will be pro-
tected with structures, elevated above the tides,
relocated landward, or left alone and potentially
given up to the rising sea (Chapter 12).
Many coastal management decisions made
today have implications for sea-level rise ad-
aptation. Existing state policies that restrict
development along the shore to mitigate hazards
or protect water quality (Appendix 1) could
preserve open space that may also help coastal
ecosystems adapt to rising sea level. On the oth-
er hand, efforts to fortify coastal development
can make it less likely that such an area would
be abandoned as sea level rises (Chapter 6). A
prime opportunity for adapting to sea-level rise
in developed areas may be in the aftermath of a
severe storm (Chapter 9).
This Product broadly synthesizes physical,
biological, social, and institutional topics in-
volved in assessing the potential vulnerability
of the mid-Atlantic United States to sea-level
rise. This includes the potential for landscape
changes and associated geological and biologi-
cal processes; and the ability of society and its
institutions to adapt to change. Current limita-
tions in the ability to quantitatively assess these
topics at local, regional, and national scales may
affect whether, when, and how some decisions
will be made.
Scientific syntheses and assessments such as
this have different types and levels of uncer-
tainty. Part I of this Product describes the physi-
cal settings and processes in the Mid-Atlantic
and how they may be impacted by sea-level rise.
There is uncertainty regarding coastal eleva-
tions and the extent to which some areas will
be inundated. In some areas, coastal elevations
have been mapped with great detail and accu-
racy, and thus the data have the requisite high
degree of certainty for local decision making
by coastal managers. In many other areas, the
coarser resolution and limited vertical accuracy
of the available elevation data preclude their use
in detailed assessments, but the uncertainty can
be explicitly quantified (Chapter 2). The range
of physical and biological processes associ-
ated with coastal change is poorly understood
at some of the time and space scales required
for decision making. For example, although
the scope and general nature of the changes
that can occur on ocean coasts in response to
sea-level rise are widely recognized, how these
changes occur in response to a specific rise
in sea level is difficult to predict (Chapter 3).
Similarly, current model projections of wetland
vulnerability on regional and national scales are
uncertain due to the coarse level of resolution
of landscape-scale models. While site-specific
model projections are quite good where local
information has been acquired on factors that
control local accretionary processes in specific
wetland settings, such projections cannot pres-
ently be generalized so as to apply to larger
regional or national scales with high confidence
(Chapter 4). The cumulative impacts of physical
and biological change due to sea-level rise on
the quality and quantity of coastal habitats are
not well understood.
Like the uncertainties associated with the physi-
cal settings, the potential human responses to
future sea-level rise described in Part II of this
Product are also uncertain. Society generally
responds to changes as they emerge. The deci-
sions that people make to respond to sea-level
rise could be influenced by the physical setting,
the properties of the built environment, social
values, the constraints of regulations and eco-
nomics, as well as the level of uncertainty in the
form and magnitude of future coastal change.
This Product examines some of the available
options and assesses actions that federal and
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Reg/on
state governments and coastal communities
could take in response to sea-level rise. For ex-
ample, as rising sea level impacts coastal lands,
a fundamental choice is whether to attempt to
hold back the sea or allow nature to takes its
course. Both choices have important costs and
uncertainties (Chapter 6).
Part III of this Product focuses on what might be
done to prepare for sea-level rise. As discussed
above, the rate, timing, and impacts of future
sea-level rise are uncertain, with important
implications for decision making. For example,
planning for sea-level rise requires examining
the benefits and costs of such issues as coastal
wetland protection, existing and planned coastal
infrastructure, and management of floodplains
in the context of temporal and spatial uncer-
tainty (Chapter 10). In addition, institutional
barriers can make it difficult to incorporate the
potential impacts of future sea-level rise into
coastal planning (Chapter 12).
ES.4.1 Enhance Understanding
An integrated scientific program of sea-level
studies would reduce gaps in current knowl-
edge and the uncertainty about the potential
responses of coasts, estuaries, wetlands, and
human populations to sea-level rise. This
program should focus on expanded efforts to
monitor ongoing physical and environmental
changes, using new technologies and higher
resolution elevation data as available. Insights
from the historic and geologic past also provide
important perspectives. A key area of uncer-
tainty is the vulnerability of coastal landforms
and wetlands to sea-level rise; therefore, it is
important to understand the dynamics of barrier
island processes and wetland accretion, wetland
migration, and the effects of land-use change as
sea-level rise continues. Understanding, predict-
ing, and responding to the environmental and
societal effects of sea-level rise would require
an integrated program of research that includes
both natural and social sciences. Social science
research is a necessary component as sea-level
rise vulnerability, sea-level rise impacts, and
the success of many adaptation strategies will
depend on characterizing the social, economic,
and political contexts in which management
decisions are made (Chapter 14).
ES.4.2 Enhance Decision Support
Decision making on regional and local levels
in the coastal zone can be supported by im-
proved understanding of vulnerabilities and
risks of sea-level rise impacts. Developing
tools, datasets, and other coastal management
information is key to supporting and promot-
ing sound coastal planning, policy making, and
decisions. This includes providing easy access
to data and information resources and applying
An integrated
program of
research including
both natural and
social sciences is
key to developing
understanding,
information, and
decision tools
to support and
promote sound
coastal planning
and policy making.
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The U.S. Climate Change Science Program Executive Summary
this information in an integrated framework
using such tools as geographic information
systems. Integrated assessments linking physi-
cal vulnerability with economic analyses and
planning options will be valuable, as will efforts
to assemble and assess coastal zone planning
adaptation options for federal, state, and local
decision makers. Stakeholder participation in
every phase of this process is important, so that
decision makers and the public have access to
the information that they need and can make
well-informed choices regarding sea-level rise
and the consequences of different management
decisions. Coastal planning and policies that are
consistent with the reality of a rising sea could
enable U.S. coastal communities to avoid or
adapt to its potential environmental, societal,
and economic impacts.
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The first part of this Product examines the potential
physical and environmental impacts of sea-level rise
on the coastal environments of the mid-Atlantic re-
gion. Rising sea level over the next century will have
a range of effects on coastal regions, including land
loss and shoreline retreat from erosion and inundation,
an increase in the frequency of storm-related flood-
ing, and intrusion of salt water into coastal freshwater
aquifers. The sensitivity of a coastal region to sea-level
rise depends both on the physical aspects (shape and
composition) of a coastal landscape and its ecological
setting. One of the most obvious impacts is that there
will be land loss as coastal areas are inundated and
eroded. Rising sea level will not only inundate the
landscape but will also be a driver of change for the
coastal landscape. These impacts will have large ef-
fects on natural environments such as coastal wetland
ecosystems, as well as effects on human development
in coastal regions (see Part II of this Product). Making
long-term projections of coastal change is difficult be-
cause of the multiple, interacting factors that contribute
to that change. Given the large potential impacts to
human and natural environments, there is a need to
improve our ability to conduct long-term projections.
Part I describes the physical settings of the mid-Atlan-
tic coast as well as the processes that influence shore-
line change and land loss in response to sea-level rise.
Part I also provides an assessment of coastal changes
that may occur over the twenty-first century, as well as
the consequences of those changes for coastal habitats
and the flora and fauna they support.
Chapter 1 provides an overview of the current under-
standing of climate change and sea-level rise and their
potential effects on both natural environments and
society, and summarizes the background information that
was used to develop this Product. Sea-level rise will have
a range of impacts to both natural systems and human de-
velopment and infrastructure in coastal regions. A major
challenge is to understand the extent of these impacts and
how to develop planning and adaptation strategies that
address both the quality of the natural environment and
human interests.
Chapter 2 highlights the important issues in analysis
of sea-level rise vulnerability based on coastal eleva-
tion data. Elevation is a critical factor in determining
vulnerability to inundation, which will be the primary
response to sea-level rise for only some locations in the
mid-Atlantic region. Because sea-level rise impact as-
sessments often rely on elevation data, it is important
to understand the inherent accuracy of the underlying
data and its effects on the uncertainty of any result-
ing vulnerability maps and statistical summaries. The
existing studies of sea-level rise vulnerability in the
Mid-Atlantic based on currently available elevation data
do not provide the level of confidence that is optimal for
local decision making. However, recent research using
newer high-resolution, high-accuracy elevation data is
leading toward development of improved capabilities for
vulnerability assessments.
Chapter 3 summarizes the factors and processes con-
trolling the dynamics of ocean coasts. The major factor
affecting the location and shape of coasts at centennial
and longer time scales is global sea-level change, which is
linked to the Earth's climate. These close linkages are well
documented in the scientific literature from field studies
conducted over the past few decades. The details of the
process-response relationships, however, are the subject
of active, ongoing research. The general characteristics
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Part I Overview
and shape of the coast (coastal morphology) reflects com-
plex and ongoing interactions between changes in sea level,
the physical processes that act on the coast (hydrodynamic
regime, e.g., waves and tidal characteristics), the availability
of sediment (sediment supply) transported by waves and tidal
currents at the shore, and underlying geology (the structure
and composition of the landscape which is often referred to
as the geologic framework). Variations in these three fac-
tors are responsible for the different coastal landforms and
environments occurring in the coastal regions of the United
States. Chapter 3 presents a synthesis and assessment of the
potential changes that can be expected for the mid-Atlantic
shores of the United States, which are primarily comprised
of beaches and barrier islands.
Chapter 4 describes the vulnerability of coastal wetlands in
the mid-Atlantic region to current and future sea-level rise.
The fate of coastal wetlands is determined in large part by
the way in which wetland vertical development processes
change with climate drivers. In addition, the processes by
which wetlands build vertically vary by geomorphic set-
ting. Chapter 4 identifies those important climate drivers
affecting wetland vertical development in the geomorphic
settings of the mid-Atlantic region. The information on
climate drivers, wetland vertical development, geomorphic
settings, and local sea-level rise trends was synthesized
and assessed using an expert decision process to determine
wetland vulnerability for each geomorphic setting in each
subregion of the mid-Atlantic region.
Chapter 5 summarizes the potential impacts to biota as
a result of habitat change or loss driven by sea-level rise.
Habitat quality, extent, and spatial distribution will change
as a result of shore erosion, wetland loss, and shifts in es-
tuarine salinity gradients. Of particular concern is the loss
of wetland habitats and the important ecosystem functions
they provide, which include critical habitat for wildlife; the
trapping of sediments, nutrients, and pollutants; the cycling
of nutrients and minerals; the buffering of storm impacts on
coastal environments; and the exchange of materials with
adjacent ecosystems.
10
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Sea-Level Rise and Its Effects
on the Coast
Lead Authors: S.Jeffress Williams, USGS; Benjamin T. Gutierrez,
USGS; James G.Titus, U.S. EPA; Stephen K. Gill, NOAA; Donald R.
Cahoon, USGS; E. Robert Thieler, USGS; K. Eric Anderson, USGS
Contributing Authors; Duncan FitzGerald, Boston Univ.;
Virginia Burkett, USGS;Jason Samenow, U.S. ERA
KEY FINDINGS
Consensus in the climate science community is that the global climate is changing, mostly due to mankind's increased
emissions of greenhouse gases such as carbon dioxide, methane, and nitrous oxide, from burning of fossil fuels and
land-use change (measurements show a 25 percent increase in the last century). Warming of the climate system
is unequivocal, but the effects of climate change are highly variable across regions and difficult to predict with high
confidence based on limited observations overtime and space. Two effects of atmospheric warming on coasts, which
are relevant at regional, national, and global scales, are sea-level rise and an increase in major cyclone intensity.
Global sea level has risen about 120 meters (at highly variable rates) due to natural processes since the end of the
Last Glacial Maximum (i.e., last Ice Age). More recently, the sea-level rise rate has increased over natural rise due to
an increase in the burning of fossil fuels. In some regions, such as the Mid-Atlantic and much of the Gulf of Mexico,
sea-level rise is significantly greater than the observed global sea-level rise due to localized sinking of the land surface.
The sinking has been attributed to ongoing adjustment of the Earth's crust due to the melting of former ice sheets,
sediment compaction and consolidation, and withdrawal of hydrocarbons from underground.
Instrumental observations overthe past 15 years show that global mean sea level has been highly variable at regional
scales around the world and, on average, the rate of rise appears to have accelerated over twentieth century rates,
possibly due to atmospheric warming causing expansion of ocean water and ice-sheet melting.
Results of climate model studies suggest sea-level rise in the twenty-first century will significantly exceed rates over
the past century. Rates and the magnitude of rise could be much greater if warming affects dynamical processes
that determine ice flow and losses in Greenland and Antarctica.
Beyond the scope of this Product but important to consider, global sea-level elevations at the peak of the last
interglacial warm cycle were 4 to 6 meters (13 to 20 feet) above present, and could be realized within the next
several hundred years if warming and glacier and ice-sheet melting continue.
Coastal regions are characterized by dynamic landforms and processes because they are the juncture between
the land, oceans, and atmosphere. Features such as barrier islands, bluffs, dunes, and wetlands constantly undergo
change due to driving processes such as storms, sediment supply, and sea-level change. Based on surveys overthe
past century, all U.S. coastal states are experiencing overall erosion at highly variable rates. Sea-level rise will have
profound effects by increasing flooding frequency and inundating low-lying coastal areas, but other processes such
as erosion and accretion will have cumulative effects that are profound but not yet predictable with high reliability.
There is some recent scientific opinion that coastal landforms such as barrier islands and wetlands may have thresholds
or tipping points with sea-level rise and storms, leading to rapid and irreversible change.
II
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The U.S. Climate Change Science Program
Chapter I
Nearly one-half of the 6.7 billion people around the world live near the coast and are highly vulnerable to storms
and sea-level rise. In the United States, coastal populations have doubled over the past 50 years, greatly increasing
exposure to risk from storms and sea-level rise. Continued population growth in low-lying coastal regions worldwide
and in the United States will increase vulnerability to these hazards as the effects of climate change become more
pronounced.
Most coastal regions are currently managed under the premise that sea-level rise is not significant and that shorelines
are static or can be fixed in place by engineering structures. The new reality of sea-level rise due to climate change
requires new considerations in managing areas to protect resources and reduce risk to humans. Long-term climate
change impact data are essential for adaptation plans to climate change and coastal zone plans are most useful if
they have the premise that coasts are dynamic and highly variable.
12
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to
A Focus on the Mid-Atlantic Region
III.Ill .•"-••:" ••.-?'
The main objective of this Product is to review and assess
the potential impacts of sea-level rise on U.S. coastal regions.
Careful review and critique of sea-level and climate change
science is beyond the scope of this Product; however, that
information is central in assessing coastal impacts. Climate
and coastal scientific disciplines are relatively recent, and
while uncertainty exists in predicting quantitatively the
magnitude and rates of change in sea level, a solid body of
scientific evidence exists that sea level has risen over the
recent geologic past, is currently rising and contributing to
various effects such as coastal erosion, and has the poten-
tial to rise at an accelerated rate this century and beyond.
Worldwide data also show that rates of global sea-level rise
are consistent with increasing greenhouse gas concentra-
tions and global warming (IPCC, 2001,2007; Hansen et al.,
2007; Broecker and Kunzig, 2008). Global climate change
is already having significant and wide ranging effects on
the Earth's ecosystems and human populations (Nicholls
etal., 2007).
In recognition of the influence of humans on the Earth,
including the global climate, the time period since the nine-
teenth century is being referred to by scientists as the An-
thropocene Era (Pearce, 2007; Zalasiewicz, 2008). Changes
to the global climate have been dramatic and the rapid rate
of climate change observed over the past two decades is an
increasing challenge for adaptation, by humans and animals
and plants alike.
Effects from climate change are not uniform, but vary
considerably from region to region and over a range of time
scales (Nicholls et al., 2007). These variations occur due to
regional and local differences in atmospheric, terrestrial,
and oceanographic processes. The processes driving climate
change are complex and so-called feedback interactions
between the processes can both enhance and diminish sea-
level rise impacts, making prediction of long-term effects
difficult. Accelerated global sea-level rise, a likely major
long-term outcome of climate change, will have increas-
ingly far-reaching impacts on coastal regions of the United
States and around the world (Nicholls et al., 2007). Relative
sea-level rise impacts are already evident for many coastal
regions and will increase significantly during this century
and beyond (FitzGerald et al, 2008; IPCC, 2007; Nicholls
et al., 2007). Sea-level rise will cause significant and often
dramatic changes to coastal landforms (e.g., barrier islands,
beaches, dunes, marshes), as well as ecosystems, estuaries,
waterways, and human populations and development in the
coastal zone (Nicholls et al., 2007; Rosenzweig et al, 2008;
FitzGerald et al., 2008). Low-lying coastal plain regions,
particularly those that are densely populated (e.g., the Mid-
Atlantic, the north central Gulf of Mexico), are especially
vulnerable to sea-level rise and land subsidence and their
combined impacts to the coast and to development in the
coastal zone (e.g., McGranahan etal., 2007; Day etal., 2007a).
The effects of sea-level rise are not necessarily obvious in
the short term, but are evident over the longer term in many
ways. Arguably, the most visible effect is seen in changing
coastal landscapes, which are altered through more frequent
flooding, inundation, and coastal erosion as barrier islands,
beaches, and sand dunes change shape and move landward in
concert with sea-level rise and storm effects. In addition, the
alteration or loss of coastal habitats such as wetlands, bays,
and estuaries has negative impacts on many animal and plant
species that depend on these coastal ecosystems.
Understanding how sea-level rise is likely to affect coastal
regions and, consequently, how society will choose to ad-
dress this issue in the short term in ways that are sustainable
for the long term, is a major challenge for both scientists and
coastal policy makers and managers. While human popula-
tions in high-risk coastal areas continue to expand rapidly,
the analyses of long-term sea-level measurements show that
sea level rose on average 19 centimeters (cm) (7.5 inches
[in]) globally during the twentieth century (Jevrejeva et al.,
2008). In addition, satellite data show global sea-level rise
has accelerated over the past 15 years, but at highly variable
rates on regional scales. Analyses indicate that the magni-
tude and rate of sea-level rise for this century and beyond is
likely to exceed that of the past century (Meehl et al., 2007;
Rahmstorf, 2007; Jevrejeva et al, 2008).
Over the last century, humans have generally responded
to eroding shorelines and flooding landscapes by using
engineering measures to protect threatened property or
by relocating development inland to higher ground. In the
future, these responses will become more widespread and
more expensive for society as sea-level rise accelerates
(Nicholls etal., 2007). Currently, the world population is 6.7
billion people and is predicted to expand to 9.1 billion by the
year 2042 (UN, 2005). Globally, 44 percent of the world's
population lives within 150 kilometers (km) (93 miles [mi])
of the ocean () and
more than 600 million people live in low elevation coastal
zone areas that are less than 10 meters (m) (33 feet [ft])
above sea level (McGranahan et al, 2007), putting them at
significant risk to the effects of sea-level rise. McGranahan
et al. (2007) chose the 10-m elevation to delineate the low
elevation coastal zone in recognition of the limits imposed
by the vertical accuracy of the best available global elevation
datasets. Eight of the 10 largest cities in the world are sited
on the ocean coast. In the United States, 14 of the 20 largest
urban centers are located within 100 km of the coast and less
than 10 m above sea level. Using the year 2000 census data
for U.S. coastal counties as defined by the National Oceanic
13
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I
and Atmospheric Administration (NOAA) and excluding
the Great Lakes states, approximately 126 million people
resided in coastal areas (Crossett et al., 2004). The Federal
Emergency Management Agency (FEMA), using the same
2000 census data but different criteria for defining coastal
counties, estimated the coastal population to be 86 million
people (Crowell, et al., 2007). Regardless, U.S. coastal
populations have expanded greatly over the past 50 years,
increasing exposure to risk from storms and sea-level rise.
Continued population growth in low-lying coastal regions
worldwide and in the United States will increase vulner-
ability to these hazards.
Modern societies around the world have developed and
populations have expanded over the past several thousand
years under a relatively mild and stable world climate and
relatively stable sea level (Stanley and Warne, 1993; Day et
al., 2007b). However, with continued population growth,
particularly in coastal areas, and the probability of acceler-
ated sea-level rise and increased storminess, adaptation to
expected changes will become increasingly challenging.
This Product reviews available scientific literature through
late 2008 and assesses the likely effects of sea-level rise
on the coast of the United States, with a focus on the mid-
Atlantic region. An important point to emphasize is that
sea-level rise impacts will be far-reaching. Coastal lands will
not simply be flooded by rising seas, but will be modified
by a variety of processes (e.g., erosion, accretion) whose
impacts will vary greatly by location and geologic setting.
For example, the frequency and magnitude of flooding may
change, and sea-level rise can also affect water table eleva-
tions, impacting fresh water supplies. These changes will
have abroad range of human and environmental impacts. To
effectively cope with sea-level rise and its impacts, current
policies and economic considerations should be examined,
and possible options for changing planning and management
activities are warranted so that society and the environment
are better able to adapt to potential accelerated rise in sea
level. This Product examines the potential coastal impacts
for three different plausible scenarios of future sea-level rise,
and focuses on the potential effects to the year 2100. The
effects, of course, will extend well beyond 2100, but detailed
discussion of effects farther into the future is outside the
scope of this Product.
I.I.I for
The scientific study of climate change and associated global
sea-level rise is complicated due to differences in observa-
tions, data quality, cumulative effects, and many other fac-
tors. Both direct and indirect methods are useful for study-
ing past climate change. Instrument records and historical
documents are most accurate, but are limited to the past 100
to 150 years in the United States. Geological information
from analyses of continuous cores sampled from ice sheets
and glaciers, sea and lake sediments, and sea corals provide
useful proxies that have allowed researchers to decipher past
climate conditions and a record of climate and sea-level
changes stretching back millions of years before recorded
history (Miller et al, 2005; Jansen et al, 2007). The most
precise methods have provided accurate high-resolution
data on the climate (e.g., global temperature, atmospheric
composition) dating back more than 400,000 years.
The Intergovernmental Panel on Climate Change (IPCC)
2007 Fourth Assessment Report provides a comprehensive
review and assessment of global climate change trends, ex-
pected changes over the next century, and the impacts and
challenges that both humans and the natural world are likely
to be confronted with during the next century (IPCC, 2007).
Some key findings from this Report are summarized in Box
1.1. A 2008 U.S. Climate Change Science Program (CCSP)
report provides a general assessment of current scientific
understanding of climate change impacts to the United
States (CENR, 2008) and the recent CCSP Synthesis and
Assessment Product (SAP) 3.4 on Abrupt Climate Change
discusses the effects of complex changes in ice sheets and
glaciers on sea level (Steffen et al, 2008). CCSP SAP 4.1
provides more specific information and scientific consensus
on the likely effects and implications of future sea-level
rise on coasts and wetlands of the United States and also
includes a science strategy for improving the understanding
of sea-level rise, documenting its effects, and devising robust
models and methods for reliably predicting future changes
and impacts to coastal regions.
1,2
The elevation of global sea level is determined by the dy-
namic balance between the mass of ice on land (in glaciers
and ice sheets) and the mass of water in ocean basins.
Both of these factors are highly influenced by the Earth's
atmospheric temperature. During the last 800,000 years,
global sea level has risen and fallen about 120 m (400 ft)
in response to the alternating accumulation and decline
of large continental ice sheets about 2 to 3 km (1 to 2 mi)
thick as climate warmed and cooled in naturally occurring
100,000 year astronomical cycles (Imbrie and Imbrie, 1986;
Lambeck et al, 2002). Figure 1.1 shows a record of large
global sea-level change over the past 400,000 years during
the last four cycles, consisting of glacial maximums with
low sea levels and interglacial warm periods with high sea
levels. The last interglacial period, about 125,000 years ago,
lasted about 10,000 to 12,000 years, with average tempera-
tures warmer than today but close to those predicted for the
next century, and global sea level was 4 to 6 m (13 to 20 ft)
higher than present (Imbrie and Imbrie, 1986). Following
the peak of the last Ice Age about 21,000 years ago, the
14
-------
Recent Global Climate Change:
Note: The likelihood scale, established by the IPCC and used throughout SAP 4.1, is described in the Preface
(page XV). The terms used in that scale will be italicized when used as such in this Product.
Warming of the climate system is unequivocal, as is now evident from observations of increases in global aver-
age air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.
Human-induced increase in atmospheric carbon dioxide is the most important factor affecting the warming
of the Earth's climate since the start of the Industrial Era. The atmospheric concentration of carbon dioxide
in 2005 exceeds by far the natural range over the last 650,000 years.
Most of the observed increase in global average temperatures since the mid-twentieth century is very likely
due to the observed increase in human-caused greenhouse gas concentrations. Discernible human influences
now extend to other aspects of climate, including ocean warming, continental-average temperatures, tem-
perature extremes, and wind patterns.
Recent Global Sea-Level Rise:
Observations since 1961 show that the average temperature of the global ocean has increased to depths of at
least 3,000 meters (m) and that the ocean has been absorbing more than 80 percent of the heat added to the
climate system. Such warming causes seawater to expand, contributing to global sea-level rise.
Mountain glaciers and snow cover have declined on average in both hemispheres. Widespread decreases in
glaciers and ice caps have contributed to global sea-level rise.
New data show that losses from the ice sheets of Greenland and Antarctica have very likely contributed to
global sea-level rise between 1993 and 2003.
Global average sea level rose at an average rate of 1.8 (1.3 to 2.3) millimeters (mm) per year between 1961
and 2003. The rate was faster between 1993 and 2003: about 3.1 (2.4 to 3.8) mm per year. Whether the
faster rate for 1993 to 2003 reflects decadal variability or an increase in the longer term trend is unclear (see
Figure 1.3).
Global average sea level in the last interglacial period (about 125,000 years ago) was Iikely4 to 6 m higherthan
during the twentieth century, mainly due to the retreat of polar ice. Ice core data indicate that average polar
temperatures at that time were 3 to 5°C higher than present, because of differences in the Earth's orbit. The
Greenland ice sheet and other arctic ice fields likely contributed no more than 4 m of the observed global
sea-level rise. There may also have been contributions from Antarctica ice sheet melting.
Projections of the Future:
Continued greenhouse gas emissions at or above current rates would cause further warming and induce many
changes in the global climate system during the twenty-first century that would very likely be larger than those
observed during the twentieth century.
Based on a range of possible greenhouse gas emissions scenarios for the next century, the IPCC estimates
the global increase in temperature will likely be between I.I and 6.4°C. Estimates of sea-level rise for the
same scenarios are 0.18 m to 0.59 m, excluding the contribution from accelerated ice discharges from the
Greenland and Antarctica ice sheets.
Extrapolating the recent acceleration of ice discharges from the polar ice sheets would imply an additional
contribution up to 0.20 m. If melting of these ice caps increases, larger values of sea-level rise cannot be
excluded.
In addition to global sea-level rise, the storms that lead to coastal storm surges could become more intense.
The IPCC indicates that, based on a range of computer models, it is likely that hurricanes will become more
intense, with larger peak wind speeds and more heavy precipitation associated with ongoing increases of
tropical sea surface temperatures, while the tracks of "winter" orextratropical cyclones are projected to shift
towards the poles along with some indications of an increase in intensity in the North Atlantic.
15
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The U.S. Climate Change Science Program
Chapter I
400,000 Years of Global Sea-Level Elevation Change
-400 -300 -200 -100
Thousands of years before present
Figure I.I Plot of large variations in global sea-level elevation over the last 400,000 years resulting
from four natural glacial and interglacial cycles. Evidence suggests that sea level was about 4 to 6 meters
(m) higher than present during the last interglacial warm period 125,000 years ago and 120 m lower
during the last Ice Age, about 21,000 years ago (see reviews in Muhs et a/., 2004 and Overpeck et a/.,
2006). (Reprinted from Quaternary Science Reviews, 21/1-3, Phillippe Huybrechts, Sea-level changes
at the LGM from ice-dynamic reconstructions of the Greenland and Antarctic ice sheets during the
glacial cycles, 203-231, Copyright [2002], with permission from Elsevier).
Global Sea-Level Rise Over Time
Present-Day Sea Level
0
10
20
f 30
to
cc 40
ffl
in
c 50
Hi
crt
£
a. 60
o
o 70
QJ 80
O
~ 90
Q 100
110
Figure 1.2 Generalized plot of
the rise in global sea level at vari-
able rates over the last 18,000
years as the Earth moved from
a glacial period to the present
interglacial warm period. This
curve is reconstructed from
radiocarbon-dated corals from
Barbados (filled circles) and
four other Caribbean island
locations (open circles). The
radiocarbon age (not calendar
years) and depth of each sample
from present mean sea level is
plotted. Modified and reprinted
by permission from Macmillan
Publishers Ltd: Nature (Fair-
banks, R.G., A 17,000-year
glacio-eustatic sea level record-
influence of glacial melting rates
on the Younger Dryas event and
deep-sea circulation, 349[6250],
637-642, ©1989).
18 17161514 1312 11 10 9876543210
Time (thousands of years before present)
Earth entered the present interglacial warm period. Global
sea level rose very rapidly at average rates of 10 to 20 mm
per year punctuated with periodic large "meltwater pulses"
with rates of more than 50 mm per year from about 21,000 to
6,000 years ago. Sea-level rise then slowed to a rate of about
0.5 mm per year from 6,000 to 3,000 years ago (Fairbanks,
1989; Rohling et al, 2008). During the past 2,000 to 3,000
years, the rate slowed to approximately 0.1 to 0.2 mm per
16
-------
year until an acceleration occurred in the late
nineteenth century (Lambeck and Bard, 2000;
IPCC, 2001).
There is growing scientific evidence that, at the
onset of the present interglacial warm period,
the Earth underwent abrupt changes when the
climate system crossed several thresholds or
tipping points (points or levels in the evolution
of the Earth's climate leading to irreversible
change) that triggered dramatic changes in tem-
perature, precipitation, ice cover, and sea level.
These changes are thought to have occurred
over a few decades to a century and the causes
are not well understood (NRC, 2002; Alley et
al., 2003). One cause is thought to be disruption
of major ocean currents by influxes of fresh
water from glacial melt. It is not known with any
confidence how anthropogenic climate change
might alter the natural glacial-interglacial cycle
or the forcings that drive abrupt change in the
Earth's climate system. Imbrie and Imbrie
(1986) surmise that the world might experience
a "super-interglacial" period with mean tem-
peratures higher than past warm periods.
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Changes in Global Mean Sea Level Since 1870
100
50-
T!
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The U.S. Climate Change Science Program
Chapter I
Twentieth Century Localized Average Sea-Level Rise Rates
130*W 120°W 110°W 100°W 90°W 80°W 7Q°W 60°W
40*N
30°N
064
2.22
2000
4000 Km
O NOAA Tide Gauge Stalions with
records exceeding 50 years.
Rales in mm/yr,
40°N
20°N
120°W HOfW IOO°W 9C°W 80°W
Figure 1.4 Map of twentieth century annual relative sea-level rise rates around the U.S.
coast. The higher rates for Louisiana (9.85 millimeters [mm] per year) and the mid-Atlantic
region (1.75 to 4.42 mm per year) are due to land subsidence. Sea level is stable or dropping
relative to the land in the Pacific Northwest, as indicated by the negative values, where the
land is tectonically active or rebounding upward in response to the melting of ice sheets since
the last Ice Age (data from Zervas, 2001).
The rate of relative sea-level rise
(see Box 1.2 for definition) mea-
sured by tide gauges at specific
locations along the Atlantic coast
of the United States varies from
1.75 mm to as much as 4.42 mm
per year (Table 1.1; Figure 1.4;
Zervas, 2001). The lower rates,
which occur along New England
and from Georgia to northern
Florida, are close to the global rate
of 1.7 (±0.5) mm peryear (Bindoff
et al., 2007). The highest rates
are in the mid-Atlantic region
between northern New Jersey and
southern Virginia. Figure 1.5 is an
example of the monthly average
(mean) sea-level record and the
observed relative sea-level rise
trend at Baltimore, Maryland.
At this location, the relative sea-
level trend is 3.12 (±0.08) mm per
year, almost twice the present rate
of global sea-level rise. Subsid-
ence of the land surface, attrib-
uted mainly to adjustments of the
BOX 1.2: Relative Sea Leve
"Global sea-level rise" results mainly from the worldwide increase in the volume of the world's oceans that
occurs as a result of thermal expansion of warming ocean water and the addition of water to the ocean from
melting ice sheets and glaciers (ice masses on land). "Relative sea-level rise" is measured directly by coastal
tide gauges, which record both the movement of the land to which they are attached and changes in global
sea level. Global sea-level rise can be estimated from tide gauge data by subtracting the land elevation change
component. Thus, tide gauges are important observation instruments for measuring sea-level change trends.
However, because variations in climate and ocean circulation can cause fluctuations over 10-year time periods,
the most reliable sea level data are from tide gauges having records 50 years or longer and for which the rates
have been adjusted using a global isostatic adjustment model (Douglas, 2001).
At regional and local scales along the coast, vertical movements of the land surface can also contribute sig-
nificantly to sea-level change and the combination of global sea-level and land-level change is referred to as
"relative sea level" (Douglas, 2001). Thus, "relative sea-level rise" refers to the change in sea level relative to
the elevation of the land, which includes both global sea-level rise and vertical movements of the land. Both
terms, global sea level and relative sea level, are used throughout this Product.
Vertical changes of the land surface result from many factors including tectonic processes and subsidence
(sinking of the land) due to compaction of sediments and extraction of subsurface fluids such as oil, gas, and
water. A principal contributor to this change along the Atlantic Coast of North America is the vertical relax-
ation adjustments of the Earth's crust to reduced ice loading due to climate warming since the last Ice Age. In
addition to glacial adjustments, sediment loading also contributes to regional subsidence of the land surface.
Subsidence contributes to high rates of relative sea-level rise (9.9 millimeters per year) in the Mississippi River
delta where thick sediments have accumulated and are compacting. Likewise, fluid withdrawal from coastal
aquifers causes the sediments to compact locally as the water is extracted. In Louisiana, Texas, and Southern
California, oil, gas, and ground-water extraction have contributed markedly to subsidence and relative sea-
level rise (Gornitz and Lebedeff, 1987; Emery and Aubrey, 1991; Nicholls and Leatherman, 1996; Galloway et
al., 1999; Morton et al., 2004). In locations where the land surface is subsiding, rates of relative sea-level rise
exceed the average rate of global rise (e.g., the north central Gulf of Mexico Coast and mid-Atlantic coast).
18
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Table I.I Rates of Relative Sea-Level Rise for Selected Long-Term Tide Gauges on the Atlantic Coast of the United
States (Zervas, 2001). For comparison, the global average rate is 1.7 millimeters (mm) per year.
Rate of Sea-Level Rise Time Span
(mmperyear) of Record
Eastport, ME
Portland, ME
Seavey Island, ME
Boston, MA
Woods Hole, MA
Providence, Rl
Newport, Rl
New London, CT
Montauk, NY
Willets Point, NY
The Battery, NY
Sandy Hook, NJ
Atlantic City, NJ
Philadelphia, PA
2.12 ±0.13
1.91 ±0.09
1.75 ±0.1 7
2.65 ±0.1
2.59 ±0.12
1.88 ±0.17
2.57 ±0.11
2.13 ±0.15
2. 58 ±0.19
2.41 ±0.15
2.77 ±0.05
3.88 ±0.15
3.98 ±0.11
2.75 ±0.12
1929-1999
1912-1999
1926-1999
1921-1999
1932-1999
1938-1999
1930-1999
1938-1999
1947-1999
1931-1999
1905-1999
1932-1999
1911-1999
1900-1999
(mmperyear)
Lewes, DE
Baltimore, MD
Annapolis, MD
Solomons Island, MD
Washington, DC
Hampton Roads, VA
Portsmouth, VA
Wilmington, NC
Charleston, SC
Fort Pulaski, GA
Fernandina Beach, FL
Mayport, FL
Miami, FL
Key West, FL
3. 16 ±0.16
3.12 ±0.16
3. 53 ±0.13
3.29 ±0.17
3.13 ±0.21
4.42 ±0.1 6
3.76 ±0.23
2.22 ±0.25
3.28 ±0.14
3.05 ±0.20
2.04 ±0.12
2.43 ±0.18
2.39 ±0.22
2.27 ±0.09
Time Span
of Record
1919-1999
1902-1999
1928-1999
1937-1999
1931-1999
1927-1999
1935-1999
1935-1999
1921-1999
1935-1999
1897-1999
1928-1999
1931-1999
1913-1999
0.60
0.45- -
0.30- -
Twentieth Century Record of Average Sea Level for Baltimore, Maryland
Baltimore, MD 3.08 +/- 0.15 millimeters/year
-0.30'
-0.45-
6
d cycfe fwwwd
- Upper 96% cnnfcoooc* interval
Source: NOAA
\ \ \ \
\ \ \ \ \ \ \ \ \ \ \ \ \
Figure 1.5 The monthly computed average sea-level record (black line) from 1900 to 2006 from the Baltimore,
Maryland tide gauge. Blue line is the observed data. The zero line is the latest 19-year National Tidal Datum Epoch
mean value. The rate, 3.12 millimeters (mm) per year, is nearly double the present rate (1.7 mm per year) of global
sea-level rise due to land subsidence (based on Zervas, 2001).
Earth's crust in response to the melting of the Laurentide ice
sheet and to the compaction of sediments due to freshwater
withdrawal from coastal aquifers, contributes to the high
rates of relative sea-level rise observed in this region (Gor-
nitz and Lebedeff, 1987; Emery and Aubrey, 1991; Kearney
and Stevenson, 1991; Douglas, 2001; Peltier, 2001).
While measuring and dealing with longer-term global aver-
ages of sea-level change is useful in understanding effects
on coasts, shorter-term and regional-scale variations due
primarily to warming and oceanographic processes can be
quite different from long-term averages, and equally impor-
tant for management and planning. As shown in Figure 1.6,
from Bindoff et al. (2007) based on a decade of data, some
of the highest rates of rise are off the U.S. Mid-Atlantic and
the western Pacific, while an apparent drop occurred off the
North and South American Pacific Coast.
Recently, the IPCC Fourth Assessment Report (IPCC, 2007)
estimated that global sea level is likely to rise 18 to 59 cm (7
19
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The U.S. Climate Change Science Program
Chapter I
a)
60
30
0
-30
-60
Trends in Mean Sea Level and Thermal Expansion
W
^*
"**W
120
180
240
300
60
30
0
-30
-eo
360
•-.
BO
120
180
240
300
360
-15 -12
9 12 15
-3-303
Millimeters pet year
Figure 1.6 (a) Geographic distribution of short-term linear trends in mean sea level (millimeters per year) for 1993 to 2003
based on TOPEX/Poseidon satellite altimetry (updated from Cazenave and Nerem, 2004) and (b) geographic distribution of
linear trends in thermal expansion (millimeters per year) for 1993 to 2003 (based on temperature data down to 700 meters
[from Ishii et al., 2006]). (Adapted from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the
Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Figure 5.15. Cambridge University Press).
to 23 in) over the next century; however, possible increased
meltwater contributions from Greenland and Antarctica
were excluded (Meehl etal, 2007; IPCC, 2007). The IPCC
projections (Figure 1.7) represent a "likely range" which
inherently allows for the possibility that the actual rise may
be higher or lower. Recent observations suggest that sea-
level rise rates may already be approaching the higher end
of the IPCC estimates (Rahmstorf et al., 2007; Jevrejeva et
Observed and Projected Sea-Level Rise
140
1900
1950
2000
Year
Figure 1.7 Plot in centimeters (cm) rise over time of past sea-level observations and sev-
eral future sea-level projections to the year 2100. The blue shaded area is the sea-level rise
projection by Meehl et al. (2007) corresponding to the AIB emissions scenario which forms
part of the basis for the IPCC (2007) estimates. The higher gray and dash line projections
are from Rahmstorf (2007). (Modified from: Rahmstorf, S., 2007: A semi-empirical approach
to projecting future sea-level rise. Science, 315(5810), 368-370. Reprinted with permission
from AAAS.)
20
al., 2008). This is because potentially important meltwater
contributions from Greenland and Antarctica were excluded
due to limited data and an inability at that time to ad-
equately model ice flow processes. It has been suggested by
Rahmstorf (2007) and other climate scientists that a global
sea-level rise of 1 m (3 ft) is plausible within this century
if increased melting of ice sheets in Greenland and Antarc-
tica is added to the factors included in the IPCC estimates.
Therefore, thoughtful precaution
suggests that a global sea-level rise
of 1 m to the year 2100 should be
considered for future planning and
policy discussions.
This Product focuses on the effects
of sea-level rise on U.S. coasts
over the next century, but climate
warming and its effects are likely to
continue well beyond that due to the
amount of greenhouse gases already
in the atmosphere. Currently, the
amount of potential melting from
land-based ice masses (primarily
Greenland and West Antarctica) is
uncertain and is therefore not fully
incorporated into all sea-level rise
model projections. Recent observa-
tions of changes in ice cover and
glacial melting on Greenland, West
Antarctica, and smaller glaciers and
ice caps around the world indicate
that ice loss could be more rapid than
the trends evaluated for the IPCC
(2007) report (Chen et al., 2006;
2050
2100
-------
Shepherd and Wingham, 2007; Meier et al, 2007; Fettweis
et al., 2007). The science needed to assign probability to
these high scenarios is not yet well established, but scientists
agree that this topic is worthy of continued study because of
the grave implications for coastal areas in the United States
and around the world.
'. ited States
Coastal communities and habitats will be increasingly
stressed by climate change impacts due to sea-level rise
and storms (Field et al., 2007). To varying degrees over
decades, rising sea level will affect entire coastal systems
from the ocean shoreline well landward. The physical and
ecological changes that occur in the near future will impact
people and coastal development. Impacts from sea-level
rise include: land loss through submergence and erosion of
lands in coastal areas; migration of coastal landforms and
habitats; increased frequency and extent of storm-related
flooding; wetland losses; and increased salinity in estuar-
ies and coastal freshwater aquifers. Each of these effects
can have impacts on both natural ecosystems and human
developments. Often the impacts act together and the effects
are cumulative. Other impacts of climate change, such as
increasingly severe droughts and storm intensity—combined
with continued rapid coastal development—could increase
the magnitude and extent of sea-level rise impacts (Nicholls,
et al., 2007). To deal with these impacts, new practices in
managing coasts and the combined impacts of mitigating
changes to the physical system (e.g., coastal erosion or mi-
gration, wetland losses) and impacts to human populations
(e.g., property losses, more frequent flood damage) should
be considered.
Global sea-level rise, in combination with the factors above,
is already having significant effects on many U.S. coastal
areas. Flooding of low-lying regions by storm surges and
spring tides is becoming more frequent. In certain areas,
wetland losses are occurring, fringe forests are dying and
being converted to marsh, farmland and lawns are being
converted to marsh (e.g., see Riggs and Ames, 2003,2007),
and some roads and urban centers in low elevation areas are
more frequently flooded during spring high tides (Douglas,
2001). In addition, "ghost forests" of standing dead trees
killed by saltwater intrusion are becoming increasingly
common in southern New Jersey, Maryland, Virginia, Loui-
siana, and North Carolina (Riggs and Ames, 2003). Relative
sea-level rise is causing saltwater intrusion into estuaries
and threatening freshwater resources in some parts of the
mid-Atlantic region (Barlow, 2003).
Continued rapid coastal development exacerbates both the
environmental and the human impact of rising sea level. Due
to the increased human population in coastal areas, once
sparsely developed coastal areas have been transformed into
high-density year-round urban complexes (e.g., Ocean City,
Maryland; Virginia Beach, Virginia; Myrtle Beach, South
Carolina). With accelerated rise in sea level and increased
intensity of storms, the vulnerability of development at the
coast and risks to people will increase dramatically unless
new and innovative coastal zone management and planning
approaches are employed.
1,4,2 Climate Change;, Sea-Level Rise, and Storms
Although storms occur episodically, they can have long-term
impacts to the physical environment and human populations.
Coupled with rise in sea level, the effects of storms could
be more extensive in the future due to changes in storm
character, such as intensity, frequency, and storm tracking.
In addition to higher sea level, coastal storm surge from hur-
ricanes could become higher and more intense rainfall could
raise the potential for flooding from land runoff. Recent
studies (e.g., Emanuel, et al, 2004, 2008; Emanuel, 2005;
Komar and Allen, 2008; Eisner et al, 2008) have concluded
that there is evidence that hurricane intensity has increased
during the past 30 years over the Atlantic Ocean; however,
it is unknown whether these trends will continue. A recent
evaluation of climate extremes concluded that it is presently
unknown whether the global frequency of hurricanes will
change (Karl et al, 2008).
Land-falling Atlantic coast hurricanes can produce storm
surges of 5 m (16 ft) or more (Karl et al, 2008). The power
and frequency of Atlantic hurricanes has increased substan-
tially in recent decades, though North American mainland
land-falling hurricanes do not appear to have increased over
the past century (Karl et al, 2008). The IPCC (2007) and
Karl et al. (2008) indicate that, based on computer models,
it is likely that hurricanes will become more intense, with
increases in tropical sea surface temperatures. Although
hurricane intensity is expected to increase on average, the
effects on hurricane frequency in the Atlantic are still not
certain and are the topic of considerable scientific study
(Eisner et al, 2008; Emanuel et al, 2008; see also review
in Karl et al, 2008).
Extratropical cyclones can also produce significant storm
surges. These storms have undergone a northward shift in
track over the last 50 years (Karl et al, 2008). This has re-
duced storm frequencies and intensities in the mid-latitudes
and increased storm frequencies and intensities at high
latitudes (Gutowski etal, 2008). Karl etal. (2008) conclude
that future intense extratropical cyclones will become more
frequent with stronger winds and more extreme wave heights
though the overall number of storms may decrease. So, while
21
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The U.S. Climate Change Science Program
Chapter I
U.S. Shoreline Erosion Over the Past Century
PACIFIC
OCEAN
am
WilmirwtonJ^
3T ATLANTIC
Arlprfdnrn m
OCEAN
ANNUAL SHORELINE CHANGE
I j Severely eroding
Moderately eroding
| Reialwely stable
UncolCKed U. 5 shoreline indicates no data
are available; clala are also lacking for parts
of Alaska, as well as Puerto Rico U.S.
Virgin Islands, and tne U.S. Pacific Islands.
which are not shown on this map
""•"""•• ii m
TampaV _
GULF OF MEXICO ^. B
'^Miami
Alaska Scale
A
U.S. Scale Alaska Scale
I ' .' .'. .I5"."'16* t^rW^
I ii r i iTT o
TOO KILOMETERS
Hawai Scale
0
Figure 1.8 Shoreline change around the United States based on surveys over the past century. All 30 coastal states are
experiencing overall erosion at highly variable rates due to natural processes (e.g., storms, sea-level rise) and human activity
(From USGS, 1985).
general storm projections are possible, specific projections
for regional changes in extratropical cyclone activity, such
as for the mid-Atlantic coast, are not yet available. Thus,
while increased storm intensity is a serious risk in concert
with sea-level rise, specific storm predictions are not so well
established that planners can yet rely on them.
1.4.3 Shoreline Change and Coastal Erosion
The diverse landforms comprising more than 152,750 km
(95,471 mi) of U.S. tidal coastline () reflect a dynamic interaction between:
(1) natural factors and physical processes that act on the
coast (e.g., storms, waves, currents, sand sources and sinks,
relative sea level), (2) human activity (e.g., dredging, dams,
coastal engineering), and (3) the geological character of the
coast and nearshore. Variations of these physical processes
in both location and time, and the local geology along the
coast, result in the majority of the U.S. coastlines undergoing
overall long-term erosion at highly varying rates, as shown
in Figure 1.8.
The complex interactions between these factors make it
difficult to relate sea-level rise and shoreline change and to
reach agreement among coastal scientists on approaches to
predict how shorelines will change in response to sea-level
rise. The difficulty in linking sea-level rise to coastal change
stems from the fact that shoreline change is not driven
solely by sea-level rise. Instead, coasts are in dynamic flux,
responding to many driving forces, such as the underlying
geological character, changes in tidal flow, and volume of
sediment in the coastal system. For example, FitzGerald et
al. (2008) discuss the dramatic effects that changes in tidal
wetland area can have on entire coastal systems by alter-
ing tidal flow, which in turn affects the size and shape of
tidal inlets, ebb and flood tide deltas, and barrier islands.
Consequently, while there is strong scientific consensus that
climate change is accelerating sea-level rise and affecting
coastal regions, there are still considerable uncertainties
predicting in any detail how the coast will respond to future
sea-level rise in concert with other driving processes.
There is some scientific opinion that barrier islands, wet-
lands, and other parts of coastal systems might have tipping
points or thresholds, such that when limits are exceeded the
landforms become unstable and undergo large irreversible
changes (NRC, 2002; Riggs and Ames, 2003; Nicholls et al,
22
-------
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
2007). These changes are thought to occur rapidly and are
thus far unpredictable. It is possible that this is happening
to barrier islands along the Louisiana coast that are subject
to high rates of sea-level rise, frequent major storms over
the past decade, and limited sediment supply (Sallenger et
al., 2007). Further deterioration of the barrier islands and
wetlands may also occur in the near future along the North
Carolina Outer Banks coast as a result of increased sea-level
rise and storm activity (Culver et al., 2007,2008; Riggs and
Ames, 2003).
1.4.4 Managing the Coastal Zone
as Sea Level Rises
A key issue for coastal zone management is how and where
to adapt to the changes that will result from sea-level rise in
ways that benefit or minimize impacts to both the natural en-
vironment and human populations. Shore protection policies
have been developed in response to shoreline retreat prob-
lems that affect property or coastal wetland losses. While
it is widely recognized that sea-level rise is an underlying
cause of these changes, there are few existing policies that
explicitly address or incorporate sea-level rise into decision
making. Many property owners and government programs
engage in coastal engineering activities designed to protect
property and beaches such as beach nourishment or seawall
or breakwater construction. Some of the current practices
affect the natural behavior of coastal landforms and disrupt
coastal ecosystems. In the short term, an acceleration of
sea-level rise may simply increase the cost of current shore
protection practices. In the long term, policy makers might
evaluate whether current approaches and justifications for
coastal development and protection need to be modified to
reflect the increasing vulnerability to accelerating rates of
sea-level rise.
To facilitate these decisions, policy makers require credible
scientific data and information. Predicting sea-level rise
impacts such as shoreline changes or wetland losses with
quantitative precision and certainty is often not possible. Re-
lated effects of climate change, including increased storms,
precipitation, runoff, drought, and sediment supply add to
the difficulty of providing accurate reliable information.
Predicting future effects is challenging because the ability to
accurately map and quantify the physical response of the
coast to sea-level rise, in combination with the wide variety
of other processes and human engineering activities along
the shoreline, has not yet been well developed.
In the United States, coastal regions are generally managed
under the premise that sea level is stable, shorelines are
static, and storms are regular and predictable. This Product
examines how sea-level rise and changes in storm intensity
and frequency due to climate change call for new consid-
erations in managing areas to protect resources and reduce
risk. This SAP 4.1 also examines possible strategies for
coastal planning and management that will be effective as
sea-level rise accelerates. For instance, broader recognition
is needed that coastal sediments are a valuable resource,
23
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Chapter I
best conserved by implementing Best Coastal Sediment
Management practices (see ) on local, regional, and national levels in order to
conserve sediment resources and maintain natural sediment
transport processes.
This Product assesses the current scientific understanding
of how sea-level rise can impact the tidal inundation of
low-lying lands, ocean shoreline processes, and the vertical
accretion of tidal wetlands. It also discusses the challenges
that will be present in planning for future sea-level rise and
adapting to these impacts. The SAP 4.1 is intended to pro-
vide information for coastal decision makers at all levels of
government and society so they can better understand this
topic and incorporate the effects of accelerating rates of sea-
level rise into long-term management and planning.
24
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
KEY FINDINGS
Coastal changes are driven by complex and interrelated processes. Inundation will be the primary response
to sea-level rise in some coastal locations; yet there has been little recognition in previous studies that
inundation is just one of a number of possible responses to sea-level rise. A challenge remains to quantify
the various effects of sea-level rise and to identify the areas and settings along the coast where inundation
will be the dominant coastal change process in response to rising seas.
Sheltered, low-energy coastal areas, where sediment influx is minimal and wetlands are absent or are
unable to build vertically in response to rising water levels, may be submerged. In these cases, the extent
of inundation is controlled largely by the slope of the land, with a greater degree of inundation occurring
in areas with more gentle gradients. In areas that are vulnerable to a simple inundation response to rising
seas, elevation is a critical factor in assessing potential impacts.
Accurate delineations of potential inundation zones are critical for meeting the challenge of fully determining
the potential socioeconomic and environmental impacts of predicted sea-level rise.
Coastal elevation data have been widely used to quantify the potential effects of predicted sea-level rise,
especially the area of land that could be inundated and the affected population. Because sea-level rise impact
assessments often rely on elevation data, it is critical to understand the inherent accuracy of the underlying
data and its effects on the uncertainty of any resulting vulnerability maps and statistical summaries.
The accuracy with which coastal elevations have been mapped directly affects the reliability and usefulness
of sea-level rise impact assessments. Although previous studies have raised awareness of the problem
of mapping and quantifying sea-level rise impacts, the usefulness and applicability of many results are
hindered by the coarse resolution of available input data. In addition, the uncertainty of elevation data is
often neglected.
Existing studies of sea-level rise vulnerability based on currently available elevation data do not provide
the degree of confidence that is optimal for local decision making.
There are important technical considerations that need to be incorporated to improve future sea-level rise
impact assessments, especially those with a goal of producing vulnerability maps and statistical summaries
that rely on the analysis of elevation data. The primary aspect of these improvements focuses on using
high-resolution, high-accuracy elevation data, and consideration and application of elevation uncertainty
information in development of vulnerability maps and area statistics.
25
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The U.S. Climate Change Science Program
Chapter 2
Studies that use elevation data as an input for vulnerability maps and/or statistics need to have a clear statement
of the absolute vertical accuracy. There are existing national standards for quantifying and reporting elevation
data accuracy.
Currently best available elevation data for the entire mid-Atlantic region do not support an assessment using
a sea-level rise increment of I meter or less, using national geospatial standards for accuracy assessment and
reporting. This is particularly important because the I-meter scenario is slightly above the range of current
sea-level rise estimates for the remainder of this century and slightly above the highest scenario used in this
Product.
High-quality lidar elevation data, such as that which could be obtained from a national lidar data collection
program, would be necessary for the entire coastal zone to complete a comprehensive assessment of sea-level
rise vulnerability in the mid-Atlantic region. The availability of such elevation data will narrow the uncertainty
range of elevation datasets, thus improving the ability to conduct detailed assessments that can be used in local
decision making.
26
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to
A Focus on the Mid-Atlantic Region
. . '
Sea-level rise is a coastal hazard that can exacerbate the
problems posed by waves, storm surges, shoreline erosion,
wetland loss, and saltwater intrusion (NRC, 2004). The
ability to identify low-lying lands is one of the key elements
needed to assess the vulnerability of coastal regions to these
impacts. For nearly three decades, a number of large area
sea-level rise vulnerability assessments have focused mainly
on identifying land located below elevations that would
be affected by a given sea-level rise scenario (Schneider
and Chen, 1980; U.S. EPA, 1989; Najjar et al, 2000; Titus
and Richman, 2001; Ericson et al, 2006; Rowley et al,
2007). These analyses require use of elevation data from
topographic maps or digital elevation models (DEMs) to
identify low-lying land in coastal regions. Recent reports
have stressed that sea-level rise impact assessments need to
continue to include maps of these areas subject to inundation
based on measurements of coastal elevations (Coastal States
Organization, 2007; Seiden, 2008). Accurate mapping of
the zones of potential inundation is critical for meeting the
challenge of determining the potential socioeconomic and
environmental impacts of predicted sea-level rise (FitzGer-
ald et al, 2008).
Identification of the socioeconomic impacts of projected
sea-level rise on vulnerable lands and populations is an im-
portant initial step for the nation in meeting the challenge of
reducing the effects of natural disasters in the coastal zone
(Subcommittee on Disaster Reduction, 2008). A number of
state coastal programs are using sea-level rise inundation
models (including linked storm surge/sea-level rise models)
to provide a basis for coastal vulnerability and socioeco-
nomic analyses (Coastal States Organization, 2007). State
coastal managers are concerned that these research efforts
and those of the federal government should be well coor-
dinated, complementary, and not redundant. Despite the
common usage of elevation datasets to investigate sea-level
rise vulnerability, there are limitations to elevation-based
analyses. These limitations are related to the relevance of
this approach in a variety of settings and to the data sources
and methodologies used to conduct these analyses. Thus, an
important objective of this Chapter is to review the available
data and techniques, as well as the suitability of elevation-
based analyses for informing sea-level rise assessments, to
provide guidance for both scientists and coastal managers.
While elevation-based analyses are a critical component
of sea-level rise assessments, this approach only addresses
a portion of the vulnerability in coastal regions. Coastal
changes are driven by complex and interrelated processes
such as storms, biological processes, sea-level rise, and
sediment transport, which operate over a range of time
scales (Carter and Woodroffe, 1994; Brinson et al, 1995;
Eisma, 1995; Pilkey and Cooper, 2004; FitzGerald et al,
2008). The response of a coastal region to sea-level rise can
be characterized by one or more of the processes in the fol-
lowing broad categories (Leatherman, 2001; Valiela, 2006;
FitzGerald et al, 2008):
land loss by inundation of low-lying lands;
land loss due to erosion (removal of material from
beaches, dunes, and cliffs);
barrier island migration, breaching, and segmenta-
tion;
wetland accretion and migration;
wetland drowning (deterioration and conversion to
open water);
expansion of estuaries;
saltwater intrusion (into freshwater aquifers and surface
waters); and
increased frequency of storm flooding (especially of
uplands and developed coastal lands).
Because large portions of the population (both in the United
States and worldwide) are located in coastal regions, each of
these impacts has consequences for the natural environment
as well as human populations. Using elevation datasets to
identify and quantify low-lying lands is only one of many
aspects that need to be considered in these assessments.
Nonetheless, analyses based on using elevation data to
identify low-lying lands provide an important foundation
for sea-level rise impact studies.
There is a large body of literature on coastal processes and
their role in both shoreline and environmental change in
coastal regions (Johnson, 1919; Curray, 1964; Komar, 1983;
Swift et al, 1985; Leatherman, 1990; Carter and Woodroffe,
1994; Brinson, 1995; Eisma, 1995; Wright, 1995; Komar,
1998; Dean and Dalrymple, 2002; FitzGerald et al, 2008).
However, there is generally little discussion of the suitability
of using elevation data to identify the vulnerability of coastal
regions to sea-level rise. While it is straightforward to reason
that low-lying lands occurring below a future sea-level rise
scenario are vulnerable, it is often generally assumed that
these lands will be inundated. Instead, inundation is likely
only one part of the response out of a number of possible
sea-level rise impacts. Despite this, some assessments have
opted for inundation-based assessments due to the lack of
any clear alternatives and the difficulty in accounting for
complex processes such as sedimentation (Najjar et al,
2000). It is plausible that extreme rates of sea-level rise (e.g.,
1 meter or more in a single year) could result in widespread
simple coastal inundation. However, in the more common
and likely case of much lower sea-level rise rates, the physi-
cal processes are more complex and rising seas do not simply
flood the coastal landscape below a given elevation contour
(Pilkey and Thieler, 1992). Instead, waves and currents will
modify the landscape as sea level rises (Bird, 1995; Wells,
27
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Chapter 2
1995). Still, inundation is an important component of coastal
change (Leatherman, 2001), especially in very low gradient
regions such as North Carolina. However, due to the com-
plexity of the interrelated processes of erosion and sediment
redistribution, it is difficult to distinguish and quantify the
individual contributions from inundation and erosion (Pilkey
and Cooper, 2004).
Inundation will be the primary response to sea-level rise only
in some coastal locations. In many other coastal settings,
long-term erosion of beaches and cliffs or wetland deterio-
ration will alter the coastal landscape leading to land loss.
To distinguish the term inundation from other processes,
especially erosion, Leatherman (2001) offered the following
important distinction:
erosion involves the physical removal of sedimentary
material
inundation involves the permanent submergence of
land.
Another term that can confuse the discussion of sea-level rise
and submergence is the term/loading (Wells, 1995; Najjare/
al., 2000), which in some cases has been used interchange-
ably with inundation. Flooding often connotes temporary,
irregular high-water conditions. The term inundation is used
in this Chapter (but not throughout the entire Product) to
refer to the permanent submergence of land by rising seas.
It is unclear whether simply modeling the inundation of the
land surface provides a useful approximation of potential
land areas at risk from sea-level rise. In many settings, the
presence of beaches, barrier islands, or wetlands indicates
that sedimentary processes (erosion, transport, or accumu-
lation of material) are active in both the formation of and/
or retreat of the coastal landscape. Sheltered, low-energy
coastal areas, where sediment influx is minimal and wet-
lands are absent or are unable to build vertically in response
to rising water levels, may be submerged. In these cases, the
extent of inundation is controlled by the slope of the land,
with a greater degree of inundation occurring in the areas
with more gentle gradients (Leatherman, 2001). In addi-
tion, inundation is a likely response in heavily developed
regions with hardened shores. The construction of extensive
seawalls, bulkheads, and revetments to armor the shores of
developed coasts and waterways have formed nearly im-
movable shorelines that may become submerged. However,
the challenge remains to quantify the various effects of
sea-level rise and to identify the areas and settings along the
coast where inundation will be the dominant coastal change
process from sea-level rise.
Despite several decades of research, previous studies do not
provide the full answers about sea-level rise impacts for the
mid-Atlantic region with the degree of confidence that is op-
timal for local decision making. Although these studies have
illuminated the challenges of mapping and quantifying sea-
level rise impacts, the usefulness and applicability of many
results are hindered by the quality of the available input
data. In addition, many of these studies have not adequately
reported the uncertainty in the underlying elevation data and
how that uncertainty affects the derived vulnerability maps
and statistics. The accuracy with which coastal elevations
have been mapped directly affects the reliability and useful-
ness of sea-level rise impact assessments. Elevation datasets
often incorporate a range of data sources, and some studies
have had to rely on elevation datasets that are poorly suited
for detailed inundation mapping in coastal regions, many of
which are gently sloping landscapes (Ericson et al., 2006;
Rowley et al, 2007; McGranahan et al, 2007). In addition
to the limited spatial detail, these datasets have elevation
values quantized only to whole meter intervals, and their
overall vertical accuracy is poor when compared to the
intervals of predicted sea-level rise over the next century.
These limitations can undermine attempts to achieve high-
quality assessments of land areas below a given sea-level
rise scenario and, consequently, all subsequent analyses that
rely on this foundation.
Due to numerous studies that used elevation data, but
have lacked general recognition of data and methodology
constraints, this Chapter provides a review of data sources
and methodologies that have been used to conduct sea-level
rise vulnerability assessments. New high-resolution, high-
accuracy elevation data, especially lidar (light detection and
ranging) data, are becoming more readily available and are
being integrated into national datasets (Gesch, 2007) as well
as being used in sea-level rise applications (Coastal States
Organization, 2007). Research is also progressing on how
to take advantage of the increased spatial resolution and
vertical accuracy of the new data (Poulter and Halpin, 2007;
Gesch, 2009). Still, there is a critical need to thoroughly
evaluate the elevation data, determine how to appropriately
utilize the data to deliver well-founded results, and accu-
rately communicate the associated uncertainty.
The widespread use of vulnerability assessments, and the
attention they receive, is likely an indication of the broad
public interest in sea-level rise issues. Because of this
extensive exposure, it is important for the coastal science
community to be fully engaged in the technical development
of elevation-based analyses. Many recent reports have been
motivated and pursued from an economic or public policy
context rather than a geosciences perspective. It is important
for scientists to communicate and collaborate with coastal
managers to actively identify and explain the applications
and limitations of sea-level rise impact assessments. Argu-
ably, sea-level rise is one of the most visible and understand-
able consequences of climate change for the general public,
28
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to
A Focus on the Mid-Atlantic Region
and the coastal science community needs to ensure that
appropriate methodologies are developed to meet the needs
for reliable information. This Chapter reviews the various
data sources that are available to support inundation vulner-
ability assessments. In addition, it outlines what is needed
to conduct and appropriately report results from elevation-
based sea-level rise vulnerability analyses and discusses the
context in which these analyses need to be applied.
2
Measurement and representation of coastal topography
in the form of elevation data provide critical information
for research on sea-level rise impacts. Elevation data in
its various forms have been used extensively for sea-level
rise studies. This section reviews elevation data sources
in order to provide a technical basis for understanding the
limitations of past sea-level rise impact analyses that have
relied on elevation data. While use of coastal elevation data
is relatively straightforward, there are technical aspects that
are important considerations for conducting valid quantita-
tive analyses.
2.2,1
Topographic maps with elevation contours are perhaps the
most recognized form of elevation information. The U.S.
Geological Survey (USGS) has been a primary source of
topographic maps for well over a century. The base topo-
graphic map series for the United States (except Alaska)
is published at a scale of 1:24,000, and the elevation infor-
mation on the maps is available in digital form as digital
elevation models. The USGS began production of DEMs
matching the l:24,000-scale quadrangle maps in the mid-
1970s using a variety of image-based (photogrammetric)
and cartographic techniques (Osborn et al., 2001). Cover-
age of the conterminous United States with 30-meter (m)
(98-foot [ft]) horizontal resolution DEMs was completed in
1999, with most of the individual elevation models being
derived from the elevation contours and spot heights on the
corresponding topographic maps. Most of these maps have
a 5-ft, 10-ft, 20-ft, or 40-ft contour interval, with 5 ft being
the contour interval used in many low relief areas along the
coast. About the time 30-m DEM coverage was completed,
the USGS began development of a new seamless raster (grid-
ded) elevation database known as the National Elevation
Dataset (NED) (Gesch et al., 2002). As the primary elevation
data product produced and distributed by the USGS, the
NED includes many USGS DEMs as well as other sources
of elevation data. The diverse source datasets are processed
to a specification with a consistent resolution, coordinate
system, elevation units, and horizontal and vertical datums
to provide the user with an elevation product that represents
the best publicly available data (Gesch, 2007). DEMs are also
produced and distributed in various formats by many other
organizations, and they are used extensively for mapping,
engineering, and earth science applications (Maune, 2007;
Maune et al, 2007a).
Because sea-level rise impact assessments often rely on
elevation data, it is important to understand the inherent
accuracy of the underlying data and its effects on the uncer-
tainty of any resulting maps and statistical summaries from
the assessments. For proper quantitative use of elevation
data, it is important to identify and understand the vertical
accuracy of the data. Vertical accuracy is an expression of
the overall quality of the elevations contained in the dataset
in comparison to the true ground elevations at corresponding
locations. Accuracy standards and guidelines exist in general
for geospatial data and specifically for elevation data. For
topographic maps, the National Map Accuracy Standards
(NMAS) issued in 1947 are the most commonly used; they
state that "vertical accuracy, as applied to contour maps on
all publication scales, shall be such that not more than 10
percent of the elevations tested shall be in error by more than
one-half the contour interval" (USGS, 1999). An alternative
way to state the NMAS vertical accuracy standard is that
an elevation obtained from the topographic map will be ac-
curate to within one-half of the contour interval 90 percent
of the time. This has also been referred to as "linear error at
90 percent confidence" (LE90) (Greenwalt and Shultz, 1962).
For example, on a topographic map with a 10-ft contour in-
terval that meets NMAS, 90 percent of the elevations will be
accurate to within 5 ft, or stated alternatively, any elevation
taken from the map will be within 5 ft of the actual elevation
with a 90-percent confidence level. Even though the NMAS
was developed for printed topographic maps and it predates
the existence of DEMs, it is important to understand its ap-
plication because many DEMs are derived from topographic
maps.
As the production and use of digital geospatial data became
commonplace in the 1990s, the Federal Geographic Data
Committee (FGDC) developed and published geospatial
positioning accuracy standards in support of the National
Spatial Data Infrastructure (Maune et al, 2007b). The
FGDC standard for testing and reporting the vertical ac-
curacy of elevation data, termed the National Standard for
Spatial Data Accuracy (NSSDA), states that the "reporting
standard in the vertical component is a linear uncertainty
value, such that the true or theoretical location of the point
falls within +/- of that linear uncertainty value 95 percent of
the time" (Federal Geographic Data Committee, 1998). In
practice, the vertical accuracy of DEMs is often reported as
the root mean square error (RMSE). The NSSDA provides
the method for translating a reported RMSE to a linear er-
ror at the 95-percent confidence level. Maune et al. (2007b)
provide a useful comparison of NMAS and NS SDA vertical
29
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Chapter 2
Table 2.1 Comparison of National Map Accuracy Standards (N MAS) and National Standard for Spatial Data Accuracy
(NSSDA) Vertical Accuracy Values with the Equivalent Common Contour Intervals (Maune et al., 2007b).
5o".«Yf** ;s>^,^', '. ' l~ ,',,^ ';''•'"'!•'•'"
1 ft
2ft
5ft
10 ft
20ft
cm = centimeters; m = meters; ft
0.5ft
1 ft
2.5ft
5ft
10 ft
= feet
''" ';\ *'',?,?,?,«;"
0.30 ft (9.25 cm)
0.61 ft (18.5 cm)
1.52 ft (46.3 cm)
3.04 ft (92.7 cm)
6.08 ft (1.853m)
?,*'- '^"'^•;i';;>;5 ••;""4^-';>-
0.60 ft (18.2 cm)
1.19 ft (36.3 cm)
2.98 ft (90.8 cm)
5.96 ft (1.816 m)
II. 92 ft (3.632m)
accuracy measures for common contour intervals (Table 2.1)
and methods to convert between the reporting standards. The
NSSDA, and in some cases even the older NMAS, provides
a useful approach for testing and reporting the important
vertical accuracy information for elevation data used in
sea-level rise assessments.
2,2,2
Currently, the highest resolution elevation datasets are those
derived from lidar surveys. Collected and post-processed
under industry-standard best practices, lidar elevation data
routinely achieve vertical accuracies on the order of 15 cen-
timeters (cm) (RMSE). Such accuracies are well suited for
analyses of impacts of sea-level rise in sub-meter increments
(Leatherman, 2001). Using the conversion methods between
accuracy standards documented by Maune et al. (2007b), it
can be shown that lidar elevation data with an accuracy of
equal to or better than 18.5 cm (RMSE) is equivalent to a
2-ft contour interval map meeting NMAS.
Lidar is a relatively recent remote sensing technology that
has advanced significantly over the last 10 years to the point
where it is now a standard survey tool used by government
agencies and the mapping industry to collect very detailed,
high-accuracy elevation measurements, both on land and
in shallow water coastal areas. The discussion of lidar in
this Chapter is limited to topographic lidar used to map
land areas. Lidar measurements are acquired using laser
technology to precisely measure distances, most often from
an aircraft, that are then converted to elevation data and in-
tegrated with Global Positioning System (GPS) information
(Fowler et al., 2007). Because of their high vertical accuracy
and spatial resolution, elevation data derived from lidar
surveys are especially useful for applications in low relief
coastal environments. The technical advantages of lidar in
dynamic coastal settings, including the ability to perform
repeat high-precision surveys, have facilitated successful
use of the data in studies of coastal changes due to storm
impacts (Brocketal, 2002; Sallengere/a/., 2003; Stockdon
et al., 2007). Numerous organizations, including many state
programs, have recognized the advantages of lidar for use in
mapping the coastal zone. As an example, the Atlantic states
of Maine, Connecticut, New Jersey, Delaware, Maryland,
North Carolina, and Florida have invested in lidar surveys
for use in their coastal programs (Coastal States Organiza-
tion, 2007; Rubinoff, et al., 2008).
2,2,3 Tides, Level,
Sea-level rise assessments typically focus on understand-
ing potential changes in sea level, but elevation datasets are
often referenced to a "vertical datum", or reference point,
that may differ from sea level at any specific location. In
any work dealing with coastal elevations, water depths, or
water levels, the reference to which measurements are made
must be carefully addressed and thoroughly documented. All
elevations, water depths, and sea-level data are referenced
to a defined vertical datum, but different datums are used
depending on the data types and the original purpose of the
measurements. A detailed treatment of the theory behind
the development of vertical reference systems is beyond
the scope of this Product. However, a basic understanding
of vertical datums is necessary for fully appreciating the
important issues in using coastal elevation data to assess
sea-level rise vulnerability. Zilkoski (2007), Maune et al.
(2007a), and NOAA (2001) provide detailed explanations of
vertical datums and tides, and the brief introduction here is
based largely on those sources.
Land elevations are most often referenced to an orthometric
(sea-level referenced) datum, which is based on a network of
surveyed (or "leveled") vertical control benchmarks. These
benchmarks are related to local mean sea level at specific
tide stations along the coast. The elevations on many topo-
graphic maps, and thus OEMs derived from those maps,
are referenced to the National Geodetic Vertical Datum of
1929 (NGVD 29), which uses mean sea level at 26 tide gauge
sites (21 in the United States and 5 in Canada). Advances
in surveying techniques and the advent of computers for
performing complex calculations allowed the development
of a new vertical datum, the North American Vertical
Datum of 1988 (NAVD 88). Development of NAVD 88
provided an improved datum that allowed for the correction
of errors that had been introduced into the national verti-
cal control network because of crustal motion and ground
30
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to
A Focus on the Mid-Atlantic Refion
subsidence. In contrast to NGVD 29, NAVD
88 is tied to mean sea level at only one tide
station, located at Father Point/Rimouski,
Quebec, Canada. Orthometric datums such
as NGVD 29 and NAVD 88 are referenced to
tide gauges, so they are sometimes informally
referred to as "sea level" datums because they
are inherently tied to some form of mean sea
level. NAVD 88 is the official vertical datum
of the United States, as stated in the Federal
Register in 1993, and as such, it should serve
as the reference for all products using land
elevation data.
Relationship of Vertical Datums for Gibson Island, Chesapeake Bay
0,72ft
0.44ft
0.00ft
-0.04 ft
-0.53 ft
-0,75 ft
-0,80 ft
MHHW
MHW
tJAYQ_80
LM31
MLW
MLLW
NGVD 29
0.219
0.134
0.000
-0.012
-0,163
-0.229
-0.244
m
m
m
m
m
m
m
Water depths (bathymetry data) are usually
referenced vertically to a tidal datum, which
is defined by a specific phase of the tides.
Unlike orthometric datums such as NGVD
29 and NAVD 88, which have national or
international coverage, tidally referenced datums are local
datums because they are relative to nearby tide stations.
Determination of tidal datums in the United States is based
on observations of water levels over a 19-year period, or
tidal epoch. The current official tidal epoch in use is the
1983-2001 National Tidal Datum Epoch (NTDE). Averag-
ing over this period is necessary to remove random and
periodic variations caused by seasonal differences and the
nearly 19-year cycle of the lunar orbit. NTDEs are updated
approximately every 25 years to account for relative sea-
level change (NOAA, 2001). The following are the most
commonly used tidal datums:
Mean higher high water (MHHW): the average of the
higher high water levels observed over a 19-year tidal
epoch (only the higher water level of the pair of high
waters in a tidal day is used);
Mean high water (MHW): the average of the high water
levels observed over a 19-year tidal epoch;
Local mean sea level (LMSL): the average of hourly
water levels observed over a 19-year tidal epoch;
Mean low water (MLW): the average of the low water
levels observed over a 19-year tidal epoch; and
Mean lower low water (MLLW): the average of the
lower low water levels observed over a 19-year tidal
epoch (only the lower water level of the pair of low wa-
ters in a tidal day is used). MLLW is the reference chart
datum used for NOAA nautical chart products.
As an illustration, Figure 2.1 depicts the relationship among
vertical datums for a point located on the shore at Gibson
Island, Chesapeake Bay. These elevations were calculated
with use of the "VDatum" vertical datum transformation
tool (Parker et al., 2003; Myers, 2005), described in the fol-
lowing section. Sea-level rise trends at specific tide stations
are generally calculated based on observed monthly mean
Figure 2.1 Diagram of the VDatum-derived relationship among vertical datums
for a point on the shore at Gibson Island, Chesapeake Bay (shown in feet [ft]
and meters [m]). The point is located between the tide stations at Baltimore and
Annapolis, Maryland, where datum relationships are based on observations. The
numbers represent the vertical difference above or below NAVD 88. For instance,
at this location in the Chesapeake Bay the estimated MLLW reference is more than
20 centimeters (cm) below the NAVD 88 zero reference, whereas local mean sea
level is only about I cm below NAVD zero.
sea level values to filter out the high frequency fluctuations
in tide levels.
Based on surveys at tide stations, NAVD 88 ranges from 15
cm below to 15 cm above LMSL in the mid-Atlantic region.
Due to slopes in the local sea surface from changes in tidal
hydrodynamics, LMSL generally increases in elevation
relative to NAVD 88 for locations increasingly farther up
estuaries and tidal rivers. For smaller scale topographic
maps and coarser resolution OEMs, the two datums are
often reported as being equivalent, when in reality they are
not. The differences should be reported as part of the uncer-
tainty analyses. Differences between NAVD 88 and LMSL
on the U.S. West Coast often exceed 100 cm and must be
taken into account in any inundation mapping application.
Similarly, but more importantly, many coastal projects still
inappropriately use NGVD 29 as a proxy for local mean sea
level in planning, designing, and reference mapping. In the
Mid-Atlantic, due to relative sea level change since 1929, the
elevation of NGVD 29 ranges from 15 cm to more than 50
cm below the elevation of LMSL (1983-2001 NTDE). This
elevation difference must be taken into account in any type
of inundation mapping. Again, because LMSL is a sloped
surface relative to orthometric datums due to the complex-
ity of tides in estuaries and inland waterways, the elevation
separation between LMSL and NGVD 29 increases for
locations farther up estuaries and tidal rivers.
High-resolution datasets that effectively depict elevations
across the land-sea boundary from land into shallow wa-
ter are useful for many coastal applications (NRC, 2004),
although they are not readily available for many areas.
Sea-level rise studies can benefit from the use of integrated
31
-------
2
topographic/bathymetric models because the dynamic land/
water interface area, including the intertidal zone, is properly
treated as one seamless entity. In addition, other coastal re-
search topics rely on elevation data that represent near-shore
topography and bathymetry (water depths), but because
existing topographic, bathymetric, and water level data have
been collected independently for different purposes, they are
difficult to use together. The USGS and the National Oceanic
and Atmospheric Administration (NOAA) have worked
collaboratively to address the difficulties in using disparate
elevation and depth information, initially in the Tampa Bay
region in Florida (Gesch and Wilson, 2002). The key to suc-
cessful integration of topographic, bathymetric, and water
level data is to place them in a consistent vertical reference
frame, which is generally not the case with terrestrial and
marine data. A vertical datum transformation tool called
VDatum developed by NOAA's National Ocean Service
provides the capability to convert topographic, bathymetric
and water level data to a common vertical datum (Parker
et al., 2003; Myers, 2005). Work was completed in mid-
2008 on providing VDatum coverage for the mid-Atlantic
region. VDatum uses tidal datum surfaces, derived from
hydrodynamic models corrected to match observations at
tide stations, to interpolate the elevation differences between
LMSL and NAVD 88. An integrated uncertainty analysis
for VDatum is currently underway by NOAA.
The National Research Council (NRC, 2004) has recog-
nized the advantages of seamless data across the land/water
interface and has recommended a national implementation
of VDatum and establishment of protocols for merged
topographic/bathymetric datasets (NOAA, 2008). Work
has continued on production of other such merged datasets
for coastal locations, including North Carolina and the
Florida panhandle (Feyen et al., 2005, 2008). Integrated
topographic/bathymetric lidar (Nayegandhi et al., 2006;
Guenther, 2007) has been identified as a valuable technol-
ogy for filling critical data gaps at the land/water interface,
which would facilitate development of more high quality
datasets (NRC, 2004).
. ": ."-. r';> . 'I1':'?
Maps that depict coastal areas at risk of potential inundation
or other adverse effects of sea-level rise are appealing
to planners and land managers that are charged with
communicating, adapting to, and reducing the risks (Coastal
States Organization, 2007). Likewise, map-based analyses of
sea-level rise vulnerability often include statistical summaries
of population, infrastructure, and economic activity in the
mapped impact zone, as this information is critical for risk
management and mitigation efforts. Many studies have relied
on elevation data to delineate potential impact zones and
quantify effects. During the last 15 years, this approach has
also been facilitated by the increasing availability of spatially
extensive elevation, demographic, land use/land cover, and
economic data and advanced geographic information system
(GIS) tools. These tools have improved access to data
and have provided the analytical software capability for
producing map-based analyses and statistical summaries.
The body of peer reviewed scientific literature cited in this
Chapter includes numerous studies that have focused on
mapping and quantifying potential sea-level rise impacts.
A number of terms are used in the literature to describe
the adverse effects of sea-level rise, including inundation,
flooding, submergence, and land loss. Likewise, multiple
terms are used to refer to what this Chapter has called vul-
nerability, including at risk, subject to, impacted by, and
affected by. Many reports do not distinguish among the
range of responses to sea-level rise, as described in Section
2.1. Instead, simple inundation, as a function of increased
water levels projected onto the land surface, is assumed to
reflect the vulnerability.
Monmonier (2008) has recognized the dual nature of sea-
level rise vulnerability maps as both tools for planning and
as cartographic instruments to illustrate the potential cata-
strophic impacts of climate change. Monmonier cites reports
that depict inundation areas due to very large increases in
global sea level. Frequently, however, the sea-level rise map
depictions have no time scales and no indication of uncer-
tainty or data limitations. Presumably, these broad-scale
maps are in the illustration category, and only site-specific,
local scale products are true planning tools, but therein is the
difficulty. With many studies it is not clear if the maps (and
associated statistical summaries) are intended simply to raise
awareness of potential broad impacts or if they are intended
to be used in decision making for specific locations.
2.3.1
Sea-level rise as a consequence of climate change is a global
concern, and this is reflected in the variety of studies con-
ducted for locations around the world as well as within the
United States. Table 2.2 summarizes the characteristics of
a number of the sea-level rise assessments conducted over
broad areas, with some of the studies discussed in more
detail below.
Schneider and Chen (1980) presented one of the early reports
on potential sea-level rise impacts along U.S. coastlines.
They used the 15-ft and 25-ft contours from USGS 1:24,000-
scale maps to "derive approximate areas flooded within
individual counties" along the coast. As with many of the
vulnerability studies, Schneider and Chen also combined
their estimates of submerged areas with population and
32
-------
Table 2.2 Characteristics of Some Sea-Level Rise Assessments Conducted over Broad Areas. GTOPO30 is a global
raster DEM with a horizontal grid spacing of 30 arc seconds (approximately I kilometer). SRTM is the Shuttle
Radar Topography Mission data. NED is the National Elevation Dataset.
j||£vX!:C:;;!iy;
Schneider and Chen
(1980)
U.S. EPA (1989)
Titus eto/. (1991)
FEMA(I99I)
Small and Nicholls
(2003)
Ericson et al. (2006)
Rowley et al. (2007)
McGranahan et al.
(2007)
Demirkesen et al.
(2007)
Demirkesen et al.
(2008)
Marfai and King (2008)
Kafalenos et al. (2008)
-/'£•' ^ ^;-l
;;;,,. , - ,
Conterminous
United States
Conterminous
United States
Conterminous
United States
United States
Global
40 deltas
distributed
worldwide
Global
Global
Izmir, Turkey
Turkey
Semarang,
Indonesia
U.S. Gulf coast
- v*' -\-%'" .' V - * -•/', "" "
IS-and25-ft
contours from USGS
l:24,000-scale maps
Contours from USGS
maps
Contours from USGS
maps, wetland delinea-
tions, and tide data
Coastal floodplain maps
GTOP030
GTOP030
GLOBE (GTOP030)
SRTM
SRTM
SRTM
Local survey data
NED
;,'':v-,::r-:>v-'\r/i
4.6 and 7.6 m
0.5, 1, and 2 m
0.5, 1, and 2 m
1 ft and 3 ft
5-m land
elevation
increments
0.5-12.5 mm per
year for years
2000-2050
1,2, 3, 4, 5, and
6 m
Land elevations 0
to 10 m
(to define the
"low elevation
coastal zone")
2 and 5 m
1, 2, and 3 m
1.2 and 1.8 m
2 and 4 ft
!;T".^i1l}
No
No
No
No
Estimated a
5-m uncertainty for
elevation data (no error
metric specified)
No
No
No, although 10-m
elevation increment was
used in recognition of
data limitations
Yes, but no error met-
ric specified
Yes, but no error met-
ric specified
No
No
/"V *,J (v f '.
Yes
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
* Abbreviations used: U.S. EPA = United States Environmental Protection Agency; FEMA = United States Federal Emergency
Management Agency; USGS = United States Geological Survey; m = meters; mm = millimeters; ft = feet
property value data to estimate socioeconomic impacts, in
this case on a state-by-state basis.
Reports to Congress by the U.S. Environmental Protection
Agency (U. S. EPA) and the Federal Emergency Management
Agency (FEMA) contributed to the collection of broad area
assessments forthe United States. The U.S. EPA report (U.S.
EPA, 1989; Titus et al., 1991) examined several different
global sea-level rise scenarios in the range of 0.5 to 2 m
(1.6 to 6.6 ft), and also discussed impacts on wetlands under
varying shoreline protection scenarios. For elevation infor-
mation, the study used contours from USGS topographic
maps supplemented with wetland delineations from Landsat
satellite imagery and tide gauge data. The study found that
the available data were inadequate for production of detailed
maps. The FEMA (1991) report estimated the increase of
land in the 100-year floodplain from sea-level rises of 1 ft
(0.3 m) and 3 ft (0.9 m). FEMA also estimated the increase
in annual flood damages to insured properties by the year
2100, given the assumption that the trends of development
would continue.
Elevation datasets with global or near-global extent have
been used for vulnerability studies across broad areas. For
their studies of the global population at risk from coastal
hazards, Small and Nicholls (2003) and Ericson et al. (2006)
used GTOPO30, a global 30-arc-second (about 1-kilometer
[km]) elevation dataset produced by the USGS (Gesch et al.,
1999). Rowley et al. (2007) used the GLOBE 30-arc-second
DEM (Hastings and Dunbar, 1998), which is derived mostly
from GTOPO30. As with many vulnerability studies, these
investigations used the delineations of low-lying lands from
the elevation model to quantify the population at risk from
33
-------
Chapter 2
sea-level rise, in one instance using increments as small as
1 m (Rowley et al, 2007).
Elevation data from the Shuttle Radar Topography Mission
(SRTM) (Farr et al, 2007) are available at a 3-arc-second
(about 90-m) resolution with near-global coverage. Because
of their broad area coverage and improved resolution over
GTOPO30, SRTM data have been used in several studies
of the land area and population potentially at risk from sea-
level rise (McGranahan et a/., 2007; Demirkesen et a/., 2007,
2008). Similar to other studies, McGranahan et al. (2007)
present estimates of the population at risk, while Demirkesen
et al. (2007) document the dominant land use/land cover
classes in the delineated vulnerable areas.
2 " Region, States,
A number of sea-level rise vulnerability studies have been
published for sites in the mid-Atlantic region, the focus area
for this Product. Table 2.3 summarizes the characteristics
for these reports, and important information from some of
the studies is highlighted.
A study by Titus and Richman (2001) is often referred to in
discussions of the land in the United States that is subject
to the effects of sea-level rise. The methods used to produce
the maps in that report are clearly documented. However,
because they used very coarse elevation data (derived from
USGS l:250,000-scale topographic maps), the resulting
products are general and limited in their applicability. The
authors acknowledge the limitations of their results because
of the source data they used, and clearly list the caveats for
proper use of the maps. As such, these maps are useful in
depicting broad implications of sea-level rise, but are not
appropriate for site-specific decision making.
Numerous studies have used the NED, or the underlying
USGS OEMs from which much of the NED is derived, as
the input elevation information. Najjar et al. (2000) show an
example of using USGS 30-m OEMs for a simple inundation
model of Delaware for a 2-ft (0.6-m) sea-level rise. In another
study, Kleinosky et al. (2007) used elevation information
from USGS 10-m and 30-m OEMs to depict vulnerability of
the Hampton Roads, Virginia area to storm surge flooding
in addition to sea-level rise. Storm surge heights were first
determined by modeling, then 30-, 60-, and 90-cm incre-
ments of sea-level rise were added to project the expansion
of flood risk zones onto the land surface. In addition, Wu
et al. (2002) conducted a study for Cape May County, New
Jersey using an approach similar to Kleinosky et al. (2007),
where they added 60 cm to modeled storm surge heights to
account for sea-level rise.
More recently, Titus and Wang (2008) conducted a study
of the mid-Atlantic states (New York to North Carolina)
using a variety of elevation data sources including USGS
l:24,000-scale topographic maps (mostly with 5- or 10-ft
Table 2.3 Characteristics of Some Sea-Level Rise Vulnerability Studies Conducted over Mid-Atlantic Locations.
GTOPO30 is a global raster DEM with a horizontal grid spacing of 30 arc seconds (approximately I kilometer).
SRTM is the Shuttle Radar Topography Mission data. NED is the National Elevation Dataset.
;>i*AAAAAAA' V " '1*
^f^f^f^f^r^ ,
Titus and Richman
(2001)
Najjar et al (2000)
Kleinosky et al (2007)
Wu et al (2002)
Gornitz et al (2002)
Titus and Wang
(2008)
Larsen et al (2004)
Gesch (2009)
.,.M.».Lsss$,
U.S. Atlantic and
Gulf coasts
Delaware
Hampton Roads,
Virginia
Cape May County,
New Jersey
New York City
area
Mid-Atlantic states
Blackwater
National Wildlife
Refuge, Maryland
North Carolina
S^^V'-'^
USGS OEMs
derived from
l:250,000-scale maps
30-m USGS OEMs
10-m and 30-m USGS
OEMs
30-m USGS OEMs
30-m USGS OEMs
Contours from USGS
l:24,000-scale maps,
lidar, local data
lidar
GTOPO30, SRTM, NED,
lidar
>'" } o;x - " <' " " '?'?'
«xxxx^xxxxxV*w4>W><'<«
1.5- and 3.5-m
land elevation
increments
2ft
30, 60, and 90 cm
60cm
5-ft land elevation
increments
0.5-m land
elevation
increments
30-cm
land elevation
increments
1 m
"^ ;';;";' /-/:;„„:-'•
No
No
No
No
No, although only
qualitative results
were reported
Yes, RMSE vs.
lidar for a portion
of the study area
No
Yes, with NSSDA
error metric
(95% confidence)
jfy>!J'V'i
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
cm = centimeters; m = meters; ft = feet
34
-------
to
A Focus on the Mid-Atlantic Region
contour intervals), lidar data, and some local data provided
by state agencies, counties, and municipalities. They used
an approach similar to that described in Titus and Richman
(2001) in which tidal wetland delineations are employed in
an effort to estimate additional elevation information below
the first topographic map contour.
In addition to reports by federal government agencies and
studies published in the peer-reviewed scientific literature,
there have been numerous assessment reports issued by
various non-governmental organizations, universities, state
and local agencies, and other private groups (e.g., Anthoff
et al., 2006; Dasgupta et al., 2007; Stanton and Ackerman,
2007; US DOT, 2008; Mazria and Kershner, 2007; Click
et al, 2008; Cooper et al, 2005; Lathrop and Love, 2007;
Johnson et al, 2006; Bin et al, 2007; Slovinsky and Dick-
son, 2006). While it may be difficult to judge the technical
veracity of the results in these reports, they do share com-
mon characteristics with the studies reviewed in Sections
2.3.1 and 2.3.2. Namely, they make use of the same elevation
datasets (GTOPO30, SRTM, NED, and lidar) to project inun-
dation from sea-level rise onto the land surface to quantify
vulnerable areas, and they present statistical summaries of
impacted population and other socioeconomic variables.
Many of these reports include detailed maps and graphics
of areas at risk. Although some are also available in printed
formats, all of the reports listed above are available online
(see Chapter 2 References for website information).
This category of reports is highlighted because some of the
reports have gained wide public exposure through press re-
leases and subsequent coverage in the popular press and on
Internet news sites. For example, the report by Stanton and
Ackerman (2007) has been cited at least eight times by the
mainstream media (see: ). The existence of this type of report,
and the attention it has received, is likely an indication of the
broad public interest in sea-level rise issues. These reports
are often written from an economic or public policy context
rather than from a geosciences perspective. Nevertheless,
it is important for the coastal science community to be
cognizant of them because the reports often cite journal
papers and they serve as a conduit for communicating recent
sea-level rise research results to less technical audiences. It
is interesting to note that all of the reports listed here were
produced over the last three years; thus, it is likely that that
this type of outlet will continue to be used to discuss sea-
level rise issues as global climate change continues to garner
more public attention. Arguably, sea-level rise is among the
most visible and understandable consequences of climate
change for the general public, and they will continue to seek
information about it from the popular press, Internet sites,
and reports such as those described here.
." I
It is clear from the literature reviewed in Sections 2.3.1,
2.3.2, and 2.3.3 that the development of sea-level rise impact
assessments has been an active research topic for the past 25
years. However, there is still significant progress to be made
in improving the physical science-based information needed
for decision making by planners and land and resource
managers in the coastal zone. Although previous studies
have brought ample attention to the problem of mapping
and quantifying sea-level rise impacts, the quality of the
available input data and the common tendency to overlook
the consequences of coarse data resolution and large uncer-
tainty ranges hinder the usefulness and applicability of many
results. Specifically, for this Product, none of the previous
studies covering the mid-Atlantic region can be used to fully
answer with high confidence the Synthesis and Assessment
Product (SAP) 4.1 prospectus question (CCSP, 2006) that
relates directly to coastal elevations: "Which lands are cur-
rently at an elevation that could lead them to be inundated
by the tides without shore protection measures?" The col-
lective limitations of previous studies are described in this
Section, while the "lessons learned", or recommendations
for required qualities of future vulnerability assessments,
are discussed in Section 2.4.
Overall, there has been little recognition in previous studies
that inundation is only one response out of a number of pos-
sible responses to sea-level rise (see Section 2.1). Some stud-
ies do mention the various types of coastal impacts (erosion,
saltwater intrusion, more extreme storm surge flooding)
(Najjar et al, 2000; Gornitz et al, 2002), and some studies
that focus on wetland impacts do consider more than just
inundation (U.S. EPA, 1989; Larsen et al, 2004). However,
in general, many vulnerability maps (and corresponding sta-
tistical summaries) imply that a simple inundation scenario
is an adequate representation of the impacts of rising seas
(Schneider and Chen, 1980; Rowley etal., 2007; Demirkesen
et al, 2008; Najjar et al, 2000).
Based on the review of the studies cited in Sections 2.3.1,
2.3.2, and 2.3.3, these general limitations have been identi-
fied:
1. Use of lower resolution elevation data with poor verti-
cal accuracy. Some studies have had to rely on elevation
datasets that are poorly suited for detailed inundation
mapping (e.g., GTOPO30 and SRTM). While these
global datasets may be useful for general depictions
of low elevation zones, their relatively coarse spatial
detail precludes their use for production of detailed
vulnerability maps. In addition to the limited spatial
detail, these datasets have elevation values quantized
only to whole meter intervals, and their overall verti-
cal accuracy is poor when compared to the intervals
35
-------
Chapter 2
of predicted sea-level rise over the next century. The
need for better elevation information in sea-level rise
assessments has been broadly recognized (Leatherman,
2001; Marbaix and Nicholls, 2007; Jacob et al, 2007),
especially for large-scale planning maps (Monmonier,
2008) and detailed quantitative assessments (Gornitz
et al, 2002).
Lack of consideration of uncertainty of input elevation
data. A few studies generally discuss the limitations
of the elevation data used in terms of accuracy (Small
and Nicholls, 2003; McGranahan et al., 2007; Titus and
Wang, 2008). However, none of these studies exhibit
rigorous accuracy testing and reporting according to
accepted national standards (NSSDA and NMAS).
Every elevation dataset has some vertical error, which
can be tested and measured, and described by accuracy
statements. The overall vertical error is a measure of
the uncertainty of the elevation information, and that
uncertainty is propagated to any derived maps and sta-
tistical summaries. Gesch (2009) demonstrates why it is
important to account for vertical uncertainty in sea-level
rise vulnerability maps and area statistics derived from
elevation data (see Box 2.1).
3. Elevation intervals or sea-level rise increments not
supported by vertical accuracy of input elevation data.
Most elevation datasets, with the exception of lidar,
have vertical accuracies of several meters or even tens
of meters (at the 95 percent confidence level). Figure
2.2 shows a graphical representation of DEM vertical
accuracy using error bars around a specified elevation.
In this case, a lidar-derived DEM locates the 1-meter
elevation to within ±0.3 m at 95-percent confidence.
(In other words, the true elevation at that
location falls within a range of 0.7 to 1.3 m.)
A less accurate topographic map-derived
DEM locates the 1-m elevation to within
±2.2 m at 95-percent confidence, which
means the true land elevation at that loca-
tion falls within a range of 0 (assuming
sea level was delineated accurately on the
original topographic map) to 3.2 m. Many
of the studies reviewed in this Chapter use
land elevation intervals or sea-level rise
increments that are 1 m or less. Mapping
of sub-meter increments of sea-level rise
is highly questionable if the elevation data
used have a vertical accuracy of a meter or
more (at the 95-percent confidence level)
(Gesch, 2009). For example, by definition
a topographic map with a 5-ft contour
interval that meets NMAS has an absolute
vertical accuracy (which accounts for all
effects of systematic and random errors) of 90.8 cm at
the 95-percent confidence level (Maune, etal., 2007b).
Likewise, a 10-ft contour interval map has an absolute
vertical accuracy of 181.6 cm (1.816 m) at the 95-percent
confidence level. If such maps were used to delineate the
inundation zone from a 50-cm sea-level rise, the results
would be uncertain because the vertical increment of
rise is well within the bounds of statistical uncertainty
of the elevation data.
4. Maps without symbology or caveats concerning the
inherent vertical uncertainty of input elevation data.
Some studies have addressed limitations of their maps
and statistics (Titus and Richman, 2001; Najjar et al.,
2000), but most reports present maps without any
indication of the error associated with the underlying
elevation data (see number 3 above). Gesch (2009)
presents one method of spatially portraying the inher-
ent uncertainty of a mapped sea-level rise inundation
zone (see Box 2.1).
5. Inundated area and impacted population estimates
reported without a range of values that reflect the
inherent vertical uncertainty of input elevation
data. Many studies use the mapped inundation zone
to calculate the at-risk area, and then overlay that
delineation with spatially distributed population data or
other socioeconomic variables to estimate impacts. If a
spatial expression of the uncertainty of the inundation
zone (due to the vertical error in the elevation data)
is not included, then only one total can be reported.
More complete and credible information would be
provided if a second total was calculated by including
the variable (area, population, or economic parameter)
Sea-Level Rise Mapped onto Land Surface
l smx al 95"v
'icg *" id 'J m
Figure 2.2 Diagram of how a sea-level rise of I meter is mapped onto the land
surface using two digital elevation models with differing vertical accuracies. The
more accurate lidar-derived DEM (±0.3 m at 95-percent confidence) results in
a delineation of the inundation zone with much less uncertainty than when the
less accurate topographic map-derived DEM (±2.2 m at 95-percent confidence)
is used (Gesch, 2009).
36
-------
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
that falls within an additional delineation that accounts
for elevation uncertainty. A range of values can then be
reported, which reflects the uncertainty of the mapped
inundation zone.
6. Lack of recognition of differences among reference or-
thometric datums, tidal datums, and spatial variations
in sea-level datums. The vertical reference frame of the
data used in a particular study needs to be specified,
especially for local studies that produce detailed maps,
since there can be significant differences between an
orthometric datum zero reference and mean sea level
(Figure 2.1; see also Section 2.2.3). As described earlier,
there are important distinctions between vertical refer-
ence systems that are used for land elevation datasets
and those that are used to establish the elevations of
sea level. Most of the reviewed studies did not specify
which vertical reference frame was used. Often, it was
probably an orthometric datum because most elevation
datasets are in reference to such datums. Ideally, a tool
such as VDatum will be available so that data may be
easily transformed into a number vertical reference
frames at the discretion of the user.
BOX 2.1: A Case Study Using Lidar Elevation Data
To illustrate the application of elevation uncertainty information and the advantages of lidar elevation data for
sea-level rise assessment, a case study for North Carolina (Gesch, 2009) is presented and summarized here.
North Carolina has a broad expanse of low-lying land (Titus and Richman, 2001), and as such is a good site
for a mapping comparison. Lidar data at l/9-arc-
second (about 3 meters [m]) grid spacing were
analyzed and compared to I-arc-second (about
30 m) OEMs derived from l:24,000-scale topo-
graphic maps. The potential inundation zone
from a l-m sea-level rise was mapped from both
elevation datasets, and the corresponding areas
were compared. The analysis produced maps and
statistics in which the elevation uncertainty was
considered. Each elevation dataset was "flooded"
by identifying the grid cells that have an elevation
at or below I m and are connected hydrologi-
cally to the ocean through a continuous path of
adjacent inundated grid cells. For each dataset,
additional areas were delineated to show a spa-
tial representation of the uncertainty of the pro-
jected inundation area. This was accomplished
by adding the linear error at 95-percent confi-
dence to the l-m sea-level increase and extract-
ing the area at or below that elevation using the
same flooding algorithm. The lidar data exhibited
±0.27 m error at 95-percent confidence based on
accuracy reports from the data producer, while
the topographic map-derived DEMs had ±2.21
m error at 95-percent confidence based on an
accuracy assessment with high-quality surveyed
control points.
Box Figure 2.1 and Box Table 2.1 show the re-
sults of the North Carolina mapping comparison.
In Box Figure 2.1 the darker blue tint represents
the area at or below I m in elevation, and the
lighter blue tint represents the additional area
in the vulnerable zone given the vertical uncer-
tainty of the input elevation datasets. The more
Box Figure 2.1 (A) Lands vulnerable to a I-meter sea-level rise, accurate lidar data for delineation of the vulner-
developed from topographic map-derived DEMs and (B) lidar el- able zone results in a more certain delineation
evation data (Gesch, 2009). The background is a recent true color (Box Figure 2.1 B), or in other words the zone of
orthoimage. uncertainty is small.
37
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The U.S. Climate Change Science Program
Chapter 2
BOX 2.1: A Case Study Using Lidar Elevation Data cont'd
Box Table 2.1 compares the vulnerable areas as delineated from the two elevation datasets. The delineation of the
I-meter (m) zone from the topographic map-derived DEMs more than doubles when the elevation uncertainty is
considered, which calls into question the reliability of any conclusions drawn from the delineation. It is apparent
that for this site the map-derived DEMs do not have the vertical accuracy required to reliably delineate a I -m sea-
level rise inundation zone. Lidar is the appropriate elevation dataset for answering the question about how much
land in the study site is vulnerable to a I -m sea-level rise, for which the answer is: "4,195 to 4,783 square kilometers
(sq km) at a 95-percent confidence level". This case study emphasizes why a range of values should be given when
reporting the size of the inundation area for a given sea-level rise scenario, especially for sites where high-accuracy
lidar data are not available. Without such a range being reported, users of an assessment report may not under-
stand the amount of uncertainty associated with area delineations from less accurate data and their implications
for any subsequent decisions based on the reported statistics.
Box Table 2.1 The Area of Land (in square kilometers [sq km]) Vulnerable to a I-Meter (m)
Sea-Level Rise (as calculated from two elevation datasets [see Box Figure 2.1], as well as the area
of vulnerability, when the uncertainty of the elevation data is considered [Gesch, 2009]).
I-arc-second (30-m) DEMs
derived from l:24,000-scale
topographic maps
l/9-arc-second
(3-m) lidar elevation grid
;a less than
.. equal to I
meter in elevation
4,014
4,195
8,578
4,783
Percent increase
in vulnerable area
•"hen elevation
tainty is
included
114%
14%
2.4 FUTURE VULNERABILITY
ASSESSMENTS
To fully answer the relevant elevation question from the
prospectus for this SAP 4.1 (see Section 2.3.4), there are
important technical considerations that need to be incorpo-
rated to improve future sea-level rise impact assessments,
especially those with a goal of producing vulnerability maps
and statistical summaries of impacts. These considerations
are important for both the researchers who develop impact
assessments, as well as the users of those assessments who
must understand the technical issues to properly apply
the information. The recommendations for improvements
described below are based on the review of the previous
studies cited in Sections 2.3.1, 2.3.2, 2.3.3, and other recent
research:
1. Determine where inundation will be the primary re-
sponse to sea-level rise. Inundation (submergence of the
uplands) is only one of a number of possible responses
to sea-level rise (Leatherman, 2001; Valiela, 2006;
FitzGerald et al. ,2008). If the complex nature of coastal
change is not recognized up front in sea-level rise as-
sessment reports, a reader may mistakenly assume that
all stretches of the coast that are deemed vulnerable will
experience the same "flooding" impact, as numerous
reports have called it. For the coastal settings in which
inundation is the primary vulnerability, elevation data-
sets should be analyzed as detailed below to produce
comprehensive maps and statistics.
Use lidar elevation data (or other high-resolution,
high-accuracy elevation source). To meet the need for
more accurate, detailed, and up-to-date sea-level rise
vulnerability assessments, new studies should be based
on recently collected high-resolution, high-accuracy,
lidar elevation data. Other mapping approaches, includ-
ing photogrammetry and ground surveys, can produce
high-quality elevation data suitable for detailed assess-
ments, but lidar is the preferred approach for cost-effec-
tive data collection overbroad coastal areas. Lidar has
the added advantage that, in addition to high-accuracy
measurements of ground elevation, it also can be used
to produce information on buildings, infrastructure, and
vegetation, which may be important for sea-level rise
impact assessments. As Leatherman (2001) points out,
inundation is a function of slope. The ability of lidar to
measure elevations very precisely facilitates the accu-
rate determination of even small slopes, thus it is quite
useful for mapping low-relief coastal landforms. The
numerous advantages of lidar elevation mapping in the
coastal zone have been widely recognized (Leatherman,
2001; Coastal States Organization, 2007; Monmonier,
2008; Subcommittee on Disaster Reduction, 2008;
38
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to
A Focus on the Mid-Atlantic Region
Feyen et al, 2008; Gesch, 2009). A recent study by the
National Research Council (NRC, 2007) concluded that
FEMA's requirements for floodplain mapping would
be met in all areas by elevation data with 1-ft to 2-ft
equivalent contour accuracy, and that a national lidar
program called "Elevation for the Nation" should be
carried out to create a new national DEM. Elevation
data meeting 1-ft contour interval accuracy (NMAS)
would allow effective sea-level rise inundation model-
ing for increments in the 0.35 m range, while data with
2-ft contour interval accuracy would be suitable for
increments of about 0.7 m.
3. Test and report absolute vertical accuracy as a measure
of elevation uncertainty. Any studies that use elevation
data as an input for vulnerability maps and/or statistics
need to have a clear statement of the absolute verti-
cal accuracy (in reference to true ground elevations).
The NSSDA vertical accuracy testing and reporting
methodology (Federal Geographic Data Committee,
1998), which uses a metric of linear error at 95-percent
confidence, is the preferred approach. Vertical accuracy
may be reported with other metrics including RMSE,
standard deviation (one sigma error), LE90, or three
sigma error. Maune et al. (2007b) and Greenwalt and
Shultz (1962) provide methods to translate among the
different error metrics. In any case, the error metric
must be identified because quoting an accuracy figure
without specifying the metric is meaningless. For lidar
elevation data, a specific testing and reporting proce-
dure that conforms to the NSSDA has been developed
by the National Digital Elevation Program (NDEP)
(2004). The NDEP guidelines are useful because they
provide methods for accuracy assessment in "open
terrain" versus other land cover categories such as for-
est or urban areas where the lidar sensor may not have
detected ground level. NDEP also provides guidance
on accuracy testing and reporting when the measured
elevation model errors are from a non-Gaussian (non-
normal) distribution.
4. Apply elevation uncertainty information in development
of vulnerability maps and area statistics. Knowledge
of the uncertainty of input elevation data should be
incorporated into the development of sea-level rise im-
pact assessment products. In this case, the uncertainty
is expressed in the vertical error determined through
accuracy testing, as described above. Other hydrologic
applications of elevation data, including rainfall runoff
modeling (Wu et al., 2008) and riverine flood inunda-
tion modeling (Yilmaz et al., 2004,2005), have benefit-
ted from the incorporation of elevation uncertainty. For
sea-level rise inundation modeling, the error associated
with the input elevation dataset is used to include a zone
of uncertainty in the delineation of vulnerable land at or
below a specific elevation. For example, assume a map
of lands vulnerable to a 1-m sea-level rise is to be devel-
oped using a DEM. That DEM, similar to all elevation
datasets, has an overall vertical error. The challenge,
then, is how to account for the elevation uncertainty
(vertical error) in the mapping of the vulnerable area.
Figure 2.2 (Gesch, 2009) shows how the elevation un-
certainty associated with the 1-m level, as expressed
by the absolute vertical accuracy, is projected onto the
land surface. The topographic profile diagram shows
two different elevation datasets with differing vertical
accuracies depicted as error bars around the 1-m eleva-
tion. One dataset has a vertical accuracy of ±0.3 m at
the 95-percent confidence level, while the other has an
accuracy of ±2.2 m at the 95-percent confidence level.
By adding the error to the projected 1-m sea-level rise,
more area is added to the inundation zone delineation,
and this additional area is a spatial representation of
the uncertainty. The additional area is interpreted as
the region in which the 1-m elevation may actually fall,
given the statistical uncertainty of the OEMs.
Recognizing that elevation data inherently have verti-
cal uncertainty, vulnerability maps derived from them
should include some type of indication of the area of
uncertainty. This could be provided as a caveat in the
map legend or margin, but a spatial portrayal with
map symbology may be more effective. Merwade et
al. (2008) have demonstrated this approach for flood-
plain mapping where the modeled inundation area has
a surrounding uncertainty zone depicted as a buffer
around the flood boundary. Gesch (2009) used a similar
approach to show a spatial representation of the un-
certainty of the projected inundation area from a 1-m
sea-level rise, with one color for the area below 1 m in
elevation and another color for the adjacent uncertainty
zone (see Box 2.1).
As with vulnerability maps derived from elevation data,
statistical summaries of affected land area, population,
land use/land cover types, number of buildings, infra-
structure extent, and other socioeconomic variables
should include recognition of the vertical uncertainty
of the underlying data. In many studies, the delineated
inundation zone is intersected with geospatial represen-
tations of demographic or economic variables in order
to summarize the quantity of those variables within the
potential impact zone. Such overlay and summarizing
operations should also include the area of uncertainty
associated with the inundation zone, and thus ranges
of the variables should be reported. The range for a
particular variable would increase from the total for just
the projected inundation zone up to the combined total
39
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Chapter 2
for the inundation zone plus the adjacent uncertainty
zone. Additionally, because the combined area of the
inundation zone and its adjacent uncertainty zone has a
known confidence level, the range can be reported with
that same confidence level. Merwade et al. (2008) have
recommended such an approach for f loodplain mapping
when they state that the flood inundation extent should
be reported as being "in the range from x units to y units
with a z-% confidence level".
An important use of elevation data accuracy informa-
tion in an assessment study is to guide the selection
of land elevation intervals or sea-level rise increments
that are appropriate for the available data. Inundation
modeling is usually a simple process wherein sea level
is effectively raised by delineating the area at and below
a specified land elevation to create the inundation zone.
This procedure is effectively a contouring process, so
the vertical accuracy of a DEM must be known to de-
termine the contour interval that is supported. DEMs
can be contoured at any interval, but, just by doing
so, it does not mean that the contours meet published
accuracy standards. Likewise, studies can use small
intervals of sea-level rise, but the underlying elevation
data must have the vertical accuracy to support those
intervals. The intervals must not be so small that they
are within the bounds of the statistical uncertainty of
the elevation data.
5. Produce spatially explicit maps and detailed statistics
that can be used in local decision making. The ultimate
use of a sea-level rise assessment is as a planning and
decision-making tool. Some assessments cover broad
areas and are useful for scoping the general extent of
the area of concern for sea-level rise impacts. However,
the smaller-scale maps and corresponding statistics
from these broad area assessments cannot be used for
local decision making, which require large-scale map
products and site-specific information. Such spatially
explicit planning maps require high-resolution, high-
accuracy input data as source information. Monmonier
(2008) emphasizes that "reliable large-scale planning
maps call for markedly better elevation data than found
on conventional topographic maps". Even with source
data that supports local mapping, it is important to
remember, as Frumhoff et al. (2007) point out, due to
the complex nature of coastal dynamics that "project-
ing the impacts of rising sea level on specific locations
is not as simple as mapping which low-lying areas will
eventually be inundated".
Proper treatment of elevation uncertainty is especially
important for development of large-scale maps that will
be used for planning and resource management decisions.
Several states have realized the advantages of using high-
accuracy lidar data to reduce uncertainty in sea-level rise
studies and development of local map products (Rubinoff
et al., 2008). Accurate local-scale maps can also be gener-
alized to smaller-scale maps for assessments over larger
areas. Such aggregation of detailed information benefits
broad area studies by incorporating the best available, most
detailed information.
Development of large-scale spatially explicit maps presents
a new set of challenges. At scales useful for local decision
making, the hydrological connectivity of the ocean to
vulnerable lands must be mapped and considered. In some
vulnerable areas, the drainage network has been artificially
modified with ditches, canals, dikes, levees, and seawalls
that affect the hydrologic paths rising water can traverse
(Poulter and Halpin, 2007; Poulter et al, 2008). Fortunately,
lidar data often include these important features, which are
important for improving large-scale inundation modeling
(Coastal States Organization, 2007). Older, lower resolu-
tion elevation data often do not include these fine-scale
manmade features, which is another limitation of these data
for large-scale maps.
Other site-specific data should be included in impact assess-
ments for local decision making, including knowledge of
local sea-level rise trends and the differences among the zero
reference for elevation data (often an orthometric datum),
local mean sea level, and high water (Marbaix and Nich-
olls, 2007; Poulter and Halpin, 2007). The high water level
is useful for inundation mapping because it distinguishes
the area of periodic submergence by tides from those areas
that may become inundated as sea-level rises (Leatherman,
2001). The importance of knowing the local relationships of
water level and land vertical reference systems emphasizes
the need for a national implementation of VDatum (Parker
et al., 2003; Myers, 2005) so that accurate information on
tidal dynamics can be incorporated into local sea-level rise
assessments.
Another useful advance for detailed sea-level rise assess-
ments can be realized by better overlay analysis of a delin-
eated vulnerability zone and local population data. Popula-
tion data are aggregated and reported in census blocks and
tracts, and are often represented in area-based statistical
thematic maps, also known as choropleth maps. However,
such maps usually do not represent actual population density
and distribution across the landscape because census units
include both inhabited and uninhabited land. Dasymetric
mapping (Mennis, 2003) is a technique that is used to
disaggregate population density data into a more realistic
spatial distribution based on ancillary land use/land cover
information or remote sensing images (Sleeter and Gould,
2008; Chen, 2002). This technique holds promise for bet-
40
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
ter analysis of population, or other socioeconomic data, to
report statistical summaries of sea-level rise impacts within
vulnerable zones.
2.5 SUMMARY, CONCLUSIONS, AND
FUTURE DIRECTIONS
The topic of coastal elevations is most relevant to the first
SAP 4.1 prospectus question (CCSP, 2006): "Which lands
are currently at an elevation that could lead them to be in-
undated by the tides without shore protection measures?"
The difficulty in directly answering this question for the
mid-Atlantic region with a high degree of confidence was
recognized. Collectively, the available previous studies do
not provide the full answer for this region with the degree
of confidence that is optimal for local decision making.
Fortunately, new elevation data, especially lidar, are becom-
ing available and are being integrated into the USGS NED
(Gesch, 2007) as well as being used in sea-level rise appli-
cations (Coastal States Organization, 2007). Also, research
is progressing on how to take advantage of the increased
spatial resolution and vertical accuracy of new data (Poulter
and Halpin, 2007; Gesch, 2009).
Using national geospatial standards for accuracy assess-
ment and reporting, the currently best available elevation
data for the entire mid-Atlantic region do not support an
assessment using a sea-level rise increment of 1 m or less,
which is slightly above the range of current estimates for
the remainder of this century and the high scenario used
in this Product. Where lidar data meeting current industry
standards for accuracy are available, the land area below
the 1-m contour (simulating a 1-m sea-level rise) can be
estimated for those sites along the coast at which inundation
will be the primary response. The current USGS holdings
of the best available elevation data include lidar for North
Carolina, parts of Maryland, and parts of New Jersey (Figure
2.3). Lidar data for portions of Delaware and more of New
Jersey and Maryland will be integrated into the NED in
2009. However, it may be some time before the full extent of
NY
Atlantic
Ocean
Elevation source
^H Lidar data
1-meter contour interval map
^Hj 5-foot contour interval map
| 1 (Moot contour interval map
| 20-foot contour interval map
Figure 2.3 The current best available elevation source data
(as of August 2008) for the National Elevation Dataset over the
mid-Atlantic region.
the mid-Atlantic region has sufficient coverage of elevation
data that are suitable for detailed assessments of sub-meter
increments of sea-level rise and development of spatially
explicit local planning maps.
Given the current status of the NED for the mid-Atlantic
region (Figure 2.3), the finest increment of sea-level rise
that is supported by the underlying elevation data varies
across the area (Table 2.4 and Figure 2.4). At a minimum, a
sea-level rise increment used for inundation modeling should
not be smaller than the range of statistical uncertainty of
the elevation data. For instance, if an elevation dataset has
a vertical accuracy of ±1 m at 95-percent confidence, the
Table 2.4 Minimum Sea-Level Rise Scenarios for Vulnerability Assessments Supported by Elevation Datasets of
Varying Vertical Accuracy.
Elevation
>ata Sourc
I -ft contour interval map
lidar
2-ft contour interval map
1-m contour interval map
5-ft contour interval map
10-ft contour interval map
20-ft contour interval map
ecu racy:
RMSE
9.3 cm
15.0cm
18.5 cm
30.4 cm
46.3 cm
92.7 cm
1.85m
al accuracy: Imea
5-percent confide
18.2cm
29.4 cm
36.3 cm
59.6 cm
90.7 cm
1.82m
3.63m
mum sea-level rise increment
for inundation modeling
36.4 cm
58.8 cm
72.6 cm
1.19m
1.82m
3.64m
7.26m
cm = centimeters; m = meters; ft = feet
41
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The U.S. Climate Change Science Program
Chapter 2
NY CT
PA
Atlantic
Ocean
Minimum sea-level rise
that can be modeled
58.8 cm
1.19m
1.82m
3.64 rn
7.26m
Figure 2.4 Estimated minimum sea-level rise scenarios (in centi-
meters [cm] and meters [m]) for inundation modeling in the mid-
Atlantic region given the current best available elevation data.
smallest sea-level rise increment that should be considered is
1 m. Even then, the reliability of the vulnerable area delinea-
tion would not be high because the modeled sea-level rise
increment is the same as the inherent vertical uncertainty
of the elevation data. Thus, the reliability of a delineation of
a given sea-level rise scenario will be better if the inherent
vertical uncertainty of the elevation data is much less than
the modeled water level rise For example, a sea-level rise
of 0.5 m is reliably modeled with elevation data having a
vertical accuracy of ±0.25 mat 95-percent confidence. This
guideline, with the elevation data being at least twice as ac-
curate as the modeled sea-level rise, was applied to derive
the numbers in Table 2.4.
High-quality lidar elevation data, such as that which could
be collected in a national lidar survey, would be necessary
for the entire coastal zone to complete a comprehensive as-
sessment of sea-level rise vulnerability in the mid-Atlantic
region. Lidar remote sensing has been recognized as a
means to provide highly detailed and accurate data for nu-
merous applications, and there is significant interest from
the geospatial community in developing an initiative for a
national lidar collection for the United States (Stoker et al.,
2007, 2008). If such an initiative is successful, then a truly
national assessment of potential sea-level rise impacts could
be realized. A U.S. national lidar dataset would facilitate
consistent assessment of vulnerability across state or juris-
dictional boundaries, an approach for which coastal states
have voiced strong advocacy (Coastal States Organization,
2007). Even with the current investment in lidar by several
states, there is a clear federal role in the development of
a national lidar program (NRC, 2007; Monmonier, 2008;
Stoker et al., 2008).
Use of recent, high-accuracy lidar elevation data, especially
with full consideration of elevation uncertainty as described
in Section 2.4, will result in a new class of vulnerability maps
and statistical summaries of impacts. These new assessment
products will include a specific level of confidence, with
ranges of variables reported. The level of statistical confi-
dence could even be user selectable if assessment reports
publish results at several confidence levels.
It is clear that improved elevation data and analysis tech-
niques will lead to better sea-level rise impact assessments.
However, new assessments must include recognition that
inundation, defined as submergence of the uplands, is the
primary response to rising seas in only some areas. In other
areas, the response may be dominated by more complex
responses such as those involving shoreline erosion, wetland
accretion, or barrier island migration. These assessments
should first consider the geological setting and the domi-
nant local physical processes at work to determine where
inundation might be the primary response. Analysis of lidar
elevation data, as outlined above, should then be conducted
in those areas.
Investigators conducting sea-level rise impact studies should
strive to use approaches that generally follow the guidelines
above so that results can be consistent across larger areas
and subsequent use of the maps and data can reference a
common baseline. Assessment results, ideally with spatially
explicit vulnerability maps and summary statistics having all
the qualities described in Section 2.4, should be published
in peer-reviewed journals so that decision makers can be
confident of a sound scientific base for their decisions made
on the basis of the findings. If necessary, assessment results
can be reformatted into products that are more easily used
by local planners and decision makers, but the scientific
validity of the information remains.
42
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Reg/on
Ocean Coasts
ad Authors: Benjamin T. Gutierrez, USGS; S. Jeffress Williams,
_SGS; E. Robert Thieler, USGS
KEY FINDINGS
Along the ocean shores of the Mid-Atlantic, which are comprised of headlands, barrier islands, and
spits, it is virtually certain that erosion will dominate changes in shoreline position in response to sea-
level rise and storms over the next century.
It is very likely that landforms along the mid-Atlantic coast of the United States will undergo large
changes if the higher sea-level rise scenarios occur. The response will vary depending on the type of
coastal landforms and the local geologic and oceanographic conditions, and could be more variable
than the changes observed over the last century.
For higher sea-level rise scenarios, it is very likely that some barrier island coasts will cross a threshold
and undergo significant changes. These changes include more rapid landward migration or segmentation
of some barrier islands.
43
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Chapter 3
3.1
The general characteristics of the coast, such as the presence
of beaches versus cliffs, reflects a complex and dynamic
interaction between physical processes (e.g., waves and
tidal currents) that act on the coast, availability of sedi-
ment transported by waves and tidal currents, underlying
geology, and changes in sea level (see review in Carter and
Woodroffe, 1994a). Variations in these factors from one
region to the next are responsible for the different coastal
landforms, such as beaches, barrier islands, and cliffs that
are observed along the coast today. Based on studies of the
geologic record, the scope and general nature of the changes
that can occur in response to sea-level rise are widely
recognized (Curray, 1964; Carter and Woodroffe, 1994a;
FitzGerald et al., 2008). On the other hand, determining
precisely how these changes occur in response to a specific
rise in sea level has been difficult. Part of the complication
arises due to the range of physical processes and factors that
modify the coast and operate over a range of time periods
(e.g., from weeks to centuries to thousands of years) (Cowell
and Thorn, 1994; Stive et al., 2002; Nicholls et al., 2007).
Because of the complex interactions between these factors
and the difficulty in determining their exact influence,
it has been difficult to resolve a quantitative relationship
between sea-level rise and shoreline change (e.g., Zhang et
al., 2004; Stive, 2004). Consequently, it has been difficult to
reach a consensus among coastal scientists as to whether or
not sea-level rise can be quantitatively related to observed
shoreline changes and determined using quantitative mod-
els (Dubois, 2002; Stive, 2004; Pilkey and Cooper, 2004;
Cowell et al, 2006).
Along many U.S. shores, shoreline changes are related to
changes in the shape of the landscape at the water's edge
(e.g., the shape of the beach). Changes in beach dimensions,
and the resulting shoreline changes, do not occur directly as
the result of sea-level rise but are in an almost continual state
of change in response to waves and currents as well as the
availability of sediment to the coastal system (see overviews
in Carter and Woodroffe, 1994b; Stive et al, 2002; Nicholls
et al., 2007). This is especially true for shoreline changes
observed over the past century, when the increase in sea level
has been relatively small (about 30 to 40 centimeters, or 12
to 16 inches, along the mid-Atlantic coast). During this time,
large storms, variations in sediment supply to the coast, and
human activity have had a more obvious influence on shore-
line changes. Large storms can cause changes in shoreline
position that persist for weeks to a decade or more (Morton
etal., 1994; Zhangetal., 2002,2004; List etal., 2006; Riggs
and Ames, 2007). Complex interactions with nearshore sand
bodies and/or underlying geology (the geologic framework),
the mechanics of which are not yet clearly understood, also
influence the behavior of beach morphology over a range
of time periods (Riggs et al., 1995; Honeycutt and Krantz,
2003; Schupp et al., 2006; Miselis and McNinch, 2006). In
addition, human actions to control changes to the shore and
coastal waterways have altered the behavior of some portions
of the coast considerably (e.g., Assateague Island, Maryland,
Dean and Perlin, 1977; Leatherman, 1984; also see reviews
in Nordstrom, 1994, 2000; Nicholls etal, 2007).
It is even more difficult to develop quantitative predictions
of how shorelines may change in the future (Stive, 2004;
Pilkey and Cooper, 2004; Cowell et al., 2006). The most eas-
ily applied models incorporate relatively few processes and
rely on assumptions that do not always apply to real-world
settings (Thieler et al., 2000; Cooper and Pilkey, 2004). In
addition, model assumptions often apply best to present con-
ditions, but not necessarily to future conditions. Models that
incorporate more factors are applied at specific locations and
require precise knowledge regarding the underlying geology
or sediment budget (e.g., GEOMBEST, Stolpere/a/., 2005),
and it is therefore difficult to apply these models over larger
coastal regions. Appendix 2 presents brief summaries of a
few basic methods that have been used to predict the poten-
tial for shoreline changes in response to sea-level rise.
As discussed in Chapter 2, recent and ongoing assessments
of sea-level rise impacts commonly examine the vulnerabil-
ity of coastal lands to inundation by specific sea-level rise
scenarios (e.g., Najjare/a/., 2000; Titus andRichman, 2001;
Rowley etal., 2007). This approach provides an estimate of
the land area that may be vulnerable, but it does not incor-
porate the processes (e.g., barrier island migration) nor the
environmental changes (e.g., salt marsh deterioration) that
may occur as sea level rises. Because of these complexities,
inundation can be used as a basic approach to approximate
the extent of land areas that could be affected by changing
sea level. Because the majority of the U.S. coasts, including
those along the Mid-Atlantic, consist of sandy shores, inun-
dation alone is unlikely to reflect the potential consequences
of sea-level rise. Instead, long-term shoreline changes will
involve contributions from both inundation and erosion
(Leatherman, 1990,2001) as well as changes to other coastal
environments such as wetland losses.
Most portions of the open coast of the United States will be
subject to significant physical changes and erosion over the
next century because the majority of coastlines consist of
sandy beaches which are highly mobile and in a continual
state of change. This Chapter presents an overview and as-
sessment of the important factors and processes that influ-
ence potential changes to the mid-Atlantic ocean coast due
to sea-level rise expected by the end of this century. This
overview is based in part on a panel assessment (i.e., expert
judgement) that was undertaken to address this topic for
this Product (Gutierrez et al., 2007). The panel assessment
44
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Reg/on
BOX 3.1: The Panel Assessment Process Used in SAP 4.1, Chapter 3
As described in this Product, there is currently a lack of scientific consensus regarding local-, regional-, and
national-scale coastal changes in response to sea-level rise, due to limited elevation and observational data and
lack of adequate scientific understanding of the complex processes that contribute to coastal change. To address
the question of potential future changes to the mid-Atlantic coast posed in the SAP 4.1 Prospectus, the authors
assembled 13 coastal scientists for a meeting to evaluate the potential outcomes of the sea-level rise scenarios
used in this Product. These scientists were chosen on the basis of their technical expertise and experience in
the coastal research community, and also their involvement with coastal management issues in the mid-Atlantic
region. Prior to the meeting, the scientists were provided with documents describing the Climate Change Sci-
ence Program, and the Prospectus for this Product. The Prospectus included key questions and topics that the
panel was charged to address. The panel was also provided a draft version of the report by Reed et al. (2008),
which documented a similar panel-assessment approach used in developing Chapter 4 of this Product.
The sea-level rise impact assessment effort was conducted as an open discussion facilitated by the USGS au-
thors over a two-day period. The main topics that the panel discussed were:
I. Approaches that can be used to conduct long-term assessments of coastal change;
2. Key geomorphic environments in the mid-Atlantic region from Long Island, New York to North Carolina;
3. Potential responses of these environments to sea-level rise based on an understanding of important factors
and processes contributing to coastal change; and
4. The likelihood of these responses to the sea-level rise scenarios used in this Product (see Section 3.7).
The qualitative, consensus-based assessment of potential changes and their likelihood developed by the panel
was based on their review and understanding of peer reviewed published coastal science literature, as well as
field observations drawn from other studies conducted in the mid-Atlantic region. The likelihood statements
reported in Section 3.7 were determined based on the results of the discussion during the two-day meeting and
revised according comments from panelists during the drafting of a summary report. The USGS report (Guti-
errez et al., 2007) summarizing the process used, the basis in the published literature, and a synthesis of the
resulting assessment was produced based on results of the meeting, reviewed as part of the USGS peer review
process, and approved by members of the panel.
process is described in Section 3.2 and Box 3.1. Section 3.3
reviews the geological characteristics of the mid-Atlanic
coast. Section 3.4 provides an overview of the basic fac-
tors that influence sea-level rise-driven shoreline changes.
Sections 3.5 and 3.6 describe the coastal landforms of the
mid-Atlantic coast of the United States and what is known
regarding how these landforms respond to changes in sea-
level based on a literature review included as part of the
panel assessment (Gutierrez et al., 2007). The potential
responses of mid-Atlantic coastal landforms to sea-level rise,
which were defined in the panel assessment, are presented
in Section 3.7 and communicated using the likelihood terms
specified in the Preface (see Figure P.I).
3.2 ASSESSING THE POTENTIAL IMPACT
OF SEA-LEVEL RISE ON THE OCEAN
COASTS OF THE MID-ATLANTIC
Lacking a single agreed-upon method or scientific consen-
sus view about shoreline changes in response to sea-level
rise at a regional scale, a panel was consulted to address
the key question that guided this Chapter (Gutierrez et
al., 2007). The panel consisted of coastal scientists whose
research experiences have focused on the mid-Atlantic
region and have been involved with coastal management in
the mid-Atlantic region1. The panel discussed the changes
that might be expected to occur to the ocean shores of the
U.S. mid-Atlantic coast in response to predicted accelera-
tions in sea-level rise over the next century, and considered
the important geologic, oceanographic, and anthropogenic
factors that contribute to shoreline changes in this region.
The assessment presented here is based on the professional
1 Fred Anders (New York State, Dept. of State, Albany, NY), K. Eric
Anderson (USGS, NOAA Coastal Services Center, Charleston,
SC), Mark Byrnes (Applied Coastal Research and Engineering,
Mashpee, MA), Donald Cahoon (USGS, Beltsville, MD), Stewart
Farrell (Richard Stockton College, Pomona, NJ), Duncan FitzGerald
(Boston University, Boston, MA), Paul Gayes (Coastal Carolina
University, Conway, SC), Benjamin Gutierrez (USGS, Woods Hole,
MA), Carl Hobbs (Virginia Institute of Marine Science, Gloucester
Pt, VA), Randy McBride (George Mason University, Fairfax, VA),
Jesse McNinch (Virginia Institute of Marine Science, Gloucester Pt.,
VA), Stan Riggs (East Carolina University, Greenville, NC), Antonio
Rodriguez (University of North Carolina, Morehead City, NC), Jay
Tanski (New York Sea Grant, Stony Brook, NY), E. Robert Thieler
(USGS, Woods Hole, MA), Art Trembanis (University of Delaware,
Newark, DE), S. Jeffress Williams (USGS, Woods Hole, MA).
45
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The U.S. Climate Change Science Program
Chapter 3
judgment of the panel. This qualitative assessment of po-
tential changes that was developed by the panel is based on
an understanding of both coastal science literature and their
personal field observations.
This assessment focuses on four sea-level rise scenarios.
As defined in the Preface, the first three sea-level rise sce-
narios (Scenarios 1 through 3) assume that: (1) the sea-level
rise rate observed during the twentieth century will persist
through the twenty-first century; (2) the twentieth century
rate will increase by 2 millimeters (mm) per year, and (3)
the twentieth century rate will increase by 7 mm per year.
Lastly, a fourth scenario is discussed, which considers a
2-meter (m) (6.6-foot [ft]) rise over the next few hundred
years. In the following discussions, sea-level change refers
to the relative sea-level change, which is the combination of
global sea-level change and local change in land elevation.
Using these scenarios, this assessment focuses on:
Identifying important factors and processes contributing
to shoreline change over the next century;
Identifying key geomorphic settings along the coast of
the mid-Atlantic region;
Defining potential responses of shorelines to sea-level
rise; and
Assessing the likelihood of these responses.
3.3 GEOLOGICAL CHARACTER OF THE
MID-ATLANTIC COAST
The mid-Atlantic margin of the United States is a gently
sloping coastal plain that has accumulated over millions of
years in response to the gradual erosion of the Appalachian
mountain chain. The resulting sedimentation has construct-
ed abroad coastal plain and a continental shelf that extends
almost 300 kilometers (approximately 185 miles) seaward
of the present coast (Colquhoun et al., 1991). The current
morphology of this coastal plain has resulted from the inci-
sion of rivers that drain the region and the construction of
barrier islands along the mainland occurring
between the river systems. Repeated ice
ages, which have resulted in sea-level fluc-
tuations up to 140 meters (460 feet) (Muhs
et al., 2004), caused these rivers to erode
large valleys during periods of low sea level
that then flooded and filled with sediments
when sea levels rose. The northern extent of
the mid-Atlantic region considered in this
Product, Long Island, New York, was also
shaped by the deposition of glacial outwash
plains and moraines that accumulated from
the retreat of the Laurentide ice sheet, which
reached its maximum extent approximately
21,000 years ago. This sloping landscape
that characterizes the entire mid-Atlantic
margin, in combination with slow rates of sea-level rise
over the past 5,000 years and sufficient sand supply, is also
thought to have enabled the formation of the barrier islands
that comprise the majority of the Atlantic Coast (Walker and
Coleman, 1987; Psuty and Ofiara, 2002).
The mid-Atlantic coast is generally described as a sediment-
starved coast (Wright, 1995). Presently, sediments from
the river systems of the region are trapped in estuaries
and only minor amounts of sediment are delivered to the
open ocean coast (Meade, 1969, 1972). In addition, these
estuaries trap sandy sediment from the continental shelf
(Meade, 1969). Consequently, the sediments that form the
mainland beach and barrier beach environments are thought
to be derived mainly from the wave-driven erosion of the
mainland substrate and sediments from the seaf loor of the
continental shelf (Niedorodae/ al, 1985; Swift et al, 1985;
Wright, 1995). Since the largest waves and associated cur-
rents occur during storms along the Atlantic Coast, storms
are often thought to be significant contributors to coastal
changes (Niedoroda et al, 1985; Swift et al, 1985; Morton
and Sallenger, 2003).
The majority of the open coasts along the mid-Atlantic
region are sandy shores that include the beach and barrier
environments. Although barriers comprise only 15 percent
of the world coastline (Glaeser, 1978), they are the dominant
shoreline type along the Atlantic Coast. Along the portion of
the mid-Atlantic coast examined here, which ranges between
Montauk, New York and Cape Lookout, North Carolina,
barriers line the majority of the open coast. Consequently,
scientific investigations exploring coastal geology of this
portion of North America have focused on understand-
ing barrier island systems (Fisher, 1962, 1968; Pierce and
Colquhoun, 1970; Kraft, 1971; Leatherman, 1979; Moslow
and Heron, 1979, 1994; Swift, 1975; Nummedal, 1983;
Oertel, 1985; Belknap and Kraft, 1985; Hine and Snyder,
1985; Davis, 1994).
46
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to
A Focus on the Mid-Atlantic Region
Several important factors influence the evolution of the mid-
Atlantic coast in response to sea-level rise including: (1) the
geologic framework, (2) physical processes, (3) the sediment
supply, and (4) human activity. Each of these factors influ-
ences the response of coastal landforms to changes in sea
level. In addition, these factors contribute to the local and
regional variations of sea-level rise impacts that are difficult
to capture using quantitative prediction methods.
, . .
An important factor influencing coastal morphology and
behavior is the underlying geology of a setting, which is
also referred to as the geological framework (Belknap and
Kraft, 1985; Demarest and Leatherman, 1985; Schwab et al.,
2000). On a large scale, an example of this is the contrast in
the characteristics of the Pacific Coast versus the Atlantic
Coast of the United States. The collision of tectonic plates
along the Pacific margin has contributed to the development
of a steep coast where cliffs line much of the shoreline (In-
man and Nordstrom, 1971; Muhs et al., 1987; Dingier and
Clifton, 1994; Griggs and Patsch, 2004; Hapke et al, 2006;
Hapke and Reid, 2007). While common, sandy barriers
and beaches along the Pacific margin are confined to river
mouths and low-lying coastal plains that stretch between
rock outcrops and coastal headlands. On the other hand,
the Gulf of Mexico and Atlantic coasts of the United States
are situated on a passive margin where tectonic activity is
minor (Walker and Coleman, 1987). As a result, these coasts
are composed of wide coastal plains and wide continental
shelves extending far offshore. The majority of these coasts
are lined with barrier beaches and lagoons, large estuaries,
isolated coastal capes, and mainland beaches that abut high
grounds in the surrounding landscape.
From a smaller-scale perspective focused on the mid-
Atlantic region, the influence of the geological framework
involves more subtle details of the regional geology. More
specifically, the distribution, structure, and orientation of
different rock and sediment units, as well as the presence
of features such as river and creek valleys eroded into these
units, provides a structural control on a coastal environ-
ment (e.g., Kraft, 1971; Belknap and Kraft, 1985; Demarest
and Leatherman, 1985; Fletcher et al., 1990; Riggs et al.,
1995; Schwab et al., 2000; Honeycutt and Krantz, 2003).
Moreover, the framework geology can control (1) the loca-
tion of features, such as inlets, capes, or sand-ridges, (2) the
erodibility of sediments, and (3) the type and abundance of
sediment available to beach and barrier island settings. In
the mid-Atlantic region, the position of tidal inlets, estuar-
ies, and shallow water embayments can be related to the
existence of river and creek valleys that were present in the
landscape during periods of lower sea level in a number of
cases (e.g., Kraft, 1971; Belknap and Kraft, 1985; Fletcher
et al., 1990). Elevated regions of the landscape, which can
of ten be identified by areas where the mainland borders the
ocean coast, form coastal headlands. The erosion of these
features supplies sand to the nearshore system. Differences
in sediment composition (e.g., sediment size or density), can
sometimes be related to differences in shoreline retreat rates
(e.g., Honeycutt and Krantz, 2003). In addition, the distri-
bution of underlying geological units (rock outcrops, hard-
grounds, or sedimentary strata) in shallow regions offshore
of the coast can modify waves and currents and influencing
patterns of sediment erosion, transport, and deposition on
the adjacent shores (Riggs etal., 1995; Schwab etal., 2000).
These complex interactions with nearshore sand bodies
and/or underlying geology can also influence the behavior
of beach morphology over a range of time scales (Riggs et
al, 1995; Honeycutt and Krantz, 2003; Schupp et al, 2006;
Miselis and McNinch, 2006).
3,4,2
The physical processes acting on the coast are a principal
factor shaping coastal landforms and consequently changes
in shoreline position (see reviews in Davis, 1987; Komar,
1998). Winds, waves, and tidal currents continually erode,
rework, winnow, redistribute, and shape the sediments that
make up these landforms. As a result, these forces also have
a controlling influence on the composition and morphology
of coastal landforms such as beaches and barrier islands.
Winds have a range of effects on coastal areas. They are the
main cause of waves and also generate currents that trans-
port sediments in shallow waters. In addition, winds are a
significant mechanism transporting sand along beaches and
barrier islands that generate and sustain coastal dunes.
Waves are either generated by local winds or result from
far-away disturbances such as large storms out at sea. As
waves propagate into shallow water, their energy decreases
but they are also increasingly capable of moving the sedi-
ment on the seabed. Close to shore each passing wave or
breaking wave suspends sediments off the seabed. Once
suspended above the bottom, these sediments can be carried
by wave- or tide-generated currents.
Wave-generated currents are important agents of change
on sandy shores. The main currents that waves generate are
longshore currents, rip currents, and onshore and offshore
directed currents that accompany the surge and retreat of
breaking waves. Longshore currents are typically the most
important for sediment transport that influences changes
in shoreline position. Where waves approach the coast at
an angle, longshore currents are generated. The speed of
these currents varies, depending on the wave climate (e.g.,
47
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Chapter 3
average wave height and direction) and more specifically,
on the power and angle of approach of the waves (e.g., high
waves during storms, low waves during fair weather). These
currents provide a mechanism for sand transport along the
coast, referred to as littoral transport, longshore drift, or
longshore transport. During storms, high incoming waves
can generate longshore currents exceeding 1 meter (3 feet)
per second and storm waves can transport thousands of cubic
meters of sand in a relatively short time period, from hours
to days. During calm conditions, waves are weaker but can
still gradually transport large volumes of sand over longer
time periods, ranging from weeks to months. Where there
are changes in coastal orientation, the angle at which waves
approach the coast changes and can lead to local reversals in
longshore sediment transport. These variations can result in
the creation of abundances or deficits of longshore sediment
transport and contribute to the seaward growth or landward
retreat of the shoreline at a particular location (e.g., Cape
Lookout, North Carolina: McNinch and Wells, 1999).
The effect of tidal currents on shores is more subtle except
for regions near the mouths of inlets, bays, or areas where
there is a change in the orientation of the shore. The rise and
fall of the water level caused by tides moves the boundary
between the land and sea (the shoreline), causing the level
that waves act on a shore to move as well. In addition, this
controls the depth of water which influences the strength
of breaking waves. In regions where there is a large tidal
range, there is a greater area over which waves can act on
a shore. The rise and fall of the water level also generates
tidal currents. Near the shore, tidal currents are small in
comparison to wave-driven currents. Near tidal inlets and
the mouths of bays or estuaries, tidal currents are strong due
to the large volumes of water that are transported through
these conduits in response to changing water levels. In these
settings, tidal currents transport sediment from ocean shores
to back-barrier wetlands, inland waterways on flood tides
and vice versa on ebb tides. Aside from these settings, tidal
currents are generally small along the mid-Atlantic region
except near changes in shoreline orientation or sand banks
(e.g., North Carolina Capes, Cape Henlopen, Delaware). In
these settings, the strong currents generated can significantly
influence sediment transport pathways and the behavior of
adjacent shores.
The availability of sediments to a coastal region also has
important effects on coastal landforms and their behavior
(Curray, 1964). In general, assuming a relatively stable sea
level, an abundance of sediment along the coast can cause
the coast to build seaward over the long term if the rate
of supply exceeds the rate at which sediments are eroded
and transported by nearshore currents. Conversely, the
coast can retreat landward if the rate of erosion exceeds
the rate at which sediment is supplied to a coastal region.
One way to evaluate the role of sediment supply in a region
or specific location is to examine the amount of sediment
being gained or lost along the shore. This is often referred
to as the sediment budget (Komar, 1996; List, 2005; Rosati,
2005). Whether or not there is an overall sediment gain or
loss from a coastal setting is a critical determinant of the
potential response to changes in sea level; however, it is
difficult if to quantify with high confidence the sediment
budget over time periods as long as a century or its precise
role in influencing shoreline changes.
The recent Intergovernmental Panel on Climate Change
(IPCC) chapter on coastal systems and low-lying regions
noted that the availability of sediment to coastal regions
will be a key factor in future shoreline changes (Nicholls
et al., 2007). In particular, the deposition of sediments in
coastal embayments (e.g., estuaries and lagoons) may be a
significant sink for sediments as they deepen in response
to sea-level rise and are able to accommodate sediments
from coastal river systems and adjacent open ocean coasts.
For this reason, it is expected that the potential for erosion
and shoreline retreat will increase, especially in the vicinity
of tidal inlets (see Nicholls et al., 2007). In addition, oth-
ers have noted an important link between changes in the
dimension of coastal embayments, the sediment budget,
and the potential for shoreline changes (FitzGerald et al.,
2006, 2008). In the mid-Atlantic region, coastal sediments
generally come from erosion of both the underlying coastal
landscape and the continental shelf (Swift et al., 1985; Nie-
doroda et al., 1985). Sediments delivered through coastal
rivers in the mid-Atlantic region are generally captured in
estuaries contributing minor amounts of sediments to the
open-ocean coast (Meade, 1969).
The human impact on the coast is another important factor
affecting shoreline changes. A variety of erosion control
practices have been undertaken over the last century along
much of the mid-Atlantic region, particularly during the lat-
ter half of the twentieth century (see reviews in Nordstrom,
1994, 2000). As discussed later in Chapter 6, shoreline en-
gineering structures such as seawalls, revetments, groins,
and jetties have significantly altered sediment transport
processes, and consequently affect the availability of sedi-
ment (e.g., sediment budget) to sustain beaches and barriers
and the potential to exacerbate erosion on a local level (see
discussion on Assateague Island inBox 3.2). Beach nourish-
ment, a commonly used approach, has been used on many
beaches to temporarily mitigate erosion and provide storm
protection by adding to the sediment budget.
The management of tidal inlets by dredging has had a large
impact to the sediment budget particularly at local levels (see
48
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Reg/on
review in Nordstrom, 1994,2000). In the past, sand removed
from inlet shoals has been transferred out to sea, thereby
depleting the amount of sand available to sustain portions
of the longshore transport system and, consequently, adja-
cent shores (Marino and Mehta, 1988; Dean, 1988). More
recently, inlet management efforts have attempted to retain
this material by returning it to adjacent shores or other shores
where sand is needed.
A major concern to coastal scientists and managers is
whether or not erosion management practices are sustainable
for the long term, and whether or how these shoreline protec-
tion measures might impede the ability of natural processes
to respond to future sea-level rise, especially at accelerated
rates. It is also uncertain whether beach nourishment will be
continued into the future due to economic constraints and
often limited supplies of suitable sand resources. Chapter 6
describes some of these erosion control practices and their
management and policy implications further. In addition,
Chapter 6 also describes the important concept of "Regional
Sediment Management" which is used to guide the manage-
ment of sediment in inlet dredging, beach nourishment, or
other erosion control activities.
3.5 COASTAL LANDFORMS OF THE MID-
ATLANTIC
For this assessment, the coastal landforms along the shores
of the mid-Atlantic region are classified using the criteria
developed by Fisher (1967, 1982), Hayes (1979), and Davis
and Hayes (1984). Four distinct geomorphic settings, includ-
ing spits, headlands, and wave-dominated and mixed-energy
barrier islands, occur in the mid-Atlantic region, as shown
and described in Figure 3.1.
3.5.1 Spits
The accumulation of sand from longshore transport has
formed large spits that extend from adjacent headlands into
the mouths of large coastal embayments (Figure 3.1, Sec-
tions 4, 9, and 15). Outstanding examples of these occur at
the entrances of Raritan Bay (Sandy Hook, New Jersey)
and Delaware Bay (Cape Henlopen, Delaware). The evolu-
tion and existence of these spits results from the interaction
between alongshore transport driven by incoming waves
and the tidal flow through the large embayments. Morpho-
logically, these areas can evolve rapidly. For example, since
1842 Cape Henlopen (Figure 3.1, Section 9) has extended
Coastal Landform Types Along U.S. Mid-Atlantic Coast
Figure 3.1 Map of the mid-Atlantic coast of the United States showing the occurrence of the four coastal landform types.
Numbers on the map designate distinct portions of the coast divided by landform type and refer to the discussions in Sections
3.5 and 3.7. Numbers on the photographs refer to specific sections of the coast that are depicted on the map. Images from
Google Earth (Gutierrez et a/., 2007).
49
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The U.S. Climate Change Science Program
Chapter 3
BOX 3.2: Evidence forThreshold Crossing of Coastal Barrier Landforms
Barrier islands change and evolve in subtle and somewhat predictable ways over time in response to storms,
changing sediment supply, and changes in sea level. Recent field observations suggest that some barrier islands
can reach a "threshold" condition: that is, a point where they become unstable and disintegrate. Two sites
where barrier island disintegration is occurring and may continue to occur are along the 72 kilometer- (about
45 mile-) long Chandeleur Islands in Louisiana, east of the Mississippi River Delta, due to impacts of Hurricane
Katrina in September 2005; and the northern 10 kilometers (6 miles) of Assateague Island National Seashore,
Maryland due to 70 years of sediment starvation caused by the construction of jetties to maintain Ocean City
Inlet.
Chandeleur Islands, Louisiana
In the Chandeleur Islands, the high storm surge (about 4 meters, or 13 feet) and waves associated with Hur-
ricane Katrina in 2005 completely submerged the islands and eroded about 85 percent of the sand from the
beaches and dunes (Sallenger et a/., 2007). Box Figure 3.2a (UTM Northing) shows the configuration of the
barriers in 2002, and in 2005 after Katrina's passage. Follow-up aerial surveys by the U.S. Geological Survey
indicate that erosion has continued since that time. When the Chandeleur Islands were last mapped in the late
1980s and erosion rates were calculated from the 1850s, it was estimated that the Chandeleurs would last
approximately 250 to 300 years (Williams et a/., 1992). The results from post-Katrina studies suggest that a
threshold has been crossed such that conditions have changed and natural processes may not contribute to the
rebuilding of the barrier in the future.
UTM HMMng (kKumtmj
3294 32M 3MB 3300 3302 33CK 3306 33 W 3310 3312 3314 3316 3318 3320 3322 3324
Box Figure 3.2a Maps showing the extent of the Chandeleur Islands in 2002, three years before Hurricane
Katrina and in 2005, after Hurricane Katrina. Land area above mean high water. Source: A. Sallenger, USGS.
Assateague Island National Seashore, Maryland
An example of one shoreline setting where human activity has increased the vulnerability of the shore to sea-level
rise is Assateague Island, Maryland. Prior to a hurricane in 1933, Assateague Island was a continuous, straight bar-
rier connected to Fenwick Island (Dolan et a/., 1980).An inlet that formed during the storm separated the island
into two sections at the southern end of Ocean City, Maryland. Subsequent construction of two stone jetties to
maintain the inlet for navigation interrupted the longshore transport of sand to the south. Since then, the jetties
have trapped sand, building the Ocean City shores seaward by 250 meters (820 feet) by the mid-1970s (Dean and
Perlin, 1977). In addition, the development of sand shoals (ebb tidal deltas) around the inlet mouth has seques-
tered large volumes of sand from the longshore transport system (Dean and Perlin, 1977; FitzGerald, 1988).
50
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Reg/on
BOX 3.2: Evidence forThreshold Crossing of Coastal Barrier Landforms cont'd
South of the inlet, the opposite has oc-
curred. The sand starvation on the north-
ern portion of Assateague Island has caused
the shore to migrate almost 700 meters
(2,300 feet) landward and transformed the
barrier into a low-relief, overwash-dom-
inated barrier (Leatherman, 1979; 1984).
This extreme change in barrier island sedi-
ment supply has caused a previously stable
segment of the barrier island to migrate.
To mitigate the effects of the jetties, and to
restore the southward sediment transport
that was present prior to the existence of
Ocean City inlet, the U.S. Army Corps of
Engineers and National Park Service me-
chanically transfer sand from the inlet and
the ebb and flood tidal deltas, where the
sand is now trapped, to the shallow near-
shore regions along the north end of the
island. Annual surveys indicate that waves
successfully transport the sediment along-
shore and have slowed the high shoreline
retreat rates present before the project
began (Schupp et a/., 2007). Current plans
call for continued biannual transfer of sand
from the tidal deltas to Assateague Island to
mitigate the continued sediment starvation
by the Ocean City inlet jetties.
.36-20 5'
36-19.tr
36-185'
Box Figure 3.2b Aerial photo of northern Assateague Island and Ocean
City, Maryland showing former barrier positions. Note that in 1850, a single
barrier island, shown in outlined in yellow, occupied this stretch of coast.
In 1933, Ocean City inlet was created by a hurricane. The inlet improved
accessibility to the ocean and was stabilized by jetties soon after. By 1942,
the barrier south of the inlet had migrated landward (shown as a green
shaded region). Shorelines acquired from the State of Maryland Geological
Survey. Photo source: NPS.
Box Figure 3.2c North oblique photographs of northern Assateague Island in
1998 after a severe winter storm. The left photo of Assateague Island barrier shows
clear evidence of overwash.The right 2006 photo shows a more robust barrier that
had been augmented by recent beach nourishment. The white circles in the photos
specify identical locations on the barrier. The offset between Fenwick Island (north)
and Assateague Island due to Ocean City inlet and jetties can be seen at the top
of the photo. Photo sources: a) National Park Service, b) Jane Thomas, IAN Photo
and Video Library.
51
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3
almost 1.5 kilometers (0.9 miles) to the north into the mouth
of Delaware Bay as the northern Delaware shoreline has
retreated and sediment has been transported north by long-
shore currents (Kraft, 1971; Kraft et al., 1978; Ramsey et
al, 2001).
3.5.2
Along the shores of the mid-Atlantic region, coastal head-
lands typically occur where elevated regions of the landscape
intersect the coast. These regions are often formed where
drainage divides that separate creeks and rivers from one
another occur in the landscape, or where glacial deposits
create high grounds (Taney, 1961; Kraft, 1971; Nordstrom
et al., 1977). The erosion of headlands provides a source of
sediment that is incorporated into the longshore transport
system that supplies and maintains adjacent beaches and
barriers. Coastal headlands are present on Long Island,
New York (see Figure 3.1), from Southampton to Montauk
(Section 1), in northern New Jersey fromMonmouthto Point
Pleasant (Section 5; Oertel and Kraft, 1994), in southern
New Jersey at Cape May (Section 8), on Delaware north
and south of Indian River and Rehoboth Bays (Sections
10 and 12; Kraft, 1971; Oertel and Kraft, 1994; Ramsey et
al., 2001), and on the Virginia Coast, from Cape Henry to
Sandbridge (Section 16).
3.5.3
Wave-dominated barrier islands occur as relatively long and
thin stretches of sand fronting shallow estuaries, lagoons, or
embayments that are bisected by widely-spaced tidal inlets
(Figure 3.1, Sections 2, 6, 11, 13, and 17). These barriers
are present in regions where wave energy is large relative
to tidal energy, such as in the mid-Atlantic region (Hayes,
1979; Davis and Hayes, 1984). Limited tidal ranges result
in flow-through tidal inlets that are marginally sufficient to
flush the sediments that accumulate from longshore sedi-
ment transport. In some cases, this causes the inlet to migrate
over time in response to a changing balance between tidal
flow through the inlet and wave-driven longshore transport.
Inlets on wave-dominated coasts often exhibit large flood-
tidal deltas and small ebb-tidal deltas as tidal currents are
often stronger during the flooding stage of the tide.
In addition, inlets on wave-dominated barriers are often
temporary features. They open intermittently in response
to storm-generated overwash and migrate laterally in the
overall direction of longshore transport. In many cases,
these inlets are prone to filling with sands from alongshore
sediment transport (e.g., McBride, 1999).
Overwash produced by storms is common on wave-domi-
nated barriers (e.g., Morton and Sallenger, 2003; Riggs and
Ames, 2007). Overwash erodes low-lying dunes into the is-
land interior. Sediment deposition from overwash adds to the
island's elevation. Overwash deposits (washover fans) that
extend into the back-barrier waterways form substrates for
back-barrier marshes and submerged aquatic vegetation.
The process of overwash is an important mechanism by
which some types of barriers migrate landward and upward
overtime. This process of landward migration has been re-
ferred to as "roll-over" (Dillon, 1970; Godfrey and Godfrey,
1976; Fisher, 1982; Riggs and Ames, 2007). Over decades
to centuries, the intermittent processes of overwash and
inlet formation enable the barrier to migrate over and erode
into back-barrier environments such as marshes as relative
sea-level rise occurs overtime. As this occurs, back-barrier
environments are eroded and buried by barrier beach and
dune sands.
3.5.4
The other types of barrier islands present along the U.S.
Atlantic coast are mixed-energy barrier islands, which are
shorter and wider than their wave-dominated counterparts
(Hayes, 1979; Figure 3.1, Sections 3, 7, and 14). The term
"mixed-energy" refers to the fact that both waves and tidal
currents are important factors influencing the morphology
of these systems. Due to the larger tidal range and conse-
quently stronger tidal currents, mixed energy barriers are
shorter in length and well-developed tidal inlets are more
abundant than for wave-dominated barriers. Some authors
have referred to the mixed-energy barriers as tide-dominated
barriers along the New Jersey and Virginia coasts (e.g.,
Oertel and Kraft, 1994).
The large sediment transport capacity of the tidal currents
within the inlets of these systems maintains large ebb-tidal
deltas seaward of the inlet mouth. The shoals that comprise
ebb-tidal deltas cause incoming waves to refract around the
large sand body that forms the delta such that local reversals
of alongshore currents and sediment transport occur down-
drift of the inlet. As a result, portions of the barrier down-
drift of inlets accumulate sediment which form recurved
sand ridges and give the barrier islands a "drumstick"-like
shape (Hayes, 1979; Davis, 1994).
Based on current understanding of the four landforms
discussed in the previous section, three potential responses
could occur along the mid-Atlantic coast in response to sea-
level rise over the next century.
3.6.1 Erosion
Shorelines along headland regions of the coast will retreat
landward with rising sea level. As sea level rises over time,
uplands will be eroded and the sediments incorporated
52
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to
A Focus on the Mid-Atlantic Region
into the beach and dune systems along these shores. Along
coastal headlands, bluff and upland erosion will persist
under all four of the sea-level rise scenarios considered in
this Product. A possible management reaction to bluff ero-
sion is shore armoring (e.g., Nordstrom, 2000; Psuty and
Ofiara, 2002; see Chapter 6). This may reduce bluff ero-
sion in the short term but could increase long-term erosion
of the adjacent coast by reducing sediment supplies to the
littoral system.
3,6,2 Processes,
For barrier islands, three main processes are agents of
change as sea level rises. First, with higher sea level, storm
overwash may occur more frequently. This is especially criti-
cal if the sand available to the barrier, such as from longshore
transport, is insufficient to allow the barrier to maintain its
width and/or build vertically over time in response to ris-
ing water levels. If sediment supplies or the timing of the
barrier recovery are insufficient, storm surges coupled with
breaking waves will affect increasingly higher elevations
of the barrier systems as mean sea level increases, possibly
causing more extensive erosion and overwash. In addition, it
is possible that future hurricanes may become more intense,
possibly increasing the potential for episodic overwash, inlet
formation, and shoreline retreat. The topic of recent and
future storm trends has been debated in the scientific com-
munity, with some researchers suggesting that other climate
change impacts such as strengthening wind shear may lead
to a decrease in future hurricane frequency (see Chapter 1
and reviews inMeehl etal., 2007; Karl etal., 2008; Gutowski
et al., 2008). It is also expected that extratropical storms will
be more frequent and intense in the future, but these effects
will be more pronounced at high latitudes (60° to 90°N) and
possibly decreased at midlatitudes (30° to 60°N) (Meehl et
al., 2007; Karl et al., 2008; Gutowski et al., 2008).
Second, tidal inlet formation and migration will contribute
to important changes in future shoreline positions. Storm
surges coupled with high waves can cause not only barrier
island overwash but also breach the barriers and create new
inlets. In some cases, breaches can be large enough to form
inlets that persist for some time until the inlet channels
fill with sediments accumulated from longshore transport.
Numerous deposits have been found along the shores of the
mid-Atlantic region, indicating former inlet positions (North
Carolina: Moslow and Heron, 1979 and Everts et al., 1983;
Fire Island, New York: Leatherman, 1985). Several inlets
along the mid-Atlantic coast were formed by the storm
surges and breaches from an unnamed 1933 hurricane, in-
cluding Shackleford inlet in North Carolina; Ocean City inlet
in Maryland; Indian River inlet in Delaware; and Moriches
inlet in New York. Recently, tidal inlets were formed in the
North Carolina Outer Banks in response to Hurricane Isabel
in 2003. While episodic inlet formation and migration are
natural processes and can occur independently of long-term
sea-level rise, a long-term increase in sea level coupled with
limited sediment supply and increases in storm frequency
and/or intensity could increase the likelihood for future
inlet breaching.
Third, the combined effect of rising sea level and stronger
storms could accelerate barrier island shoreline changes.
These will involve both changes to the seaward facing and
landward facing shores of some barrier islands. Assessments
of shoreline change on barrier islands indicate that barriers
have thinned in some areas over the last century (Leather-
man, 1979; Jarrett, 1983; Everts etal., 1983; Penland etal.,
2005). Evidence of barrier migration is not widespread on the
mid-Atlantic coast (Morton et al., 2003), but is documented
at northern Assateague Island in Maryland (Leatherman,
1979) and Core Banks, North Carolina (Riggs and Ames,
2007).
3,6,3
Barrier islands are dynamic environments that are sensitive
to a range of physical and environmental factors. Some evi-
dence suggests that changes in some or all of these factors
can lead to conditions where a barrier system becomes less
stable and crosses a geomorphic threshold. Once a thresh-
old is crossed, the potential for significant and irreversible
changes to the barrier island is high. These changes can
involve landward migration or changes to the barrier island
dimensions such as reduction in size or an increased pres-
ence of tidal inlets. Although it is difficult to precisely define
an unstable barrier, indications include:
Rapid landward migration of the barrier;
Decreased barrier width and height, due to a loss of sand
eroded from beaches and dunes;
Increased frequency of overwash during storms;
Increased frequency of barrier breaching and inlet
formation; and
Segmentation of the barrier.
Given the unstable state of some barrier islands under cur-
rent rates of sea-level rise and climate trends, it is very likely
that conditions will worsen under accelerated sea-level rise
rates. The unfavorable conditions for barrier maintenance
could result in significant changes, for example, to barrier
islands as observed in coastal Louisiana (further discussed
in Box 3.2; McBride et al., 1995; McBride and Byrnes,
1997; Penland et al., 2005; Day et al., 2007; Sallenger et al.,
2007; FitzGerald et al., 2008). In one case, recent observa-
tions indicate that the Chandeleur Islands are undergoing a
significant land loss due to several factors which include:
(1) limited sediment supply by longshore or cross-shore
transport, (2) accelerated rates of sea-level rise, and (3) per-
manent sand removal from the barrier system by storms such
tf .'.'., V
i ' *C "U>
53
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Chapter 3
as Hurricanes Camilla, Georges, and Katrina. Likewise, a
similar trend has been observed for Isle Dernieres, also on
the Louisiana coast (see review in FitzGerald et al., 2008).
In addition, recent studies from the North Carolina Outer
Banks indicate that there have been at least two periods
during the past several thousand years where fully open-
ocean conditions have occurred in Albemarle and Pamlico
Sounds, which are estuaries fronted by barrier islands at the
present time (Mallinson et al., 2005; Culver et al., 2008).
This indicates that portions of the North Carolina barrier
island system may have segmented or become less continu-
ous than the present time for periods of a few hundred years,
and later reformed. Given future increases in sea level and/
or storm activity, the potential for a threshold crossing ex-
ists, and portions of these barrier islands could once again
become segmented.
Changes in sea level coupled with changes in the hydrody-
namic climate and sediment supply in the broader coastal en-
vironment contribute to the development of unstable barrier
island behavior. The threshold behavior of unstable barriers
could result in: barrier segmentation, barrier disintegration,
or landward migration and rollover. If the barrier were to
disintegrate, portions of the ocean shoreline could migrate
or back-step toward and/or merge with the mainland.
The mid-Atlantic coastal regions most vulnerable to
threshold behavior can be estimated based on their physical
dimensions. During storms, large portions of low-elevation,
narrow barriers can be inundated under high waves and
storm surge. Narrow, low-elevation barrier islands, such
as the northern portion of Assateague Island, Maryland
are most susceptible to storm overwash, which can lead to
landward migration and the formation of new tidal inlets
(e.g., Leatherman, 1979; see also Box 3.2).
The future evolution of some low-elevation, narrow barriers
could depend in part on the ability of salt marshes in back-
barrier lagoons and estuaries to keep pace with sea-level rise
(FitzGerald et al., 2006,2008; Reed et al., 2008). A reduction
of salt marsh in back-barrier regions could increase the vol-
ume of water exchanged with the tides (e.g., the tidal prism)
of back-barrier systems, altering local sediment budgets and
leading to a reduction in sandy materials available to sustain
barrier systems (FitzGerald et al., 2006, 2008).
In this Section, the responses to the four sea-level rise sce-
narios considered in this Chapter are described according to
coastal landform types (Figure 3.2). The first three sea-level
rise scenarios (Scenarios 1 through 3) are: (1) a continuation
of the twentieth century rate, (2) the twentieth century rate
plus 2 mm per year, and (3) the twentieth century rate plus 7
mm per year. Scenario 4 specifies a 2-m rise (6.6-ft) over the
next few hundred years. Because humans have a significant
impact on portions of the mid-Atlantic coast, this assessment
focuses on assessing the vulnerability of the coastal system
as it currently exists (see discussion in Section 3.4). However,
there are a few caveats to this approach:
This is a regional-scale assessment and there are local
exceptions to these geomorphic classifications and
potential outcomes;
Given that some portions of the mid-Atlantic coast
are heavily influenced by development and erosion
mitigation practices, it cannot be assumed that current
practices will continue into the future given uncertain-
ties regarding the decision-making process that occurs
when these practices are pursued; but,
At the same time, there are locations where some mem-
bers of the panel believe that erosion mitigation will be
implemented regardless of cost.
To express the likelihood of a given outcome for a particu-
lar sea-level rise scenario, the terminology advocated by
ongoing CCSP assessments was used (see Preface, Figure
P.I; CCSP, 2006). This terminology is used to quantify and
communicate the degree of likelihood of a given outcome
specified by the assessment. These terms should not be
construed to represent a quantitative relationship between a
specific sea-level rise scenario and a specific dimension of
coastal change, or rate at which a specific process operates
on a coastal geomorphic compartment. The potential coastal
responses to the sea-level rise scenarios are described below
according to the coastal landforms defined in Section 3.5.
3.7.1
For sea-level rise Scenarios 1 through 3, it is virtually certain
that the spits along the mid-Atlantic coast will be subject to
increased storm overwash, erosion, and deposition over the
next century (see Figure 3.2, Sections 4, 9, 15). It is virtu-
ally certain that some of these coastal spits will continue to
grow through the accumulation of sediments from longshore
transport as the erosion of updrift coastal compartments oc-
curs. For Scenario 4, it is likely that threshold behavior could
occur for this type of coastal landform (rapid landward and/
or alongshore migration).
3,7,2 I
Over the next century, it is virtually certain that these
headlands along the mid-Atlantic coast will be subject to
increased erosion for all four sea-level rise scenarios (see
Figure 3.2, Sections 1, 5, 8, 10, 12, and 16). It is very likely
that shoreline and upland (bluff) erosion will accelerate in
response to projected increases in sea level.
54
-------
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Reg/on
Potential Mid-Atlantic Landform Responses to Sea-Level Rise
Atlantic Ocean
100
150
37=
EXPLANATION
SLR Scenario M^"L
LD
EH
CD
•
•
BUE
OEIB
OEIB
OEIB
T?
20th Cenl
*2 mm1,'!
BUE
OEIB
OEIB
T?
T
iOlhCenl.
+T tniftlyt
BUE
OEIB
T?
T
T
35"
BUE = Bluff and Upland Erosion
OEIB =QvBwssh, Erosion, Island Breaching
? = Indicates that Ihe condition could be marginal
T = Threshold Condition
76* 74' 72'
Figure 3.2 Map showing the potential sea-level rise responses (in millimeters [mm] per year [yr])
for each coastal compartment. Colored portions of the coastline indicate the potential response
for a given sea-level rise scenario according to the inset table. The color scheme was created
using ColorBrewer by Cindy Brewer and Mark Narrower. After Gutierrez et. al. (2007).
3.7.3 Wave-Dominated Barrier Islands
Potential sea-level rise impacts on wave-dominated barri-
ers in the Mid-Atlantic vary by location and depend on the
sea-level rise scenario (see Figure 3.2, Sections 2, 6, 11, 13,
17). For Scenario 1, it is virtually certain that the majority of
the wave-dominated barrier islands along the mid-Atlantic
coast will continue to experience morphological changes
through erosion, overwash, and inlet formation as they
have over the last several centuries, except for the northern
portion of Assateague Island (Section 13). In this area, the
shoreline exhibits high rates of erosion and large portions of
this barrier are submerged during moderate storms. In the
past, large storms have breached and segmented portions of
northern Assateague Island (Morton et al., 2003). Therefore,
it is possible that these portions of the coast are already at a
geomorphic threshold. With any increase in the rate of sea-
level rise, it is virtually certain that this barrier island will
exhibit large changes in morphology, ultimately leading to
the degradation of the island. At this site, however, periodic
55
-------
Chapter 3
transfer of sand from the shoals of Ocean City inlet appear to
be reducing erosion and shoreline retreat in Section 13 (see
Box 3.2). Portions of the North Carolina Outer Banks (Figure
3.2) may similarly be nearing a geomorphic threshold.
For Scenario 2, it is virtually certain that the majority of the
wave-dominated barrier islands in the mid-Atlantic region
will continue to experience morphological changes through
overwash, erosion, and inlet formation as they have over the
last several centuries. It is also about as likely as not that
a geomorphic threshold will be reached in a few locations,
resulting in rapid morphological changes in these barrier
systems. Along the shores of northern Assateague Island
(Section 13) and a substantial portion of Section 17 it is
very likely that the barrier islands could exhibit threshold
behavior (barrier segmentation). For this scenario, the ability
of wetlands to maintain their elevation through accretion at
higher rates of sea-level rise may be reduced (Reed et al.,
2008). It is about as likely as not that the loss of back-barrier
marshes will lead to changes in hydrodynamic conditions
between tidal inlets and back-barrier lagoons, thus affecting
the evolution of barrier islands (e.g., FitzGerald et al., 2006;
FitzGerald et al., 2008).
For Scenario 3, it is very likely that the potential for thresh-
old behavior will increase along many of the mid-Atlantic
barrier islands. It is virtually certain that a 2-m (6.6-ft) sea-
level rise will lead to threshold behavior (segmentation or
disintegration) for this landform type.
3.7.4
The response of mixed-energy barrier islands will vary (see
Figure 3.2, Sections 3, 7, 14). For Scenarios 1 and 2, the
mixed-energy barrier islands along the mid-Atlantic will
be subject to processes much as have occurred over the last
century such as storm overwash and shoreline erosion. Given
the degree to which these barriers have been developed, it is
difficult to determine the likelihood of future inlet breaches,
or whether these would be allowed to persist due to common
management decisions to repair breaches when they occur.
In addition, changes to the back-barrier shores are uncertain
due to the extent of coastal development.
It is about as likely as not that four of the barrier islands
along the Virginia Coast (Wallops, Assawoman, Metomp-
kin, and Cedar Islands) are presently at a geomorphic
threshold. Thus, it, it is very likely that further sea-level
rise will contribute to significant changes resulting in the
segmentation, disintegration and/or more rapid landward
migration of these barrier islands.
For the higher sea-level rise scenarios (Scenarios 3 and 4),
it is about as likely as not that these barriers could reach a
geomorphic threshold. This threshold is dependent on the
availability of sand from the longshore transport system to
supply the barrier. It is virtually certain that a 2-m sea-level
rise will have severe consequences along the shores of this
portion of the coast, including one or more of the extreme
responses described above. For Scenario 4, the ability of
wetlands to maintain their elevation through accretion
at higher rates of sea-level rise may be reduced (Reed et
al., 2008). It is about as likely as not that the loss of back-
barrier marshes could lead to changes in the hydrodynamic
conditions between tidal inlets and back-barrier lagoons,
affecting the evolution of barrier islands (FitzGerald et al.,
2006, 2008).
56
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Coastal Wetland Sustainability
Lead Authors: Donald R. Cahoon, USGS; DeniseJ. Reed, Univ. of
New Orleans; Alexander S. Kolker, Louisiana Universities Marine
Consortium; Mark M. Brinson, East Carolina Univ.
Contributing Authors: J. Court Stevenson, Univ. of Maryland;
Stanley Riggs, East Carolina Univ.; Robert Christian, East Carolina
Univ.; Enrique Reyes, East Carolina Univ.; Christine Voss, East
Carolina Univ.; David Kunz, East Carolina Univ.
KEY FINDINGS
It is virtually certain that tidal wetlands already experiencing submergence by sea-level rise and associated high rates
of loss (e.g., Mississippi River Delta in Louisiana, Blackwater River marshes in Maryland) will continue to lose area
in response to future accelerated rates of sea-level rise and changes in other climate and environmental drivers
(factors that cause measurable changes).
It is very unlikely that there will be an overall increase in tidal wetland area in the United States over the next 100
years, given current wetland loss rates and the relatively minor accounts of new tidal wetland development (e.g.,
Atchafalaya Delta in Louisiana).
Current model projections of wetland vulnerability on regional and national scales are uncertain due to the coarse
level of resolution of landscape-scale models. In contrast, site-specific model projections are quite good where
local information has been acquired on factors that control local accretionary processes in specific wetland settings.
However, the authors have low confidence that site-specific model simulations can be successfully generalized so
as to apply to larger regional or national scales.
An assessment of the mid-Atlantic region based on an opinion approach by scientists with expert knowledge of
wetland accretionary dynamics projects with a moderate level of confidence that those wetlands keeping pace with
twentieth century rates of sea-level rise (Scenario I) would survive a 2 millimeter per year acceleration of sea-level
rise (Scenario 2) only under optimal hydrology and sediment supply conditions, and would not survive a 7 millimeter
per year acceleration of sea-level rise (Scenario 3). There may be localized exceptions in regions where sediment
supplies are abundant, such as at river mouths and in areas where storm overwash events are frequent.
The mid-Atlantic regional assessment revealed a wide variability in wetland responses to sea-level rise, both within
and among subregions and for a variety of wetland geomorphic settings. This underscores both the influence of
local processes on wetland elevation and the difficulty of generalizing from regional/national scale projections of
wetland sustainability to the local scale in the absence of local accretionary data. Thus, regional or national scale
assessments should not be used to develop local management plans where local accretionary dynamics may override
regional controls on wetland vertical development.
57
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The U.S. Climate Change Science Program
Chapter 4
Several key uncertainties need to be addressed in order to improve confidence in projecting wetland vulnerability
to sea-level rise, including: a better understanding of maximum rates at which wetland vertical accretion can be
sustained; interactions and feedbacks among wetland elevation, flooding, and soil organic matter accretion; broad-
scale, spatial variability in accretionary dynamics; land use change effects (e.g., freshwater runoff, sediment supply,
barriers to wetland migration) on tidal wetland accretionary processes; and local and regional sediment supplies,
particularly fine-grain cohesive sediments needed for wetland formation.
4.1 INTRODUCTION
Given an expected increase in the rate of sea-level rise in
the next century, effective management of highly valuable
coastal wetland habitats and resources in the United States
will be improved by an in-depth assessment of the effects of
accelerated sea-level rise on wetland vertical development
(i.e., vertical accretion), the horizontal processes of shore
erosion and landward migration affecting wetland area, and
the expected changes in species composition of plant and
animal communities (Nicholls et al, 2007). This Chapter
assesses current and projected future rates of vertical buildup
of coastal wetland surfaces and wetland sustainability during
the next century under the three sea-level rise scenarios, as
described briefly above, and in greater detail in Chapter 1.
Many factors must be considered in such an assessment,
including: the interactive effects of sea-level rise and other
environmental drivers (e.g., changes in sediment supplies
related to altered river flows and storms); local processes
controlling wetland vertical and horizontal development
and the interaction of these processes with the array of
environmental drivers; geomorphic setting; and limited
opportunities for landward migration
(e.g., human development on the coast,
or steep slopes) (Figures 4.1 and 4.2).
Consequently, there is no simple, direct
answer on national or regional scales
to the key question facing coastal
wetland managers today, namely, "Are
wetlands building vertically at a pace
equal to current sea-level rise, and will
they build vertically at a pace equal to
future sea-level rise?" This is a difficult
question to answer because of the vari-
ous combinations of local drivers and
processes controlling wetland elevation
across the many tidal wetland settings
found in North America, and also due
to the lack of available data on the criti-
cal drivers and local processes across
these larger landscape scales.
The capacity of wetlands to keep pace with sea-level rise
can be more confidently addressed at the scale of individual
sites where data are available on the critical drivers and local
processes. However, scaling up from the local to the national
perspective is difficult, and rarely done, because of data
constraints and because of variations in climate, geology,
species composition, and human-induced stressors that be-
come influential at larger scales. Better estimates of coastal
wetland sustainability under rising sea levels and the fac-
tors influencing future sustainability are needed to inform
coastal management decision making. This Chapter provides
an overview of the factors influencing wetland sustainability
(e.g., environmental drivers, accretionary processes, and
geomorphic settings), the state of knowledge of current and
future wetland sustainability, including a regional case study
analysis of the mid-Atlantic coast of the United States, and
information needed to improve projections of future wetland
sustainability at continental, regional, and local scales.
Environmental Influences on Wetland Development
^A Horizontal A Vwfcal.^S.
*_ Wodsnd DainiopnwntJI,
Figure 4.1 Climate and environmental drivers influencing vertical and horizontal
wetland development.
58
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4.2 WETLAND SETTINGS OF THE MID-
ATLANTIC REGION
Coastal wetlands in the continental United States occur in
a variety of physical settings (Table 4.1). The geomorphic
classification scheme presented in Table 4.1, developed by
Reed et al. (2008) (based on Woodroffe, 2002 and Cahoon et
al., 2006), provides a useful way of examining and compar-
ing coastal wetlands on a regional scale. Of the geomorphic
settings described in Table 4.1, saline fringe marsh, back-
barrier lagoon marsh, estuarine brackish marsh, tidal fresh
marsh, and tidal fresh forest are found in the mid-Atlantic
region of the United States. Back-barrier lagoon salt marshes
are either attached to the backside of the barrier island, or are
islands either landward of a tidal inlet or behind the barrier
island. Saline fringe marshes are located on the landward
side of lagoons where they may be able to migrate upslope
in response to sea-level rise (see Section 4.3 for a description
of the wetland migration process). Estuarine marshes are
brackish (a mixture of fresh and salt water) and occur along
channels rather than open coasts, either bordering tidal rivers
or embayments; or as islands within tidal channels. Tidal
fresh marshes and tidal fresh forests occur along river chan-
nels, usually above the influence of salinity but not of tides.
These wetlands can be distinguished based on vegetative
type (species composition; herbaceous versus forested) and
the salinity of the area. Given the differing hydrodynamics,
sediment sources, and vegetative community characteristics
of these geomorphic settings, the relationship between sea-
level rise and wetland response will also differ.
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
an intertidal mudf lat or to open water over a period of many
decades (Morris et al., 2002).
The processes contributing to the capacity of a coastal
wetland to maintain a stable relationship with changing
sea levels are complex and often nonlinear (Cahoon et al.,
2006). For example, the response of tidal wetlands to fu-
ture sea-level rise will be influenced not only by local site
characteristics, such as slope and soil erodibility influences
on sediment flux, but also by changes in drivers of vertical
accretion, some of which are themselves influenced by cli-
mate change (Figure 4.1). In addition to the rate of sea-level
rise, vertical accretion dynamics are sensitive to changes
in a suite of human and climate-related drivers, including
alterations in river and sediment discharge from changes in
precipitation patterns and in discharge and runoff related
to dams and increases in impervious surfaces, increased
frequency and intensity of hurricanes, and increased atmo-
spheric temperatures and carbon dioxide concentrations.
Vertical accretion is also affected by local environmental
drivers such as shallow (local) and deep (regional) subsid-
ence and direct alterations by human activities (e.g., dredg-
ing, diking). The relative roles of these drivers of wetland
vertical development vary with geomorphic setting.
4.3.1 Wetland Vertical Development
Projecting future wetland sustainability is made more dif-
ficult by the complex interaction of processes by which
wetlands build vertically (Figure 4.2) and vary across
geomorphic settings (Table 4.1). Figure 4.2 shows how en-
vironmental drivers, mineral and organic soil development
4.3 VERTICAL
DEVELOPMENT AND
ELEVATION CHANGE
A coastal marsh will survive if it
builds vertically at a rate equal to
the rise in sea level; that is, if it
maintains its elevation relative to
sea level. It is well established that
marsh surface elevation changes
in response to sea-level rise. Tidal
wetland surfaces are frequently
considered to be closely coupled
with local mean sea level (e.g.,
Pethick, 1981; Allen, 1990). If a
marsh builds vertically at a slower
rate than the sea rises, however,
then a marsh area cannot maintain
its elevation relative to sea level. In
such a case, a marsh will gradually
become submerged and convert to
Drivers and Processes that Influence Wetland Vertical Development
Figure 4.2 A conceptual diagram illustrating how environmental drivers (white boxes) and
accretionary processes (grey boxes) influence vertical wetland development.
59
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Chapter 4
Table 4.1 Wetland Types and Their Characteristics as They Are Distributed Within Geomorphic Settings in the
Continental United States.
>-»- if. f /./:,...-:.„ /
•^fir'
S=V
Open Coast
Back-
Barrier
Lagoon
Marsh (BB)
Estuarine
Embayment
Estuarine
Embayment
a. Saline
Fringe
Marsh (SF)
Estuarine
Embayment
b. Stream
Channel
Wetlands
Estuarine
Brackish
Marshes
(ES)
\ "\v /"^SxV/
tf.h:^ }}•{•><:,
Areas sheltered
from waves and
currents due to
coastal topogra-
phy or bathym-
etry
Occupies fill
within transgres-
sive back-barrier
lagoons
Shallow coastal
embayments with
some river dis-
charge, frequently
drowned river
valleys
Transgressive
marshes border-
ing uplands at the
lower end of
estuaries (can also
be found in back-
barrier lagoons)
Occupy estuarine/
alluvial channels
rather than open
coast
Located in vicinity
of turbidity
maxima zone
\\ r\ / \
\*ft/:. ;!fs-v,;.4:
-------
Table 4.1 Continued
•' - " ,' •"
Tidal Fresh
Marsh (FM)
Tidal Fresh
Forests (FF)
Nontidal
Brackish
Marsh
Nontidal
Forests
Delta
\"'- ' /" - :
•
Located above
turbidity maxima
zone; develop in
drowned river
valleys as filled
with sediment
Develop in
riparian zone
along rivers and
backwater areas
beyond direct
influence of
seawater
Transgressive
marshes
bordering uplands
in estuaries with
restricted tidal
signal
Develop in
riparian zone
along rivers and
backwater
areas beyond
direct influence of
seawater in
estuaries with
restricted tidal
signal
Develop on
riverine sedi-
ments in shal-
low open water
during
active deposition;
reworked by
marine processes
after
abandonment
'•-'. '--,'•''-'."' ./-""
Deepwater
Swamps (perma-
nently flooded)
Bottomland
Hardwood For-
ests (seasonally
flooded)
Alluvial input
Peat
accumulation
Bottomland
Hardwood For-
ests (seasonally
flooded)
- , ' '*" ! *' *K ' ' * '
Alluvial and tidal
inputs
Peat accumulation
Alluvial input
Peat accumulation
Alluvial input
Peat accumulation
Alluvial input
Peat accumulation
Alluvial input
Peat accumulation
Compaction/
Subsidence
Storm sedimentation
Marine Processes
Upper
Nanticoke
River,
Maryland;
Anacostia
River,
Washington,
D.C.
Upper Raritan
Bay, New
Jersey;
Upper
Hudson River,
New York
Pamlico Sound,
North Carolina
Roanoke River,
North
Carolina;
Albemarle
Sound, North
Carolina
Mississippi
Delta, Louisiana
" • ' i •> »,-' •' , -'•
arrow arum
(Peltandra virginica)
pickerelweed
(Pontederis cordata)
arrowhead (Sagitarria spp.)
bur-marigold (Bidens laevis)
halberdleaf tearthumb
(Polygonum arifolium)
scarlet rose-mallow
(Hibiscus coccineus)
wild-rice
(Zizannia aquatica)
cattails (Typha spp.)
giant cut grass
(Zizaniopsis miliacea)
big cordgrass (Spartina
cynosuroides)
bald cypress
(Taxodium distichum)
blackgum (Nyssa sylvatica)
oak (Quercus spp.)
green ash
(Fraxinus pennsylvanica)
(var. lanceolata)
black needlerush
(Juncus roemerianus)
smooth cordgrass
(Spartina alterniflora)
spike grass
(Distichlis spicata)
salt hay
(Spartina patens)
big cordgrass
(Spartina cynosuroides)
bald cypress
(Taxodium distichum)
blackgum (Nyssa sylvatica)
oak (Quercus spp.)
Green ash
(Fraxinus pennsylvanica)
smooth cordgrass
(Spartina alterniflora)
black needlerush
(Juncus roemerianus)
spike grass
(Distichlis spicata)
salt hay (Spartina patens)
glasswort (Salicornia spp.)
saltwort (Batis maritima)
maidencane
(Panicum haemitomon)
arrowhead (Sagitarria spp.)
61
-------
Chapter 4
processes, and wetland elevation interact. Tidal wetlands
build vertically through the accumulation of mineral sedi-
ments and plant organic matter (primarily plant roots). The
suite of processes shown in Figure 4.2 controls the rates
of mineral sediment deposition and accumulation of plant
organic matter in the soil, and ultimately elevation change.
Overall mineral sedimentation represents the balance be-
tween sediment import and export, which is influenced
by sediment supply and the relative abundance of various
particle sizes, and varies among geomorphic settings and
different tidal and wave energy regimes. Sediment deposi-
tion occurs when the surface of a tidal wetland is flooded.
Thus, flooding depth and duration are important controls
on deposition. The source of sediment may be supplied from
within the local estuary (Reed, 1989), and by transport from
riverine and oceanic sources. Sediments are remobilizedby
storms, tides, and, in higher latitudes, ice rafting.
The formation of organic-rich wetland soils is an important
contributor to elevation in both mineral sediment rich and
mineral sediment poor wetlands (see review by Ny man et al.,
2006). Organic matter accumulation represents the balance
between plant production (especially by roots and rhizomes)
and decomposition and export of plant organic matter
(Figure 4.2). Accumulation comes from root and rhizome
growth, which contributes mass, volume, and structure to the
sediments. The relative importance of mineral and organic
matter accumulation can vary depending on local factors
such as rates of subsidence and salinity regimes.
on
Projections of wetland sustainability are further complicated
by the fact that sea-level rise is not the only factor influ-
encing accretionary dynamics and sustainability (Figure
4.1). The influence of sea-level rise and other human- and
climate-related environmental drivers on mineral sediment
delivery systems is complex. For example, the timing and
amount of river flows are altered by changes in discharge
related to both the effects of dams and impervious surfaces
built by humans and to changes in precipitation patterns from
changing climate. This results in a change in the balance of
forces between river discharge and the tides that control the
physical processes of water circulation and mixing, which
in turn determines the fate of sediment within an estuary.
Where river discharge dominates, highly stratified estuar-
ies prevail, and where tidal motion dominates, well-mixed
estuaries tend to develop (Dyer, 1995). Many mid-Atlantic
estuaries are partially mixed systems because the influence
of river discharge and tides are more balanced.
River discharge is affected by interannual and interseasonal
variations and intensities of precipitation and evapotranspi-
ration patterns, and by alterations in land use (e.g., impervi-
ous surfaces and land cover types) and control over river
flows (e.g., impoundments and withdrawals). Sea-level rise
can further change the balance between river discharge and
tides by its effect on tidal range (Dyer, 1995). An increase in
tidal range would increase tidal velocities and, consequently,
tidal mixing and sediment transport, as well as extend the
reach of the tide landward. In addition, sea-level rise can
affect the degree of tidal asymmetry in an estuary (i.e., ebb
versus flood dominance). In flood dominant estuaries, ma-
rine sediments are more likely to be imported to the estuary.
However, an increase in sea level without a change in tidal
range may cause a shift toward ebb dominance, thereby re-
ducing the input of marine sediments that might otherwise
be deposited on intertidal flats and marshes (Dyer, 1995).
Estuaries with relatively small intertidal areas and small
tidal amplitudes would be particularly susceptible to such
changes. The current hydrodynamic status of estuaries today
is the result of thousands of years of interaction between
rising sea level and coastal landforms.
The degree of influence of sea-level rise on wetland flood-
ing, sedimentation, erosion, and salinity is directly linked
with the influence of altered river flows and storm impacts
(Figure 4.2). Changes in freshwater inputs to the coast can
affect coastal wetland community structure and function
(Sklar and Browder, 1998) through fluctuations in the salt
balance up and down the estuary. Low-salinity and fresh-
water wetlands are particularly affected by increases in
salinity. In addition, the location of the turbidity maximum
zone (the region in many estuaries where suspended sedi-
ment concentrations are higher than in either the river or
sea) can shift seaward with increases in river discharge,
and the size of this zone will increase with increasing tidal
ranges (Dyer, 1995). Heavy rains (freshwater) and tidal
surges (salty water) from storms occur over shorter time
periods than interannual and interseasonal variation. This
can exacerbate or alleviate (at least temporarily) salinity and
inundation effects of altered freshwater input and sea-level
rise in all wetland types. The direction of elevation change
depends on the storm characteristics, wetland type, and lo-
cal conditions at the area of storm landfall (Cahoon, 2006).
Predicted increases in the magnitude of coastal storms from
higher sea surface temperatures (Webster et al., 2005) will
likely increase storm-induced wetland sedimentation in the
mid-Atlantic regional wetlands. Increased storm intensity
could increase the resuspension of nearshore sediments
and the storm-related import of oceanic sediments into
tidal marshes.
In addition to sediment supplies, accumulation of plant
organic matter is a primary process controlling wetland
vertical development of soil. The production of organic
matter is influenced by factors associated with climate
change, including increases in atmospheric carbon dioxide
62
-------
concentrations, rising temperatures, more frequent and ex-
tensive droughts, higher nutrient loading from f loodwaters
and ground waters, and increases in salinity of flood waters.
Therefore, a critical question that scientists must address
is: "How will these potential changes in plant growth affect
wetland elevations and the capacity of the marsh to keep
pace with sea-level rise?" Some sites depend primarily on
plant matter accumulation to build vertically. For example,
in many brackish marshes dominated by salt hay (Spartina
patens) (McCaffrey and Thomson, 1980) and mangroves on
oceanic islands with low mineral sediment inputs (McKee
et al., 2007), changes in root production (Cahoon et al.,
2003, 2006) and nutrient additions (McKee et al., 2007)
can significantly change root growth and wetland elevation
trajectories. These changes and their interactions warrant
further study.
Wetland vertical development can lead to horizontal expan-
sion of wetland area (both landward and seaward; Redfield,
1972), depending on factors such as slope, sediment sup-
ply, shoreline erosion rate, and rate of sea-level rise. As
marshes build vertically, they can migrate inland onto dry
uplands, given that the slope is not too steep and there is no
human-made barrier to migration (Figure 4.1). Some of the
best examples of submerged upland types of wetlands in
the mid-Atlantic region are found on the Eastern Shore of
Chesapeake Bay, a drowned river valley estuary (Darmody
and Foss, 1979). Given a setting with a low gradient slope,
low wave energy, and high sediment supply (e.g., Barn-
stable Marsh on Cape Cod, Massachusetts), a marsh can
migrate both inland onto uplands and seaward onto sand
flats as the shallow lagoon fills with sediment (Redfield,
1972). Most coasts, however, have enough wave energy
to prevent seaward expansion of the wetlands. The more
common alternative is erosion of the seaward boundary of
the marsh and retreat. In these settings, as long as wetland
vertical development keeps pace with sea-level rise, wetland
area will expand where inland migration is greater than
erosion of the seaward boundary, remain unchanged where
inland migration and erosion of the seaward boundary are
equal, or decline where erosion of the seaward boundary is
greater than inland migration (e.g., Brinson et al., 1995). If
wetland vertical development lags behind sea-level rise (i.e.,
wetlands do not keep pace), the wetlands will eventually
become submerged and deteriorate even as they migrate,
resulting in an overall loss of wetland area, as is occur-
ring at Blackwater National Wildlife Refuge in Dorchester
County, Maryland (Stevenson et al., 1985). Thus, wetland
migration is dependent on vertical accretion, which is the key
process for both wetland survival and expansion. If there is
a physical obstruction preventing inland wetland migration,
such as a road or a bulkhead, and the marsh is keeping pace
with sea-level rise, then the marsh will not expand but will
survive in place as long as there is no lateral erosion at its
seaward edge. Otherwise, the wetland will become narrower
as waves erode the shoreline. Thus, having space available
with a low gradient slope for inland expansion is critical for
maintaining wetland area in a setting where seaward erosion
of the marsh occurs.
A recent evaluation of accretion and elevation trends from
49 salt marshes located around the world, including sites
from the Atlantic, Gulf of Mexico, and Pacific coasts of the
United States, provides insights into the mechanisms and
variability of wetland responses to twentieth century trends
of local sea-level rise (Cahoon et al., 2006). Globally, aver-
age wetland surface accretion rates were greater than and
positively related to local relative sea-level rise, suggesting
that the marsh surface level was being maintained by surface
accretion within the tidal range as sea level rose. In contrast,
average rates of elevation rise were not significantly related
to sea-level rise and were significantly lower than average
surface accretion rates, indicating that shallow soil subsid-
ence occurs at many sites. Regardless, elevation changes at
many sites were greater than local sea-level rise (Cahoon et
al., 2006). Hence, understanding elevation change, in ad-
dition to surface accretion, is important when determining
wetland sustainability. Secondly, accretionary dynamics
differed strongly among geomorphic settings, with deltas
and embayments exhibiting high accretion and high shallow
subsidence compared to back-barrier and estuarine settings
(see Cahoon et al., 2006). Thirdly, strong regional differ-
ences in accretion dynamics were observed for the North
American salt marshes evaluated, with northeastern U.S.
marshes exhibiting high rates of both accretion and eleva-
tion change, southeastern Atlantic and Gulf of Mexico salt
marshes exhibiting high rates of accretion and low rates of
elevation change, and Pacific salt marshes exhibiting low
rates of both accretion and elevation change (see Cahoon et
al., 2006). The marshes with low elevation change rates are
likely vulnerable to current and future sea-level rise, with
the exception of those in areas where the land surface is
rising, such as on the Pacific Northwest coast of the United
States.
4,5,1 Di<
An increasing number of reports available online (see
e.g., , , , ) of widespread
"sudden marsh dieback" and "brown marsh dieback" from
Maine to Louisiana, along with published studies document-
ing losses of marshes dominated by saltmarsh cordgrass
63
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Chapter 4
(Spartina alterniflord) and other halophytes (plants that
naturally grow in salty soils), suggest that a wide variety of
marshes may be approaching or have actually gone beyond
their tipping point where they can continue to accrete enough
inorganic material to survive (Delaune et al., 1983; Steven-
son et al., 1985; Kearney et al, 1988,1994; Mendelssohn and
McKee, 1988; Hartig et al., 2002; McKee et al., 2004; Turner
et al., 2004). Sudden dieback was documented over 40 years
ago by marsh ecologists (Goodman and Williams, 1961).
However, it is not known whether all recently identified
events are the same phenomenon and caused by the same
factors. There are biotic factors, in addition to insufficient
accretion, that have been suggested to contribute to sudden
marsh dieback, including fungal diseases and overgrazing
by animals such as waterfowl, nutria, and snails. Interacting
factors may cause marshes to decline even more rapidly than
scientists would predict from one driver, such as sea-level
rise. There are few details about the onset of sudden dieback
because most studies are done after it has already occurred
(Ogburn and Alber, 2006). Thus, more research is needed to
understand sudden marsh dieback. The apparent increased
frequency of this phenomenon over the last several years
suggests an additional risk factor for marsh survival over
the next century (Stevenson and Kearney, in press).
"..-'••'• •'•" '
Projections of future wetland sustainability on regional-to
national-scales are constrained by the limitations of the
two modeling approaches used to evaluate the relationship
between future sea-level rise and coastal wetland elevation:
landscape-scale models and site-specific models. Large-scale
landscape models, such as the Sea Level Affecting Marshes
Model (SL AMM) (Park et al., 1989), simulate general trends
over large areas, but typically at a very coarse resolution.
These landscape models do not mechanistically simulate the
processes that contribute to wetland elevation; the processes
are input as forcing functions and are not simulated within
the model. Thus, this modeling approach does not account
for infrequent events that influence wetland vertical develop-
ment, such as storms and floods, or for frequent elevation
feedback mechanisms affecting processes (for example,
elevation change alters flooding patterns that in turn affect
sediment deposition, decomposition, and plant production).
In addition, these models are not suitable for site-specific
research and management problems because scaling down of
results to the local level is not feasible. Therefore, although
landscape models can simulate wetland sustainability on
broad spatial scales, their coarse resolution limits their ac-
curacy and usefulness to the local manager.
On the other hand, process oriented site-specific models
(e.g., Morris et al, 2002; Rybczyk and Cahoon, 2002) are
more mechanistic than landscape models and are used to
simulate responses for a specific site with a narrow range
of conditions and settings. These site-specific models can
account for accretion events that occur infrequently, such as
hurricanes and major river floods, and the feedback effects
of elevation on inundation and sedimentation that influence
accretionary processes over timeframes of a century. The
use of site-specific conditions in a model makes it possible to
predict long-term sustainability of an individual wetland in a
particular geomorphic setting. However, like the landscape
models, site-specific models also have a scaling problem.
Using results from an individual site to make long-term
projections at larger spatial scales is problematic because ac-
cretionary and process data are not available for the variety
of geomorphic settings across these larger-scale landscapes
for calibrating and verifying models. Thus, although site-
specific models provide high resolution simulations for a
local site, at the present time future coastal wetland response
to sea-level rise over large areas can be predicted with only
low confidence.
Recently, two different modeling approaches have been used
to provide regional scale assessments of wetland response
to climate change. In a hierarchical approach, detailed site-
specific models were parameterized with long-term data to
generalize landscape-level trends with moderate confidence
for inland wetland sites in the Prairie Pothole Region of the
Upper Midwest of the United States (Carroll et al, 2005;
Voldsethe/a/., 2007; Johnson et al, 2005). The utility of this
approach for coastal wetlands has not yet been evaluated. Al-
ternatively, an approach was used to assess coastal wetland
vulnerability at regional-to-global scales from three broad
environmental drivers: (1) ratio of relative sea-level rise to
tidal range, (2) sediment supply, and (3) lateral accommoda-
tion space (i.e., barriers to wetland migration) (McFadden
et al, 2007). This model suggests that, from 2000 to 2080,
there will be global wetland area losses of 33 percent for a
36 centimeter (cm) rise in sea level and 44 percent for a 72
cm rise; and that regionally, losses on the Atlantic and Gulf
of Mexico coasts of the United States will be among the
most severe (Nicholls et al, 2007). However, this model,
called the Wetland Change Model, remains to be validated
and faces similar challenges when downscaling, as does the
previously described model when scaling up.
Taking into account the limitations of current predictive
modeling approaches, the following assessments can be
made about future wetland sustainability at the national
scale:
It is virtually certain that tidal wetlands already expe-
riencing submergence by sea-level rise and associated
high rates of loss (e.g., Mississippi River Delta in Loui-
64
-------
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
siana, Blackwater National Wildlife Refuge marshes in
Maryland) will continue to lose area under the influence
of future accelerated rates of sea-level rise and changes
in other climate and environmental drivers.
It is very unlikely that there will be an overall increase in
tidal wetland area on a national scale over the next 100
years, given current wetland loss rates and the relatively
minor accounts of new tidal wetland development (e.g.,
Atchafalaya Delta in Louisiana).
Current model projections of wetland vulnerability on
regional and national scales are uncertain because of the
coarse levelof resolution of landscape-scale models. In
contrast, site-specific model projections are quite good
where local information has been acquired on factors
that control local accretionary processes in specific
wetland settings. However, the authors have low confi-
dence that site-specific model simulations, as currently
portrayed, can be successfully scaled up to provide
realistic projections at regional or national scales.
The following information is needed to improve the confi-
dence in projections of future coastal wetland sustainability
on regional and continental scales:
• Models and validation data. To scale up site-specific
model outputs to regional and continental scales with
high confidence, detailed data are needed on the various
local drivers and processes controlling wetland eleva-
tion across all tidal geomorphic settings of the United
States. Obtaining and evaluating the necessary data
will be an enormous and expensive task, but not an
impractical one. It will require substantial coordination
with various private and government organizations in
order to develop a large, searchable database. Until
this type of database becomes a reality, current model-
ing approaches need to improve or
adapt such that they can be applied
across a broad spatial scale with
better confidence. For example,
evaluating the utility of applying
the multi-tiered modeling approach
used in the Prairie Pothole Region to
coastal wetland systems and validat-
ing the broad scale Wetland Change
Model for North American coastal
wetlands will be important first
steps. Scientists' ability to predict
coastal wetland sustainability will
improve as specific ecological and
geological processes controlling
accretion and their interactions on
local and regional scales are better
understood.
• Expert opinion. Although models driven by empirical
data are preferable, given the modeling limitations
described, an expert opinion (i.e., subjective) approach
canbe used to develop spatially explicit landscape-scale
predictions of coastal wetland responses to future sea-
level rise with a low-to-moderate level of confidence.
This approach requires convening a group of scientists
with expert knowledge of coastal wetland geomorphic
processes, with conclusions based on an understanding
of the processes driving marsh survival during sea-
level rise and of how the magnitude and nature of these
processes might change due to the effects of climate
change and other factors. Because of the enormous
complexity of these issues at the continental scale, the
expert opinion approach would be applied with greater
confidence at the regional scale. Two case studies are
presented in Sections 4.6.1 and 4.6.2; the first, using
the expert opinion approach applied to the mid-Atlantic
region from New York to Virginia, the second, using
a description of North Carolina wetlands from the
Albemarle-Pamlico Region and an evaluation of their
potential response to sea-level rise, based on a review
of the literature.
4.6.1 Case Study: Mid-Atlantic Regional
Assessment, New York to Virginia
A panel of scientists with diverse and expert knowledge of
wetland accretionary processes was convened to develop
spatially explicit landscape-scale predictions of coastal
wetland response to the three scenarios of sea-level rise as-
sessed in this Product (see Chapter 1) for the mid-Atlantic
region from New York to Virginia (see Box 4.1). The results
of the panel's effort (Reed et al., 2008) inform this Product
assessment of coastal elevations and sea-level rise.
V
65
-------
Chapter 4
As described in this Product, scientific consensus regarding regional-scale coastal changes in response to sea-
level rise is currently lacking. To address the issue of future changes to mid-Atlantic coastal wetlands, Denise
Reed, a wetlands specialist at the University of New Orleans, was contracted by the U.S. EPA to assemble a
panel of coastal wetland scientists to evaluate the potential outcomes of the sea-level rise scenarios used in
this Product. Denise Reed chose the eight members of this panel on the basis of their technical expertise and
experience in the coastal wetland research community, particularly with coastal wetland geomorphic processes,
and also their involvement with coastal management issues in the mid-Atlantic region. The panel was charged to
address the question, "To what extent can wetlands vertically accrete and thus keep pace with rising sea level,
that is, will sea-level rise cause the area of wetlands to increase or decrease?"
The sea-level rise impact assessment effort was conducted as an open discussion facilitated by Denise Reed over
a two-day period. Deliberations were designed to ensure that conclusions were based on an understanding of
the processes driving marsh survival as sea level rises and how the magnitude and nature of these processes
might change in the future in response to climate change and other factors. To ensure a systematic approach
across regions within the mid-Atlantic region, the panel:
I. Identified a range of geomorphic settings to assist in distinguishing among the different process regimes
controlling coastal wetland accretion (see Figure 4.3 and Table 4.1);
2. Identified a suite of processes that contribute to marsh accretion (see Table 4.1) and outlined potential
future changes in current process regimes caused by climate change;
3. Divided the mid-Atlantic into a series of regions based on similarity of process regime and current sea-level
rise rates; and
4. Delineated geomorphic settings within each region on 1:250,000 scale maps, and agreed upon the fate of
the wetlands within these settings under the three sea-level rise scenarios, with three potential outcomes:
keeping pace, marginal, and loss (see Figure 4.4).
The qualitative, consensus-based assessment of potential changes and their likelihood developed by the panel
is based on their review and understanding of published coastal science literature (e.g., 88 published rates of
wetland accretion from the mid-Atlantic region, and sea-level rise rates based on NOAA tide gauge data), as
well as field observations drawn from other studies conducted in the mid-Atlantic region. A report by Reed
et a/. (2008) summarizing the process used, basis in the published literature, and a synthesis of the resulting
assessment was produced and approved by all members of the panel.
The report was peer reviewed by external subject-matter experts in accordance with U.S. EPA peer review
policies. Reviewers were asked to examine locality-specific maps for localities with which they were familiar,
and the documentation for how the maps were created. They were then asked to evaluate the assumptions
and accuracy of the maps, and errors or omissions in the text. The comments of all reviewers were carefully
considered and incorporated, wherever possible, throughout the report. The final report was published and
made available online in February 2008 as a U.S. Environmental Protection Agency report:
4,6,1,1 PANEL ASSESSMENT METHODS tion in freshwater systems (Neubauer 2008) is expected
The general approach used by the panel is summarized in to increase in response to sea-level rise up to a threshold
Box 4.1. The panel recognized that accretionary processes capacity, beyond which peat accumulation can no longer
differ among settings and that these processes will change increase. However, if salinities also increase in freshwater
in magnitude and direction with future climate change, systems, elevation gains from increased peat accumulation
For example, it is expected that the magnitude of coastal could be offset by increased decomposition from sulfate
storms will increase as sea surface temperatures increase reduction. Enhanced microbial breakdown of organic-rich
(Webster et al., 2005), likely resulting in an increase in soils is likely to be most important in formerly fresh and
storm sedimentation and oceanic sediment inputs. Also, brackish environments where the availability of sulfate,
the importance of peat accumulation to vertical accre- and not organic matter, generally limits sulfate-reduction
66
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
rates (Goldhaber and Kaplan, 1974). Increases in air and
soil temperatures are expected to diminish the importance
of ice effects. Changes in precipitation and human land-use
patterns will alter fluvial sediment inputs.
The fate of mid-Atlantic wetlands for the three sea-level rise
scenarios evaluated in this Product was determined by the
panel through a consensus opinion after all information was
considered (see Figure 4.4). The wetlands were classified as
keeping pace, marginal, or loss (Reed et al., 2008):
1.
Keeping pace: Wetlands will not be submerged by ris-
ing sea levels and will be able to maintain their relative
elevation.
3.
Marginal: Wetlands will be able to maintain their
elevation only under optimal conditions. Depending
on the dominant accretionary processes, this could
include inputs of sediments from storms or floods, or
the maintenance of hydrologic conditions conducive for
optimal plant growth. Given
the complexity and inher-
ent variability of climatic
and other factors influenc-
ing wetland accretion, the
panel cannot predict the fate
of these wetlands. Under
optimal conditions they are
expected to survive.
Loss: Wetlands will be sub-
ject to increased flooding be-
yond that normally tolerated
by vegetative communities,
leading to deterioration and
conversion to open water
habitat.
The panel recognized that wet-
lands identified as marginal or
loss will become so at an uneven
rate and that the rate and spatial
distribution of change will vary
within and among similarly des-
ignated areas. The panel further
recognized that wetland response
to sea-level rise over the next
century will depend upon the rate
of sea-level rise, existing wetland
condition (e.g., elevation relative
to sea level), and local controls of
accretion processes. In addition,
changes in flooding and salinity
patterns may result in a change of
dominant species (i.e., less flood-tolerant high marsh species
replaced by more flood-tolerant low marsh species), which
could affect wetland sediment trapping and organic matter
accumulation rates. A wetland is considered marginal when
it becomes severely degraded (greater than 50 percent of
vegetated area is converted to open water) but still supports
ecosystem functions associated with that wetland type. A
wetland is considered lost when its function shifts primarily
to that of shallow open water habitat.
There are several caveats to the expert panel approach,
interpretations, and application of findings. First, regional-
scale assessments are intended to provide a landscape-scale
projection of wetland vulnerability to sea-level rise (e.g.,
likely trends, areas of major vulnerability) and not to re-
place assessments based on local process data. The authors
recognize that local exceptions to the panel's regional scale
assessment likely exist for some specific sites where de-
tailed accretionary data are available. Second, the panel's
projections of back-barrier wetland sustainability assume
Mid-Atlantic Wetland Geomorphic Settings
New YorWlong Island
Raman Bay I
New York Bay
Pennsylvania
Atlantic
Ocean
Geomofphie Setting
Bad; barrier iajoon. other
Back barrier lagoofi flood Udai delta
Back barrier lagoon, lagoonal fill
Eshtanw marsh
Esluarino. Fringe
Estuariro, meander
Saline fringe
Trial fresh tores!
Tidal frwh marsh
37'
Figure 4.3 Geomorphic settings of mid-Atlantic tidal wetlands (data source: Reed et al., 2008;
map source: Titus et al., 2008).
67
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The U.S. Climate Change Science Program
Chapter 4
Table 4.2 The Range of Wetland Responses to Three Sea-Level Rise Scenarios (twentieth century rate, twentieth
century rate plus 2 mm per year, and twentieth century plus 7 mm per year) Within and Among Geomorphic
Settings and Subregions of the Mid-Atlantic Region from New York to Virginia.
^^^B
1
morphic ° Bay, New
. New York ' ,
setting York
Back-
barrier
lagoon,
other
Back-
barrier
lagoon,
flood tide
delta
Back-
barrier
lagoon,
lagoonal
fill
Estuarine
marsh
Estuarine
fringe
Estuarine
meander
Saline
fringe
Tidal
fresh
forest
Tidal
fresh
marsh
sir
K
K
K,L
K
+2
K,M
K
K,M,
L
K,L
+7
K,L
M
K,L
M
sir
K
K
K
K
K
+2
M
M
M
M
K
+7
L
L
L
L
K
sir
K
K
K
K
K
K
K,L
K
+2
M
M
M
M
M
M
M,L
M
+7
L
L
L
L
L
L
L
L
• •^T^^WW^B ry^^j^^>H
sir
K,M
K
K
+2
M,L
M
K
+7
L
L
K
sir
K
K
K
K,L
+2
M
M
M
M,L
+7
L
L
L
L
sir
K,M,
L
K
+2
M-L
K
+7
L
K
sir
L,M
K
K
+2
L
K
K
+7
L
K
K
Currituck
Sound
sir
M
K
M
M
K
+2
M-L
M
M-L
M-L
K
+7
L
L
L
K
K = keeping pace; M = marginal; L = loss; multiple letters under a single sea-level rise scenario (e.g., K,M or K,M,L) indicate more than one
response for that geomorphic setting; M-L indicates that the wetland would be either marginal or lost.
that protective barrier islands retain their integrity. Should
barrier islands collapse (see Section 3.7.3), the lagoonal
marshes would be exposed to an increased wave energy
environment and erosive processes, with massive marsh
loss likely over a relatively short period of time. (In such a
case, vulnerability to marsh loss would be only one of a host
of environmental problems.) Third, the regional projections
of wetland sustainability assume that the health of marsh
vegetation is not adversely affected by local outbreaks of
disease or other biotic factors (e.g., sudden marsh dieback).
Fourth, the panel considered the effects of a rate acceleration
above current of 2 mm per year (Scenario 2) and 7 mm per
year (Scenario 3), but not rates inbetween. Determining wet-
land sustainability at sea-level rise rates between Scenarios
2 and 3 requires greater understanding of the variations in
the maximum accretion rate regionally and among vegeta-
tive communities (Reed et al., 2008). Currently, there are
few estimates of the maximum rate at which marsh vertical
accretion can occur (Bricker-Urso et al., 1989; Morris et al.,
2002) and no studies addressing the thresholds for organic
matter accumulation in the marshes considered by the panel.
Lastly, the panel recognized the serious limitations of scaling
down their projections from the regional to local level and
would place a low level of confidence on such projections
in the absence of local accretionary and process data. Thus,
findings from this regional scale approach should not be
used for local planning activities where local effects on
accretionary dynamics may override regional controls on
accretionary dynamics.
4.6.1.2 PANEL FINDINGS
The panel developed an approach for predicting wetland
response to sea-level rise that was more constrained by
available studies of accretion and accretionary processes in
68
-------
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
some areas of the mid-Atlantic region (e.g., Lower Maryland
Eastern Shore) than in other areas (e.g., Virginia Beach/
Currituck Sound). Given these inherent data and knowledge
constraints, the authors classified the confidence level for
all findings in Reed et al. (2008) as likely (i.e., greater than
66 percent likelihood but less than 90 percent).
Figure 4.4 and Table 4.2 present the panel's consensus find-
ings on wetland vulnerability of the mid-Atlantic region. The
panel determined that a majority of tidal wetlands settings
in the mid-Atlantic region (with some local exceptions) are
likely keeping pace with Scenario 1, that is, continued sea-
level rise at the twentieth century rate, 3 to 4 mm per year
(Table 4.2, and areas depicted in brown, beige, yellow, and
green in Figure 4.4) through either mineral sediment deposi-
tion, organic matter accumulation, or both. However, under
this scenario, extensive areas of estuarine marsh in Delaware
Bay and Chesapeake Bay are marginal (areas depicted in red
in Figure 4.4), with some areas currently being converted
to subtidal habitat (areas depicted in blue in Figure 4.4). It
is virtually certain that estuarine marshes currently so con-
verted will not be rebuilt or replaced by natural processes.
Human manipulation of hydro-
logic and sedimentary processes
and the elimination of barriers to
onshore wetland migration would
be required to restore and sustain
these degrading marsh systems.
The removal of barriers to onshore
migration invariably would result
in land use changes that have other
societal consequences such as
property loss.
Under accelerated rates of sea-
level rise (Scenarios 2 and 3), the
panel agreed that wetland survival
would very likely depend on opti-
mal hydrology and sediment sup-
ply conditions. Wetlands primarily
dependent on mineral sediment
accumulation for maintaining el-
evation would be very unlikely to
survive Scenario 3, (i.e., at least 10
mm per year rate of sea-level rise
when added to the twentieth centu-
ry rate). Exceptions may occur lo-
cally where sediment inputs from
inlets, overwash events, or rivers
are substantial (e.g., back-barrier
lagoon and lagoonal fill marshes
depicted in green on western Long
Island, Figure 4.4).
Wetland responses to sea-level rise are typically complex.
A close comparison of Figure 4.3 and Figure 4.4 reveals
that marshes from all geomorphic settings, except estuarine
meander (which occurs in only one subregion), responded
differently to sea-level rise within and/or among subregions,
underscoring why local processes and drivers must be taken
into account. Given the variety of marsh responses to sea-
level rise among and within subregions (Table 4.2), assessing
the likelihood of survival for each wetland setting is best
done by subregion, and within subregion, by geomorphic
setting.
The scientific panel determined that tidal fresh marshes and
forests in the upper reaches of rivers are likely to be sustain-
able (i.e., less vulnerable to future sea-level rise than most
other wetland types) (Table 4.2), because they have higher
accretion rates and accumulate more organic carbon than sa-
line marshes (Craft, 2007). Tidal fresh marshes have access
to reliable and often abundant sources of mineral sediments,
and their sediments typically have 20 to 50 percent organic
matter content, indicating that large quantities of plant or-
ganic matter are also available. Assuming that salinities do
Potential Mid-Atlantic Wetland Survival
7 • WMtondi woukf b* nwfllnil YHT • W*lt«i
-------
Chapter 4
not increase, a condition that may reduce soil organic matter
accumulation rates, and current mineral sediment supplies
are maintained, the panel considered it likely that tidal fresh
marshes and forests would survive under Scenario 3. Verti-
cal development, response to accelerated sea-level rise, and
movement into newly submerged areas are rapid for tidal
fresh marshes (Orson, 1996). For several tidal fresh marshes
in the high sediment-load Delaware River Estuary, vertical
accretion through the accumulation of both mineral and
plant matter ranged from 7 mm per year to 17.4 mm per year
from the 1930s to the 1980s as tidal influences became more
dominant (Orson et al, 1992). Exceptions to the finding that
fresh marshes and forests would survive under Scenario 3
are the New Jersey shore, where tidal fresh marsh is consid-
ered marginal under Scenario 2 and lost under Scenario 3,
and Virginia Beach-Currituck Sound where fresh forest is
marginal under Scenario 1, marginal or lost under Scenario
2, and lost under Scenario 3.
Different marshes from the geomorphic settings back-barrier
other, back-barrier lagoonal fill, estuarine marsh, and sa-
line fringe settings responded differently to sea-level rise
within at least one subregion as well as among subregions
(Table 4.2). For example, back-barrier lagoonal fill marshes
on Long Island, New York were classified as either keep-
ing pace or lost at the current rate of sea-level rise. Those
marshes surviving under Scenario 1 were classified as
either marginal (brown) or keeping up (beige and green)
under Scenario 2 (Figure 4.4). Under Scenario 3, only the
lagoonal fill marshes depicted in green in Figure 4.4 are
expected to survive.
The management implications of these findings are impor-
tant on several levels. The expert panel approach provides a
regional assessment of future wetland resource conditions,
defines likely trends in wetland change, and identifies ar-
eas of major vulnerability. However, the wide variability
of wetland responses to sea-level rise within and among
subregions for a variety of geomorphic settings underscores
not only the influence of local processes on wetland eleva-
tion but also the difficulty of scaling down predictions of
wetland sustainability from the regional to the local scale
in the absence of local accretion data. Most importantly for
managers, regional scale assessments such as this should
not be used to develop local management plans because
local accretionary effects may override regional controls
on wetland vertical development (McFadden et al., 2007).
Instead, local managers are encouraged to acquire data on
the factors influencing the sustainability of their local wet-
land site, including environmental stressors, accretionary
processes, and geomorphic settings, as a basis for developing
local management plans.
The Albemarle-Pamlico (A-P) region of North Carolina is
distinct in the manner and the extent to which rising sea level
is expected to affect coastal wetlands. Regional wetlands
influenced by sea level are among the most extensive on the
U.S. East Coast because of large regions that are less than
3 meters (m) above sea level, as well as the flatness of the
underlying surface. Further, the wetlands lack astronomic
tides as a source of estuarine water to wetland surfaces in
most of the A-P region. Instead, wind-generated water level
fluctuations in the sounds and precipitation are the principal
sources of water. This "irregular flooding" is the hallmark of
the hydrology of these wetlands. Both forested wetlands and
marshes can be found; variations in salinity of f loodwater
determine ecosystem type. This is in striking contrast to
most other fringe wetlands on the East Coast.
4.6.2.1 DISTRIBUTION OF TYPES
Principal flows to Albemarle Sound are from the Chowan
and Roanoke Rivers, and to Pamlico Sound from the Tar and
Neuse Rivers. Hardwood forests occupy the floodplains of
these major rivers. Only the lower reaches of these rivers
are affected by rising sea level. Deposition of riverine sedi-
ments in the estuaries approximates the current rate of rising
sea level (2 to 3 mm per year) (Benninger and Wells, 1993).
These sediments generally do not reach coastal marshes,
in part because they are deposited in subtidal areas and in
part because astronomical tides are lacking to carry them to
wetland surfaces. Storms, which generate high water levels
(especially nor'easters and tropical cyclones), deposit sedi-
ments on shoreline storm levees and to a lesser extent onto
the surfaces of marshes and wetland forests. Blackwater
streams that drain pocosins (peaty, evergreen shrub and
forested wetlands), as well as other tributaries that drain the
coastal plain, are a minor supply of suspended sediment to
the estuaries.
Most wetlands in the A-P region were formed upon Pleis-
tocene sediments deposited during multiple high stands of
sea level. Inter-stream divides, typified by the Albemarle-
Pamlico Peninsula, are flat and poorly drained, resulting in
extensive developments of pocosin swamp forest habitats.
The original accumulation of peat was not due to rising
sea level but to poor drainage and climatic controls. Basal
peat ages of even the deepest deposits correspond to the
last glacial period when sea level was over 100 m below its
current position. Rising sea level has now intercepted some
of these peatlands, particularly those at lower elevations on
the extreme eastern end of the A-P Peninsula. As a result,
eroding peat shorelines are extensive, with large volumes of
peat occurring below sea level (Riggs and Ames, 2003).
70
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Large areas of nontidal marshes and forested wetlands in this
area are exposed to the influence of sea level. They can be
classified as fringe wetlands because they occur along the
periphery of estuaries that flood them irregularly. Salinity,
however, is the major control that determines the dominant
vegetation type. In the fresh-to-oligohaline (slightly brack-
ish) Albemarle Sound region, forested and shrub-scrub
wetlands dominate. As the shoreline erodes into the forested
wetlands, bald cypress trees become stranded in the per-
manently flooded zone and eventually die and fall down.
This creates a zone of complex habitat structure of fallen
trees and relic cypress knees in shallow water. Landward, a
storm levee of coarse sand borders the swamp forest in areas
exposed to waves (Riggs and Ames, 2003).
Trees are killed by exposure to extended periods of salinity
above approximately one-quarter to one-third sea water, and
most trees and shrubs have restricted growth and reproduc-
tion at much lower salinities (Conner et al., 1997). In brack-
ish water areas, marshes consisting of halophytes replace
forested wetlands. Marshes are largely absent from the shore
of Albemarle Sound and mouths of the Tar and Neuse Rivers
where salinities are too low to affect vegetation. InPamlico
Sound, however, large areas consist of brackish marshes with
few tidal creeks. Small tributaries of the Neuse and Pamlico
River estuaries grade from brackish marsh at estuary mouths
to forested wetlands in oligohaline regions further upstream
(Brinson et al, 1985).
4.6.2.2 FUTURE SEA-LEVEL RISE SCENARIOS
Three scenarios were used to frame projections of the ef-
fects of rising sea level over the next few decades in the
North Carolina non-tidal coastal wetlands. The first is a
non-drowning scenario that assumes rising sea level will
maintain its twentieth century, constant rate of 2 to 4 mm
peryear (Scenario 1). Predictions in this case canbe inferred
from wetland response to sea-level changes in the recent
past (Spaur and Snyder, 1999; Horton et al., 2006). Accel-
erated rates of sea-level rise (Scenarios 2 and 3), however,
may lead to a drowning scenario. This is more realistic if
IPCC predictions and other climate change models prove
to be correct (Church and White, 2006), and the Scenario
1 rates double or triple. An additional scenario possible in
North Carolina involves the collapse of barrier islands, as
hypothesized by Riggs and Ames (2003). This scenario is
more daunting because it anticipates a shift from the current
non-tidal regime to one in which tides would be present to
initiate currents capable of transporting sediments without
the need of storms and frequently possibly flooding wetland
surfaces now only flooded irregularly. The underlying ef-
fects of these three scenarios and effects on coastal wetlands
are summarized in Table 4.3.
Under the non-drowning scenario, vertical accretion would
keep pace with rising sea level as it has for millennia. Cur-
rent rates (Cahoon, 2003) and those based on basal peats
suggest that vertical accretion roughly matches the rate of
rising sea level (Riggs etal, 2000; Erlich, 1980; Whitehead
andOakes, 1979). Sources of inorganic sediment to supple-
ment vertical marsh accretion are negligible due to both the
large distance between the mouths of piedmont-draining
Neuse, Tar, Roanoke, and Chowan Rivers and the absence
of tidal currents and tidal creeks to transport sediments to
marsh surfaces.
Under the drowning scenario, the uncertainty of the effects
of accelerated rates lies in the untested capacity of marshes
and swamp forests to biogenically accrete organic matter at
sea-level rise rates more rapid than experienced currently.
It has been suggested that brackish marshes of the Missis-
sippi Delta cannot survive when subjected to relative rates
of sea-level rise of 10 mm per year (Day et al., 2005), well
over twice the rate currently experienced in Albemarle and
Pamlico Sounds. As is the case for the Mississippi Delta
Table 4.3 Comparison of Three Scenarios of Rising Sea Level and Their Effects on Coastal Processes.
Scenario
Vertical accretion Shoreline erosion
of wetland surface rate
Non-drowning: historical exposure
of wetlands (past hundreds to several
thousand years) is predictive of future
behavior. Vertical accretion will keep
pace with rising sea level (about 2 to 4
millimeters peryear)
Keeps pace with
rising sea level
Recent historical
patterns are
maintained
Sediment supply
Low due to a lack of sources;
vertical accretion mostly biogenic
Drowning: vertical accretion rates
cannot accelerate to match rates of
rising sea level; barrier islands remain
intact
Wetlands undergo
collapse and marshes
break up from within
Rapid acceleration
when erosion reaches
collapsed regions
Local increases of organic and
inorganic suspended sediments as
wetlands erode
Barrier islands breached: change to
tidal regime throughout Pamlico Sound
Biogenic accretion
replaced by inorganic
sediment supply
Rapid erosion where
high tides overtop
wetland shorelines
Major increase in sediments and
their redistribution; tidal creeks
develop along antecedent drainages
mostly in former upland regions
71
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Chapter 4
(Reed et al, 2006), external sources of mineral sediments
would be required to supplement or replace the process of
organic accumulation that now dominates wetlands of the
A-P region. Where abundant supplies of sediment are avail-
able and tidal currents strong enough to transport them, as
in North Inlet, South Carolina, Morris et al. (2002) reported
that the high salt marsh (dwarf Spartind) could withstand
a 12 mm per year rate. In contrast to fringe wetlands,
swamp forests along the piedmont-draining rivers above the
freshwater-seawater interface are likely to sustain them-
selves under drowning scenario conditions because there
is a general abundance of mineral sediments during flood
stage. This applies to regions within the f loodplain but not
at river mouths where shoreline recession occurs in response
to more localized drowning.
Pocosin peatlands and swamp forest at higher elevations of
the coastal plain will continue to grow vertically since they
are both independent of sea-level rise. Under the drowning
scenario, however, sea-level influenced wetlands of the
lower coastal plain would convert to aquatic ecosystems, and
the large, low, and flat pocosin areas identified by Poulter
(2005) would transform to aquatic habitat. In areas of po-
cosin peatland, shrub and forest vegetation first would be
killed by brackish water. It is unlikely that pocosins would
undergo a transition to marsh for two reasons: (1) the pocosin
root mat would collapse due to plant mortality and decom-
position, causing a rapid subsidence of several centimeters,
and resulting in a transition to ponds rather than marshes
and (2) brackish water may accelerate decomposition of peat
due to availability of sulfate to drive anaerobic decompo-
sition. With the simultaneous death of woody vegetation
and elimination of potential marsh plant establishment,
organic-rich soils would be exposed directly to the effects of
decomposition, erosion, suspension, and transport without
the stabilizing properties of vegetation.
Under the collapsed barrier island scenario (see Section
3.7.3), the A-P regions would undergo a change from a
non-tidal estuary to one dominated by astronomic tides due
to the collapse of some portions of the barrier islands. A
transition of this magnitude is difficult to predict in detail.
However, Poulter (2005), using the ADCIRC-2DDI model
of Luettich et al. (1992), estimated that conversion from a
non-tidal to tidal estuary might flood hundreds of square
kilometers. The effect is largely due to an increase in tidal
amplitude that produces the flooding rather than a mean
rise in sea level itself. While the mechanisms of change are
speculative, it is doubtful that an intermediate stage of marsh
colonization would occur on former pocosin and swamp for-
est areas because of the abruptness of change. Collapse of
the barrier islands in this scenario would be so severe due to
the sediment-poor condition of many barrier segments that
attempts to maintain and/or repair them would be extremely
difficult, or even futile.
The conversion of Pamlico Sound to a tidal system would
likely re-establish tidal channels where ancestral streams
are located, as projected by Riggs and Ames (2003). The
remobilization of sediments could then supply existing
marshes with inorganic sediments. It is more likely, how-
ever, that marshes would become established landward on
newly inundated mineral soils of low-lying uplands. Such
a state change has not been observed elsewhere, and com-
puter models are seldom robust enough to encompass such
extreme hydrodynamic transitions.
A few key uncertainties must be addressed in order to
increase confidence in the authors' predictions of wetland
vulnerability to sea-level rise. First, determining the fate of
coastal wetlands over a range of accelerated sea-level rise
rates requires more information on variations in the maxi-
mum accretion rate regionally, within geomorphic settings,
and among vegetative communities. To date, few studies
have specifically addressed the maximum rates at which
marsh vertical accretion can occur, particularly the thresh-
olds for organic accumulation. Second, although the inter-
actions among changes in wetland elevation, sea level, and
wetland flooding patterns are becoming better understood,
the interaction of these feedback controls between flooding
and changes in other accretion drivers, such as nutrient sup-
ply, sulfate respiration, and soil organic matter accumulation
is less well understood. Third, scaling up from numerical
model predictions of local wetland responses to sea-level rise
to long-term projections at regional or continental scales is
severely constrained by a lack of available accretionary and
process data at these larger landscape scales. Newly emerg-
ing numerical models used to predict wetland response to
sea-level rise need to be applied across the range of wetland
settings. Fourth, scientists need to better understand the role
of changing land use on tidal wetland processes, including
space available for wetlands to migrate landward and al-
teration in the amount and timing of freshwater runoff and
sediment supply. Finally, sediment supply is a critical factor
influencing wetland vulnerability, but the amount and source
of sediments available for wetland formation and develop-
ment is often poorly understood. Coastal sediment budgets
typically evaluate coarse-grain sediments needed for beach
and barrier development. In contrast, fine-grain cohesive
sediments needed for wetland formation and development
are typically not evaluated. Improving our understanding
of each of these factors is critical for predicting the fate of
tidal marshes.
72
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Vulnerable Species: the Effects of Sea-Level
Rise on Coastal Habitats
Authors: Ann Shellenbargerjones, Industrial Economics, Inc.;
Christina Bosch, Industrial Economics, Inc.; Elizabeth Strange,
Stratus Consulting, Inc.
KEY FINDINGS
The quality, quantity, and spatial distribution of coastal habitats change continuously as a result of shore erosion,
salinity changes, and wetland dynamics; however, accelerated rates of sea-level rise will change some of the major
controls of coastal wetland maintenance. Shore protection and development now prevent migration of coastal habitats
in many areas. Vulnerable species that rely on these habitats include an array of biota ranging from endangered beetles
to commercially important fish and shellfish; and from migratory birds to marsh plants and aquatic vegetation.
Three key determinants of future tidal marsh acreage are: (I) the capacity of the marsh to raise its surface to match
the rate of rising sea level, (2) the rate of erosion of the seaward boundary of the marsh, and (3) the availability of
space for the marsh to migrate inland. Depending on local conditions, a tidal marsh may be lost or migrate landward
in response to sea-level rise.
Where tidal marshes become submerged or are eroded, the expected overall loss of wetlands would cause wetland-
dependent species of fish and birds to have reduced population sizes. Tidal marshes and associated submerged
aquatic plant beds are important spawning, nursery, and shelter areas for fish and shellfish, including commercially
important species like the blue crab.
Many estuarine beaches may also be lost in areas with vertical shore protection and insufficient sediment supply.
Endangered beetles, horseshoe crabs, the red knot shorebird, and diamondback terrapins are among many species
that rely on sandy beach areas.
Loss of isolated marsh islands already undergoing submersion will reduce available nesting for bird species, especially
those that rely on island habitat for protection from predators. Additional temporary islands may be formed as tidal
marshes are inundated, although research on this possibility is limited.
Many freshwater tidal forest systems such as those found in the Mid-Atlantic are considered globally imperiled, and
are at risk from sea-level rise among other threats.
Tidal flats, a rich source of invertebrate food for shorebirds, may be inundated, though new areas may be created
as other shoreline habitats are submerged.
73
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Chapter 5
J
Coastal ecosystems consist of a variety of environments,
including tidal marshes, tidal forests, aquatic vegetation
beds, tidal flats, beaches, and cliffs. For tidal marshes, Table
4.1 in Chapter 4 outlines the major marsh types, relevant
accretionary processes, and the primary vegetation. These
environments provide important ecological and human use
services, including habitat for endangered and threatened
species. The ecosystem services, described in detail within
this Chapter, include not only those processes that support
the ecosystem itself, such as nutrient cycling, but also the
humanbenefits derived from those processes, including fish
production, water purification, water storage and delivery,
and the provision of recreational opportunities that help
promote human well-being. The high value that humans
place on these services has been demonstrated in a number
of studies, particularly of coastal wetlands (NRC, 2005).
The services provided by coastal ecosystems could be af-
fected in a number of ways by sea-level rise and coastal
engineering projects designed to protect coastal properties
from erosion and inundation. As seas rise, coastal habitats
are subject to inundation, storm surges, saltwater intrusion,
and erosion. In many cases, the placement of hard structures
along the shore will reduce sediment inputs from upland
sources and increase erosion rates in front of the structures
(USGS, 2003). If less sediment is available, marshes that are
seaward of such structures may have difficulty maintaining
appropriate elevations in the face of rising seas. Wetlands
that are unable to accrete sufficient substrate as sea level
rises will gradually convert to open water, even if there is
space available for them to migrate inland, thereby elimi-
nating critical habitat for many coastal species. In addition,
landward migration of wetlands may replace current upland
habitats that are blocked from migration (NRC, 2007; MEA,
2005). Shallow water and shore habitats are also affected
by shore responses. Table 6.1 in Chapter 6 provides a pre-
liminary overview of the expected environmental effects of
human responses to sea-level rise.
Habitat changes in response to sea-level rise and related
processes may include structural changes (such as shifts in
vegetation zones or loss of vegetated area) and functional
changes (such as altered nutrient cycling). In turn, degraded
ecosystem processes and habitat fragmentation and loss
may not only alter species distributions and relative abun-
dances, but may ultimately reduce local populations of the
species that depend on coastal habitats for feeding, nesting,
spawning, nursery areas, protection from predators, and
other activities that affect growth, survival, and reproduc-
tive success.
Tidal salt marshes are among the most productive habitats in the world (Teal, 1986). While this productivity
is used within the marshes, marsh-associated organic matter is also exported to food webs supporting marine
transient fish production in open waters. Marine transients are adapted to life on a "coastal conveyor belt",
often spawning far out on the continental shelf and producing estuarine-dependent young that are recruited into
coastal embayments year-round (Deegan et a/., 2000). These fish comprise more than 80 percent of species of
commercial and recreational value that occupy inshore waters.
Tidal salt marshes serve two critical functions for young finfish (Boesch and Turner, 1984). First, abundant food
and the warm shallow waters of the marsh are conducive to rapid growth of both resident and temporary
inhabitants. Second, large predators are generally less abundant in subtidal marsh creeks; consequently marshes
and their drainage systems may serve as a shelter from predators for the young fish. Protection, rapid growth,
and the ability to deposit energy reserves from the rich marsh diet prepare young fish for the rigors of migration
and/or overwintering (Weinstein et a/., 2005; Litvin and Weinstein, in press).
Effects of Sea-Level Rise
Intertidal and shallow subtidal waters of estuarine wetlands are "epicenters" of material exchange, primary
(plant) and secondary (animal) production, and are primary nurseries for the young of many fish and shellfish
species (Childers et a/., 2000; Weinstein, 1979; Deegan et a/., 2000). The prospect of sea-level rise, sometimes
concomitant with land subsidence, human habitation of the shore zone, and shore stabilization, place these critical
resources at risk. Such ecological hotspots could be lost as a result of sea-level rise because human presence
in the landscape leaves tidal wetlands little or no room to migrate inland. Because of the lack of a well-defined
drainage system, small bands of intertidal marsh located seaward of armored shorelines have little ecological
value in the production of these finfish (Weinstein et a/., 2005; Weinstein, 1983). Due to their interconnectedness
with adjacent habitats, loss of tidal salt marshes would significantly affect fish populations, both estuarine and
marine, throughout the mid-Atlantic region.
74
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Habitat interactions are extremely complex. Each habitat
supports adjacent systems—for example, the denitrifying
effects of wetlands aid adjacent submerged vegetation beds
by reducing algal growth; the presence of nearshore oyster
or mussel beds reduces wave energy which decreases erosion
of marsh edges; and primary productivity is exported from
marsh to open waters (see Box 5.1). This Chapter presents
simplifications of these interactions in order to identify
primary potential effects of both increased rates of sea-level
rise and likely shore protections on vulnerable species. In
particular, sea-level rise is just one factor among many af-
fecting coastal areas: sediment input, nutrient runoff, fish
and shellfish management, and other factors all contribute
to the ecological condition of the various habitats discussed
in this Section. Sea-level rise may also exacerbate pollution
through inundation of upland sources of contamination such
as landfills, industrial storage areas, or agricultural waste
retention ponds. Under natural conditions, habitats are also
continually shifting; the focus of this Chapter is the effect
that shoreline management will have on the ability for those
shifts to occur (e.g., for marshes or barrier islands to migrate,
for marsh to convert to tidal flat or vice versa) and any inter-
ruption to the natural shift.
While habitat migration, loss, and gain have all occurred
throughout geological history, the presence of developed
shorelines introduces a new barrier. Although the potential
ecological effects are understood in general terms, few stud-
ies have sought to demonstrate or quantify how the interac-
tions of sea-level rise and different types of shore protec-
tions may affect the ecosystem services provided by coastal
habitats, and in particular the abundance and distribution
of animal species (see Chapter 6 for discussion of shore
protections). While some studies have examined impacts of
either sea-level rise (e.g., Erwinetal., 2006; Galbraithe/a/.,
2002) or shore protections (e.g., Seitz et al., 2006) on coastal
fauna, minimal literature is available on the combined ef-
fects of rising seas and shore protections. Nonetheless, it is
possible in some cases to identify species most likely to be
affected based on knowledge of species-habitat associations.
Therefore, this Chapter draws upon the ecological literature
to describe the primary coastal habitats and species that are
vulnerable to the interactive effects of sea-level rise and
shore protection activities, and highlights those species
that are of particular concern. While this Chapter provides
a detailed discussion on a region-wide scale, Appendix 1
of this Product provides much more detailed discussions of
specific local habitats and animal populations that may be
at risk on a local scale along the mid-Atlantic coast.
to
A focus on the Mid-Atlantic Region
In addition to their dependence on tidal influence, tidal
marshes are defined primarily in terms of their salinity: salt,
brackish, and freshwater. Chapter 4 describes the structure
and flora of these marshes as well as their likely responses
to sea-level rise. Table 5.1 presents a general overview of
the habitat types, fauna, and vulnerability discussed in this
Chapter. Localized information on endangered or threat-
ened species is available through the state Natural Heritage
Programs (see Box 5.2).
Salt marshes (back-barrier lagoon marsh or saline fringe
marsh, described in Table 4.1) are among the most produc-
tive systems in the world because of the extraordinarily
high amount of above- and below-ground plant matter that
many of them produce, up to 25 metric tons per hectare (ha)
aboveground alone (Mitsch and Gosselink, 1993). In turn,
this large reservoir of primary production supports a wide
variety of invertebrates, fish, birds, and other animals that
make up the estuarine food web (Teal, 1986). Insects and
other small invertebrates feed on this organic material of the
marsh as well as detritus and algae on the marsh surface.
These in turn provide food for larger organisms, including
crabs, shrimp, and small fishes, which then provide food
for larger consumers such as birds and estuarine fishes
that move into the marsh to forage (Mitsch and Gosselink,
1993).
Although much of the primary production in a marsh is used
within the marsh itself, some is exported to adjacent estuar-
ies and marine waters. In addition, some of the secondary
production of marsh resident fishes, particularly mummi-
chog, and of juveniles, such as blue crab, is exported out of
the marsh to support both nearshore estuarine food webs as
well as fisheries in coastal areas (Boesch and Turner, 1984;
Kneib, 1997, 2000; Deegan et al., 2000; Beck et al., 2003;
Dittel etal., 2006; Stevens etal., 2006)1. As studies of flood
pulses have shown, the extent of the benefits provided by
wetlands may be greater in regularly flooded tidal wetlands
than in irregularly flooded areas (Bayley, 1991; Zedler and
Calloway, 1999).
Tidal creeks and channels (Figure 5.1) frequently cut through
low marsh areas, draining the marsh surface and serving as
routes for nutrient-rich plant detritus (dead, decaying organic
material) to be flushed out into deeper water as tides recede
and for small fish, shrimp, and crabs to move into the marsh
during high tides (Mitsch and Gosselink, 1993; Lippson and
Lippson, 2006). In addition to mummichog, fish species
found in tidal creeks at low tide include Atlantic silverside,
1 See Scientific Names section for a list of correspondence between
common and scientific names.
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The U.S. Climate Change Science Program
Table 5.1 Key Fauna/Habitat Associations and Degree of Dependence
Chapter 5
Fish (Juvenile)
Fish (Adult)
Crustaceans/Moll usks
Other invertebrates
Turtles/Terrapins
Other reptiles/Amphibians
Wading Birds
Shorebirds
Waterbirds
Songbirds
Mammals
Notes.
Symbols represent the degree of dependence that particular fauna have on habitat types, as described in the
sections below.
^ indicates that multiple species, or certain rare or endangered species, depend heavily on that habitat.
V indicates that the habitat provides substantial benefits to the fauna.
* indicates that some species of that fauna type may rely on the habitat, or that portions of their life cycle may be
carried out there.
- indicates that negligible activity by a type of fauna occurs in the habitat.
Further details on these interactions, including relevant references, are in the sections by habitat below.
SAV is submerged aquatic vegetation, discussed later in this Chapter (Section 5.5).
striped killifish, and sheepshead minnow (Rountree and
Able, 1992). Waterbirds such as great blue herons and egrets
are attracted to marshes to feed on the abundant small fish,
snails, shrimp, clams, and crabs found in tidal creeks and
marsh ponds.
Brackish marshes support many of the same wildlife species
as salt marshes, with some notable exceptions. Bald eagles
forage inbrackish marshes and nest in nearby wooded areas.
Because there are few resident mammalian predators (such
as red fox and raccoons), small herbivores such as meadow
voles thrive in these marshes. Fish species common in the
brackish waters of the Mid-Atlantic include striped bass and
white perch, which move in and out of brackish waters year-
round. Anadromous fish found in the Mid-Atlantic (those
that live primarily in salt water but return to freshwater to
spawn) include herring and shad, while marine transients
such as Atlantic menhaden and drum species are present in
summer and fall (White, 1989).
Tidal fresh marshes are characteristic of the upper reaches of
estuarine tributaries. In general, the plant species composi-
tion of freshwater marshes depends on the degree of flood-
ing, with some species germinating well when completely
submerged, while others are relatively intolerant of flooding
(Mitsch and Gosselink, 2000). Some tidal fresh marshes
possess higher plant diversity than other tidal marsh types
(Perry and Atkinson, 1997).
Tidal fresh marshes provide shelter, forage, and spawning
habitat for numerous fish species, primarily cyprinids (min-
nows, shiners, carp), centrarchids (sunfish, crappie, bass),
Figure 5.1 Marsh and tidal creek, Bethels Beach (Mathews
County) Virginia (June 2002) [Photo source: ®James G. Titus,
used with permission].
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BOX 5.2 Identifying Local Ecological Communities and Species at Risk
Every state and Washington, D.C. has Natural Heritage Programs (NHPs) that inventory and track the natural
diversity of the state, including rare or endangered species. These programs provide an excellent resource for
identifying local ecological communities and species at risk.
Box Table 5.2 State Natural Heritage Program Contact Information
New York State Department of
Environmental Conservation, Division
of Fish, Wildlife and Marine Resources
New Jersey Department of
Environmental Protection, Division of
Parks and Forestry, Office of Natural
Lands Management
Pennsylvania Department of
Conservation and Natural Resources,
Office of Conservation Science
Delaware Department of Natural
Resources and Environmental Control,
Division of Fish and Wildlife
Maryland Department of Natural
Resources, Wildlife and Heritage
Service
The District of Columbia's
Department of Health, Fisheries and
Wildlife Division
Virginia Department of Conservation
and Recreation
North Carolina Department of
Environment and Natural Resources,
Office of Conservation and
Community Affairs
(518)402-8935
(609)984-1339
(717)783-1639
(302) 653-2880
(410) 260-8DNR
(202)671-5000
(804) 786-7951
(919)715-4195
A useful resource for species data outside of each state's own NHP is NatureServe Explorer. NatureServe () is a non-profit conservation organization which represents the state Natural Heritage
Programs and other conservation data centers. NatureServe Explorer allows users to search for data on the
geographic incidence of plant and animal species in the United States and Canada. The program provides an
extensive array of search criteria, including species' taxonomies, classification status, ecological communities, or
their national and sub-national distribution. For example, one could search for all vertebrate species federally listed
as threatened that live in Delaware's section of the Chesapeake Bay. For identifying threatened and endangered
species extant in vulnerable areas, the smallest geographic unit of analysis is county level.
and ictalurids (catfish). In addition, some estuarine fish and
shellfish species complete their life cycles in freshwater
marshes. Tidal fresh marshes are also important for a wide
range of bird species. Some ecologists suggest that fresh-
water tidal marshes support the greatest diversity of bird
species of any marsh type (Mitschand Gosselink, 2000). The
avifauna of these marshes includes waterfowl; wading birds;
rails and shorebirds; birds of prey; gulls, terns, kingfishers,
and crows; arboreal birds; and ground and shrub species.
Perching birds such as red-winged blackbirds are common in
stands of cattail. Tidal freshwater marshes support additional
species that are rare in saline and brackish environments,
such as frogs, turtles, and snakes (White, 1989).
Marsh islands are a critical subdivision of the tidal marshes.
These islands are found throughout the mid-Atlantic study
region, and are particularly vulnerable to sea-level rise
(Kearney and Stevenson, 1991). Islands are common fea-
tures of salt marshes, and some estuaries and back-barrier
bays have islands formed by deposits of dredge spoil. Many
islands are a mixture of habitat types, with vegetated and
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The U.S. Climate Change Science Program
Chapter 5
Figure 5.2 Fringing marsh and bulkhead, Monmouth County,
New Jersey (August 2003) [Photo source: ®James G. Titus, used
with permission].
unvegetated wetlands in combination with upland areas2.
These isolated areas provide nesting sites for various bird
species, particularly colonial nesting waterbirds, where they
are protected from terrestrial predators such as red fox. Gull-
billed terns, common terns, black skimmers, and American
oystercatchers all nest on marsh islands (Rounds et al., 2004;
Eyler et al., 1999; McGowan et al., 2005).
As discussed in Chapter 4, tidal marshes can keep pace with
sea-level rise through vertical accretion (i.e., soil build up
through sediment deposition and organic matter accumula-
tion) as long as a sufficient sediment supply exists. Where
inland movement is not impeded by artificial shore struc-
tures (Figure 5.2) or by geology (e.g., steeply sloping areas
between geologic terraces, as found around Chesapeake
Bay) (Ward et al, 1998; Phillips, 1986), tidal marshes can
expand inland, which would increase wetland area if the rate
of migration exceeds that of erosion of the marsh's seaward
boundary. However, wetland area would decrease even
when a marsh migrates inland if the rate of erosion of the
seaward boundary exceeds the rate of migration. Further, in
areas where sufficient accretion does not occur, increased
tidal flooding will stress marsh plants through waterlogging
and changes in soil chemistry, leading to a change in plant
species composition and vegetation zones. If marsh plants
become too stressed and die, the marsh will eventually
convert to open water or tidal flat (Callaway et al., 1996;
Morris et al., 2002)3.
Sea-level rise is also increasing salinity upstream in some
rivers, leading to shifts in vegetation composition and the
conversion of some tidal fresh marshes into brackish marsh-
2 Thompson's Island in Rehoboth Bay, Delaware, is a good example
of a mature forested upland with substantial marsh and beach area.
The island hosts a large population of migratory birds. See Maryland
and Delaware Coastal Bays in Strange et al. (2008).
3 The Plum Tree Island National Wildlife Refuge is an example of
a marsh deteriorating through lack of sediment input. Extensive
mudflats front the marsh (see Appendix l.F for additional details).
es (MD DNR, 2005). At the same time, brackish marshes
can deteriorate as a result of ponding and smothering of
marsh plants by beach wrack (seaweed and other marine
detritus left on the shore by the tide) as salinity increases
and storms accentuate marsh fragmentation4 (Strange et
al., 2008). While this process may allow colonization by
lower-elevation marsh species, that outcome is not certain
(Stevenson and Kearney, 1996). Low brackish marshes can
change dynamically in area and composition as sea level
rises. If they are lost, forage fish and invertebrates of the
low marsh, such as fiddler crabs, grass shrimp, and ribbed
mussels, may also be lost, which would affect fauna further
up the food chain (Strange etal., 2008). Though more pond-
ing may provide some additional foraging areas as marshes
deteriorate, the associated increase in salinity due to evapo-
rative loss can also inhibit the growth of marsh plants (MD
DNR, 2005). Many current marsh islands will be inundated;
however, in areas with sufficient sediment, new islands may
form, although research on this possibility is limited (Cleary
and Hosier, 1979). New or expanded marsh islands are also
formed through dredge spoil projects5.
Effects of marsh inundation on fish and shellfish species are
likely to be complex. In the short term, inundation may make
the marsh surface more accessible, increasing production.
However, benefits will decrease as submergence decreases
total marsh habitat (Rozas and Reed, 1993). For example,
increased deterioration and mobilization of marsh peat sedi-
ments increases the immediate biological oxygen demand
and may deplete oxygen in marsh creeks and channels below
levels needed to sustain fish. In these oxygen-deficient con-
ditions, mummichogs and other killifish may be among the
few species able to persist (Stevenson et al., 2002).
Figure 5.3 Marsh drowning and hummock in Blackwater Wildlife
Refuge, Maryland (November 2002) [Photo source: ®James G.
Titus, used with permission].
4 Along the Patuxent River, Maryland, refuge managers have noted
marsh deterioration and ponding with sea-level rise. See Appendix
l.F for additional details.
5 For example, see discussions of Hart-Miller and Poplar Islands in
Chesapeake Bay in Appendix l.F.
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Coastal Sensitivity to Sea-Level Rise:
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In areas where marshes are reduced, remnant marshes may
provide lower quality habitat, fewer nesting sites, and greater
predation risk for a number of bird species that are marsh
specialists and are also important components of marsh food
webs, including the clapper rail, black rail, least bittern,
Forster's tern, willet, and laughing gull (Figure 5.3) (Erwin
et al., 2006). The majority of the Atlantic Coast breeding
populations of Forster's tern and laughing gull are consid-
ered to be at risk because of loss of lagoonal marsh habitat
due to sea-level rise (Erwin et al., 2006). In a Virginia study,
scientists found that the minimum marsh size to support
significant marsh bird communities was 4.1 to 6.7 hectares
(ha) (10.1 to 16.6 acres [ac]) (Watts, 1993). Some species may
require even larger marsh sizes; minimum marsh size for
successful communities of the saltmarsh sharp-tailed spar-
row and the seaside sparrow, both on the Partners in Flight
Watch List, are estimated at 10 and 67 ha (25 and 166 ac),
respectively (Benoit and Askins, 2002).
5.3 FRESHWATER FORESTED WETLANDS
Forested wetlands influenced by sea level line the mid-
Atlantic coast. Limited primarily by their requirements
for low-salinity water in a tidal regime, tidal fresh forests
occur primarily in upper regions of tidal tributaries in
Virginia, Maryland, Delaware, New Jersey, and New York
(NatureServe, 2006). The low-lying shorelines of North
Carolina also contain large stands of forested wetlands,
including cypress swamps and pocosins (Figure 5.4). Also
in the mid-Atlantic coastal plains (e.g., around Barnegat
Bay, New Jersey) are Atlantic white cedar swamps, found
in areas where a saturated layer of peat overlays a sandy
substrate (NatureServe, 2006). Forested wetlands support
a variety of wildlife, including the prothonotary warbler,
the two-toed amphiuma salamander, and the bald eagle.
Forested wetlands with thick understories provide shelter
and food for an abundance of breeding songbirds (Lippson
and Lippson, 2006). Various rare and greatest conservation
Figure 5.5 Inundation and tree mortality in forested wetlands
at Swan's Point, Lower Potomac River. These wetlands are irregu-
larly flooded by wind-generated tides, unaffected by astronomic
tides; their frequency of inundation is controlled directly by sea
level (October 2006) [Photo source: ^Elizabeth M. Strange and
Stratus Consulting, used with permission].
need (GCN) species reside in mid-Atlantic tidal swamps,
including the Delmarva fox squirrel (federally listed as
endangered), the eastern red bat, bobcats, bog turtles, and
the redbellied watersnake (MD DNR, 2005).
Tidal fresh forests, such as those found in the Mid-Atlantic,
face a variety of threats, including sea-level rise, and are cur-
rently considered globally imperiled6. The responses of these
forests to sea-level rise may include retreat at the open-water
boundary, drowning in place, or expansion inland. Fleming
et al. (2006) noted that, "Crown dieback and tree mortal-
ity are visible and nearly ubiquitous phenomena in these
communities and are generally attributed to sea-level rise
and an upstream shift in the salinity gradient in estuarine
rivers". Figure 5.5 presents an example of inundation and
tree mortality. In Virginia, tidal forest research has indicated
that where tree death is present, the topography is limiting
inland migration of the hardwood swamp and the understory
is converting to tidal marsh (Rheinhardt, 2007).
5.4 SEA-LEVEL FENS
Sea-level fens are a rare type of coastal wetland with a mix
of freshwater tidal and northern bog vegetation, resulting in
a unique assemblage that includes carnivorous plants such
as sundew and bladderworts (Fleming et al., 2006; VNHP,
2006). Their geographic distribution includes isolated
locations on Long Island's South Shore; coastal New Jersey;
Sussex County, Delaware; and Accomack County, Virginia.
The eastern mud turtle and the rare elfin skimmer dragonfly
are among the animal species found in sea-level fens. Fens
may occur in areas where soils are acidic and a natural seep
from a nearby slope provides nutrient-poor groundwater
Figure 5.4 Pocosin in Green Swamp, North Carolina (May 2004)
[Photo source: ®Sam Pearsall, used with permission].
' As presented in NatureServe (), the
prevalent tidal forest associations such as freshwater tidal wood-
lands and tidal freshwater cypress swamps are considered globally
imperiled.
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5
(VNHP, 2006). Little research has been conducted on the
effects of sea-level rise on groundwater fens; however, the
Virginia Natural Heritage Program has concluded that sea-
level rise is a primary threat to the fens (VNHP, 2006).
Submerged aquatic vegetation (SAV) is distributed
throughout the mid-Atlantic region, dominated by eelgrass
in the higher-salinity areas and a large number of brackish
and freshwater species elsewhere (e.g., widgeon grass, wild
celery) (Hurley, 1990). SAV plays a key role in estuarine
ecology, helping to regulate the oxygen content of nearshore
waters, trapping sediments and nutrients, stabilizing bottom
sediments, and reducing wave energy (Short and Neckles,
1999). SAV also provides food and shelter for a variety
of fish and shellfish and the species that prey on them.
Organisms that forage in SAV beds feed on the plants
themselves, the detritus and the epiphytes on plant leaves,
and the small organisms found within the SAV bed (e.g.,
Stockhausen and Lipcius [2003] for blue crabs; Wyda et al.
[2002] for fish). The commercially valuable blue crab hides
in eelgrass during its molting periods, when it is otherwise
vulnerable to predation. In Chesapeake Bay, summering sea
turtles frequent eelgrass beds. The Kemp's ridley sea turtle,
federally listed as endangered, forages in eelgrass beds and
flats, feeding on blue crabs in particular (Chesapeake Bay
Program, 2007). Various waterbirds feed on SAV, including
brant, canvasback, and American black duck (Perry and
Deller, 1996).
Forage for piscivorous birds and fish is also provided by resi-
dents of nearby marshes that move in and out of SAV beds
with the tides, including mummichog, Atlantic silverside,
naked goby, northern pipefish, fourspine stickleback, and
threespine stickleback (Strange et al., 2008). Juveniles of
many commercially and recreationally important estuarine
and marine fishes (such as menhaden, herring, shad, spot,
croaker, weakfish, red drum, striped bass, and white perch)
and smaller adult fish (such as bay and striped anchovies)
use SAV beds as nurseries (NOAA Chesapeake Bay Office,
2007; Wyda et al., 2002). Adults of estuarine and marine
species such as sea trout, bluefish, perch, and drum search
for prey in SAV beds (Strange et al. ,2008).
Increased erosion, with concomitant increased transport
and delivery of sediment, would also reduce available light
(MD DNR, 2000).
Although plants in some portion of an SAV bed may decline
as a result of such factors, landward edges may migrate
inland depending on shore slope and substrate suitability.
SAV growth is significantly better in areas where erosion
provides sandy substrate, rather than fine-grained or high
organic matter substrates (Stevenson et al., 2002).
Sea-level rise effects on the tidal range could also impact
SAV, and the effect could be either detrimental or beneficial.
In areas where the tidal range increases, plants at the lower
edge of the bed will receive less light at high tide, increasing
plant stress (Koch and Beer, 1996). In areas where the tidal
range decreases, the decrease in intertidal exposure at low
tide on the upper edge of the bed will reduce plant stress
(Short and Neckles, 1999).
Shore construction and armoring will impede shoreward
movement of SAV beds (Short and Neckles, 1999) (see
Chapter 6 for additional information on shore protections).
First, hard structures tend to affect the immediate geomor-
phology as well as any adjacent seagrass habitats (Strange et
al., 2008). Particularly during storm events, wave reflection
off of bulkheads or seawalls can increase water depth and
magnify the inland reach of waves on downcoast beaches
(Plant and Griggs, 1992; USGS, 2003; Small and Carman,
2005). Second, as sea level rises in armored areas, the
nearshore area deepens and light attenuation increases,
restricting and finally eliminating seagrass growth (Strange
et al., 2008). Finally, high nutrient levels in the water limit
vegetation growth. Sediment trapping behind breakwaters,
which increases the organic content, may limit eelgrass suc-
cess (Strange etal., 2008). Low-profile armoring, including
stone sills and other "living shorelines" projects, may be
beneficial to SAV growth (NRC, 2007). Projects to protect
wetlands and restore adjacent SAV beds are taking place
and represent a potential protection against SAV loss (e.g.,
U.S. Army Corps of Engineers restoration for Smith Island
in Chesapeake Bay) (USACE, 2004).
Effects of sea-level rise on SAV beds are uncertain because
fluctuations in SAV occur on a year-to-year basis, a signifi-
cantly shorter timescale than can be attributed to sea-level
rise7. However, Short and Neckles (1999) estimate that a 50
centimeter (cm) increase in water depth as a result of sea-
level rise could reduce light penetration to current seagrass
beds in coastal areas by 50 percent. This would result in a
30 to 40 percent reduction in seagrass growth in those areas
due to decreased photosynthesis (Short and Neckles, 1999).
7 For example, nutrient enrichment and resultant eutrophication are
a common problem for SAV beds (USFWS, undated).
Loss of SAV affects numerous animals that depend on the
vegetation beds for protection and food. By one estimate, a
50-percent reduction in SAV results in a roughly 25-percent
reduction in Maryland striped bass production (Kahn and
Kemp, 1985). For diving and dabbling ducks, a decrease in
SAV in their diets since the 1960s has been noted (Perry and
Deller, 1996). The decreased SAV in Chesapeake Bay is cited
as a major factor in the substantial reduction in wintering
waterfowl (Perry and Deller, 1996).
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5.6 TIDAL FLATS
Tidal flats are composed of mud or sand and provide habitat
for a rich abundance of invertebrates. Tidal flats are critical
foraging areas for numerous birds, including wading birds,
migrating shorebirds, and dabbling ducks (Strange et al.,
2008).
In marsh areas where accretion rates lag behind sea-level
rise, marsh will eventually revert to unvegetated flats and
eventually open water as seas rise (Brinson et al., 1995).
For example, in New York's Jamaica Bay, several hundred
acres of low salt marsh have converted to open shoals (see
Appendix l.B for additional details). In a modeling study,
Galbraith et al. (2002) predicted that under a 2°C global
warming scenario, sea-level rise could inundate significant
areas of intertidal flats in some regions. In some cases where
tidal range increases with increased rates of sea-level rise,
however, there may be an overall increase in the acreage of
tidal flats (Field et al, 1991).
In low energy shores with high sediment supplies, where
sediments accumulate in shallow waters, flats may become
vegetated as low marsh encroaches waterward, which will
increase low marsh at the expense of tidal flats (Redfield,
1972). If sediment inputs are not sufficient, tidal flats will
convert to subtidal habitats, which may or may not be
vegetated depending on substrate composition and water
transparency (Strange et al., 2008).
Loss of tidal flats would eliminate a rich invertebrate food
source for migrating birds, including insects, small crabs,
and other shellfish (Strange et al., 2008). As tidal flat area
declines, increased crowding in remaining areas could lead
to exclusion and reductions in local shorebird populations
(Galbraith et al., 2002). At the same time, ponds within
marshes may become more important foraging sites for the
birds if flats are inundated by sea-level rise (Erwin et al.,
2004).
5.7 ESTUARINE BEACHES
Throughout most of the mid-Atlantic region and its tributar-
ies, estuarine beaches front the base of low bluffs and high
cliffs as well as bulkheads and revetments (see Figure 5.6)
(Jackson et al., 2002). Estuarine beaches can also occur in
front of marshes and on the mainland side of barrier islands
(Jackson et al., 2002).
The most abundant beach organisms are microscopic inver-
tebrates that live between sand grains, feeding on bacteria
and single-celled protozoa. It is estimated that there are over
two billion of these organisms in a single square meter of
sand (Bertness, 1999). They play a critical role inbeachfood
Figure 5.6 Estuarine beach and bulkhead along Arthur Kills,
Woodbridge Township, New Jersey (August 2003) [Photo source:
®James G. Titus, used with permission].
webs as a link between bacteria and larger consumers such
as sand diggers, fleas, crabs, and other macroinvertebrates
that burrow in sediments or hide under rocks (Strange etal.,
2008). In turn, shorebirds such as the piping plover, Ameri-
can oystercatcher, and sandpipers feed on these resources
(USFWS, 1988). Various rare and endangered beetles also
live on sandy shores. Diamondback terrapins and horseshoe
crabs bury their eggs in beach sands. The insects and crus-
taceans found in deposits of wrack on estuarine beaches
are also an important source of forage for birds (Figure 5.7)
(Dugane/a/.,2003).
As sea level rises, the fate of estuarine beaches depends on
their ability to migrate and the availability of sediment to
replenish eroded sands (Figure 5.8) (Jackson et al., 2002). Es-
tuarine beaches continually erode, but under natural condi-
tions the landward and waterward boundaries usually retreat
by about the same distance. Shoreline protection structures
may prevent migration, effectively squeezing beaches be-
tween development and the water. Armoring that traps sand
in one area can limit or eliminate longshore transport, and,
as a result, diminish the constant replenishment of sand
Figure 5.7 Peconic Estuary Beach, Riverhead, New York
(September 2006) [Photo source: ®James G. Titus, used with
permission].
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Chapter 5
Figure 5.8 Beach with beach wrack and marsh in Bethel Beach
(Mathews County), Virginia (June 2002) [Photo source: ®James
G. Titus, used with permission].
necessary for beach retention in nearby locations (Jackson
etal., 2002). Waterward of bulkheads, the foreshore habitat
will likely be lost through erosion, frequently even without
sea-level rise. Only in areas with sufficient sediment input
relative to sea-level rise (e.g., upper tributaries and upper
Chesapeake Bay) are beaches likely to remain in place in
front of bulkheads.
In many developed areas, estuarine beaches may be
maintained with beach nourishment if there are sufficient
sources and the public pressure and economic ability to do
so. However, the ecological effects of beach nourishment
remain uncertain. Beach nourishment will allow retention in
areas with a sediment deficit, but may reduce habitat value
through effects on sediment characteristics and beach slope
(Peterson and Bishop, 2005).
Beach loss will cause declines in local populations of rare
beetles found in Calvert County, Maryland. While the North-
eastern beach tiger beetle is able to migrate in response to
changing conditions, suitable beach habitat must be available
nearby (USFWS, 1994).
At present, the degree to which horseshoe crab populations
will decline as beaches are lost remains unclear. Early re-
search results indicate that horseshoe crabs may lay eggs
in intertidal habitats other than estuarine beaches, such as
sandbars and the sandy banks of tidal creeks (Loveland and
Botton, 2007). Nonetheless, these habitats may only provide
a temporary refuge for horseshoe crabs if they are inundated
as well (Strange et al, 2008).
Where horseshoe crabs decline because of loss of suitable
habitat for egg deposition, there can be significant implica-
tions for migrating shorebirds, particularly the red knot, a
candidate for protection under the federal Endangered Spe-
cies Act, which feeds almost exclusively on horseshoe crab
eggs during stopovers in the Delaware Estuary (Karpanty
et al, 2006).
In addition, using high-precision elevation data from nest
sites, researchers are beginning to examine the effects that
sea-level rise will have on oystercatchers and other shore
birds (Rounds and Erwin, 2002). To the extent that estuarine
and riverine beaches, particularly on islands, survive better
than barrier islands, shorebirds like oystercatchers might be
able to migrate to these shores (McGowan et al., 2005).
5.8 CLIFFS
Unvegetated cliffs and the sandy beaches sometimes pres-
ent at their bases are constantly reworked by wave action,
providing a dynamic habitat for cliff beetles and birds. Little
vegetation exists on the cliff face due to constant erosion, and
the eroding sediment augments nearby beaches. Cliffs are
present on Chesapeake Bay's western shore and tributaries
and its northern tributaries (see Figure 5.9), as well as in
Hempstead Harbor on Long Island's North Shore and other
areas where high energy shorelines intersect steep slopes
(Strange et al, 2008).
If the cliff base is armored to protect against rising seas,
erosion rates may decrease, eliminating the unvegetated cliff
faces that are sustained by continuous erosion and provide
habitat for species such as the Puritan tiger beetle and bank
swallow. Cliff erosion also provides a sediment source to
sustain the adjacent beach and littoral zone (the shore zone
between high and low water marks) (Strange et al., 2008).
Naturally eroding cliffs are "severely threatened by shoreline
erosion control practices" according to the Maryland Depart-
ment of Natural Resource's Wildlife Diversity Conservation
Plan (MD DNR, 2005). Shoreline protections may also
subject adjacent cliff areas to wave undercutting and higher
recession rates as well as reduction in beach sediment (Wil-
cock et al., 1998). Development and shoreline stabilization
Figure 5.9 Crystal Beach, along the Elk River, Maryland (May
2005) [Photo source: ®James G. Titus, used with permission].
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structures that interfere with natural erosional processes are
cited as threats to bank-nesting birds as well as two species
of tiger beetles (federally listed as threatened) at Maryland's
Calvert Cliffs (USFWS, 1993, 1994; CCB, 1996).
Based on currently available information, it is possible to
identify particular taxa and even some individual species
that appear to be at greatest risk if coastal habitats are
degraded or diminished in response to sea-level rise and
shoreline hardening:
Degradation and loss of tidal marshes will affect fish
and shellfish production inboth the marshes themselves
and adjacent estuaries.
Bird species that are marsh specialists, including the
clapper rail, black rail, least bittern, Forster's tern, wil-
let, and laughing gull, are particularly at risk. At pres-
ent, the majority of the Atlantic Coast breeding popula-
tions of Forster's tern and laughing gull are considered
to be at risk from loss of lagoonal marshes.
Increased turbidity and eutrophication in nearshore
areas and increased water depths may reduce light
penetration to SAV beds, reducing photosynthesis,
and therefore the growth and survival of the vegeta-
tion. Degradation and loss of SAV beds will affect the
numerous organisms that feed, carry on reproductive
activities, and seek shelter in seagrass beds.
Diamondback terrapin are at risk of losing both marsh
habitat that supports growth and adjoining beaches
where eggs are buried.
Many marsh islands along the Mid-Atlantic, and par-
ticularly in Chesapeake Bay, have already been lost
or severely reduced as a result of lateral erosion and
flooding related to sea-level rise. Loss of such islands
poses a serious, near-term threat for island-nesting bird
species such as gull-billed terns, common terns, black
skimmers, and American oystercatchers.
Many mid-Atlantic tidal forest associations may be at
risk from sea-level rise and a variety of other threats,
and are now considered globally imperiled.
Shoreline stabilization structures interfere with natural
erosional processes that maintain unvegetated cliff
faces that provide habitat for bank-nesting birds and
tiger beetles.
Loss of tidal flats could lead to increased crowding of
foraging birds in remaining areas, resulting in exclu-
sion of many individuals; if alternate foraging areas
are unavailable, starvation of excluded individuals
may result, ultimately leading to reductions in local
bird populations.
Where horseshoe crabs decline because of loss of suit-
able beach substrate for egg deposition, there could
be significant implications for migrating shorebirds,
particularly the red knot, a candidate for protection
under the federal Endangered Species Act. Red knot
feed almost exclusively on horseshoe crab eggs during
stopovers in the Delaware Estuary.
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The U.S. Climate Change Science Program Chapter 5
,r_™i«!
f)i
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
o
Societal Impacts and Implications
Authors: James G. Titus, U.S. EPA; Stephen K. Gill, NOAA
The previous chapters in Part I examined some of the
impacts of sea-level rise on the Mid-Atlantic, with a
focus on the natural environment. Part II examines
the implications of sea-level rise for developed lands.
Although the direct effects of sea-level rise would
be similar to those on the natural environment,
people are part of this "built environment"; and
people will generally respond to changes as they
emerge, especially if important assets are threatened.
The choices that people make could be influenced
by the physical setting, the properties of the built
environment, human aspirations, and the constraints
of laws and economics.
The chapters in Part II examine the impacts on four
human activities: shore protection and retreat, human
habitation, public access, and flood hazard mitigation.
This assessment does not predict the choices that
people will make; instead it examines some of the
available options and assesses actions that federal and
state governments and coastal communities can take
in response to sea-level rise.
As rising sea level threatens coastal lands, the most
fundamental choice that people face is whether
to attempt to hold back the sea or allow nature to
takes its course. Both choices have important costs
and uncertainties. "Shore protection" allows homes
and businesses to remain in their current locations,
but often damages coastal habitat and requires
substantial expenditure. "Retreat" can avoid the costs
and environmental impacts of shore protection, but
often at the expense of lost land and—in the case of
developed areas—the loss of homes and possibly entire
communities. In nature reserves and major cities, the
preferred option may be obvious. Yet because each
choice has some unwelcome consequences, the decision
may be more difficult in areas that are developing or only
lightly developed. Until this choice is made, however,
preparing for long-term sea-level rise in a particular
location may be impossible.
Chapter 6 outlines some of the key factors likely to be a
part of any dialogue on whether to protect or retreat in
a given area:
What are the technologies available for shore
protection and the institutional measures that might
help foster a retreat?
What is the relationship between land use and shore
protection?
What are the environmental and social consequences
of shore protection and retreat?
Is shore protection sustainable?
Most areas lack a plan that specifically addresses
whether the shore will retreat or be protected. Even in
those areas where a state plans to hold the line or a park
plans to allow the shore to retreat, the plan is based on
existing conditions. Current plans do not consider the
costs or environmental consequences of sustaining shore
protection for the next century and beyond.
One of the most important decisions that people make
related to sea-level rise is the decision to live or build
in a low-lying area. Chapter 7 provides an uncertainty
range of the population and number of households with
a direct stake in possible inundation as sea level rises.
The results are based on census data for the year 2000,
and thus are not estimates of the number of people
or value of structures that will be affected, but rather
estimate the number of people who have a stake today
in the possible future consequences of rising sea level.
Because census data estimates the total population of
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The U.S. Climate Change Science Program
Part II Overview
a given census block, but does not indicate where in that
block the people live or the elevation of their homes, the
estimates in Chapter 7 should not be viewed as the number
of people whose homes would be lost. Rather, it estimates
the number of people who inhabit a parcel of land or city
block with at least some land within a given elevation above
the sea. The calculations in this Chapter build quantitatively
on some of the elevation studies discussed in Chapter 2, and
consider uncertainties in both the elevation data and the
location of homes within a given census block. Chapter 7
also summarizes a study sponsored by the U.S Department
of Transportation on the potential impacts of global sea-level
rise on the transportation infrastructure.
Chapter 8 looks at the implications of sea-level rise for public
access to the shore. The published literature suggests that
the direct impact of sea-level rise on public access would
be minor because the boundary between public and private
lands moves inland as the shore retreats. But responses to
sea-level rise could have a substantial impact. One common
response (publicly funded beach nourishment) sometimes
increases public access to the shore; but another class
of responses (privately funded shoreline armoring) can
eliminate public access along the shore if the land seaward
of the shore protection structure erodes. In parts of New
Jersey, regulations governing permits for shoreline armoring
avoid this impact by requiring property owners to provide
access along the shore inland of the new shore protection
structures.
Finally, Chapter 9 examines the implications of rising sea
level for flood hazard mitigation, with a particular focus on
the implications for the Federal Emergency Management
Agency (FEMA) and other coastal floodplain managers.
Rising sea level increases the vulnerability of coastal areas
to flooding because higher sea level increases the frequency
of floods by providing a higher base for flooding to build
upon. Erosion of the shoreline could also make flooding
more likely because erosion removes dunes and other natural
protections against storm waves. Higher sea level also raises
groundwater levels, which can increase basement flooding
and increase standing water. Both the higher groundwater
tables and higher surface water levels can slow the rate at
which areas drain, and thereby increase the flooding from
rainstorms.
Chapter 9 opens with results of studies on the relationship
of coastal storm tide elevations and sea-level rise in the
Mid-Atlantic. It then provides background on government
agency floodplain management and on state activities
related to flooding and sea-level rise under the Coastal
Zone Management Act. Federal agencies, such as FEMA,
are beginning to specifically plan for future climate change
in their strategic planning. Some coastal states, such as
Maryland, have conducted state-wide assessments and
studies of the impacts of sea-level rise and have taken steps
to integrate this knowledge with local policy decisions.
The chapters in Part II incorporate the underlying sea-level
rise scenarios of this Product differently, because of the
differences in the underlying analytical approaches. Chapter
7 evaluates the population and property vulnerable to a
100-centimeter rise in sea level, and summarizes a study
by the U.S. Department of Transportation concerning the
impact of a 59-centimeter rise. Chapters 6, 8, and 9 provide
qualitative analyses that are generally valid for the entire
uncertainty range of future sea-level rise.
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Coastal Sensitivity to Sea-Level Rise:
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Shore Protection and Retreat
a.
I
U
Authors: James G. Titus, U.S. EPA; Michael Craghan, Middle
Atlantic Center for Geography and Environmental Studies
KEY FINDINGS
Many options are available for protecting land from inundation, erosion, and flooding ("shore protection"),
or for minimizing hazards and environmental impacts by removing development from the most vulnerable
areas ("retreat").
Coastal development and shore protection can be mutually reinforcing. Coastal development often encourages
shore protection because shore protection costs more than the market value of undeveloped land, but less
than the value of land and structures. Shore protection sometimes encourages coastal development by making
a previously unsafe area safe for development. Under current policies, shore protection is common along
developed shores and rare along shores managed for conservation, agriculture, and forestry. Policymakers
have not decided whether the practice of protecting development should continue as sea level rises, or be
modified to avoid adverse environmental consequences and increased costs of shore protection.
Most shore protection structures are designed for the current sea level, and retreat policies that rely on
setting development back from the coast are designed for the current rate of sea-level rise. Those structures
and policies would not necessarily accommodate a significant acceleration in the rate of sea-level rise.
Although shore protection and retreat both have environmental impacts, the long-term impacts of shore
protection are likely to be greater.
In the short term, retreat is more socially disruptive than shore protection. In the long term, however, shore
protection may be more disruptive—especially if it fails or proves to be unsustainable.
We do not know whether "business as usual" shore protection is sustainable.
A failure to plan now could limit the flexibility of future generations to implement preferred adaptation
strategies. Short-term shore protection projects can impair the flexibility to later adopt a retreat strategy. By
contrast, short-term retreat does not significantly impair the ability to later erect shore protection structures
inland from the present shore.
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The U.S. Climate Change Science Program
Chapter 6
6.1 TECHNIQUES FORSHORE PROTECTION
AND RETREAT
Most of the chapters in this Product discuss some aspect
of shore protection and retreat. This Section provides an
overview of the key concepts and common measures for
holding back the sea or facilitating a landward migration of
people, property, wetlands, and beaches. Chapter 9 discusses
floodproofing and other measures that accommodate ris-
ing sea level without necessarily choosing between shore
protection and retreat.
6.1.1 Shore Protection
The term "shore protection" generally refers to a class of
coastal engineering activities that reduce the risk of flood-
ing, erosion, or inundation of land and structures (USAGE,
2002). The term is somewhat of a misnomer because shore-
protection measures protect land and structures immediately
inland of the shore ratherthanthe shore itself1. Shore-protec-
tion structures sometimes eliminate the existing shore, and
shore protection does not necessarily mean environmental
preservation. This Product focuses on shore-protection mea-
sures that prevent dry land from being flooded or converted
to wetlands or open water.
Shore-protection measures can be divided into two cat-
egories: shoreline armoring and elevating land surfaces.
Shoreline armoring replaces the natural shoreline with an
artificial surface, but areas inland of the shore are gener-
ally untouched. Elevating land surfaces, by contrast, can
maintain the natural character of the shore, but requires
rebuilding all vulnerable land. Some methods are hybrids
of both approaches. For centuries, people have used both
shoreline armoring (Box 6.1) and elevating land surfaces
(Box 6.2) to reclaim dry land from the sea. This Section
discusses how those approaches might be used to prevent a
rising sea level from converting dry land to open water. For
a comprehensive discussion, see the Coastal Engineering
Manual (USAGE, 2002).
6.1.1.1 SHORELINE ARMORING
Shoreline armoring involves the use of structures to keep
the shoreline in a fixed position or to prevent flooding when
water levels are higher than the land. Although the term
is often synonymous with "shoreline hardening", some
structures are comprised of relatively soft material, such as
earth and sand.
BOX 6.1: Historic Use of Dikes to Reclaim Land in the Delaware Estuary
Until the twentieth century, tidal wetlands were often converted to dry land through the use of dikes and drainage
systems very similar to the systems that might be used to prevent land from being inundated as sea level rises.
Nowhere in the United States was more marsh converted to dry land than along the Delaware River and Delaware
Bay. A Dutch govern or of New Jersey diked the marsh on Burlington Island. In 1680, after the English governor took
possession of the island, observers commented that the marsh farm had achieved greater yields of grain than nearby
farms created by clearing woodland (Danckaerts, 1913). In 1675, an English governor ordered the construction of
dikes to facilitate construction of a highway through the marsh in New Castle County, Delaware (Sebold, 1992).
Colonial (and later state) governments in New Jersey chartered and authorized "meadow companies" to build
dikes and take ownership of the reclaimed lands. During the middle of the nineteenth century, the state agriculture
department extolled the virtues of reclaimed land for growing salt hay. By 1866, 20,000 acres of New Jersey's
marshes had been reclaimed from Delaware Bay, mostly in Salem and Cumberland counties (Sebold, 1992). In 1885,
the U.S. Department of Agriculture cited land reclamation in Cumberland County, Newjersey, as among the most
impressive in the nation (Nesbit, 1885, as quoted in Sebold, 1992). By 1885, land reclamation had converted 10,000
out of 15,000 acres of the marsh in New Castle County to agricultural lands, as well as 8,000 acres in Delaware's
other two counties (Nesbit, 1885). In Pennsylvania, most of the reclaimed land was along the Delaware River, just
south of the mouth of the Schuylkill near the present location of Philadelphia International Airport.
During the twentieth century, these land reclamation efforts were reversed. In many cases, lower prices for
salt hay led farmers to abandon the dikes (DDFW, 2007). In some cases, where dikes remain, rising sea level
has limited the ability of dikes to drain the land, and the land behind the dike has converted to marsh, such as
the land along the Gibbstown Levee (See Box AI.4 in Appendix I and Figure ll.4c and d). Efforts are underway
to restore the hydrology of many lands that were formerly diked (DDFW, 2007). In areas where dikes protect
communities from flooding, however, public officials area also considering the possibility of upgrading the dikes and
drainage systems.
The shore is the land immediately in contact with the water.
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Coastal Sensitivity to Sea-Level Rise:
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Keeping the shoreline in a fixed position
Seawalls are impermeable barriers designed to withstand the
strongest storm waves and to prevent overtopping during a
storm. During calm periods, their seaward side may either
be landward of a beach or in the water. Seawalls are often
used along important transportation routes such as highways
or railroads (Figure 6.la).
Bulkheads are vertical walls designed to prevent the land
from slumping toward the water (Figure 6.1b). They must
resist waves and currents to accomplish their design intent,
but unlike seawalls, they are not designed to withstand se-
vere storms. They are usually found along estuarine shores
where waves have less energy, particularly in marinas and
other places where boats are docked, and residential areas
where homeowners prefer a tidy shoreline. Bulkheads hold
soils in place, but they do not normally extend high enough
to keep out foreseeable floods. Like seawalls, their seaward
sides may be inland of a beach (or marsh) or in the water.
Retaining structures include several types of structures that
serve as a compromise between a seawall and a bulkhead.
They are often placed at the rear of beaches and are unseen.
Sometimes they are sheet piles driven downward into the
sand; sometimes they are long, cylindrical, sand-filled "geo-
tubes" (Figure 6.2). Retaining structures are often concealed
as the buried core of an artificial sand dune. Like seawalls,
they are intended to be a final line of defense against waves
after a beach erodes during a storm; but they can not survive
wave attack for long.
Revetments are walls whose sea side follows a slope. Like
the beach they replace, their slope makes them more effec-
tive at dissipating the energy of storm waves than bulkheads
BOX 6.2: Creation of the National Monument Area in Washington D.C. through
Nineteenth Century Dredge and Fill
Like many coastal cities, important parts of Washington, D.C. are on land that was previously created by filling
wetlands and navigable waterways. When the city of Washington was originally planned, the Potomac River was
several times as wide immediately south of Georgetown as above Georgetown (see Box Figure 6.2). L'Enfant's
plan put the President's residence just northeast of the mouth of Tiber Creek. Thus, the White House grounds
originally had a tidal shoreline.
To improve navigation, canals
connected Tiber Creek to the
Anacostia River (Bryan, 1914).
The White House and especially
White House
the Capitol were built on high
ground immune from flooding,
but much of the land between
the two was quite low.
During the nineteenth century,
soil eroded from upstream farm-
ing was deposited in the wide
part of the river where the cur-
rent slowed, which created wide
mudflats below Georgetown.
The success of railroads made
canals less important, while the
increasing population converted
the canals into open sewers.
During the early 1870s, Gover-
nor Boss Shephard had the ca-
nals filled and replaced with drain
pipes. A large dredge-and-fill op-
eration excavated Washington
Channel from the mudflats, and used the material to create the shores of the Tidal Basin and the dry land on
which the Lincoln Memorial, Jefferson Memorial, Reflecting Pool, East Potomac Park, and Hains Point sit today
(Bryan, 1914). Similarly, about half of the width of the Anacostia River was filled downstream from Poplar Point,
creating what later became the U.S. Naval Air Station (now part of Boiling Air Force Base).
I.OH15,
Poplar Point
Box Figure 6.2 L'Enfant's Plan for the City of Washington.
Source: Library of Congress (Labels for White House, Georgetown, and Tiber
Creek added).
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The U.S. Climate Change Science Program
Figure 6.1 Seawalls and bulkheads (a) Galveston Seawall in Texas (May 2003) and (b) bulkheads with intervening beach along
Magothy River in Anne Arundel County, Maryland (August 2005) [Photo source: ®James G. Titus, used with permission].
Figure 6.2 Geotube (a) before and (b) after being buried by beach sand at Bolivar Peninsula, Texas (May 2003) [Photo source:
®James G. Titus, used with permission].
(a)
Figure 6.3 Two types of stone revetments (a) near Surfside, Texas (May 2003) and (b) at Jamestown, Virginia (September 2004)
[Photo source: ®James G. Titus, used with permission].
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Coastal Sensitivity to Sea-Level Rise:
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Figure 6.4 (a) A dike in Miami-Dade County, Florida (June 2005), and (b) a newly-created dune in Surf City, New Jersey (June 2007)
[Photo source: ®James G. Titus, used with permission].
and seawalls. As a result, revetments are less likely than
bulkheads and seawalls to cause the beach immediately
seaward to erode (USAGE, 1995), which makes them less
likely to fail during a storm (Basco, 2003; USAGE, 1995).
Some revetments are smooth walls (Figure 6.3b), while oth-
ers have a very rough appearance (Figure 6.3a).
Protecting Against Flooding or Permanent Inundation
Dikes are high, impermeable earthen walls designed to
keep the area behind them dry. They can be set back from
the shoreline if the area to be protected is a distance inland
and usually require an interior drainage system. Land be-
low mean low water requires a pumping system to remove
rainwater and any water that seeps through the ground
below the dike. Land whose elevation is between low and
high tide can be drained at low tide, except during storms
(Figure 6.4a).
Figure 6.5 The tide gate at the mouth of Army Creek on the
Delaware side of the Delaware River. The tide gate drains flood
and rain water out of the creek to prevent flooding. The five
circular mechanisms on the gate open and close to control water
flow [Photo source: courtesy NOAA Photo Library].
Dunes are accumulations of windblown sand and other ma-
terials which function as a temporary barrier against wave
runup and overwash (Figure 6.4b, see also Section 6.1.1.2).
Tide gates are barriers across small creeks or drainage
ditches. By opening during low tides and closing during high
tides, they enable a low-lying area above mean low water to
drain without the use of pumps (Figure 6.5).
Storm surge barriers are similar to tide gates, except that
they close only during storms rather than during high tides,
and they are usually much larger, closing off an entire river
or inlet. The barrier in Providence, Rhode Island (Figure
6.6) has gates that are lowered during a storm; the Thames
River Barrier in London, by contrast, has a submerged bar-
rier, which allows tall ships to pass. As sea level rises and
storm surges become higher (see Chapter 9), these barriers
must be closed more frequently. The gates in Providence,
Rhode Island (Figure 6.6), for example, are currently closed
an average of 19 days per year (NOAA Coastal Services
Center, 2008).
6.1.1.2 ELEVATING LAND SURFACES
A second general approach to shore protection is to elevate
land and structures. Tidal marshes have long adapted to sea-
level rise by elevating their land surfaces to keep pace with
the rising sea (Chapter 4). Elevating land and structures by
the amount of sea-level rise can keep a community's assets
at the same elevation relative to the sea and thereby prevent
them from becoming more vulnerable as sea level rises.
These measures are sometimes collectively known as "soft"
shore protection.
Beachfill, also known as beach nourishment or sand replen-
ishment, involves the purposeful addition of the native beach
material (usually sand but possibly gravel) to a beach to make
it higher and wider. Sand from an offshore or inland source
is added to a beach to provide a buffer against wave action
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Chapter 6
Figure 6.6 Storm surge barriers, (a) Fox Point Hurricane Barrier and Providence River Bridge, Providence, Rhode Island (August
2008) and (b) Moses Lake Floodgate, Texas City, Texas (March 2006) [Photo sources: (a) Marcbela; (b) ®James G. Titus, used with
permission].
and flooding (USAGE, 2002; Dean and Dalrymple, 2002).
Placing sand onto an eroding beach can offset the erosion
that would otherwise occur over a limited time; but erosion
processes continue, necessitating periodic re-nourishment.
Dunes are often part of a beach nourishment program.
Although they also occur naturally, engineered dunes are
designed to intercept wind-transported sand and keep it from
being blown inland and off the beach. Planting dune grass
and installing sand fencing increases the effectiveness and
stability of dunes.
Elevating land and structures is the equivalent of abeachfill
operation in the area landward of the beach. In most cases,
existing structures are temporarily elevated with hydraulic
jacks and a new masonry wall is built up to the desired el-
evation, after which the house is lowered onto the wall (see
Figure 12.5). In some cases the house is moved to the side,
pilings are drilled, and the house is moved onto the pilings.
Finally, sand, soil, or gravel are brought to the property to
elevate the land surface. After a severe hurricane in 1900,
most of Galveston, Texas was elevated by more than one
meter (NRC, 1987). This form of shore protection can be
implemented by individual property owners as needed, or
as part of a comprehensive program. Several federal and
state programs exist for elevating homes, which has become
commonplace in some coastal areas, especially after a major
flood (see also Chapters 9 and 10).
Dredge and fill was a very common approach until the
1970s, but it is rarely used today because of the resulting
loss of tidal wetlands. Channels were dredged through the
marsh, and the dredge material was used to elevate the re-
maining marsh to create dry land (e.g., Nordstrom, 1994).
The overall effect was that tidal wetlands were converted
to a combination of dry land suitable for home construction
and navigable waterways to provide boat access to the new
homes. The legacy of previous dredge-and-fill projects in-
cludes a large number of very low-lying communities along
estuaries, including the bay sides of many developed barrier
islands. Recently, some wetland restoration projects have
used a similar approach to create wetlands, by using material
from dredged navigation channels to elevate shallow water
up to an elevation that sustains wetlands. (USFWS, 2008;
see Section 11.2.2 in Chapter 11).
6.1.1.3 HYBRID APPROACHES TO SHORE PROTECTION
Several techniques are hybrids of shoreline armoring and
the softer approaches to shore protection. Often, the goal of
these approaches is to retain some of the storm-resistance of
a hard structure, while also maintaining some of the features
of natural shorelines.
Groins are hard structures perpendicular to the shore
extending from the beach into the water, usually made of
large rocks, wood, or concrete (see Figure 6.7b). Their pri-
mary effect is to diminish forces that transport sand along
the shore. Their protective effect is often at the expense of
increased erosion farther down along the shore; so they are
most useful where an area requiring protection is updrift
from an area where shore erosion is more acceptable. Jetties
are similar structures intended to guard a harbor entrance,
but they often act as a groin, causing large erosion on one
side of the inlet and accretion on the other side.
Breakwaters are hard structures placed offshore, generally
parallel to the shore (see Figure 6.7a). They can mitigate
shore erosion by preventing large waves from striking the
shore. Like groins, breakwaters often slow the transport of
sand along the shore and thereby increase erosion of shores
adjacent to the area protected by the breakwaters.
Dynamic revetments (also known as cobble beaches) are
a hybrid of beach nourishment and hard structures, in
which an eroding mud or sand beach in an area with a
light wave climate is converted to a cobble or pebble beach
92
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
(a)
(b)
Figure 6.7 Hybrid approaches to shore protection, (a) Breakwaters and groins along Chesapeake Bay in Bay Ridge (near An-
napolis) Maryland (July 2008). The rock structures parallel to the shore in the bay are breakwaters; the structures perpendicular to
the shore are groins; (b) wooden groins and bulkhead along the Peconic Estuary on Long Island, New York (September 2006). The
beach is wider near the groin and narrower between groins; (c) a nourished beach with a terminal groin at North Beach (Maryland)
(September 2008); (d) a dynamic revetment placed over the mud shore across Swan Creek from the Fort Washington (Maryland)
unit of National Capital Parks East. Logs have washed onto the shore since the project was completed (July 2008) [Photo source:
®James G. Titus, used with permission].
(see Figure 6.7d). The cobbles are heavy enough to resist ero-
sion, yet small enough to create a type of beach environment
(USAGE, 1998; Komar, 2007; Allan et al, 2005).
Recently, several state agencies, scientists, environmental
organizations, and property owners have become interested
in measures designed to reduce erosion along estuarine
shores, while preserving more habitat than bulkheads and
revetments (see Box 6.3). "Living Shorelines" are shoreline
management options that allow for natural coastal processes
to remain through the strategic placement of plants, stone,
sand fill, and other structural and organic materials. They
often rely on native plants, sometimes supplemented with
groins, breakwaters, stone sills, or biologs2 to reduce wave
energy, trap sediment, and filter runoff, while maintaining
(or increasing) beach or wetland habitat (NRC, 2007).
2 A sill is a hard structure placed along the edge of a marsh to reduce
wave erosion of the marsh. A biolog is an assemblage of woody,
organic, biodegradable material in a log-shaped form.
In addition to the hybrid techniques, communities often use
a combination of shoreline armoring and elevation. Many
barrier island communities apply beach nourishment on
the ocean side, while armoring the bay side. Ocean shore
protection projects in urban areas sometimes include both
beach nourishment and a seawall to provide a final line of
defense if the beach erodes during a storm. Beach nourish-
ment projects along estuaries often include breakwaters to
reduce wave erosion (Figure 6.7a), or a terminal groin to
keep the sand within the area meant to be nourished (see
Figure 6.7c).
6.1.2 Retreat
The primary alternative to shore protection is commonly
known as retreat (or relocation). Shore protection generally
involves coastal engineering to manage the forces of nature
and environmental engineering to manage environmental
consequences. By contrast, retreat often emphasizes the
management of human expectations, so that people do not
make investments inconsistent with the eventual retreat.
93
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The U.S. Climate Change Science Program
Chapter 6
BOX 6.3: Shore Protection Alternatives in Maryland: Living Shorelines
Shore erosion and methods for its control are a major concern in estuarine and marine ecosystems. However,
awareness of the negative impacts that many traditional shoreline protection methods have, including loss of
wetlands and their buffering capacities, impacts on nearshore biota, and ability to withstand storm events, has
grown in recent years. Non-structural approaches, or hybrid-type projects that combine a marsh fringe with
groins or breakwaters, are being considered along all shorelines except for those with large waves (from either
boat traffic or a long fetch). The initial cost for these projects is often significantly less than for bulkheads or
revetments; the long-run cost can be greater or less depending on how frequently the living shoreline must be
rebuilt. These projects typically combine marsh replanting (generally Spartina patens and Spartina alterniflora)
and stabilization through sills, groins, or breakwaters. A survey of projects on the eastern and western sides
of Chesapeake Bay (including Wye Island, Epping Forest near Annapolis, and the Jefferson Patterson Park and
Museum on the Patuxent) found that the sill structures or breakwaters were most successful in attenuating wave
energy and allowing the development of a stable marsh environment.
tnm High TI«M * **i*n
»£•*
•MkMfhTHi
'?E3v3?-
TIDAL MAH5H
SAV
LIVING BREAKWATER
UPLAKD BUFFER
BANKFACE COAiTALWfTLAWil BEACH STRAND
SUBTKML WATERS
NlBrt
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irm m
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PUiM MMCM4 14 Tl ill
t V
-------
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Figure 6.8 Relocating structures along the Outer Banks (a) Cape Hatteras Lighthouse after relocation at the Cape Hatteras Na-
tional Seashore, Buxton, North Carolina (June 2002); the original location is outlined in the foreground, and (b) a home threatened
by shore erosion in Kitty Hawk, North Carolina (June 2002) The geotextile sand bags are used to protect the septic system [Photo
source: ®James G. Titus, used with permission].
Appendix 1). More commonplace are the routine "struc-
tural moving" activities involved in relocating a house
back several tens of meters within a given shorefront lot,
and the removal of structures threatened by shore erosion
(Figure 6.8b).
Buyout programs provide funding to compensate landown-
ers for losses from coastal hazards by purchasing vulnerable
property. In effect, these programs transfer some of the risk
of sea-level rise from the property owner to the public, which
pays the cost (see Chapter 12).
Conservation easements are an interest in land that allows
the owner of the easement to prevent the owner of the land
from developing it. Land conservation organizations have
purchased non-development easements along coastal bays
and Chesapeake Bay in Maryland (MALPF, 2003). In most
cases, the original motivation for these purchases has been
the creation of a buffer zone to protect the intertidal ecology
(MDCPB, 1999; MALPF, 2003). These vacant lands also
leave room for landward migration of wetlands and beaches,
(NJDEP, 2006). Organizations can also create buffers spe-
cifically for the purpose of accommodating rising sea level.
Blackwater Wildlife Refuge in Maryland and Gateway Na-
tional Recreation Area in New York both own considerable
amounts of land along the water onto which wetlands and
beaches, respectively, could migrate inland.
Acquisition programs involve efforts by a government or
conservation entity to obtain title to the land closest to
the sea. Titles may be obtained by voluntary transactions,
eminent domain, or dedication of flood-prone lands as part
of a permitting process. In Barnegat Light, New Jersey and
Virginia Beach, Virginia, for example, governments own
substantial land along the shore between the Atlantic Ocean
and the oceanside development.
Setbacks are the regulatory equivalent of conservation
easements and purchase programs. The most common type
of setback used to prepare for sea-level rise is the erosion-
based setback, which prohibits development on land that
is expected to erode within a given period of time. North
Carolina requires new structures to be set back from the
primary dune based on the current erosion rate times 30
years for easily moveable homes, or 60 years for large im-
moveable structures (see Section Al.G.4.1 in Appendix 1).
Maine's setback rule assumes a 60 centimeter (cm) rise in
sea level during the next 100 years3.
Flood hazard regulations sometimes prohibit development
based on elevation, rather than proximity to the shore. Aside
from preventing flood damages, these elevation-based
setbacks can ensure that there is room for wetlands or other
intertidal habitat to migrate inland as sea level rises in areas
that are vulnerable to inundation rather than wave-generated
erosion. Two counties in Delaware prohibit development
in the 100-year floodplain along the Delaware River and
Delaware Bay (Section Al.D.2.2 in Appendix 1).
Rolling easements are regulatory mechanisms (Burka,
1974) or interests in land (Titus, 1998) that prohibit shore
protection and instead allow wetlands or beaches to migrate
inland as sea level rises. Rolling easements transfer some of
the risk of sea-level rise from the environment or the public
to the property owner (Titus, 1998). When implemented
as a regulation, they are an alternative to prohibiting all
development in the area at risk, which may be politically
infeasible, inequitable, or a violation of the "takings clause"
of the U.S. Constitution (Titus, 1998; Caldwell and Segall,
2007). When implemented as an interest in land, they are an
alternative to outright purchases or conservation easements
(Titus, 1998).
06-096 Code of Maine Rules §355.5(C), (2007).
95
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Chapter 6
The purpose of a rolling easement is to align the property
owner's expectations with the dynamic nature of the shore
(Titus, 1998). If retreat is the eventual objective, property
owners can more efficiently prepare for that eventuality if
they expect it than if it takes them by surprise (Yohe et al.,
1996; Yohe and Neumann, 1997). Preventing development
in the area at risk through setbacks, conservations ease-
ments, and land purchases can also be effective—but such
restrictions could be costly if applied to thousands of square
kilometers of valuable coastal lands (Titus, 1991). Because
rolling easements allow development but preclude shore
protection, they are most appropriate for areas where pre-
venting development is not feasible and shore protection is
unsustainable. Conversely, rolling easements are not useful
in areas where shore protection or preventing development
are preferred outcomes.
Rolling easements were recognized by the common law
along portions of the Texas Gulf Coast (Feinman v. State;
Matcha v. Mattox) and reaffirmed by the Texas Open
Beaches Act4, with the key purpose being to preserve the
public right to traverse the shore. Massachusetts and Rhode
Island prohibit shoreline armoring along some estuarine
shores so that ecosystems can migrate inland, and several
states limit armoring along ocean shores (see Chapter 11).
Rolling easements can also be implemented as a type of
conservation easement, purchased by government agencies
or conservancies from willing sellers, or dedicated as part of
a planning review process (Titus, 1998); but to date, rolling
easements have only been implemented by regulation.
Density restrictions allow some development but limit densi-
ties near the shore. In most cases, the primary motivation
has been to reduce pollution runoff into estuaries; but they
also can facilitate a retreat by decreasing the number of
structures potentially lost if shores retreat. Maryland limits
development to one home per 8.1 hectares (20 acres) within
305 meters (m) (1000 feet [ft]) of the shore in most coastal
areas (see Section Al.F.2.1 in Appendix 1). In areas without
public sewer systems, zoning regulations often restrict densi-
ties (e.g., Accomack County, 2008; U.S. EPA, 1989).
Size limitations also allow development but limit the inten-
sity of the development placed at risk. Small structures are
relocated more easily than large structures. North Carolina
limits the size of new commercial or multi-family residential
buildings to 464 square meters (sq m) (5,000 square feet [sq
ft]) in the area that would be subject to shore erosion during
the next 60 years given the current rate of shore erosion,
or within 36.6 m (120 ft) of the shore, whichever is farther
inland5. Maine's Sand Dune Rules prohibit structures taller
than 10.7 (35 ft) or with a "footprint" greater than 232 sq m
(2,500 sq ft) in all areas that are potentially vulnerable to a
60 cm rise in sea level6.
6.1.3
Although shore protection and retreat are fundamentally dif-
ferent responses to sea-level rise, strategies with elements of
both approaches are possible. In most cases, a given parcel
of land at a particular time is either being protected or not—
but a strategy can vary with both time and place, or hedge
against uncertainty about the eventual course of action.
Time. Sometimes a community switches from retreat to
protection. It is common to allow shores to retreat as long as
only vacant land is lost, but to erect shore protection struc-
tures once homes or other buildings are threatened. Setbacks
make it more likely that an eroding shore will be allowed to
retreat (Beatley etal, 2002; NRC, 1987; NOAA, 2007); once
the shore erosion reaches the setback line, the economics of
shore protection are similar to what they would have been
without the setback. Conversely, protection can switch to
retreat. Property owners sometimes erect low-cost shore
protection that extends the lifetimes of their property, but
ultimately fails in a storm (e.g., geotextile sandbags, shown
in Figure 6.7b). Increasing environmental implications or
costs of shore protection may also motivate a switch from
protection to retreat (see Section 6.5). To minimize economic
and human impacts, retreat policies based on rolling ease-
ments can be designed to take effect 50 to 100 years hence,
until then protection might be allowed (Titus, 1998).
Place. Different responses operate on different scales. In
general, a project to retreat or protect a given parcel will
usually have effects on other parcels. For example, sand
provided to an open stretch of ocean beach will be trans-
ported along the shore a significant distance by waves and
currents; hence, beach nourishment along the ocean coast
generally involves at least a few kilometers of shoreline or
an entire island. Along estuaries, however, sands are not
transported as far—especially when the shoreline has an
indentation—so estuarine shore protection can operate on
a smaller scale. Shoreline armoring that protects one parcel
may cause adjacent shores to erode or accrete. Neverthe-
less, along tidal creeks and other areas with small waves, it
is often feasible to protect one home with a hard structure,
while allowing an adjacent vacant lot to erode. In areas with
low density zoning, it may be possible to protect the land
4 Tex. Nat. Res. Code Ann. §§ 61.001-.178 (West 1978 & Supp. 1998).
5 15ANCAC 07H. 0305-0306. The required setback for single-family
homes and smaller commercial structures is half as great (see Section
A1.G.4 in Appendix 1 for details).
6 06-096 Code of Maine Rules §355 (5) (D) (2007).
96
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immediately surrounding a home while the rest of the lot
converts to marsh, mudf lat, or shallow water habitat.
Uncertainty. Some responses to sea-level rise may be ap-
propriate in communities whose eventual status is unknown.
Floodproofing homes (see Chapter 9), elevating evacuation
routes, and improving drainage systems can provide cost-
effective protection from flooding in the short term, whether
or not a given neighborhood will eventually be protected or
become subjected to tidal inundation. A setback can reduce
hazards whether or not a shore protection project will even-
tually be implemented.
6,2,1 Site-Specific Factors
Private landowners and government agencies who contem-
plate possible shore protection are usually motivated by
either storm damages or the loss of land (NRC, 2007). They
inquire about possible shore protection measures, investigate
the costs and consequences of one or more measures, and
consider whether undertaking the costs of shore protection
is preferable to the consequences of not doing so. For most
homeowners, the costs of shore protection include the costs
of both construction and necessary government permits;
the benefits include the avoided damages or loss of land
and structures. Businesses might also consider avoided
disruptions in operations. Regulatory authorities that issue
or deny permits for private shore protection consider pos-
sible impacts of shore protection on the environment, public
access along ocean shores, and whether the design mini-
mizes those impacts (NRC, 2007). Government agencies
consider the same factors as private owners as well as public
benefits of shore protection, such as greater recreational
opportunities from wider beaches, increased development
made possible by the shore protection (where applicable),
and public safety.
Accelerated sea-level rise would not change the character of
those considerations, but it would increase the magnitude
of both the benefits and the consequences (monetary and
otherwise) of shore protection. In some areas, accelerated
sea-level rise would lead communities that are unprotected
today to protect the shore; in other areas, the increased costs
of shore protection may begin to outweigh the benefits. No
published study provides a comprehensive assessment of
how sea-level rise changes the costs and benefits of shore
protection. However, the available evidence suggests that the
environmental and social impacts could increase more than
proportionately with the rate of sea-level rise (see Sections
6.3 and 6.4). A case study of Long Beach Island, New Jersey
(a densely developed barrier island with no high-rise build-
ings) concluded that shore protection is more cost-effective
than retreat for the first 50 to 100 cm of sea-level rise (Titus,
1990). If the rise continues to accelerate, however, then
eventually the costs of protection would rise more rapidly
than the benefits, and a strategic retreat would then become
the more cost-effective response, assuming that the island
could be sustained by a landward migration (see Box A1.2
in Appendix 1). An economic analysis by Yohe et al. (1996)
found that higher rates of sea-level rise make shore protec-
tion less cost-effective in marginal cases.
6,2,2 Regional Scale Factors
Potential benefits and consequences are usually the key
to understanding whether a particular project will be a-
dopted. At a broader scale, however, land use and shoreline
environment are often indicators of the likelihood of shore
protection. Land use provides an indicator of the demand for
protection, and the shoreline environment provides an indi-
cator of the type of shore protection that would be needed.
Most land along the mid-Atlantic ocean coast is either de-
veloped or part of a park or conservation area. This region
has approximately 1,100 kilometers (almost 700 miles) of
shoreline along the Atlantic Ocean. Almost half of this coast-
line consists of ocean beach resorts with dense development
and high property values. Federal shore protection has been
authorized along most of these developed shores. These
lands are fairly evenly spread throughout the mid-Atlantic
states, except Virginia (see Section Al.E.2.1 in Appendix 1).
However, a large part of the coast is owned by landowners
who are committed to allowing natural shoreline processes
to operate, such as The Nature Conservancy, National Park
Service (see Section 11.2.1), and U.S. Fish and Wildlife
Service. These shores include most of North Carolina's
Outer Banks, all of Virginia's Atlantic coast except for part
of Virginia Beach and a NASA installation, more than two-
thirds of the Maryland coast, and New York's Fire Island.
The rest of the ocean coast in this region is lightly developed,
yet shore protection is possible for these coasts as well due
to the presence of important coastal highways.
Development is less extensive along many estuaries than
along the ocean coast. The greatest concentrations of low-
lying undeveloped lands along estuaries are in North Caro-
lina, the Eastern Shore of Chesapeake Bay, and portions of
Delaware Bay. Development has come more slowly to the
lands along the Albemarle and Pamlico Sounds in North
Carolina than to other parts of the mid-Atlantic coast (Hart-
gen, 2003). Maryland law limits development along much of
the Chesapeake Bay shore (Section Al.F.2.1 in Appendix 1),
and a combination of floodplain regulations and aggressive
agricultural preservation programs limit development along
the Delaware Bay shore in Delaware (Section Al.D.2.2 in
Appendix 1). Yet there is increasing pressure to develop land
97
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Chapter >
along tidal creeks, rivers, and bays (USCOP, 2004; DNREC,
2000; Titus, 1998), and barrier islands are in a continual state
of redevelopment in which seasonal cottages are replaced
with larger homes and high-rises (e.g., Randall, 2003).
If threatened by rising sea level, these developed lands (e.g.,
urban, residential, commercial, industrial, transportation)
would require shore protection for current land uses to con-
tinue. Along estuaries, the costs of armoring, elevating, or
nourishing shorelines are generally less than the value of the
land to the landowner, suggesting that under existing trends
shore protection would continue in most of these areas. But
there are also some land uses for which the cost and effort of
shore protection may be less attractive than allowing the land
to convert to wetland, beach, or shallow water. Those land
uses might include marginal farmland, conservations lands,
portions of some recreational parks, and even portions of
back yards where lot sizes are large. Along the ocean, shore
protection costs are greater—but so are land values.
Shore protection is likely along much of the coastal zone,
but substantial areas of undeveloped (but developable)
lands remain along the mid-Atlantic estuaries, where either
shore protection or wetland migration could reasonably be
expected to occur (NRC, 2007; Yohe et al, 1996; Titus et
al., 1991). Plans and designs for the development of those
lands generally do not consider implications of future sea-
level rise (see Chapter 11). A series of studies have been
undertaken that map the likelihood of shore protection along
the entirety of the U. S. Atlantic Coast as a function of land
use (Nicholls et al, 2007; Titus, 2004, 2005; Clark, 2001;
Nuckols, 2001).
6,2.3 Coastal
Protection
Lands with substantial shore protection are more extensively
developed than similar lands without shore protection, both
because shore protection encourages development and
development encourages shore protection. People develop
f loodplains, which leads to public funding for flood control
structures, which in turn leads to additional development
in the area protected (e.g., Burby, 2006). Few studies have
measured this effect, but possible mechanisms include:
Flood insurance rates are lower in protected areas (see
Chapter 10);
Development may be allowed in locations that might
otherwise be off limits;
Erosion-based setbacks require less of a setback if shore
protection slows or halts erosion (see Section 6.1); and
Fewer buildings are destroyed by storms, so fewer post-
disaster decisions to abandon previously developed land
(e.g., Weiss, 2006) would be expected.
The impact of coastal development on shore protection is
more firmly established. Governments and private landown-
ers generally implement a shore protection project only when
the value of land and structures protected is greater than the
cost of the project (see Sections 6.1 and 12.2.3).
In the natural setting, sea-level rise can significantly alter
barrier islands and estuarine environments (see Chapters 3,
4, and 5). Because a policy of retreat allows natural processes
to work, the environmental impacts of retreat in a developed
area can be similar to the impacts of sea-level rise in the
natural setting, provided that management practices are
adopted to restore lands to approximately their natural con-
dition before they are inundated, eroded, or flooded. In the
absence of management practices, possible environmental
implications of retreat include:
Contamination of estuarine waters from flooding of
hazardous waste sites (Flynn et al., 1984) or areas where
homes and businesses store toxic chemicals;
• Increased flooding (Wilcoxen, 1986; Titus et al., 1987)
or infiltration into public sewer systems (Zimmerman
and Cusker, 2001);
Groundwater contamination as septic tanks and their
drain fields become submerged;
Debris from abandoned structures; and
Interference with the ability of wetlands to keep pace
or migrate inland due to features of the built landscape
(e.g., elevated roadbeds, drainage ditches, and imper-
meable surfaces).
Shore protection generally has a greater environmental im-
pact than retreat (see Table 6.1). The impacts of beach nour-
ishment and other soft approaches are different than the im-
pacts of shoreline armoring.
Beach nourishment affects the environment of both the
beach being filled and the nearby seaf loor "borrow areas"
that are dredged to provide the sand. Adding large quanti-
ties of sand to a beach is potentially disruptive to turtles
and birds that nest on dunes and to the burrowing species
that inhabit the beach (NRC, 1995), though less disruptive
in the long term than replacing the beach and dunes with a
hard structure. The impact on the borrow areas is a greater
concern: the highest quality sand for nourishment is often
contained in a variety of shoals which are essential habitat
for shellfish and related organisms (USACE, 2002). For this
reason, the U.S. Army Corps of Engineers has denied per-
mits to dredge sand for beach nourishment in New England
(e.g., NOAA Fisheries Service, 2008; USACE, 2008a). As
technology improves to recover smaller, thinner deposits of
98
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Table 6.1 Selected Measures for Responding to Sea-Level Rise: Objective and Environmental Effects
Measure
Breakwater
Groin
rmoring that interferes with waves and c
Reduces erosion
Reduces erosion
Key Environmental Effects
urrents
May attract marine life; downdrift erosion
May attract marine life; downdrift erosion
Seawall
Bulkhead
Revetment
Dike
Tide gate
Storm surge barrier
^J ^f^^Tf^J^PJfi
Dune
Beachfill
Elevate land and
structures
Retreat
Setback
Rolling easement
Density or size
restriction
Reduces erosion, protects against flood
and wave overtopping
Reduces erosion, protects new landfill
Reduces erosion, protects land from
storm waves, protects new landfill
tUwStn-Mn fffflmii!' ^y^ffl TTJBMfS!
Prevents flooding and permanent
inundation (when combined with a
drainage system)
Reduces tidal range by draining water at
low tide and closing at high tide
Eliminates storm surge flooding; could
protect against all floods if operated on a
tidal schedule
Elimination of beach; scour and deepening in
front of wall; erosion exacerbated at terminus
Prevents inland migration of wetlands and
beaches; wave reflection erodes bay bottom,
preventing submerged aquatic vegetation;
prevents amphibious movement from water
to land
Prevents inland migration of wetlands and
beaches; traps horseshoe crabs and prevents
amphibious movement; may create habitat for
oysters and refuge for some species
Prevents wetlands from migrating inland;
thwarts ecological benefits of floods (e.g.,
annual sedimentation, higher water tables,
habitat during migrations, productivity
transfers)
Restricts fish movement; reduced tidal range
reduces intertidal habitat; may convert saline
habitat to freshwater habitat
Necessary storm surge flooding in salt
marshes is eliminated
Protects inland areas from storm waves;
provides a source of sand during storms
to offset erosion
Reverses shore erosion, and provides
some protection from storm waves
Avoids flooding and inundation from sea-
level rise by elevating everything as much
as sea rises
Delay the need for shore protection by
keeping development out of the most
vulnerable lands
Prohibit shore protection structures
Reduce the benefits of shore protection
and thereby make it less likely
Can provide habitat; can set up habitat for
secondary dune colonization behind it
Short-term loss of shallow marine habitat;
could provide beach and dune habitat
Deepening of estuary unless bay bottoms are
elevated as well
Impacts of shore protection delayed until
shore erodes up to the setback line; impacts of
development also reduced
Impacts of shore protection structures
avoided
Depends on whether owners of large lots
decide to protect shore; impacts of intense
development reduced
99
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Chapter >
sand offshore, a greater area of ocean floor must be disrupted
to provide a given volume of sand. Moreover, as sea level
rises, the required volume is likely to increase, further ex-
panding the disruption to the ocean floor.
As sea level rises, shoreline armoring eventually eliminates
ocean beaches (IPCC, 1990); estuarine beaches (Titus, 1998),
wetlands (IPCC, 1990), mudflats (Galbraithe/a/, 2002), and
very shallow open water areas by blocking their landward
migration. By redirecting wave energy, these structures can
increase estuarine water depths and turbidity nearby, and
thereby decrease intertidal habitat and submerged aquatic
vegetation. The more environmentally sensitive "living
shoreline" approaches to shore protection preserve a narrow
strip of habitat along the shore (NRC, 2007); however, they
do not allow large-scale wetland migration. To the extent
that these approaches create or preserve beach and marsh
habitat, it is at the expense of the shallow water habitat that
would otherwise develop at the same location.
The issue of wetland and beach migration has received
considerable attention in the scientific, planning, and legal
literature for the last few decades (Earth and Titus, 1984;
NRC, 1987; IPCC, 1990). Wetlands and beaches provide
important natural resources, wildlife habitat, and storm
protection (see Chapter 5). As sea level rises, wetlands and
beaches can potentially migrate inland as new areas become
subjected to waves and tidal inundation—but not if human
activities prevent such a migration. For example, early esti-
mates (e.g., U.S. EPA, 1989) suggested that a 70 cm rise in
sea level over the course of a century would convert 65 per-
cent of the existing mid-Atlantic wetlands to open water, and
that this region would experience a 65 percent overall loss
if all shores were protected so that no new wetlands could
form inland. That loss would only be 27 percent, however, if
new wetlands were able to form on undeveloped lands, and
16 percent if existing developed areas converted to marsh
as well. The results in Chapter 4 are broadly consistent with
the 1989 study.
Very little land has been set aside for the express purpose of
ensuring that wetlands and other tidal habitat can migrate
inland as sea level rises (see Chapter 11 of this Product;
Titus, 2000), but those who own and manage estuarine con-
servation lands do allow wetlands to migrate onto adjacent
dry land. With a few notable exceptions7, the managers of
most conservation lands along the ocean and large bays al-
low beaches to erode as well (see Chapter 11). The potential
for landward migration of coastal wetlands is limited by the
7 Exceptions include Cape May Meadows in New Jersey (protect-
ing freshwater wetlands near the ocean), beaches along both sides
of Delaware Bay (horseshoe crab habitat) and Assateague Island,
Maryland (to prevent the northern part of the island from disintegrat-
ing)-
likelihood that many shorelines will be preserved for exist-
ing land uses (e.g., U.S. EPA, 1989; IPCC, 1990; Nicholls
et al, 1999). Some preliminary studies (e.g., Titus, 2004)
indicate that in the mid-Atlantic region, the land potentially
available for new wetland formation would be almost twice
as great if future shore protection is limited to lands that
are already developed, than if both developed and legally
developable lands are protected.
6.4.1 Short-Term Consequences
Shore protection generally is designed to enable existing
land uses to continue. By insulating a community from ero-
sion, storms, and other hazards, the social consequences of
sea-level rise can be minimal, at least for the short term. In
the Netherlands, shore protection helped to foster a sense of
community as residents battled a common enemy (Disco,
2006). In other cases, the interests of some shorefront prop-
erty owners may diverge from the interests of other residents
(NRC, 2007). For example, many property owners in parts
of Long Beach Island, New Jersey strongly supported beach
nourishment—but some shorefront owners in areas with
wide beaches and dunes have been reluctant to provide the
state with the necessary easements (NJDEP, 2006; see Sec-
tion A1.C.2 in Appendix 1).
Allowing shores to retreat can be disruptive. If coastal ero-
sion is gradual, one often sees a type of coastal blight in what
would otherwise be a desirable community, with exposed
septic tanks and abandoned homes standing on the beach,
and piles of rocks or geotextile sand bags in front of homes
that remain occupied (Figures 6.8b and 6.9). If homes are
destroyed during a storm, communities can be severely dis-
rupted by the sudden absence of neighbors who previously
contributed to the local economy and sense of community
(IPCC, 1990; Perrin et al, 2008; Birsch and Wachter, 2006).
People forced to relocate after disasters are often at increased
risk to both health problems (Yzermans et al., 2005) and
depression (Najarian et al., 2001).
6,4,2 Long-Term Consequences
The long-term consequences of a retreat can be similar to
the short-term consequences. In some areas, however, the
consequences may become more severe over time. For ex-
ample, a key roadway originally set far back from the shore
may become threatened and have to be relocated. In the
case of barrier islands, the long-term implications of retreat
depend greatly on whether new land is created on the bay
side to offset oceanfront erosion (see Section 12.2.1). If so,
100
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
(a)
Figure 6.9 The adverse impacts of retreat on safety and aesthetic appeal of recreational beaches, (a) Exposed septic tank and con-
demned houses at Kitty Hawk, North Carolina (June 2002); (b) Beach unavailable for recreation where homes were built to withstand
shore erosion and storms, at Nags Head, North Carolina (June 2007) [Photo source: ®James G. Titus, used with permission].
communities can be sustained as lost oceanfront homes are
rebuilt on the bay side; if not, the entire community could
be eventually lost.
The long-term consequences of shore protection could be
very different from the short-term consequences. As dis-
cussed below, shore protection costs could escalate. The
history of shore protection in the United States suggests that
some communities would respond to the increased costs by
tolerating a lower level of shore protection, which could lead
eventually to dike failures (Seed et al., 2005; Collins, 2006)
and resulting unplanned retreat. In other cases, communi-
ties would not voluntarily accept a lower level of protection,
but the reliance on state or federal funding could lead to a
lower level while awaiting funds (a common situation for
communities awaiting beach nourishment). For communities
that are able to keep up with the escalated costs, tax burdens
would increase, possibly leading to divisive debates over a
reconsideration of the shore protection strategy.
6.5 HOW SUSTAINABLE ARE SHORE
PROTECTION AND RETREAT?
Coastal communities were designed and built without
recognition of rising sea level. Thus, people in areas
without shore protection will have to flood-proof structures
(see Section 9.7.2), implement shore protection, (Section
6.1.1) or plan a retreat (Section 6.1.2). Those who inhabit
areas with shore protection are potentially vulnerable as
well. Are the known approaches to shore protection and
retreat sustainable? That is: can they be maintained for the
foreseeable future?
Most shore protection structures are designed for current sea
level and may not accommodate a significant rise. Seawalls
(Kyperand Sorenson, 1985; NRC, 1987), bulkheads (Soren-
son et al., 1984.), dikes, (NRC, 1987), sewers (Wilcoxen,
1986), and drainage systems (Titus et al., 1987) are designed
based on the waves, water levels, and rainfall experienced
in the past. If conditions exceed what the designers expect,
disaster can result—especially when sea level rises above
the level of the land surface. The failure of dikes protecting
land below sea level resulted in the deaths of approximately
1800 people in the Netherlands in a 1953 storm (Roos and
Jonkman, 2006), and more than 1000 people in the New
Orleans area from Hurricane Katrina in 2005 (Knabb et al.,
2005). A dike along the Industrial Canal in New Orleans
which failed during Katrina had been designed for sea level
approximately 60 cm lower than today, because designers
did not account for the land subsidence during the previous
50 years (Interagency Performance Evaluation Taskforce,
2006).
One option is to design structures for future conditions.
Depending on the incremental cost of designing for higher
sea level compared with the cost of rebuilding later, it may
be economically rational to build in a safety factor today
to account for future conditions, such as higher and wider
shore protection structures (see Section 10.5). But doing so is
not always practical. Costs generally rise more than propor-
tionately with higher water levels8. Project managers would
generally be reluctant to overdesign a structure for today's
conditions (Schmeltz, 1984). Moreover, aesthetic factors
such as loss of waterfront views or preservation of historic
structures (e.g., Charleston Battery in South Carolina, see
Figure 6.10) can also make people reluctant to build a dike
or seawall higher than what is needed today.
6.5.1 Is "Business as Usual" Shore
Protection Sustainable?
Public officials and property owners in densely developed
recreational communities along the mid-Atlantic coast
generally expect governmental actions to stabilize shores.
But no one has assessed the cost and availability of sand
5 Weggel et al. (1989) estimate that costs are proportional to the height
of the design water level raised to the 1.5 power.
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The U.S. Climate Change Science Program
Chapter 6
Figure 6.10. Historic homes along the Charleston Battery. Charleston, South Carolina (April 2004). [Photo source: ®James G.
Titus, used with permission]
required to keep the shorelines in their current locations
through beach nourishment even if required sand is pro-
portional to sea-level rise, which previous assessments of
the cost of sea-level rise have assumed (e.g., U.S. EPA,
1989; Leatherman, 1989; Titus et al., 1991). The prospects
of barrier island disintegration and segmentation examined
in Chapter 3 would require much more sand to stabilize the
shore. Maintaining the shore may at first seem to require
only the simple augmentation of sand along a visible beach,
but over a century or so other parts of the coastal environ-
ment would capture increasing amounts of sand to maintain
elevation relative to the sea. In effect, beach nourishment
would indirectly elevate those areas as well (by replacing
sand from the beach that is transported to raise those areas),
including the ocean floor immediately offshore, tidal deltas,
and eventually back-barrier bay bottoms and the bay sides
of barrier islands. Similarly, along armored shores in urban
areas, land that is barely above sea level today would become
farther and farther below sea level, increasing the costs of
shore protection and setting up greater potential disasters
in the event of a dike failure. It is not possible to forecast
whether these costs will be greater than what future gen-
erations will choose to bear. But in those few cases where
previous generations have bequeathed this generation with
substantial communities below sea level, a painful involun-
tary relocation has sometimes occurred after severe storms
(e.g., New Orleans after Katrina).
Most retreat policies are designed for current rates of sea-
level rise and would not necessarily accommodate a signifi-
cant acceleration in the rate of sea-level rise. Erosion-based
setbacks along ocean shores generally require homes to be
set back from the primary dune by a distance equal to the
annual erosion rate times a number of years intended to rep-
resent the economic lifetime of the structure (e.g., in North
Carolina, 60 years times the erosion rate for large buildings;
see Section Al.G.l in Appendix 1). If sea-level rise acceler-
ates and increases the erosion rate, then the buildings will not
have been protected for the presumed economic lifetimes.
Yet larger setback distances may not be practicable if they
exceed the depth of buildable lots. Moreover, erosion-based
setback policies generally do not articulate what will hap-
pen once shore erosion consumes the setback. The retreat
policies followed by organizations that manage undeveloped
land for conservation purposes may account for foreseeable
erosion, but not for the consequences of an accelerated ero-
sion that consumes the entire coastal unit.
6.5.2 Sustainable Shore Protection May
Require Regional Coordination
Regional Sediment Management is a strategy for managing
sand as a resource (NRC, 2007). The strategy recognizes
that coastal engineering projects have regional impacts on
sediment transport processes and availability. This approach
includes:
Conservation and management of sediments along the
shore and immediate offshore areas, viewing sand as
a resource;
Attempt to design with nature, understanding sediment
movement in a region and the interrelationships of
projects and management actions;
Conceptual and programmatic connections among all
activities that involve sediment in a region (e.g., navi-
gation channel maintenance, flood and storm damage
reduction, ecosystem restoration and protection, ben-
eficial uses of dredged material);
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Coastal to
A Focus on the Mid-Atlantic Region
Connections between existing and new projects to use
sediment more efficiently;
Improved program effectiveness through collaborative
partnerships between agencies; and
Overcoming institutional barriers to efficient manage-
ment (Martin, 2002).
The Philadelphia and New York Districts of the U.S. Army
Corps of Engineers have a joint effort at regional sediment
management for the Atlantic coast of New Jersey (USAGE,
2008b). By understanding sediment sources, losses, and
transport, how people have altered the natural flow, and
ways to work with natural dynamics, more effective re-
sponses to rising sea level are possible.
One possible way to promote better regional sediment man-
agement would be the development of a set of "best sediment
management practices". Previously, standard practices have
been identified to minimize the runoff of harmful sediment
into estuaries (NJDEP, 2004; City of Santa Cruz, 2007). A
similar set of practices for managing sediments along shores
could help reduce the environmental and economic costs of
shore protection, without requiring each project to conduct
a regional sediment management study.
6,5,3 or a to
of
The economic feasibility of sustained shore protection as
sea level rises is unknown, as is the political and social
feasibility of a planned retreat away from the shore. The
absence of a comprehensive long-term shoreline plan often
leaves property owners with the assumption that the exist-
ing development can and should be maintained. Property-
specific shoreline armoring and small beach nourishment
projects further reinforce the expectation that the existing
shoreline will be maintained indefinitely, often seeming to
justify additional investments by property owners in more
expensive dwellings (especially if there is a through-road
parallel to the shore).
Shore protection generally limits flexibility more than
retreat. Once shore protection starts, retreat can be very
difficult to enact because the protection influences expecta-
tions and encourages investments, which in turn increases
the economic justification for continued shore protection. A
policy of retreat can be more easily replaced with a policy
of shore protection because people do not make substantial
investments on the assumption that the shore will retreat.
This is not to say that all dikes and seawalls would be main-
tained and enlarged indefinitely if sea level continues to rise.
Nevertheless, the abandonment of floodprone communities
rarely (if ever) occurs because of the potential vulnerability
or cost of flood protection, but rather in the aftermath of a
flood disaster (e.g., Missouri State Emergency Management
Agency, 1995).
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The U.S. Climate Change Science Program Chapter 6
104
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Population, Land Use, and
Infrastructure
Lead Authors: Stephen K. Gill, NOAA; Robb Wright, NOAA;
James G. Titus, U.S. EPA
Contributing Authors: Robert Kafalenos, US DOT; Kevin Wright,
ICF International, Inc.
KEY FINDINGS
The comprehensive, high-resolution, and precise analyses of the spatial distributions of population and
infrastructure vulnerable to sea-level rise in the Mid-Atlantic required for planning and response do
not exist at the present time. Existing studies do not have the required underlying land elevation data
with the degree of confidence necessary for local and regional decision making (see Chapter 2 of this
Product).
Existing generalized data can only support a range of estimates. For instance, in the Mid-Atlantic, be-
tween approximately 900,000 and 3,400,000 people (between 3 and 10 percent of the total population
in the mid-Atlantic coastal region) live on parcels of land or city blocks with at least some land less than
I meter above monthly highest tides. Approximately 40 percent of this population is located along the
Atlantic Ocean shoreline or small adjacent inlets and coastal bays (as opposed to along the interior
shorelines of the large estuaries, such as Delaware Bay and Chesapeake Bay).
Agriculture lands, forests, wetlands,
and developed lands in lower eleva-
tion areas are likely to be most im-
pacted by a I-meter sea-level rise for
the Mid-Atlantic.
The coupling of sea-level rise with
storm surge is one of the most im-
portant considerations for assessing
impacts of sea-level rise on infrastruc-
ture. Sea-level rise poses a risk to
transportation in ensuring reliable and
sustained transportation services.
105
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Chapter 7
7.J
Coastal areas in the United States have competing interests
of population growth (accompanied by building of the neces-
sary supporting infrastructure), the preservation of natural
coastal wetlands, and creation of buffer zones. Increasing
sea level will put increasing stress on the ability to manage
these competing interests effectively and in a sustained
manner. This Chapter examines the current population,
infrastructure, and socioeconomic activity that may poten-
tially be affected by sea-level rise.
'-. •/':;.-_• ••. '•.;• :>. " .*••••.
The population assessment for the Mid-Atlantic can be put
into a regional perspective by first examining some recent
national statistics and trends that illustrate the relative so-
cioeconomic stress on our coasts:
Using an analysis of coastal counties defined to have
a coastline bordering the ocean or associated water
bodies, or those containing special velocity zones (V
Zones) defined by the Federal Emergency Management
Administration (FEMA), Crowell etal. (2007) estimate
that 37 percent of the total U.S. population is found in
364 coastal counties, including the Great Lakes. Ex-
cluding the Great Lakes counties, 30 percent of the total
U.S. population is found in 281 coastal counties.
Using an analysis with a broader definition of a coastal
county to include those found in coastal watersheds in
addition to those bordering the ocean and associated
water bodies, the National Oceanic and Atmospheric
Administration (NOAA) estimates that U.S. coastal
counties, including the Great Lakes and excluding
Alaska, contain 53 percent of the nation's population,
yet account for only 17 percent of the total U.S. land
area (Crossett et al, 2004).
Twenty-three of the 25 most densely populated U.S.
counties are coastal counties. From 1980 to 2003,
population density (defined as persons per unit area)
increased in coastal counties by 28 percent and was
expected to increase another 4 percent by 2008 (Cros-
sett et al, 2004).
Construction permits can be used to indicate economic
growth and urban sprawl. More than 1,540 single fam-
ily housing units are permitted for construction every
day in coastal counties across the United States. From
1999 to 2003,2.8 million building permits were issued
for single family housing units (43 percent of U.S.
total) and 1.0 million building permits were issued for
multi-family housing units (51 percent of the U. S. total)
(Crossett et al, 2004).
• In 2000, there were approximately 2.1 million seasonal
or vacation homes in coastal counties (54 percent of the
U.S. total) (Crossett et al, 2004).
Regional trends for the Mid-Atlantic can also be summa-
rized, based on Crossett et al. (2004). This Product includes
the mid-Atlantic states, defined in the report to include the
area from New York to Virginia, as part of their defined
Northeast region, with North Carolina included in the
Southeast region. The statistics serve to illustrate the relative
vulnerability of the coastal socioeconomic infrastructure,
either directly or indirectly, to sea-level rise.
Of the 10 largest metropolitan areas in the United States,
three (New York, Washington, D.C., and Philadelphia)
are located in the coastal zone of the mid-Atlantic
region.
The coastal population in the Northeast (Maine to
Virginia) is expected to increase by 1.7 million people
from 2003 to 2008, and this increase will occur mostly
in counties near or in major metropolitan centers. Six
of the counties near metropolitan areas with the largest
expected population increases are in the New York City
area and four are in the Washington, D.C. area.
The greatest percent population changes from 2003
to 2008 in the U.S. Northeast are expected to occur in
Maryland and Virginia. Eight of the 10 coastal coun-
ties with the greatest expected percent population
increases are located in Virginia and two are located
in Maryland.
North Carolina coastal counties rank among the highest
in the U.S. Southeast for expected percent population
change from 2003 to 2008. For instance, Brunswick
County is expected to have the greatest percent increase,
at 17 percent.
Crossett et al. (2004) show the mid-Atlantic states in context
with the larger Atlantic Coast region. By presenting total
land area and coastal land area, as well as total and coastal
county population statistics, both in absolute numbers and
in population density, the NOAA report quantifies the so-
cioeconomic stressor of population change on the coastal
region. As pointed out by Crowell et al. (2007), the coastal
counties used in the NOAA study represent counties in a
broader watershed area that include more than those coun-
ties that border the land-water interface and that detailed
analyses and summary statistics for populations at direct
risk for inundation due to sea-level rise must use only that
subset of coastal counties subject to potential inundation.
The analyses and statistics discussed in subsequent sections
of this Product use those subsets. Crossett et al. (2004) is
used simply to illustrate the increasing stress on coastal areas
in general. The mid-Atlantic coastal counties are among the
106
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to
A Focus on the Mid-Atlantic Region
most developed and densely populated coastal areas in the
nation. It is this environment that coastal managers must
plan strategies for addressing impacts of climate change,
including global sea-level rise.
Several regionally focused reports on examining popula-
tions at risk to sea-level rise in the Mid-Atlantic are found
in the literature. For example, Gornitz etal. (2001) includes
a general discussion of population densities and flood risk
zones in the New York metropolitan region and examines
impacts of sea-level rise on this area. In this report, the au-
thors also consider that low-lying areas will be more at risk
to episodic flooding from storm events because storm tide
elevations for a given storm will be higher with sea-level
rise than without. They suggest that the overall effect for
any given location will be a reduction in the return period
of the 100-year storm flooding event. A similar analysis
was performed for the Hampton Roads, Virginia area by
Kleinosky et al. (2006) that attempts to take into account
increased population scenarios by 2100.
Bin et al. (2007) studied the socioeconomic impacts of sea-
level rise in coastal North Carolina, focusing on four rep-
resentative coastal counties (New Hanover, Dare, Carteret,
and Bertie) that range from high development to rural, and
from marine to estuarine shoreline. Their socioeconomic
analyses studied impacts of sea-level rise on the coastal
real estate market and coastal recreation and tourism, and
the impacts of tropical storms and hurricanes on business
activity using a baseline year of 2004.
Comprehensive assessments of impacts of sea-level rise on
transportation and infrastructure are found in the CCSP
Synthesis and Assessment Product (SAP) 4.7 (CCSP, 2008),
which focuses on the Gulf of Mexico, but provides a general
overview of the scope of the impacts on transportation and
infrastructure. In the Mid-Atlantic, focused assessments on
the effects of sea-level rise to infrastructure in the New York
City area are available in Jacob et al. (2007).
Some of the recent regional population and infrastructure
assessments typically use the best available information
layers (described in the following section), gridded eleva-
tion data, gridded or mapped population distributions, and
transportation infrastructure maps to qualitatively depict
areas at risk and vulnerability (Gornitz et al., 2001). The
interpretation of the results from these assessments is lim-
ited by the vertical and horizontal resolution of the various
data layers, the difference in resolution and matching of the
fundamental digital-layer data cells, and the lack of spatial
resolution of the population density and other data layers
within the fundamental area blocks used (see Chapter 2 for
further discussion). As discussed in Chapter 2, the available
elevation data for the entire mid-Atlantic region do not sup-
port inundation modeling for sea-level rise scenarios of 1
meter or less. Therefore, the results reported in this Chapter
should not be considered as reliable quantitative findings,
and they serve only as demonstrations of the types of analy-
ses that should be done when high-accuracy elevation data
become available.
In this Chapter, the methodology for addressing population
and land use utilizes a Geographic Information Systems
(GIS) analysis approach, creating data layer overlays and
joining of data tables to provide useful summary informa-
tion. GIS data are typically organized in themes as data
layers. Data can then be input as separate themes and
overlaid based on user requirements. Essentially, the GIS
analysis is a vertical layering of the characteristics of the
Earth's surface and is used to logically order and analyze
data in most GIS software. Data layers can be expressed
visually as map layers with underlying tabular information
of the data being depicted. The analysis uses data layers of
information and integrates them to obtain the desired output
and estimated uncertainties in the results. The GIS layers
used here are population statistics, land use information,
and land elevation data.
The population and land use statistics tabulated in the
regional summary tables (Tables 7.1 through 7.6) use an
area-adjusted system that defines regions and subregions
for analysis such that they are (1) higher than the zero
reference contour (Spring High Water) used in a vertical
datum-adjusted elevation model, and (2) not considered a
wetland or open water, according to the state and National
Wetlands Inventory wetlands data compiled by the U. S. Fish
and Wildlife Service (USFWS, 2007). Uncertainties are
expressed in the tables in terms of low and high statistical
estimates (a range of values) in each case to account for the
varying quality of topographic information and the varying
spatial resolution of the other data layers. The estimated
elevation of spring high water is used as a boundary that
distinguishes between normal inundation that would oc-
cur due to the normal monthly highest tides and the added
inundation due to a 1-meter (m) rise in sea level (Titus and
Cacela, 2008).
Census block statistics determined for the estimated area
and the percent of a block affected by sea-level rise and
the estimated number of people and households affected
by sea-level rise are based on two methods: (1) a uniform
distribution throughout the block and (2) a best estimate
based on assumptions concerning elevation and population
density. For instance, there is an uncertainty regarding where
the population resides within the census block, and the re-
107
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The U.S. Climate Change Science Program
Chapter 7
lationship between the portion of a block's area that is lost
to sea-level rise and the portion of the population residing
in the vulnerable area is also uncertain. Analysis estimates
of vulnerable population are based on the percentage of a
census block that is inundated. Homes are not necessarily
distributed uniformly throughout a census block. In addi-
tion, the differences in grid sizes between the census blocks
and the elevation layers result in various blocks straddling
differing elevation grids and add to the uncertainty of the
process.
Discussion on coastal elevations and mapping limitations
and uncertainties as applied for inundation purposes is
provided in Chapter 2. Given these limitations and uncer-
tainties, the population and land use analyses presented here
are only demonstrations of techniques using a 1-m sea-level
rise scenario. More precise quantitative estimates require
high-resolution elevation data and population data with
better horizontal resolution.
Figure 7.1 illustrates the three GIS data layers used in the
population and land use analysis: the elevation layer (Titus
and Wang, 2008), a census layer (GeoLytics, 2001), and a
land use layer (USGS, 2001).
Figures 7.2, 7.3, and 7.4 show the fundamental underlying
layers used in this study, using Delaware Bay as an example.
The GIS layers used here are:
Elevation data: The elevation data is the driving pa-
rameter in the population analysis. The elevation data
Input Data Layers
is gridded into 30-m pixels throughout the region. All
other input datasets are gridded to this system from their
source format (Titus and Wang, 2008). The elevations
are adjusted such that the zero-contour line is set rela-
tive to the Spring High Water vertical datum, which is
interpolated from point sources derived from NOAA
tide station data (Titus and Cacela, 2008).
Census data: Census 2000 dataset (GeoLytics, 2001) is
used in the analysis. Block boundaries are the finest-
scale data available, and are the fundamental units of
area of the census analysis. Tract, county, and state
boundaries are derived from appropriate aggregations
from their defining blocks. The census tract boundaries
are the smallest census unit that contain property and
tax values. Tract and county boundaries also extend
fully into water bodies. For this analysis, these bound-
aries are cropped back to the sea-level boundary, but
source census data remain intact.
Land use data: The National Land Cover Data (NLCD)
(USGS, 2001) dataset is used in this analysis. It consists
of a 30-m pixel classification from circa 2001 satellite
imagery and is consistently derived across the region.
The caveat with the product is that pixels are classified
as "wetland" and "open water" in places that are not
classified as such by the wetland layer. Wetland layers
are derived from state wetlands data (Titus and Wang,
2008). Usually, the NLCD Wetland class turns out to be
forested land and the water tends to be edge effects (or
uncertainty due to lack of resolution) along the shore or
near farm ponds. This analysis folds the NLCD wetland
pixels into forested land.
Census Layer
Land Use Layer
DEM Elevation Layer
1 1
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s 1
** i
W* 1
nw t
s !
-
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ti ;: ii
*« i" » 11 M
»l
• 1 I '
*i 'j " « MI
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-
Figure 7.1 The three input data layers to the GIS analysis.
Figure 7.2 presents an example of the county
overlay, and Figure 7.3 provides an example
of the census tract overlay. A census tract
is a small, relatively permanent statistical
subdivision of a county used for presenting
census data. Census tract boundaries nor-
mally follow visible features such as roads
and rivers, but may follow governmental
unit boundaries and other non-visible fea-
tures in some instances; they are always
contained within counties. Census tracts are
designed to be relatively homogeneous units
with respect to population characteristics,
economic status, and living conditions at
the time of establishment, and they average
about 4,000 inhabitants. The tracts may be
split by any sub-county geographic entity.
Figure 7.4 provides an example of the
census block overlay. A census block is a
subdivision of a census tract (or, prior to
2000, a block numbering area). A block is
108
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Delaware Bay County Overlay
Delaware Bay Census Tract Overlay
Figure 7.2 The county overlay example for Delaware
Bay with each colored area depicting a county.
Delaware Bay Census Block Overlay
Figure 7.3 The census tract overlay example for Delaware
Bay with each colored area depicting a census tract.
the smallest geographic unit for which the Census Bureau
tabulates data. Many blocks correspond to individual city
blocks bounded by streets; however, blocks—especially in
rural areas—may include many square kilometers and due
to lack of roads, may have some boundaries that are other
features such as rivers and streams. The Census Bureau
established blocks covering the entire nation for the first
time in 1990. Previous censuses back to 1940 had blocks
established only for part of the United States. More than 8
million blocks were identified for Census 2000 (U. S. Census
Bureau, 2007).
The Digital Elevation Model (DEM) (Titus and Wang, 2008)
was the base for this analysis. The areas of various land use,
counties, tracts, and blocks are rasterized (converted in a
vector graphics format [shapes]) into a gridded raster image
(pixels or dots) to the DEM base. This ensures a standard
projection (an equal-area projection), pixel size (30 m), grid
system (so pixels overlay exactly), and geographic extent.
A GIS data layer intersection was completed for each of
the geographic reporting units (land use, county, tract, and
block) with elevation ranges to produce a table of unique
combinations.
Figure 7.4 The census block overlay example for Delaware Bay
with gray lines outlining individual areas of a census block.
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The U.S. Climate Change Science Program
Chapter 7
Mid-Atlantic Watersheds
Figure 7.5 The mid-Atlantic region generalized watersheds.
This Chapter examines the mid-Atlantic region and makes
some inferences on the populations that may be affected
by sea-level rise. This assessment divides the mid-Atlantic
region into sub-regions defined by watersheds (Crossett et
al., 2004), as shown in Figure 7.5. The general populations
within the various watersheds, although sometimes in more
than one state, have to address common problems driven by
common topographies and natural hydrological regimes.
Most of the watershed boundaries are clear, for instance
the Potomac River and Chesapeake Bay. The watershed
boundaries used do not include the upland portions of the
watershed located in upland mountains and hills; those por-
tions are not required for the analyses of the low-lying areas.
The Atlantic Ocean watershed is the most complex because
it is not defined by a discrete estuarine river watershed
boundary, but by exposure to the outer coastline, and it has
components in several states.
7.3.1 Example Population Analysis Results
Not everyone who resides in a watershed lives in a low-
lying area that may be at risk to the effects of sea-level rise.
Table 7.1 provides a summary analysis of those populations
in each watershed at potential risk for a 1-m sea-level rise.
The low and high estimates in Table 7.1 provide the range
of uncertainty by using the low and high DEMs (Titus and
Wang, 2008; Titus and Cacela, 2008). The high elevation
is equal to the best estimate plus the vertical error of the
elevation data; the low elevation estimate is equal to the best
estimate minus the vertical error. The high vulnerability es-
timate uses the low elevation estimate because if elevations
are lower than expected a greater population is vulnerable.
Similarly, the low vulnerability estimate uses the high end
of the uncertainty range of elevation estimates. These DEMs
are required to express the uncertainty in the numerical
results because of the varying scales and resolutions of the
data in the various overlays (for instance, the census block
boundaries may not line up with specific elevation contours
being used and interpolation algorithms must be used to
derive population statistics within certain contour intervals.
As previously mentioned, this analysis is also limited by the
assumption that population has uniform density within the
inhabited portion of a particular census block. The census
data provide no information where the population resides
within a particular block.
The uncertainty in how much of a particular census tract or
block may be inundated must also be addressed by listing
high and low estimates. Table 7.1 is a maximum estimate
of the potential populations because it is for census blocks
that could have any inundation at all and thus includes a
maximum count. Similarly, it should be noted that Table 7.3
also provides maximum estimates for the Chesapeake Bay
and the Atlantic Ocean.
To illustrate the nature of using the various sets of data and
layers for analyses, and the uncertainty in the population dis-
tributions within a census block, a second type of analysis is
useful. Because there is an uncertainty regarding where the
population resides within the census block, the relationship
Table 7.1 Estimated Mid-Atlantic Low and High
Population Estimates by Watershed for a I-Meter Sea-
Level Rise (population is based on Census 2000 data).
The reported numbers are subject to the caveat given
at the end of Section 7.2.
Long Island Sound
Peconic Bay
NYH-Raritan Bay
Delaware Bay
Delaware River
Chesapeake Bay
Potomac River
Albemarle Sound
Pamlico Sound
Atlantic Ocean
All Watersheds
1,640
7,870
35,960
22,660
19,380
326,830
61,140
69,720
362,800
908,020
191,210
29,140
678,670
62,770
239,480
807,720
124,510
75,830
147,290
1,109,280
3,465,940
110
-------
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
between the portion of a block's
area that is lost to sea-level rise
and the portion of the popula-
tion residing in the vulnerable
area is also uncertain. Analysis
estimates of vulnerable popula-
tion are based on the percentage
of a census block that is inun-
dated. For instance, the total
2000 population low and high
estimated counts for a 1-m sea-
level rise for all watersheds are
908,020 and 3,465,940 for "any
inundation" of census block
(see Table 7.1). However, homes
are not necessarily distributed
uniformly throughout a census
block. If 10 percent of a block is
very low, for example, that land
may be part of a ravine, below a
bluff, or simply the low part of a
large parcel of land. Therefore,
the assumption of uniform den-
sity would often overstate the
vulnerable population. Table 7.2 provides estimates that
assume distributions other than uniform density regarding
the percentage of a block that must be vulnerable before
one assumes that homes are at risk. (This table presents the
results by state rather than by subregion.) If it is assumed
that 90 percent of a block must be lost before homes are at
risk, and that the population is uniformly distributed across
the highest 10 percent of the block, then between 26,000
and 959,000 people live less than one meter above the el-
evation spring high water (see NOAA, 2000 and Titus and
Wang, 2008), allowing for low and high elevation estimates.
The estimated elevation of spring high water is used as a
boundary that distinguishes between normal inundation that
would occur due to the normal monthly highest tides and the
added inundation due to a 1-m rise in sea level. The spread
of these estimated numbers, depending upon the underly-
ing assumptions listed at the end of Table 7.2, underscore
the uncertainty inherent in making population assessments
based in limited elevation data. As reported in Chapter 2,
the disaggregation of population density data into a more
realistic spatial distribution would be to use a Dasymetric
mapping technique (Mennis, 2003) which holds promise for
better analysis of population or other socioeconomic data,
and to report statistical summaries of sea-level rise impacts
within vulnerable zones.
The census information also allows further analysis of the
population, broken down by owner- and renter-occupied
residences. This information gives a sense of the character-
ization of permanent home owners versus the more transient
Table 7.2 Low and High Estimates of Population Living on Land Within I Meter Above
Spring High Water (using assumptions other than uniform population density about
how much of the land must be lost before homes are lost). The reported numbers
are subject to the caveat given at the end of Section 7.2.
Q^£ rHiiRiitrlHiIiTTiWWii FrH •JiTiT^''*H^E
NY
NJ
DE
PA
VA
MD
DC
NC
Total
780
12,540
480
640
950
610
0
1,920
17,920
421,900
302,800
7,200
7,830
59,310
4,840
0
14,140
818,020
780
15,770
810
640
1,020
1,890
0
5,320
26,230
470,900
352,510
9,230
8,940
84,360
8,040
0
25,090
959,070
2,610
41,260
2,040
1,530
5,190
4,380
0
17,450
74,460
685,500
498,650
16,650
15,090
173,950
17,710
40
60,090
1,467,680
42,320
177,500
44,290
10,360
232,120
46,890
0
283,590
837,070
1,126,290
834,440
85,480
43,450
662,400
137,490
9,590
345,530
3,244,670
' Population estimates in this column assume that no homes are vulnerable unless 99 percent of the
dry land in census block is within 1 meter above spring high water.
b Population estimates in this column assume that no homes are vulnerable unless 90 percent of the
dry land in census block is within 1 meter above spring high water.
c Population estimates in this column assume that no homes are vulnerable unless 50 percent of the
dry land in census block is within 1 meter above spring high water.
d Assumes uniform population distribution.
rental properties that could translate to infrastructure and
local economy at risk as well. The estimated number of
owner- and renter-occupied housing units in each watershed
are shown in Tables 7.3 and 7.4. Similar to the estimates in
Table 7.1, these are high estimates for which any portion of
a particular census block is inundated.
Table 7.3 Low and High Estimates of Number of Owner-
Occupied Residences in Each Watershed Region for a
I-Meter Sea-Level Rise Scenario. The reported numbers
are subject to the caveat given at the end of Section
7.2.
er-occupied residences
ter rise in sea
ow Estimate High Estimate
Long Island Sound
Peconic Bay
NYH-Raritan Bay
Delaware Bay
Delaware River
Chesapeake Bay
Potomac River
Albemarle Sound
Pamlico Sound
Atlantic Ocean
All Watersheds
0
3,400
13,440
8,720
6,010
120,790
0
22,760
26,730
140,670
342,520
0
11,650
269,420
23,610
89,710
299,550
46,070
28,720
52,450
423,540
1,244,720
III
-------
The U.S. Climate Change Science Program
Chapter 7
Table 7.4 Low and High Estimates of the Number of
Renter-Occupied Housing Units by Watershed for
a 1-Meter Sea-Level Rise Scenario. The reported
numbers are subject to the caveat given at the end
of Section 7.2.
umber of renter-occupied residenc.
I-meter rise in sea level
Long Island Sound
Peconic Bay
NYH-Raritan Bay
Delaware Bay
Delaware River
Chesapeake Bay
Potomac River
Albemarle Sound
Pamlico Sound
Atlantic Ocean
All Watersheds
70
520
4,270
2,630
2,110
35,880
5,260
6,000
40,220
96,960
30,010
2,460
178,790
5,880
32,760
84,630
17,470
6,830
10,660
154,500
524,990
The actual coastal population potentially affected by sea-
level rise also includes hotel guests and those temporarily
staying at vacation properties. Population census data on
coastal areas are rarely able to fully reflect the population
and resultant economic activity. The analysis presented in
this Product does not include vacant properties used for sea-
sonal, recreational, or occasional use, nor does it character-
ize the "transient" population, who make up a large portion
of the people found in areas close to sea level in the Mid-
Atlantic during at least part of the year. These temporary
residents include the owners of second homes. A significant
portion of coastal homes are likely to be second homes oc-
cupied for part of the year by owners or renters who list an
inland location as their permanent residence for purposes
of census data. In many areas, permanent populations are
expected to increase as retirees occupy their seasonal homes
for longer portions of the year.
7.4 LAND USE
The National Land Cover Database (USGS, 2001) is used to
overlay land use onto the DEMs for a 1-m scenario of sea-
level rise. Major land-use categories used for this analysis
include: agriculture, barren land, developed land, forest,
grassland, shrub-scrub, water, and wetland. An estimate of
the area of land categorized by land use for all watersheds for
the Mid-Atlantic is listed in Table 7.5. Table 7.6 provides in-
formation similar to Table 7.5, specific to each of the defined
watersheds. In the land use tables, ranges of uncertainty are
provided by showing the low and high estimated size of the
areas for the 1-m sea-level rise scenario. The high and low
estimates show significant differences in area and express
the uncertainty in using this type of data layer integration.
Table 7.5 Mid-Atlantic All Watersheds Summary
by Land Use Category, Depicting Low and High
Estimates of Areas Affected by a 1-Meter Sea-Level
Rise (in hectares; I hectare is equal to 2.47 acres). The
reported numbers are subject to the caveat given at
the end of Section 7.2.
Area (in hectares)
^^^^^^^^^^^^^^^^^^m
Agriculture
Barren Land
Developed
Forest
Grassland
Shrub-scrub
Water
Wetland
1 -meter rise in sea level
^^^v^^^^^^^^y^^t
43,180
5,040
11,970
27,050
7,640
3,790
1,960
34,720
141,800
14,750
92,950
94,280
14,200
7,720
4,110
66,590
The developed land-use acreage dominates northeast wa-
tersheds such as Long Island Sound and New York Harbor,
as well as the Atlantic Coast watershed. This is in contrast
to the Chesapeake Bay watershed that is dominated by ag-
riculture and forest.
7.5 TRANSPORTATION
INFRASTRUCTURE
7.5.1 General Considerations
The coupling of sea-level rise with storm surge is one of
the most important considerations for assessing impacts of
sea-level rise on infrastructure. Sea-level rise poses a risk to
transportation in ensuring reliable and sustained transporta-
tion services. Transportation facilities serve as the lifeline
to communities, and inundation of even the smallest com-
ponent of an intermodal system can result in a much larger
system shut-down. For instance, even though a port facility
or a railway terminal may not be affected, the access roads
to the port and railways could be, thus forcing the terminal
to cease or curtail operation.
Sea-level rise will reduce the 100-year flood return periods
and will lower the current minimum critical elevations of
infrastructure such as airports, tunnels, and ship terminals
(Jacob etal., 2007). Some low-lying railroads, tunnels, ports,
runways, and roads are already vulnerable to flooding and a
rising sea level will only exacerbate the situation by causing
more frequent and more serious disruption of transportation
services. It will also introduce problems to infrastructure
not previously affected by these factors.
The CCSP SAP 4.7 (Kafalenos et al, 2008) discusses
impacts of sea-level rise on transportation infrastructure
by addressing the impacts generally on highways, transit
systems, freight and passenger rail, marine facilities and
112
-------
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Table 7.6 Low and High Area Estimates by Land Use Category for the Mid-Atlantic for a I-Meter Sea-Level Rise
Scenario (in hectares). The reported numbers are subject to the caveat given at the end of Section 7.2.
Area (in
hectares)
,-meter rise in sea level
Watershed ^t a
Long Island
Sound
Agriculture
Barren Land
Developed
Forest
Grassland
Shrub-scrub
Water
Wetland
1
HPH
0
0
90
0
0
0
0
0
20
180
3,280
210
100
60
90
530
Peconic Bay
Agriculture
Barren Land
Developed
Forest
Grassland
Shrub-scrub
Water
Wetland
20
20
100
50
0
0
10
70
360
340
1,580
760
170
70
150
770
NYH-
Raritan Bay
Agriculture
Barren Land
Developed
Forest
Grassland
Shrub-scrub
Water
Wetland
30
40
330
40
0
0
9
140
870
340
21,090
720
10
10
230
2,600
Delaware
Bay
Agriculture
Barren Land
Developed
Forest
Water
Wetland
950
280
210
590
80
900
9,590
1,040
1,760
4,280
130
2,420
Delaware
River
Agriculture
Barren Land
Developed
Forest
Water
Wetland
310
20
430
90
20
330
8,190
560
10,960
2,130
200
3,010
n^Tares) 1 -meter rise in sea level
Chesapeake
Bay
Agriculture
Barren Land
Developed
Forest
Water
Wetland
11,180
2,070
2,220
9,100
160
5,010
40,460
4,650
13,180
38,370
660
14,280
Potomac
River
Agriculture
Barren Land
Developed
Forest
Water
Wetland
0
0
0
0
0
0
490
460
1,830
4,630
130
1,120
Albemarle
Sound
Agriculture
Barren Land
Developed
Grassland
Shrub-scrub
Forest
Water
Wetland
16,440
320
2,460
8,680
4,790
2,720
750
14,480
12,810
5,900
8,270
4,950
44,720
10
8,440
920
Pamlico
Sound
Agriculture
Barren Land
Developed
Forest
Grassland
Shrub-scrub
Water
Wetland
1,3130
470
1,620
5,490
2,010
670
210
8,500
3,9670
1,327
4,583
1,380
3,570
1,430
290
12,070
Atlantic
Ocean
Agriculture
Barren Land
Developed
Forest
Grassland
Shrub-scrub
Water
Wetland
1,090
1,800
4,470
2,980
820
380
690
5,260
8,20
5,410
29,210
11,540
2,010
1,360
1,210
10,870
113
-------
Chapter 7
waterways, aviation, pipelines, and implications for trans-
portation emergency management and also specifically for
the U.S. Gulf Coast region. Each of these transportation
modes also apply to the mid-Atlantic region.
One impact of sea-level rise not generally mentioned is
the decreased clearance under bridges. Even with precise
timing of the stage of tide and passage under fixed bridges,
sea-level rise will affect the number of low water windows
available for the large vessels now being built. Bridge clear-
ance has already become an operational issue for major
ports, as evidenced by the installation of real-time report-
ing air gap/bridge clearance sensors in the NOAA Physical
Oceanographic Real-Time System (PORTS) (NOAA, 2005).
Clearance under bridges has become important because the
largest vessels need to synchronize passage with the stage
of tide and with high waters due to weather effects and high
river flows. To provide pilots with this critical information,
air gap sensors in the Mid-Atlantic have been deployed at
the Verrazano Narrows Bridge at the entrance to New York
Harbor, the Chesapeake Bay Bridge located in mid-Chesa-
peake Bay, and on bridges at both ends of the Chesapeake
and Delaware Canal connecting the upper Chesapeake Bay
with mid-Delaware Bay (NOAA, 2008).
There are other potential navigation system effects as well
because of sea-level rise. Estuarine navigation channels may
need to be extended landward from where they terminate
now to provide access to a retreating shoreline. The corol-
lary benefit is that less dredging will be required in deeper
water because a rising water elevation will provide extra
clearance.
This discussion is limited in scope to transportation infra-
structure. Complete infrastructure assessments need to in-
clude other at-risk engineering and water control structures
such as spillways, dams, levees, and locks, with assessments
of their locations and design capacities.
of
The U.S. Department of Transportation (US DOT) studied
the impacts of sea-level rise on transportation, as discussed
in US DOT (2002). The study addresses the impacts of
sea-level rise on navigation, aviation, railways and tunnels,
and roads, and describes various options to address those
impacts, such as elevating land and structures, protecting
low-lying infrastructure with dikes, and applying retreat and
accommodation strategies.
The US DOT has recently completed an update of the first
phase of a study, "The Potential Impacts of Global Sea
Level Rise on Transportation Infrastructure" (US DOT,
2008). The study covers the mid-Atlantic region and is be-
ing implemented in two phases: Phase 1 focuses on North
Carolina, Virginia, Washington, D.C., and Maryland.
Phase 2 focuses on New York, New Jersey, Pennsylvania,
Delaware, South Carolina, Georgia, and the Atlantic Coast
of Florida. This second phase is expected to be completed
by the end of 2008. This study was designed to produce
rough quantitative estimates of how future climate change,
specifically sea-level rise and storm surge, might affect
transportation infrastructure on a portion of the East Coast
of the United States. The major purpose of the study is to aid
policy makers responsible for transportation infrastructure
including roads, rails, airports, and ports in incorporating
potential impacts of sea-level rise in planning and design
of new infrastructure and in maintenance and upgrade of
existing infrastructure.
The report considers that the rising sea level, combined with
the possibility of an increase in the number of hurricanes and
other severe weather-related incidents, could cause increased
inundation and more frequent flooding of roads, railroads,
and airports, and could have major consequences for port
facilities and coastal shipping.
The CIS approach (US DOT, 2008) produces maps and
statistics that demonstrate the location and quantity of trans-
portation infrastructure that could be regularly inundated
by sea-level rise and at risk to storm surge under a range of
potential sea-level rise scenarios. The elevation data for the
transportation facilities is the estimated elevation of the land
upon which the highway or rail line is built.
The three basic steps involved in the US DOT analysis help
identify areas expected to be regularly inundated or that are
at risk of periodic flooding due to storm surge:
Digital Elevation Models were used to evaluate the el-
evation in the coastal areas and to create tidal surfaces
in order to describe the current and future predicted
sea water levels.
Land was identified that, without protection, will regu-
larly be inundated by the ocean or is at risk of inundation
due to storm surge under each sea-level rise scenario.
Transportation infrastructure was identified that, with-
out protection, will regularly be inundated by the ocean
or be at risk of inundation due to storm surge under the
given sea-level rise scenario.
The US DOT study compares current conditions (for 2000)
to estimates of future conditions resulting from increases
in sea level. The study examines the effects of a range of
potential increases in sea level up to 59 centimeters (cm).
The estimates of increases in sea level are based upon two
sources: (1) the range of averages of the Atmosphere-Ocean
114
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
General Circulation Models for all 35 SRES (Special Report
on Emission Scenarios), as reported in Figure 11.121 from
the IPCC Third Assessment Report and (2) the highest sce-
nario (59 cm) that corresponds with the highest emissions
scenario modeled by the IPCC Fourth Assessment Report
(Meehle/a/.,2007).
As noted above, the US DOT study was not intended to
create a new estimate of future sea levels or to provide a
detailed view of a particular area under a given scenario;
similarly, the results should not be viewed as predicting the
specific timing of any changes in sea levels. The inherent
value of this study is the broad view of the subject and the
overall estimates identified. Due to the overview aspect of
the US DOT study, and systematic and value uncertainties
in the involved models, this US DOT analysis appropriately
considered sea-level rise estimates from the IPCC reports as
uniform sea-level rise estimates, rather than estimates for
a particular geographic location. The confidence stated by
IPCC in the regional distribution of sea-level change is low,
due to significant variations in the included models; thus,
it would be inappropriate to use the IPCC model series to
estimate local changes. Local variations, whether caused by
erosion, subsidence (sinking of land) or uplift, local steric
(volumetric increase in water due to thermal expansion)
factors, or even coastline protection, were not considered
in this study2. Given the analysis and cautionary statements
presented in Chapter 2 regarding using the USGS National
Elevation Data (NED) with small increments of sea-level rise
as used in this US DOT study, only representative statisti-
cal estimations are presented here for just the largest 59-cm
scenario. Because the 59-cm sea-level rise scenario is within
the statistical uncertainty of the elevation data, the statistics
are representative of the types of analyses that could be done
if accurate elevation data were available.
The study first estimates the areas that would be regularly
inundated or at risk during storm conditions, given nine
potential scenarios of sea-level rise. It defines regularly
inundated areas or base sea level as NOAA's mean higher
high water (MHHW) for 2000. The regularly inundated
areas examined are the regions of the coast that fall between
MHHW in 2000 and the adjusted MHHW levels (MHHW
in 2000 plus for several scenarios up to 59 cm). For at-risk
areas or areas that could be affected by storm conditions, the
study uses a base level of NOAA's highest observed water
levels (HOWL) for 2000, and adjusts this upwards based on
the nine sea-level rise scenarios. The at-risk areas examined
are those areas falling between the adjusted MHHW levels
and the adjusted HOWL levels.
Table 7.7 A Representative Output Table for Virginia Showing Estimates of Regularly Inundated and
At-Risk Areas and Lengths Under the 59-Centimeter (cm) Scenario. This is the highest level exam-
ined in the U.S. Department of Transportation (US DOT) study. The percent affected represent the
proportion for the entire state, not only coastal areas (From US DOT, 2008). The reported numbers
are subject to the caveat given at the end of Section 7.2.
State of Virginia Statistics
entimeter rise in sea level
Interstates
Non-Interstate Principal Arterials
National Highway System (NHS)
NHS Minor Arterials
Rails
Area (hectares [ha])
Ports
Airport Property
Airport Runways
Total Land Area Affected
arly Inundated
At Risk to St
Surge
12
22
10
60
277
29
68,632
0%
0%
0%
0%
0%
16
62
64
64
1%
1%
1%
1%
1%
23
74
86
83
1%
2%
2%
0%
1%
Affected
Affected
11%
2%
2%
\%
132
365
37
120,996
24%
3%
3%
\%
192
642
66
189,628
35%
4%
5%
2%
1 IPCC3, WG1, c.ll, page 671. .
2 It is recognized that protection such as bulkheads, seawalls, or other
protective measures may exist or be built that could protect specific
land areas but, due to the overview nature of this study, they were
not included in the analysis.
115
-------
The U.S. Climate Change Science Program
Chapter 7
Table 7.8 Summary of Estimated Areas and Lengths for the Total of Regularly Inundated and At-Risk Infrastruc-
ture Combined for a 59-Centimeter (cm) Increase in Sea-Level Rise (based on US DOT, 2008). The reported
numbers are subject to the caveat given at the end of Section 7.2.
Total, regularly inundated and at risk for a 59-cm increase in sea level
Washington, DC Virginia
Interstates
Non-Interstate Principal
Arte rials
Minor Arte rials
National Highway System
(NHS)
Rails
Ports
Airport Property
Airport Runways
Total Land Area
Affected
1
7
0
7
3
B~^L^^^3 1
5%
4%
0%
5%
5%
UpijiM
25
75
II
87
84
H^^^^L^L^^H
1%
2%
0%
2%
1%
Percent . . Percent
Hectares .,, . . Hectares .,, . ,
Affected Affected
n/a
n/a
n/a
968
n/a
n/a
n/a
6%
192
642
66
189,628
35%
4%
5%
2%
Maryland
2
21
66
19
44
120
59
1
192,044
0%
1%
4%
1%
2%
^^^W
32%
1%
0%
8%
^Sj^£^^H
i
130
209
305
105
88
434
27
743,029
^^ffiPJH|H
0%
2%
4%
4%
1%
^^^3
47%
3%
2%
6%
A sample of output tables from the US DOT study are
shown in Table 7.7, which covers the state of Virginia. The
numerical values for length and area in Tables 7.7 and 7.8
have been rounded down to the nearest whole number to be
conservative in the estimates for lengths and areas at risk.
This was done to avoid overstating the estimates as there
are no estimates of uncertainty or error in the numbers
presented.
Table 7.7 indicates there is some transportation infrastruc-
ture at risk under the 59-cm sea level rise scenario. Less
than 1 percent (7 kilometers [km] of interstates, 12 km of
non-interstate principal arterials) of the Virginia highways
examined in the US DOT study would be regularly inun-
dated, while an additional 1 percent (16 km of interstates, 62
km of non-interstate principal arterials) could be affected by
storm conditions. It should be noted that these percentages
are given as a percentage of the total for each state, not only
for coastal counties.
Table 7.8 provides the areas and percent of total areas af-
fected of the various regularly inundated and at-risk trans-
portation categories for the US DOT (2008) 59-cm sea-level
rise scenario for Washington, D.C., Virginia, Maryland, and
North Carolina.
Based on the small percentage (1 to 5 percent) statistics in
Table 7.8, the combination of rising sea level and storm surge
appears to have the potential to affect only a small portion
of highways and roads across the region. However, because
these transportation systems are basically networks, just a
small disruption in one portion could often be sufficient to
have far-reaching effects, analogous to when a storm causes
local closure of a major airport, producing ripple effects
nationwide due to scheduling and flight connections and
delays. Local flooding could have similar ripple effects in
a specific transportation sector.
North Carolina appears slightly more vulnerable to regular
inundation due to sea-level rise, both in absolute terms and
as a percentage of the state highways: less than 1 percent
of interstates (0.3 km), 1 percent of non-interstate principal
arterials (59 km) and 2 percent of National Highway Sys-
tem (NHS) minor arterials (93 km) in the state would be
regularly inundated given a sea-level rise of 59 cm. This US
DOT study focuses on larger roads but there are many miles
of local roads and collectors that could also be affected. In
general, areas at risk to storm surge are limited. Washing-
ton, D.C. shows the greatest vulnerability on a percentage
basis for both interstates and NHS roads for all sea-level rise
scenarios examined.
Please refer to the US DOT study for complete results,
at: .
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Public Access
Author: James G. Titus, U.S. EPA
KEY FINDINGS
The Public Trust Doctrine provides access along the shore below mean high water, but it does not include the
right to cross private property to reach the shore. Therefore, access to the shore varies greatly, depending on
the availability of roads and public paths to the shore.
Rising sea level alone does not have a significant impact on either access to the shore or access along the shore;
however, responses to sea-level rise can decrease or increase access.
Shoreline armoring generally eliminates access along estuarine shores, by eliminating the intertidal zone along
which the public has access. New Jersey has regulatory provisions requiring shorefront property owners in
some urban areas to provide alternative access inland of new shore protection structures. Other mid-Atlantic
states lack similar provisions to preserve public access.
Beach nourishment has minimal impact in areas with ample access; however, it can increase access in areas
where public access is restricted. Federal and state policies generally require public access to and along a shore
before providing subsidized beach nourishment. In several communities, property owners have assigned public
access easements in return for beach nourishment.
Responses based on allowing shores to retreat have minimal impact on public access.
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The U.S. Climate Change Science Program
Chapter 8
8.1 INTRODUCTION
8.2 EXISTING PUBLIC ACCESS AND THE
PUBLIC TRUST DOCTRINE
The right to access tidal waters and shores is well estab-
lished. Both access to and ownership of tidal wetlands and
beaches is defined by the "Public Trust Doctrine", which
is part of the common law of all the mid-Atlantic states.
According to the Public Trust Doctrine, navigable waters
and the underlying lands were publicly owned at the time
of statehood and remain so today.
Rising sea level does not inherently increase or decrease
public access to the shore, but the response to sea-level
rise can. Beach nourishment tends to increase public ac-
cess along the shore because federal (and some state) laws
preclude beach nourishment funding unless the public has
access to the beach that is being restored. Shoreline armor-
ing, by contrast, can decrease public access along the shore,
because the intertidal zone along which the public has access
is eliminated.
The Public Trust Doctrine is so well established that it often
overrides specific governmental actions that seem to transfer
ownership to private parties (Lazarus, 1986; Rose, 1986).
Many courts have invalidated state actions that extinguished
public ownership or access to the shore (Illinois CentralR.R.
v. Illinois; Arnold v. Mundy; see also Slade, 1990). Even
if a land deed states that someone's property extends into
the water, the Public Trust Doctrine usually overrides that
language and the public still owns the shore2. In those cases
when government agencies do transfer ownership of coastal
land to private owners, the public still has the right to access
along the shore for fishing, hunting, and navigation, unless
the state explicitly indicates
Legal and Tidal Geological Tideland Zonation an intent to extinguish the
public trust (Lazarus, 1986;
Slade, 1990).
This Chapter examines the impacts of sea-level rise on public
access to the shore. The following sections describe existing
public access to the shore (Section 8.2), the likely impacts
of shoreline changes (Section 8.3), and how responses to
sea-level rise might change public access (Section 8.4). The
focus of this Chapter is on the public's legal right to access
the shore, not on the transportation and other infrastructure
that facilitates such access1.
OCEAN BEACH
••; -t,, : •.:;
Line
Stain
W»va Runup aiMHW
MHW
'.-! ,V
::.-, B**d
BAY SHORE
SHW =
MHW =
MSL =
MLW =
Storm =
Spring High Waler
Mean High Waler
Mean Sea Level
Wean Law Waler
Average Annual Storm
Slfln-i
MHW
Tr»n*HKXl
'.'.Tli.--.-!•,
Land
Figure 8.1 The area below mean high water is usually publicly owned, and in all cases is subject
to public access for fishing and navigation. Along the ocean, the dry beach above mean high water
may be privately owned; however, in several states the public has an easement. Along the bay, the
high marsh above mean high water is also privately owned, but wetland protection laws generally
prohibit or discourage development.
Figure 8.1 illustrates some
key terminology used in this
Chapter. Along sandy shores
with few waves, the wet beach
lies between mean high water
and mean low water. (Along
shores with substantial waves,
the beach at high tide is wet
inland from the mean high
water mark, as waves run up
the beach.) The dry beach
extends from approximately
mean high water inland to
the seaward edge of the dune
grass or other terrestrial plant
life, sometimes called the
vegetation line (Slade, 1990).
The dune grass generally ex-
tends inland from the point
where a storm in the previous
year struck with sufficient
force to erode the vegetation
(Pilkey, 1984), which is well
above mean high water. Along
Chapter 7 discusses impacts on transportation infrastructure.
2 The "mean low water states" (i.e., Virginia, Delaware, and Penn-
sylvania), are an exception. See Figure 8.2.
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
(a)
(b)
Figure 8.2 Traditional purposes of the Public Trust Doctrine include fishing and transportation along the shore, (a) New Jersey side
of Delaware River, below Delaware Memorial Bridge (March 2003). (b) Beach provided primary access to homes along the beach
at Surfside, Texas (May 2003) [Photo source: ®James G. Titus, used with permission].
marshy shores, mudflats are found between mean low water
and mean sea level, low marsh is found between mean sea
level and mean high water, and high marsh extends from
mean high water to spring high water. Collectively, the
lands between mean high water and mean low water (mud-
flats, low marsh, and wet beaches) are commonly known
as tidelands.
The Public Trust Doctrine includes these wetlands and
beaches because of the needs associated with hunting, fish-
ing, transportation along the shore, and landing boats for rest
or repairs (Figure 8.2). In most states, the public owns all
land below the high water mark (Slade, 1990), which is gen-
erally construed as mean high water. The precise boundary
varies in subtle ways from state to state. The portion of the
wet beach inland of mean high water resulting from wave
runup has also been part of the public trust lands in some
cases (see e.g., State v. Ibbison and Freedman
and Higgins, undated). Thus, in general, the
public trust includes mudflats, low marsh,
and wet beach, while private parties own
the high marsh and dry beach (Figure 8.3).
Nevertheless, Figure 8.4 shows that there are
some exceptions. In Pennsylvania, Delaware,
and Virginia, the publicly owned land extends
only up to the low water mark (Slade, 1990).
In New York, by contrast, the inland extent
of the public trust varies; in some areas the
public owns the dry beach as well3. The public
has also obtained ownership to some beaches
through government purchase, land dedica-
tion by a developer, or other means (see Slade
1990; Figure 8.5).
Figure 8.3 Privately owned dunes adjacent to publicly owned
intertidal beach. Southold, New York (September 2006) [Photo
source: ®James G. Titus, used with permission].
Public's Common Law Interest in Shores
The Public Owns:
Below mean low water; access to wet
beach for hunting, fishing, navigation
Wet beach below high water
Wtel and dry beach
Wei beach; access along dry beach
Figure 8.4 The public's common law interest in the shores of various coastal
states. Source: Titus (1998).
3 e.g. Dolphin Lane Assocs. v. Town of Southampton, 333 N.E.2d 358,
360 (N.Y. 1975).
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The U.S. Climate Change Science Program
Chapter 8
Figure 8.5 Public beach owned by local government. Beaches that are owned by local governments sometimes have access
restrictions for nonresidents. Atlantic Beach, New York (September, 2006).
Ownership, however, is only part of the picture. In Penn-
sylvania, Delaware, and Virginia, the Public Trust Doctrine
provides an easement along the tidelands for hunting, fish-
ing, and navigation. In New Jersey, the Public Trust Doctrine
includes access along the dry part of the beach for recreation,
as well as the traditional public trust purposes (Matthews v.
Bay Head). Other states have gradually obtained easements
for access along some dry beaches either through purchases
or voluntary assignment by the property owners in return
for proposed beach nourishment. Federal policy precludes
funding for beach nourishment unless the public has access
(USAGE, 1996). Some state laws specify that any land cre-
ated with beach nourishment belong to the state (e.g., MD.
CODE ANN., NAT. RES. II 8-1103 [1990]).
The right to access along the shore does not mean that the
public has a right to cross private land to get to the shore.
Unless there is a public road or path to the shore, access
along the shore is thus only useful to those who either reach
the shore from the water or have permission to cross private
land. Although the public has easy access to most ocean
beaches and large embayments like Long Island Sound and
Delaware Bay, the access points to the shores along most
small estuaries are widely dispersed (e.g., Titus, 1998). How-
ever, New Jersey is an exception: its Public Trust Doctrine
recognizes access to the shore in some cases (Matthews v.
Bay Head); and state regulations require new developments
with more than three units along all tidal waters to include
public access to the shore (NJAC 7:7E-8.11 [d-f]). Given
the federal policy promoting access, the lack of access to
the shore has delayed several beach nourishment projects.
To secure the funding, many communities have improved
public access to the shore, not only with more access ways
to the beach, but also by upgrading availability of parking,
restrooms, and other amenities (e.g., New Jersey, 2006).
8.3 IMPACT OF SHORE EROSION ON
PUBLIC ACCESS
The rule that property lines retreat whenever shores erode
gradually has been part of the common law for over one
thousand years (County of St. Clair v. Lovingston; DNR v.
Ocean City), assuming that the shoreline change is natural.
Therefore, as beaches migrate landward, the public's access
rights to tidal wetlands and beaches do not change, they sim-
ply migrate landward along with the wetlands and beaches.
Nevertheless, the area to which the public has access may
increase or decrease, if sea-level rise changes the area of
wetlands or beaches.
When riparian landowners caused the shorelines to advance
seaward, the common law did not vest owners with title to
land reclaimed from the sea, although legislatures some-
times have (ALR, 1941). If beach nourishment or a federal
navigation jetty artificially creates new land, a majority of
states (e.g., MD. CODE ANN., ENVIR. 16-201) award the new
land to the riparian owner if he or she is not responsible for
creating the land (Slade, 1990); a minority of states (e.g.,
Garrettv. State of New Jersey, N.C. Gen Stat §146-6[f]) vest
the state public trust with the new land. Although these two
approaches were established before sea-level rise was widely
recognized, legal scholars have evaluated the existing rules
in the analogous context of shore erosion (e.g., Slade, 1990).
Awarding artificially created land to the riparian owner has
two practical advantages over awarding it to the state. First,
determining what portion of a shoreline change resulted
from some artificial causes, (e.g., sedimentation from a jetty
or a river diversion) is much more difficult than determining
how much the shoreline changed when the owner filled some
wetlands. Second, this approach prevents the state from de-
priving shorefront owners of their riparian access by pump-
ing sand onto the beach and creating new land (e.g., Board
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Initial condition
10 years later
20 years later
of Public Works v. Larmar Corp). A key disad-
vantage is that federal and state laws generally
prevent the use of public funds to create land
that accrues to private parties. Therefore, part
of the administrative requirements of a beach
nourishment project is to obtain easements or
title to the newly created land. Obtaining those
rights can take time, and significantly delayed
a beach nourishment project at Ocean City,
Maryland (Titus, 1998).
Sea-level rise causes shores to retreat both
through inundation and erosion. Although the
case law generally assumes that the shore is
moving as a result of sediment being trans-
ported, inundation and shore erosion are legally
indistinguishable. Among the causes of natural
shoreline change, the major legal distinction
has been between gradual and imperceptible
shifts, and sudden shifts that leave land in-
tact but on the other side of a body of water,
often known as "avulsion". Shoreline erosion
changes ownership; avulsion does not. If an
inlet formed 200 meters (m) west of one's home
during a storm after which an existing inlet 200
m east of the home closed, an owner would
still own her home because this shoreline
change is considered to be avulsion. But if the
inlet gradually migrated 400 m west, entirely
eroding the property but later creating land in the same loca-
tion, all of the newly created land will belong to the owner
to the east (see Figure 8.6). The public trust has the same
rights of access to beaches created through avulsion as to
beaches migrating by gradual erosion in New York (People
v. Steeplechase Park Co.) and North Carolina (Kalo, 2005).
In other states, the law is less clear (Slade, 1990).
Because the public has access to the intertidal zone as long
as it exists, the direct effect of sea-level rise on public ac-
cess depends on how the intertidal zone changes. Along an
undeveloped or lightly developed ocean beach, public access
is essentially unchanged as the beach migrates inland (except
perhaps where a beach is in front of a rocky cliff, which is
rare in the Mid-Atlantic). If privately owned high marsh
becomes low marsh, then the public will have additional
lands on which they may be allowed to walk (provided that
environmental regulations to protect the marsh do not pro-
hibit it). Conversely, if sea-level rise reduces the area of low
marsh, then pedestrian access may be less, although areas
that convert to open water remain in the public trust.
Gradual inlet migration (erosion)
county parit
30 years later
ptVBW owned J f"
Inlet breech followed by inlet dosing (avulsion)
Initial condition
After storm creates new inlet
After oW inlet closes
•- -i
pm»my porwl j
counly park
Figure 8.6 Impact of inlet migration and inlet breech on land ownership. In
this example, the island to the west is privately owned while the island to the
east is a county park.
8.4 IMPACT OF RESPONSES TO SEA-
LEVEL RISE ON PUBLIC ACCESS
Although sea-level rise appears to have a small direct effect
on public access to the shore, responses to sea-level rise can
have a significant impact, especially in developed areas.
Along developed bay beaches, public access along the shore
can be eliminated if the shorefront property owner erects
a bulkhead, because the beach is eventually eliminated. A
number of options are available for state governments that
wish to preserve public access along armored shores, such as
public purchases of the shorefront (Figure 8.7) and protecting
public access in permits for shore protection structures. New
Jersey requires a public path between the development and
the shore-protection structure for all new developments (or
new shore protection structures for existing developments)
with more than three units along urban tidal rivers (NJAC
7.7E-8.11[e]; see also Section A1.D.2 in Appendix 1) and
some other areas, and has a more general requirement to
preserve public access elsewhere (NJAC 7.7E-8.11 [d] [1]).
However, single-family homes are generally exempt (NJAC
7.7E-8.11[f] [7])—and other mid-Atlantic states have no such
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The U.S. Climate Change Science Program
Chapter 8
Figure 8.7 Public access along a bulkheaded shore. In North
Beach, Maryland, one block of Atlantic Avenue, is a walkway
along Chesapeake Bay (May 2006) [Photo source: ®James G.
Titus, used with permission].
requirements. Therefore, sea-level rise has reduced public
access along many estuarine shores and is likely to do so in
the future as well.
Government policies related to beach nourishment, by con-
trast, set a minimum standard for public access (USAGE,
1996), which often increases public access along the shore.
Along the ocean shore from New York to North Carolina,
the public does not have access along the dry beach under
the Public Trust Doctrine (except in New Jersey)4. How-
ever, once a federal beach nourishment project takes place,
the public gains access. Beach nourishment projects have
increased public access along the shore in Ocean City,
Maryland and Sandbridge (Virginia Beach), Virginia, where
property owners had to provide easements to the newly cre-
ated beach before the projects began (Titus, 1998; Virginia
Marine Resources Commission, 1988).
Areas where public access to the beach is currently limited
by a small number of access points include the area along the
Outer Banks from Southern Shores to Corolla, North Caroli-
na (NC DENR, 2008); northern Long Beach Township, New
Jersey (USACE, 1999); and portions of East Hampton, South
Hampton, Brookhaven, and Islip along the South Shore of
Long Island, New York (Section ALA.2 in Appendix 1). In
West Hampton, landowners had to provide six easements for
perpendicular access from the street to the beach in order to
meet the New York state requirement of public access every
one-half mile (see Section A1.A.2 in Appendix 1). Aplanned
$71 million beach restoration project for Long Beach Island
has been stalled (Urgo, 2006), pending compliance with the
1 In some places, the public has obtained access through government
purchase, land dedication by a developer, or other means. See Slade
(1990).
New Jersey state requirement of perpendicular access every
one-quarter mile (USACE, 1999). An additional 200 parking
spaces forbeachgoers must also be created in Northern Long
Beach Township (USACE, 1999). Private communities along
Delaware Bay have granted public access to the beaches in
return for state assistance for beach protection (Beaches
2000 Planning Group, 1988).
If other communities with limited access seek federal beach
nourishment in the future, public access would similarly
increase. Improved access to the beach for the disabled may
also become a requirement for future beach nourishment
activities (e.g., Rhode Island CRMC, 2007). This is not to
say that all coastal communities would provide public ac-
cess in return for federal funds. But aside from the portion
of North Carolina southwest of Cape Lookout, the Mid-
Atlantic has no privately owned gated barrier islands, unlike
the Southeast, where several communities have chosen to
expend their own funds on beach nourishment rather than
give up their exclusivity.
Ultimately, the impact of sea-level rise on public access will
depend on the policies and preferences that prevail over the
coming decades. Sometimes the desire to protect property
as shores erode will come at the expense of public access.
Sometimes it will promote an entire re-engineering of the
coast, which under today's policies generally favors public
access. It is possible that rising sea level is already starting
to cause people to rethink the best way to protect property
along estuarine shores (NRC, 2007) to protect the environ-
mental benefits of natural shores. If access along estuarine
shores becomes a policy goal, techniques are available for
preserving public access as sea level rises.
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u
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Coastal Flooding, Floodplains, and
Coastal Zone Management Issues
Lead Authors: Stephen K. Gill, NOAA; Doug Marcy, NOAA
Contributing Author: Zoe Johnson, Maryland Dept. of Natural
Resources
KEY FINDINGS
Rising sea level increases the vulnerability of coastal areas to flooding. The higher sea level provides a higher
base for storm surges to build upon. It also diminishes the rate at which low-lying areas drain, thereby increasing
the risk of flooding from rainstorms. Increased shore erosion can further increase flood damages by removing
protective dunes, beaches, and wetlands, thus leaving previously protected properties closer to the water's
edge. In addition to flood damages, many other effects, responses, and decisions are likely to occur during or
in the immediate aftermath of severe storms. Beach erosion and wetlands loss often occur during storms, and
the rebuilding phase after a severe storm often presents the best opportunity for developed areas to adapt to
future sea-level rise.
Coastal storms could have higher flooding potential in the future due to higher sea levels relative to the land.
The most recent Federal Emergency Management Agency (FEMA) study on the potential effects of sea-level rise
on the nation's flood insurance program was published in 1991. Because of the uncertainties in the projections of
potential changes in sea level at the time and the ability of the rating system to respond easily to a 0.3 meter rise
in sea level, FEMA (1991) concluded
that no immediate program changes
were needed.
The mid-Atlantic coastal zone
management community is
increasingly recognizing that sea-
level rise is a high-risk coastal
hazard as evidenced by the recent
comprehensive analyses and studies
needed to make recommendations
for state policy formulation
performed by Maryland.
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Chapter '
•• . ..
This Chapter examines the effects of sea-level rise on
coastal floodplains and on coastal flooding management
issues confronting the U.S. Federal Emergency Management
Agency (FEMA), the floodplain management community,
the coastal zone management community, coastal resource
managers, and the public, including private industry. Sea-
level rise is just one of numerous complex scientific and soci-
etal issues these groups face. There is also uncertainty in the
local rate of sea-level change, which needs to be taken into
account along with the interplay with extreme storm events
(see Chapter 1). In addition, impacts of increased flooding
frequency and extent on coastal areas can be significant for
marine ecosystem health and human health in those areas
(Boesch et al., 2000). This Chapter provides a discussion
of the current state of knowledge and provides assessments
for a range of actions being taken by many state and federal
agencies and other groups related to coastal flooding.
9.2
9,2.1
In general, a floodplain is any normally dry land sur-
rounding a natural water body that holds the overflow of
water during a flood. Because they border water bodies,
floodplains have been popular sites to establish settlements,
which subsequently become susceptible to flood-related
disasters. Most management and regulatory definitions of
floodplains apply to rivers; however, open-coast floodplains
characterized by beach, dunes, and shrub-forest are also
important since much of the problematic development and
infrastructure is concentrated in these areas (see Chapter 3
for a detailed description of this environment).
The federal regulations governing FEMA (2008) via Title
44 of the Code of Federal Regulations defines floodplains
as "any land area susceptible to being inundated by flood
waters from any source". The FEMA (2002) Guidelines and
Specifications for Flood Hazard Mapping Partners Glos-
sary of Terms defines floodplains as:
1. A flat tract of land bordering a river, mainly in its lower
reaches, and consisting of alluvium deposited by the
river. It is formed by the sweeping of the meander belts
downstream, thus widening the valley, the sides of
which may become some kilometers apart. In times of
flood, when the river overflows its banks, sediment is
deposited along the valley banks and plains.
2. Synonymous with the 100-year floodplain, which is
defined as the land area susceptible to being inundated
by stream derived waters with a 1-percent-annual-
chance of being equaled or exceeded in a given year.
The National Oceanic and Atmospheric Administration
(NOAA) National Weather Service (NWS) defines a flood-
plain as the portion of a river valley that has been inundated
by the river during historic floods. None of these formal
definitions of floodplains include the word "coastal". How-
ever, as river systems approach coastal regions, river base
levels approach sea level, and the rivers become influenced
not only by stream flow, but also by coastal processes such
as tides, waves, and storm surges. In the United States, this
complex interaction takes place near the governing water
body, either open ocean, estuaries, or the Great Lakes.
The slope and width of the coastal plain determines the
size and inland extent of coastal influences on river sys-
tems. Coastal regions are periodically inundated by tides,
and frequently inundated by high waves and storm surges.
Therefore, a good working definition of a coastal floodplain,
borrowing from the general river floodplain definition, is
any normally dry land area in coastal regions that is suscep-
tible to being inundated by water from any natural source,
including oceans (e.g., tsunami runup, coastal storm surge,
relative sea-level rise), rivers, streams, and lakes.
Floodplains generally contain unconsolidated sediments,
often extending below the bed of the stream or river. These
accumulations of sand, gravel, loam, silt, or clay are often
important aquifers; the water drawn from them is pref iltered
compared to the water in the river or stream. Geologically
ancient floodplains are often revealed in the landscape by
terrace deposits, which are old floodplain deposits that re-
main relatively high above the current floodplain and often
indicate former courses of rivers and streams.
Floodplains can support particularly rich ecosystems, both
in quantity and diversity. These regions are called riparian
zones or systems. Wetting of the floodplain soil releases an
immediate surge of nutrients, both those left over from the
last flood and those from the rapid decomposition of organic
matter that accumulated since the last flood. Microscopic
organisms thrive and larger species enter a rapid breeding
cycle. Opportunistic feeders (particularly birds) move into
take advantage of these abundant populations. The produc-
tion of nutrients peaks and then declines quickly; however,
the surge of new growth endures for some time, thus making
floodplains particularly valuable for agriculture. Markedly
different species grow within floodplains compared to sur-
rounding regions. For instance, certain riparian tree species
(that grow in floodplains near river banks) tend to be very
tolerant of root disturbance and thus tend to grow quickly,
compared to different tree species growing in a floodplain
some distance from a river.
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Assessing the impacts of sea-level rise on coastal f loodplains
is a complicated task, because those impacts are coupled
with impacts of climate change on other coastal and riverine
processes and can be offset by human actions to protect life
and property. Impacts may range from extended periods of
drought and lack of sediments to extended periods of above-
normal freshwater runoff and associated sediment loading.
Some seasons may have higher than normal frequency and
intensity of coastal storms and flooding events. Impacts
will also depend on construction and maintenance of dikes,
levees, waterways, and diversions for flood management.
With no human intervention, the hydrologic and hydraulic
characteristics of coastal and river floodplain interactions
will change with sea-level rise. Fundamentally, the flood-
plains will become increasingly vulnerable to inundation.
In tidal areas, the tidal inundation characteristics of the
floodplain may change with the range of tide and associated
tidal currents increasing with sea-level rise. With this inun-
dation, floodplains will be vulnerable to increased coastal
erosion from waves, river and tidal currents, storm-induced
flooding, and tidal flooding. Upland floodplain boundaries
will be vulnerable to horizontal movement. Coastal marshes
could be vulnerable to vertical buildup or inundation (see
Chapter 4 for further discussion).
In a study for the state of Maine (Slovinsky and Dickson,
2006), the impacts of sea-level rise on coastal floodplains
were characterized by marsh habitat changes and flooding
implications. The coast of Maine has a significant spring
tidal range of 2.6 to 6.7 meters (m) (8.6 to 22.0 feet [ft]),
such that impacts of flooding are coupled with the timing of
storms and the highest astronomical tides on top of sea-level
rise. The study found that there was increasing susceptibility
to inlet and barrier island breaches where existing breach
areas were historically found, increased stress on existing
flood-prevention infrastructure (levees, dikes, roads), and
a gradual incursion of low marsh into high marsh with de-
velopment of a steeper bank topography. On the outer coast,
impacts included increased overwash and erosion.
In addition, the effects of significant local or regional
subsidence of the land will add to the effects of sea-level
rise on coastal floodplains. Regional areas with significant
subsidence include the Mississippi River Delta region (AGU,
2006), the area around the entrance to the Chesapeake Bay
(Poag, 1997), and local areas such as the Blackwater National
Wildlife Refuge on the Eastern Shore of Maryland (Larsen
et al, 2004).
The potential interaction among increased sea levels, storm
surges, and upstream rivers is complex. The storm surge of
any individual storm is a function of storm intensity defined
by storm strength and structure, forward speed, landfall
location, angle of approach, and local bathymetry and to-
pography. However, the absolute elevation of the maximum
water levels observed relative to the land during a storm
(operationally defined as storm tides) are a combination of
the storm surge defined above, plus the non-storm-related
background water level elevations due to the stage of tide,
the time of year (sea level varies seasonally), river flow, local
shelf circulation patterns (such as the Gulf Loop Current/
eddies and the El Nino-Southern Oscillation [especially on
the West Coast]). Storm surge "rides" on top of these other
variations, including sea-level rise (NOAA, 2008). Storm
surge can travel several hundred kilometers up rivers at more
than 40 kilometers (km) (25 miles [mi]) per hour, as on the
Mississippi River, where storm surge generated by land-
falling hurricanes in the Gulf of Mexico can be detected on
stream gauges upstream of Baton Rouge, Louisiana, more
than 480 km (300 mi) from the mouth of the river (Reed
and Stucky, 2005).
Both NWS (for flood forecasting) andFEMA (for insurance
purposes and land use planning) recognize the complexity
of the interactions among sea-level rise, storm surge, and
river flooding. For instance, NWS uses both a hurricane
storm surge model (the Sea, Lakes, and Overland Surge
from Hurricanes [SLOSH] model, Jelesnianskie/a/., 1992)
and a riverine hydraulic model (the Operational Dynamic
Wave Model) to forecast effects of storm surge on river
stages on the Mississippi River. The two models are coupled
such that the output of the storm surge model is used as the
downstream boundary of the river model. This type of model
coupling is needed to determine the effects of sea-level rise
and storm surge on riverine systems. Other modeling efforts
are starting to take into account river and coastal physical
process interactions, such as use of the two-dimensional
hydrodynamic model (the Advanced Circulation Model or
ADCIRC; Luettich et al, 1992) on the Wacammaw River
in South Carolina to predict effects of storm surge on river
stages as far inland as Conway, 80 km (50 mi) from the
Atlantic Ocean (Hagen et al., 2004). These model coupling
routines are becoming increasingly more common and have
been identified as future research needs by such agencies as
NOAA and the U.S. Geological Survey (USGS), as scientists
strive to model the complex interactions between coastal
and riverine processes. As sea level rises, these interactions
will become ever more important to the way the coastal and
riverine floodplains respond (Pietrafesa et al., 2006).
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The U.S. Climate Change Science Program
Chapter 9
9.4.1 Historical Comparison at Tide Stations
There is the potential for higher elevations of coastal
flooding from coastal storms over time as sea level rises
relative to the land. Looking at storms in historical context
and accounting for sea-level change is one way to estimate
maximum potential stormwater levels. For example, this
assessment can be made by analyzing the historical record
of flooding elevations observed at NOAA tide stations in the
Chesapeake Bay. The following analysis compares the eleva-
tion of the storm tides for a particular storm at a particular
tide station; that is, from when it occurred historically to
as if the same exact storm occurred today under the same
exact conditions, but adjusted for relative sea-level rise at
that station. These comparisons are enabled because NOAA
carefully tabulates water level elevations over time relative
to a common reference datum that is connected to the local
land elevations at each tide station. From this, relative sea-
level trends can be determined and maximum water level
elevations recorded during coastal storms can be directly
compared over the time period of record (Zervas, 2001). The
relative sea level trend provides the numerical adjustment
needed depending on the date of each storm.
The NOAA post-hurricane report (Hovis, 2004) on the ob-
served storm tides of Hurricane Isabel assessed the potential
effects of sea-level rise on maximum observed storm tides
for four long-term tide stations in the Chesapeake Bay. Prior
to Hurricane Isabel, the highest water levels reached at the
NOAA tide stations at Baltimore, Maryland; Annapolis,
Maryland; Washington, D.C.; and Sewells Point, Virginia
occurred during the passage of an unnamed hurricane in
August, 1933. At the Washington, D.C. station, the 1933
hurricane caused the third highest recorded water level, sur-
passed only by river floods in October 1942 and March 1936.
Hurricane Isabel caused water levels to exceed the August
1933 levels at Baltimore, Annapolis and Washington, D.C.
by 0.14, 0.31, and 0.06 meters (m), respectively. At Sewells
Point, the highest water level from Hurricane Isabel was only
0.04 mbelow the level reached in August 1933. Zervas (2001)
calculated sea-level rise trends for Baltimore, Annapolis,
Washington, and Sewells Point of 3.12, 3.53, 3.13, and 4.42
millimeters (mm) per year, respectively. Using these rates,
the time series of monthly highest water level were adjusted
for the subsequent sea-level rise up to the year 2003. The
resulting time series, summarized in Tables 9.1, 9.2,9.3, and
9.4, indicate the highest level reached by each storm as if
it had taken place in 2003 under the same conditions, thus
allowing an unbiased comparison of storms. The purpose of
Tables 9.1 through 9.4 is to show that the relative ranking of
the flooding elevations from particular storm events changes
at any given station once the adjustment for sea level trend is
taken into account. The 1933 hurricane, especially, moves up
in ranking at Baltimore and Washington, DC once adjusted
for the local sea level trend. Hurricane Hazel moved up in
ranking at Annapolis. If the 1933 hurricane occurred today
under the same conditions, it would have had the highest
water level of record at Baltimore, not Hurricane Isabel. El-
evations are relative to the tidal datum of mean higher high
Table 9.1 Five Highest Water Levels for Baltimore, Maryland in Meters Above Mean Higher
High Water. Ranked first by absolute elevation and then ranked again after adjustment for
sea-level rise.
1 JTjj
Hurricane Isabel
Hurricane
Hurricane Connie
Hurricane Hazel
Hurricane
e Water Level
Date ,
(meters)
Sept. 2003
Aug. 1933
Aug. 1955
Oct. 1954
Aug. 1915
1.98
1.84
1.44
1.17
l.ll
Corrected for
Event
Hurricane
Hurricane Isabel
Hurricane Connie
Hurricane
Hurricane Hazel
sea-level rise to 2003
_ Elevation
(meters)
Aug. 1933
Sept. 2003
Aug. 1955
Aug. 1915
Oct. 1954
2.06
1.98
1.59
1.38
1.32
Table 9.2 Five Highest Water Levels for Annapolis, Maryland in Meters Above Mean Higher
High Water. Ranked first by absolute elevation and then ranked again after adjustment for
sea-level rise.
absolute Water Level
Hurricane Isabel
Sept. 2003
1.76
Corrected for sea-level rise to 2003
Hurricane Isabel
Sept. 2003
levation
1.76
Hurricane
Aug. 1933
1.45
Hurricane
Aug. 1933
1.69
Hurricane Connie
Aug. 1955
1.08
Hurricane Connie
Aug. 1955
1.25
Hurricane Fran
Sept. 1996
1.04
Hurricane Hazel
Oct. 1954
1.19
Hurricane Hazel
Oct. 1954
1.02
Hurricane Fran
Sept. 1996
1.06
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Table 9.3 Five highest water levels for Washington, D.C. in meters above mean higher high
water. Ranked first by absolute elevation and then ranked again after adjustment for sea-
level rise.
Flood
Oct. 1942
2.40
Flood
Oct. 1942
2.59
Flood
Mar. 1936
2.25
Flood
Mar. 1936
2.46
Hurricane Isabel
Sept. 2003
2.19
Hurricane
Aug. 1933
2.35
Hurricane
Aug. 1933
2.13
Hurricane Isabel
Sept. 2003
2.19
Flood
Apr. 1937
1.70
Flood
Apr. 1937
1.91
Table 9.4 Five highest water levels for Sewells Point, Virginia in meters above mean higher
high water. Ranked first by absolute elevation and then ranked again after adjustment for
sea-level rise.
1 JTjjj
Hurricane
Hurricane Isabel
Winter Storm
Hurricane
Winter Storm
e Water Level
Date ,
(meters)
Aug. 1933
Sept. 2003
Mar. 1962
Sept. 1936
Feb. 1998
1.60
1.56
1.36
1.21
1.16
Corrected for
Event
Hurricane
Hurricane Isabel
Winter Storm
Hurricane
Hurricane
sea-level rise to 2003
Elevation
(meters)
Aug. 1933
Sept. 2003
Mar. 1962
Sept. 1936
Sept. 1933
1.91
1.56
1.54
1.50
1.33
water (MHHW). Noting the earlier discussion in this section
on the operational difference between storm surge and the
actual observed storm tide elevation, the tables suggest that,
while not affecting intensity of storms and the resulting am-
plitude of storm surges, sea-level rise could increasingly add
to the potential maximum water level elevations observed
relative to the land during coastal storms.
9.4.2 Typical 100-Year Storm Surge
Elevations Relative to Mean Higher High
Water within the Mid-Atlantic Region
A useful application of long-term tide gauge data is a return
frequency analysis of the monthly and annual highest and
lowest observed water levels. This type of analysis provides
information on how often extreme water levels can be ex-
pected to occur (e.g., once every 100 years, once every 50
years, once every 10 years, etc.) On the East Coast and in
the Gulf of Mexico, hurricanes and winter storms interact
with the wide, shallow, continental shelf to produce large
extreme storm tides. A generalized extreme value distribu-
tion can be derived for each station after correcting the
values for the long-term sea-level trend (Zervas, 2005).
Theoretical exceedance probability statistics give the
99-percent, 50-percent, 10-percent, and 1-percent annual
exceedance probability levels. These levels correspond to
average storm tide return periods of 1,2,10, and 100 years.
The generalized extreme value analyses are run on the his-
torical data from each tide station. Interpolating exceedance
probability results away from the tide station location is not
recommended as elevations of tidal datums and the extremes
are highly localized. Figures 9.1 and 9.2 show the variations
in these statistics along the mid-Atlantic coast. Figure 9.1
shows exceedance elevations above local mean sea level
(LMSL) at mid-Atlantic stations relative to the 1983 to 2001
National Tidal Datum Epoch (NTDE). Figure 9.2 shows the
same exceedance elevations, except the elevations are rela-
tive to mean higher high water (MHHW) computed for the
same 1983 to 2001 NTDE.
In Figure 9.1, the elevations relative to LMSL are highly cor-
related with the range of tide at each station (Willets Point,
New York has avery high range of tide, 2.2 m), exceptforthe
1-percent level at Washington, D.C., which is susceptible to
high flows of the Potomac River. Due to their varying loca-
tions, the 1-percent elevation level varies the most among the
stations. Figure 9.2 shows a slightly geographically decreas-
ing trend in the elevations from north to south.
Examining the effects of sea-level rise on the highest water
level during a hurricane or coastal storm does not provide
a complete picture because the impacts of sea-level rise on
the duration of the inundation can be as important as the
maximum height. Sea-level rise, coupled with any increased
frequency of extra-tropical storms (nor'easters), may also
increase the durations of inundation from extra-tropical
storms (NOAA, 1992). For instance, some of the most severe
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The U.S. Climate Change Science Program
Chapter 9
Exceedance Probability Elevations: Mid-Atlantic Tide
Stations Relative to Local Mean Sea Level
4.00 i
Figure 9.1 Exceedance probabilities for mid-Atlantic tide stations relative to local mean sea level.
Exceedance Probability Elevations: Mid-Atlantic Tide
Stations Relative to Mean Higher High Water
Figure 9.2 Exceedance probabilities at mid-Atlantic tide stations relative to mean higher high water.
128
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
BOX 9.1: Ecological Effects of Sea-Level Rise—NOAA North Carolina Study
An ongoing National Oceanic and Atmospheric Administration (NOAA)-sponsored study on the ecological effects
of sea-level rise is just one example of the type of integrated applied research that will be required to fully describe
the effects of sea-level rise in the coming century. The study incorporates and integrates features including high
resolution data of the littoral zone, geography, ecology, biology, and coastal process studies in a region of concern.
A complete overview of the NOAA program can be found at:
Box Figure 9.1 (a) The Coastal Flooding Model grid and (b) one preliminary result of shoreline change due to various sea-
level rise scenarios.
The North Carolina pilot study demonstrates the ability to design a meaningful product for regional coastal
managers that integrates capabilities in vertical reference frames, mapping, and modeling, with targeted applied
research led by the local academic marine science research community. The applied research program is designed
to help coastal managers and planners better prepare for changes in coastal ecosystems due to land subsidence
and sea-level rise. Starting with the southern Pamlico Sound, the approach is to simulate projected sea-level
rise using a coastal flooding model that combines a hydrodynamic model (Figure 9.1 a) of water levels with a high
resolution digital elevation model (DEM). When completed, the coastal flooding model will be used to simulate
long-term rises in water levels (Figure 9.1 b). Sub-models will then be developed to forecast ecological changes in
coastal wetland and forested areas, and will be integrated with the coastal flooding model. The final goal of the
program is to produce mapping and modeling tools that allow managers and planners to see projected shoreline
changes and to display predictions of ecosystem impacts. Using these ecological forecasts, proactive mitigation
will be possible.
impacts of nor'easters are generally felt in bays where water
can get in but not out for several days as the storms slowly
transit parallel to the coast.
Other federal agencies, such as NOAA, have been spon-
soring applied research programs to bring an integrated
approach to understanding the effects of sea-level rise into
operations. One such study on the ecological effects of sea-
level rise is discussed in Box 9.1 (NOAA, 2007), which is
due to come out with a final report in 2009.
9.5 FLOODPLAIN MAPPING AND SEA-
LEVEL RISE
A nationwide study was performed by FEMA (1991) (see
Box 9.2) in which costs for remapping f loodplains were esti-
mated at $150,000 per county (in 1991 dollars) or $1,500 per
map panel (the standard map presentation used by FEMA).
With an estimated 283 counties (5,050 map panels) poten-
tially in need of remapping, the total cost of restudies and
remapping was estimated at $30 million (in 1991). Based
on this study and assuming that the maps are revised on a
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The U.S. Climate Change Science Program
Chapter 9
BOX 9.2: 1991 FEMA Study—Projected Impact of Relative Sea-Level Rise
on the National Flood Insurance Program
In 1989, Congress authorized and signed into law a study of the impact of sea-level rise on the National
Flood Insurance Program (NFIP). The legislation directed FEMA to determine the impact of sea-level rise on
flood insurance rate maps and project the economic losses associated with estimated sea-level rise. The final
report was delivered to Congress in 1991. The primary objectives of the study were to quantify the impacts
of relative sea-level rise on: (I) the location and extent of the U.S. coastal floodplain; (2) the relationship be-
tween the elevation of insured properties and the 100-year base flood elevation (BFE); and (3) the economic
structure of the NFIP.
In the 1991 study, FEMA used both a 0.3 and 0.9 meter (I and 3 feet) projected increase in relative sea level by
2100, based on previous studies (Titus and Green, 1989; IPCC, 1990). For both scenarios it was assumed that
the current 100-year floodplain would increase by the exact amount as the change in sea level. This assumption
was made to simplify some of the hydrodynamic interactions such as the effect of the increased water depth
due to sea-level rise on storm surge, and how sea-level rise will propagate up tidally affected rivers to a point
where sea-level rise will no longer affect water flood levels. The study did not attempt to model the effects
of sea-level rise in upstream river areas, a task that would have required site-specific hydraulic calculations.
I_ AAMion to Fioodpliw _|
dun to SIM Level Ftoe I
Submerged and Eroded
-ArtMDueto 1
Sea Level Rise •
1990 100-Yp.irSlilW.i5w
Sw Lav* (2100)
S*a Lewi (1990)
• Frodnd Profile
Box Figure 9.2 Schematic illustrating the effect of sea-level rise on the 100-year coastal floodplain
(FEMA, 1991).
For each coastal county, a still water flood level (SWFL) was estimated, as were the V Zone flood level (V
Zones are coastal high hazard areas where wave action and/or high velocity water can cause structural dam-
age in the 100-year flood), the estimated area covered by the Special Flood Hazard Area (SFHA), and the
fraction for which coastal V Zones were estimated. The equation divides the amount of sea-level rise by the
SWFL and multiplies the result by the current floodplain area. Another assumption was that shoreline erosion
and inundation due to sea-level rise, causing an overall loss in floodplain, would cancel out the overall gain
in floodplain associated with rising flood levels. Box Figure 9.2 shows this relationship. Using this method,
coastal areas where shore protection measures such as beach nourishment and construction of groins, levees,
bulkheads, and sea walls are used would reduce the amount of land lost to sea-level rise and thus cause some
overestimation in the amount of floodplain lost due to rising sea levels (Titus, 1990).
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
BOX 9.2: 1991 FEMA Study—Projected Impact of Relative Sea-Level Rise
on the National Flood Insurance Program cont'd
The study notes that these numbers differ slightly from a previous sea-level rise study (Titus and Green, 1989) but
supports the conclusion from both studies that the size of the floodplain will not increase as sea level rises because
of the balancing of land lost through submergence. Box Tables 9.2a and 9.2b show the breakdown of impacted land
areas for 0.3 meter (m) rise and 0.9 m rise by regions in A Zones versus V Zones (A Zones are areas inundated in a
100-year storm event that experience conditions of less severity than conditions experienced in V Zones).
Box Table 9.2a Area Affected by a 0.3-Meter Rise in Sea Level by 2100 (in square kilometers).
Entire U.S.
Mid-Atlantic
Floodplain 1990
41,854
10,782
8,637
891
50,491
11,673
Due to Sea Level Ris
4,677
1,411
937
114
5,614
1,525
Box Table 9.2b Area Affected by a 0.9-Meter Rise in Sea Level by 2100 (in square kilometers).
Entire U.S.
Mid-Atlantic
Floodplain 1990
41,854
10,782
8,637
891
50,491
11,673
ditional Area Affected
'•ie to Sea Level Rise
14,045
4,229
2,800
347
16,845
4,756
The total land area nationwide estimated by the study to be in a floodplain was close to 50,491 square kilometers
(sq km), with approximately 5,614 sq km added to the floodplain for a 0.3 m rise scenario and an additional 16,845
added for a 0.9 m rise. These numbers do not account for subsidence rates in the Louisiana region. For the mid-
Atlantic region, the floodplain was estimated to be about 11,673 sq km, with 15,250 sq km added to the floodplain
for a 0.3 m rise and 4,576 sq km added for a 0.9 m rise.
The study also estimates the number of households in the coastal floodplain. Based on the 1990 Census, 2.7 million
households were currently in the 100-year floodplain, including 624,000 in the mid-Atlantic region. For the 0.3 m
and 0.9 m rise scenarios, respectively, 5.6 million and 6.6 million households would be in the floodplain, with I.I
million and 1.3 million in the mid-Atlantic region.
This projected rise in population, in combination with the sea-level rise scenarios, would increase the expected
annual flood damage by 2100 for an average NFIP-insured property by 36 to 58 percent for a 0.3 m rise and 102 to
200 percent for a 0.9 m rise. This would lead to actuarial increases in insurance premiums for building subject to
sea-level rise of 58 percent for a 0.3 m rise and 200 percent for a 0.9 m rise. The study estimated that a 0.3 m rise
would gradually increase the expected annual NFIP flood losses by $150 million by 2100. Similarly, a 0.9 m rise would
gradually increase expected losses by about $600 million by 2100. Per policy holder, this increase would equate to
$60 more than in 1990 for the 0.3m rise and $200 more for the 0.9 m rise.
The study concludes that based on the aspects of flood insurance rates that already account for the possibility of
increasing risk and the tendency of new construction to be built more than 0.3 m above the base flood elevation,
the NFIP would not be significantly impacted under a 0.3 m rise in sea level by the year 2100. For a high projection
of a 0.9 m rise, the incremental increase of the first 0.3 m would not be expected until the year 2050. The study
concludes that the 60-year timeframe over which this gradual change would occur provides the opportunity for
the NFIP to consider alternative approaches to the loss control and insurance mechanisms. Because of the present
uncertainties in the projections of potential changes in sea level and the ability of the rating system to respond easily
to a 0.3 m rise in sea level, the study concluded that there were no immediate program changes needed.
131
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9
regular basis, such an undertaking today would cost about
$46.5 million. The 1991 study concluded that "there are no
immediate program changes needed" (FEMA, 1991).
At present, FEMA periodically revises Flood Insurance Rate
Maps (FIRMs) to reflect new engineering, scientific, and
imagery data. In addition, under their Map Modernization
and post-Map Modernization Programs, FEMA intends to
assess the integrity of the flood hazard data by reviewing
the flood map inventory every five years. Where the review
indicates the flood data integrity has degraded the flood
maps (due to outdated data and known changes in hydrology
and floodplain elevation since the last maps were issued),
updates will be provided or new studies will be performed.
Whenever an update or remap of coastal areas is made,
changes that had occurred in the interim due to sea-level
rise will be accounted for. An upcoming Impact of Climate
Change on the National Flood Insurance Program study
(scheduled to begin at the end of fiscal year 2008 and last
1.5 years) may come up with different conclusions than the
1991 study and cause FEMA to rethink the issue.
The primary floodplain management adjustment for sea-
level rise is the local increase in required base flood eleva-
tion (BFE) for new construction. Elevating a building's
lowest floor above predicted flood elevations by a small
additional height, generally 0.3 to 0.9 m (1 to 3 ft) above
National Flood Insurance Program (NFIP) minimum height
requirements, is termed a freeboard addition. Freeboard
additions are generally justified for other more immediate
purposes including the lack of safety factor in the 1-percent
flood and uncertainties in prediction and modeling. FEMA
encourages freeboard adoptions through the Community
Rating System, which offers community-wide flood insur-
ance premium discounts for higher local standards and for
individuals through premium discounts for higher than
minimum elevation on higher risk buildings. Velocity flood
zones, known as V Zones or coastal high hazard areas, have
been identified by FEMA as areas "where wave action and/
or high velocity water can cause structural damage in the
100-year flood", a flood with a 1 percent chance of occur-
ring or being exceeded in a given year. FEMA also defines
A Zones as areas inundated in a 100-year storm event that
experience conditions of less severity, for example, wave
heights less than 1 m, than conditions experienced in V
Zones. Accurate determination of the spatial extent of
these zones is vital to understanding the level of risk for a
particular property or activity.
A recent historical overview of FEMA's Coastal Risk As-
sessment process is found in Crowell et al. (2007), and
includes overviews of the FEMA Map Modernization Pro-
gram, revised coastal guidelines, and FEMA's response to
recommendations of a Heinz Center report, Evaluation of
Erosion Hazards (Heinz Center, 2000).
Currently, communities can opt to use future conditions
(projected) hydrology for mapping according to FEMA rules
established in December 20011. Showing future conditions
flood boundaries has been provided at the request of some
communities in Flood Map Modernization, but it is not a
routine product. As outlined in those rules, showing a future
condition boundary in addition to the other boundaries nor-
mally shown on a FIRM is acceptable. FEMA shows future
condition boundaries for informational purposes only and
carries with it no additional requirements for floodplain
management. Insurance would not be rated using a future
condition boundary. The benefits showing future condition
flood boundaries relate to the fact that future increases in
flood risk can lead to significant increases in both calculated
and experienced flood heights, resulting in serious flood
losses (structural damage and economic) as well as loss of
levee certification and loss of flood protectionfor compliant
post-FIRM structures. Providing this information to com-
munities may lead to coordinated watershed-wide actions to
manage for, or otherwise mitigate, these future risks.
A recent increase in losses from coastal storms has been
recognized by FEMA. In 2005, Hurricane Katrina clearly
illustrated this, reporting the most losses of any U.S. natural
disaster to date. This fact, coupled with the facts that new
developments in modeling and mapping technology have
allowed for more accurate flood hazard assessment over the
past few years and that populations at risk are growing in
coastal areas, has caused FEMA to develop a new national
coastal strategy. This strategy consists of assessing coastal
Flood Insurance Studies on a national scale and developing
a nationwide plan for improved coastal flood hazard iden-
tification. The assessment will prioritize regional studies,
look at funding allocations, and develop timelines for coastal
study updates.
River models that are affected by tides and storm surge
require the downstream boundary starting water surface
elevation to be the "1-percent-annual-chance" base flood
elevation (BFE) from an adjacent coastal study. If the coastal
study BFE is raised by 0.3 m or even 0.9 m because of sea-
level rise, the river study flood profile will be changed as
' Input to author team during CCSP SAP 4.1 Federal Advisory Com-
mittee review, Mark Crowell, FEMA.
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well and this will ultimately affect the resulting FIRMs that
are published. This is a complicated issue and points out
the fact that simply raising the coastal BFEs to estimate a
new 1-percent-annual-chance floodplain is not taking into
account the more complex hydraulics that will have unde-
termined effects on the upstream 1-percent-annual-chance
floodplains as well. The 1991 study does not factor in the
complexity of different tidal regimes that would be occur-
ring because of an increased sea level and how those regimes
would affect the geomorphology of the floodplains. This is
because FEMA is restricted in what it can and cannot do in
the regulated NFIP process.
Maryland has completed a comprehensive state strategy
document in response to sea-level rise (Johnson, 2000).
The Maryland Department of Natural Resources (Johnson,
2000) requires all communities to adopt standards that call
for all structures in the non-tidal floodplain to be elevated
0.3 m (1 ft) above the 100-year floodplain elevation, and all
coastal counties except Worcester, Somerset, and Dorchester
(the three most vulnerable to exacerbated flooding due to
sea-level rise) have adopted the 1-ft freeboard standard.
Although 1 foot of freeboard provides an added cushion of
protection to guard against uncertainty in floodplain projec-
tions, it may not be enough in the event of 0.6 to 0.9 m (2 to
3 ft) of sea-level rise, as Johnson (2000) points out.
Crowell et al. (2007) identified a need for a tide-gauge
analysis for FEMA Region III, which encompasses the mid-
Atlantic states, similar to new studies being done currently
on Chesapeake Bay by the state of Maryland. Each coastal
FEMA region has been evaluated and new guidelines and
specifications have been developed by FEMA for future
coastal restudies, the first of which was for the Pacific
Coast region. These guidelines outline new coastal storm
surge modeling and mapping procedures and allow for new
flooding and wave models to be used for generating coastal
BFEs.
To aid in ongoing recovery and rebuilding efforts, FEMA
initiated short-term projects in 2004 and 2005 to produce
coastal flood recovery maps for areas that were most se-
verely affected by Hurricanes Ivan, Katrina, and Rita. The
Katrinamaps, for example, show high water marks surveyed
after the storm, an inundation limit developed from these
surveyed points, and FEMA's Advisory Base Flood Eleva-
tions (ABFEs) and estimated zone of wave impacts.
These maps and associated ABFEs (generated for Katrina
and Rita only) were based on new flood risk assessments
that were done immediately following the storms to assist
communities with rebuilding. The recovery maps provide a
graphical depiction of ABFEs and coastal inundation associ-
ated with the observed storm surge high water mark values,
in effect documenting the flood imprint of the event to be
used in future studies and policy decisions. Adherence to
the ABFEs following Katrina affected eligibility for certain
FEMA-funded mitigation and recovery projects. They were
used until the Flood Insurance Studies (FIS) were updated
for the Gulf region and are available as advisory information
to assist communities in rebuilding efforts.
FEMA cannot require the use of future conditions data based
on planned land-use changes or proposed development for
floodplain management or insurance rating purposes unless
statutory and regulatory changes to the NFIP are made.
In addition, using projected coastal erosion information
for land-use management and insurance rating purposes
through the NFIP would require a legislative mandate and
regulatory changes.
9,6,2 Mapping Potential Impacts of Sea-
Level Rise on Coastal Floodplains
Floodplain management regulations are intended to mini-
mize damage as a result of flooding disasters, in conjunction
with other local land-use requirements and building codes.
Meeting only these minimum requirements will not guaran-
tee protection from storm damages. Management activities
that focus on mitigating a single, short-term hazard can result
in structures that are built only to withstand the hazards as
they are identified today, with no easy way to accommodate
an increased risk of damage in the coming decades (Honey-
cutt and Mauriello, 2005). The concept of going above and
beyond current regulations to provide additional hazards
information other than BFEs and the 1-percent-annual-
chance flood (coastal erosion and storm surge inundation
potential) has been advocated in some quarters with a No
Adverse Impact (NAI) program (Larson and Plasencia,
2002). A NAI toolkit was developed that outlines a strategy
for communities to implement a NAI approach to floodplain
management (ASFPM, 2003, 2008).
The International Codes (FEMA, 2005) include freeboard
(elevations above the BFE) and standards for coastal A Zones
that are more stringent than the NFIP criteria. The Inter-
national Codes also incorporate criteria from the national
consensus document ASCE 24-05 Flood Resistant Design
and Construction Standard (ASCE, 2006).
The Association of State Floodplain Mangers (ASFPM)
recently completed a study that contains a broad spectrum
of recommendations for improving the management of U. S.
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Chapter 9
floodplains (ASFPM, 2007). In their study, ASFPM noted
that changing climate was one of the major challenges
for the significant changes in social, environmental, and
political realities and their impact on floodplain manage-
ment, and highlights the widespread implications for flood
protection.
9.7.2
The U.S. Army Corps of Engineers heads the national
f loodproofing committee, established through the USAGE'S
floodplain management services program, to promote the
development and use of proper floodproofing techniques
throughout the United States (USAGE, 1996). The USAGE
publication on floodproofing techniques, programs, and
references gives an excellent overview of currently accepted
flood mitigation practices from an individual structure
perspective.
Mitigating flooding or "floodproofing" is a process for
preventing or reducing flood damages to structures and/or
to the contents of buildings located in flood hazard areas.
It mainly involves altering or changing existing properties;
however, it can also be incorporated into the design and
construction of new buildings. There are three general ap-
proaches to floodproofing:
1. Raising or moving the structure. Raising or mov-
ing the structure such that floodwaters cannot reach
damageable portions of it is an effective floodproofing
approach.
2. Constructing barriers to stop floodwaterfrom entering
the building. Constructing barriers can be an effec-
tive approach used to stop floodwaters from reaching
the damageable portions of structures. There are two
techniques employed in constructing barriers. The first
technique involves constructing free-standing barriers
that are not attached to the structure. The three primary
types of free-standing barriers used to reduce flood
damages are berms, levees, or f loodwalls. The second
technique that can be used to construct a barrier against
floodwaters is known as "dry floodproofing". With this
technique, a building is sealed such that floodwaters
cannot get inside.
3. Wet Floodproofing. This approach to floodproofing
involves modifying a structure to allow floodwaters
inside, but ensuring that there is minimal damage to
the building's structure and to its contents. Wet flood-
proofing is often used when dry floodproofing is not
possible or is too costly. Wet floodproofing is generally
appropriate in cases where an area is available above
flood levels to which damageable items can be relocated
or temporarily stored.
The recommended techniques of levees, berms, f loodwalls
and wet floodproofing are not allowed under the NFIP to
protect new individual structures. These techniques may
also have limited use in protecting older existing structures
in coastal areas. Although dry floodproofing is allowed in A
Zones (not V Zones), FEMA does not generally recommend
its use for new non-residential structures in the coastal A
Zones due to the potential flood forces. Under the NFIP, all
new construction and substantial improvements of residen-
tial buildings in A Zones must have the lowest floor elevated
to or above the BFE. All new construction and substantial
improvement of non-residential buildings in A Zones must
have either the lowest floor elevated to or above the BFE
or the building must be dry floodproofed to the BFE. In V
Zones, all new construction and substantial improvements
must have the bottom of the lowest horizontal structural
member of the lowest floor elevated to or above the BFE
on a pile or column foundation. Although the NFIP allows
dry floodproofing in coastal A Zone areas, FEMA does
not recommend its use in the coastal A Zone because of the
potential for severe flood hazards. While Base Flood Eleva-
tions in coastal A Zones contain a wave height of less than
3 feet, the severity of the hazard in coastal A Zones is often
much greater than in non-coastal A Zones due to the com-
bination of water velocity, wave action, and debris impacts
that can occur in these areas. For existing, older structures
in the coastal area, the best way to protect the structure is
elevating or relocating the structure.
9.7.3
Dramatic population growth along the coast brings new
challenges to managing national coastal resources. Coastal
and floodplain managers are challenged to strike the right
balance between a naturally changing shoreline and the
growing population's desire to use and develop coastal
areas. Challenges include protecting life and property from
coastal hazards; protecting coastal wetlands and habitats
while accommodating needed economic growth; and settling
conflicts between competing needs such as dredged material
disposal, commercial development, recreational use, nation-
al defense, and port development. Coastal land loss caused
by chronic erosion has been an ongoing management issue
in many coastal states that have Coastal Zone Management
(CZM) programs and legislation to mitigate erosion using a
basic retreat policy. With the potential impacts of sea-level
rise, managers and lawmakers must now decide how or
whether to adapt their current suite of tools and regulations
to face the prospect of an even greater amount of land loss
in the decades to come.
The U.S. Congress recognized the importance of meeting
the challenge of continued growth in the coastal zone and
responded by passing the Coastal Zone Management Act
in 1972. The amended act (CZMA, 1996), administered by
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to
A Focus on the Mid-Atlantic Region
NOAA, provides for management of U. S. coastal resources,
including the Great Lakes, and balances economic develop-
ment with environmental conservation.
As a voluntary federal-state partnership, the CZMA is
designed to encourage state-tailored coastal management
programs. It outlines two national programs, the National
Coastal Zone Management Program and the National
Estuarine Research Reserve System, and aims to balance
competing land and water issues in the coastal zone, while
estuarine reserves serve as field laboratories to provide a
greater understanding of estuaries and how humans impact
them. The overall program objectives of CZMA remain
balanced to "preserve, protect, develop, and where possible,
to restore or enhance the resources of the nation's coastal
zone" (CZMA, 1996).
9,7,4 The
Rise Issues
The CZMA language (CZMA, 1996) refers specifically to
sea-level rise issues (16 U.S.C. §1451). Congressional find-
ings (§302) calls for coastal states to anticipate and plan for
sea-level rise and climate change impacts.
In 16 U.S.C. §1452, Congressional declaration of policy
(§303), the Congress finds and declares that it is the national
policy to manage coastal development to minimize the loss
of life and property caused by improper development in
flood-prone, storm surge, geological hazard, and erosion-
prone areas, and in areas likely to be affected by or vulnera-
ble to sea-level rise, land subsidence, and saltwater intrusion,
and by the destruction of natural protective features such as
beaches, dunes, wetlands, and barrier islands; to study and
develop plans for addressing the adverse effects upon the
coastal zone of land subsidence and of sea-level rise; and to
encourage the preparation of special area management plans
which provide increased specificity in protecting significant
natural resources, reasonable coastal-dependent economic
growth, improved protection of life and property in hazard-
ous areas, including those areas likely to be affected by land
subsidence, sea-level rise (or fluctuating water levels of the
Great Lakes), and improved predictability in governmental
decision making.
" ( a
The reauthorization of CZMA in 1996 by the U. S. Congress
led to the establishment of the Coastal Zone Enhancement
Program (CZMA §309), which allows states to request ad-
ditional funding to amend their coastal programs in order to
support attainment of one or more coastal zone enhancement
objectives. The program is designed to encourage states and
territories to develop program changes in one or more of the
following nine coastal zone enhancement areas of national
significance: wetlands, coastal hazards, public access, ma-
rine debris, cumulative and secondary impacts, special area
management plans, ocean/Great Lakes resources, energy
and government facility citing, and aquaculture. The Coastal
Zone Enhancement Grants (§309) defines a "Coastal zone
enhancement objective" as "preventing or significantly
reducing threats to life and destruction of property by elimi-
nating development and redevelopment in high-hazard areas,
managing development in other hazard areas, and anticipat-
ing and managing the effects of potential sea-level rise and
Great Lakes level rise".
Through a self-assessment process, state coastal programs
identify high-priority enhancement areas. In consultation
with NOAA, state coastal programs then develop five-year
strategies to achieve changes (enhancements) to their coastal
management programs within these high-priority areas.
Program changes often include developing or revising a
law, regulation or administrative guideline, developing or
revising a special area management plan, or creating a new
program such as a coastal land acquisition or restoration
program.
For coastal hazards, states base their evaluation on the fol-
lowing criteria:
1. What is the general level or risk from specific coastal
hazards (i.e., hurricanes, storm surge, flooding, shore-
line erosion, sea-level rise, Great Lakes level fluctua-
tions, subsidence, and geological hazards) and risk to
life and property due to inappropriate development in
the state?
2. Have there been significant changes to the state's
hazards protection programs (e.g., changes to building
setbacks/restrictions, methodologies for determining
building setbacks, restriction of hard shoreline protec-
tion structures, beach/dune protection, inlet manage-
ment plans, local hazard mitigation planning, or local
post-disaster redevelopment plans, mapping/GIS/track-
ing of hazard areas)?
3. Does the state need to direct future public and private
development and redevelopment away from hazardous
areas, including the high hazard areas delineated as
FEMA V Zones and areas vulnerable to inundation
from sea- and Great Lakes-level rise?
4. Does the state need to preserve and restore the protec-
tive functions of natural shoreline features such as
beaches, dunes, and wetlands?
5. Does the state need to prevent or minimize threats to
existing populations and property from both episodic
and chronic coastal hazards?
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Chapter 9
Section 309 grants have benefited states such as Virginia
in developing local conservation corridors that identify and
prioritize habitat areas for conservation and restoration; and
New Jersey for supporting new requirements for permittees
to submit easements for land dedicated to public access,
when such access is required as a development permit
condition and is supporting a series of workshops on the
Public Trust Doctrine and ways to enhance public access
(see ).
• - - .'
Organizations such as the Coastal States Organization have
recently become more proactive in how coastal zone man-
agement programs consider adaptation to climate change,
including sea-level rise (Coastal States Organization, 2007)
and are actively leveraging each other's experiences and
approaches as to how best obtain baseline elevation in-
formation and inundation maps, how to assess impacts of
sea-level rise on social and economic resources and coastal
habitats, and how to develop public policy. There have also
been several individual statewide studies on the impact of
sea-level rise on local state coastal zones (e.g., Johnson, 2000
for Maryland; Cooper et al., 2005 for New Jersey). Many
state coastal management websites show an active public
education program with regards to providing information
on impacts of sea-level rise:
New Jersey:
Delaware:
Maryland: .
9,7,6.1
The evaluation of sea-level rise response planning in Mary-
land and the resulting strategy document constituted the bulk
of the state's CZMA §309 Coastal Hazard Assessment and
Strategy for 2000-2005 and in the 2006-2010 Assessment
and Strategy (MD DNR, 2006). Other mid-Atlantic states
mention sea-level rise as a concern in their assessments, but
have not yet developed a comprehensive strategy.
The sea-level rise strategy is designed to achieve the desired
outcome within a five-year time horizon. Implementa-
tion of the strategy is evolving over time and is crucial to
Maryland's ability to achieve sustainable management of
its coastal zone. The strategy states that planners and leg-
islators should realize that the implementation of measures
to mitigate impacts associated with erosion, flooding, and
wetland inundation will also enhance Maryland's ability to
protect coastal resources and communities whether sea level
rises significantly or not.
Maryland has taken a proactive step towards addressing
a growing problem by committing to implementation of
this strategy and increasing awareness and consideration
of sea-level rise issues in both public and governmental
arenas. The strategy suggests that Maryland will achieve
success in planning for sea-level rise by establishing effec-
tive response mechanisms at both the state and local levels.
Sea-level rise response planning is crucial in order to ensure
future survival of Maryland's diverse and invaluable coastal
resources.
Since the release of Maryland's sea-level rise response
strategy (Johnson, 2000), the state has continued to pro-
gressively plan for sea-level rise. The strategy is being used
to guide Maryland's current sea-level rise research, data
acquisition, and planning and policy development efforts
at both the state and local level. Maryland set forth a design
vision for "resilient coastal communities" in its CZMA §309
Coastal Hazard Strategy for 2006-2010 (MD DNR, 2006).
The focus of the approach is to integrate the use of recently
acquired sea-level rise data and technology-based products
into both state and local decision-making and planning
processes. Maryland's coastal program is currently work-
ing with local governments and other state agencies to: (1)
build the capacity to integrate data and mapping efforts into
land-use and comprehensive planning efforts; (2) identify
specific opportunities (i.e., statutory changes, code changes,
comprehensive plan amendments) for advancing sea-level
rise at the local level; and (3) improve state and local agency
coordination of sea-level rise planning and response activi-
ties (MD DNR, 2006).
In April 2007, Maryland's Governor, Martin O'Malley,
signed an Executive Order establishing a Commission on
Climate Change (Maryland, 2007) that is charged with
advising both the Governor and Maryland's General As-
sembly on matters related to climate change, and also with
developing a Plan of Action that will address climate change
on all fronts, including both its drivers and its consequences.
The Maryland Commission on Climate Change released its
Climate Action Plan in August 2008 (Maryland, 2008). A
key component of the Action Plan is The Comprehensive
Strategy to Reduce Maryland's Vulnerability to Climate
Change. The Strategy, which builds upon Maryland's
sea-level rise response strategy (Johnson, 2000), sets forth
specific actions necessary to protect Maryland's people,
property, natural resources, and public investments from
the impacts of climate change, sea-level rise, and coastal
storms. A comprehensive strategy and plan of action were
presented to the Maryland's Governor and General Assem-
bly in April 2008.
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
BOX 9.3: A Maryland Case Study—Implications for Decision Makers:
Worcester County Sea-Level Rise Inundation Modeling
The Maryland Department of Natural Resources (MD DNR) and the U.S. Geological Survey (USGS) completed the
development of a Worcester County Sea Level Rise Inundation Model in November 2006 (Johnson et a/., 2006).
Taking advantage of recent lidar coverage for the county, a Digital Elevation Model (DEM) was produced as the
base layer on which to overlay various sea-level rise scenarios modeled for three time periods: 2025, 2050, and
2100. The three scenarios were the historic rate of regional sea-level rise estimated from tide station records (3.1
millimeters per year), the average accelerated rate of sea-level rise projected by the 2001 IPCC report, and the
worst case scenario using the maximum projection of accelerated sea-level rise by the 2001 IPCC report (85 to
90 centimeters by 2100). The scenarios were applied to present day elevations of mean sea level (MSL), Mean high
water (MHW), and springtides derived at local tide stations. Box Figures 9.3aand 9.3b below show a typical result
for the year 2100 using an accelerated rate of sea-level rise scenario from the IPCC 2001 Report. An agricultural
block overlay depicts the potential loss of agricultural land to sea-level rise for Public Landing, Maryland.
MLW-MSL | j MSL-MHW
Box Figure 9.3a Day Public Landing.
Spring Tides
Agricultural
Box Figure 9.3b Public Landing at 2100 with
current rate of sea-level rise.
Development of the tool was completed in November 2006 and the results of the analyses will not be fully realized
until it is used by the Worcester County and Ocean City Planning and Emergency Management offices. Prior to
final release of this study, the MD DNR and USGS study team met with Worcester County planners to discuss
the model and how it could be applied to understanding of how existing structures and proposed growth areas
could be affected by future sea-level rise.
The tool is now being used by county plan-
ners to make decisions on development and
growth in the implementation of the March
2006 Comprehensive Plan for Worcester
County. For Emergency Response Planning,
the county is considering next steps and
how to best utilize this tool. As part of the
Comprehensive Plan (Worcester County
Planning Commission, 2006), Worcester
County is already is directing future growth
to outside of the category 3 hurricane storm
surge zone and the sea level overlays will be
used to perform risk assessments for exist-
ing and proposed development. Box Figure 9.3c Sea-level rise in 2100 using present day sea-level trends
coupled with a category 2 hurricane storm surge.
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Chapter 9
The Maryland Department of Natural Resources has
been active in developing an online mapping tool for gen-
eral information and educational purposes that provides
user-driven maps for shoreline erosion and for various sea-
level rise scenarios (see ) and has completed case studies
with other agencies (see Box 9.3) for studying implication
of sea-level rise for county-level planning. Although this
particular case study did not base results on a numerical
storm surge model, it represents the type of initial analyses
that local planners need to undertake.
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
o
Preparing for Sea-Level Rise
Author: James G. Titus, U.S. EPA
For at least the last four centuries, people have been
erecting permanent settlements in the coastal zone of
the Mid-Atlantic without regard to the fact that the
sea is rising. Because the sea has been rising slowly
and only a small part of the coast was developed,
the consequences have been relatively isolated and
manageable. Part I of this Product suggests, however,
that a 2-millimeter-per-year acceleration of sea-level
rise could transform the character of the mid-Atlantic
coast, with a large-scale loss of tidal wetlands and
possible disintegration of barrier islands. A 7-milli-
meter-per-year acceleration is likely to cause such a
transformation, although shore protection may prevent
some developed barrier islands from disintegrating
and low-lying communities from being taken over by
wetlands.
For the last quarter-century, scientific assessments
have concluded that regardless of possible policies
to reduce emissions of greenhouse gases, people will
have to adapt to a changing climate and rising sea
level. Adaptation assessments differentiate "reactive
adaptation" from "anticipatory adaptation".
Part III focuses on what might be done to prepare for
sea-level rise. Chapter 10 starts by asking whether
preparing for sea-level rise is even necessary. In many
cases, reacting later is more justifiable than preparing
now, because the rate and timing of future sea-level
rise are uncertain and the additional cost of acting
now can be high when the impacts are at least several
decades in the future. Nevertheless, for several types
of impacts, the cost of preparing now is very small
compared to the cost of reacting later. Examples where
preparing can be justified include:
Coastal wetland protection. It may be possible to
reserve undeveloped lands for wetland migration,
but once developed, it is very difficult to make land
available for wetland migration. Therefore, it is far
more feasible to aid wetland migration by setting
aside land before it is developed, than to require
development to be removed as sea level rises.
• Some long-lived infrastructure. Whether it is ben-
eficial to design coastal infrastructure to anticipate
rising sea level depends on the incremental cost of
designing for a higher sea level now, and the retrofit
cost of modifying the structure at some point in the
future. Most long-lived infrastructure in the threat-
ened areas is sufficiently sensitive to rising sea level
to warrant at least an assessment of the costs and
benefits of preparing for rising sea level.
• Floodplain management. Rising sea level increases
the potential disparity between rates and risk. Even
without considering the possibility of accelerated
sea-level rise, the National Academy of Sciences and
a Federal Emergency Management Agency (FEMA)-
supported study by the Heinz Center recommended
to Congress that insurance rates should reflect the
changing risks resulting from coastal erosion.
Chapter 11 discusses organizations that are preparing for
a possible acceleration of sea-level rise. Few organizations
responsible for managing coastal resources vulnerable
to sea-level rise have modified their activities. Most
examples of preparing for the environmental impacts of
sea-level rise are in New England, where several states
have enacted policies to enable wetlands to migrate inland
as sea-level rises. Ocean City, Maryland is an example
of a town considering future sea-level rise in its infra-
structure planning.
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Part III Overview
Chapter 12 examines the institutional barriers that make it
difficult to take the potential impacts of future sea-level rise
into account. Although few studies have discussed the chal-
lenge of institutional barriers and biases in coastal decision
making, their implications for sea-level rise are relatively
straightforward:
• Inertia and short-term thinking. Most institutions are
slow to take on new challenges, especially those that
require preparing for the future rather than fixing a
current problem.
• The interdependence of decisions reinforces institu-
tional inertia. In many cases, preparing for sea-level rise
requires a decision as to whether a given area will ulti-
mately be given up to the sea, protected with structures
and drainage systems, or elevated as the sea rises. Until
communities decide which of those three pathways they
will follow in a given area, it is difficult to determine
which anticipatory or initial response measures should
be taken.
• Policies favoring protection of what is currently there.
In some cases, longstanding policies for shore protection
(as discussed in Chapter 6) discourage planning mea-
sures that foster retreat. Because retreat may require a
greater lead time than shore protection, the presumption
that an area will be protected may imply that planning
is unnecessary. On the other hand, these policies may
help accelerate the response to sea-level rise in areas
where shore protection is needed.
• Policies favoring coastal development. One possible
response to sea-level rise is to invest less in the lands
likely to be threatened. However, longstanding policies
that encourage coastal development can discourage
such a response. On the other hand, increasingly dense
coastal development improves the ability to raise funds
required for shore protection. Therefore, policies that
encourage coastal development may be part of an insti-
tutional bias favoring shore protection, but they are not
necessarily a barrier to responding to sea-level rise.
Although most institutions have not been preparing for a ris-
ing sea (Chapter 11), that may be changing. As these chapters
were drafted, several states started to seriously examine
possible responses. For example, Maryland enacted a statute
to limit the adverse environmental impact of shore protec-
tion structures as sea level rises; and FEMA is beginning
to assess possible changes to the National Flood Insurance
Program. It is too soon to tell whether the increased interest
in the consequences of climate change will overtake—or be
thwarted by—the institutional barriers that have discouraged
action until now.
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Implications for Decisions
Lead Author: James G. Titus, U.S. EPA
Contributing Author: James E. Neumann, Industrial Economics, Inc.
KEY FINDINGS
In many cases, it is difficult to determine whether taking a specific action to prepare for sea-level rise
is justified, due to uncertainty in the timing and magnitude of impacts, and difficulties in quantifying
projected benefits and costs. Nevertheless, published literature has identified some cases where acting
now can be justified.
Key opportunities for preparing for sea-level rise concern coastal wetland protection, flood insurance
rates, and the location and elevation of coastal homes, buildings, and infrastructure.
Incorporating sea-level rise into coastal wetlands programs can be justified because the Mid-Atlantic
still has substantial vacant land onto which coastal wetlands could migrate as sea level rises. Policies
to ensure that wetlands are able to migrate inland are likely to be less expensive and more likely to
succeed if the planning takes place before people develop these dry lands than after the land becomes
developed. Possible tools include rolling easements, density restrictions, coastal setbacks, and vegetative
buffers.
Sea-level rise does not threaten the financial integrity of the National Flood Insurance Program.
Incorporating sea-level rise into the program, however, could allow flood insurance rates to more
closely reflect changing risk and enable participating local governments to more effectively manage
coastal floodplains.
Long-term shoreline planning is likely to yield benefits greater than the costs; the more sea level rises,
the greater the value of that planning.
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Chapter 10
I... .-
Most decisions of everyday life in the coastal zone have
little to do with the fact that the sea is rising. Some day-to-
day decisions depend on today's water levels. For example,
sailors, surfers, and fishermen all consult tide tables before
deciding when to go out. People deciding whether to evacu-
ate during a storm consider how high the water is expected
to rise above the normal level of the sea. Yet the fact that
the normal sea level is rising about 0.01 millimeters (mm)
per day does not affect such decisions.
Sea-level rise can have greater impacts on the outcomes of
decisions with long-term consequences. Those impacts do
not all warrant doing things differently today. In some cases,
the expected impacts are far enough in the future that people
will have ample time to respond. For example, there is little
need to anticipate sea-level rise in the construction of docks,
which are generally rebuilt every few decades, because the
rise can be considered when they are rebuilt (NRC, 1987).
In other cases, the adverse impacts of sea-level rise can be
more effectively addressed by preparing now than by react-
ing later. If a dike will eventually be required to protect a
community, for example, it can be more cost-effective to
leave a vacant right-of-way when an area is developed or
redeveloped, rather than tear buildings down later.
Society will have to adapt to a changing climate and rising
sea level (NRC, 1983; Hoffman et al, 1983; IPCC, 1990,
1996, 2001, 2007). The previous chapters (as well as Ap-
pendix 1) discuss vulnerable private property and public
resources, including ecosystems, real estate, infrastructure
(e.g., roads, bridges, parks, playgrounds, government build-
ings), and commercial buildings (e.g., hotels, office build-
ings, industrial facilities). People responsible for managing
those assets will have to adapt to changing climate and rising
sea level regardless of possible efforts to reduce greenhouse
gases, because human activity has already changed the
atmosphere and will continue to do so for at least the next
few decades (NRC, 1983; Hoffman e/a/., 1983; IPCC, 1990,
1996,2001,2007). Some of these assets will be protected or
preserved in their current locations, while others will have
to be moved inland or be lost. Chapters 6, 8, and 9 examine
government policies that are, in effect, the current response
to sea-level rise. Previous assessments have emphasized the
need to distinguish the problems that can be solved by future
generations reacting to changing climate from problems
that could be more effectively solved by preparing today
(Titus, 1990; Scheraga and Grambsch, 1998; Klein et al,
1999; Frankhausere/a/., 1999; OTA, 1993). Part III (i.e., this
Chapter and the next two chapters) makes that distinction.
This Chapter addresses the question: "Which decisions and
activities (if any) have outcomes sufficiently sensitive to sea-
level rise so as to justify doing things differently, depending
on how much the sea is expected to rise?" (CCSP, 2006).
Doing things differently does not always require novel
technologies or land-use mechanisms; most measures for
responding to erosion or flooding from sea-level rise have
already been used to address erosion or flooding caused by
other factors (see Section 6.1 in Chapter 6). Section 10.2
describes some categories of decisions that may be sensitive
to sea-level rise, focusing on the idea that preparing now
is not worthwhile unless the expected present value of the
benefits of preparing is greater than the cost. Sections 10.3
through 10.7 examine five issues related to rising sea level:
wetland protection, shore protection, long-lived structures,
elevating homes, and floodplain management.
The examples discussed in this Chapter focus on activities
by governments and homeowners, not by corporations. Most
published studies about responses to sea-level rise have been
funded by governments attempting to improve government
programs, communicate risk, or provide technical support
to homeowners and small businesses. Corporations also
engage in many of the activities discussed in this Chapter. It
is possible that privately funded (and unpublished) strategic
assessments have identified other near-term decisions that
are sensitive to sea-level rise.
A central premise of this Chapter is that the principles of
economics and risk management provide a useful paradigm
for thinking about the implications of sea-level rise for deci-
sion making. In this paradigm, decision makers have a well-
defined objective concerning potentially vulnerable coastal
resources, such as maximizing return on an investment (for a
homeowner or investor) or maximizing overall social welfare
(for a government). Box 10.1 elaborates on this analytical
framework. Economic analysis is not the only method for
evaluating a decision, but emotions, perceptions, ideology,
cultural values, family ties, and other non-economic factors
are beyond the scope of this Chapter.
This Chapter is not directly tied to specific sea-level rise
scenarios. Instead, it considers a wide range of plausible
sea-level rise over periods of time ranging from decades to
centuries, depending on the decision being examined. The
Chapter does not quantify the extent to which decisions
might be affected by sea-level rise. All discussions of costs
assume constant (inflation-adjusted) dollars.
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This Chapter's conceptual framework for decision making starts with the basic assumption that homeowners or
governments with an interest in coastal resources seek to maximize the value of those resources to themselves
(homeowners) or to the public as a whole (governments), over a period of time (planning horizon). Each year,
coastal resources provide some value to its owner. In the case of the homeowner, a coastal property might
provide rental income, or it might provide "imputed rent" that the owner derives from owning the home rather
than renting a similar home. The market value of a property reflects an expectation that property will generate
similar income over many years. Because a dollar of income today is worth more than a dollar in the future,
however, the timing of the income stream associated with a property also affects the value (see explanation of
"discounting" in Section 10.2).
Natural hazards and other risks can also affect the income a property provides over time. Erosion, hurricane
winds, episodic flooding, and other natural hazards can cause damages that reduce the income from the property
or increase the costs of maintaining it, even without sea-level rise. These risks are taken into account by owners,
buyers, and sellers of property to the extent that they are known and understood.
Sea-level rise changes the risks to coastal resources, generally by increasing existing risks. This Chapter focuses
on investments to mitigate those additional risks.
In an economic framework, investing to mitigate coastal hazards will only be worthwhile if the cost of the
investment (incurred in the short term) is less than net expected returns (which accrue over the long term).
Therefore, these investments are more likely to be judged worthwhile when (I) there is a large risk of near-term
damage (and it can be effectively reduced); (2) there is a small cost to effectively reduce the risk; or (3) the invest-
ment shifts the risk to future years.
Sea-level rise justifies changing what people do today if the
outcome from considering sea-level rise has an expected net
benefit, that is, the benefit is greater than the cost. Thus,
when considering decisions where sea-level rise justifies
doing things differently, one can exclude from further con-
sideration those decisions where either (1) the administra-
tive costs of preparing are large compared to the impacts
or (2) the net benefits are likely to be small or negative.
Few, if any, studies have analyzed the administrative costs
of preparing for sea-level rise. Nevertheless, one can infer
that administrative costs exceed any benefits from preparing
for a very small rise in sea level1. Most published studies
that investigate which decisions are sensitive to sea-level
rise (IPCC, 1990; NRC, 1987; Titus and Narayanan, 1996)
concern decisions whose consequences last decades or lon-
ger, during which time a significant rise in sea level might
occur. Those decisions mostly involve long-lived structures,
1 Administrative costs (e.g., studies, regulations, compliance, training)
of addressing a new issue are roughly fixed regardless of how small
the impact may be, while the benefits of addressing the issue depend
on the magnitude of sea-level rise. There would be a point below
which the administrative costs would be greater than any benefits
from addressing the issue.
land-use planning, or infrastructure, which can influence the
location of development for centuries, even if the structures
themselves do not remain that long.
For what type of decision is a net benefit likely from con-
sidering sea-level rise? Most analyses of this question have
focused on cases where (1) the more sea level rises, the
greater the impact; (2) the impacts will mostly occur in the
future and are uncertain because the precise impact of sea-
level rise is uncertain; and (3) preparing now will reduce the
eventual adverse consequences (see e.g., Figure 10.1).
In evaluating a specific activity, the first question is whether
preparing now would be better than never preparing. If so, a
second question is whether preparing now is also better than
preparing during some future year. Preparing now to avoid
possible effects in the future involves two key economic
principles: uncertainty and discounting.
Uncertainty. Because projections of sea-level rise and its
precise effects are uncertain, preparing now involves spend-
ing today for the sake of uncertain benefits. If sea level
rises less than expected, then preparing now may prove, in
retrospect, to have been unnecessary. Yet if sea level rises
more than expected, whatever one does today may prove to
be insufficient. That possibility tends to justify waiting to
prepare later, if people expect that a few years later (1) they
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The U.S. Climate Change Science Program
Chapter 10
Figure I O.I Homes set back from the shore. Myrtle Beach, South Carolina (April 2004) [Photo source: ®James G. Titus, used
with permission].
will know more about the threat and (2) the opportunity to
prepare will still be available2. Given these reasons to delay,
responding now may be difficult to justify, unless preparing
now is either fairly inexpensive or part of a "robust" strategy
(i.e., it works for a wide range of possible outcomes). For
example, if protecting existing development is important,
beach nourishment is a robust way to prepare because the
sand will offset some shore erosion no matter how fast or
slow the sea rises.
Discounting. Discounting is a procedure by which econo-
mists determine the "present value" of something given or
received at a future date (U. S. EPA, 2000). A dollar today is
preferred over a dollar in the future, even without inflation
(Samuelson and Nordhaus, 1989); therefore, a future dollar
must be discounted to make costs and benefits received in
different years comparable. Economists generally agree that
the appropriate way to discount is to choose an assumed
annual interest rate and compound it year by year (just as
interest compounds) and use the result to discount future
dollars (U.S. EPA, 2000; Congressional Research Service,
2003; OMB, 1992; Nordhaus, 2007a, b; Dasgupta, 2007).
Most of the decisions where preparing now has a positive
net benefit fall into at least one of three categories: (1) the
'- There is extensive economic literature on decision making and
planning under uncertainty, particularly where some effects are
irreversible. A review of this literature on the topic of "quasi-option
value" can be found in Freeman (2003). Quasi-option value arises
from the value of information gained by delaying an irreversible
decision (e.g., to rebuild a structure to withstand higher water levels).
In the sea-level rise context, it applies because the costs and benefits
of choosing to retreat or protect are uncertain, and it is reasonable
to expect that uncertainty will narrow over time concerning rates of
sea-level rise, the effects, how best to respond, and the costs of each
response option. Two influential works in this area include Arrow
and Fisher (1974) and Fisher and Hanemann (1987); an application
to climate policy decisions can be found in Ha-Duong (1998).
near-term impact is large; (2) preparing now costs little
compared to the cost of the possible impact; or (3) preparing
now involves options that reallocate (or clarify) risk.
10.2.1 Decisions That Address Large
Near-Term Impacts
If the near-term impact of sea-level rise is large, preparing
now may be worthwhile. Such decisions might include:
Beach nourishment to protect homes that are in immi-
nent danger of being lost. The cost of beach nourishment
is often less than the value of the threatened structures
(USAGE, 2000a).
• Enhancing vertical accretion (build-up) of wetlands that
are otherwise in danger of being lost in the near term
(Kentula, 1999; Kussler, 2006). Once wetlands are lost,
it can be costly (or infeasible) to bring them back.
Elevating homes that are clearly below the expected
flood level due to historic sea-level rise (see Sections
10.6 and 10.7). If elevating the home is infeasible (e.g.,
historic row houses), flood-proofing walls, doors,
and windows may provide a temporary solution (see
Chapter 9).
Fortifying dikes to the elevation necessary to protect
from current floods. Because sea level is rising, dikes
that once protected against a 100-year storm would be
overtopped by a similar flood on top of today's higher
sea level (see e.g., IPET, 2006).
10.2.2 Decisions Where Preparing Now
Costs Little
These response options can be referred to as "low regrets"
and "no regrets", depending on whether the cost is little or
nothing. The measures are justifiable, in spite of the uncer-
tainty about future sea-level rise, because little or nothing
is invested today, in return for possibly averting or delaying
a serious impact. Examples include:
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Coastal to
A Focus on the Mid-Atlantic Region
• Setting a new home back from the sea within a given
lot. Setting a home back from the water can push the
eventual damages from sea-level rise farther into the fu-
ture, lowering their expected present value3. Unlike the
option of not building, this approach retains almost the
entire value of using the property—especially if nearby
homes are also set back so that all properties retain the
complete panorama view of the waterfront—provided
that the lot is large enough to build the same house as
would have been built without the setback requirement
(see Figure 10.1).
• Building a new house with a higher floor elevation.
While elevating an existing house can be costly, build-
ing a new house on pilings one meter (a few feet) higher
only increases the construction cost by about 1 percent
(Jones et al, 2006).
• Designing new coastal drainage systems with larger
pipes to incorporate future sea-level rise. Retrofitting
or rebuilding a drainage system can cost 10 to 20 times
as much as including larger pipes in the initial construc-
tion (Titus et al., 1987).
• Rebuilding roads to a higher elevation during routine
reconstruction. If a road will eventually be elevated, it
is least expensive to do so when it is rebuilt for other
purposes.
• Designing bridges and other major facilities. As sea
level rises, clearance under bridges declines, impairing
navigation (TRB, 2008). Building the bridge higher in
the first place can be less expensive than rebuilding it
later.
1 . n That or
ft - a-Level Rise
Instead of imposing an immediate cost to avoid problems
that may or may not occur, these approaches impose a future
cost, but only if and when the problem emerges. The premise
for these measures is that current rules or expectations can
encourage people to behave in a fashion that increases costs
more than necessary. People make better decisions when
all of the costs of a decision are internalized (Samuelson
and Nordhaus, 1989). Changing rules and expectations can
avoid some costs, for example, by establishing today that the
eventual costs of sea-level rise will be borne by a property
owner making a decision sensitive to sea-level rise, rather
than by third parties (e.g., governments) not involved in the
decision. Long-term shoreline planning and rolling ease-
ments are two example approaches.
Long-term shoreline planning can reduce economic or en-
vironmental costs by concentrating development in areas
that will not eventually have to be abandoned to the rising
sea. People logically invest more along eroding shores if
they assume that the government will provide subsidized
shore protection (see Box 10.2) than in areas where own-
ers must pay for the shore protection or where government
rules require an eventual abandonment. The value to a buyer
of that government subsidy is capitalized into higher land
prices, which can further encourage increased construction.
Identifying areas that will not be protected can avoid misal-
location of both financial and human resources. If residents
wrongly assume that they can expect shore protection and
the government does not provide it, then real estate prices
can decline; in extreme cases, people can lose their homes
unexpectedly. People's lives and economic investments
can be disrupted if dunes or dikes fail and a community is
destroyed. A policy that clearly warns that such an area will
not be protected (see Section 12.3 in Chapter 12) could lead
owners to strategically depreciate the physical property4 and
avoid some of the noneconomic impacts that can occur after
an unexpected relocation (see Section6.4.1 and Section 12.3
for further discussion).
Rolling easements can also reallocate or clarify the risks of
sea-level rise, depending on the pre-existing property rights
of a given jurisdiction (Titus, 1998). A rolling easement is
an arrangement under which property owners have no right
or expectation of holding back the sea if their property is
threatened. Rolling easements have been implemented by
regulation along ocean and sheltered shores in three New
England states (see Section 11.2 in Chapter 11) and along
ocean shores in Texas and South Carolina. Rolling easements
can also be implemented as a type of conservation easement,
with the easement donated, purchased at fair market value,
or exacted as a permit condition for some type of coastal
development (Titus, 1998). In either case, they prevent
property owners from holding back the sea but otherwise
do not alter what an owner can do with the property. As the
sea advances, the easement automatically moves or "rolls"
landward. Without shoreline armoring, sediment transport
remains undisturbed and wetlands and other tidal habitat can
migrate naturally. Because the dry beach and intertidal land
continues to exist, the rolling easement also preserves the
public's lateral access right to walk along the shore5 (Matcha
versus Mattox, 1986).
3 The present value of a dollar! years in the future is l/(l+i)T, where
i is the interest rate (discount rate) used for the calculations (see
Samuelson and Nordhaus, 1989).
4 Yohe etal. (1996) estimated that the nationwide value of "foresight"
regarding response to sea-level rise is $20 billion, based largely on
the strategic depreciation that foresight makes possible.
5 Another mechanism for allowing wetlands and beaches to migrate
inland are setbacks, which prohibit development near the shore.
Setbacks can often result in successful "takings" claims if a property
is deemed undevelopable due to the setback line. By contrast, rolling
easements place no restrictions on development and hence are not
constitutional takings (see, e.g., Titus, 1998).
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Chapter
Do government shore protection and flood insurance programs increase property values and encourage coastal
development? Economic theory would lead one to expect that in areas with high land values, the benefits of coastal
development are already high compared to the cost of development, and thus most of these areas will become de-
veloped unless the land is acquired for other purposes. In these areas, government programs that reduce the cost
of maintaining a home should generally be reflected in higher land values; yet they would not significantly increase
development because development would occur without the programs. By contrast, in marginal areas with low land
prices, coastal programs have the potential to reduce costs enough to make a marginal investment profitable.
Several studies have investigated the impact of flood insurance on development, with mixed results. Leatherman
(1997) examined North Bethany Beach, Delaware, a community with a checkerboard pattern of lands that were eli-
gible and ineligible for federal flood insurance due to the Coastal Barrier Resources Act. He found that ocean-front
lots generally sold for $750,000, with homes worth about $250,000. Development was indistinguishable between
areas eligible and ineligible for flood insurance. In the less affluent areas along the back bays, however, the absence
of federal flood insurance was a deterrent to developing some of the lower-priced lots. Most other studies have
not explicitly attempted to distinguish the impact of flood insurance on low- and high-value lands. Some studies
(e.g., Cordes and Yezer, 1998; Shilling et a/., 1989) have concluded that the highly subsidized flood insurance policies
increased development during the 1970s, but the actuarial policies since the early 1980s have had no detectable
impact on development. Others have concluded that flood insurance has a minimal impact on development (e.g.,
GAO, 1982; Miller, 1981). The Heinz Center (2000) examined the impacts of the National Flood Insurance Program
(NFIP) and estimated that "the density of structures built within the V Zone after 1981 may be 15 percent higher
than it would have been if the NFIP had not been adopted. However, the expected average annual flood and erosion
damage to these structures dropped close to 35 percent. Thus, overall, the damage to V Zone structures built after
1981 is between 25 and 30 percent lower than it would have been if development had occurred at the lower densi-
ties, but higher expected damage that would have occurred absent the NFIP". A report to the Federal Emergency
Management Agency (FEMA) reviewed 36 published studies and commentaries concerning the impacts of flood
insurance on development and concluded that none of the studies offer irrefutable evidence that the availability, or
the lack of availability, of flood insurance is a primary factor in floodplain development today (Evatt, 1999, 2000).
Considering shore protection and flood insurance together, The Heinz Center (2000) estimated that "in the ab-
sence of insurance and other programs to reduce flood risk, development density would be about 25 percent lower
in areas vulnerable to storm wavers (i.e., V Zones) than in areas less susceptible to damage from coastal flooding".
Cordes and Yezer (1998) modeled the impact on new building permit activity in coastal areas of shore protection
activity in 42 coastal counties, including all of the counties with developed ocean coasts in New York, New Jersey,
Maryland, and Virginia. They did not find a statistically significant relationship between shore protection and build-
ing permits.
The impact of federal programs on property values has not been assessed to the same extent. The Heinz Center
(2000) reported that along the Atlantic coast, a house with a remaining lifetime of 10 to 20 years before succumb-
ing to erosion is worth 20 percent less than a home expected to survive 200 years. Landry et a/. (2003) found that
property values tend to be higher with wide beaches and low erosion risk. It would therefore follow that shore
protection programs that widen beaches, decrease erosion risk, and lengthen a home's expected lifetime would
increase property values. Nevertheless, estimates of the impact on property values are complicated by the fact that
proximity to the shore increases the risk of erosion but also improves access to the beach and views of the water
(Bin et a/., 2008).
Under a rolling easement, the property owner bears all of the
risk of sea-level rise. Without a rolling easement, property
owners along most shores invest as if their real estate is
sustainable, and then expend resources—or persuade gov-
ernments to expend resources—to sustain the property. The
overall effect of the rolling easement is that a community
clearly decides to pursue retreat instead of shore protection
in the future. The same result could also be accomplished
by purchasing (or prohibiting development on) the land that
would potentially be eroded or submerged as sea level rises.
That approach, however, would have a large near-term social
cost because the coastal land would then be unavailable for
valuable uses. By contrast, rolling easements do not prevent
the property from being used for the next several decades
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Landward Migration of Wetlands onto
Property Subject to Rolling Easement
*SO YEARS
Figure 10.2 A rolling easement allows construc-
tion near the shore, but requires the property
owner to recognize nature's right-of-way to ad-
vance inland as sea level rises. In the case depicted,
the high marsh reaches the footprint of the house
40 years later. Because the house is on pilings, it
can still be occupied (assuming that it is hooked
to a sewerage treatment plant. A flooded septic
system would probably fail, because the drainfield
must be a minimum distance above the water
table). After 60 years, the marsh has advanced
enough to require the owner to park their car
along the street and construct a catwalk across
the front yard. After 80 years, the marsh has taken
over the entire yard; moreover, the footprint of
the house is now seaward of mean high water and
hence, on public property. At this point, additional
reinvestment in the property is unlikely. Twenty
years later, the particular house has been re-
moved, although other houses on the same street
may still be occupied. Eventually, the entire area
returns to nature. A home with a rolling easement
would depreciate in value rather than appreciate
like other coastal real estate. But if the loss is
expected to occur 100 years from today, it would
only reduce the current property value by I to 5
percent, which could be compensated or offset by
other permit considerations (Titus, 1998).
while the land remains dry. (Even if the government pur-
chases the rolling easement, the purchase price is a transfer
of wealth, not a cost to society6.) The landward migration
from the rolling easement should also have lower eventual
costs than having the government purchase property at fair
market value as it becomes threatened (Titus, 1991). Prop-
erty owners can strategically depreciate their property and
make other decisions that are consistent with the eventual
abandonment of the property (Yohe et al., 1996; Titus, 1998),
efficiently responding to information on sea-level rise as it
becomes available. Figure 10.2 shows how a rolling easement
might work over time in an area already developed when
rolling easements are obtained.
10.3 PROTECTING COASTAL WETLANDS
The nation's wetland programs generally protect wetlands
in their current locations, but they do not explicitly consider
retreating shorelines. As sea level rises, wetlands can adapt
by accreting vertically (Chapter 4) and migrating inland.
Most tidal wetlands are likely to keep pace with the current
' A "social cost" involves someone losing something of value (e.g,.
the right to develop coastal property) without a corresponding gain
by someone else. A "wealth transfer" involves one party losing
something of value with another party gaining something of equal
value (e.g., the cost of a rolling easement being transferred from the
government to a land owner). For additional details, see Samuelson
and Nordhaus (1989).
rate of sea-level rise but could become marginal with an
acceleration of 2 millimeters (mm) per year, and are likely
to be lost if sea-level rise accelerates by 7 mm per year (see
Chapter 4). Although the dry land available for potential
wetland migration is estimated to be less than 20 percent
of the current area of wetlands (see Titus and Wang, 2008),
these lands could potentially become important wetland
areas in the future. However, given current policies and
land-use trends, they may not be available in the future
(Titus, 1998,2001). Much of the coast is developed or being
Figure 10.3 Coastal wetlands migrating onto previously dry
lowland. Webbs Island, just east of Machipongo, in Northampton
County, Virginia (June 2007) [Photo source: ®James G. Titus, used
with permission].
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The U.S. Climate Change Science Program
Chapter 10
Figure 10.4 Wetland migration thwarted by development and
shore protection. Elevating the land surface with fill prevents
wetlands from migrating into the back yard with a small or modest
rise in sea level. The bulkhead prevents waves from eroding the
land, which would otherwise provide sand and other soil materi-
als to help enable the wetlands to accrete with rising sea level
(Monmouth, New Jersey, August 2003) [Photo source: ®James
G. Titus, used with permission].
developed, and those who own developed dry land adjacent
to the wetlands increasingly take measures to prevent the
wetlands from migrating onto their property (see Figure
10.4 and Chapter 6).
Continuing the current practice of protecting almost all de-
veloped estuarine shores could reverse the accomplishments
of important environmental programs. Until the mid-twenti-
eth century, tidal wetlands were often converted to dredge-
and-fill developments (see Section 6.1.1.2 in Chapter 6 for an
explanation of these developments and their vulnerability to
sea-level rise). By the 1970s, the combination of federal and
state regulations had, for all practical purposes, halted that
practice. Today, most tidal wetlands in the Mid-Atlantic are
off-limits to development. Coastal states generally prohibit
the filling of low marsh, which is publicly owned in most
states under the Public Trust Doctrine (see Section 8.2).
A landowner who wants to fill tidal wetlands on private
property must usually obtain a permit from the U.S. Army
Corps of Engineers (USAGE)7. These permits are generally
not issued unless the facility is inherently water-related, such
as a marina8. Even then, the owners usually must mitigate
the loss of wetlands by creating or enhancing wetlands
elsewhere (U.S. EPA and USACE, 1990). (Activities with
small impacts on wetlands, however, are often covered
by a nationwide permit, which exempts the owner from
having to obtain a permit [see Section 12.2]). The overall
effect of wetland programs has been to sharply reduce the
rate of coastal wetland loss (e.g., Stockton and Richardson,
1987; Hardisky and Klemas, 1983) and to preserve an al-
33 U.S.C. §§403, 409, 1344(a).
40 C.F.R. §230.10(a)(3).
most continuous strip of marshes, beaches, swamps, and
mudflats along the U.S. coast. If sea-level rise accelerates,
these coastal habitats could be lost unless this generation
maintains open space for their inland migration or future
generations use technology to ensure that wetland surfaces
rise as rapidly as the sea (NRC, 2007).
Current approaches would not protect wetlands for future
generations if sea level rises beyond the ability of wetlands
to accrete, which is likely for most of Chesapeake Bay's
wetlands if sea level rises 50 centimeters (cm) in the next
century, and for most of the Mid-Atlantic if sea level rises
100 cm (see Figure 4.4).
Current federal statutes are designed to protect existing
wetlands, but the totality of the nation's wetland protection
program is the end result of decisions made by many actors.
Federal programs discourage destruction of most existing
coastal wetlands, but the federal government does little to
allow tidal wetlands to migrate inland (Titus, 2000). North
Carolina, Maryland, New Jersey, and New York own the
tidal wetlands below mean high water; and Virginia, Dela-
ware, and Pennsylvania have enough ownership interest un-
der the Public Trust Doctrine to preserve them (Titus, 1998).
However, most states give property owners a near-universal
permit to protect property by preventing wetlands from
migrating onto dry land. Farmers rarely erect shore protec-
tion structures, but homeowners usually do (Titus, 1998;
NRC, 2007). Only a few coastal counties and states have
decided to keep shorefront farms and forests undeveloped
(see Sections Al.D, ALE, and Al.F in Appendix 1). Govern-
ment agencies that hold land for conservation purposes are
not purchasing the land or easements necessary to enable
wetlands to migrate inland (Section 11.2.1 discusses private
conservancies). In effect, the nation has decided to save its
existing wetlands. Yet the overall impact of the decisions
made by many different agencies is very likely to eliminate
wetlands by blocking their landward migration as a rising
sea erodes their outer boundaries.
Not only is the long-term success of wetland protection
sensitive to sea-level rise, it is also sensitive to when people
decide to prepare. The political and economic feasibility of
allowing wetlands to take over a given parcel as sea level
rises is much greater if appropriate policies are in place
before that property is intensely developed. Many coastal
lands are undeveloped today, but development continues.
Deciding now that wetlands will have land available to
migrate inland could protect more wetlands at a lower
cost than deciding later (Titus, 1991). In some places, such
policies might discourage development in areas onto which
wetlands may be able to migrate. In other areas, development
could occur with the understanding that eventually land will
revert to nature if sea level rises enough to submerge it. As
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with beach nourishment, artificially elevating the surfaces
of tidal wetlands would not always require a lead-time of
several decades; but developing technologies to elevate the
wetlands, and determining whether and where they are ap-
propriate, could take decades. Finally, in some areas, the
natural vertical accretion (build-up) of tidal wetlands is
impaired by human activities, such as water flow manage-
ment, development that alters drainage patterns, and beach
nourishment and inlet modification, which thwarts barrier
island overwash. In those areas, restoring natural processes
before the wetlands are lost is more effective than artificially
re-creating them (U.S. EPA, 1995; U.S. EPA and USAGE,
1990; Kruczynski, 1990).
Although the long-term success of the nation's efforts to pro-
tect wetlands is sensitive to sea-level rise, most of the indi-
vidual decisions that ultimately determine whether wetlands
can migrate inland depend on factors that are not sensitive to
sea-level rise. The desire of bay-front homeowners to keep
their homes is strong, and unlikely to diminish even with a
significant acceleration of sea-level rise9. State governments
must balance the public interest in tidal wetlands against
the well-founded expectations of coastal property owners
that they will not have to yield their property. Only a few
states (none in the Mid-Atlantic) have decided in favor of the
wetlands (see Section 11.2.1). Local government decisions
regarding land use reflect many interests. Objectives such
as near-term tax revenues (often by seasonal residents who
make relatively few demands for services) and a reluctance
to undermine the economic interests of landowners and
commercial establishments are not especially sensitive to
rising sea level.
Today's decentralized decision-making process seems to
protect existing coastal wetlands reasonably well at the
current rate of sea-level rise; however, it will not enable
wetlands to migrate inland as sea level rises. A large-scale
landward migration of coastal wetlands is very unlikely to
occur in most of the Mid-Atlantic unless a conscious deci-
sion is made for such a migration by a level of government
with the authority to see it through. Tools for facilitating a
landward migration include coastal setbacks, density restric-
tions, rolling easements, vegetation buffers, and building
design standards (see Sections 6.1.2, and Al.D and Al.F in
Appendix 1 for further details).
The case for anticipating sea-level rise as part of efforts
to prevent erosion and flooding has not been as strong as
the case for wetland protection. Less lead time is required
for shore protection than for a planned retreat and wetland
migration (NRC, 1987). Dikes, seawalls, bulkheads, and
revetments can each be built within a few years. Beach
nourishment is an incremental periodic activity; if the
sea rises more than expected, communities can add more
sand.
The U.S. Army Corps of Engineers has not evaluated
whether sea-level rise will ultimately require fundamental
changes in shore protection; such changes do not appear to
be urgent. Since the early 1990s, USAGE has recommended
robust strategies: "Feasibility studies should consider which
designs are most appropriate for a range of possible future
rates of rise. Strategies that would be appropriate for the
entire range of uncertainty should receive preference over
those that would be optimal for a particular rate of rise
but unsuccessful for other possible outcomes" (USAGE,
2000a). To date, this guidance has not significantly altered
USAGE'S approach to shore protection. Nevertheless, there
is some question as to whether continued beach nourishment
would be sustainable in the future if the rate of sea-level
rise accelerates. It may be possible to double or triple the
rate at which USAGE nourishes beaches and to elevate the
land surfaces of barrier islands 50 to 100 cm, and thereby
enable land surfaces to keep pace with rising sea level in
the next century. Yet continuing such a practice indefinitely
would eventually leave back-barrier bays much deeper than
today (see Chapter 5), with unknown consequences for the
environment and the barrier islands themselves. Similarly,
it may be possible to build a low bulkhead along mainland
shores as sea level rises 50 to 100 cm; however, it could be
more challenging to build a tall dike along the same shore
because it would block waterfront views, require continual
pumping, and expose people behind the dike to the risk of
flooding should that dike fail (Titus, 1990).
The fact that eventually a landowner will either hold back
the sea or allow it to inundate a particular parcel of land
does not, by itself, imply that the owner must respond
today. A community that will not need a dike until the sea
rises 50 to 100 cm has little reason to build that dike today.
Nevertheless, if the land where the dike would eventually
be constructed is vacant now, the prospect of future sea-
level rise might be a good reason to leave that land vacant.
A homeowner whose house will be inundated (or eroded)
in 30 to 50 years has little reason to move the house back
today, but if the house is damaged by fire or storms, it
might be advisable to rebuild the house on a higher (or
more inland) part of the lot to provide the rebuilt structure
a longer lifetime.
' See Weggel et al. (1989), Titus et al. (1991), and NRC (2007) for an
examination of costs and options for estuarine shore protection.
149
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Chapter
Whether one must be concerned about long-term sea-level
rise ultimately depends on the lead time of the response
options and on the costs and benefits of acting now versus
acting later. A fundamental premise of cost-benefit analy-
sis is that resources not deployed on a given project can be
invested profitably in another activity and yield a return on
investment. Delaying the response is economically efficient
if the most effective response can be delayed with little or
no additional cost, which is the case with most engineering
responses to sea-level rise. For a given level of protection,
dikes, seawalls, beach nourishment, and elevating struc-
tures and roadways are unlikely to cost more in the future
than they cost today (USAGE, 2000b, 2007). Moreover,
these approaches can be implemented within the course of
a few years. If shore protection is the primary approach to
sea-level rise, responding now may not be necessary, with
two exceptions.
The first exception could be called the "retrofit penalty" for
failure to think long-term. It may be far cheaper to design for
rising sea level in the initial design of a new (or rebuilt) road
or drainage system than to modify it later because modify-
ing it later requires the facility, in effect, to be built twice.
For example, in a particular watershed in Charleston, South
Carolina, if sea level rises 30 cm (1 ft), the planned drainage
system would fail and need to be rebuilt, but it would only
cost an extra 5 percent to initially design the system for a
30-cm rise (Titus et al., 1987). Similarly, bridges are often
designed to last for 100 years, and although roads are paved
every 10 to 20 years, the location of a road may stay the same
for centuries. Thus, choices made today about the location
and design of transportation infrastructure can have a large
impact on the feasibility and cost of accommodating rising
sea level in the future (TRB, 2008). The design and location
of a house is yet another example. If a house is designed to
be movable, it can be relocated away from the shore; but non-
moveable houses, such as a brick house on a slab foundation,
could be more problematic. Similarly, the cost of building a
house 10 meters (m) farther from the shore may be minor if
the lot is large enough, whereas the cost of moving it back
10 m could be substantial (U.S. EPA, 1989).
The second exception concerns the incidental benefits of
acting sooner. If a dike is not needed until the sea rises 0.5
m, because at that point a 100-year storm would flood the
streets with 1 m of water, the decision to not build the dike
today implicitly accepts the 0.5m of water that such a storm
would provide today. If a dike is built now, it would stop this
smaller flood as well as protect from the larger flood that
will eventually occur. This reasoning was instrumental in
leading the British to build the Thames River Barrier, which
protects London. Some people argued that this expensive
structure was too costly given the small risk of London
flooding, but rising sea level implied that such a structure
would eventually have to be built to prevent a flood disaster.
Hence, the Greater London Council decided to build it dur-
ing the 1970s (Gilbert and Homer, 1984). As expected, the
barrier closed 88 times to prevent relatively minor flooding
between 1983 and 2005 (Lavery and Donovan, 2005).
While most engineering responses canbe delayed with little
penalty, failure to consider sea-level rise when making land-
use decisions could be costly. Once an area is developed,
the cost of vacating it as the sea rises is much greater than
that cost would have been if the area was not developed.
This does not mean that eventual inundation should auto-
matically result in placing land off-limits to development.
Even if a home has to be torn down 30 to 50 years hence, it
might still be worth building. In some coastal areas where
demand for beach access is great and land values are higher
than the value of the structures, rentals may recover the cost
of home construction in less than a decade. However, once
an area is developed, it is unlikely to be abandoned unless
either the eventual abandonment was part of the original
construction plan or the owners can not afford to hold
back the sea. Therefore, the most effective way to preserve
natural shores is to make such a decision before an area is
developed. Because the coast is being developed today, a
failure to deal with this issue now is, in effect, a decision to
allow the loss of wetlands and bay beaches along most areas
where development takes place.
Many options can be delayed because the benefits of pre-
paring for sea-level rise would still accrue later. Delaying
action decreases the present value of the cost of acting and
may make it easier to tailor the response to what is actually
necessary. Yet delay can also increase the likelihood that
people do not prepare until it is too late. One way to ad-
dress this dilemma is to consider the lead times associated
with particular types of adaptation (IPCC CZMG, 1992;
O'Callahan, 1994). Emergency beach nourishment and
bulkheads along estuarine shores canbe implemented in less
than a year. Large-scale beach nourishment generally takes a
few years. Major engineering projects to protect London and
the Netherlands took a few decades to plan, gain consensus,
and construct (e.g., Gilbert and Horner, 1984). To minimize
the cost of abandoning an area, land use planning requires a
lead time of 50 to 100 years (Titus, 1991, 1998).
Ill"
People are increasingly elevating homes to reduce the risk of
flooding during severe storms and, in very low-lying areas,
people are also elevating their yards. The cost of elevating
even a small wood-frame cottage on a block foundation
is likely to be $15,000 to $20,000; larger houses cost pro-
portionately more (Jones et al, 2006; FEMA, 1998). If it
ISO
-------
is necessary to drill pilings, the cost is higher because the
house must be moved to the side and then moved back onto
the pilings. If elevating the home prevents its subsequent
destruction within a few decades, it will have been worth-
while. At a 5 percent discount rate, for example, it is worth
investing 25 percent of the value of a structure to avoid a
guaranteed loss 28 years later10. In areas where complete
destruction is unlikely, people sometimes elevate homes to
obtain lower insurance rates and to avoid the risk of water
damages to walls and furniture. The decision to elevate
involves other factors, both positive and negative, including
better views of the water, increased storage and/or parking
spaces, and greater difficulty for the elderly or disabled to
enter their homes. Rising sea level can also be a motivating
factor when an owner is uncertain about whether the current
risks justify elevating the house, because rising water levels
would eventually make it necessary to elevate it (unless there
is a good chance that the home will be rebuilt or replaced
before it is flooded).
In cases where a new home is being constructed, or an exist-
ing home is elevated for reasons unrelated to sea-level rise
(such as a realization of the risk of flooding), rising sea level
would justify a higher floor elevation that would otherwise
be the case. For example, elevating a $200,000 home on
pilings to 30 cm above the base flood elevation when the
home is built would increase the construction cost by ap-
proximately $500 to $1000 more than building the home at
the base flood elevation (Jones et al., 2006). Yet a 30 cm
rise in sea level would increase the actuarial annual flood
insurance premium by more than $2000 if the home was not
elevated the extra 30 cm (NFIP, 2008).
The Federal Emergency Management Agency (FEMA)
works with state and local governments on a wide array of
activities that are potentially sensitive to rising sea level,
including f loodplain mapping, f loodplain regulations, flood
insurance rates, and the various hazard mitigation activities
that often take place in the aftermath of a serious storm.
Although the outcomes of these activities are clearly sensi-
tive to sea-level rise, previous assessments have focused
on coastal erosion rather than on sea-level rise. Because
implications of sea-level rise and long-term erosion overlap
in many cases, previous efforts provide insights on cases
where the risks of future sea-level rise may warrant chang-
ing the way things are done today.
10 i.e., $25 invested today would be worth $25 x (1.05)28 = $98 twenty-
eight years hence. Therefore, it is better to invest $25 today than to
face a certain loss of $100 twenty-eight years hence (see glossary
for definition of discount rate).
10.7.1
The flood insurance program requires new or substantially
rebuilt structures in the coastal floodplain to have the first
floor above the base flood elevation, i.e., 100-year flood level
(see Chapter 9). The program vests considerable discretion
in local officials to tailor specific requirements to local con-
ditions, or to enact regulations that are more stringent than
FEMA's minimum requirements. Several communities have
decided to require floor levels to be 30 cm (or more) above
the base flood elevation (e.g., Township of Long Beach,
2008; Town of Ocean City, 1999; see also Box A1.5 in Ap-
pendix 1). In some cases, past or future sea-level rise has
been cited as one of the justifications for doing so (e.g., Cape
Cod Commission, 2002). There is considerable variation in
both the costs and benefits of designing buildings to accom-
modate future sea-level rise. If local governments believe
that property owners need an incentive to optimally address
sea-level rise, they can require more stringent (i.e., higher)
floor elevations. A possible reason for requiring higher floor
elevations in anticipation of sea-level rise (rather than allow-
ing the owner to decide) is that, under the current structure of
the program, the increased risk from sea-level rise does not
lead to proportionately higher insurance rates (see Section
10.7.3.1) (although rates can rise for other reasons).
Local jurisdictions have pointed out (see Box A1.6 in Ap-
pendix 1) that requiring floor elevations above the base flood
elevation to prepare for sea-level rise can create a disparity
between property inside and outside the existing 100-year
floodplain.
Unless floodplain mapping also takes sea-level rise into
account, a building in the current floodplain would have
to be higher than adjacent buildings on higher ground just
outside the floodplain (see Figure 10.5). Thus, the ability of
local officials to voluntarily prepare for rising sea level is
somewhat constrained by the lack of floodplain mapping
that takes sea-level rise into account. Incorporating sea-level
rise into floodplain maps would be a low-regrets activity,
because it is relatively inexpensive and would enable local
officials to modify requirements where appropriate.
I§,7,3 Federal Flood Insurance
The available reports on the impacts of rising sea level or
shoreline retreat on federal flood insurance have generally
examined one of two questions:
What is the risk to the financial integrity of the flood
insurance program?
Does the program discourage policyholders from pre-
paring for sea-level rise by shielding them from the
consequences of increased risk?
151
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The U.S. Climate Change Science Program
Chapter 10
Rationale for Incorporating Sea-Level Rise into Floodplain Mapping
iQQ-ysaf flood wtlTi rtigrwr ssa level
Today's 100-year flood
Open Water
Figure 10.5 The (left) three houses in the existing floodplain have first floor elevations about 80 centimeters (cm) above the
level of the 100-year storm, to account for a projected 50-cm rise in sea level and the standard requirement for floors to be
30 cm above the base flood elevation. The (right) three homes outside of the regulated floodplain are exempt from the require-
ment. Actual floods, however, do not comply with floodplain regulations. A 100-year storm on top of the higher sea level would
thus flood the buildings to the right which are outside of today's floodplain, while the regulated buildings would escape the flooding.
This potential disparity led the city of Baltimore to suggest that floodplain mapping should account for sea-level rise as part of any
process to increase the freeboard requirement (see Box AI.6 in Appendix I).
No assessment has found that sea-level rise threatens the
federal program's financial integrity. A 1991 report to
Congress by FEMA, for example, concluded that there was
little need to change the Flood Insurance Program because
rates would be adjusted as sea level rises and flood maps are
revised (FEMA, 1991). Nevertheless, the current rate struc-
ture can discourage some policy holders from preparing for
increases in flood risks caused by sea-level rise, shore ero-
sion, and other environmental changes. For new and rebuilt
homes, the greater risks from sea-level rise cause a roughly
proportionate increase in flood insurance premiums. For
existing homes, however, the greater risks from sea-level
rise cause premiums to rise much less than proportionately,
and measures taken to reduce vulnerability to sea-level rise
do not necessarily cause rates to decline.
10.7.3.1 ACTUARIAL (PosT-FIRM) POLICIES
Flood Insurance Rate Maps show various hazard zones, such
as V Zone (wave velocity), A Zone (stillwater flooding dur-
ing a 100-year storm) and the "shaded X Zone"12 (stillwater
flooding during a 500-year storm) (see Chapter 9). These
zones are used as classes for setting rates. The post-FIRM
classes pay actuarial rates. For example, the total premi-
ums by all post-FIRM policyholders in the A Zone equals
FEMA's estimate of the claims and administrative costs for
the A Zone13. Hypothetically, if sea-level rise were to double
flood damage claims in the A Zone, then flood insurance
premiums would double (ignoring administrative costs)14.
Therefore, the impact of sea-level rise on post-FIRM policy
holders would not threaten the program's financial integrity
under the current rate structure.
Flood insurance policies can be broadly divided into actu-
arial and subsidized. "Actuarial" means that the rates are
designed to cover the expected costs; "subsidized" means
that the rates are designed to be less than the cost, with the
government making up the difference. Most of the subsi-
dized policies apply to "pre-FIRM" construction, that is,
homes that were built before the Flood Insurance Rate Map
(FIRM) was adopted for a given locality11; and most actu-
arial policies are for post-FIRM construction. Nevertheless,
there are also a few small classes of subsidized policies for
post-FIRM construction; and some owners of pre-FIRM
homes pay actuarial rates. The following subsections discuss
these two broad categories in turn.
11 Flood Insurance Rate Maps display the flood hazards of particular
locations for purposes of setting flood insurance rates. The maps
do not show flood insurance rates (see Chapter 9 for additional
details).
The rate structure can, however, insulate property owners
from the effects of sea-level rise, removing the market sig-
nal15 that might otherwise induce a homeowner to prepare or
152
12 The shaded X Zone was formerly known as the B Zone.
13 Owners of pre-FIRM homes can also pay the actuarial rate, if it is
less than the subsidized rate.
14 The National Flood Insurance Program (NFIP) modifies flood
insurance rates every year based on the annual "Actuarial Rate
Review". Rates can either be increased, decreased, or stay the same,
for any given flood insurance class. The rates for post-FIRM policies
are adjusted based on the risk involved and accepted actuarial
principals. As part of this rate adjustment, hydrologic models are
used to estimate loss exposure in flood-prone areas. These models
are rerun every year using the latest hydrologic data available. As
such, the models incorporate the retrospective effects of sea-level
rise. The rates for pre-FIRM (subsidized) structures are also modified
every year based in part on a determination of what is known as
the "Historical Average Loss Year". The goal of the NFIP is for
subsidized policyholders to pay premiums that are sufficient, when
combined with the premium paid by actuarially priced (post-FIRM)
policyholders, to provide the NFIP sufficient revenue to pay losses
associated with the historical average loss year.
15 In economics, "market signal" refers to information passes indirectly
or unintentionally between participants in a market. For example,
higher flood insurance rates convey the information that a property
is viewed as being riskier than previously thought.
-------
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
$250,000 House Built Today
60 cm above BFE
150cm above BFE
Today
4
J
&
n
^
Annual
Premium:
$355,'yr
£**L
Sea Level
Rises
90cm
Grandfathering?
Wllh Without
S355 S4720
Li
Grandlathering?
With Without
>SMO $356
Owner
elevates
house
90cm
Annual
Premium:
n
Annual
Premium:
$2BO/yr
100-tear flood
Note; BFE = base flood elevation for the 100 - year storm
Figure 10.6 Impact of grandfathering and floor
elevation on flood insurance rates in the A Zone
as sea level rises. Without grandfathering, a 90-
centimeter (cm) rise in sea level would increase the
flood insurance rate from $355 to $4720 per year
(yr), for a home built 60 cm above today's lOO-yr
flood elevation (left column); if the home is built ISO
cm above the lOO-yr flood, sea-level rise increases
the rate from $280 to $355. Elevating the house 90
cm after sea-level rise lowers the rate to what it had
been originally, Thus, if the 90-cm rise is expected
during the owner's planning horizon, there would
be a significant incentive to either build the house
higher or elevate it later. With grandfathering, how-
ever, sea-level rise does not increase the rate and
elevating the home later does not reduce the rate.
Thus, grandfathering reduces the incentive to antici-
pate sea-level rise or react to it after the fact.
Caveat. The numerical example is based on rates
published in NFIP (2008), Table 3B, and does not
include the impact of the annual changes in the rate
structure. Such rate changes would complicate the
numerical illustration, but would not fundamentally
alter the incentives illustrated, because the annual
rate changes are across-the-board within a given
class. For example, if rates increased by 50 percent
by the time sea level rises 90 cm, then all of the
premiums shown in the bottom four boxes would
rise 50 percent.
respond to sea-level rise. Although shoreline erosion and ris-
ing sea level increase the expected flood damage to a given
home, the increased risk to a specific property does not cause
the rate on that specific property to rise. Unless a home is
substantially changed, its assumed risk is grandfathered16,
that is, FEMA assumes that the risk has not increased when
calculating the flood insurance rate (e.g., NFIP, 2007; Heinz
Center, 2000)17. Because the entire class pays an actuarial
16 Under the NFIP grandfathering policy, whenever FEMA revises the
flood risk maps used to calculate the premium for specific homes,
a policy holder can choose between the new map and the old map,
whichever results in the lower rate (NFIP, 2007).
17 Although rates for individual policies may be grandfathered, rates for
the entire A or V Zone (or any flood zone) can still increase each year
up to a maximum of 10 percent; therefore, a grandfathered policy may
still see annual rate increases. For example, a post-FIRM structure
might be originally constructed in an A Zone at 30 cm (1 ft) above
base flood elevation. If shore erosion, sea-level rise, or a revised
mapping procedure leads to a new map that shows the same property
to be in the V Zone and 60 cm (2 ft) below base flood elevation, the
policy holder can continue to pay as if the home was 30 cm above
base flood elevation in the A Zone. However, the entire class of A
Zone rates could still increase as a result of annual class-wide rate
adjustments based on the annual "Actuarial Rate Review". Those
class-wide increases could be caused by long-term erosion, greater
flooding from sea-level rise, increased storm severity, higher recon-
struction or administrative costs, or any other factors that increase
the cost of paying claims by policyholders.
rate, the grandfathering causes a "cross-subsidy" between
new or rebuilt homes and the older grandfathered homes.
Grandfathering can discourage property owners from either
anticipating or responding to sea-level rise. If anticipated
risk is likely to increase, for example, by about a factor of
10 and a total loss would occur eventually (e.g., a home on
an eroding shore), grandfathering the assumed risk may
allow the policy holder to secure compensation for a total
loss at a small fraction of the cost of that loss. For instance,
the owner of a $250,000 home built at the base flood eleva-
tion in the A Zone would typically pay about $900 per year
(NFIP, 2008); but if shore erosion left the property in the
V Zone, the annual rate would rise to more than $10,000
(NFIP, 2008 )18 if the property was not grandfathered. Under
such circumstances, the $9,100 difference in eventual insur-
ance premiums might be enough of a subsidy to encourage
owners to build in locations more hazardous than where
they might have otherwise built had they anticipated that
they would bear the entire risk (cf. Heinz Center, 2000). For
homes built in the A Zone, the effect of grandfathering is
less, but still potentially significant (compare the top four
panels of Figure 10.6).
18 This calculation assumes a storm-wave height adjustment of 90 cm
and no sea-level rise (see NFIP, 2008).
153
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Chapter 10
Grandfathering can also remove the incentive to respond as
sea level rises. Consider a home in the A Zone that is origi-
nally 30 cm (about 1 ft) above the base flood elevation. If
sea level rises 30 to 90 cm (1 to 3 ft), then the actuarial rates
would typically rise by approximately two to ten times the
original amount (NFIP, 2008), but because of grandfather-
ing, the owners would continue to pay the same premium.
Therefore, if the owner were to elevate the home 30 to 90
cm, the insurance premium would not decline because the
rate already assumes that the home is 30 cm above the flood
level (compare the bottom four panels of Figure 10.6).
The importance of grandfathering is sensitive to the rate
of sea-level rise. At the current rate of sea-level rise (3 mm
per year), most homes would be rebuilt (and thus lose the
grandfathering benefit) before the 100 to 300 years it takes
for the sea to rise 30 to 90 cm. By contrast, if sea level rises
1 cm per year, this effect would only take 30 to 90 years—
and many coastal homes survive that long.
Previous assessments have examined this issue (although
they were focused on shoreline erosion from all causes,
rather than from sea-level rise). The National Academy of
Sciences (NAS) has recommended that the Flood Insur-
ance Program create mechanisms to ensure that insurance
rates reflect the increased risks caused by long-term coastal
erosion (NAS, 1990). NAS pointed out that Congress has
explicitly included storm-related erosion as part of the dam-
ages covered by flood insurance (42 U.S.C. §4121), and that
FEMA's regulations (44 CFRPart 65.1) have already defined
special "erosion zones", which consider storm-related ero-
sion (NAS, 1990)19. AFEMA-supportedreportto Congress
by The Heinz Center (2000) and a theme issue in the Journal
of Coastal Research (Crowell and Leatherman, 1999) also
concluded that, because of existing long-term shore erosion,
there can be a substantial disparity between actual risk and
insurance rates.
Would sea-level rise justify changing the current approach?
Two possible alternatives would be to (1) shorten the period
during which the assumed risk is kept fixed so that rates
can respond to risk and property owners can respond, or
(2) lengthen the duration of the insurance policy to the
period of time between risk calculations, that is, instead
of basing rates on the risk when the house is built, which
tends to increasingly underestimate the risk, base the rate
on an estimate of the average risk over the lifetime of the
structure, using "erosion-hazard mapping" with assumed
19 Note that: (1) the NFIP insures against damages caused by flood-
related erosion; (2) the probability of flood-related erosion is con-
sidered in defining the landward limit of V Zones; and (3) flood
insurance rates in the V Zone are generally much higher than A Zone
rates. Part of the reason for this is consideration of the potential for
flood-related erosion.
rates of sea-level rise, shore erosion, and structure life-
time. Both of these alternatives more accurately account
for changing risk by estimating risk over a time horizon
equal to the period of time between risk recalculation. The
erosion-hazard mapping approach has received consider-
able attention; the Heinz Center study also recommended
that Congress authorize erosion-hazard mapping. Although
Congress has not provided FEMA with authority to base
rates on erosion hazard mapping, FEMA has raised rates in
the V Zone by 10 percent per year (during most years) as a
way of anticipating the increased flood damages resulting
from the long-term erosion that The Heinz Center evaluated
(Crowell et ai, 2007).
The Heinz Center study and recent FEMA efforts have
assumed current rates of sea-level rise. FEMA has not in-
vestigated whether accelerated sea-level rise would increase
the disparity between risks and insurance rates enough to
institute additional changes in rates; nor has it investigated
the option of relaxing the grandfathering policy so that pre-
miums on existing homes rise in proportion to the increasing
risk. Nevertheless, the Government Accountability Office
(2007) recently recommended that FEMA analyze the
potential long-term implications of climate change for the
National Flood Insurance Program (NFIP). FEMA agreed
to undertake such a study (Buckley, 2007) and initiated it
in September 2008 (Department of Homeland Security,
2008).
10.7.3.2
Since the 1970s, the flood insurance program has provided a
subsidized rate for homes built before the program was im-
plemented, that is, before the release of the first flood insur-
ance rate map for a given location (Hayes et al., 2006). The
premium on a $100,000 home, for example, is generally $650
and $1170 for the A and V Zones, respectively—regardless of
how far above or below the base flood elevation the structure
may be (NFIP, 2008). Not all pre-FIRM homes obtain the
subsidized policy. The subsidized rate is currently greater
than the actuarial rate in the A and V Zones for homes that
are at least 30 cm and 60 cm, respectively, above the base
flood elevation (NFIP, 2008). But the subsidy is substantial
for homes that are below the base flood elevation. Homes
built in the V Zone between 1975 and 1981 also receive a
subsidized rate; which is about $1500 for a $100,000 home
built at the base flood elevation (NFIP, 2008). Because the
pre-FIRM subsidies only apply to homes that are several de-
cades old, they do not encourage hazardous construction. As
with grandfathering, the subsidized rate discourages owners
of homes below the base flood elevation from elevating or
otherwise reducing the risk to their homes as sea level rises,
154
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Coastal to
A Focus on the Mid-Atlantic Region
because the premium is already as low as it would be from
elevating the home to the base flood elevation20.
Does sea-level rise justify changing the rate structure for
subsidized policies? Economics alone can not answer that
question because the subsidies are part of the program for
reasons other than risk management and economic efficien-
cy, such as the original objective of providing communities
with an incentive to join the NFIP and the policy goal of not
pricing people out of their homes (Hayes et al., 2006). More-
over, the implications depend in large measure on whether
the NFIP responds to increased damages from sea-level rise
by increasing premiums or the subsidy, a decision that has
not yet been made. Sea-level rise elevates the base flood
elevation; and the subsidized rate is the same regardless of
how far below the base flood elevation a home was built.
Considering those factors alone, sea-level rise increases
expected damages, but not the subsidized rate. However,
the NFIP sets the subsidized rates to ensure that the entire
program covers its costs during the average non-catastrophic
year21. Therefore, if total damages (which include inland
flooding) rise by the same proportion as damages to subsi-
dized policies, the subsidized portion of pre-FIRM policies
would stay the same as sea level rises.
FEMA has not yet quantified whether climate change is
likely to increase total damages by a greater or smaller
proportion than the increase due to sea-level rise. Without
an assessment of whether the subsidy would increase or
decrease, it would be premature to conclude that sea-level
rise warrants a change inFEMA's subsidized rate structure.
Nevertheless, sea-level rise is unlikely to threaten the fi-
nancial integrity of the flood insurance program as long as
subsidized rates are set high enough for the entire program
to cover claims during all but the catastrophic loss years,
and Congress continues to provide the program with the
necessary funds during the catastrophic years.
The practical importance of the pre-FIRM subsidy is sensi-
tive to the future rate of sea-level rise. Today, pre-FIRM
policies account for 24 percent of all policies (Hayes et al.,
2006). However, that fraction is declining (Crowell et al.,
2007) because development continues in coastal floodplains,
and because the total number of homes eligible forpre-FIRM
rates is declining, as homes built before the 1970s are lost to
fire and storms, enlarged, or replaced with larger homes. A
substantial rise in sea level over the next few decades would
affect a large class of subsidized policy holders. By the year
20 pre-pjRiy[ owners of homes a few feet below the base flood elevation
could achieve modest saving by elevating homes a few feet above
the base flood elevation; but those savings are small compared to
the savings available to the owner of a post-FIRM home at the same
elevation relative to base flood elevation.
21 The year 2005 (Hurricanes Katrina, Rita, and Wilma) is excluded
from such calculations.
2100, however, the portion of pre-FIRM houses is likely to
be very small, unless there is a shift in the factors that have
caused people to replace small cottages with larger houses
and higher-density development (see Section 12.2.3).
Two other classes, which together account for 2 percent
of policies, also provide subsidized rates. The A99 Zone
consists of areas that are currently in the A Zone, but for
which structural flood protection such as dikes are at least
50 percent complete. Policyholders in such areas pay a rate
as if the structural protection was already complete (and
successful). The AR Zone presents the opposite situation:
locations where structural protection has been decertified.
Provided that the structures are on a schedule for being re-
built, the rates are set to the rate that applies to the X Zone
or the pre-FIRM subsidized rate, whichever is less. As sea
level rises, the magnitude of these subsidies may increase,
both because the base flood elevations (without the protec-
tion) will be higher, and because more coastal lands may be
protected with dikes and other structural measures. Unlike
the pre-FIRM subsidies, the A99 and AR Zone subsidies
may encourage construction in hazardous areas; but unlike
other subsidies, the A99 and AR Zone subsidies also encour-
age protection measures that reduce hazards.
10,7,4 I
If a coastal community is ultimately going to be abandoned
to the rising sea, a major rebuilding effort in the current loca-
tion may be less useful than expending the same resources
to rebuild the community on higher ground. On the other
hand, if the community plans to remain in its current loca-
tion despite the increasing costs of shore protection, then
it is important for people to understand that commitment.
Unless property owners know which path the community is
following, they do not know whether to reinvest. Moreover,
if the community is going to stay in its current location,
owners need to know whether their land will be protected
with a dike or if land surfaces are likely to be elevated over
time (see Section 12.3).
10.;.' ':-: ::
The need to prepare for rising sea level depends on the length
of time over which the decision will continue to have conse-
quences; how sensitive those consequences are to sea level;
how rapidly the sea is expected to rise and the magnitude
of uncertainty over that expectation; the decision maker's
risk tolerance; and the implications of deferring a decision
to prepare. Considering sea-level rise may be important if
the decision has outcomes over a long period of time and
concerns an activity that is sensitive to sea level, especially
if what can be done to prepare today would not be feasible
later. Those making decisions with outcomes over a short
period of time concerning activities that are not sensitive to
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Chapter
sea level probably need not consider sea-level rise, especially
if preparing later would be as effective as preparing today.
Instances where the existing literature provides an eco-
nomic rationale for preparing for accelerated sea-level rise
include:
Coastal wetland protection. Wetlands and the success
of wetland-protection efforts are almost certainly sen-
sitive enough to sea-level rise to warrant examination
of some changes in coastal wetland protection efforts,
assuming that the objective is to ensure that most estuar-
ies that have extensive wetlands today will continue to
have tidal wetlands in the future. Coastal wetlands are
sensitive to rising sea level, and many of the possible
measures needed to ensure their survival as sea level
rises are least disruptive with a lead time of several
decades. Changes in management approaches would
likely involve consideration of options by federal, state,
and local governments.
Coastal infrastructure. Whether it is beneficial to de-
sign coastal infrastructure to anticipate rising sea level
depends on the ratio of the incremental cost of designing
for a higher sea level now, compared with the retrofit
cost of modifying the structure later. No general state-
ment is possible because this ratio varies and relatively
few engineering assessments of the question have been
published. However, because the cost of analyzing this
question is very small compared with the retrofit cost,
it is likely that most long-lived infrastructure in the
coastal zone is sufficiently sensitive to rising sea level to
warrant an analysis of the comparative cost of designing
for higher water levels now and retrofitting later.
• Building along the coast. In general, the economics of
coastal development alone does not currently appear
to be sufficiently sensitive to sea-level rise to stop
construction in coastal areas. Land values are so high
that development is often profitable even if a home is
certain to be lost within a few decades. Nevertheless,
the optimal location and elevation of new homes may
be sensitive to sea-level rise.
Shoreline planning. A wide array of measures for
adapting to rising sea level depend on whether a given
area will be elevated, protected with structures, or
abandoned to the rising sea. Several studies have shown
that in those cases where the shores will retreat and
structures will be removed, the economic cost will be
much less if people plan for that retreat. The human toll
of an unplanned abandonment may be much greater than
if people gradually relocate when it is convenient to do
so. Conversely, people may be reluctant to invest in an
area without some assurance that lands will not be lost
to the sea. Therefore, long-term shoreline planning is
generally justified and will save more than it costs; the
more the sea ultimately rises, the greater the value of
that planning.
Rolling easements, density restrictions, and coastal
setbacks. Several studies have shown that, in those
cases where the shores will retreat and structures will
be removed, the economic cost will be much less if
people plan for that retreat. Along estuaries, a retreat
in developed areas rarely occurs and thus is likely to
only occur if land remains lightly developed. It is very
likely that options such as rolling easements, density
restrictions, coastal setbacks, and vegetative buffers,
would increase the ability of wetlands and beaches to
migrate inland.
Floodplain management: Consideration of reflecting
actual risk in flood insurance rates. Economists and
other commentators generally agree that insurance
works best when the premiums reflect the actual risk.
Even without considering the possibility of acceler-
ated sea-level rise, the National Academy of Sciences
(NAS, 1990) and a FEMA-supported study by The
Heinz Center (2000) concluded and recommended to
Congress that insurance rates should reflect the chang-
ing risks resulting from coastal erosion. Rising sea level
increases the potential disparity between rates and risks
of storm-related flooding.
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u
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
V .
i
Ongoing Adaptation
Author: James G. Titus, U.S. EPA
KEY FINDINGS
Most organizations are not yet taking specific measures to prepare for rising sea level. Recently, however, many
public and private organizations have begun to assess possible response options.
Most of the specific measures that have been taken to prepare for accelerated sea-level rise have had the purpose
of reducing the long-term adverse environmental impacts.
11.1 INTRODUCTION
Preparing for the consequences of rising sea level has been
the exception rather than the rule in the Mid-Atlantic. Nev-
ertheless, many coastal decision makers are now starting to
consider how to prepare.
This Chapter examines those cases in which organizations
are taking specific measures to consciously anticipate the ef-
fects of sea-level rise. It does not include most cases in which
an organization has authorized a study but not yet acted upon
the study. Nor does it catalogue the activities undertaken for
other reasons that might also help to prepare for accelerated
sea-level rise1, or cases where people responded to sea-level
rise after the fact (see Box 11.1). Finally, it only considers
measures that had been taken by March 2008. Important
measures may have been adopted between the time this
Product was drafted and its final publication.
11.2 ADAPTATION FOR ENVIRONMENTAL
PURPOSES
Within the Mid-Atlantic, environmental regulators gener-
ally do not address the effects of sea-level rise. Many or-
ganizations that manage land for environmental purposes,
however, are starting to anticipate these effects. Outside
the Mid-Atlantic, some environmental regulators have also
begun to address this issue.
11.2.1 Environmental Regulators
Organizations that regulate land use for environmental
purposes generally have not implemented adaptation options
to address the prospects of accelerated sea-level rise. Con-
gress has given neither the U.S. Army Corps of Engineers
(USAGE) nor the U.S. Environmental Protection Agency
(EPA) a mandate to modify existing wetland regulations to
address rising sea level; nor have those agencies developed
approaches for moving ahead without such a mandate (see
Chapter 12). For more than a decade, Maine2, Massachu-
J^*r\J
1 Appendix 1, however, does examine such policies.
06-096 Code of Maine Rules §355(3)(B)(1) (2007).
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Chapter I I
BOX I I. I: Jamestown—A Historic Example of Retreat in Response to Sea-Level Rise
Established in 1607 along the James
River, Jamestown was the capital of
Virginia until 1699, when a fire de-
stroyed the statehouse. Nevertheless,
rising sea level was probably a contrib-
uting factor in the decision to move
the capital to Williamsburg, because it
was making the Jamestown peninsula
less habitable than it had been during
the previous century. Fresh water
was scarce, especially during droughts
(Blanton, 2000). The James River was
brackish, so groundwater was the
only reliable source of freshwater.
But the low elevations on Jamestown
limited the thickness of the freshwater
table—especially during droughts. As
Box Figure 11.1 shows, a 10 centime-
ter (cm) rise in sea level can reduce
the thickness of the freshwater table
by four meters on a low-lying island
where the freshwater lens floats atop
the saltwater.
Rising sea level has continued to al-
ter Jamestown. Two hundred years
ago, the isthmus that connected the
peninsula to the mainland eroded,
creating Jamestown Island (Johnson
and Hobbs, 1994). Shore erosion also
threatened the location of the historic
town itself, until a stone revetment
was constructed (Johnson and Hobbs,
1994). As the sea rose, the shallow
valleys between the ridges on the
island became freshwater marsh, and
then tidal marsh (Johnson and Hobbs,
1994). Maps from the seventeenth
century show agriculture on lands that
today are salt marsh. Having converted
mainland to island, the rising sea will
eventually convert the island to open
water, unless the National Park Service
continues to protect it from the rising
water.
Impact of Sea-Level Rise on Island Water Table
~] Fresh water
:—.— ' ""' •'•
Box Figure I I.I Impact of sea-level rise on an island freshwater table, (a) Ac-
cording to the Ghyben-Herzberg relation, the freshwater table extends below
sea level 40 centimeters (cm) for every I cm by which it extends above sea level
(Ghyben, 1889 and Herzberg, 1901, as cited by Freeze and Cherry, 1979). (b) For
islands with substantial elevation, a I-meter (m) rise in sea level simply shifts the
entire water table up I m, and the only problem is that a few wells will have to be
replaced with shallower wells, (c) However, for very low islands the water table
cannot rise because of runoff, evaporation, and transpiration. A rise in sea level
would thus narrow the water table by 40 cm for every I cm that the sea level
rises, effectively eliminating groundwater supplies for the lowest islands.
Other shorelines along Chesapeake
Bay have also been retreating over the last four centuries. Several bay island fishing villages have had to relocate to
the mainland as the islands on which they were located eroded away (Leatherman eta/., 1995). Today, low-lying farms
on the Eastern Shore are converting to marsh, while the marshes in wildlife refuges convert to open water.
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
(b)
Figure 11.1 Allowing beaches and wetlands to migrate inland in the national parks, (a) Cape Hatteras National Seashore (June
2002). Until it was relocated inland in 1999, the lighthouse was just to the right of the stone groin in the foreground; it is now about
450 m (1500 ft) inland, (b) Jamestown Island, Virginia (September 2004). As sea level rises, marshes have taken over land that was
cultivated during colonial times [Photo source: ®James G. Titus, used with permission].
setts3, and Rhode Island4 have had statutes or regulations
that restrict shoreline armoring to enable dunes or wetlands
to migrate inland with an explicit recognition of rising sea
level (Titus, 1998).
None of the eight mid-Atlantic states require landowners to
allow wetlands to migrate inland as sea level rises (NOAA,
2006). During 2008, however, the prospect of losing ecosys-
tems to a rising sea prompted Maryland to enact the "Living
Shoreline Protection Act"5. Under the Act, the Department
of Environment will designate certain areas as appropri-
ate for structural shoreline measures (e.g., bulkheads and
revetments). Outside of those areas, only nonstructural
measures (e.g., marsh creation, beach nourishment) will be
allowed unless the property owner can demonstrate that
nonstructural measures are infeasible6. The new statute
does not ensure that wetlands are able to migrate inland; but
Maryland's coastal land use statute limits development to
one home per 8.1 hectares (ha) (20 acres [ac]) in most rural
areas within 305 meters (m) (1000 feet [ft]) of the shore (see
Section Al.F.2.1 in Appendix 1). Although that statute was
enacted in the 1980s to prevent deterioration of water qual-
ity, the state now considers it to be part of its sea-level rise
adaptation strategy7.
11.2.2 Environmental Land Managers
Those who manage land for environmental purposes have
taken some initial steps to address rising sea level.
Federal Land Managers
The Department of Interior (Secretarial Order 3226, 2001)
requires climate change impacts be taken into account in
3 310 Code Mass Regulations §10.30 (2005).
4 Rhode Island Coastal Resource Management Program §210.3(B)(4)
and §300.7(0) (2007).
5 Maryland House Bill 973-2008.
6 MD Code Environment §16-201(c).
7 Maryland House Bill 973-2008 (preamble).
planning and decision making (Scarlett, 2007). The National
Park Service has worked with the United States Geological
Survey (USGS) to examine the vulnerability of 25 of its
coastal parks (Pendleton et al., 2004). The U.S. Fish and
Wildlife Service is incorporating studies of climate change
impacts, including sea-level rise, in its Comprehensive
Conservation Plans where relevant.
The National Park Service and the U.S. Fish and Wildlife
Service each have large coastal landholdings that could
erode or become submerged as sea level rises (Thieler et al.,
2002; Pendleton et al., 2004). Neither organization has an ex-
plicit policy concerning sea-level rise, but both are starting to
consider their options. The National Park Service generally
favors allowing natural shoreline processes to continue (NFS
Management Policies §4.8.1), which allows ecosystems to
migrate inland as sea level rises. In 1999, this policy led the
Park Service to move the Cape Hatteras Lighthouse inland
approximately 900 m (2,900 ft) to the southwest at a cost
of $10 million (see Figure 11.1). The U.S. Fish and Wildlife
Service generally allows dry land to convert to wetlands,
but it is not necessarily passive as rising sea level erodes the
seaward boundary of tidal wetlands. Blackwater National
Wildlife Refuge, for example, has used dredge material to
rebuild wetlands on a pilot basis, and is exploring options
to recreate about 3,000 ha (7,000 ac) of marsh (see Figure
11.2). Neither agency has purchased land or easements to
enable parks or refuges to migrate inland.
The Nature Conservancy
The Nature Conservancy (TNC) is the largest private holder
of conservation lands in the Mid-Atlantic. It has declared as a
matter of policy that it is trying to anticipate rising sea level
and climate change. Its initial focus has been to preserve
ecosystems on the Pamlico-Albemarle Peninsula, such as
those shown in Figure 11.3 (Pearsall and Poulter, 2005; TNC,
2007). Options under consideration include: plugging canals
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The U.S. Climate Change Science Program
Chapter I I
(a)
Figure 11.2 Responding to sea-level rise at Blackwater National Wildlife Refuge, Maryland (October 2002). (a) Marsh Deteriora-
tion, (b) Marsh Creation. The dredge fills the area between the stakes to create land at an elevation flooded by the tides, after which
marsh grasses are planted [Photo source: ®James G. Titus, used with permission].
(a)
•Lr
Figure 11.3 The Albemarle Sound environment that the Nature Conservancy seeks to preserve as sea level rises (June 2002). (a)
Nature Conservancy lands on Roanoke Island depict effects of rising sea level. Tidal wetlands (juncus and spartina patens) have taken
over most of the area depicted as sea level rises, but a stand of trees remains in a small area of higher ground, (b) Mouth of the
Roanoke River, North Carolina. Cypress trees germinate on dry land, but continue to grow in the water after the land is eroded or
submerged by rising sea level [Photo source: ®James G. Titus, used with permission].
to prevent subsidence-inducing saltwater intrusion, planting
cypress trees where pocosins have been converted to dry
land, and planting brackish marsh grasses in areas likely to
be inundated. As part of that project, TNC undertook the
first attempt by a private conservancy to purchase rolling
easements (although none were purchased). TNC also owns
the majority of barrier islands along the Delmarva Peninsula,
but none of the mainland shore. TNC is starting to examine
whether preserving the ecosystems as sea level rises would
be best facilitated by purchasing land on the mainland side as
well, to ensure sediment sources for the extensive mudflats
so that they might keep pace with rising sea level.
State conservation managers have not yet started to prepare
for rising sea level (NOAA, 2006). But at least one state
(Maryland) is starting to refine a plan for conservation that
would consider the impact of rising sea level.
11.3 OTHER ADAPTATION OPTIONS
BEING CONSIDERED BY FEDERAL,
STATE, AND LOCAL GOVERNMENTS
II.3.1 Federal Government
Federal researchers have been examining how best to adapt
to sea-level rise for the last few decades, and now those
charged with implementing programs are also beginning
to consider implications and options. The longstanding as-
sessment programs will enable federal agencies to respond
more rapidly and reasonably if and when policy decisions
are made to begin preparing for the consequences of rising
sea level.
The Coastal Zone Management Act is a typical example.
The Act encourages states to protect wetlands, minimize
vulnerability to flood and erosion hazards, and improve
public access to the coast. Since 1990, the Act has included
sea-level rise in the list of hazards that states should address.
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
This congressional mandate has induced NOAA to fund
state-specific studies of the implications of sea-level rise,
and encouraged states to periodically designate specific
staff to keep track of the issue. But it has not yet altered
what people actually do along the coast (New York, 2006;
New Jersey, 2006; Pennsylvania, 2006; Delaware, 2005;
Maryland, 2006; Virginia, 2006; North Carolina, 2006).
Titus (2000) and CSO (2007) have examined ways to fa-
cilitate implementation of this statutory provision, such as
federal guidance and/or additional interagency coordination.
Similarly, the U.S. Army Corps of Engineers (USAGE) has
formally included the prospect of rising sea level for at least
a decade in its planning guidance (USAGE, 2000), and staff
have sometimes evaluated the implications for specific deci-
sions (e.g., Knuuti, 2002). But the prospect of accelerated
sea-level rise has not caused a major change in the agency's
overall approach to wetland permits and shore protection
(see Chapter 12).
11.3.2 State Government
Maryland has considered the implications of sea-level rise
in some decisions since the 1980s. Rising sea level was one
reason that the state gave for changing its shore protection
strategy at Ocean City from groins to beach nourishment
(see Section Al.F in Appendix 1). Using NOAA funds, the
state later developed a preliminary strategy for dealing with
sea-level rise. As part of that strategy, the state also recently
obtained a complete lidar dataset of coastal elevations.
Delaware officials have long considered how best to modify
infrastructure as sea level rises along Delaware Bay, al-
though they have not put together a comprehensive strategy
(CCSP, 2007).
Because of the vulnerability of the New Jersey coast to
flooding, shoreline erosion, and wetland loss (see Figure
11.4), the coastal management staff of the New Jersey De-
partment of Environmental Protection has been guided by
a long-term perspective on coastal processes, including the
impacts of sea-level rise. So far, neither Delaware nor New
Jersey has specifically altered their activities because of
projected sea-level rise. Nevertheless, New Jersey is cur-
rently undertaking an assessment that may enable it to factor
rising sea level into its strategy for preserving the Delaware
Estuary (CCSP, 2007).
In the last two years, states have become increasingly in-
terested in addressing the implications of rising sea level.
Figure 11.4 Vulnerability of New Jersey's coastal zone, (a) Wetland fringe lacks room for wetland migration (Monmouth,
August 2003). (b) Low bay sides of barrier islands are vulnerable to even a modest storm surge (Ship Bottom, September 2, 2006).
(c) Gibbstown Levee and (d) associated tide gate protect lowlying areas of Greenwich Township (March 2003) [Photo source: ®James
G. Titus, used with permission].
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Chapter
In 2007, the New York General Assembly created a Sea-
Level Rise Task Force8 Maryland and Virginia have climate
change task forces that have focused on adapting to rising
sea level. (For a comprehensive survey of what state govern-
ments are doing in response to rising sea level, see Coastal
States Organization, 2007.)
11.3.3
A few local governments have considered the implications
of rising sea level for roads, infrastructure, and f loodplain
management (see Boxes A1.2, A1.5, and A1.6 in Appendix
1). New York City's plan for the year 2030 includes adapt-
ing to climate change (City of New York, 2008). The New
York City Department of Environmental Protection is
looking at ways to decrease the impacts of storm surge by
building flood walls to protect critical infrastructure such
as waste plants, and is also examining ways to prevent the
sewer system from backing up more frequently as sea level
rises (Rosenzweig et al., 2006). The city has also been in-
vestigating the possible construction of a major tidal flood
gate across the Verizano Narrows to protect Manhattan
(Velasquez-Manoff, 2006).
Outside of the Mid-Atlantic, Miami-Bade County in Florida
has been studying its vulnerability to sea-level rise, includ-
ing developing maps to indicate which areas are at greatest
risk of inundation. The county is hardening facilities to
better withstand hurricanes, monitoring the salt front, exam-
ining membrane technology for desalinating sea water, and
creating a climate advisory task force to advise the county
commission (Yoder, 2007).
! LAWS OF NEW YORK (2007), Chapter 613.
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Institutional Barriers
Q_
..-«.- '
Author: James G. Titus, U.S. EPA
I
u
KEY FINDINGS
Most coastal institutions were designed without considering sea-level rise.
Some regulatory programs were created in order to respond to a demand for hard shoreline structures
(e.g., bulkheads) to hold the coast in a fixed location, and have not focused on retreat or soft shore
protection (e.g., beach nourishment).
The interdependence of decisions made by property owners and federal, state, and local governments
creates an institutional inertia that currently impedes preparing for sea-level rise, as long as no decision
has been made regarding whether particular locations will be protected or yielded to the rising sea.
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:er
7U
Chapter 10 described several categories of decisions where
the risk of sea-level rise can justify doing things differently
today. Chapter 11, however, suggested that only a few orga-
nizations have started to prepare for rising sea level since
the 1980s when projections of accelerated sea-level rise first
became widely available.
It takes time to respond to new problems. Most coastal insti-
tutions were designed before the 1980s. Therefore, land-use
planning, infrastructure, home building, property lines,
wetland protection, and flood insurance all were designed
without considering the dynamic nature of the coast (see
Chapters 6, 8, 9,10). A common mindset is that sea level and
shores are stable, or that if they are not then shores should be
stabilized (NRC, 2007). Even when a particular institution
has been designed to account for shifting shores, people are
reluctant to give up real estate to the sea. Although scientific
information can quickly change what people expect, it takes
longer to change what people want.
Short-term thinking often prevails. The costs of planning
for hazards like sea-level rise are apparent today, while the
benefits may not occur during the tenure of current elected
officials (Mileti, 1999). Local officials tend to be responsive
to citizen concerns, and the public is generally less con-
cerned about hazards and other long-term or low-probability
events than about crime, housing, education, traffic, and
other issues of day-to-day life (Mileti, 1999; Depoorter,
2006). Land-use and transportation planners generally have
horizons of 20 to 25 years (TRB, 2008), while the effects of
sea-level rise may emerge over a period of several decades.
Although federal law requires transportation plans to have
a time horizon of at least 20 years1, some officials view that
time horizon as the maximum (TRB, 2008). Uncertainty
about future climate change is a logical reason to prepare
for the range of uncertainty (see Chapter 10) but cognitive
dissonance2 can lead people to disregard the new informa-
tion and ignore the risk entirely (Kunreuther et al., 2004;
Bradshaw andBorchers, 2000; Akerlof and Dickens, 1982).
Some officials resist changing procedures unless they are
provided guidance (TRB, 2008).
1 23U.S.C. §135(f)(l) (2008).
2 Cognitive dissonance is a feeling of conflict or anxiety caused by
holding two contradictory ideas simultaneously, especially when
there is a discrepancy between one's beliefs or actions and informa-
tion that contradicts those beliefs or actions. When confronted with
information (e.g., about risk) that contradicts one's pre-existing
beliefs or self-image (e.g., that they are acting reasonably), people
often respond by discounting, denying, or ignoring the information
(e.g., Festinger, 1957, Harmon-Jones and Mills, 1999).
Finally, a phenomenon known as "moral hazard" can dis-
courage people from preparing for long-term consequences.
Moral hazard refers to a situation in which insurance or
the expectation of a government bailout reduces someone's
incentive to prevent or decrease the risk of a disaster (Pauly,
1974). The political process tends to sympathize with those
whose property is threatened, rather than allowing them
to suffer the consequences of the risk they assumed when
they bought the property (Burby, 2006). It can be hard to
say "no" to someone whose home is threatened (Viscusi and
Zeckhauser, 2006).
This Chapter explores some of the institutional barriers that
discourage people and organizations from preparing for
the consequences of rising sea level. "Institution" refers to
governmental and nongovernmental organizations and the
programs that they administer. "Institutional barriers" refer
to characteristics of an institution that prevent actions from
being taken. This discussion has two general themes. First,
institutional biases are more common than actual barriers.
For example, policies that encourage higher densities in the
coastal zone may be barriers to wetland migration, but they
improve the economics of shore protection. Such a policy
might be viewed as creating a bias in favor of shore protec-
tion over wetland migration, but it is not really a barrier to
adaptation from the perspective of a community that prefers
protection anyway. A bias encourages one path over another;
a barrier can block a particular path entirely.
Second, interrelationships between various decisions tend
to reinforce institutional inertia. For instance, omission of
sea-level rise from a land-use plan may discourage infra-
structure designers from preparing for the rise; and a fed-
eral regulatory preference for hard structures may prevent
state officials from encouraging soft structures. Although
inertia currently slows action to respond to the risk of sea-
level rise, it could just as easily help to sustain momentum
toward a response once key decision makers decide which
path to follow.
The barriers and biases examined in this Chapter mostly
concern governmental rather than private sector institu-
tions. Private institutions do not always exhibit foresight.
In fact, their limitations have helped motivate the creation
of government flood insurance (Kunreuther et al., 1978),
wetland protection (Scodari, 1997), shore protection, and
other government programs (Bator, 1958; Arrow, 1970).
This Chapter omits an analysis of private institutions for two
reasons. First, there is little literature available on private
institutional barriers to preparing for sea-level rise. It is
unclear whether this absence implies that the private barri-
ers are less important, or simply that private organizations
keep their affairs private. Second, the published literature
provides no reason to expect that private institutions have
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Coastal Sensitivity to Sea-Level Rise:
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Figure 12.1 Recently nourished beach and artificially created dune in Surf City, New Jersey, with recent plantings of dune grass
(June 2007) [Photo source: ®James G. Titus, used with permission].
important barriers different from those of public institutions.
The duty of for-profit corporations to maximize shareholder
wealth, for example, may prevent a business from giving up
property to facilitate future environmental preservation as
sea level rises. At first glance, this duty might appear to be
a barrier to responding to sea-level rise, or at least a bias in
favor of shore protection over retreat. Yet that same duty
would lead a corporation to sell the property to an environ-
mental organization willing to offer a profitable price. Thus,
the duty to maximize shareholder wealth is a bias in favor of
profitable responses over money-losing responses, but not a
barrier to preparing for sea-level rise.
12.2 SOME SPECIFIC INSTITUTIONAL
BARRIERS AND BIASES
to limit erosion and flooding (see Figure 12.1). The planning
guidance documents for USAGE appear to provide the dis-
cretion to relocate or purchase homes if a policy of retreat
is the locally preferred approach and is more cost-effective
than shore protection (USAGE, 2000). In part because the
federal government generally pays for 65 percent of the ini-
tial cost3, retreat is rarely the locally preferred option (Lead
and Meiners, 2002; NRG, 2004). USAGE'S environmental
policies discourage its Civil Works program from seriously
considering projects to foster the landward migration of
developed barrier islands (see Wetland Protection discussed
further below). Finally, the general mission of this agency,
its history (LockhartandMorang, 2002), staff expertise, and
funding preferences combine to make shore protection far
more common than a retreat from the shore.
Productive institutions are designed to accomplish a mission,
and rules and procedures are designed to help accomplish
those objectives. These rules and procedures are inherently
biased toward achieving the mission, and against anything
that thwarts the mission. By coincidence more than design,
the rules and procedures may facilitate or thwart the ability
of others to achieve other missions.
No catalogue of institutional biases in the coastal zone is
available; but three biases have been the subject of substan-
tial commentary: (1) shore protection versus retreat; (2) hard
structures versus soft engineering solutions; and (3) coastal
development versus preservation.
12.2.1 Shore Protection versus Retreat
Federal, state, local, and private institutions generally have
a strong bias/avor/'wg shore protection over retreat in devel-
oped areas. Many institutions also have a bias against shore
protection in undeveloped areas.
U.S. Army Corps of Engineers (USAGE) Civil Works. Con-
gressional appropriations for shore protection in coastal
communities provide funds for various engineering projects
State Shore Protection. North Carolina, Virginia, Mary-
land, Delaware, and New Jersey all have significant state
programs to support beach nourishment along the Atlantic
Ocean (see Figure 12.1 and Sections A1.C.2, A1.E.2, and
A1.G.4 in Appendix 1). Virginia, Maryland, Delaware,
and New Jersey have also supported beach nourishment
in residential areas along estuaries (see Figure 12.2). Some
agencies in Maryland encourage private shore protection to
avoid the environmental effects of shore erosion (see Section
A1.F.2 in Appendix 1), and the state provides interest-free
loans for up to 75 percent of the cost of nonstructural ero-
sion control projects on private property (MD DNR, 2008).
Although a Maryland guidance document for property
owners favors retreat over shore protection structures (MD
DNR, 2006), none of these states has a program to support
a retreat in developed areas.
FEMA Programs. Some aspects of the National Flood In-
surance Program (NFIP) encourage shore protection, while
others encourage retreat. The Federal Emergency Manage-
ment Agency (FEMA) requires local governments to ensure
33 USC §2213.
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Chapter 12
Figure 12.2 Beach nourishment along estuaries, (a) The Department of Natural Resources provided an interest-free loan to private
landowners for a combined breakwater and beach nourishment project to preserve the recreational beach and protect homes in
Bay Ridge, Maryland (July 2008). (b) The Virginia Beach Board and Town of Colonial Beach nourished the public beach along the
Potomac River for recreation and to protect the road and homes to the left (October 2002) [Photo source: ®James G. Titus, used
with permission].
that new homes along the ocean are built on pilings sunk
far enough into the ground so that the homes will remain
standing even if the dunes and beach are largely washed
out from under the house during a storm4. The requirement
for construction on pilings can encourage larger homes;
after a significant expense for pilings, people rarely build
a small, inexpensive cottage. These larger homes provide a
better economic justification for government-funded shore
protection than the smaller homes.
Beaches recover to some extent after storms, but they fre-
quently do not entirely recover. In the past, before homes
were regularly built to withstand the 100-year storm, retreat
from the shore often occurred after major storms (/'. e., people
did not rebuild as far seaward as homes had been before the
storm). Now, many homes can withstand storms, and the
tendency is for emergency beach nourishment operations to
protect oceanfront homes. A FEMA emergency assistance
program often funds beach nourishment in areas where the
beach was nourished before the storm5 (FEMA, 2007a). For
example, Topsail Beach, North Carolina received over $1
million for emergency beach nourishment after Hurricane
Ophelia in 2005, even though it is ineligible for USAGE
shore protection projects and flood insurance under the
Coastal Barrier Resources Act (GAO, 2007a). In portions of
Florida that receive frequent hurricanes, these projects are
a significant portion of total beach nourishment (see Table
12.1). They have not yet been a major source of fundingfor
beach nourishment in the Mid-Atlantic.
Several FEMA programs are either neutral or promote re-
treat. In the wake of Hurricane Floyd in 1999, one county
in North Carolina used FEMA disaster funds to elevate
structures, while an adjacent county used those funds to
4 44 Code of Federal Regulations §60.3(e)(4).
5 44 CFR §206.226(j).
help people relocate rather than rebuild (see Section Al.G
in Appendix 1). Repetitively flooded homes have been eli-
gible for relocation assistance under a number of programs.
Because of FEMA's rate map grandfathering policy (see
Section 10.7.3.1 in Chapter 10), a statutory cap on annual
flood insurance rate increases, and limitations of the hazard
mapping used to set rates, some properties have rates that
are substantially less than the actuarial rate justified by the
risk. As a result, relocation programs assist property owners
and save the flood insurance program money by decreasing
claims. From 1985 to 1995, the Upton-Jones Amendment to
the National Flood Insurance Act helped fund the relocation
of homes in imminent danger from erosion (Crowell et al.,
2007). FEMA's Severe Repetitive Loss Program is autho-
rized to spend $80 million to purchase or elevate homes
that have made either four separate claims or at least two
claims totaling more than the value of the structure (FEMA,
2008a). Several other FEMA programs provide grants for
reducing flood damages, which states and communities can
use for relocating residents out of the flood plain, erecting
flood protection structures, or floodproofing homes (FEMA,
2008b, c, d, e).
Flood insurance rates are adjusted downward to reflect the
reduced risk of flood damages if a dike or seawall decreases
flood risks during a 100-year storm. Because rates are based
on risk, this adjustment is not a bias toward shore protec-
tion, but rather a neutral reflection of actual risk.
Wetland Protection. The combination of federal and state
regulatory programs to protect wetlands in the Mid-Atlantic
strongly discourages development from advancing into
the sea, by prohibiting or strongly discouraging the filling
or diking of tidal wetlands for most purposes (see Chap-
ter 9). Within the Mid-Atlantic, New York promotes the
landward migration of tidal wetlands in some cases (see
166
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Table 12.1 Selected Beach Nourishment Projects in Florida Authorized
by FEMA's Public Assistance Grant Program
1987
1999
2001
2001
2001
2001
2004
2004
2004
2004
2004
2004
2004
2004
2004
2004
2005
2005
2005
2005
2005
'•'•• •'' '• ','''}, ' •
Jupiter Island
Jupiter Island
Longboat Key
Collier County
Vanderbilt Beach
Vanderbilt Beach
Manasota Kay /
Knights Island
Bonita Beach
Lovers Key
Lido Key
Boca Raton
Sabastian Inlet
Recreation Area
Hillsboro Beach
Jupiter Island
Pensacola Beach
Bay County
Pensacola Beach
Naples Beach
Pensacola Beach
Naples Beach
Longboat Key
•;_,'; •!- ",';•• ••'--.• ;
Floyd
Irene
Gabrielle
Gabrielle
Gabrielle
Gabrielle
Charley et o/.c
Charley et o/.c
Charley et o/.c
Charley et o/.c
Frances
Frances
Frances
Frances
Ivan
Ivan
Dennis
Katrina
Katrina
Wilma
Wilma
-'/'' '•'!'•:'"•'•.""•'• \f
90,000
48,500
48,253
37,800
61,534
b
115,700
21,652
13,300
67,600
297,572
184,755
83,444
871,187
2,500,000
56,520
400,000
34,988
482,000
44,834
66,272
?,,.-•; ':'.!''"'••,.
637,670
343,101
596,150
452,881
1,592,582
738,821
2,272,521
1,678,221
102,709
2,319,322
3,313,688
10,097,507
1,947,228
8,317,345
11,069,943
1,883,850
2,338,248
1,221,038
4,141,019
3,415,844
1,093,011
Source: Federal Emergency Management Agency, 2008. "Project Worksheets Involving
'Beach Nourishment' Obligated Under FEMA's Public Assistance Grant Program: As of
June 19, 2008".
' For some projects, the figure may include costs other than placing sand into the
beach system, such as reconstructing dunes and planting dune vegetation, as
well as associated planning and engineering costs.
b Supplemental grant. Applicant lost original sand source and had to go 50
kilometers offshore to collect the sand that had to be used. This increased the cost to
$30.82 per cubic meter ($23.57 per cubic yard), compared with originally
assumed cost of $10.80 per cubic meter ($8.25 per cubic yard).
c Cumulative impact of the 2004 hurricanes Charley, Frances, Ivan, Jeanne.
d Converted from cubic yards, preserving significant digits from the original
source, which varies by project.
Section Al. A.2 in Appendix 1), and Maryland favors shore
protection in some cases. The federal wetlands regulatory
program has no policy on the question of retreat versus
shore protection. Because the most compelling argument
against estuarine shore protection is often the preservation
of tidal ecosystems (e.g., NRC, 2007), a neutral regulatory
approach has left the strong demand for shore protection
from property owners without an effective countervailing
force for allowing wetlands to migrate (Titus 1998, 2000).
Wetlands continue to migrate inland in many undeveloped
areas (see Figure 12.3) but not in developed areas, which
account for an increasing portion of the coast.
Neither federal nor most state regulations encourage de-
velopers to create buffers that might enable wetlands to
migrate inland, nor do they encourage landward migration
in developed areas (Titus, 2000). In fact, USAGE has issued
a nationwide permit for bulkheads and other erosion-control
structures6. Titus (2000) concluded that this permit often en-
sures that wetlands will not be able to migrate inland unless
11 See 61 Federal Register 65,873, 65,915 (December 13, 1996) (reis-
suing Nationwide Wetland Permit 13, Bank Stabilization activities
necessary for erosion prevention). See also Reissuance of Nationwide
Permits, 72 Fed. Reg. 11,1108-09, 11183 (March 12, 2007) (reissuing
Nationwide Wetland Permit 13 and explaining that construction of
erosion control structures along coastal shores is authorized).
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Chapter 12
Figure 12.3 Tidal wetland migration, (a) Marshes taking over land on Hooper Island (Maryland) that had been pine forest until
recently, with some dead trees standing in the foreground and a stand of trees on slightly higher ground visible in the rear (Octo-
ber 2004). (b) Marshes on the mainland opposite Chintoteague Island, Virginia (June 2007) [Photo source: ®James G. Titus, used
with permission].
the property owner does not want to control the erosion. For
this and other reasons, the State of New York has decided
that bulkheads and erosion structures otherwise authorized
under the nationwide permit will not be allowed without
state concurrence (NYDOS, 2006; see Section ALA.2 in
Appendix 1).
Federal statutes discourage regulatory efforts to promote
landward migration of wetlands. Section 10 of the Rivers
and Harbors Act of 1899 and Section 404 of the Clean Wa-
ter Act require a permit to dredge or fill any portion of the
navigable waters of the United States7. Courts have long
construed this jurisdiction to include lands within the "ebb
and flow of the tides", (e.g., Gibbons v. Ogden; Zabelv. Tabb;
40 C.F.R. §230.3[s][l], 2004), but it does not extend inland
to lands that are dry today but would become wet if the sea
were to rise one meter (Titus, 2000). The absence of federal
jurisdiction over the dry land immediately inland of the
wetlands can limit the ability of federal wetlands programs
to anticipate sea-level rise.
Although the federal wetlands regulatory program generally
has a neutral effect on the ability of wetlands to migrate as
sea level rises, along the bay sides of barrier islands, regu-
latory programs discourage or prevent wetland migration.
Under natural conditions, barrier islands often migrate
inland as sea level rises (see Chapter 3). Winds and waves
tend to fill the shallow water immediately inland of the
islands, allowing bayside beaches and marshes to slowly
advance into the bay toward the mainland (Dean and Dal-
rymple, 2002; Wolf, 1989). Human activities on developed
islands, however, limit or prevent wetland migration (Wolf,
1989). Artificial dunes limit the overwash (see Section 6.2
in Chapter 6). Moreover, when a storm does wash sand from
the beach onto other parts of the island, local governments
bulldoze the sand back onto the beach; wetland rules against
filling tidal waters prevent people from artificially imitat-
ing the overwash process by transporting sand directly to
the bay side (see Section 10.3). Although leaving the sand
in place would enable some of it to wash or blow into the
bay and thereby accrete (build land) toward the mainland,
doing so is generally impractical. If regulatory agencies
decided to make wetland migration a priority, they would
have more authority to encourage migration along the bay
sides of barrier islands than elsewhere, because the federal
government has jurisidiction over the waters onto which
those wetlands would migrate.
In addition to the regulatory programs, the federal govern-
ment preserves wetlands directly through acquisition and
land management. Existing statutes give the U.S. Fish and
Wildlife Service and other coastal land management agen-
cies the authority to foster the landward migration of wet-
lands (Titus, 2000). A 2001 Department of Interior (DOI)
order directed the Fish and Wildlife Service and the National
Park Service to address climate change8. However, resource
managers have been unable to implement the order because
(1) they have been given no guidance on how to address
climate change and (2) preparing for climate change has not
been a priority within their agencies (GAO, 2007b).
Relationship to Coastal Development. Many policies en-
courage or discourage coastal development, as discussed in
Section 12.2.3. Even policies that subsidize relocation may
have the effect of encouraging development by reducing the
risk of an uncompensated loss of one's investment.
' See The Clean Water Act of 1977, §404, 33U.S.C. §1344; The Rivers
and Harbors Act of 1899, §10, 33 U.S.C. §§403, 409 (1994).
Department of Interior Secretarial Order 3226.
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
BOX 12.1: The Existing Decision-Making Process for Shoreline Protection on Sheltered Coasts
• There is an incentive to install seawalls, bulkheads, and revetments on sheltered coastlines because these
structures can be built landward of the federal jurisdiction and thus avoid the need for federal permits.
• Existing biases of many decision makers in favor of bulkheads and revetments with limited footprints limit
options that may provide more ecological benefits.
• The regulatory framework affects choices and outcomes. Regulatory factors include the length of time
required for permit approval, incentives that the regulatory system creates, [and] general knowledge of
available options and their consequences.
• Traditional structural erosion control techniques may appear to be the most cost-effective. However, they
do not account for the cumulative impacts that result in environmental costs nor the undervaluation of the
environmental benefits of the nonstructural approaches.
• There is a general lack of knowledge and experience among decision makers regarding options for shoreline
erosion mitigation on sheltered coasts, especially options that retain more of the shorelines' natural
features.
• The regulatory response to shoreline erosion on sheltered coasts is generally reactive rather than proactive.
Most states have not developed plans for responding to erosion on sheltered shores.
Source: NRC (2007)
12.2.2 Shoreline Armoring versus
Living Shorelines
The combined effect of federal and state wetland protec-
tion programs is a general preference for hard shoreline
structures over soft engineering approaches to stop erosion
along estuarine shores (see Box 12.1). USAGE has issued
nationwide permits to expedite the ability of property own-
ers to erect bulkheads and revetments9, but there are no
such permits for soft solutions such as rebuilding an eroded
marsh or bay beach10. The bias in favor of shoreline armor-
ing is the indirect result of a statute that focuses on filling
navigable waterways, not on the environmental impact of
the shore protection. Rebuilding a beach or marsh requires
more of the land below high water to be filled than building
a bulkhead.
Until recently, state regulatory programs shared the prefer-
ence for hard structures, but Maryland now favors "living
shorelines" (see Chapter 11), a soft engineering approach
9 Reissuance ofNationwide Permits, 72 Federal Register 11,1108-09,
11183 (March 12, 2007) (reissuing Nationwide Wetland Permit 13
and explaining that construction of erosion control structures along
coastal shores is authorized). See also Nationwide Permits 3 (Main-
tenance), 31 (Maintenance of Existing Flood Control Facilities), and
45 (Repair of Uplands Damaged by Discrete Events). 72 Federal
Register 11092-11198 (March 12, 2007).
10 Reissuance ofNationwide Permits, 72 Federal Register 11, 11183,
11185 (March 12, 2007) (explaining that permit 13 requires fill to be
minimized and that permit 27 does not allow conversion of open to
water to another habitat such as beach or tidal wetlands).
that mitigates coastal erosion while preserving at least some
of the features of a natural shoreline (compare Figure 12.4a
with 12.4b). Nevertheless, federal rules can be a barrier to
these state efforts (see e.g., Section Al.F.2.2 in Appendix 1),
because the living shoreline approaches generally include
some filling of tidal waters or wetlands, which requires a
federal permit (see Section 10.3).
The regulatory barrier to soft solutions appears to result
more from institutional inertia than from a conscious bias
in favor of hard structures. The nationwide permit program
is designed to avoid the administrative burden of issuing a
large number of specific but nearly-identical permits (Cope-
land, 2007). For decades, many people have bulkheaded their
shores, so in the 1970s USAGE issued Nationwide Permit
13 to cover bulkheads and similar structures. Because few
people were rebuilding their eroding tidal wetlands, no na-
tionwide permit was issued for this activity. Today, as people
become increasingly interested in more environmentally
sensitive shore protection, they must obtain permits from
institutions that were created to respond to requests for hard
shoreline structures. During the last few years however,
those institutions have started to investigate policies for soft
shore protection measures along estuarine shores.
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Chapter 12
Figure 12.4 Hard and soft shore protection, (a) Stone revetment along Elk River at Port Herman, Maryland (May 2005). (b)
Dynamic revetment along Swan Creek, at Fort Washington, Maryland (September 2008) [Photo source: ®James G. Titus, used
with permission].
12.2.3 Coastal Development
Federal, state, local, and private institutions all have a
modest bias favoring increased coastal development in de-
veloped areas. The federal government usually discourages
development in undeveloped areas, while state and local
governments have a more neutral effect.
Coastal counties often favor coastal development because
expensive homes with seasonal residents can substantially
increase property tax receipts without much demand for the
most costly governmental services such as schools (GAO,
2007a). Thus, local governments provide police, fire, and
trash removal to areas in Delaware and North Carolina that
are ineligible for federal funding under the Coastal Barrier
Resources Act11. The property tax system often encourages
coastal development. A small cottage on a lot that has ap-
preciated to $1 million can have an annual property tax bill
greater than the annual rental value of the cottage.
Governments at all levels facilitate the continued human
occupation of low-lying lands by providing roads, bridges,
and other infrastructure. As coastal farms are replaced with
development, sewer service is often extended to the new
communities—helping to protect water quality but also
making it possible to develop these lands at higher densities
than would be permitted by septic tank regulations.
Congressional appropriations for shore protection can en-
courage coastal development along shores that are protected
by reducing the risk that the sea will reclaim the land and
structures (NRC, 1995; Wiegel, 1992). This reduced risk
increases land values and property taxes, which may en-
courage further development. In some cases, the induced
development has been a key justification for the shore
protection (GAO, 1976; Burby, 2006). Shore protection
policies may also encourage increased densities in lightly
developed areas. The benefit-cost formulas used to deter-
mine eligibility (USAGE, 2000) find greater benefits in the
most densely developed areas, making increased density a
possible path toward federal funding for shore protection.
Keeping hazardous areas lightly developed, by contrast, is
not a path for federal funding (USACE, 1998; cf. Cooper
and McKenna, 2008).
Several authors have argued that the National Flood Insur-
ance Program (NFIP) encourages coastal development (e.g.,
Tibbetts, 2006; Suffin, 1981; Simmons, 1988; USFWS,
1997). Insurance converts a large risk into a modest annual
payment that people are willing to pay. Without insurance,
some people would be reluctant to risk $250,00012 on a home
that could be destroyed in a storm. However, empirical stud-
ies suggest that the NFIP no longer has a substantial impact
on the intensity of coastal development (Evatt, 2000; see
Chapter 10). The program provided a significant incentive
for construction in undeveloped areas during the 1970s,
when rates received a substantial subsidy (Cordes and Yezer,
1998; Shilling et al., 1989; Evatt, 1999). During the last few
decades, however, premiums on new construction have not
been subsidized, and hence the program has had a marginal
impact on construction in undeveloped areas (Evatt, 2000;
Leatherman, 1997; Cordes and Yezer, 1998; see Chapter
10). Nevertheless, in the aftermath of severe storms, the
program provides a source of funds for reconstruction—and
subsidized insurance while shore protection structures are
being repaired (see Section 10.7.3.2). Thus, in developed
areas the program helps rebuild communities that might be
slower to rebuild (or be abandoned) if flood insurance and
federal disaster assistance were unavailable. More broadly,
the combination of flood insurance and the various post-
disaster and emergency programs that offer relocation as-
sistance, mitigation (e.g., home elevation), reconstruction of
11 16U.S.Code. §3501 etseq.
2 NFIP only covers the first $250,000 in flood losses (44 CFR 61.6).
For homes with a construction cost greater than $250,000, federal
insurance reduces a property owner's risk, but to a lesser extent.
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to
A Focus on the Mid-Atlantic Region
infrastructure, and emergency beach nourishment provide
property owners with a federal safety net that makes coastal
construction a safe investment.
Flood ordinances have also played a role in the creation
of three-story homes where local ordinances once limited
homes to two stories. Flood regulations have induced some
people to build their first floor more than 2.5 meters (8
feet) above the ground (FEMA, 1984, 1994, 2000, 2007b).
Local governments have continued to allow a second floor
no matter the elevation of the first floor. Property owners
often enclose the area below the first floor (e.g., FEMA,
2002), creating ground-level (albeit illegal13 and uninsur-
able14) living space.
The totality of federal programs, in conjunction with sea-
level rise, creates moral hazard. Coastal investment is
profitable but risky. If government assumes much of this
risk, then the investment can be profitable without being
risky—an ideal situation for investors (Loucks etal., 2006).
The "moral hazard" concern is that when investors make
risky decisions whose risk is partly borne by someone else,
there is a chance that they will create a dangerous situation
by taking on too much risk (Pauly, 1974). The government
may then be called upon to take on even the risks that the
private investors had supposedly assumed because the risk
of cascading losses could harm the larger economy (Kun-
reuther and Michel-Kerjant, 2007). Investors assume that
shore protection is cost-effective and governments assume
that flood insurance rates reflect the risk in most cases;
however, if sea-level rise accelerates, will taxpayers, coastal
property owners, or inland flood insurance policyholders
have to pay the increased costs?
The Coastal Barrier Resources Act (16 U.S.C. U.S.C. §3501
et seq.) discourages the development of designated unde-
veloped barrier islands and spits, by denying them shore
protection, federal highway funding, mortgage funding,
flood insurance on new construction, some forms of fed-
eral disaster assistance15, and most other forms of federal
spending. Within the Mid-Atlantic, this statute applies to
approximately 90 square kilometers of land, most of which
is in New York or North Carolina (USFWS, 2002)16. The
increased demand for coastal property has led the most
developable of these areas to become developed anyway
(GAO, 1992, 2007a). "Where the economic incentive for
development is extremely high, the Act's funding limitations
can become irrelevant" (USFWS, 2002).
13 44 CFR §60.3(c)(2).
1444CFR§61.5(a).
15 Communities are eligible for emergency beach nourishment after a
storm, provided that the beach had been previously nourished (GAO,
2007a).
16 The other mid-Atlantic states each have less than 6 square kilometers
within the CBRA system. A small area within the system in Delaware
is intensely developed (see Box 9.2).
Uncertainty can be a hurdle to preparing for sea-level rise.
Uncertainty about sea-level rise and its precise effects is one
problem, but uncertainty about how others will react can also
be a barrier. For environmental stresses such as air pollution,
a single federal agency (U.S. EPA) is charged with devel-
oping and coordinating the nation's response. By contrast,
the response to sea-level rise would require coordination
among several agencies, including U.S. EPA (protecting the
environment), USAGE (shore protection), Department of In-
terior (managing conservation lands), FEMA (flood hazard
management), and NOAA (coastal zone management). State
and local governments generally have comparable agencies
that work with their federal counterparts. No single agency
is in charge of developing a response to sea-level rise, which
affects the missions of many agencies.
The decisions that these agencies and the private sector make
regarding how to respond to sea-level rise are interdepen-
dent. From the perspective of one decision maker, the fact
that others have not decided on their response can be a bar-
rier to preparing his or her own response. One of the barriers
of this type is the uncertainty whether the response to sea-
level rise in a particular area will involve shoreline armoring,
elevating the land, or retreat (see Chapter 6 for a discussion
of specific mechanisms for each of these pathways).
1,1 Three
or
Long-term approaches for managing low coastal lands as the
sea rises can be broadly divided into three pathways:
Protect the dry land with seawalls, dikes, and other
structures, eliminating wetlands and beaches (also
known as "shoreline armoring") (see Figure 12.4a and
Section6.1.1).
Elevate the land, and perhaps the wetlands and beaches
as well, enabling them to survive (see Figures 12.1 and
12.5).
Retreat by allowing the wetlands and beaches to take
over land that is dry today (see Figure 12.6).
Combinations of these three approaches are also possible.
Each approach will be appropriate in some locations and
inappropriate in others. Shore protection costs, property
values, the environmental importance of habitat, and the
feasibility of protecting shores without harming the habitat
all vary by location. Deciding how much of the coast should
be protected may require people to consider social priori-
ties not easily included in a cost-benefit analysis of shore
protection.
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The U.S. Climate Change Science Program
Chapter 12
(a)
Figure 12.5 Elevating land and house (January through June 2005). (a) Initial elevation of house in Brant Beach, New Jersey, (b)
Structural beams placed under house, which is lifted approximately 1.5 meters by hydraulic jack in blue truck, (c) Three course of
cinder blocks added then house set down onto the blocks, (d) Soil and gravel brought in to elevate land surface. [Photo source:
®James G. Titus, used with permission].
Table 12.2 Pathways for Responding to Sea-Level Rise. The best way to prepare for sea-
level rise depends on whether a community intends to hold back the sea, and if so, how.
Rebuild drainage
systems
Rebuild roads
Location of roads
Replace septics
with public sewer
Setbacks/
subdivisions
Easements
Pathway for responding to sea-level rise
Check valves, holding
tanks; room for pumps
Keep roads at same
elevation; owners will
not have to elevate lots
Shore-parallel road
needed for dike
maintenance
Extending sewer helps
improve drainage
Setback from shore to
leave room for dike
Easement or option to
purchase land for dike
No change needed
Rebuild road
higher; motivates
property owners
to elevate lots
No change needed
Mounds systems;
elevate septic
system; extending
sewer also accept-
able
No change needed
No change needed
Install larger pipes, larger
rights of way for ditches
Elevate roads to facilitate
evacuation
Shore-parallel road will be
lost; all must have access to
shore-perpendicular road
Extending sewer undermines
policy; mounds system
acceptable
Erosion-based setbacks
Rolling easements to ensure
that wetlands and beaches
migrate
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Like land-use planning, the purpose of selecting a pathway
would be to foster a coordinated response to sea-level rise,
not to lock future generations into a particular approach.
Some towns may be protected by dikes at first, but eventu-
ally have to retreat as shore protection costs increase beyond
the value of the assets protected. In other cases, retreat may
be viable up to a point, past which the need to protect critical
infrastructure and higher density development may justify
Figure 12.6 Retreat, (a) June 2002. Houses along the shore in
Kitty Hawk, North Carolina. Geotextile sand bags protect the
septic tank buried in the dunes, (b) October 2002. (c) June 2003
[Photo source: ®James G. Titus, used with permission].
shore protection. Shoreline armoring may be appropriate
over the next few decades to halt shoreline erosion along
neighborhoods that are about one meter above high water;
but as sea level continues to rise, the strategy may switch to
elevating land surfaces and homes, because relying on dikes
would eventually lead to land becoming below sea level.
12.3.2 Decisions that Cannot be Made
Until the Pathway is Chosen
In most cases, the appropriate response to rising sea level
depends on which of the three pathways a particular com-
munity intends to follow. This subsection examines the
relationship between the three pathways and six example
activities, summarized in Table 12.2.
Coastal Drainage Systems in Urban Areas. Sea-level rise
slows natural drainage and the flow of water through drain
pipes that rely on gravity. If an area will not be protected
from increased inundation, then larger pipes or wider ditches
(see Figure 12.7) may be necessary to increase the speed at
which gravity drains the area. If an area will be protected
with a dike, then it will be more important to pump the water
out and to ensure that sea water does not back up into the
streets through the drainage system; so then larger pipes
will be less important than underground storage, check
valves, and ensuring that the system can be retrofitted to
allow for pumping (Titus et al., 1987). If land surfaces will
be elevated, then sea-level rise will not impair drainage.
In many newly developed areas, low-impact development
attempts to minimize runoff into the drainage system in
favor of on-site recharge. In areas where land surfaces will
be elevated over time, the potential for recharge would
remain roughly constant as land surfaces generally rise as
much as the water table (i.e., groundwater level). In areas
that will ultimately be protected with dikes, by contrast,
centralized drainage would eventually be required because
land below sea level can not drain unless artificial measures
keep the water table even farther below sea level.
Road Maintenance. As the sea rises, roads flood more fre-
quently. If a community expects to elevate the land with the
sea, then routine repaving projects would be a cost-effective
time to elevate the streets. If a dike is expected, then repav-
ing projects would consciously avoid elevating the street
above people's yards, lest the projects cause those yards to
flood or prompt people to spend excess resources on elevat-
ing land, when doing so is not necessary in the long run.
The Town of Ocean City, Maryland, currently has policies in
place that could be appropriate if the long-term plan was to
build a dike and pumping system, but not necessarily cost-
effective if land surfaces are elevated as currently expected.
The town has an ordinance that requires property owners to
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Chapter 12
Figure 12.7 Tidal ditches in the Mid-Atlantic, (a) Hoopers Island, Maryland (October 2004). (b) Poquoson, Virginia (June 2002).
(c) Swan Quarter, North Carolina (October 2002). (d) Sea Level, North Carolina (October 2002). The water rises and falls with
the tides in all of these ditches, although the astronomic tide is negligible in (c) Swan Quarter. Wetland vegetation is often found
in these ditches. Bulkheads are necessary to prevent the ditch from caving in and blocking the flow of water in (b) [Photo source:
®James G. Titus, used with permission].
maintain a 2 percent grade so that rainwater drains into the
street. The city engineer has interpreted this rule as imposing
a reciprocal responsibility on the town itself to not elevate
roadways above the level where yards can drain, even if the
road is low enough to flood during minor tidal surges. Thus,
the lowest lot in a given area dictates how high the street can
be. As sea level rises, the town will be unable to elevate its
streets, unless it changes this rule. Yet public health reasons
require drainage to prevent standing water in which mosqui-
toes breed. Therefore, Ocean City has an interest in ensuring
that all property owners gradually elevate theiryards so that
the streets can be elevated as the sea rises without causing
public health problems. The town has developed draft rules
that would require that, during any significant construction,
yards be elevated enough to drain during a 10-year storm
surge for the life of the project, considering projections of
future sea-level rise. The draft rules also state that Ocean
City's policy is for all lands to gradually be elevated as the
sea rises (see Box A1.5 in Appendix 1).
Locations of Roads. As the shore erodes, any home that is
accessed only by a road seaward of the house could lose ac-
cess before the home itself is threatened. Homes seaward of
the road might also lose access if that road were washed out
elsewhere. Therefore, if the shore is expected to erode, it is
important to ensure that all homes are accessible by shore-
perpendicular roads, a fact that was recognized in the layout
of early beach resorts along the New Jersey and other shores.
If a dike is expected, then a road along the shore would be
useful for dike construction and maintenance. Finally, if all
land is likely to be elevated, then sea-level rise may not have
a significant impact on the best location for new roads.
Septics and Sewer. Rising sea level can elevate the water
table (ground water) to the point where septic systems no
longer function properly (U.S. EPA, 2002)17. If areas will
17 "Most current onsite wastewater system codes require minimum
separation distances of at least 18 inches from the seasonally high
water table or saturated zone irrespective of soil characteristics. Gen-
erally, 2- to 4-foot separation distances have proven to be adequate
in removing most fecal coliforms in septic tank effluent", U.S. EPA
(2002).
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Coastal Sensitivity to Sea-Level Rise:
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Mounds-Based Septic System
im*£mwww8fri!&ftF
MIOH WAItK
ALA*M 1W| I(.M
SEPTIC TANK
DOSING CHAMBER
Figure 12.8 Schematic of mounds-based septic system for areas with high water tables. For areas with high water tables, where
traditional septic/drainfield systems do not work, sand mounds are often used. In this system, a sand mound is contructed on the
order of 50 to 100 cm above the ground level, with perforated drainage pipes in the mound above the level of adjacent ground, on
top of a bed of gravel to ensure proper drainage. Effluent is pumped from the septic tank up to the perforated pipe drainage pipe.
Source: Converse and Tyler (1998).
Figure 12.9 Mounds-based septic system next to house along the back side of Pickering Beach, Delaware (March 2009). [Photo
source: ®James G. Titus, used with permission].
be protected with a dike, then all of the land protected must
eventually be artificially drained and sewer lines further
extended to facilitate drainage. On the other hand, extending
sewer lines would be entirely incompatible with allowing
wetlands to migrate inland, because the high capital invest-
ment tends to encourage coastal protection; a mounds-based
septic system (Bouma et al., 1975; see Figures 12.8 and
12.9) is more compatible. If a community's long-term plan
is to elevate the area, then either a mounds-based system or
extended public sewage will be compatible.
Subdivision and Setbacks. If a dike is expected, then houses
need to be set back enough from the shore to allow room
for the dike and associated drainage systems. Setbacks and
larger coastal lot sizes are also desirable in areas where a
retreat policy is preferred for two reasons. First, the setback
provides open lands onto which wetlands and beaches can
migrate inland without immediately threatening property.
Second, larger lots mean lower density and hence fewer
structures that would need to be moved, and less justification
for investments in central water and sewer. By contrast, in
areas where the plan is to elevate the land, sea-level rise does
not alter the property available to the homeowner, and hence
would have minor implication for setbacks and lot sizes.
Covenants and Easements Accompanying Subdivision.
Although setbacks are the most common way to anticipate
eventual dike construction and the landward migration of
wetlands and beaches, a less expensive method would often
be the purchase of (or regulatory conditions requiring) roll-
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Chapter 12
ing easements, which allow development but prohibit hard
structures that stop the landward migration of ecosystems.
The primary advantage of a rolling easement is that society
makes the decision to allow wetlands to migrate inland
long before the property is threatened, so owners can plan
around the assumption of migrating wetlands, whether that
means leaving an area undeveloped or building structures
that can be moved.
Local governments can also obtain easements for future
dike construction. This type of easement, as well as rolling
easements, would each have very low market prices in most
areas, because the fair market value is equal to today's land
value discounted by the rate of interest compounded over
the many decades that will pass before the easement would
have any effect (Titus, 1998). As with setbacks, a large area
would have to be covered by the easements if wetlands are
going to migrate inland; a narrow area would be required
along the shore for a dike; and no easements are needed if
the land will be elevated in place.
on
At the local level, officials make assumptions about which
land will be protected in order to understand which lands
will truly become inundated (see Chapter 2) and how shore-
lines will actually change (see Chapter 3), which existing
wetlands will be lost (see Chapter 4), whether wetlands will
be able to migrate inland (see Chapter 6), and the potential
environmental consequences (see Chapter 5); the population
whose homes would be threatened (see Chapter 7) and the
implications of sea-level rise for public access (see Chapter
8) and floodplain management (see Chapter 9). Assumptions
about which shores will be protected are also necessary in
order to estimate the level of resources that would be needed
to fulfill property owners' current expectations for shore
protection (e.g., Titus, 2004).
Improving the ability to project the impacts of sea-level
rise is not the only for such analyses utility of data regard-
ing shore protection. Another use of such studies has been
to initiate a dialogue about what should be protected, so
that state and local governments can decide upon a plan of
what will actually be protected. Just as the lack of a plan
can be a barrier to preparing for sea-level rise, the adoption
of a plan could remove an important barrier and signal to
decision makers that it may be possible for them to plan for
sea-level rise as well.
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o
>
National Implications and a Science Strategy for
Moving Forward
Authors: S. Jeffress Williams, USGS; E. Robert Thieler, USGS; Benjamin T. Gutierrez, USGS;
Dean B. Gesch, USGS; Donald R. Cahoon, USGS; K. Eric Anderson, USGS
Climate change and effects such as sea-level rise have
global implications and will increasingly affect the
entire nation. While this Product focuses primarily
on the mid-Atlantic region of the United States, many
of the issues discussed in earlier chapters are relevant
at the national scale.
Chapter 13 draws on findings from the mid-Atlantic fo-
cus area that have relevance to other parts of the United
States, provides an overview of coastal environments
and landforms in the United States, and describes the
issues faced in understanding how these environments
may be impacted and respond to sea-level rise. The
diversity of U.S. coastal settings includes bedrock
coasts in Maine; glacial bluffs in New York; barrier
islands in the Mid-Atlantic and Gulf of Mexico; coral
reefs in Florida, the Caribbean, and Hawaii; one of
the world's major delta systems in Louisiana; a wide
variety of pocket beaches and cliffed coasts along the
Pacific coast; Pacific atolls; and a number of arctic
coastline types in Alaska. In addition, the large bays
and estuaries around the country also exhibit a diverse
range of shoreline types, large wetland systems, and
extensive coastal habitats.
Understanding how the different coastal environments
of the United States will respond to future climate and
sea-level change is a major challenge. In addition, as high-
lighted in earlier Parts of this Product, human actions and
policy decisions also substantially influence the evolution
of the coast. The knowledge gaps and data limitations
identified in this Product focusing on the Mid-Atlantic
have broad relevance to the rest of the United States.
Chapter 14 identifies opportunities for increasing the
scientific understanding of future sea-level rise impacts.
This includes basic and applied research in the natural
and the social sciences. A significant emphasis is placed
on developing linkages between scientists, policy makers,
and stakeholders at all levels, so that information can be
shared and utilized efficiently and effectively as sea-level
rise mitigation and adaptation plans evolve.
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The U.S. Climate Change Science Program Part IV Overview
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Coastal Sensitivity to Sea-Level Rise:
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KEY FINDINGS
Nationwide, more than one-third of the U.S. population currently lives in the coastal zone and movement to the
coast and development continues, along with the current and growing vulnerability to coastal hazards such as storms
and sea-level rise. Fourteen of the 20 largest U.S. urban centers are located along the coast. With the very likely
accelerated rise in sea level and increased storm intensity, the conflicts between people and development at the
coast and the natural processes will increase, causing economic and societal impacts.
For much of the United States, shores comprised of barrier islands, dunes, spits, and sandy bluffs, erosion processes
will dominate at highly variable rates in response to sea-level rise and storms over the next century and beyond. Some
coastal landforms in the United States may undergo large changes in shape and location if the rate of sea-level rise
increases as predicted. Increased inundation and more frequent flooding will affect estuaries and low-lying coastal
areas. The response to these driving forces will vary depending on the type of coastal landform and local conditions,
but will be more extreme, more variable, and less predictable than the changes observed over the last century.
For higher sea-level rise scenarios, some barrier island coasts and wetlands may cross thresholds and undergo
significant and irreversible changes. These changes include rapid landward migration and segmentation of some
barrier islands and disintegration and drowning of wetlands.
Nationally, tidal wetlands already experiencing submergence by sea-level rise and associated land loss, in concert
with other factors, will continue to deteriorate in response to changing climate.
Coastal change is driven by complex and interrelated processes. Over the next century and beyond, with an expected
acceleration in sea-level rise, the potential for coastal change is likely to be greater than has been observed in historic
past. These changes to coastal regions will have especially large impacts on urban centers and developed areas.
Some portions of the U.S. coast will be subject primarily to inundation from sea-level rise over the next century.
A substantial challenge remains to quantify the various effects of sea-level rise and to identify the dominant coastal
change processes for each region of the U.S. coast.
Many coastal areas in the United States will likely experience an increased frequency and magnitude of storm-surge
flooding and coastal erosion due to storms over the next century in response to sea-level rise. The impacts from
these storm events are likely to extend farther inland from the coast than those that would be affected by sea-level
rise alone.
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Chapter I 3
Understanding, predicting, and responding to the environmental and societal effects of sea-level rise would
benefit from a national program of integrated research that includes the natural and social sciences. Research on
adaptation, mitigation, and avoidance-of-risk measures would enable improved understanding of the many and
varied potential societal impacts of sea-level rise that would benefit the United States as well as coastal nations
around the world.
13.1 INTRODUCTION
As defined in the SAP 4.1 Prospectus and discussed in
earlier chapters, this Product focuses on assessing potential
impacts to the mid-Atlantic region; however, some discus-
sion of impacts to other regions and the nation as a whole
is warranted. The mid-Atlantic region is highly vulnerable
to sea-level rise, but regions like the central Gulf Coast
(Louisiana, Texas) are just as vulnerable or more so. The
challenge in carrying out a national assessment is that na-
tionwide databases and scientific publications of national
scale and scope are limited. Modest efforts at monitoring
and observations for national-scale assessments of coastal
change and hazards are underway by various organizations,
but more effort is needed. The discussion in Section 13.3 is
largely the expert opinions of the lead authors, informed by
results of the two expert science panel reports (Reed et al.,
2008, Gutierrez, etal., 2007) and available scientific litera-
ture. Because of the relative lack of adequate background
literature and high reliance on expert opinion, the likehood
statements as used in other chapters are not included in this
discussion of potential impacts to the nation.
A large and expanding proportion of the U.S. population
and related urban development is located along the Atlantic,
Gulf of Mexico, and Pacific coasts and
increasingly conflicts with the natu-
ral processes associated with coastal
change from storms and sea-level rise
(see review in Williams et al., 1991).
Development in low-lying regions
(e.g., New Orleans) and islands (e.g.,
in the Chesapeake Bay, Caribbean,
Pacific Ocean) are particularly at risk
(see Gibbons and Nicholls, 2006). In
the future, as the effects of climate
change intensify, these interactions
will become more frequent and more
challenging to society. Currently,
more than one-third of the U.S.
population lives in the coastal zone
and movement to the coast and de-
velopment continues, along with the
growing vulnerability to coastal hazards. Fourteen of the
20 largest U.S. urban centers are located along the coast
(Crossett et al., 2004; Crowell et al, 2007). With the likely
accelerated rise in sea level and increased storm intensity,
the conflicts between people and development at the coast
and the natural processes will increase, affecting all parts of
society (Leatherman, 2001; FitzGerald et al, 2008).
Global sea-level rise associated with climate change is likely
to be in the range of 19 centimeters (cm) (7.5 inches [in])
to as much as 1 meter (m) (about 3 feet [ft]) over the next
century and possibly as much as 4 to 6 m (about 13 to 20
ft) over the next several centuries (IPCC, 2007; Rahmstorf,
2007; Rahmstorf, Qt al, 2007; Overpeck et al, 2006). The
expected rise will increase erosion and the frequency of
flooding, and coastal areas will be at increasing risk. For
some regions, adaptation using engineering means may
be effective; for other coastal areas, however, adaption by
relocation landward to higher elevated ground may be ap-
propriate for longer-term sustainability (NRC, 1987).
Coastal landforms reflect the complex interaction between
the natural physical processes that act on the coast, the
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geologic characteristics of the coast, and human activities.
Spatial and temporal variations in these physical processes
and the geology along the coast are responsible for the
wide variety of landforms around the United States (Wil-
liams, 2003). With future sea-level rise, portions of the U.S.
ocean coast are likely to undergo long-term net erosion, at
rates higher than those that have been observed over the
past century (see Chapter 3). The exact manner and rates
at which these changes are likely to occur depends on the
character of coastal landforms (e.g., barrier islands, cliffs)
and the physical processes (e.g., waves and winds) that shape
these landforms (see Chapters 3 and 4). Low-relief coastal
regions, areas undergoing land subsidence, and land subject
to frequent storm landfalls, such as the northern Gulf of
Mexico, Florida, Hawaii, Puerto Rico, the San Francisco-
Sacramento Delta region, and the Mid-Atlantic region, are
particularly vulnerable.
13.2 TYPES OF COASTS
Coasts are dynamic junctions of the oceans, atmosphere,
and land and differ greatly in physical character and vulner-
ability to erosion, storms, and sea-level rise (NRC, 1990).
The principal coastal types are described in Chapters 3 and
4, and summarized below. With future sea-level rise, all of
these landforms will become more dynamic (Nicholls et
al., 2007), but predicting and quantifying changes that are
likely to occur with high confidence is currently scientifi-
cally challenging.
13.2.1 Cliff and Bluff Shorelines
Substantial portions of the U. S. coast are comprised of coast-
al cliffs and bluffs that vary greatly in height, morphology,
and composition. These occur predominantly along the New
England and Pacific coasts, Hawaii, and Alaska. Coastal
cliff is a general term that refers to steep slopes along the
shoreline that commonly form in response to long-term rise
in sea-level. The term "bluff" also can refer to escarpments
eroded into unlithified material, such as glacial till, along
the shore (Hampton and Griggs, 2004). The terms "cliff"
and "bluff" are often used interchangeably. Coastal cliffs
erode in response to a variety of both marine and terrestrial
processes. Cliff retreat can be fairly constant, but can also
be episodic. In contrast to sandy coasts, which may erode
landward or accrete seaward, cliffs retreat only in a land-
ward direction. Because rocky cliff coasts are composed
of resistant materials, erosion can can occur more slowly
than for those comprised of unconsolidated sediments and
response times to sea-level rise can be much longer than for
sandy coasts (NRC, 1987), but land slumping due to wave
action or land surface water runoff can result in rapid retreat.
Hampton and Griggs (2004) provide a review of the origin,
U.S. distribution, evolution, and regional issues associated
with coastal cliffs. Predicting the response of coastal cliffs
to future sea-level rise is a topic of active research (Tren-
haile, 2001; Walkden and Hall, 2005; Dickson et al., 2007;
Walkden and Dickson, 2008).
13.2.2 Sandy Shores, Pocket Beaches,
Barrier Beaches, Spits, and Dunes
Sandy beaches are often categorized into a few basic types
which commonly include mainland, pocket, and barrier
beaches (Wells, 1995; Davis and FitzGerald, 2004). The
sediments that comprise beaches are derived mainly from
the erosion of the adjacent mainland and continental shelf,
and sometimes from sediments supplied from coastal rivers.
Mainland beaches occur where the land intersects the shore.
Some mainland beaches occur in low-relief settings and are
backed by coastal dunes, while others occur along steep
portions of the coast and are backed by bluffs. Examples of
mainland beaches include the shores of eastern Long Island,
northern New Jersey (Oertel and Kraft, 1994), and parts
of Delaware, (Kraft, 1971). Pocket
beaches form in small bays, often oc-
curring between rocky headlands and
are common along parts of the south-
ern New England coast, portions of
California and Oregon (Hapke et al.,
2006), and in parts of the Hawaiian
Islands. Barrier beaches and spits are
the most abundant coastal landforms
along the Atlantic and Gulf of Mexico
coasts. In general, it is expected that
accelerations in sea-level rise will en-
hance beach erosion globally, but on a
local scale this response will depend
on the sediment budget (Nicholls et
al, 2007).
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Chapter I 3
13.2.3 Coastal Marshes, Mangroves, and
Mud Flat Shorelines
Coastal wetlands include swamps and tidal flats,
salt and brackish marshes, mangroves, and bayous.
They form in low-relief, low-energy sheltered coastal
environments, often in conjunction with river deltas,
landward of barrier islands, and along the flanks
of estuaries (e.g., Delaware Bay, Chesapeake Bay,
Everglades, Lake Pontchartrain, Galveston Bay,
San Francisco Bay, and Puget Sound). Most coastal
wetlands are in Louisiana, North and South Carolina,
south Florida, and Alaska (Dahl, 1990; NRC, 1995a).
Wetlands are extremely vulnerable to sea-level rise
and can maintain their elevation and viability only
if sediment accumulation (both mineral and organic
matter) keeps pace with sea-level rise (Cahoon et al., 2006;
Nyman et al, 2006; Morris et al, 2002; Rybczyk and Ca-
hoon, 2002). Future wetland area will also be determined, in
part, by the amount of space (e.g., mud flat or tidal flat area)
available for landward migration and the rates of lateral ero-
sion of the seaward edge of the marsh (see Chapter 4; Poulter,
2005). Wetlands will be especially vulnerable to the higher
projected rates of future sea-level rise (e.g., greater than 70
cm by the year 2100), but some will survive a 1-meter rise
(Morris etal, 2002). Even under lower accelerated sea-level
rise rates, wetlands may be sustained only where conditions
are optimal for vertical wetland development (e.g., abundant
sediment supply and low regional subsidence rate) (Rybczyk
and Cahoon, 2002).
Mud flat shorelines represent a relatively small portion of
U. S. coasts, but are important in providing the foundation for
wetlands and marshes (Mitsch and Gosselink, 1986). They
are frequently associated with wetlands, and occur predomi-
nately in low-energy, low-relief regions with high inputs of
fine-grained, river-born sediments and organic materials
and large tidal ranges. These shoreline types are common
in western Louisiana (i.e., Chenier Plain) and along north-
eastern parts of the Gulf Coast of Florida. Muddy coasts
may be drowned with sea-level rise unless sediment
inputs are sufficiently large, such as the Atchafalaya
River delta region of southwestern Louisiana, where
the flats are able to be colonized by plants.
13.2.4 Tropical Coral Reef Coasts
Tropical coral reefs, made up of living organisms
very sensitive to ocean temperature and chemis-
try, are found in the U.S. along the south coast of
Florida; around the Hawaiian Islands, Puerto Rico,
the Virgin Islands, and many of the U.S. territories
in the Pacific (Riegl and Dodge, 2008). In tropical
environments, living coral organisms build reefs
that are important ecological resources (Smith and
Buddemeier, 1992; Boesche/a/., 2000). Most corals are able
to tolerate rates of sea-level rise of 10 to 20 mm per year
or more (Smith and Buddemeier, 1992; Bird, 1995; Wells,
1995; Hallock, 2005). Nonetheless, the ability of coral reef
systems to survive future sea-level rise will depend heavily
on other climate change impacts such as increase in ocean
temperature and/or acidity, sediment runoff from the land,
as well as episodic storm erosion (Hallock, 2005; Nicholls
et al, 2007). In addition, human caused stresses such as
overfishing or pollution can contribute to the vulnerability
of these systems to climate change (Buddemeier et al, 2004;
Mimura et al, 2007).
13.3 POTENTIAL FOR FUTURE
SHORELINE CHANGE
Over the next century and beyond, with an expected ac-
celeration in sea-level rise, the potential for coastal change
will increase and coastal change is likely to be more wide-
spread and variable than has been observed in the historic
past (NRC, 1987; Brown and McLachlan, 2002; Nicholls
et al, 2007). However, it is difficult at present to quantita-
tively attribute shoreline changes directly to sea-level rise
(Rosenzweig et al, 2007). The potential changes include
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A Focus on the Mid-Atlantic Repion
increased coastal erosion, more frequent tidal and storm-
surge flooding of low-relief areas, and wetland deterioration
and losses. Many of these changes will occur in all coastal
states. These changes to the coastal zone can be expected to
have especially large impacts to developed areas (Nicholls
etal., 2007). Some portions of the U.S. coast will be subject
principally to inundation from sea-level rise over the next
century, including upper reaches of bays and estuaries (e.g.,
Chesapeake and Delaware Bays, Tampa Bay, Lake Pontchar-
train, San Francisco Bay), and hardened urban shorelines.
Erosion, sediment transport, and sediment deposition in
coastal environments are active processes and will drive
coastal change in concert with the combined effects of future
sea-level rise and storms (Stive, 2004).
Coastal landforms may become even more dynamic and that
erosion will dominate changes in shoreline position over the
next century and beyond (Nicholls et al., 2007). Wetlands
with sufficient sediment supply and available land for inland
migration may be able to maintain elevation, keeping pace
with sea-level rise, but sediment starved wetlands and those
constrained by engineering structures (e.g., seawalls, revet-
ments) or steep uplands are likely to deteriorate and convert
to open water through vertical accretion deficits and lateral
erosion (see Chapter 4). On barrier island shores, erosion is
likely to occur on both the ocean front and the landward side
of the island due to a combination of storm activity, changes
in sediment budget, more frequent tidal flooding, and rising
water levels (Nicholls et al, 2007).
Sea-level rise is a particular concern for islands (Mimura et
al., 2007). Especially at risk are islands comprised of coral
atolls (e.g., Midway Atoll), which are typically low-lying
and dependent on the health of coral reefs that fringe the
atolls. Populated islands with higher elevations (e.g., the
Northern Mariana Islands) are also frequently at risk as
the infrastructure is frequently located in low-lying coastal
regions along the periphery of the islands.
Many coastal areas in the United States will likely experi-
ence an increased frequency and magnitude of storm-surge
flooding, greater wave heights, and more erosion due to
storms as part of the response to sea-level rise (NRC, 1987;
Woodworth and Blackman, 2004; Nicholls et al, 2007;
Gutowski et al, 2008). Impacts from these storm events
may extend farther inland than those that would be affected
by sea-level rise alone. Many regions may also experience
large changes to coastal systems, such as increased rates
of erosion, barrier island and dune landward migration,
and potential barrier island collapse (Nicholls et al, 2007;
see also Chapters 1, 3, and 14 for discussion of geomorphic
thresholds). The potential of crossing thresholds, potentially
leading to barrier and wetland collapse, may increase with
higher rates of sea-level rise.
The use of so called "soft" coastal engineering mitigation
measures, such as beach nourishment, usually using sand
dredged from offshore Holocene-age sand bodies, may
reduce the risk of storm flooding and coastal erosion tem-
porarily (NRC, 1987,1995b). However, an important issue is
whether or not these practices are able to be maintained into
the future to provide sustainable and economical shoreline
protection in the face of high cost, need for periodic re-
nourishment, and limited sand resources of suitable quality
for nourishment for many regions of the country (NRC,
1995b; Magoon et al., 2004). Results from offshore geologic
mapping studies indicate that most continental shelf regions
of the United States have relatively limited Holocene-age
sediment that can be deemed available and suitable for uses
such as beach nourishment (Schwab et al, 2000; Gayes et
al, 2003; Pilkey et al, 1981; Kraft, 1971). In some cases,
potential sand volumes are reduced because of economic
and environmental factors such as water depth, benthic
environmental concerns, and concerns that sand removal
may alter sediment exchange with the adjacent coast (Bliss
et al, 2009). The result is limited volumes of high-quality
offshore sand resources readily available for beach nourish-
ment. The issue of relying long term on using offshore sand
for beach nourishment to mitigate erosion is important and
needs to be addressed.
More widespread implementation of regional sediment or
best sediment management practices to conserve valuable
coastal clean sandy dredged spoils can enhance the long-
term sustainability of sandy coastal landforms (NRC, 2007).
The use of so called "hard" engineering structures (e.g.,
seawalls, breakwaters) to protect property from erosion and
flooding may be justified for urban coasts, but their use on
sandy shores can further exacerbate erosion over time due
to disruption of sediment transport processes. Alternatives,
such as relocation landward, strategic removal of develop-
ment or limiting redevelopment following storm disasters in
highly vulnerable parts of the coast, may provide longer term
sustainability of both coastal landforms and development,
especially if the higher rates of sea-level rise are realized
(NRC, 1987). An example of abandonment of an island in
Chesapeake Bay due to sea-level rise is detailed in Gibbons
and Nicholls (2006). If coastal development is relocated,
those areas could be converted to marine protected areas,
public open-space lands that would serve to buffer sea-level
rise effects landward and also provide recreation benefits
and wildlife habitat values (see Salm and Clark, 2000).
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Chapter I 3
: :
Global climate is changing, largely due to carbon emissions
from human activities (IPCC, 2001, 2007). Sea-level rise
is one of the impacts of climate change that will affect all
coastal regions of the United States over the next century
and beyond (NRC, 1987; Nicholls et al, 2007). The scien-
tific tools and techniques for assessing the effects of future
sea-level rise on coastal systems are improving, but much
remains to be done in order to develop useful forecasts
of potential effects. Chapter 14 of this Product identifies
research opportunities that, if implemented, would lead to
better understanding and prediction of sea-level rise effects
that are likely to further impact the United States in the
near future. Planning for accelerating sea-level rise should
include thorough evaluation of a number of alternatives,
such as cost-effective and sustainable shore protection and
strategic relocation of development within urban centers.
Important decisions like these should ideally be based on the
best available science and careful consideration of long-term
benefits for a sustainable future, and the total economic,
social, and environmental costs of various methods of shore
protection, relocation, and adaptation.
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
KEY FINDINGS
Understanding, predicting, and responding to the environmental and human effects of sea-level rise requires an
integrated program of research that includes natural and social sciences.
Monitoring of modern processes and environments could be improved by expanding the network of basic
observations and observing systems, developing time series data on environmental and landscape changes, and
assembling baseline data for the coastal zone.
The historic and geologic record of coastal change should be used to improve the understanding of natural and
human-influenced coastal systems, increase knowledge of sea-level rise and coastal change over the past few
millennia, identify thresholds or tipping points in coastal systems, and more closely relate past changes in climate
to coastal change.
Increases in predictive capabilities can be achieved by improving quantitative assessment methods and integrating
studies of the past and present into predictive models.
Research on adaptation, mitigation, and avoidance measures will enable better understanding of the societal impacts
of sea-level rise.
Decision making in the coastal zone can be supported by providing easy access to data and resources, transferring
knowledge of vulnerability and risk that affect decision making, and educating the public about consequences and
alternatives.
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14
! - ! ••, ' '
Chapter 14 identifies several major themes that present
opportunities to improve the scientific understanding of
future sea-level rise and its impacts on U.S. coastal regions.
Advances in scientific understanding will enable the devel-
opment of higher quality and more reliable information for
planners and decision makers at all levels of government,
as well as the public.
A number of recent studies have focused specifically on
research needs in coastal areas. Two National Research
Council (NRC) studies, Science for Decision-making (NRC,
1999) and A Geospatial Framework for the Coastal Zone
(NRC, 2004) contain recommendations for science activities
that can be applied to sea-level rise studies. Other relevant
NRC reports include Responding to Changes in Sea Level
(NRC, 1987), Sea Level Change (NRC, 1990b), wA Abrupt
Climate Change (NRC, 2002). The Marine Board of the Eu-
ropean Science Foundation's Impacts of Climate Change on
the European Marine and Coastal Environment (Philippart
et al., 2007) identified numerous research needs, many of
which have application to the United States. Recent stud-
ies on global climate change by the Pew Charitable Trusts
also included the coastal zone (e.g., Neumann et al., 2000;
Panetta, 2003; Kennedy et al., 2002). Other studies by the
NRC (1990a, b, c, 2001,2006a, 2007) and the Heinz Center
(2000,2002a, b, 2006) have addressed issues relevant to the
impacts of sea-level rise on the coastal zone. These reports
and related publications have helped guide the development
of the potential research and decision-support activities
described in the following sections.
• \~ .' ' '.",; ,-"•••:' • • .
An integrated scientific program of sea level studies that
seeks to learn from the historic and geologic past, and
monitors ongoing physical and environmental changes, will
improve the level of knowledge and reduce the uncertainty
about potential responses of coasts, estuaries, and wetlands
to sea-level rise. Outcomes of both natural and social sci-
entific research will support decision making and adaptive
management in the coastal zone. The main elements of a
potential science strategy and their interrelationships are
shown in Figure 14.1.
Building on and complementing ongoing efforts at federal
agencies and universities, a research and observation pro-
gram could incorporate new technologies to address the
complex scientific and societal issues highlighted in this
Product. These studies could include further development of
a robust monitoring program for all coastal regions, leverag-
ing the existing network of site observations, as well as the
growing array of coastal observing systems. Research should
also include studies of the historic and recent geologic past
to understand how coastal systems evolved in response to
past changes in sea level. The availability of higher resolu-
tion data collected over appropriate time spans, coupled with
conceptual and numerical models of coastal evolution, will
provide the basis for improved quantitative assessments and
the development of predictive models useful for decision
making. Providing ready access to interpretations from
scientific research—as well as the underlying data—by
means of publications, data portals, and decision-support
systems will allow coastal managers to evaluate alternative
strategies for mitigation, develop appropriate responses to
sea-level rise, and practice adaptive management as new
information becomes available.
*n
Studies of the recent geologic and historical record of
sea-level rise and coastal and environmental change are
needed to improve the state of knowledge of the key physi-
cal and biological processes involved in coastal change. As
described throughout this Product, particularly in Chapters
1 through 5, significant knowledge gaps exist that inhibit
useful prediction of future changes. The following research
activities will help refine our knowledge of past changes
and their causes.
Improve understanding of natural and human-influenced
coastal systems
Significant opportunities exist to improve predictions of
coastal response to sea-level rise. For example, scientists'
understanding of the processes controlling rates of sedi-
ment flux in both natural and especially in human-modified
coastal systems is still evolving. This is particularly true at
the regional (littoral cell) scale, which is often the same scale
at which management decisions are made. As described in
Chapters 3 and 6, the human impact on coastal processes at
management scales is not well understood. Shoreline engi-
neering such as bulkheads, revetments, seawalls, groins, jet-
ties, and beach nourishment can fundamentally alter the way
a coastal system behaves by changing the transport, storage,
and dispersal of sediment. The same is true of development
and infrastructure on mobile landforms such as the barrier
islands that comprise much of the mid-Atlantic coast.
Develop better information on the effects of sea-level rise
over the past 5,000 years
The foundation of modern coastal barrier island and wetland
systems has evolved over the past 5,000 years as the rate of
sea-level rise slowed significantly (see Chapters 1,3, and 4).
More detailed investigation of coastal sedimentary deposits
is needed to understand the rates and patterns of change dur-
ing this part of the recent geologic past. Advances in
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
A Science Strategy for Sea-Level Rise
Monitor Modern Processes
and Environments
• Expand network of basic observations
• Develop and maintain observing
systems
• Develop brne-series data to monitor
environmental and landscape changes
' Assemble and update t*a«tine data
fqr (he coastal zone
Learn from the Past
" Improve understanding of natural and
human-influenced coastal systems
Develop belief Information on the effects
of sea-level rise over the past 5,000
years
• Identify Ihresrtolds or topping points in
coastal systems
* Relate climate proxies to coastal change
I
Improve Predictive Capability
• Improve quantitative assessment
methods
* Integrals studns of past and present
, rejdctive model*
Improve Understanding of
Societal Impacts
ise research on adaptation, mitigation,
and avoidance measures
Develop rn«jn>-di&»plir»a«y groups that Integrals
rcaturaf and socal sciences
' Expand institutional capacity and overcome
barifen
Support Decision Making
• Provide easy access to data and resources for federal, state, local,
academic and public users
HI knowledge o( vulnerability, risk and societal impacts trial
affect decision making
• Develop decision-support systems
* Educate itie public on consequences and alternatives
Figure 14.1 Schematic flow diagram summarizing a science strategy for improvement
of scientific knowledge and decision-making capability that can address the impacts of
future sea-level rise.
methods to obtain samples of the geologic record, along with
improvements in analytical laboratory techniques since the
early 1990s, have significantly increased the resolution of
the centennial-to-millennial scale record of sea-level rise and
coastal environmental change (e.g., Gehrels, 1994; Gehrels
et al., 1996; van de Plassche et al, 1998; Donnelly et al.,
2001; Horton et al., 2006) and provide a basis for future
work. Archaeological records of past sea-level change also
exist in many locales, and provide additional opportunities to
understand coastal change and impacts on human activity.
Understand thresholds in coastal systems that, if crossed,
could lead to rapid changes to coastal and wetland
systems
Several aspects of climate change studies, such as atmo-
sphere-ocean interactions, vegetation change, sea ice ex-
tent, and glacier and ice cap responses to temperature and
precipitation, involve understanding the potential for abrupt
climate change or "climate surprises" (NRC, 2002; Meehl
et al., 2007). Coastal systems may also respond abruptly
to changes in sea-level rise or other physical and biologi-
cal processes (see Box 3.1 in Chapter 3). Coastal regions
that may respond rapidly to even modest changes in future
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Chapter 14
external forcing need to be identified, as well as the impor-
tant variables driving the changes. For example, limited
sediment supply, and/or permanent sand removal from the
barrier system, in combination with an acceleration in the
rate of sea-level rise, could result in the development of an
unstable state for some barrier island systems (i.e., a behav-
ioral threshold or tipping point, as described in Chapters 1
and 3). Coastal responses could result in landward migra-
tion or rollover, or barrier segmentation. Understanding and
communicating the potential for such dramatic changes in
the form and rate of coastal change will be crucial for the
development of adaptation, mitigation, and other strategies
for addressing sea-level rise.
The future evolution of low-elevation, narrow barriers will
likely depend in part on the ability of salt marshes in back-
barrier lagoons and estuaries to keep pace with sea-level
rise (FitzGerald et al, 2004,2008; Reed et al, 2008). It has
been suggested that a reduction of salt marsh in back-barrier
regions could change the hydrodynamics of back-barrier
systems, altering local sediment budgets and leading to a
reduction in sandy materials available to sustain barrier
systems (FitzGerald et al., 2004, 2008).
Relate climate proxies to coastal change
Links betweenpaleoclimate proxies (e.g., atmospheric gases
in ice cores, isotopic composition of marine microfossils,
tree rings), sea-level rise, and coastal change should be
explored. Previous periods of high sea level, such as those
during the last several interglacial periods, provide tangible
evidence of higher-than-present sea levels that are broadly
illustrative of the potential for future shoreline changes. For
example, high stands of sea level approximately 420,000 and
125,000 years ago left distinct shoreline and other coastal
features on the U.S. Atlantic coastal plain (Colquhoune/a/.,
1991; Baldwin et al., 2006). While the sedimentary record
of these high stands is fragmentary, opportunities exist to
relate past shoreline positions with climate proxies to im-
prove the state of knowledge of the relationships between the
atmosphere, sea level, and coastal evolution. Future studies
may also provide insight into how coastal systems respond
to prolonged periods of high sea level and rapid sea-level
fluctuations during a high stand. Examples of both exist in
the geologic record and have potential application to under-
standing and forecasting future coastal evolution.
~ "
The status and trends of sea-level change, and changes in
the coastal environment, are monitored through a network
of observation sites, as well as through coastal and ocean
observing systems. Monitoring of modern processes and
environments could be improved by expanding the network
of basic observations, as well as the continued development
of coastal and ocean observing systems. There are numer-
ous ongoing efforts that could be leveraged to contribute to
understanding patterns of sea-level rise over space and time
and the response of coastal environments.
Expand the network of basic observations
An improvement in the coverage and quality of the U.S.
network of basic sea-level observations could better in-
form researchers about the rate of sea-level rise in various
geographic areas. Tide gauges are a primary source of
information for sea-level rise data at a wide range of time
scales, from minutes to centuries. These data contribute to
a multitude of studies on local to global sea-level trends.
Tide gauge data from the United States include some of the
longest such datasets in the world and have been especially
valuable for monitoring long-term trends. A denser network
of high-resolution gauges would more rigorously assess re-
gional trends and effects. The addition of tide gauges along
the open ocean coast of the United States would be valuable
in some regions. These data can be used in concert with
satellite altimetry observations.
Tide-gauge observations also provide records of terrestrial
elevation change that contributes to relative sea-level change,
and can be coupled with field- or model-based measurements
or estimates of land elevation changes. Existing and new
gauges should be co-located with continuously operating
Global Positioning System (GPS) reference stations (CORS)
or surveyed periodically using GPS and other Global
Navigation Satellite System technology. This will enable
the coupling of the geodetic (earth-based) reference frame
and the oceanographic reference frame at the land-sea inter-
face. Long time series from CORS can provide precise local
vertical land movement information in the ellipsoidal frame
(e.g., Snay etal., 2007; Woppelmanne/a/., 2007). Through
a combined effort of monitoring ellipsoid heights and the
geoid, as well as through gravity field monitoring, changes
in coastal elevations can be adequately tracked.
Develop and maintain coastal observing systems
Observing systems have become an important tool for exam-
ining environmental change. They can be place-based (e.g.,
specific estuaries or ocean locations) or consist of regional
aggregations of data and scientific resources (e.g., the devel-
oping network of coastal observing systems) that cover an
entire region. Oceanographic observations also need to be
integrated with observations of the physical environment,
as well as habitats and biological processes.
An example of place-based observing systems is the Na-
tional Estuarine Research Reserve System (NERRS: ), a network of 27 reserves for long-
term research, monitoring, education, and resource steward-
ship. Targeted experiments in such settings can potentially
elucidate impacts of sea-level rise on the physical environ-
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to
A Focus on the Mid-Atlantic Reg/on
ment, such as shoreline change or impacts to groundwater
systems, or on biological processes, such as species changes
or ecosystem impacts. Important contributions can also be
made by the Long Term Ecological Research sites () such as the Virginia Coast Reserve in the
mid-Atlantic area (part of the focus area of this Product).
The sites combine long-term data with current research to
examine ecosystem change over time. Integration of these
ecological monitoring networks with the geodetic and tide
gauge networks mentioned previously would also be an
important enhancement.
The Integrated Ocean Observing System (IOOS) () will bring together observing systems and
data collection efforts to understand and predict changes
in the marine environment. Many of these efforts can
contribute to understanding changes in sea-level rise over
space and time. These observing systems incorporate a wide
range of data types and sources, and provide an integrated
approach to ocean studies. Such an approach should enable
sea-level rise-induced changes to be distinguished from
the diverse processes that drive changes in the coastal and
marine environment.
A new initiative began in 2005 with a worldwide effort
to build a Global Earth Observation System of Systems
(GEOSS) () over the
next 10 years. GEOSS builds upon existing national, re-
gional, and international systems to provide comprehensive,
coordinated Earth observations from thousands of instru-
ments worldwide, which have broad application to sea-level
rise studies.
Develop time series data to monitor environmental and
landscape changes
Observations of sea level using satellite altimetry (e.g.,
TOPEX/Poseidon and Jason-1) have provided new and
important insights into the patterns of sea-level change
across space and time. Such observations have allowed
scientists to examine sea-level trends and compare them to
the instrumental record (Church et al., 2001, 2004), as well
as predictions made by previous climate change assessments
(Rahmstorf, 2007). The satellite data provide spatial cover-
age not available with ground-based methods such as tide
gauges, and provide an efficient means for making global
observations. Plans for future research could include a ro-
bust satellite observation program to ensure comprehensive
coverage.
Studies of environmental and landscape change can also be
expanded across larger spatial scales and longer time scales.
Examples include systematic mapping of shoreline changes
and coastal barriers and dunes around the United States
(e.g., Morton and Miller, 2005), and other national map-
ping efforts to document land-use and land-cover changes
(e.g., the NOAA Coastal Change Analysis Program: ). It is also important
to undertake a rigorous study of land movements beyond the
point scale of tide gauges and GPS networks. For example,
the application of an emerging technology—Interferometric
Synthetic Aperture Radar (InSAR)—enables the develop-
ment of spatially-detailed maps of land-surface displacement
overbroad areas (Brooks et al., 2007).
Determining wetland sustainability to current and future
sea-level rise requires a broader foundation of observations
if they are to be applied with high confidence at regional and
national scales. In addition, there is a significant knowledge
gap concerning the viability or sustainability of human-
impacted and restored wetlands in a time of accelerating
sea-level rise. The maintenance of a network of sites that
utilize surface elevation tables and soil marker horizons for
measuring marsh accretion or loss will be essential in un-
derstanding the impacts on areas of critical wetland habitat.
The addition of sites to the network would aid in delineating
regional variations (Cahoone/a/., 2006). Similar long-term
studies for coastal erosion, habitat change, and water quality
are also essential.
Coastal process studies require data to be collected over a
long period of time in order to evaluate changes in beach and
barrier profiles and track morphological changes over a time
interval where there has been a significant rise in sea level.
These data will also reflect the effects of storms and the sedi-
ment budget that frequently make it difficult to extract the
coastal response to sea-level change. For example, routine
lidar mapping updates to track morphological changes and
changes in barrier island area above mean high water (e.g.,
Morton and Sallenger, 2003), as well as dune degradation
and recovery, and shore-face profile and near-shore bathy-
metric evolution may provide insight into how to distinguish
various time and space scales of coastal change and their
relationship to sea-level rise.
Time series observations can also be distributed across the
landscape and need not be tied to specific observing systems
or data networks. They do, however, need a means to have
their data assimilated into a larger context. For example,
development of new remote sensing and in situ technolo-
gies and techniques would help fill critical data gaps at the
land-water interface.
Assemble and update baseline data for the coastal zone
Baseline data for the coastal zone, including elevation, ba-
thymetry, shoreline position, and geologic composition of
the coast, as well as biologic and ecologic parameters such
as vegetation and species distribution, and ecosystem and
habitat boundaries, should be collected at high spatial resolu-
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Chapter 14
tion. As described in Chapter 2, existing 30-m (100-ft) digital
elevation models are generally inadequate for meaningful
mapping and analyses in the coastal zone. The use of lidar
data, with much better horizontal and vertical accuracy, is
essential. While some of these mapping data are being col-
lected now, there are substantial areas around the United
States that would benefit from higher quality data. More
accurate bathymetric data, especially in the nearshore, is
needed for site-specific analyses and to develop a complete
topographic-bathymetric model of the coastal zone to be
able to predict with greater confidence wave and current
actions, inundation, coastal erosion, sediment transport,
and storm effects.
Projecting long-term wetland sustainability to future sea-
level rise requires data on accretionary events over suf-
ficiently long time scales that include the return periods of
major storms, floods, and droughts, as well as information
on the effects of wetland elevation feedback on inundation
and sedimentation processes that affect wetland vertical ac-
cretion. Numerical models can be applied to predict wetland
sustainability at the local scale, but there is not sufficient
data to populate these models at the regional or national
scale (see Chapter 4). Given this data constraint, current
numerical modeling approaches will need to improve or
adapt such that they can be applied at broader spatial scales
with more confidence.
To improve confidence in model predictions of wetland
vulnerability to sea-level rise, more information is needed
on: (1) maximum accretion rates (i.e., thresholds) regionally
and among vegetative communities; (2) wetland dynamics
across larger landscape scales; (3) the interaction of feed-
back controls on flooding with other accretion drivers (e.g.,
nutrient supply and soil organic matter accumulation); (4)
fine-grained, cohesive sediment supplies; and (5) changing
land use in the watershed (i.e., altered river flows and ac-
commodation space for landward migration of wetlands). In
addition, population data on different species in nearshore
areas are needed to accurately judge the effects of habitat
loss or transformation. More extensive and detailed habitat
mapping will enable preservation efforts to be focused on
the most important areas.
Studies of the past history of sea-level rise and coastal
response, combined with extensive monitoring of present
conditions, will enable more robust predictions of future
sea-level rise impacts. Substantial opportunities exist to
improve methods of coastal impact assessment and predic-
tion of future changes.
Develop quantitative assessment methods that identify high-
priority areas needing useful predictions
Assessment methods are needed to identify both geographic
and topical areas most in need of useful predictions of sea-
level rise impacts. For example, an assessment technique
for objectively assessing potential effects of sea-level rise
on open coasts, the Coastal Vulnerability Index (CVI), has
been employed in the United States and elsewhere (e.g.,
Gomitzetal., 1997; Shawetal, 1998; Thieler and Hammar-
Klose, 1999, 2000a, 2000b). Although the CVI is a fairly
simplistic technique, it can provide useful insights and has
found application as a coastal planning and management
tool (Thieler et al., 2002). Such assessments have also been
integrated with socioeconomic vulnerability criteria to yield
a more integrative measure of community vulnerability
(Boruffe/a/.,2005).
Integrate studies of past and present coastal behavior into
predictive models
Existing shoreline-change prediction techniques are
typically based on assumptions that are either difficult to
validate or too simplistic to be reliable for many real-world
applications (see Appendix 2). As a result, the usefulness of
these modeling approaches has been debated in the coastal
science community (see Chapter 3). Newer models that
include better representations of real-world settings and
processes (e.g., Cowell et al., 1992; Stolper et al, 2005;
Pietrafesa et al., 2007) have shown promise in predicting
coastal evolution. Informing these models with improved
data on past coastal changes should result in better predic-
tions of future changes.
The process of marine transgression across the continental
shelf has left an incomplete record of sea-level and environ-
mental change. An improved understanding of the rate and
timing of coastal evolution will need to draw on this incom-
plete record, however, in order to improve models of coastal
change. Using a range of techniques, such as high-resolution
seafloor and geologic framework mapping coupled with
geochronologic and paleoenvironmental studies, the record
of coastal evolution during the Pleistocene (1.8 million to
11,500 years ago) and the Holocene (the last 11,500 years)
can be explored to identify the position and timing of former
shorelines and coastal environments.
Research in the social sciences will be critical to under-
standing the potential effects on society and social systems
resulting from sea-level rise.
Increase research on adaptation, mitigation, and avoidance
measures
This Product describes a wide variety of potential impacts
of sea-level rise, including the effects on the physical envi-
ronment, biological systems, and coastal development and
infrastructure. While the ability to predict future changes is
currently inadequate for many decisions, adaptation, miti-
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Coastal to
A Focus on the Mid-Atlantic Region
gallon, and avoidance strategies must evolve as scientific
knowledge and predictive ability increase. For example,
expanded research and assessments of the economic and
environmental costs of present and future actions are needed
to allow a more complete analysis of the tradeoffs involved
in sea-level rise decision making. In addition, opportuni-
ties to engage stakeholders such as federal agencies, states,
counties, towns, non-government organizations, and private
landowners in the design and implementation of sea-level
rise impact and response planning should be created.
Develop multi-disciplinary groups that integrate natural
and social sciences
Interdisciplinary research that combines natural and social
sciences will be crucial to understanding the interplay of the
physical, environmental, and societal impacts of sea-level
rise. Development of programs that facilitate such collabora-
tions should be encouraged.
Expand institutional capacity and overcome barriers
Substantial opportunities exist to expand and improve upon
the ability of institutions to respond to sea-level rise (see
Chapters 10, 11, and 12). Research is needed to define the
capacity needed for decision making, as well as the meth-
ods that can be best employed (e.g., command and control,
economic incentive) to achieve management goals. Over-
coming the institutional barriers described in Chapter 12
is also necessary for effective response to the management
challenges presented by sea-level rise.
14,2,5
For coastal zone managers in all levels of government, there
is a pressing need for more scientific information, a reduc-
tion in the ranges of uncertainty for processes and impacts,
and new methods for assessing options and alternatives for
management strategies. Geospatial information on a wide
range of themes such as topography, bathymetry, land cover,
population, and infrastructure, that is maintained on a regu-
lar cycle will be a key component of planning for mitigation
and adaptation strategies. For example, specialized themes of
data such as hydric (abundantly moist) soils may be critical to
understanding the potential for wetland survival in specific
areas. Developing and maintaining high-resolution maps that
incorporate changes in hazard type and distribution, coastal
development, and societal risk will be critical. Regularly
conducting vulnerability assessments and reviews will be
necessary in order to adapt to changing conditions.
Provide easy access to data and information resources for
federal, state, local, academic, and public users
Understanding and acting on scientific information about
sea-level rise and its impacts will depend upon common,
consistent, shared databases for integrating knowledge
and providing a basis for decision making. Thematic data
and other value-added products should adhere to predeter-
mined standards to make them universally accessible and
transferable through internet portals. All data should be
accompanied by appropriate metadata describing its method
of production, extent, quality, spatial reference, limitations
of use, and other characteristics (NRC, 2004).
An opportunity exists to undertake a national effort to de-
velop and apply data integration tools to combine terrestrial
and marine data into a seamless geospatial framework.
For example, this could involve the collection of real-time
oceanographic data and the development of more sophisti-
cated hydrodynamic models for the entire U.S. coastline, as
well as the establishment of protocols and tools for merging
bathymetric and topographic datasets (NRC, 2004). Modern
and updated digital flood insurance rate maps (DFIRM) that
incorporate future sea-level rise are needed in the coastal
zone (see Chapter 9).
Transfer scientific knowledge to studies of vulnerability,
risk, and societal impacts
In addition to basic scientific research and environmental
monitoring, a significant need exists to integrate the results
of these efforts into comprehensive vulnerability and risk
assessments. Tools are needed for mapping, modeling, and
communicating risk to help public agencies and communi-
ties understand and reduce their vulnerability to, and risk
of, sea-level rise hazards. Social science research activities
are also needed that examine societal consequences and
economic impacts of sea-level rise, as well as identify
institutional frameworks needed to adapt to changes in the
coastal zone. For example, analyses of the economic costs of
armoring shores at risk of erosion and the expected lifespan
of such efforts will be required, as will studies on the dura-
bility of armored shorefronts under different sea-level rise
scenarios. The physical and biological consequences of
armoring shores will need to be quantified and the tradeoffs
communicated. Effective planning for sea-level rise will also
require integrated economic assessments on the impact to
fisheries, tourism, and commerce.
Applied research in the development of coastal flooding
models for the subsequent study of ecosystem response to
sea-level rise is underway in coastal states such as North
Carolina (Feyen et al., 2006). There is also a need for fo-
cused study on the ecological impacts of sea-level rise and
in how the transfer of this knowledge can be made to coastal
managers for decision making.
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The U.S. Climate Change Science Program
Develop decision-support systems
Local, county, and state planners need tools to analyze
vulnerabilities, explore the implications of alternative re-
sponse measures, assess the costs and benefits of options,
and provide decision-making support. These might take the
form of guidelines, checklists, or software tools. In addition,
there is a need to examine issues in a landscape or ecosystem
context rather than only administrative boundaries.
In addition to new and maintained data, models, and re-
search, detailed site studies are needed to assess potential
impacts on a site-specific basis and provide information that
allows informed decision making. Appropriate methodolo-
gies need to be developed and made available. These will
have to look at a full range of possible impacts including
aquifer loss by saltwater intrusion, wetland loss, coastal ero-
sion, and infrastructure implications, as well as the impact
of adaptation measures themselves. Alternative strategies of
adaptive management will be required. Each locality may
need a slightly different set of responses to provide a bal-
anced policy of preserving ecosystems, protecting critical
infrastructure, and adjusting to property loss or protection.
Providing a science-based set of decision support tools will
provide a sound basis for making these important deci-
sions.
Chapter 14
Educate the public on consequences and alternatives
Relative to other natural hazards such as earthquakes,
volcanic eruptions, and severe weather (e.g., hurricanes,
tornadoes) that typically occur in a time frame of minutes
to days, sea-level rise has a long time horizon over which
effects become clear. Thus, it is often difficult to commu-
nicate the consequences of this sometimes slow process
that occurs over many years. The impacts of sea-level rise,
however, are already being felt across the United States (see
Chapter 13). Public education will be crucial for adapting
to physical, environmental, economic, and social changes
resulting from sea-level rise. Research activities that result
in effective means to conduct public education and outreach
concerning sea-level rise consequence and alternatives
should be encouraged.
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
X
Q
Q_
Q_
State and Local Information on Vulnerable Species and
Coastal Policies in the Mid-Atlantic
OVERVIEW
Appendix 1 discusses many of the species that depend
on potentially vulnerable habitat in specific estuaries,
providing local elaboration of the general issues exam-
ined in Chapter 5. It also describes key statutes, regula-
tions, and other policies that currently define how state
and local governments are responding to sea-level rise,
providing support for some of the observations made in
Part III. This set of information was not developed as
a quantitative nor analytical assessment and therefore
is not intended as a complete or authoritative basis for
decision making; rather, it is a starting point for those
seeking to discuss local impacts and to examine the
types of decisions and potential policy responses related
to sea-level rise.
The sections concerning species and habitat are largely
derived from a U.S. EPA report developed in support
of this Synthesis and Assessment Product (U.S. EPA,
2008), with additional input from stakeholders as well
as expert and public reviewers. That report synthesized
what peer-reviewed literature was available, and aug-
mented that information with reports by organizations
that manage the habitats under discussion, databases,
and direct observations by experts in the field. The
sections that concern state and local policies are based
on statutes, regulations, and other official documents
published by state and local governments.
Characterizations of likelihood in this Product are
largely based on the judgment of the authors and on
published peer-reviewed literature and existing poli-
cies, rather than a formal quantification of uncertainty.
Data on how coastal ecosystems and specific species
may respond to climate change are limited to a small
number of site-specific studies, often carried out for
purposes unrelated to the potential impact of sea-
level rise. Although being able to characterize current
understanding—and the uncertainty associated with that
information—is important, quantitative and qualitative
assessments of likelihood are not available for the site-
specific issues discussed in this Appendix. Unlike the
main body of the Product, any likelihood statements in
this Appendix regarding specific habitat or species reflect
likelihood as expressed in particular reports being cited.
Statements about the implications of coastal policies in
this Appendix are based on the authors' qualitative assess-
ment of available published literature and of the policies
themselves. Published information, data, and tools are
evolving to further examine sea-level rise at this scale.
The synthesis was compiled by the following authors for
the specific areas of focus and edited by K. Eric Ander-
son, USGS; Stephen K. Gill, NOAA; Daniel Hudgens,
Industrial Economics, Inc.; and James G. Titus, U.S.
EPA:
A. Long Island, pages 194-198
Lead Authors: Daniel E. Hudgens, Industrial
Economics Inc.; Ann Shellenbarger Jones,
Industrial Economics Inc.; James G. Titus, U.S.
EPA
Contributing Authors: Elizabeth M. Strange,
Stratus Consulting Inc.; Joseph J. Tanski, New
York Sea Grant; Gaurav Sinha, University of
Ohio
B. New York Metropolitan Area, pages 198-200
Lead Author: Elizabeth M. Strange, Stratus
Consulting Inc.
Contributing Authors: Daniel E. Hudgens, In-
dustrial Economics Inc.; Ann Shellenbarger Jones,
Industrial Economics Inc.
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I
C. New Jersey Shore, pages 201-205
Lead Author: James G. Titus, U.S. EPA
Contributing Author: Elizabeth M. Strange, Stratus
Consulting Inc.
D. Delaware Estuary, pages 205-211
Lead Author: James G. Titus, U.S. EPA
Contributing Authors: Christopher J. Linn,
Delaware Valley Regional Planning Commission;
Kreeger, Danielle A., Partnership for the Delaware
Estuary, Inc.; Michael Craghan, Middle Atlantic
Center for Geography & Environmental Studies;
Michael P. Weinstein, New Jersey Marine Sciences
Consortium and New Jersey Sea Grant College
Program
E. The Atlantic Coast of Virginia, Maryland, and
Delaware, pages 211-215
Lead Author: James G. Titus, U.S. EPA
Contributing Author: Elizabeth M. Strange, Stratus
Consulting Inc.
F. Chesapeake Bay, pages 215-229
Lead Author: James G. Titus, U.S. EPA
Contributing Authors: Ann Shellenbarger Jones,
Industrial Economics Inc.; Peter G. Conrad, City of
Baltimore; Elizabeth M. Strange, Stratus Consulting
Inc.; Zoe Johnson, Maryland Department of Natu-
ral Resources; Michael P. Weinstein, New Jersey
Marine Sciences Consortium and New Jersey Sea
Grant College Program
G. North Carolina, pages 229-238
Lead Authors: Rebecca L. Feldman, NOAA; James
G. Titus, U.S. EPA; Ben Poulter, Potsdam Institute
for Climate Impact Research
Contributing Authors: Jeffrey DeBlieu, The Nature
Conservancy; Ann Shellenbarger Jones, Industrial
Economics Inc.
The North Shore of Long Island is generally characterized by
high bluffs of glacial origin, making this area less susceptible
to problems associated with increased sea level. The South
Shore, by contrast, is generally low lying and fronted by bar-
rier islands, except for the easternmost portion. As a result,
there are already major planning efforts underway in the
region to preserve the dry lands under threat of inundation.
A brief discussion of these efforts, especially on the South
Shore, is provided in Section Al. A.2. Maps and estimates of
the area of land close to sea level are provided in Titus and
Richman (2001). Further information on portions of the South
Shore can be found in Gornitz et al. (2002).
Long Island is surrounded by Long Island Sound to the
north; the Peconic Estuary to the East; the Atlantic Ocean
and barrier bays to the south; and New York Harbor to the
west. This section first examines the shores adjacent to Long
Island Sound and the Peconic Estuary, and then the southern
shores. Because the western portion of Long Island is within
New York City, Section Al.B.l discusses New York harbor,
Jamaica Bay, and other back-barrier bays.
North Shore and Peconic Bay
Of the 8,426 hectares (ha) (20,820 acres [ac]) of tidal wet-
lands in the Long Island Sound watershed, only about 15
percent are in the state of New York, and those wetlands are
primarily along the shores of Westchester and Bronx counties
rather than on Long Island (Hoist et al., 2003). On the north
shore of Long Island the primary areas of marsh are in and
around Stony Brook Harbor and West Meadow, bordering
the Nissequogue River and along the Peconic Estuary (NYS
DOS, 2004). In general, tidal wetlands along the North Shore
are limited; the glacial terminal moraine1 resulted in steep
uplands and bluffs and more kettle-hole2 wetlands along
the eastern portion (LISHRI, 2003). In the eastern portion,
there has already been a significant loss of the historical area
of vegetated tidal wetlands (Hoist et al., 2003; Hartig and
Gornitz, 2004), which some scientists partially attribute to
sea-level rise (Mushacke, 2003; Strange, 2008f).
The loss of vegetated low marsh reduces habitat for several
rare bird species (e.g., seaside sparrow) that nest only or
primarily in low marsh (see Section 5.2). Low marsh also
provides safe foraging areas for small resident and transient
fishes (e.g., weakfish, winter flounder). Diamondback ter-
rapin live in the creeks of the low marsh, where they feed
on plants, mollusks, and crustaceans (LISF, 2008; Strange,
2008f). Some wetlands along Long Island Sound may be
allowed to respond naturally to sea-level rise, including
some in the Peconic Estuary. Where migration is possible,
preservation of local biodiversity as well as some regionally
rare species is possible (Strange, 2008f).
Beaches are far more common than tidal wetlands in the Long
Island Sound study area. Several notable barrier beaches
exist. For example, the sandy barrier-beach system fronting
Hempstead Harbor supports a typical community progression
from the foreshore to the bay side, or backshore (LISHRI,
1 A glacial terminal moraine is a glacial deposit landform that marks
the limit of glacial advance.
2 A kettle hole is a depression landform formed in glacial deposit
sediments from a time when a large block of glacial ice remained and
melted after a glacial retreat.
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A Focus on the Mid-Atlantic Region
2003). The abundant invertebrate fauna provide forage for
sanderling, semipalmated plovers, and other migrating
shorebirds (LISHRI, 2003). The maritime beach community
between the mean high tide and the primary dune provides
nesting sites for several rare bird species, including piping
plover (see Box Al.l), American oystercatcher, black skim-
mer, least tern, common tern, roseate tern, the Northeastern
beach tiger beetle, and horseshoe crab (LISHRI, 2003).
Diamondback terrapin use dunes and the upper limit of the
backshore beach for nesting (LISHRI, 2003).
Since nearly all of the Long Island Sound shoreline is densely
populated and highly developed, the land may be armored
in response to sea-level rise, raising the potential for beach
loss. The Long Island Sound Habitat Restoration Initiative
cautions: "Attempts to alter the natural cycle of deposition
and erosion of sand by construction of bulkheads, seawalls,
groins, and jetties interrupt the formation of new beaches"
(LISHRI, 2003).
Shallow water habitats are a major ecological feature in and
around the Peconic Estuary. Eelgrass beds provide food,
shelter, and nursery habitats to diverse species, including
worms, shrimp, scallops and other bivalves, crabs, and fish
(PEP, 2001). Horseshoe crabs forage in the eelgrass beds of
Cedar Point-Hedges Bank, where they are prey for logger-
head turtles (federally listed as threatened), crabs, whelks,
and sharks (NYS DOS, 2004). Atlantic silverside spawn
here; silverside eggs provide an important food source for
seabirds, waterfowl, and blue crab, while adults are prey
for bluefish, summer flounder, rainbow smelt, white perch,
Atlantic bonito, and striped bass (NYS DOS, 2004). The
Cedar Point-Hedges Bank Shallows eelgrass beds are known
for supporting a bay scallop fishery of statewide importance
(NYS DOS, 2004).
Other noteworthy habitats that could be affected by sea-level
rise include the sea-level fen vegetation community that
grows along Flanders Bay (NYS DOS, 2004), and the Long
Island's north shore tidal flats, where longshore drift carries
material that erodes from bluffs and later deposits it to form
flats and barrier spits or shoals (LISHRI, 2003). One of the
largest areas of tidal mudflats on the North Shore is near
Conscience Bay, Little Bay, and Setauket Harbor west of
Port Jefferson (NYS DOS, 2004). Large beds of hard clams,
soft clams, American oysters, and ribbed mussels are found
in this area (NYS DOS, 2004).
South Shore
Extensive back-barrier salt marshes exist to the west of Great
South Bay in southern Nassau County (USFWS, 1997). These
marshes are particularly notable given widespread marsh
loss on the mainland shoreline of southern Nassau County
(NYS DOS and USFWS, 1998; USFWS, 1997). To the east
of Jones Inlet, the extensive back-barrier and fringing salt
marshes are keeping pace with current rates of sea-level rise,
but experts predict that the marshes' ability to keep pace is
likely to be marginal if the rate of sea-level rise increases
moderately, and that the marshes are likely to be lost under
higher sea-level rise scenarios (Strange et al., 2008, inter-
preting the findings of Reed et al., 2008). Opportunities for
marsh migration along Long Island's South Shore would be
limited if the mainland shores continue to be bulkheaded.
Outside of New York City, the state requires a minimum
22.9-meter (m) (75-foot [ft]) buffer around tidal wetlands to
allow marsh migration, but outside of this buffer, additional
development and shoreline protection are permitted3 (NYS
DEC, 2006). Numerous wildlife species could be affected by
salt marsh loss. For example, the Dune Road Marsh west of
Shinnecock Inlet provides nesting sites for several species that
are already showing significant declines, including clapper
rail, sharp-tailed sparrow, seaside sparrow, willet, and marsh
wren (USFWS, 1997). The salt marshes of Gilgo State Park
provide nesting sites for northern harrier, a species listed by
the state as threatened (NYS DOS, 2004).
Of the extensive tidal flats along Long Island's southern
shoreline, most are found west of Great South Bay and east
of Fire Island Inlet, along the bay side of the barrier islands,
(USFWS, 1997) in the Hempstead Bay-South Oyster Bay
complex, (USFWS, 1997) and around Moriches and Shin-
necock Inlets (NYS DOS and USFWS, 1998). These flats
provide habitat for several edible shellfish species, including
soft clam, hard clam, bay scallop, and blue mussel. The tidal
flats around Moriches and Shinnecock Inlets are particularly
important foraging areas for migrating shorebirds. The South
Shore Estuary Reserve Council asserts that "because shore-
birds concentrate in just a few areas during migration, loss or
degradation of key sites could devastate these populations"
(NYS DOS and USFWS, 1998).
The back-barrier beaches of the South Shore also provide
nesting sites for the endangered roseate tern and horseshoe
crabs (USFWS, 1997). Shorebirds, such as the red knot, feed
preferentially on horseshoe crab eggs during their spring
migrations.
Increased flooding and erosion of marsh and dredge spoil is-
lands will reduce habitat for many bird species that forage and
nest there, including breeding colonial waterbirds, migratory
shorebirds, and wintering waterfowl. For example, erosion
on Warner Island is reducing nesting habitat for the federally
endangered roseate tern and increasing flooding risk during
nesting (NYS DOS and USFWS, 1998). The Hempstead Bay-
3 The state has jurisdiction up to 91.4 m (300 ft) beyond the tidal wetland
boundary in most areas (but only 45.7 m [150 ft] in New York City).
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I
South Oyster Bay complex includes a network of salt marsh
and dredge spoil islands that are important for nesting by
herons, egrets, and ibises. Likewise, Lanes Island and Warner
Island in Shinnecock Bay support colonies of the state-listed
common tern and the roseate tern (USFWS, 1997).
New York State does not have written policies or regulations
pertaining specifically to sea-level rise in relation to coastal
zone management, although sea-level rise is becoming recog-
nized as a factor in coastal erosion and flooding by the New
York State Department of State (NYS DOS) in the develop-
ment of regional management plans.
Policies regarding management and development in shoreline
areas are primarily based on three laws. Under the Tidal
Wetlands Act program, the Department of Environmental
Conservation (DEC) classifies various wetland zones and
adjacent areas where human activities may have the potential
to impair wetland values or adversely affect their function;
permits are required for most activities that take place in
these areas. New construction greater than 9.3 square meters
(sq m) (100 square feet [sq ft]), excluding docks, piers, and
bulkheads) as well as roads and other infrastructure must be
set back 22.9 m (75 ft) from any tidal wetland, except within
New York City where the setback is 9.1 m (30 ft)4.
The Waterfront Revitalization and Coastal Resources Act
(WRCRA) allows the DOS to address sea-level rise indirectly
through policies regarding flooding and erosion hazards
(NOAA, 1982). Seven out of 44 written policies related to
management, protection, and use of the coastal zone address
flooding and erosion control. These polices endeavor to move
development away from areas threatened by coastal erosion
and flooding hazards, to ensure that development activities do
not exacerbate erosion or flooding problems and to preserve
natural protective features such as dunes. They also provide
guidance for public funding of coastal hazard mitigation
projects and encourage the use of nonstructural erosion and
flood control measures where possible (NYS DOS, 2002).
Under the Coastal Erosion Hazard Areas Act program, the
DEC identified areas subject to erosion and established two
types of erosion hazard areas (structural hazard and natural
protective feature areas) where development and construc-
tion activities are regulated5. Permits are required for most
activities in designated natural protective feature areas. New
development (e.g., building, permanent shed, deck, pool,
garage) is prohibited in nearshore areas, beaches, bluffs, and
primary dunes. These regulations, however, do not extend
far inland and therefore do not encompass the broader area
vulnerable to sea-level rise.
New York State regulates shore protection structures along
estuaries and the ocean coast differently. The state's Coastal
Erosion Hazard Law defines coastal erosion hazard areas
as those lands with an average erosion rate of at least 30 cm
(1 ft) per year6. Within those erosion hazard areas, the local
governments administer the programs to grant or deny per-
mits, generally following state guidelines7. Those guidelines
require that individual property owners first evaluate non-
structural approaches; but if they are unlikely to be effective,
hard structures are allowed (New York State, 2002).
Shoreline structures, which by definition include beach nour-
ishment in New York State, are permitted only when it can
be shown that the structure can prevent erosion for at least
30 years and will not cause an increase in erosion or flooding
at the local site or nearby locations (New York State, 2002).
Setbacks, relocation, and elevated walkways are also encour-
aged before hardening.
Currently, all of the erosion hazard areas are along the open
coast. Therefore, the state does not directly regulate shore pro-
tection structures along estuarine shores. However, under the
federal Coastal Zone Management Act, New York's coastal
management program reviews federal agency permit applica-
tions, to ensure consistency with policies of the state's coastal
management program (NOAA, 2008a; USACE, 2007). The
state has objected to nationwide permit 13 issued by the U.S.
Army Corps of Engineers' (USACE) wetlands regulatory
program (see Section 12.2.2 in Chapter 12), which provides
a general authorization for erosion control structures (NYS
DOS, 2006). The effect of that objection is that nationwide
permit 13 does not automatically provide a property owner
with a permit for shore protection unless the state concurs
with such an application (NYS DOS, 2006). The state has also
objected to the application of nationwide permits 3 (which
includes maintenance of existing shore protection structures)
and 31 (maintenance of existing flood control activities)
within special management areas (NYS DOS, 2006).
Similar to the New York metropolitan area, the policies
for Long Island reflect the fact that the region is intensely
developed in the west and developing fast in the east. Much
of the South Shore, particularly within Nassau County, is
already developed and has already been protected, primarily
by bulkheads. The Long Island Sound Management Program
estimates that approximately 50 percent of the Sound's shore-
line is armored (NYS DOS, 1999).
4 Article 25, Environmental Conservation Law Implementing
Regulations-6NYCRR PART 661.
5 Environmental Conservation Law, Article 34.
6 New York Environmental Conservation Law §34-0103(3)(a).
7 New York Environmental Conservation Law §34-0105.
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Photo Source: USFWS, New Jersey Field Office,
Gene Nieminen, 2006.
BOX Al. I: Effects on the Piping Plover
Piping Plover Charadrius melodus
Habitat:
The piping plover, federally listed as threatened, is a small migratory shorebird that primarily inhabits open sandy
barrier island beaches on Atlantic coasts (USFWS, 1996). Major contributing factors to the plover's status as threat-
ened are beach recreation by pedestrians and vehicles that disturb or destroy plover nests and habitat, predation by
mammals and other birds, and shoreline development that inhibit the natural renewal of barrier beach and overwash
habitats (USFWS, 1996). In some locations, dune maintenance for
protection of access roads associated with development appears to
be correlated with absence of piping plover nests from former nest-
ing sites (USFWS, 1996).
Locations:
The Atlantic population of piping plovers winters on beaches from
the Yucatan Peninsula to North Carolina. In the summer, they mi-
grate north and breed on beaches from North Carolina to New-
foundland (CLO, 2004). In the mid-Atlantic region, breeding pairs of
plovers can be observed on coastal beaches and barrier islands, al-
though suitable habitat is limited in some areas. In New York, piping
plovers breed more frequently on Long Island's sandy beaches, from
Queens to the Hamptons, in the eastern bays and in the harbors of
northern Suffolk County. New York's Breezy Point barrier beach, at
the mouth of Jamaica Bay, consistently supports one of the largest piping plover nesting sites in the entire New York
Bight coastal region (USFWS, 1997). New York has seen an increase in piping plover breeding pairs in the last decade
from less than 200 in 1989 to near 375 in recent years (2003 to 2005), representing nearly a quarter of the Atlantic
coast's total breeding population (USFWS, 2004a). Despite this improvement, piping plovers remain state listed as
endangered in New York (NYS DEC, 2007).
Impact of Sea-Level Rise:
Where beaches are prevented from migrating inland by shoreline
armoring, sea-level rise will negatively impact Atlantic coast piping
plover populations. To the degree that developed shorelines result
in erosion of ocean beaches, and to the degree that stabilization is
undertaken as a response to sea-level rise, piping plover habitat will
be lost. In contrast, where beaches are able to migrate landward,
plovers may find newly available habitat. For example, on Assateague
Island, piping plover populations increased after a storm event that
created an overwash area on the north of the island (Kumer, 2004).
This suggests that if barrier beaches are allowed to migrate in re-
sponse to sea-level rise, piping plovers might adapt to occupy new
inlets and beaches created by overwash events.
Beach nourishment, the anticipated protection response for much of
New York's barrier beaches such as Breezy Point, can benefit piping
plovers and other shorebirds by increasing available nesting habitat
in the short term, offsetting losses at eroded beaches, but may also
be detrimental, depending on timing and implementation (USFWS,
1996). For instance, a study in Massachusetts found that plovers for-
aged on sandflats created by beach nourishment (Cohen et a/., 2005).
However, once a beach is built and people spread out to enjoy it, many areas become restricted during nesting sea-
son. Overall, throughout the Mid-Atlantic, coastal development and shoreline stabilization projects constitute the
most serious threats to the continuing viability of storm-maintained beach habitats and their dependent species,
including the piping plover (USFWS, 1996).
Photo Source: Wayne Hathaway, In Plains Sight.
Provided courtesy of the Tern and Plover Con-
servation Partnership, July 2005.
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I
Some of the South Shore's densely developed communities
facing flooding problems, such as Freeport and Hempstead,
have already implemented programs that call for elevating
buildings and infrastructure in place and installing bulkheads
for flood protection. The Town of Hempstead has adopted the
provisions of the state's Coastal Erosion Hazards Area Act
because erosion and flooding along Nassau County's ocean
coast have been a major concern. The Town of Hempstead has
also been actively working with USAGE to develop a long-
term storm damage reduction plan for the heavily developed
Long Beach barrier island (USAGE, 2003).
Beach nourishment and the construction of flood and erosion
protection structures are also common on the island. For ex-
ample, in the early 1990s USAGE constructed a substantial
revetment around the Montauk Lighthouse at the eastern
tip of Long Island and after a new feasibility study has
proposed construction of a larger revetment (Bleyer, 2007).
USAGE is also reformulating a plan for the development of
long-term storm damage prevention projects along the 134
kilometer (km) (83 mile [mi]) portion of the South Shore of
Suffolk County. As part of this effort, USAGE is assessing
at-risk properties within the 184 square kilometer (sq km)
(71 square miles [sq mi]) floodplain, present and future sea-
level rise, restoration and preservation of important coastal
landforms and processes, and important public uses of the
area (USACE, 2008b).
To obtain state funding for nourishment, communities must
provide public access every 800 m (0.5 mi) (New York State,
2002). In 1994, as terms of a legal settlement between federal,
state, and local agencies cooperating on the rebuilding of the
beach through nourishment, the community of West Hampton
provided six walkways from the shorefront road to allow
public access to the beach (Dean, 1999). In communities that
have not had such state-funded projects, however, particularly
along portions of the bay shore communities in East Hampton,
South Hampton, Brookhaven, and Islip, public access to tidal
waters can be less common (NYS DOS, 1999).
The Comprehensive Coastal Management Plan (CCMP) of
the Peconic Bay National Estuary Program Management
Plan calls for "no net increase of hardened shoreline in the
Peconic Estuary". The intent of this recommendation is to
discourage individuals from armoring their coastline; yet
this document is only a management plan and does not have
any legal authority. However, towns such as East Hampton
are trying to incorporate the plan into their own programs. In
2006, the town of East Hampton adopted and is now enforc-
ing a defined zoning district overlay map that prevents shore
armoring along much of the town's coastline (Town of East
Hampton, 2006). Despite such regulations, authorities in East
Hampton and elsewhere recognize that there are some areas
where structures will have to be allowed to protect existing
development.
The New York Department of State (DOS) is also examining
options for managing erosion and flood risks through land use
measures, such as further land exchanges. For example, there
is currently an attempt to revise the proposed Fire Island to
Montauk Point Storm Damage Reduction Project to consider a
combination of nourishment and land-use measures. One op-
tion would be to use beach nourishment to protect structures
for the next few decades, during which time development
could gradually be transferred out of the most hazardous
locations. Non-conforming development could eventually
be brought into conformance as it is reconstructed, moved,
damaged by storms or flooding, or other land use manage-
ment plans are brought into effect.
: : , . . - - ••
The New York metropolitan area has a mixture of elevated
and low-lying coastlines. Low-lying land within 3 m (9.8 ft)
of mean sea level (Gornitz et al., 2002) include the borough
of Queens' northern and southeastern shore, respectively
(where New York's two major airports, LaGuardia and John
F Kennedy International Airport, are located); much of the
recreational lands along Jamaica Bay's Gateway National
Recreation Area (e.g., Floyd Bennett Field, Jamaica Bay
Wildlife Refuge, Fort Tilden, Riis Park); and the Staten Island
communities of South Beach and Oakwood Beach. In New
Jersey, the heavily developed coast of Hudson County (includ-
ing Hoboken, Jersey City, and Bayonne) is also within 3 m, as
is much of the area known as the Meadowlands (area around
Giants Stadium). Other areas with sections of low-lying lands
are found in Elizabeth and Newark, New Jersey (near Newark
Airport). The area also includes the ecologically-significant
Raritan Bay-Sandy Hook habitat complex at the apex of the
New York region (also known as the New York Bight), where
the east-west oriented coastline of New England and Long
Island intersects the north-south oriented coastline of the
Mid-Atlantic at Sandy Hook.
Given its large population, the effects of hurricanes and
other major storms combined with higher sea levels could
be particularly severe in the New York metropolitan area.
With much of the area's transportation infrastructure at low
elevation (most at 3 m or less), even slight increases in the
height of flooding could cause extensive damage and bring
the thriving city to a relative standstill until the flood waters
recede (Gornitz et al., 2002).
Comprehensive assessments of the vulnerability of the New
York City metropolitan area are found in Jacob et al. (2007)
and Gornitz et al. (2002). Jacob et al. summarize vulner-
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A Focus on the Mid-Atlantic Region
ability, coastal management, and adaptation issues. Gornitz
et al. detail the methodology and results of a study that sum-
marizes vulnerability to impacts of climate change, including
higher storm surges, shoreline movement, wetland loss, beach
nourishment, and some socioeconomic implications. These
assessments use sea-level rise estimates from global climate
models available in 2002. Generalized maps depicting lands
close to sea level are found in Titus and Richman (2001) and
Titus and Wang (2008).
If sea-level rise impairs coastal habitat, many estuarine spe-
cies would be at risk. This Section provides additional details
on the possible environmental implications of sea-level rise
for the greater New York metropolitan area, including New
York City, the lower Hudson River, the East River, Jamaica
Bay, the New Jersey Meadowlands, Raritan Bay, and Sandy
Hook Bay. The following subsections discuss tidal wetlands,
beaches, tidal flats, marsh and bay islands, and shallow
waters. (Sections A1.A.2 and A1.D.2 discuss the statewide
coastal policies of New York and New Jersey.)
Tidal Wetlands. Examples of this habitat include:
• Staten Island: The Northwest Staten Island/Harbor
Herons Special Natural Waterfront Area is an important
nesting and foraging area for herons, ibises, egrets, gulls,
and waterfowl (USFWS, 1997). Several marshes on Stat-
en Island, such as Arlington Marsh and Saw Mill Creek
Marsh, provide foraging areas for the birds of the island
heronries. Hoffman Island and Swinburne Island, east
of Staten Island, provide important nesting habitat for
herons and cormorants, respectively (Bernick, 2006).
Manhattan: In the marsh and mudflat at the mouth of
the Harlem River at Inwood Hill Park (USFWS, 1997)
great blue herons are found along the flat in winter, and
snowy and great egrets are common from spring through
fall (NYC DPR, 2001).
• Lower Hudson River: The Piermont Marsh, a 412 ha
(1,017 ac) brackish wetland on the western shore of the
lower Hudson River has been designated for conserva-
tion management by New York State and the National
Oceanic and Atmospheric Administration (NOAA)
(USFWS, 1997). The marsh supports breeding birds,
including relatively rare species such as Virginia rail,
swamp sparrow, black duck, least bittern, and sora rail.
Anadromous and freshwater fish use the marsh's tidal
creeks as a spawning and nursery area. Diamondback
terrapin reportedly nest in upland areas along the marsh
(USFWS, 1997).
• Jamaica Bay: Located in Brooklyn and Queens, this
bay is the largest area of protected wetlands in a major
metropolitan area along the U.S. Atlantic Coast. The bay
includes the Jamaica Bay Wildlife Refuge, which has
been protected since 1972 as part of the Jamaica Bay
Unit of the Gateway National Recreation Area. Despite
extensive disturbance from dredging, filling, and devel-
opment, Jamaica Bay remains one of the most important
migratory shorebird stopover sites in the New York Bight
(USFWS, 1997). The bay provides overwintering habitat
for many duck species, and mudflats support foraging
migrant species (Hartig et al., 2002). The refuge and
Breezy Point, at the tip of the Rockaway Peninsula, sup-
port populations of 214 species that are state or federally
listed or of special emphasis, including 48 species offish
and 120 species of birds (USFWS, 1997). Salt marshes
such as Four Sparrow Marsh provide nesting habitat
for declining sparrow species and serve 326 species of
migrating birds (NYC DPR, undated). Wetlands in some
parts of the bay currently show substantial losses (Hartig
et al, 2002).
Meadowlands: The Meadowlands contain the largest
single tract of estuarine tidal wetland remaining in the
New York/New Jersey Harbor Estuary and provide criti-
cal habitat for a diversity of species, including a number
of special status species. Kearney Marsh is a feeding area
for the state-listed endangered least tern, black skimmer,
and pied-billed grebe. Diamondback terrapin, the only
turtle known to occur in brackish water, is found in the
Sawmill Wildlife Management Area (USFWS, 1997).
• Raritan Bay-Sandy Hook: The shorelines of southern
Raritan Bay include large tracts of fringing salt marsh at
Conaskonk Point and from Flat Creek to Thorn's Creek.
These marshes are critical for large numbers of nesting
and migrating bird species. The salt marsh at Conaskonk
Point provides breeding areas for bird species such as
green heron, American oystercatcher, seaside sparrow,
and saltmarsh sharp-tailed sparrow, as well as feeding ar-
eas for herons, egrets, common tern, least tern, and black
skimmer. In late May and early June, sanderlings, ruddy
turnstones, semipalmated sandpipers, and red knots feed
on horseshoe crab eggs near the mouth of Chingarora
Creek. Low marsh along the backside of Sandy Hook spit
provides forage and protection for the young of marine
fishes, including winter flounder, Atlantic menhaden,
bluefish, and striped bass, and critical habitat for char-
acteristic bird species of the low marsh such as clapper
rail, willet, and marsh wren (USFWS, 1997).
Estuarine Beaches. Relatively few areas of estuarine beach
remain in the New York City metropolitan area, and most have
been modified or degraded (USFWS, 1997; Strange, 2008a).
In Jamaica Bay, remaining estuarine beaches occur off Belt
Parkway (e.g., on Plumb Beach) and on the bay islands (US-
FWS, 1997). Sandy beaches are still relatively common along
the shores of Staten Island from Tottenville to Ft. Wadsworth.
The southern shoreline of Raritan Bay includes a number of
beaches along Sandy Hook Peninsula and from the Highlands
199
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Appendix I
to South Amboy, some of which have been nourished. There
are also beaches on small islands within the Shrewsbury-
Navesink River system (USFWS, 1997).
Although limited in area, the remaining beaches support an
extensive food web. Mud snails and wrack-based species (e.g.,
insects, isopods, and amphipods) provide food for shorebirds
including the piping plover, federally listed as threatened
(USFWS, 1997). The beaches around Sandy Hook Bay have
become important nestling places in winter for several species
of seals (USFWS, 1997). The New Jersey Audubon Society
reports that its members have observed gulls and terns at the
Raritan Bay beach at Morgan on the southern shore, includ-
ing some rare species such as black-headed gull, little gull,
Franklin's gull, glaucous gulls, black tern, sandwich tern, and
Hudsonian godwit. Horseshoe crabs lay their eggs on area
beaches, supplying critical forage for shorebirds (Botton et
al., 2006). The upper beach is used by nesting diamondback
terrapins; human-made sandy trails in Jamaica Bay are also
an important nest site for terrapins in the region, although
the sites are prone to depredations by raccoons (Feinberg
and Burke, 2003).
Tidal flats. Like beaches, tidal flats are limited in the New
York City metropolitan region, but the flats that remain pro-
vide important habitat, particularly for foraging birds. Tidal
flats are also habitat for hard and soft shell clams, which are
important for recreational and commercial fishermen where
not impaired by poor water quality. Large concentrations of
shorebirds, herons, and waterfowl use the shallows and tidal
flats of Piermont Marsh along the lower Hudson River as
staging areas for both spring and fall migrations (USFWS,
1997). Tidal flats in Jamaica Bay are frequented by shorebirds
and waterfowl, and an intensive survey of shorebirds in the
mid-1980s estimated more than 230,000 birds of 31 spe-
cies in a single year, mostly during the fall migration (NYS
DOS and USFWS, 1998, citing Burger, 1984). Some 1,460
ha (3,600 ac) of intertidal flats extend offshore an average
of 0.4 km (0.25 mi) from the south shore of the Raritan and
Sandy Hook Bays, from the confluence of the Shrewsbury
and Navesink rivers, west to the mouth of the Raritan River.
These flats are important foraging and staging areas for
migrating shorebirds, averaging over 20,000 birds, mostly
semipalmated plover, sanderling, and ruddy turnstone. The
flats at the mouth of Whale Creek near Pirate's Cove attract
gulls, terns, and shorebirds year round. Midwinter waterfowl
surveys indicate that an average of 60,000 birds migrate
through the Raritan Bay-Sandy Hook area in winter (USFWS,
1997). Inundation with rising seas will eventually make flats
unavailable to short-legged shorebirds, unless they can shift
feeding to marsh ponds and pannes (Erwin et al., 2004). At
the same time, disappearing salt marsh islands in the area
are transforming into intertidal mudflats. This may increase
habitat for shorebirds at low tide, but it leaves less habitat for
refuge at high tide (Strange, 2008a).
Shallow water habitat. This habitat is extensive in the Hud-
son River, from Stony Point south to Piermont Marsh, just
below the Tappan Zee Bridge (USFWS, 1997). This area
features the greatest mixing of ocean and freshwater, and
concentrates nutrients and plankton, resulting in a high level
of both primary and secondary productivity. Thus, this part
of the Hudson provides key habitat for numerous fish and
bird species. It is a major nursery area for striped bass, white
perch, tomcod, and Atlantic sturgeon, and a wintering area
for the federally endangered shortnose sturgeon. Waterfowl
also feed and rest here during spring and fall migrations.
Some submerged aquatic vegetation (SAV) is also found
here, dominated by water celery, sago pondweed, and horned
pondweed (USFWS, 1997).
Marsh and bay islands. Throughout the region, these islands
are vulnerable to sea-level rise (Strange, 2008a). Between
1974 and 1994, the smaller islands of Jamaica Bay lost nearly
80 percent of their vegetative cover (Strange, 2008a, citing
Hartig et al., 2002). Island marsh deterioration in Jamaica Bay
has led to a 50 percent decline in area between 1900 and 1994
(Gornitz et al., 2002). Marsh loss has accelerated, reaching
an average annual rate of 18 ha (45 ac) per year between 1994
and 1999 (Hartig et al., 2002). The islands provide specialized
habitat for an array of species:
Regionally important populations of egrets, herons,
and ibises are or have been located on North and South
Brother islands in the East River and on Shooter's Island,
Frail's Island, and Isle of Meadows in Arthur Kill and
Kill VanKull (USFWS, 1997).
North and South Brother Islands have the largest black
crowned night heron colony in New York State, along
with large numbers of snowy egret, great egret, cattle
egret, and glossy ibis (USFWS, 1997).
Since 1984, an average of 1,000 state threatened common
tern have nested annually in colonies on seven islands of
the Jamaica Bay Wildlife Refuge (USWFS, 1997).
The heronry on Canarsie Pol also supports nesting by
great black-backed gull, herring gull, and American
oystercatcher (USFWS, 1997).
The only colonies of laughing gull in New York State,
and the northernmost breeding extent of this species,
occur on the islands of East High Meadow, Silver Hole
Marsh, Jo Co Marsh, and West Hempstead Bay (USFWS,
1997).
Diamondback terrapin nest in large numbers along the
sandy shoreline areas of the islands of Jamaica Bay, pri-
marily Ruler's Bar Hassock (USFWS, 1997).
200
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EY:
The New Jersey shore has three types of ocean coasts (see
Chapter 3 of this Product). At the south end, Cape May and
Atlantic Counties have short and fairly wide "tide-dominated"
barrier islands. Behind the islands, 253 sq km (97 sq mi)
of marshes dominate the relatively small open water bays.
To the north, Ocean County has "wave dominated" coastal
barrier islands and spits. Long Beach Island is 29 km (18
mi) long and only two to three blocks wide in most places;
Island Beach to the north is also long and narrow. Behind
Long Beach Island and Island Beach lie Barnegat and Little
Egg Harbor Bays. These shallow estuaries range from 2 to 7
km (about 1 to 4 mi) wide, and have 167 sq km (64 sq mi) of
open water (USFWS, 1997) with extensive eelgrass, but only
125 sq km (48 sq mi) of tidal marsh (Jones and Wang, 2008).
Monmouth County's ocean coast is entirely headlands, with
the exception of Sandy Hook at the northern tip of the Jersey
Shore. Non-tidal wetlands are immediately inland of the tidal
wetlands along most of the mainland shore8.
AI.C.I
There have been many efforts to conserve and restore spe-
cies and habitats in the barrier island and back-barrier lagoon
systems in New Jersey. Some of the larger parks and wildlife
areas in the region include Island Beach State Park, Great
Bay Boulevard State Wildlife Management Area, and the
E.B. Forsythe National Wildlife Refuge (Forsythe Refuge) in
Ocean and Atlantic counties. Parts of the Cape May Peninsula
are protected by the Cape May National Wildlife Refuge (US-
FWS, undated[a]), the Cape May Point State Park (NJDEP,
undated) and The Nature Conservancy's (TNC's) Cape May
Migratory Bird Refuge (TNC, undated).
Tidal and Nearshore Nontidal Marshes. There are 18,440
ha (71 sq mi), 29,344 ha (113 sq mi), and 26,987 ha (104 sq
mi) of tidal salt marsh in Ocean, Atlantic, and Cape May
counties, respectively (Jones and Wang, 2008). The marshes
in the study area are keeping pace with current local rates of
sea-level rise of 4 millimeters (mm) per year, but are likely
to become marginal with a 2 mm per year acceleration and
be lost with a 7 mm per year acceleration, except where there
are near local sources of sediments (e.g., rivers such as the
Mullica and Great Harbor rivers in Atlantic County) (Strange
2008b, interpreting the findings of Reed et al., 2008).
There is potential for wetland migration in Forsythe Refuge,
and other lands that preserve the coastal environment such as
parks and wildlife management areas. Conservation lands are
also found along parts of the Mullica and Great Egg Harbor
! For comprehensive discussions of the New Jersey shore and the
implications of sea level rise, see Cooper et al. (2005), Lathrop and
Love (2007), Najjar et al. (2000), and Psuty and Ofiara (2002).
Coastal to
A Focus on the Mid-Atlantic Region
rivers in Atlantic County. However, many estuarine shorelines
in developed areas are hardened, limiting the potential for
wetland migration (Strange, 2008b).
As marshes along protected shorelines experience increased
tidal flooding, there may be an initial benefit to some spe-
cies. If tidal creeks become wider and deeper, fish may have
increased access to forage on the marsh surface (Weinstein,
1979). Sampling of larval fishes in high salt marsh on Cattus
Island, Beach Haven West, and Cedar Run in Ocean County
showed that high marsh is important for mummichog, rain-
water killifish, spotfin killifish, and sheepshead minnow
(Talbot and Able, 1984). The flooded marsh surface and
tidal and nontidal ponds and ditches appear to be especially
important for the larvae of these species (Talbot and Able,
1984). However, as sea level rises, and marshes along hard-
ened shorelines convert to open water, marsh fishes will
lose access to these marsh features and the protection from
predators, nursery habitat, and foraging areas provided by
the marsh (Strange 2008b).
Loss of marsh area would also have negative implications
for the dozens of bird species that forage and nest in the
region's marshes. Initially, deeper tidal creeks and marsh
pools will become inaccessible to short-legged shorebirds
such as plovers (Erwinetal., 2004). Long-legged waterbirds
such as the yellow-crowned night heron, which forage almost
exclusively on marsh crabs (fiddler crab and others), will
lose important food resources (Riegner, 1982). Eventually,
complete conversion of marsh to open water will affect the
hundreds of thousands of shorebirds that stop in these areas
to feed during their migrations. The New Jersey Coastal
Management Program estimates that some 1.5 million mi-
gratory shorebirds stopover on New Jersey's shores during
their annual migrations (Cooper et al., 2005). Waterfowl also
forage and overwinter in area marshes. Mid-winter aerial
waterfowl counts in Barnegat Bay alone average 50,000
birds (USFWS, 1997). The tidal marshes of the Cape May
Peninsula provide stopover areas for hundreds of thousands
of shorebirds, songbirds, raptors, and waterfowl during their
seasonal migrations (USFWS, 1997). The peninsula is also
an important staging area and overwintering area for seabird
populations. Surveys conducted by the U.S. Fish and Wild-
life Service from July through December 1995 in Cape May
County recorded more than 900,000 seabirds migrating along
the coast (USFWS, 1997).
As feeding habitats are lost, local bird populations may no
longer be sustainable (Strange, 2008b). For example, avian
biologists suggest that if marsh pannes and pools continue
to be lost in Atlantic County as a result of sea-level rise, the
tens of thousands of shorebirds that feed in these areas may
shift to feeding in impoundments in the nearby Forsythe
201
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Appendix I
Refuge. Such a shift would increase shorebird densities in
the refuge ten-fold and reduce population sustainability due
to lower per capita food resources and disease from crowding
(Erwine/a/.,2006).
Local populations of marsh nesting bird species will also be at
risk where marshes drown. This will have a particularly nega-
tive impact on rare species such as seaside and sharp-tailed
sparrows, which may have difficulty finding other suitable
nesting sites. According to a synthesis of published studies in
Greenlaw and Rising (1994) and Post and Greenlaw (1994),
densities in the region ranged from 0.3 to 20 singing males
per hectare and 0.3 to 4.1 females per hectare for the seaside
and sharp-tailed sparrows, respectively (Greenlaw and Ris-
ing, 1994). Loss and alteration of suitable marsh habitats
are the primary conservation concerns for these and other
marsh-nesting passerine birds (BBNEP, 2001).
Shore protection activities (nourishment and vegetation
control) are underway to protect the vulnerable freshwater
ecosystems of the Cape May Meadows (The Meadows), which
are located behind the eroding dunes near Cape May Point
(USAGE, 2008a). Freshwater coastal ponds in The Meadows
are found within about one hundred meters (a few hundred
feet) of the shoreline and therefore could easily be inundated
as seas rise. The ponds provide critical foraging and resting
habitat for a variety of bird species, primarily migrating
shorebirds (NJDEP, undated). Among the rare birds seen in
The Meadows by local birders are buff-breasted sandpipers,
arctic tern, roseate tern, whiskered tern, Wilson's phalarope,
black rail, king rail, Hudsonian godwit, and black-necked stilt
(Kerlinger, 2006; Strange 2008b). The Nature Conservancy,
the United States Army Corps of Engineers (USAGE), and
the New Jersey Department of Environmental Protection
(NJDEP) have undertaken an extensive restoration project
in the Cape May Migratory Bird Refuge, including beach
replenishment to protect a mile-long stretch of sandy beach
that provides nesting habitat for the piping plover (federally
listed as threatened), creation of plover foraging ponds, and
creation of island nesting sites for terns and herons (TNC,
2007).
Estuarine Beaches. Estuarine beaches are largely disappear-
ing in developed areas where shoreline armoring is the pre-
ferred method of shore protection. The erosion or inundation
of bay islands would also reduce the amount of beach habitat.
Many species of invertebrates are found within or on the sandy
substrate or beach wrack (seaweed and other decaying marine
plant material left on the shore by the tides) along the tide line
of estuarine beaches (Bertness, 1999). These species provide
a rich and abundant food source for bird species. Small beach
invertebrates include isopods and amphipods, blood worms,
and beach hoppers, and beach macroinvertebrates include
soft shell clams, hard clams, horseshoe crabs, fiddler crabs,
and sand shrimp (Shellenbarger Jones, 2008a).
Northern diamondback terrapin nest on estuarine beaches
in the Barnegat Bay area (BBNEP, 2001). Local scientists
consider coastal development, which destroys terrapin nesting
beaches and access to nesting habitat, to be one of the primary
threats to diamondback terrapins, along with predation, road
kills, and crab trap bycatch (Strange, 2008b, citing Wetland
Institute, undated).
Loss of estuarine beach could also have negative impacts
on various beach invertebrates, including rare tiger beetles
(Strange, 2008b). Two sub-species likely exist in coastal New
Jersey: Cicindela dor sails dor sails, the northeastern beach
tiger beetle, which is a federally listed threatened species
and a state species of special concern and regional priority,
and Cicindela dorsalls media, the southeastern beach tiger
beetle, which is state-listed as rare (NJDEP, 2001). In the
mid-1990s, the tiger beetle was observed on the undeveloped
ocean beaches of Holgate and Island Beach. Current surveys
do not indicate whether this species is also found on the area's
estuarine beaches, but it feeds and nests in a variety of habi-
tats (USFWS, 1997). The current abundance and distribution
of the northeastern beach tiger beetle in the coastal bays is
a target of research (State of New Jersey, 2005). At present,
there are plans to reintroduce the species in the study region
at locations where natural ocean beaches remain (State of
New Jersey, 2005).
Tidal Flats. The tidal flats of New Jersey's back-barrier bays
are critical foraging areas for hundreds of species of shore-
birds, passerines, raptors, and waterfowl (BBNEP, 2001).
Important shorebird areas in the study region include the
flats of Great Bay Boulevard Wildlife Management Area,
North Brigantine Natural Area, and the Brigantine Unit of
the Forsythe Refuge (USFWS, 1997). The USFWS estimates
that the extensive tidal flats of the Great Bay alone total 1,358
ha (3,355 ac). Inundation of tidal flats with rising seas would
eliminate critical foraging opportunities for the area's abun-
dant avifauna. As tidal flat area declines, increased crowding
in remaining areas could lead to exclusion and mortality of
many foraging birds (Galbraith et al., 2002; Erwin el al.,
2004). Some areas may become potential sea grass restoration
sites, but whether or not "enhancing" these sites as eelgrass
areas is feasible will depend on their location, acreage, and
sediment type (Strange, 2008b).
Shallow Neat-shore Waters and Submerged Aquatic Vegeta-
tion (SAV). The Barnegat Estuary is distinguished from the
lagoons to the south by more open water and SAV and less
emergent marsh. Within the Barnegat Estuary, dense beds of
eelgrass are found at depths under 1 m, particularly on sandy
202
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Coastal to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
shoals along the backside of Long Beach Island and Island
Beach, and around Barnegat Inlet, Manahawkin Bay, and
Little Egg Inlet. Eelgrass is relatively uncommon from the
middle of Little Egg Harbor south to Cape May, particularly
locations where water depths are more than 1 m, such as
portions of Great South Bay (USFWS, 1997).
Seagrass surveys from the 1960s through the 1990s indicate
that there has been an overall decline in seagrass beds in
Barnegat Estuary, from 6,823 ha (16,847 ac) in 1968 to an
average of 5,677 ha (14,029 ac) during the period 1996 to 1998
(BBNEP, 2001). Numerous studies indicate that eelgrass has
high ecological value as a source of both primary (Thayer
et ai, 1984) and secondary production (Jackson et ai, 2001)
in estuarine food webs. In Barnegat Estuary, eelgrass beds
provide habitat for invertebrates, birds, and fish that use the
submerged vegetation for spawning, nursery, and feeding
(BBNEP, 2001). Shallow water habitat quality may also be
affected by adjacent shoreline protections. A Barnegat Bay
study found that where shorelines are bulkheaded, SAV,
woody debris, and other features of natural shallow water
habitat are rare or absent, with a resulting reduction in fish
abundance (Byrne, 1995).
Marsh and Bay Islands. Large bird populations are found on
marsh and dredge spoil islands of the New Jersey back-barrier
bays. These islands include nesting sites protected from
predators for a number of species of conservation concern,
including gull-billed tern, common tern, Forster's tern, least
tern, black skimmer, American oystercatcher, and piping plo-
ver (USFWS, 1997). Diamondback terrapins are also known
to feed on marsh islands in the bays (USFWS, 1997).
Some of the small islands in Barnegat Bay and Little Egg
Harbor extend up to about 1 m above spring high water (Jones
and Wang, 2008), but portions of other islands are very low,
and some low islands are currently disappearing. Mordecai
(MLT, undated) and other islands (Strange, 2008b) used by
nesting common terns, Forster's terns, black skimmers, and
American oystercatchers are vulnerable to sea-level rise and
erosion (MLT, undated). With the assistance of local govern-
ments, the Mordecai Land Trust is actively seeking grants to
halt the gradual erosion of Mordecai Island, an 18-ha (45-ac)
island just west of Beach Haven on Long Beach Island (MLT,
undated). Members of the land trust have documented a 37
percent loss of island area since 1930. The island's native salt
marsh and surrounding waters and SAV beds provide habitat
for a variety of aquatic and avian species. NOAA National
Marine Fisheries Service considers the island and its waters
Essential Fish Habitat for spawning and all life stages of
winter flounder as well as juvenile and adult stages of Atlan-
tic sea herring, bluefish, summer flounder, scup, and black
sea bass (MLT, undated). The island is also a strategically-
located nesting island for many of New Jersey's threatened
and endangered species, including black skimmers, least
terns, American bitterns, and both yellow-crowned and black-
crowned night herons (MLT, 2003).
Sea-level Fens. New Jersey has identified 12 sea-level fens,
encompassing 51 ha (126 ac). This rare ecological community
is restricted in distribution to Ocean County, New Jersey,
between Forked River and Tuckerton, in an area of artesian
groundwater discharge from the Kirkwood-Cohansey aquifer.
Additional recent field surveys have shown possible occur-
rences in the vicinity of Tuckahoe in Cape May and Atlantic
counties (Walz et al., 2004). These communities provide
significant wetland functions in the landscape as well as
supporting 18 rare plant species, one of which is state-listed
as endangered (Walz et al., 2004).
I'
At least five state policies affect the response to sea-level
rise along New Jersey's Atlantic Coast: the Coastal Facility
Review Act, the Wetlands Act, the State Plan, an unusually
strong Public Trust Doctrine, and the state's strong support for
beach nourishment—and opposition to both erosion-control
structures and shoreline retreat—along ocean shores. This
Section discusses the latter policy; the first four are discussed
in Section A1.D.2 of this Appendix.
In 1997, then-Governor Whitman promised coastal commu-
nities that "there will be no forced retreat", and that the gov-
ernment would not force people to leave the shoreline. That
policy does not necessarily mean that there will always be
government help for shore protection. Nevertheless, although
subsequent administrations have not expressed this view so
succinctly, they have not withdrawn the policy either. In fact,
the primary debate in New Jersey tends to be about the level
of public access required before a community is eligible to
receive beach nourishment, not the need for shore protection
itself (see Chapter 8 of this Product).
With extensive development and tourism along its shore, New
Jersey has a well-established policy in favor of shore protec-
tion along the ocean9. The state generally prohibits new hard
structures along the ocean front; but that was not always the
case. A large portion of the Monmouth County shoreline was
once protected with seawalls, with a partial or total loss of
beach (Pilkey et al., 1981). Today, beach nourishment is the
' For example, the primary coastal policy document during the Whit-
man administration suggested that even mentioning the term "retreat"
would divide people and impede meaningful discussion of appropriate
policies, in part because retreat can mean government restrictions on
development or simply a decision by government not to fund shore
protection (see NJDEP, 1997).
203
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The U.S. Climate Change Science Program
Appendix I
BOX AI.2: Shore Protection on Long Beach Island
The effects of sea-level rise can be observed on both the ocean and bay sides of this 29-km (18-mi) long barrier
island. Along the ocean side, shore erosion has threatened homes in Harvey Cedars and portions of Long Beach
township. During the 1990s, a steady procession of dump trucks brought sand onto the beach from inland
sources. In 2007, the USAGE began to restore the beach at Surf City and areas immediately north. The beach
had to be closed for a few weeks, however, after officials discovered that munitions (which had been dumped
offshore after World War II) had been inadvertently pumped onto the beach.
High tides regularly flood the main boulevard in the commercial district of Beach Haven, as well as the south-
ern two blocks of Central Avenue in Ship Bottom. Referring to the flooded parking lot during spring tides, the
billboard of a pizza parlor in Beach Haven Crest boasts "Occasional Waterfront Dining".
U.S. EPA's 1989 Report to Congress used Long Beach Island as a model for analyzing alternative responses to
rising sea level, considering four options: a dike around the island, beach nourishment and elevating land and
structures, an engineered retreat which would include the creation of new bayside lands as the ocean eroded,
and making no effort to maintain the island's land area (U.S. EPA, 1989; Titus et a/., 1991). Giving up the island
was the most expensive option (Weggel et a/., 1989; Titus, 1990). The study concluded that a dike would be the
least expensive in the short run, but unacceptable to most residents due to the lost view of the bay and risk
of being on a barrier island below sea level (Titus, 1990). In the long run, fostering a landward migration would
be the least expensive, but it would unsettle the expectations of bay front property owners and hence require
a lead time of a few generations between being enacted and new bayside land actually being created. Thus, the
combination of beach nourishment and elevating
land and structures appeared to be the most re-
alistic, and U.S. EPA used that assumption in its
nationwide cost estimate (U.S. EPA, 1989; Titus
etc/., 1991).
Long Beach Township, Ship Bottom, Harvey Ce-
dars, and Beach Haven went through a similar
thinking process in considering their preferred
response to sea-level rise. In resolutions enacted
by their respective boards of Commissioners,
they concluded that a gradual elevation of their
communities would be preferable to either dikes
or the retreat option. In the last ten years, sev-
eral structural moving companies have had ongo-
Box Figure AI.2 Spring high tide at Ship Bottom, Long Beach ing operations, continually elevating homes (see
Island, September I, 2002. Figure 11.4b shows the same area during Figure 12.5).
a minor storm surge. [Photo source: ®James G. Titus, used with
permission].
preferred method for reversing beach erosion and providing
ocean front land with protection from coastal storms (Mau-
riello, 1991). The entire Monmouth County shoreline now
has a beach in front of the old seawalls. Beach nourishment
has been undertaken or planned for at least one community
in every coastal county from Middlesex along Raritan Bay,
to Salem along the Delaware River. Island Beach State Park,
a barrier spit along the central portion of Barnegat Bay just
north of Long Beach Island, is heavily used by New Jersey
residents and includes the official beach house of the Gov-
ernor. Although it is a state park, it is currently included
in the authorized USAGE Project for beach nourishment
from Manasquan to Barnegat Inlet. In the case of Cape May
Meadows10, environmental considerations have prompted
shore protection efforts (USAGE, 2008a). The area's criti-
cal freshwater ecosystem is immediately behind dunes that
have eroded severely as a result of the jetties protecting the
entrance to the Cape May Canal.
Some coastal scientists have suggested the possibility of
disintegrating barrier islands along the New Jersey shore (see
Chapter 3). Although the bay sides of these islands are bulk-
10 The Meadows are within Cape May Point State Park and the Nature
Conservancy's Cape May Migratory Bird Refuge.
204
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Coastal to
A Focus on the Mid-Atlantic Region
headed, communities are unlikely to seriously consider the
option of being encircled by a dike as sea level rises (see Box
A1.2). Nevertheless, Avalon uses a combination of floodwalls
and checkvalves to prevent tidal flooding; and Atlantic City's
stormwater management system includes underground tanks
with checkvalves. These systems have been implemented to
address current flooding problems; but they would also be a
logical first step in a strategy to protect low-lying areas with
structural solutions as sea level rises11. Other authors have
suggested that a gradual elevation of barrier islands is more
likely (see Box A1.2).
Wetlands along the back-barrier bays of New Jersey's Atlantic
coast are likely to have some room to migrate inland, because
they are adjacent to large areas of non-tidal wetlands. One
effort at the state level to preserve such coastal resources is
the state's Stormwater Management Plan, which establishes
a special water resource protection area that limits develop-
ment within 91.4 m (300 ft) of tidal wetlands along most of its
coastal shore (NJDEP DWM, 2004). Although the primary
objective of the regulation is to improve coastal water quality
and reduce potential flood damage, it serves to preserve areas
suitable for the landward migration of wetlands.
' t
'
On both sides of Delaware Bay, most shores are either tidal
wetlands or sandy beaches with tidal wetlands immediately
behind them. In effect, the sandy beach ridges are similar to
the barrier islands along the Atlantic, only on a smaller scale.
Several substantial communities with wide sandy beaches
on one side and marsh on the other side are along Delaware
Bay—especially on the Delaware side of the bay. Although
these communities are potentially vulnerable to inundation,
shoreline erosion has been a more immediate threat to these
communities. Detailed discussions of the dynamics of Dela-
ware shorelines are found in Kraft and John (1976).
Delaware Bay is home to hundreds of species of ecologi-
cal, commercial, and recreational value (Dove and Nyman,
1995; Kreeger and Titus, 2008). Unlike other estuaries in
the Mid-Atlantic, the tidal range is greater than the ocean
tidal range, generally about 2 m. In much of Delaware Bay,
tidal marshes appear to be at the low end of their potential
elevation range, increasing their vulnerability to sea-level
rise (Kearney et al., 2002). Recent research indicates that
50 to 60 percent of Delaware Bay's tidal marsh has been de-
graded, primarily because the surface of the marshes is not
rising as fast as the sea (Kearney et al., 2002). One possible
reason is that channel deepening projects and consumptive
11 See Chapter 6 of this Product for explanation of structural mechanisms
to combat flooding.
withdrawals of fresh water have changed the sediment sup-
ply to the marshes (Sommerfield and Walsh, 2005). Many
marsh restoration projects are underway in the Delaware
Bay (cf. Teal and Peterson, 2005): dikes have been removed
to restore tidal flow and natural marsh habitat and biota;
however, in some restoration areas invasion by common reed
(Phragmites australis) has been a problem (Abel and Hagan,
2000; Weinsteine/a/., 2000).
The loss of tidal marsh as sea level rises would harm species
that depend on these habitats for food and shelter, including
invertebrates, finfish, and a variety of bird species (Kreeger
and Titus, 2008). Great blue herons, black duck, blue and
green-winged teal, Northern harrier, osprey, rails, red winged
blackbirds, widgeon, and shovelers all use the salt marshes in
Delaware Bay. Blue crab, killifish, mummichog, perch, weak-
fish, flounder, bay anchovy, silverside, herring, and rockfish
rely on tidal marshes for feeding on the mussels, fiddler crabs,
and other invertebrates and for protection from predators
(Dove and Nyman, 1995; Kreeger and Titus, 2008).
Delaware Bay is a major stopover area for six species of
migratory shorebirds, including most of the Western Hemi-
sphere's population of red knot (USFWS, 2003). On their
annual migrations from South America to the Arctic, nearly
a million shorebirds move through Delaware Bay, where they
feed heavily on invertebrates in tidal mudflats, and particu-
larly on horseshoe crab eggs on the bay's sandy beaches and
foreshores (Walls et al., 2002). Horseshoe crabs have been
historically abundant on the Delaware Bay shores. A sea-level
rise modeling study estimated that a 60-centimeter (cm) (2-ft)
rise in relative sea level over the next century could reduce
shorebird foraging areas in Delaware Bay by 57 percent or
more by 2100 (Galbraith et al, 2002).
Invertebrates associated with cordgrass stands in the low
intertidal zone include grass shrimp, ribbed mussel, coffee-
bean snail, and fiddler crabs (Kreamer, 1995). Blue crab, sea
turtles, and shorebirds are among the many species that prey
on ribbed mussels; fiddler crabs are an important food source
for bay anchovy and various species of shorebirds (Kreamer,
1995). Wading birds such as the glossy ibis feed on marsh
invertebrates (Dove and Nyman, 1995; Kreeger and Titus,
2008). Waterfowl, particularly dabbling ducks, use low marsh
areas as a wintering ground.
Sandy beaches and foreshores account for the majority of the
Delaware and New Jersey shores of Delaware Bay. As sea
level rises, beaches can be lost if either shores are armored
or if the land behind the existing beach has too little sand to
sustain a beach as the shore retreats (Nordstrom, 2005). As
shown in Table Al.l, so far only 4 percent (Delaware) and 6
percent (New Jersey) of the natural shores have been replaced
205
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The U.S. Climate Change Science Program
Appendix I
Table Al.l The Shores of Delaware Bay: Habitat Type and Conservation Status of
Shores Suitable for Horseshoe Crabs (in kilometers [km]).
New Jersey
nd Delaware
Armored Shore
Tota Shore ine
Shore Protection Structures
Optimal Habitat
Suitab e Habitat
Less Suitable Habitat
Unsuitab e Habitat
Optimal Habitat
Optimal and Suitable Habitat
Optimal, Suitable, and Less Suitable
Habitat
Source: Kreeger and Titus (2008), compiling data developed by Latnrop et a/. (2006).
with shoreline armoring. Another 15 percent (Delaware) and
nearly 4 percent (New Jersey) of the shore is developed. Al-
though conservation areas encompass 58 percent of Delaware
Bay's shores, they include only 32 percent of beaches that
are optimal or suitable habitat for horseshoe crabs (Kreeger
and Titus, 2008).
Beach nourishment has been relatively common along the
developed beach communities on the Delaware side of the
bay. Many Delaware Bay beaches have a relatively thin layer
of sand. Although these small beaches currently have enough
sand to protect the marshes immediately inland from wave
action, some beaches may not be able to survive accelerated
sea-level rise even in areas without shoreline armoring, unless
artificial measures are taken to preserve them (Kreeger and
Titus, 2008). Most beach nourishment along the New Jersey
shore of Delaware Bay has been justified by environmental
benefits (Kreeger and Titus, 2008; USAGE, 1998b,c;); and
Delaware has also nourished beaches with the primary pur-
pose of restoring horseshoe crab habitat (Smith et al., 2002;
see Box A1.3). Although beach nourishment can diminish the
quality of habitat for horseshoe crabs, nourished beaches are
more beneficial than an armored shore, or a rapidly eroding
marsh exposed to the waves of Deleware Bay.
Numerous other animals, including diamondback terrapins,
and Kemp's ridley sea turtles, rely on the sandy beaches of
Delaware Bay to lay eggs or forage on invertebrates such as
amphipods and clams. When tides are high, numerous fish
also forage along the submerged sandy beaches, such as kil-
lifish, mummichog, rockfish, perch, herring, silverside, and
bay anchovy (Dove and Nyman, 1995; Kreeger and Titus,
2008).
AI.D.2 Development, Shore Protection, and
Coastal Policies
AI.D.2.1 NEW JERSEY
Policies that may be relevant for adapting to sea-level rise in
New Jersey include policies related to the Coastal Facility
Review Act (CAFRA), the (coastal) Wetlands Act of 1970,
the State Plan, an unusually strong Public Trust Doctrine, and
strong preference for beach nourishment along the Atlantic
Ocean over hard structures or shoreline retreat. This Section
discusses the first four of these policies (nourishment of ocean
beaches is discussed in Section Al.C of this Appendix).
CAFRA applies to all shores along Delaware Bay and the
portion of the Delaware River south of Killcohook National
Wildlife Area, as well as most tidal shores along the tributar-
ies to Delaware Bay. The act sometimes limits development
206
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Photo source: USFWS, Robert Pos.
BOX AI.3: Horseshoe Crabs and Estuarine Beaches
The Atlantic horseshoe crab (Limulus polyphemus), an ancient spe-
cies that has survived virtually unchanged for more than 350 million
years, enters estuaries each spring to spawn along sandy beaches.
The species has experienced recent population declines, apparently
due to overharvesting as well as habitat loss and degradation (Berk-
son and Shuster, 1999).
Population Status and Sea-Level Rise
In Delaware Bay, as elsewhere along its range, horseshoe crabs de-
pend on narrow sandy beaches and the alluvial and sand bar de-
posits at the mouths of tidal creeks for essential spawning habitat.
A product of wave energy, tides, shoreline configuration, and over
longer periods, sea-level rise, the narrow sandy beaches utilized by
horseshoe crabs are diminishing at sometimes alarming rates due
to beach erosion as a product of land subsidence and sea-level increases (Nordstrom, 1989; Titus et a/., 1991). At
Maurice Cove in Delaware Bay, for example, portions of the shoreline eroded at a rate of 4.3 m (14.1 ft) per year
between 1842 and 1992 (Weinstein and Weishar, 2002); an estimate by Chase (1979) suggests that the shoreline
retreated 150 m (about 500 ft) landward in a 32-year period, exposing ancient peat deposits that are believed to be
suboptimal spawning habitat (Botton eta/., 1988). If human infrastructure along the coast leaves estuarine beaches
little or no room to transgress inland as sea level rises, concomitant loss of horseshoe crab spawning habitat is
likely (Galbraith et a/., 2002). Kraft et a/. (1992) estimated this loss, along with wetland "drowning", as greater than
90 percent in Delaware Bay (about 33,000 ha, or 81,500 ac).
Horseshoe Crab Spawning and Shorebird Migrations
Each spring, horseshoe crab spawning coincides with the arrival of hundreds of thousands of shorebirds migrat-
ing from South America to their sub-Arctic nesting areas. While in Delaware Bay, shorebirds feed extensively on
horseshoe crab eggs to increase their depleted body mass before continuing their migration (Castro and Myers,
1993; Clark, 1996). Individual birds may increase their body weight by nearly one-third before leaving the area.
There is a known delicate relationship between the horseshoe crab and red knots (Baker et a/., 2004). How other
shorebirds might be affected by horseshoe crab population decline is uncertain (Smith et a/., 2002).
in the coastal zone, primarily to reduce runoff of pollution
into the state's waters (State of New Jersey, 2001). Regula-
tions promulgated under the Wetlands Act of 1970 prohibit
development in tidal wetlands unless the development is water
dependent and there is no prudent alternative (NJAC 7:7E-
2.27 [c]). Regulations prohibit development of freshwater
wetlands under most circumstances (NJAC 7:7E-2.27 [c]).
The regulations also prohibit development within 91.4 m (300
ft) of tidal wetlands, unless the development has no significant
adverse impact on the wetlands (NJAC 7:7-3.28 [c]). These
regulations, like Maryland's Critical Areas Act (see Section
A1.E.2), may indirectly reduce the need for shore protection
by ensuring that homes are set back farther from the shore
than would otherwise be the case (NOAA, 2007; see Section
6.2 in Chapter 6). For the same reason, existing restrictions
of development in nontidal wetlands (see Section 10.3) may
also enable tidal wetlands to migrate inland.
The New Jersey state plan provides a statewide vision of
where growth should be encouraged, tolerated, and dis-
couraged—but local government has the final say. In most
areas, lands are divided into five planning areas. The state
encourages development in (1) metropolitan and (2) suburban
planning areas, and in those (3) fringe planning areas that
are either already developed or part of a well-designed new
development. The state discourages development in most
portions of (4) rural planning areas and (5) land with valuable
ecosystems, geologic features, or wildlife habitat, including
coastal wetlands and barrier spits/islands (State of New Jer-
sey, 2001). However, even these areas include developed en-
claves, known as "centers", where development is recognized
as a reality (State of New Jersey, 2001). The preservation of
rural and natural landscapes in portions of planning areas
(4) and (5) is likely to afford opportunities for wetlands to
migrate inland as sea level rises. Nevertheless, New Jersey
has a long history of building dikes along Delaware Bay and
the Delaware River to convert tidal wetlands to agricultural
207
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I
The Gibbstown Levee along the Delaware River in New Jersey once served a function similar to the dikes in Cum-
berland County, preventing tidal inundation and lowering the water table to a level below mean sea level. When
the dike was built 300 years ago (USACE, undated[a]), the tides were I meter (m) lower and the combination dike
and tide gate kept the water levels low enough to permit cultivation. But rising sea level and land subsidence have
left this land barely above low tide, and many lands drain too slowly to completely drain during low tide. Hence,
farmland has converted to non-tidal wetland.
By keeping the creek a meter or so lower than it would be if it rose and fell with the tides, the levee improves
drainage during rainstorms for Greenwich Township. Nevertheless, it is less effective today than when the sea was
0.5 to I m lower. During extreme rainfall, the area can flood fairly easily because the tide gates have to be closed
most of the day. Heavy rain during a storm surge is even more problematic because for practical purposes there is
no low tide to afford the opportunity to get normal drainage by opening the tide gate. Evacuations were necessary
during Hurricane Floyd when part of this dike collapsed as a storm tide brought water levels of more than ten feet
above mean low water (NCDC, 1999).
Officials in Greenwich Township are concerned that the dikes in Gloucester County are in danger of failing (DiMuz-
io, 2006). "The Gibbstown Levee was repaired in many places in 1962 by the U.S. Army Corps of Engineers under
Public Law 84-99" (USACE, 2004). Part of the problem appears to be that most of these dikes are the respon-
sibility of meadow companies originally chartered in colonial times. These companies were authorized to create
productive agricultural lands from tidal marshes. Although harvests of salt hay once yielded more than enough
revenue to maintain the dikes, this type of farming became less profitable during the first half of the twentieth cen-
tury. Moreover, as sea level has continued to rise, the land protected by the dikes has mostly reverted to marsh
(Weinstein et a/., 2000; Abel et a/., 2000). Revenues from these lands, if any, are insufficient to cover the cost of
maintaining the dikes (DiMuzio, 2006). As a result, the dikes are deteriorating, leading officials to fear a possible
catastrophic dike failure during storm (DiMuzio, 2006), or an increase in flood insurance rates (DELO, 2006). The
officials hope to obtain federal funding (DELO, 2006).
Even if these dikes and their associated tide gates are fortified, the dry land will gradually be submerged unless
pumping facilities are installed (see Section 6.2 in Chapter 6), because much of the area is barely above low tide
even today (Titus and Wang, 2008). Although freshwater marshes in general seem likely to be able to keep pace
with rising sea level (Reed et a/., 2008), wetlands behind dikes do not always fare as well as those exposed to normal
tidal currents (Reed et a/., 2008). Over longer periods of time, increases in salinity of the Delaware River resulting
from rising sea level and reduced river flows during droughts could enable salt water to invade these fresh marshes
(Hull and Titus, 1986), which would convert them to open water ponds.
If pumping facilities are not sufficient for a daily pumping of all the very low lands protected by the dikes, the
primary impact of the dikes could be to prevent flooding from storm surges and ordinary tides. For the isolated
settlements along Marsh Dike Road and elsewhere, elevating homes and land surfaces may be possible; although
property values are less than along the barrier islands, sources for fill material are closer. One could envision that
Gibbstown, Bridgetown, and other more populated communities could be encircled with a ring dike with a pump-
ing system that drains only the densely developed area; or they too may elevate land as the sea rises.
lands (see Box 6.1 in Chapter 6) and dikes still protect some notably Public Service Enterprise Group (PSEG) in its efforts
undeveloped lands. to offset possible environmental effects of a nuclear power
plant. Although the trend is for dike removal, the fact that
In Cumberland County, salt marsh has been reclaimed for diked farms have been part of the landscape for centuries
agricultural purposes for more than 200 years (Sebold, 1992 leads one to the logical inference that dikes may be used to
and references therein). Over the last few decades, many of hold back a rising sea once again. Cumberland County has
the dikes that were constructed have been dismantled. Some relatively little coastal development, yet the trend there in
have failed during storms. Others have been purchased by coastal communities that have not become part of a conserva-
conservation programs seeking to restore wetlands, most tion program has been for a gradual retreat from the shore.
208
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Table AI.2 New Jersey Regulatory Requirements for (Parallel) Access along, and (Perpendicular) to the Shore for
New Development or Shore Protection Structures Along Delaware Estuary.
Designated Urban Rivers3 h
Beaches along Major Bodies /
ofWaterb b
All other Coastal Areas .
p
(Except Hudson River)0
•Jo requirement
Access along and to the
each is required.
•Jo requirement
I i;t?,^fjjs^^8<^f^?i(£is?»$*?i| |
Along the shore: 20 -foot (ft)
preservation buffer, including
10-ft wide walkway
To the shore: 10-ft wide walkway
every half mile.
Access along and to the beach
is required.
Alternative access on site or
nearby.
Along the Shore: 30-foot (ft)
preservation buffer, including 16-ft
wide walkway
To the Shore: 20-ft wide preserva-
tion buffer, including 10-ft wide
walkway, every half mile
Access along and to the beach is
required.
Access along the beach and shore
is required.
a Within this region, Cohansey River within Bridgeton, Maurice River within Millville, and Delaware River from the CAFRA boundary up
stream to the Trenton Makes Bridge (Trenton). Also applies to Arthur Kill, Kill Van Kull west of Bayonne Bridge, Newark Bay, Elizabeth
River, Hackensack River, Rahway River, and Raritan River.
Delaware Bay within this region. Also Atlantic Ocean, Sandy Hook Bay, and Raritan Bay.
c See Section B of this Appendix for Hudson River requirements.
dNJAC 7:7E-8.II (f)(6-7).
eNJAC 7:7E-8.II (f)(4-5).
fNJAC 7:7E-8.II (d-e).
Several small settlements along Delaware Bay are gradually
being abandoned.
The state plan contemplates a substantial degree of agricul-
tural and environmental preservation along the Delaware
River and its tidal tributaries in Salem and lower Gloucester
County. An agricultural easement program in Gloucester
County reinforces that expectation. Farther up the river, in
the industrial and commercial areas, most of the shoreline is
already bulkheaded, to provide the vertical shore that facili-
tates docking—but the effect is also to stop coastal erosion.
The eventual fate of existing dikes, which protect lightly
developed areas, is unclear (Box A1.4).
The Public Trust Doctrine in New Jersey has two unique
aspects. First, the public has an easement along the dry beach
between mean high water and the vegetation line. Although
other states have gradually acquired these easements in
most recreational communities, few states have general ac-
cess along the dry beach. As a result, people are entitled to
walk along river and bay beaches. The laws of Delaware and
Pennsylvania, by contrast, grant less public access along the
shore. In most states, the public owns the land below mean
high water. In these two states, the public owns the land be-
low mean low water. The public has an easement along the
wet beach between mean low and mean high water, but only
for navigation, fishing, and hunting—not for recreation (see
Chapter 8 of this Product for additional details).
Second, the New Jersey Supreme Court has held that the
public is entitled to perpendicular access to the beach12. The
holding does not mean that someone can indiscriminately
walk across any landowner's property to get to the water,
but it does require governments to take prudent measures
to ensure that public access to the water accompanies new
subdivisions13.
As trustee, the New Jersey Department of Environmental
Protection has promulgated rules preserving the public trust
rights to parallel and perpendicular access. The regulations
divide new construction (including shore protection struc-
tures) into three classes: single family homes (or duplexes);
development with two or three homes; and all other resi-
dential and nonresidential development. Along most of the
tidal Delaware River, any development other than a single
family home requires a public walkway at least 3 m (10 ft)
wide along the shore. By contrast, along Delaware Bay, areas
where one might walk along the beach rather than require a
walkway, the regulations have a more general requirement
for public access (see Table A1.2). The legislature recently
suspended application of these regulations as they apply to
marinas until 201114.
AI. D .2.2 D E L AW A R E
Kent County does not permit subdivisions—and gener-
ally discourages most development—in the 100-year coastal
f loodplain, as does New Castle County south of the Chesa-
uMatthews v Bay Head Improvement Association, 471 A.2d 355. Su-
preme Court of NJ (1984).
13 Federal law requires similar access before an area is eligible for beach
nourishment.
14P.L. 2008, c. 82 (NJ Code §13:19-40).
209
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Appendix I
peake and Delaware Canal15. Because the 100-year flood-
plain for storm surge extends about 2 m above spring high
water, which is often more than 1 km inland, the floodplain
regulations often require a greater setback than the erosion-
hazard (see e.g., A1.G.2) and environmental (e.g., ALE.2
and A1.F.2) setbacks elsewhere in the mid-Atlantic. Thus, a
greater amount of land may be available for potential wetland
migration (see Section 6.2 in Chapter 6). Nevertheless, if sea
level continues to rise, it is logical to assume that this buffer
would not last forever.
Preservation easements and land purchases have also con-
tributed to a major conservation buffer (DDA, 2008), which
would leave room for wetlands to migrate inland as sea level
rises (see Section 6.2). The state is purchasing agricultural
preservation easements in the coastal zone, and a significant
portion of the shore is in Prime Hook or Bombay Hook Na-
tional Wildlife Refuge. The majority of the shore south of the
canal is part of some form of preservation or conservation
land.
AI.D.2.3
Pennsylvania is the only state in the nation along tidal water
without an ocean coast16. As a result, the state's sensitivity
to sea-level rise is different than other states. Floods in the
tidal Delaware River are as likely to be caused by extreme
rainfall over the watershed as storm surges. The Delaware
River is usually fresh along almost all of the Pennsylvania
shore. Because Philadelphia relies on freshwater intakes in
the tidal river, the most important impact may be the impact
of salinity increases from rising sea level on the city's water
supply (Hull and Titus, 1986).
The state of Pennsylvania has no policies that directly address
the issue of sea-level rise17. Nevertheless, the state has several
coastal policies that might form the initial basis for a response
to sea-level rise, including state policies on tidal wetlands
and f loodplains, public access, and redeveloping the shore in
response to the decline of water-dependent industries.
Tidal Wetlands and Floodplains
Pennsylvania's Dam Safety and Waterway Management
Rules and Regulations18 require permits for construction in
the 100-year floodplain or wetlands. The regulations do not
explicitly indicate whether landowners have a right to protect
property from erosion or rising water level. A permit for a
bulkhead or revetment seaward of the high-water mark canbe
awarded only if the project will not have a "significant adverse
impact" on the "aerial extent of a wetland" or on a " wetland's
values and functions". A bulkhead seaward of the high-water
mark, however, eliminates the tidal wetlands on the landward
side. If such long-term impacts were viewed as "significant,"
permits for bulkheads could not be awarded except where
the shore was already armored. But the state has not viewed
the elimination of mudflats or beaches as "significant" for
purposes of these regulations; hence it is possible to obtain a
permit for a bulkhead.
The rules do not restrict construction of bulkheads or revet-
ments landward of the high water mark. However, they do
prohibit permits for any "encroachment located in, along,
across, or projecting into a wetland, unless the applicant
affirmatively demonstrates that...the...encroachment will
not have an adverse impact on the wetland..."19. Therefore,
shoreline armoring can eliminate coastal wetlands (or at least
prevent their inland expansion20) as sea level rises by pre-
venting their landward migration. Like the shore protection
regulations, Pennsylvania's Chapter 105 floodplains regula-
tions consider only existing floodplains, not the floodplains
that would result as the sea rises.
Public Access
Public access for recreation is an objective of the Pennsylva-
nia Coastal Zone Management program. This policy, coupled
with ongoing redevelopment trends in Pennsylvania, may tend
to ensure that future development includes access along the
shore. If the public access is created by setting development
back from the shore, it may tend to also make a gradual retreat
possible. If keeping public access is a policy goal of the gov-
ernmental authority awarding the permit for shore protection,
then public access need not be eliminated, even if shores are
armored (see Titus, 1998 and Table A1.2).
Development and Redevelopment
Industrial, commercial, residential, recreational, wooded, va-
cant, transportation, and environmental land uses all occupy
portions of Pennsylvania's 100-km coast. Generally speaking,
however, the Pennsylvania coastal zone is consistently and
15 See Kent County Ordinances §7.3 and New Castle Ordinance
40.10.313.
16 This statement also applies to the District of Columbia.
"Philadelphia's flood regulations do consider sea-level rise.
18 These regulations were issued pursuant to the Dam Safety and
Encroachment Act of 1978. Laws of Pennsylvania, The Dam Safety
and Encroachments Act of November 26, 1978, PL. 1375, No. 325.
19 Pennsylvania Code, Chapter 105. Dam Safety and Waterway
Management, Pennsylvania Department of Environmental Protection,
1997. Subchapter 105.18K
20 Chapter 4 of this Product concludes that most tidal wetlands in
Pennsylvania are likely to keep pace with projected rates of sea-level
rise. However, that finding does not address erosion of wetlands at
their seaward boundary. Even though wetlands can keep vertical pace
with the rising water level, narrow fringing wetlands along rivers can
be eliminated by shoreline armoring as their seaward boundaries erode
and their landward migration is prevented. Moreover, even where the
seaward boundary keeps pace, preventing an expansion of wetlands
might be viewed as significant.
210
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heavily developed. Only about 18 percent of the coastal area
is classified as undeveloped (DVRPC, 2003a). Much of the
shoreline has been filled or modified with bulkheads, docks,
wharfs, piers, revetments, and other hard structures over the
past two centuries.
The Pennsylvania coast is moving from an industrial to a post-
industrial landscape. The coastal zone is still dominated by
manufacturing and industrial land uses, but a steady decline
in the industrial economy over the past 60 years has led to the
abandonment of many industrial and manufacturing facilities.
Some of these facilities sit empty and idle; others have been
adapted for uses that are not water dependent.
A majority of Pennsylvania's Delaware River shore is classi-
fied as developed, but sizable expanses (especially near the
water) are blighted and stressed (DVRPC, 2003b; U.S. Census
Bueau, 2000). Because of the decaying industrial base, many
residential areas along the Delaware River have depressed
property values, declining population, high vacancy rates,
physical deterioration, and high levels of poverty and crime
(DVRPC, 2003b; U.S. Census Bureau, 2000). Many—perhaps
most—of the refineries, chemical processing plants, and other
manufacturing facilities that operate profitably today may
close in the next 50 to 100 years (Pennsylvania, 2006).
New paradigms of waterfront development have emerged that
offer fresh visions for southeastern Pennsylvania's waterfront.
In late 2001, Philadelphia released the Comprehensive Rede-
velopment Plan for the North Delaware Riverfront—a 25 -year
redevelopment vision for a distressed ten-mile stretch of
waterfront led by the design firm Field Operations. Delaware
County, meanwhile, developed its Coastal Zone Compendium
of Waterfront Provisions (Delaware County, 1998) to guide
revitalization efforts along its coast. Likewise, Bucks County
just finished a national search for a design firm to create a
comprehensive plan outlining the revitalization of its water-
front. Meanwhile, the Schuylkill River Development Corpo-
ration produced the Tidal Schuylkill River Master Plan.
All of these plans and visions share common elements. They
view the region's waterfronts as valuable public amenities
that can be capitalized on, and they view the estuary as
something for the region to embrace, not to turn its back on.
They emphasize public access along the water's edge, the
creation of greenways and trails, open spaces, and the resto-
ration of natural shorelines and wetlands where appropriate
(DRCC, 2006).
Between Delaware and Chesapeake Bays is the land com-
monly known as the Delmarva Peninsula. The Atlantic coast
of the Delmarva consists mostly of barrier islands separated
by tidal inlets of various sizes (Theiler and Hammar-Klose,
1999; Titus et al, 1985). Behind these barrier islands, shallow
estuaries and tidal wetlands are found. The large area of tidal
wetlands behind Virginia's barrier islands to the south are
mostly mudflats; marshes and shallow open water are more
common in Maryland and adjacent portions of Virginia and
Delaware. The barrier islands themselves are a small portion
of the low land in this region (Titus and Richman, 2001). The
northern portion of the Delaware shore consists of headlands,
rather than barrier islands (see Chapter 3 of this Product).
All .E.I Environmental Implications
Tidal Marshes and Marsh Islands. The region's tidal marshes
and marsh-fringed bay islands provide roosting, nesting, and
foraging areas for a variety of bird species, both common
and rare, including shorebirds (piping plover, American
oystercatcher, spotted sandpiper), waterbirds (gull-billed,
royal, sandwich, and least terns and black ducks), and wading
birds such as herons and egrets (Conley, 2004). Particularly
at low tide, the marshes provide forage for shorebirds such
as sandpipers, plovers, dunlins, and sanderlings (Burger
et al., 1997). Ducks and geese, including Atlantic brants,
buffleheads, mergansers, and goldeneyes, overwinter in the
bays' marshes (DNREC, undated). The marshes also provide
nesting habitat for many species of concern to federal and
state agencies, including American black duck, Nelson's
sparrow, salt marsh sharp-tailed sparrow, seaside sparrow,
coastal plain swamp sparrow, black rail, Forster's tern, gull-
billed tern, black skimmers, and American oystercatchers
(Erwine/a/.,2006).
The marshes of the bay islands in particular are key resources
for birds, due to their relative isolation and protection from
predators and to the proximity to both upland and intertidal
habitat. For example, hundreds of horned grebes prepare for
migration at the north end of Rehoboth Bay near Thompson's
Island (Ednie, undated; Strange, 2008c). Several bird species
of concern in this region nest on shell piles (shellrake) on
marsh islands, including gull-billed terns, common terns,
black skimmers, royal tern, and American oystercatchers
(Erwin, 1996; Rounds et al., 2004). Dredge spoil islands in
particular are a favorite nesting spot for the spotted sandpiper,
which has a state conservation status of vulnerable to criti-
cally imperiled in Maryland, Delaware, and Virginia (Na-
tureserve, 2008; Strange 2008c). However, marsh islands are
211
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Appendix I
also subject to tidal flooding, which reduces the reproductive
success of island-nesting birds (Eyleretal., 1999).
Sea-level rise is considered a major threat to bird species
in the Virginia Barrier Island/Lagoon Important Bird Area
(IBA) (Watts, 2006; Strange 2008d). Biologists at the Patux-
ent Wildlife Research Center suggest that submergence of
lagoonal marshes in Virginia would have a major negative
effect on marsh-nesting birds such as black rails, seaside
sparrows, saltmarsh sharp-tailed sparrows, clapper rails,
and Forster's terns (Erwin et al., 2004). The U.S. Fish and
Wildlife Service considers black rail and both sparrow spe-
cies "birds of conservation concern" because populations are
already declining in much of their range (USF WS, 2002). The
number of bird species in Virginia marshes was found to be
directly related to marsh size; the minimum marsh size found
to support significant marsh bird communities was 4 to 7 ha
(10 to 15 ac) (Watts, 1993; Strange, 2008d).
The region's tidal marshes also support a diversity of resident
and transient estuarine and marine fish and shellfish spe-
cies that move in and out of marshes with the tides to take
advantage of the abundance of decomposing plants in the
marsh, the availability of invertebrate prey, and refuge from
predators (Boesch and Turner, 1984; Kneib, 1997). Marine
transients include recreationally and commercially important
species that depend on the marshes for spawning and nursery
habitat, including black drum, striped bass, bluefish, Atlantic
croaker, sea trout, and summer flounder. Important forage
fish that spawn in local marsh areas include spot, menhaden,
silver perch, and bay anchovy. Shellfish species found in the
marshes include clams, oysters, shrimps, ribbed mussels, and
blue crabs (Casey and Doctor, 2004).
Salt Marsh Adaptation to Sea-level Rise. Salt marshes occupy
thousands of acres in eastern Accomack and Northampton
counties in Virginia (Fleming et al., 2006). Marsh accretion
experts believe that most of these marshes are keeping pace
with current rates of sea-level rise, but are unlikely to continue
to do so if the rate of sea-level rise increases by another 2 mm
per year (Strange 2008c, interpreting the findings of Reed et
al., 2008). However, some very localized field measurements
indicate that accretion rates may be insufficient to keep pace
even with current rates of sea-level rise (Strange, 2008d). For
instance, accretion rates as low as 0.9 mm per year (Phillips
Creek Marsh) and as high as 2.1 mm per year (Chimney Pole
Marsh) have been reported (Kastler and Wiberg, 1996), and
the average relative sea-level rise along the Eastern Shore is
estimated as 2.8 to 4.2 mm per year (May, 2002).
In some areas, marshes may be able to migrate onto adjoining
dry lands. For instance, lands in Worcester County that are
held for the preservation of the coastal environment might
allow for wetland migration. Portions of eastern Accomack
County that are opposite the barrier islands and lagoonal
marshes owned by The Nature Conservancy are lightly devel-
oped today, and in some cases already converting to marsh.
In unprotected areas, marshes may be able to migrate inland
in low-lying areas. From 1938 to 1990 mainland salt marshes
on the Eastern Shore increased in area by 8.2 percent, largely
as a result of encroachment of salt marsh into upland areas
(Kastler and Wiberg, 1996).
The marsh islands of the coastal bays are undergoing rapid
erosion; for example, Big Piney Island in Rehoboth Bay
experienced erosion rates of 10 m (30 ft) per year between
1968 and 1981, and is now gone (Swisher, 1982; Strange et
al., 2008). Seal Island in Little Assawoman Bay is eroding
rapidly after being nearly totally devegetatedby greater snow
geese (Strange, 2008c). Island shrinking is also apparent
along the Accomack County, Virginia shore; from 1949 to
1990, Chimney Pole marsh showed a 10-percent loss to open
water (Kastler and Wiberg, 1996). The U.S. Army Corps of
Engineers (USAGE) has created many small dredge spoil
islands in the region, many of which are also disappearing
as a result of erosion (USACE, 2006c).
Sea-Level Fens. The rare sea-level fen vegetation community
is found in a few locations along the coastal bays, including
the Angola Neck Natural Area along Rehoboth Bay in Dela-
ware and the Mutton Hunk Fen Natural Area Preserve front-
ing Gargathy Bay in eastern Accomack County (VA OCR,
undated[a][b]). The Division of Natural Heritage within the
Virginia Department of Conservation and Recreation believes
that chronic sea-level rise with intrusions of tidal flooding
and salinity poses "a serious threat to the long-term viability"
of sea-level fens (VA OCR, 2001).
Shallow Waters and Submerged Aquatic Vegetation (SAV).
Eelgrass beds are essential habitat for summer flounder,
bay scallop, and blue crab, all of which support substantial
recreational and commercial fisheries in the coastal bays
(MCBP, 1999). Various waterbirds feed on eelgrass beds,
including brant, canvasback duck, and American black duck
(Perry and Deller, 1996). Shallow water areas of the coastal
bays that can maintain higher salinities also feature beds of
hard and surf clams (DNREC, 2001).
Tidal Flats. Abundant tidal flats in this region provide a
rich invertebrate food source for a number of bird species,
including whimbrels, dowitchers, dunlins, black-bellied
plovers, and semi-palmated sandpipers (Watts and Truitt,
2000). Loss of these flats could have significant impacts.
The Nature Conservancy has placed a priority on preserv-
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to
A Focus on the. Mid-Atlantic Region
ing these flats based on the assumption that 80 percent of
the Northern Hemisphere's whimbrel population feed on
area flats, in large part on fiddler crabs (TNC, 2006). The
whimbrel is considered a species "of conservation concern"
by the U.S. Fish and Wildlife Service, Division of Migratory
Bird Management (USFWS, 2002).
Beaches. Loss of beach habitat due to sea-level rise and
erosion below protective structures could have a number of
negative consequences for species that use these beaches:
Horseshoe crabs rarely spawn unless sand is at least
deep enough to nearly cover their bodies, about 10
cm (4 inches [in]) (Weber, 2001). Shoreline protection
structures designed to slow beach loss can also block
horseshoe crab access to beaches and can entrap or strand
spawning crabs when wave energy is high (Doctor and
Wazniak, 2005).
The rare northeastern tiger beetle depends on beach
habitat (USFWS, 2004b).
Photuris bethaniensis is a globally rare firefly located
only in interdunal swales on Delaware barrier beaches
(DNREC, 2001).
Erosion and inundation may reduce or eliminate beach
wrack communities of the upper beach, especially in
developed areas where shores are protected (Strange,
2008c). Beach wrack contains insects and crustaceans
that provide food for many species, including migrating
shorebirds (Dugan et al., 2003).
Many rare beach-nesting birds, such as piping plover,
least tern, common tern, black skimmer, and American
oystercatcher, nest on the beaches of the coastal bays
(DNREC, 2001).
Coastal Habitat for Migrating Neotropical Songbirds.
Southern Northampton County is one of the most important
bird areas along the Atlantic Coast of North America for
migrating neotropical songbirds such as indigo buntings and
ruby-throated hummingbirds (Watts, 2006; Strange 2008d).
Not only are these birds valued for their beauty but they also
serve important functions in dispersing seeds and control-
ling insect pests. It is estimated that a pair of warblers can
consume thousands of insects as they raise a brood (Mabey
et al., undated). Migrating birds concentrate within the tree
canopy and thick understory vegetation found within the
lower 10 km (6 mi) of the peninsula within 200 m (650 ft) of
the shoreline. Loss of this understory vegetation as a result
of rising seas would eliminate this critical stopover area for
neotropical migrants, many of which have shown consistent
population declines since the early 1970s (Mabey et al., un-
dated; Strange, 2008d).
AI.E.2
ALE,2,1 ATLANTIC COAST
Less than one-fifth of the Delmarva's ocean coast is devel-
oped, and the remaining lands are owned by private conser-
vation organizations or government agencies. Almost all of
the Virginia Eastern Shore's 124-km (77-mi) ocean coast is
owned by the U.S. Fish and Wildlife Service, NASA, the state,
or The Nature Conservancy21. Of Maryland's 51 km (32 mi)
of ocean coast, 36 km (22 mi) are along Assateague Island
National Seashore. The densely populated Ocean City occu-
pies approximately 15 km (9 mi). More than three-quarters of
the barrier islands and spits in Delaware are part of Delaware
Seashore State Park, while the mainland coast is about evenly
divided between Cape Henlopen State Park and resort towns
such as Rehoboth, Dewey Beach, and Bethany Beach. With
approximately 15 km of developed ocean coast each, Mary-
land and Delaware have pursued beach nourishment to protect
valuable coastal property and preserve the beaches that make
the property so valuable (Hedrick et al., 2000).
Because development accounts for only 15 to 20 percent of
the ocean coast, the natural shoreline processes are likely to
dominate along most of these shores. Within developed areas,
counteracting shoreline erosion in developed areas withbeach
nourishment may continue as the primary activity in the
near term. A successful alternative to beach nourishment, as
demonstrated by a USAGE (2001a) and National Park Service
project to mitigate jetty impacts along Assateague Island, is
to restore sediment transport rates by mechanically bypassing
sand from the inlet and tidal deltas into the shallow nearshore
areas that have been starved of their natural sand supply.
Beginning in 1990, the USAGE and the Assateague Island
National Seashore partnered to develop a comprehensive
restoration plan for the northern end of Assateague Island.
The "North End Restoration Project" included two phases.
The first phase, completed in 2002, provided a one-time
placement of sand to replace a portion of sand lost over the
past 60 years due to the formation of the inlet and subsequent
jetty stabilization efforts. The second phase is focused on
re-establishing a natural sediment supply by mechanically
bypassing sand from the inlet and tidal deltas into the shal-
low nearshore areas22.
ALE,2,2 COASTAL BAY SHORES
The mainland along the back-barrier bays has been developed
to a greater extent than the respective ocean coast in all three
states (MRLCC, 2002; MDP, 1999; DOSP, 1997). Along the
coastal bays, market forces have led to extensive develop-
21 A few residential structures are on Cedar Island, and Cobbs and Hog
islands have some small private inholdings (Ayers, 2005).
22 See .
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I
Logistically, the easiest time to elevate low land is when it is still vacant, or during a coordinated rebuilding. Low
parts of Ocean City's bay side were elevated during the initial construction. As sea level rises, the town of Ocean
City has started thinking about how it might ultimately elevate.
Ocean City's relatively high bay sides make it much less vulnerable to inundation by spring tides than other barrier
islands. Still, some streets are below the 10-year flood plain, and as sea level rises, flooding will become increasingly
frequent.
However, the town cannot elevate the lowest streets without considering the implications for adjacent properties.
A town ordinance requires property owners to maintain a 2-percent grade so that yards drain into the street. The
town construes this rule as imposing a reciprocal responsibility on the town itself to not elevate roadways above
the level where yards can drain, even if the road is low enough to flood during minor tidal surges. Thus, the lowest
lot in a given area dictates how high the street can be.
As sea level rises, failure by a single property owner to elevate could prevent the town from elevating its streets,
unless it changes this rule. Yet public health reasons require drainage, to prevent standing water in which mosqui-
toes breed. Therefore, the town has an interest in ensuring that all property owners gradually elevate their yards
so that the streets can be elevated as the sea rises without causing public health problems.
The Town of Ocean City (2003) has developed draft rules that would require that, during any significant con-
struction, yards be elevated enough to drain during a 10-year storm surge for the life of the project, considering
projections of future sea-level rise. The draft rules also state that Ocean City's policy is for all land to gradually be
elevated as the sea rises.
ment at the northern end of the Delmarva due to the rela-
tively close proximity to Washington, D.C., Baltimore, and
Philadelphia. Although connected to the densely populated
Hampton Roads area by the Chesapeake Bay Bridge-Tunnel,
southern portions of the Delmarva are not as developed as
the shoreline to the north. Worcester County, Maryland,
reflects a balance between development and environmental
protection resulting from both recognition of existing market
forces and a conscious decision to preserve Chincoteague
Bay. Development is extensive along most shores opposite
Ocean City and along the bay shores near Ocean City Inlet.
In the southern portion of the county, conservation easements
or the Critical Areas Act preclude development along most of
the shore. Although the Critical Areas Act encourages shore
protection, and conservation easements in Maryland preserve
the right to armor the shore (MET, 2006), these low-lying
lands are more vulnerable to inundation than erosion (e.g.,
Titus et al., 1991) and are therefore possible candidates for
wetland migration.
Of the three states, Maryland has the most stringent policies
governing development along coastal bays. Under the Chesa-
peake and Atlantic Coastal Bays Critical Areas Protection
Program, new development must be set back at least 100 ft
from tidal wetlands or open water23. In most undeveloped
areas, the statute also limits future development density to one
home per 8.1 ha (20 ac) within 305 m (1000 ft) of the shore24
and requires a 61-m (200-ft) setback25. In Virginia, new de-
velopment must be setback at least 30.5 m (100 ft) (see Sec-
tion A1.F.2 in this Appendix for additional discussion of the
Maryland and Virginia policies). The Delaware Department
of Natural Resources has proposed a 30.5-ft setback along
the coastal bays (DNREC, 2007); Sussex County currently
requires a 15.2-m (50-ft) setback26.
While shore protection is currently more of a priority along
the Atlantic Ocean coast, preventing the inundation of low-
lying lands along coastal bays may eventually be necessary as
well. Elevating these low areas appears to be more practical
than erecting a dike around a narrow barrier island (Titus,
1990). Most land surfaces on the bayside of Ocean City
were elevated during the initial construction of residences
(McGean, 2003). In an appendix for U.S. EPAs 1989 Report
to Congress, Leatherman (1989) concluded that the only por-
tion of Fenwick Island where bayside property would have
to be elevated with a 50-cm (20-in) rise in sea level would be
the portion in Delaware (i.e., outside of Ocean City). He also
concluded that Wallops Island, South Bethany, Bethany, and
23 Maryland Natural Resources Code
Regulations §27.01.09.01 (C).
8-1807(a); Code of Maryland
24 Code of Maryland Regulations §27.01.02.05(C)(4).
25 Maryland Natural Resources Code §8-1808.10.
26 Sussex County, DE. 2007. Buffer zones for wetlands and tidal and
perennial non-tidal waters. §115-193, Sussex County Code. Enacted
July 19, 1988 by Ord. No. 521.
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Rehoboth Beach are high enough to avoid tidal inundation
for the first 50 to 100 cm (20 to 40 in) of sea-level rise. The
Town of Ocean City has begun to consider how to respond to
address some of the logistical problems of elevating a densely
developed barrier island (see Box A1.5).
The Maryland Coastal Bays Program considers erosion (due
to sea-level rise) and shoreline hardening major factors that
contribute to a decline in natural shoreline habitat available
for estuarine species in the northern bays (MCBP, 1999).
Much of the shoreline of Maryland's northern coastal bays
is protected using bulkheads or stone riprap, resulting in
unstable sediments and loss of wetlands and shallow water
habitat (MCBP, 1999). Armoring these shorelines will prevent
inland migration of marshes, and any remaining fringing
marshes will ultimately be lost (Strange 2008c). The Coastal
Bays Program estimated that more than 600 ha (1,500 ac) of
salt marshes have already been lost in the coastal bays as a
result of shoreline development and stabilization techniques
(MCBP, 1999). If shores in the southern part of Maryland's
coastal bays remain unprotected, marshes in low-lying areas
would be allowed to potentially (see Chapter 4) expand inland
as sea level rises (Strange 2008c).
The Chesapeake Bay region accounts for more than one-third
of the lowland in the Mid-Atlantic (see Titus and Richman,
2001). Accordingly, the first subsection (Al.F.l) on develop-
ment, shore protection, and vulnerable habitat divides the re-
gion into seven subregions. Starting with Hampton Roads, the
subsections proceed clockwise around the Bay to Virginia's
Middle Peninsula and Northern Neck, then up the Potomac
River to Washington, D.C., then up Maryland's Western
Shore, around to the Upper Eastern Shore, and finally down
to the Lower Eastern Shore. The discussions for Virginia are
largely organized by planning district; the Maryland discus-
sions are organized by major section of shore. The second
subsection compares the coastal policies of Maryland and
Virginia that are most relevant to how these states respond
to rising sea level27.
AI.F.I Development, Protection,
Vulnerable
Ai.F.l.i HAMPTON ROADS
Most of the vulnerable dry land in the HamptonRoads region
is located within Virginia Beach and Chesapeake. These low
areas are not, however, in the urban portions of those jurisdic-
tions. Most of Virginia Beach's very low land is either along
27 As this report was being finalized, a comprehensive study of the
impacts of sea-level rise on the Chesapeake Bay region was completed
by the National Wildlife Federation (Click et al, 2008).
the back-barrier bays near the North Carolina border, or along
the North Landing River. Most of Chesapeake's low land is
around the Northwest River near the North Carolina border,
or the along the Intracoastal Waterway. The localities located
farther up the James and York rivers have less low land. An
important exception is historic Jamestown Island, which has
been gradually submerged by the rising tides since the colony
was established 400 years ago (see Box 11.1 in Chapter 11).
Development and Shore Protection
Norfolk is home to the central business district of the Hamp-
ton Roads region. Newport News has similar development
to Norfolk along its southern shores, with bluffs giving rise
to less dense residential areas further north along the coast.
The city of Hampton is also highly developed, but overall
has a much smaller percentage of commercial and industrial
development than Norfolk or Newport News.
Outside of the urban core, localities are more rural in nature.
These localities find themselves facing mounting develop-
ment pressures and their comprehensive plans outline how
they plan to respond to these pressures (e.g., Suffolk, 1998;
York County, 1999; James City County, 2003; Isle of Wight
County, 2001). Overall, however, the makeup of these out-
lying localities is a mix of urban and rural development,
with historic towns and residential development dotting the
landscape.
Virginia Beach has sandy shores along both the Atlantic
Ocean and the mouth of Chesapeake Bay. Dunes dominate
the bay shore, but much of the developed ocean shore is
protected by a seawall, and periodic beach nourishment has
occurred since the mid-1950s (Hardaway etai, 2005). Along
Chesapeake Bay, by contrast, the Virginia Beach shore has
substantial dunes, with homes set well back from the shore
in some areas. Although the ground is relatively high, beach
nourishment has been required on the bay beaches at Ocean
Park (Hardaway et al., 2005). Norfolk has maintained its
beaches along Chesapeake Bay mostly with breakwaters and
groins. Shores along other bodies of water are being armored.
Of Norfolk's 269 km (167 mi) of shoreline, 113 km (70 mi)
have been hardened (Berman et al., 2000).
Overall trends in the last century show the dunes east of the
Lynn Haven inlet advancing into the Bay (Shellenbarger
Jones and Bosch, 2008c). West from the inlet, erosion, beach
nourishment, and fill operations as well as condominium
development and shoreline armoring have affected the ac-
cretion and erosion patterns (Hardaway et al., 2005). Along
the shores of Norfolk, the rate of erosion is generally low, and
beach accretion occurs along much of the shore (Berman et
al., 2000). Most of the shore along Chesapeake Bay is pro-
tected by groins and breakwaters, and hence relatively stable
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Appendix I
(Hardaway etal., 2005). On the other side of the James River,
the bay shoreline is dominated by marshes, many of which
are eroding (Shellenbarger Jones and Bosch, 2008c).
Since 1979, Virginia Beach has had a "Green Line", south
of which the city tries to maintain the rural agricultural way
of life. Because development has continued, Virginia Beach
has also established a "Rural Area Line", which coincides
with the Green Line in the eastern part of the city and runs 5
km (3 mi) south of it in the western portion. Below the Rural
Area Line, the city strongly discourages development and
encourages rural legacy and conservation easements (VBCP,
2003). In effect, the city's plan to preserve rural areas will
also serve to preserve the coastal environment as sea level
rises throughout the coming century and beyond (see Sec-
tions 6.1.3, 6.2, 10.3). To the west, by contrast, the City of
Chesapeake is encouraging development in the rural areas,
particularly along major corridors. Comprehensive plans
in the more rural counties such as Isle of Wight and James
City tend to focus less on preserving open space and more
on encouraging growth in designated areas (Isle of Wight,
2001; James City County, 2003). Therefore, these more remote
areas may present the best opportunity for long-range plan-
ning to minimize coastal hazards and preserve the ability of
ecosystems to migrate inland.
Vulnerable Habitat
Much of the tidal wetlands in the area are within Poquoson's
Plum Tree Island National Wildlife Refuge. Unlike most
mid-Atlantic wetlands, these wetlands are unlikely to keep
pace with the current rate of sea-level rise (Shellenbarger
Jones and Bosch, 2008c, interpreting the findings of Reed
et al., 2008). The relative isolation of the area has made it
a haven for over 100 different species of birds. The refuge
has substantial forested dune hummocks (CPCP, 1999), and
a variety of mammals use the higher ground of the refuge.
Endangered sea turtles, primarily the loggerhead, use the
near shore waters. Oyster, clams, and blue crabs inhabit the
shallow waters and mudflats, and striped bass, mullet, spot,
and white perch have been found in the near shore waters and
marsh (USFWS, undated[b]).
The wetlands in York County appear able to keep pace with
the current rate of sea-level rise. Assuming that they are
typical of most wetlands on the western side of Chesapeake
Bay, they are likely to become marginal with a modest ac-
celeration and be lost if sea-level rise accelerates to 1 cm per
year (Shellenbarger Jones and Bosch, 2008c, interpreting the
findings of Reed et al., 2008). Bald eagles currently nest in the
Goodwin Islands National Estuarine Research Reserve (Watts
and Markham, 2003; Shellenbarger Jones and Bosch 2008c).
This reserve includes intertidal flats, 100 ha (300 ac) of eel-
grass and widgeon grass (VIMS, undated), and salt marshes
dominated by salt marsh cordgrass and salt meadow hay.
AI.F.1.2 TO
Two planning districts lie between the York and Potomac riv-
ers. The Middle Peninsula Planning District includes the land
between the York and Rappahannock rivers. The Northern
Neck is between the Rappahannock and Potomac rivers.
Development and Shore Protection
A large portion of the necks along Mobjack Bay has a con-
servation zoning that allows only low-density residential
development "in a manner which protects natural resources
in a sensitive environment28. The intent is to preserve contigu-
ous open spaces and protect the surrounding wetlands29. The
county also seeks to maintain coastal ecosystems important
for crabbing and fishing. As a result, existing land use would
not prevent wetlands and beaches along Mobjack Bay from
migrating inland as sea level rises.
Gloucester County also has suburban countryside zoning,
which allows for low-density residential development, includ-
ing clustered sub-developments30 along part of the Guinea
Neck and along the York River between Carter Creek and
the Catlett islands. These developments often leave some
open space that might convert to wetlands as sea level rises
even if the development itself is protected. The county plan
anticipates development along most of the York River. Never-
theless, a number of areas are off limits to development. For
example, the Catlett islands are part of the Chesapeake Bay
National Estuarine Research Reserve in Virginia, managed
as a conservation area31.
Along the Northern Neck, shoreline armoring is already very
common, especially along Chesapeake Bay and the Rappah-
annock River shores of Lancaster County. Above Lancaster
County, however, development is relatively sparse along the
Rappahannock River and shoreline armoring is not common.
Development and shoreline armoring are proceeding along
the Potomac River.
28 Gloucester County Code of Ordinances, accessed through Municode
Online Codes: : "The intent of the SC-1 district is to allow
low density residential development... Cluster development is encour-
aged in order to protect environmental and scenic resources".
29 Gloucester County Code of Ordinances, accessed through Municode
Online Codes; .
30 Definition of suburban countryside in Gloucester County Code
of Ordinances, accessed through Municode Online Codes: :
"The intent of the SC-1 district is to allow low density residential
development.. .Cluster development is encouraged in order to protect
environmental and scenic resources".
31 See the Research Reserve's web page at .
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to
A Focus on the Mid-Atlantic Region
Vulnerable Habitat
Like the marshes of Poquosonto the south, the marshes of the
Guinea Neck and adjacent islands are not keeping pace with
the current rates of sea-level rise (Shellenbarger Jones and
Bosch, 2008a, interpreting the findings of Reed et al., 2008).
For more than three decades, scientists have documented their
migration onto farms and forests (Moore, 1976). Thus, the
continued survival of these marshes depends on land-use and
shore protection decisions.
Upstream from the Guinea Neck, sea-level rise is evident
in the York River's tributaries, not because wetlands are
converting to open water but because the composition of
wetlands is changing. Along the Pamunkey and Mattaponi
rivers, dead trees reveal that tidal hardwood swamps are
converting to brackish or freshwater marsh as the water level
rises (Rheinhardt, 2007). Tidal hardwood swamps provide
nesting sites for piscivorous (fish eating) species such as os-
preys, bald eagles, and double-crested cormorants (Robbins
and Blom, 1996).
In Mathews County, Bethel Beach (a natural area preserve
separating Winter Harbor from Chesapeake Bay) is currently
migrating inland over an extensive salt marsh area (Shel-
lenbarger Jones and Bosch, 2008a). The beach is currently
undergoing high erosion (Berman et al., 2000), and is home to
a population of the Northeastern beach tiger beetle (federally
listed as threatened) and a nesting site for rare least terns,
which scour shallow nests in the sand (VA DCR, 1999). In
the overwash zone extending toward the marsh, a rare plant
is present, the sea-beach knotweed (Polygonum glaucum)
(VA DCR, 1999). The marsh is also one of few Chesapeake
Bay nesting sites for northern harriers (Circus cyaneus), a
hawk that is more commonly found in regions further north
(VA DCR, 1999). As long as the shore is able to migrate,
these habitats will remain intact; but eventually, overwash
and inundation of the marsh could reduce habitat populations
(Shellenbarger Jones and Bosch, 2008a).
AI.F. 1.3 THE POTOMAC RIVER
Virginia Side. Many coastal homes are along bluffs, some
of which are eroding (Bernd-Cohen and Gordon, 1999). Le-
wisetta is one of the larger vulnerable communities along the
Potomac. Water in some ditches rise and fall with the tides,
and some areas drain through tide gates. With a fairly modest
rise in sea level, one could predict that wetlands may begin
to take over portions of people's yards, the tide gates could
close more often, and flooding could become more frequent.
Somewhat higher in elevation than Lewisetta, Old Town
Alexandria and Belle Haven (Fairfax County) both flood
occasionally from high levels in the Potomac River.
Maryland Side. Much of the low-lying land is concentrated
around St. George Island and Piney Point in St. Mary's
County, and along the Wicomico River and along Neal Sound
opposite Cobb Island in Charles County. Relatively steep
bluffs, however, are also common.
Development and Shore Protection
West of Chesapeake Bay, the southwestern shoreline of the
Potomac River is the border between Maryland and Vir-
ginia32. As a result, islands in the Potomac River, no matter
how close they are to the Virginia side of the river, are part
of Maryland or the District of Columbia. Moreover, most
efforts to control erosion along the Virginia shore take place
partly in Maryland (or the District of Columbia) and thus
could potentially be subject to Maryland (or Washington,
D.C.) policies33.
Development is proceeding along approximately two-thirds of
the Potomac River shore. Nevertheless, most shores in Charles
County, Maryland are in the resource conservation area
defined by the state's Critical Areas Act (and hence limited
to one home per 8.1 ha [20 ac]) (MD DNR, 2007). A signifi-
cant portion of Prince George's County's shoreline along the
Potomac and its tributaries are owned by the National Park
Service and other conservation entities that seek to preserve
the coastal environment (MD DNR, 2000).
In Virginia, parks also account for a significant portion of the
shore (ESRI, 1999). In King George County, several develop-
ers have set development back from low-lying marsh areas,
which avoids problems associated with flooding and poor
drainage. Water and sewer regulations that only apply for lot
sizes less than 4 ha (10 ac) may provide an incentive for larger
lot sizes. In Stafford County, the CSX railroad line follows
the river for several miles, and is set back to allow shores to
erode, but not so far back as to allow for development between
the railroad and the shore (ADC, 2008).
Vulnerable Habitat
The Lower Potomac River includes a diverse mix of land uses
and habitat types. Freshwater tidal marshes in the Lower
Potomac are found in the upper reaches of tidal tributaries.
In general, freshwater tidal marshes in the Lower Potomac
are keeping pace with sea-level rise through sediment and
peat accumulation, and are likely to continue to do so, even
under higher sea-level rise scenarios (Strange and Shellen-
barger Jones, 2008a, interpreting the findings of Reed et al.,
2008).
32 See Maryland v. Virginia, 540 US (2003).
33 The Virginia Shore across from Washington, D.C. is mostly owned
by the federal government, which would be exempt from District of
Columbia policies.
217
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Appendix i
Brackish tidal marshes are a major feature of the downstream
portions of the region's rivers. In general, these marshes are
keeping pace with sea-level rise today, but are likely to be
marginal if sea-level rise accelerates by 2 mm per year, and
be lost if sea-level rise accelerates 7 mm per year (Strange and
Shellenbarger Jones, 2008a, interpreting the findings of Reed
et al., 2008). Loss of brackish tidal marshes would eliminate
nesting, foraging, roosting, and stopover areas for migrating
birds (Strange and Shellenbarger Jones, 2008a). Significant
concentrations of migrating waterfowl forage and overwinter
in these marshes in fall and winter. Rails, coots, and migrant
shorebirds are transient species that feed on fish and inver-
tebrates in and around the marshes and tidal creeks (Strange
and Shellenbarger Jones, 2008a). The rich food resources of
the tidal marshes also support rare bird species such as bald
eagle and northern harrier (White, 1989).
Unnourished beaches and tidal flats of the Lower Potomac
are likely to erode as sea levels rise. Impacts on beaches are
highly dependent on the nature of shoreline protection mea-
sures selected for a specific area. For example, the developed
areas of Wicomico Beach and Cobb Island are at the mouth of
the Wicomico River in Maryland. Assuming that the shores of
Cobb Island continue to be protected, sea-level rise is likely
to eliminate most of the island's remaining beaches and tidal
flats (Strange and Shellenbarger Jones, 2008a).
Finally, where the cliffs and bluffs along the Lower Potomac
are not protected (e.g., Westmoreland State Park, Caledon
Natural Area), natural erosional processes will generally
continue, helping to maintain the beaches below (Strange and
Shellenbarger Jones, 2008a).
Above Indian Head, the Potomac River is fresh. Tidal wet-
lands are likely to generally keep pace with rising sea level
in these areas (see Chapter 4 of this Product). Nevertheless,
the Dyke Marsh Preserve faces an uncertain future. Its fresh-
water tidal marsh and adjacent mud flats are one of the last
major remnants of the freshwater tidal marshes of the Upper
Potomac River (Johnston, 2000). A recent survey found 62
species offish, nine species of amphibians, seven species of
turtles, two species of lizards, three species of snakes, 34
species of mammals, and 76 species of birds in Dyke Marsh
(Engelhardt et al., 2005; Strange and Shellenbarger Jones,
2008b). Many of the fish species present (e.g., striped bass,
American shad, yellow perch, blueback herring) are impor-
tant for commercial and recreational fisheries in the area
(Mangold e/a/., 2004).
Parklands on the Mason Neck Peninsula are managed for
conservation, but shoreline protection on adjacent lands may
result in marsh loss and reduced abundance of key bird spe-
cies (Strange and Shellenbarger Jones, 2008b). The Mason
Neck National Wildlife Refuge hosts seven nesting bald
eagle pairs and up to 100 bald eagles during winter, has one
of the largest great blue heron colonies in Virginia, provides
nesting areas for hawks and waterfowl, and is a stopover for
migratory birds.
AI.F.1.4 DISTRICT OF
Within the downtown area, most of the lowest land is the
area filled during the 1870s, such as Hains Point and the
location of the former Tiber and James Creeks, as well as
the Washington City Canal that joined them (See Box 6.2
in Chapter 6). The largest low area is the former Naval Air
Station, now part of Boiling Air Force Base, just south of the
mouth of the Anacostia River, which was part of the mouth
of the Anacostia River during colonial times. A dike protects
this area, where most of the low land between Interstate-295
and the Anacostia River was open water when the city of
Washington was originally planned.
Development and Shore Protection
The central city is not likely to be given up to rising sea
level; city officials are currently discussing the flood control
infrastructure necessary to avoid portions of the downtown
area from being classified as part of the 100-year f loodplain.
Nevertheless, natural areas in the city account for a substan-
tial portion of the city's shore, such as Roosevelt Island and
the shores of the Potomac River within C&O Canal National
Historic Park.
As part of the city's efforts to restore the Anacostia River,
District officials have proposed a series of environmental
protection buffers along the Anacostia River with widths
between 15.2 and 91.4 m (50 and 300 ft). Bulkheads are
being removed except where they are needed for naviga-
tion, in favor of natural shores in the upper part of the river
and bioengineered "living shorelines" in the lower portion
(DCOP, 2003).
Vulnerable Habitat
The Washington, D.C. area features sensitive wetland habitats
potentially vulnerable to sea-level rise. Several major areas
are managed for conservation or are the target of restoration
efforts, making ultimate impacts uncertain. The wetlands
around the Anacostia River are an example. Local organiza-
tions have been working to reverse historical modifications
and restore some of the wetlands around several heavily
altered lakes. Restoration of the 13-ha (32-ac) Kenilworth
Marsh was completed in 1993; restoration of the Kingman
Lake marshes began in 2000 (USGS, undated). Monitoring of
the restored habitats demonstrates that these marshes can be
very productive. A recent survey identified 177 bird species
in the marshes, including shorebirds, gulls, terns, passerines,
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A Focus on the Mid-Atlantic Region
and raptors as well as marsh nesting species such as marsh
wren and swamp sparrow (Paul et al., 2004).
Roosevelt Island is another area where sea-level rise effects
are uncertain. Fish in the Roosevelt Island marsh provide food
for herons, egrets, and other marsh birds (NFS, undated). The
ability of the tidal marshes of the island to keep pace with
sea-level rise will depend on the supply of sediment, and in-
creased inundation of the swamp forest could result in crown
dieback and tree mortality (Fleming et al., 2006).
Al.l .1.5 WESTERN SHORE: POTOMAC RIVER TO
SUSQUEHANNA RIVER
The Western Shore counties have relatively little low land,
unlike the low counties across the Bay. The Deale/Shady Side
Peninsula (Anne Arundel County) and Aberdeen Proving
Grounds (Harford County) are the only areas with substantial
amounts of low-lying land. The block closest to the water,
however, is similarly low in many of the older communities,
including parts of Baltimore County, Fells Point in Baltimore
(see Box A1.6), downtown Annapolis, North Beach, and
Chesapeake Beach, all of which flooded during Hurricane
Isabel.
Between the Potomac and the Patuxent rivers, the bay shore
is usually a sandy beach in front of a bank less than 3 m (10
ft) high. Cliffs and bluffs up to 35 m (115 ft) above the water
dominate the shores of Calvert County (Shellenbarger Jones
and Bosch, 2008b). The shores north of Calvert County tend
to be beaches; but these beaches become narrower as one
proceeds north, where the wave climate is milder.
Development and Shore Protection
The Western Shore was largely developed before Maryland's
Critical Areas Act was passed. Stone revetments are common
along the mostly developed shores of Anne Arundel and Bal-
timore counties. Yet Calvert County has one of the only shore
protection policies in the nation that prohibits shore protection
along an estuary, even when the prohibition means that homes
will be lost. Calvert County's erosion policy is designed to
preserve unique cliff areas that border Chesapeake Bay.
The county allows shoreline armoring in certain developed
areas to protect property interests, but also bans armoring
in other areas to protect endangered species and the unique
landscape34. Cliffs in Calvert County are separated into cat-
egories according to the priority for preservation of the land.
Although a county policy prohibiting shore protection would
appear to run counter to the state law granting riparian own-
34 Calvert County Zoning Ordinance (Revised, June 10, 2008), Article
8, Environmental Requirements; Section 8-2.02, Shoreline and Cliff
Areas on the Chesapeake Bay, Patuxent River, and their tributaries
.
ers the right to shore protection, to date no legal challenges
to the cliff policy have been made. The state has accepted the
county's policy, which is embodied in the county's critical
areas plan submitted to the state under the Critical Areas Act.
Recognizing the potential environmental implications, living
shoreline protection is becoming increasingly commonplace
along the Western Shore.
Vulnerable Habitat
A range of sea-level rise impacts are possible along the
Western Shore of Chesapeake Bay, including potential loss
of key habitats. First, marshes are expected to be marginal
with mid-range increases in sea-level rise, and to be lost with
high-range increases in sea-level rise (Shellenbarger Jones
and Bosch, 2008b, interpreting the findings of Reed et al.,
2008). The ability to migrate is likely to determine coastal
marsh survival as well as the survival of the crustaceans, mol-
lusks, turtles, and birds that depend on the marshes. In upper
reaches of tributaries, however, marsh accretion is likely to be
sufficient to counter sea-level rise (Shellenbarger Jones and
Bosch, 2008b, interpreting the findings of Reed et al, 2008).
Several key locations warrant attention:
In the Jug Bay Sanctuary, along the upper Patuxent
River, marsh inundation is causing vegetation changes,
compounding stress on local bird species (Shellenbarger
Jones and Bosch, 2008b).
Cove Point Marsh in Calvert County is a 60-ha (150-ac)
freshwater, barrier-beach marsh. Numerous state-defined
rare plant species are present, including American frog's-
bit, silver plumegrass, various ferns, and unique wetland
communities (Steury, 2002), as well as several rare or
threatened beetle species. With current rates of sea-level
rise, the marsh is continuing to migrate, but will soon hit
the northern edge of local residential development.
The potential loss of the wide mudflats at Hart-Miller
Island would eliminate major foraging and nesting areas
for several high conservation priority species (Shellen-
barger Jones and Bosch, 2008b).
Given the extent of development and shoreline armor-
ing in Anne Arundel County, Baltimore, and Baltimore
County, both intertidal areas and wetlands are likely to
be lost with even a modest acceleration in sea-level rise
(Shellenbarger Jones and Bosch, 2008b).
Beach loss, particularly in St. Mary's, Calvert, and Anne
Arundel counties along Chesapeake Bay, may occur in ar-
eas without nourishment. In general, beach loss will lead to
habitat loss for resident insects (including the Northeastern
beach tiger beetle, federally listed as threatened) and other
invertebrates, as well as forage loss for larger predators such
as shorebirds (Lippson and Lippson, 2006)35.
35 For more detail on beach habitats and the species that occur in the
mid-Atlantic region, see Shellenbarger Jones (2008a).
219
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The U.S. Climate Change Science Program
Appendix I
BOXAI.6: Planning for Sea-Level Rise in Baltimore
Only 3.2 percent of the City of Baltimore's 210 square kilometer (sq km) (81 square miles [sq mi]) of land is
currently within the coastal floodplain. This land, however, includes popular tourist destinations such as Inner
Harbor and the Fells Point Historic District, as well as industrial areas, some of which are being redeveloped into
mixed use developments with residential, commercial, and retail land uses. The map below depicts the areas that
the city expects to be flooded by category I, 2, 3, and 4 hurricanes, which roughly correspond to water levels
of 1.8 meters (m) (6 feet [ft]), 3.0 m (10 ft), 4.2 m (14 ft), and 5.5 m (18 ft) above North Amercan Vertical Datum
(NAVD88). Approximately 250 homes are vulnerable to a category I, while 700 homes could be flooded by a
category 2 hurricane (Baltimore, 2006). As Hurricane Isabel passed in September 2003, water levels in Baltimore
Harbor generally reached approximately 2.4 m (8 ft) above NAVD, flooding streets and basements, but resulting
in only 16 flood insurance claims (Baltimore, 2006).
City of Baltimore
Hurricane Inundation Zone
Huni«*ne Innundation Zon*
AIM
/'
\S^^
IC-^41.™*™ ^ -S5i V^
«•« *^M» "^^" """- ' ^
Bon Figure AI.6 Inundation Zone for Baltimore Harbor under category I, 2, 3, and 4 hurricanes.
220
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The city's All Hazards Plan explicitly includes rising sea level as one of the factors to be considered in land-use
and infrastructure planning. The All Hazards Plan has as an objective to "develop up-to-date research about haz-
ards" and a strategy under that objective to "study the threat, possible mitigation and policy changes for sea-level
rise". As a first step toward accurate mapping of possible sea-level rise scenarios, the city is exploring options for
acquiring lidar. Policies developed for floodplain management foreshadow the broad methods the city is likely to
use in its response.
Property values are high, and there is a long-standing practice of armoring shores to facilitate port-related activi-
ties and more recently, protect waterfront structures from shore erosion. In most areas, there is not enough
room between the harbor and waterfront buildings to fit a dike. Even where there is room, the loss of waterfront
views would be unacceptable in tourist and residential areas (see Section 6.5 in Chapter 6; Titus, 1990). In addi-
tion, storm sewers, which drain by gravity into the harbor, would have to be fitted with pumping systems.
Fells Point Historic District
This historic community has 24 hectare (ha) (60 acres [ac]) within the 100-year flood plain. Fells Point is a Federal
Historic District and pending approval as a Local Historic District. The row houses here were built predominantly
in the early-to-mid-nineteenth century and cannot be easily elevated. Elevating brick and stone structures is al-
ways more difficult than elevating a wood frame structure. But because row houses are, by definition, attached
to each other, elevating them one at a time is not feasible. Many of these homes have basements, which already
flood. FEMA regulations do not permit basements in new construction in the floodplain, 44 CFR §60.3(c) (2), and
treat existing basements as requiring mitigation. Possible mitigation for basements includes relocation of utilities,
reinforcement of walls, and eliminating the basement by filling it with soil.
In theory, homes could be remodeled to add stairways and doors to convert what is now the second floor to a
first floor and convert the first floors to basements. But doing so would reduce the livable space. Moreover, fed-
eral and local preservation laws, as well as community sensibilities, preclude adding third stories to these homes.
Elevating streets is also problematic because below-grade utilities need to be elevated. In the last decade only one
street (one block of Caroline Street) has been elevated specifically to reduce flooding.
FEMA Flood Hazard Mapping and Sea-Level Rise
Baltimore City is a participating jurisdiction in the National Flood Insurance Program through its regulation of
development in the floodplain and through overall floodplain management. The city is currently funded through
the Cooperative Technical Partnership (CTP) to update its flood maps. Federal flood mapping policies require
that Flood Insurance Rate Maps be based on existing conditions (see Figure 10.5 in Chapter 10). Therefore, the
floodplain maps do not consider future sea-level rise. As a result, the city will be permitting new structures with
effective functional lifespan of 50 to 100 years but elevated only to current flood elevations. One strategy to sur-
mount this limitation is to add "freeboard", or additional elevation to the effective BFE. Baltimore already requires
one additional foot of freeboard.
The City of Baltimore is concerned, however, that 0.3 to 0.6 additional meter (m) (I to 2 feet [ft]) of freeboard
is inequitable and inefficient. If flood levels will be, for example, I m (3.3 ft) higher than the flood maps currently
assume, then lands just outside the current flood boundary are also potentially vulnerable. If the city were to add
I meter of freeboard to property in the floodplain, without addressing adjacent properties outside the floodplain,
then adjacent property owners would have divergent requirements that city officials would find difficult to justify
(see Figure 10.6).
Infrastructure
Baltimore has two regional sewerage plants. One of them, the Patapsco Wastewater Treatment Plant, sits on
ground that is less than 2 m (7 ft) above mean sea level and floods occasionally (see Box Figure AI.6). The facility
itself is elevated and currently drains by gravity into the Patapsco River (USGS 7.5-minute map series). With a
significant rise in sea level, however, pumping will be needed and possibly additional protections against storms
(Smith, 1998; Titus et a/., 1987). Numerous streets, with associated conduits and utility piping, are within the exist-
ing coastal floodplain and would potentially be affected by sea-level rise (see Box Figure AI.6).
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Appendix i
The Calvert County cliffs represent unique habitat that could
be degraded by sea-level rise; however, the cliffs are not likely
to be lost entirely. The Puritan tiger beetle and Northeastern
beach tiger beetle, both federally listed, are present in the
area (Shellenbarger Jones and Bosch, 2008b). While natural
erosion processes are allowed to continue in the protected cliff
areas in the southern portion of the county, shoreline protec-
tions in the more northern developed areas are increasing
erosion rates in adjacent areas (Wilcock et ai, 1998).
AI.F.1.6
The Eastern Shore above Rock Hall is dominated by bluffs
and steep slopes rising to above 6 m (20 ft). Tolchester Beach,
Betterton Beach, and Crystal Beach are typical in that regard.
From Rock Hall south to around the middle of Kent Island, all
of the land within a few kilometers of the Chesapeake Bay or
its major tributaries consists of low-lying land.
Between the Choptank River and Ocohannock Creek along
the Eastern Shore of Chesapeake Bay lies one of the larg-
est concentrations of land close to sea level. Water levels in
roadside ditches rise and fall with the tides in the areas west
of Golden Hill in Dorchester County and several necks in
Somerset County. Many farms abut tidal wetlands, which
are gradually encroaching onto those farms. Some land-
owners have responded by inserting makeshift tide gates
over culverts, decreasing their own flooding but increasing
it elsewhere. Throughout Hoopers Island, as well as the
mainland nearby, there are: numerous abandoned driveways
that once led to a home but are now ridges flooded at high
tide and surrounded by low marsh or open water; recently
abandoned homes that are still standing but surrounded by
marsh; and dead trees still standing in areas where marsh
has invaded a forest.
Development and Shore Protection
Along the Chesapeake Bay, recent coastal development has
not placed a high value on the beach. The new bay front sub-
divisions often provide no public access to the beach, and as
shores erode, people erect shore-protection structures that
eventually eliminate the beach (see Chapter 6 of this Prod-
uct; Titus, 1998). Some traditional access points have been
closed (Titus, 1998). Maintaining a beach remains important
to some of the older bay resort communities where residents
have long had a public beach—but even towns with "Beach"
in the name are seeing their beaches replaced with shore
protection structures.
Maryland's Critical Areas Act, however, is likely to restrict
the extent of additional development along the Eastern Shore
of Chesapeake Bay to a greater extent than along the Western
Shore. The resource conservation areas where development
is discouraged include half of the Chesapeake Bay shoreline
between the Susquehanna and Choptank rivers. Among the
major tributaries, most of the Sassafras, Chester, and Chop-
tank rivers are similarly preserved; the Act did not prevent
development along most of the Wye, Elk, and North East
rivers. Existing development is most concentrated in the
northern areas near Interstate-95, Kent Island, and the various
necks near Easton and St. Michaels.
Vulnerable Habitat
Above Kent Island. The environmental implications of sea-
level rise effects in the upper Chesapeake Bay are likely to be
relatively limited. The Susquehanna River provides a large
(though variable) influx of sediment to the upper Chesapeake
Bay, as well as almost half of Chesapeake Bay's freshwater
input (CBP, 2000). This sediment generally is retained above
the Chesapeake Bay Bridge and provides material for accre-
tion in the tidal wetlands of the region (CBP, 2000). The other
upper Chesapeake Bay tributaries characteristically have
large sediment loads as well, and currently receive sufficient
sediment to maintain wetlands and their ecological function.
As such, the upper Chesapeake Bay will continue to provide
spawning and nursery habitat for crabs and fish, as well as
nesting and foraging habitat for migratory and residential
birds, including bald eagles and large numbers of waterfowl.
Likewise, while some of the beaches may require nourishment
for retention, the general lack of shoreline protections will
minimize interferences with longshore sediment transport.
Hence, beaches are likely to remain intact throughout much
of the region (Shellenbarger Jones, 2008b).
Two areas in the upper bay—Eastern Neck and Elk Neck—
appear most vulnerable to sea-level rise effects. First, Eastern
Neck Wildlife Refuge lies at the southern tip of Maryland's
Kent County. Ongoing shoreline protection efforts seek to
reduce erosion of habitats supporting many migratory water-
fowl and residential birds, as well as turtles, invertebrates, and
the Delmarva fox squirrel, federally listed as endangered. In
many marsh locations, stands of invasive common reed are
the only areas retaining sufficient sediment (Shellenbarger
Jones, 2008b). Local managers have observed common reed
migrating upland into forested areas as inundation at marsh
edges increases, although widespread marsh migration of
other species has not been observed (Shellenbarger Jones,
2008b). The three-square bulrush marshes on Eastern Neck
have been largely inundated, as have the black needle rush
marshes on Smith Island and other locations, likely causes
of reductions in black duck counts (Shellenbarger Jones,
2008b).
Other sea-level rise impacts are possible in Cecil County, in
and around the Northeast and Elk rivers. The headwaters of
the rivers are tidal freshwater wetlands and tidal flats, spawn-
ing and nursery areas for striped bass and a nursery area for
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A Focus on the Mid-Atlantic Region
alewife, blueback herring, hickory shad, and white perch, as
well as a wintering and breeding area for waterfowl (USF WS,
1980). Accretion is likely to be sufficient in some areas due to
the large sediment inputs in the Upper Bay. Where accretion
rates are not sufficient, wetland migration would be difficult
due to the upland elevation adjacent to the shorelines. These
conditions increase the chances of large tidal fresh marsh
losses (Shellenbarger Jones, 2008b). Other sensitive Cecil
County habitats exist such as the cliffs at Elk Neck State
Park and the Sassafras River Natural Resource Management
Area, which will be left to erode naturally (Shellenbarger
Jones, 2008b). Finally, marsh loss is possible in and around
the Aberdeen Proving Ground in Harford County. The Prov-
ing Ground is primarily within 5 m (16 ft) of sea level and
contains 8000 ha (20,000 ac) of tidal wetlands.
Kent Island to Choptank River. The central Eastern Shore
region of Chesapeake Bay contains diverse habitats, and sea-
level rise holds equally diverse implications, varying greatly
between subregions. Large expanses of marsh and tidal flats
are likely to be lost, affecting shellfish, fish, and waterfowl
populations (Shellenbarger Jones, 2008c). Several subregions
merit consideration:
Marshes along the Chester River are likely to be marginal
with moderate sea-level rise rate increases (Shellenbarger
Jones, 2008c, interpreting the findings of Reed et al.,
2008; see Chapter 4 of this Product).
Loss of the large tidal flats exist at the mouth of the Ches-
ter River (Tiner and Burke, 1995) may result in a decline
in the resident invertebrates and fish that use the shallow
waters as well as the birds that feed on the flats (Shel-
lenbarger Jones, 2008c; Robbins and Blom, 1996).
The Eastern Bay side of nearby Kent Island has several
tidal creeks, extensive tidal flats, and wetlands. Existing
marshes and tidal flats are likely to be lost (see Chapter 4)
(although some marsh may convert to tidal flat). Increas-
ing water depths are likely to reduce the remaining SAV;
a landward migration onto existing flats and marshes
will depend on sediment type and choice of shoreline
structure (Shellenbarger Jones, 2008c).
Portions of the Wye River shore are being developed. If
these shores are protected and the marshes and tidal flats
in these areas are lost, the juvenile fish nurseries will be
affected and species that feed in the marshes and SAV
will lose an important food source (MD DNR, 2004).
Certain key marsh areas are likely to be retained. The upper
reaches of tributaries, including the Chester and Choptank
rivers, are likely to retain current marshes and the associated
ecological services. Likewise, Poplar Island will provide a
large, isolated marsh and tidal flat area (USAGE, undated[b]).
In addition, the marshes of the Wye Island Natural Resource
Management Area support a large waterfowl population (MD
DNR, 2004). Maryland DNR will manage Wye Island to
protect its biological diversity and structural integrity, such
that detrimental effects from sea-level rise acceleration are
minimized (MD DNR, 2004).
Beach loss is also possible in some areas. The Chesapeake
Bay shore of Kent Island historically had narrow sandy
beaches with some pebbles along low bluffs, as well as some
wider beaches and dune areas (e.g., Terrapin Park). As de-
velopment continues, however, privately owned shores are
gradually being replaced with stone revetments. The beaches
will be unable to migrate inland, leading to habitat loss for
the various resident invertebrates, including tiger beetles,
sand fleas, and numerous crab species (Shellenbarger Jones,
2008c). Shorebirds that rely on beaches for forage and nest-
ing will face more limited resources (Lippson and Lippson,
2006). Likewise, on the bay side of Tilghman Island, the
high erosion rates will tend to encourage shoreline protection
measures, particularly following construction of waterfront
homes (MD DNR, undated). Beach loss, combined with
anticipated marsh loss in the area, will eliminate the worms,
snails, amphipods, sand fleas, and other invertebrates that
live in the beach and intertidal areas and reduce forage for
their predators (Shellenbarger Jones, 2008c).
AI.F.1.7. LOWER EASTERN
Approximately halfway between Crisfield on the Eastern
Shore and the mouth of the Potomac River on the Western
Shore are the last two inhabited islands in Chesapeake Bay
unconnected by bridges to the mainland: Smith (Maryland)
and Tangier (Virginia). Both islands are entirely below the
5-ft elevation contour on a USGS topographic map. Along the
Eastern Shore of Northampton County, by contrast, elevations
are higher, often with bluffs of a few meters.
Development and Shore Protection
Along Chesapeake Bay, islands are threatened by a combi-
nation of erosion and inundation. Wetlands are taking over
portions of Hoopers and Deal islands, but shore erosion is the
more serious threat. During the middle of the nineteenth cen-
tury, watermen who made their living by fishing Chesapeake
Bay made their homes on various islands in this region. Today,
Bloodsworth and Lower Hoopers islands are uninhabitable
marsh, and the erosion of Barren and Poplar islands led people
to move their homes to the mainland (Leatherman, 1992).
Smith Island is now several islands, and has a declining popu-
lation. Hoopers and Deal islands are becoming gentrif ied, as
small houses owned by watermen are replaced with larger
houses owned by wealthier retirees and professionals.
Virtually all of the beaches along Chesapeake Bay are erod-
ing. Shore erosion of beaches and clay shores along the Chop-
tank, Nanticoke and Wicomico rivers is slower than along
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The U.S. Climate Change Science Program
Appendix I
BOXAI.7: The DiamondbackTerrapin
The diamondback terrapin (Malaclemys terrapin), comprising seven subspecies, is the only turtle that is fully adapted
to life in the brackish salt marshes of estuarine embayments, lagoons, and impoundments (Ernst and Barbour,
1972). Its range extends from Massachusetts to Texas in the narrowest of coastal strips along the Atlantic and Gulf
coasts of the United States (Palmer and Cordes, 1988). Extreme
fishing pressure on the species resulted in population crashes
over much of their range so that by 1920 the catch in Chesapeake
Bay had fallen to less than 900 pounds. The Great Depression
put a halt to the fishery, and during the mid-twentieth century,
populations began to recover (CBP, 2006). Although a modest
fishery has been reestablished in some areas, stringent harvest
regulations are in place in several states. In some instances, states
have listed the species as endangered (Rhode Island), threatened
(Massachusetts), or as a "species of concern" (Georgia, Delaware,
Newjersey, Louisiana, North Carolina, and Virginia). In Maryland,
the status of the northern diamondback subpopulation is under
review (MD DNR, 2006a). Photo source: NOAA, Mary Hollinger.
Effects of Sea-Level Rise
The prospect of sea-level rise (along with land subsidence at many coastal locations, increasing human habitation
of the shore zone, and the implementation of shoreline stabilization measures) places the habitat of terrapins at
increasing risk. Loss of prime nesting beaches remains a major threat to the diamondback terrapin population
in Chesapeake Bay (MD DTTF, 2001). Because human infrastructure (i.e., roadways, buildings, and impervious
surfaces) leaves tidal salt marshes with little or no room to transgress inland, one can infer that the ecosystem
that terrapins depend on maybe lost with concomitant extirpation of the species.
the Bay but enough to induce shoreline armoring along most
developed portions. The lower Eastern Shore has a history
of abandoning lowlands to shore erosion and rising sea level
to a greater extent than other parts of the state (Leatherman,
1992).
Today, Smith and Tangier are the only inhabited islands
without a bridge connection to the mainland. Government
officials at all levels are pursuing efforts to prevent the loss
of these lands, partly because of their unique cultural status
and—in the case of Tangier—a town government that works
hard to ensure that the state continues to reinvest in schools
and infrastructure. The USAGE has several planned projects
for halting shore erosion, but to date, no efforts are underway
to elevate the land (USAGE, 2001b; Johnson, 2000). The
replacement of traditional lifestyles with gentrified second
homes may increase the resources available to preserve these
islands.
The mainland of Somerset County vulnerable to sea-level rise
is mostly along three necks. Until recently, a key indicator of
the cost-effectiveness of shore protection was the availability
of a sewer line36. As sea level rises, homes without sewer may
be condemned as septic systems fail. The incorporated town
of Crisfield, in the southernmost neck, has long had sewer ser-
vice, which has been recently expanded to nearby areas. The
town itself is largely encircled by an aging dike. Deal Island,
no longer the thriving fishing port of centuries gone by, still
has moderate density housing on most of the dry land.
Wicomico County's low-lying areas are along both the
Wicomico andNanticoke rivers. Unlike Somerset, Wicomico
has a large urban/suburban population, with the Eastern
Shore's largest city, Salisbury. Planners accept the general
principles of the state's Critical Areas Act, which discourages
development along the shore.
Much of coastal Dorchester County is already part of Black-
water Wildlife Refuge. The very low land south of Cambridge
that is not already part of the refuge is farmland. Because
most of the low-lying lands west of Cambridge are within
Resource Conservation Areas (CBCAC, 2001), significant
development would be unlikely under the state's Critical
Areas Act (see Section A1.F.2). On the higher ground along
36 The mounds systems have made it possible to inhabit low areas with
high water tables (see Figure 12.8 and accompanying text).
224
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A Focus on the Mid-Atlantic Region
the Choptank River, by contrast, many waterfront parcels are
being developed. In July 2008, the State of Maryland Board
of Public Works approved the purchase of 295 ha (729 ac) of
land along the Little Blackwater River, near the town to Cam-
bridge in Dorchester County. Funded by the state's Program
Open Space, the purchase will allow for the preservation and
restoration of more than two-thirds of a 434-ha (1,072-ac)
parcel that was previously slated for development37.
Vulnerable Habitat
On the lower Eastern Shore of Chesapeake Bay in Maryland,
habitats vulnerable to sea-level rise are diverse and include
beaches, various types of tidal marsh, non-tidal marshes, and
upland pine forests.
Narrow sandy beaches exist along discrete segments of shore-
line throughout the region, particularly in Somerset County.
Given the gradual slope of the shoreline, one might infer
that these habitats could accommodate moderate sea-level
rise by migrating upslope, assuming no armoring or other
barriers exist. Many of the beaches provide critical nesting
habitat for the diamondback terrapin (Malaclemys terrapin),
and proximity of these nesting beaches to nearby marshes
provides habitat for new hatchlings (see Box A1.7).
Of the 87,000 ha (340 sq mi) of tidal marsh in the Chesapeake
Bay, a majority is located in the three-county lower Eastern
Shore region (Darmondy and Foss, 1979). The marshes are
critical nursery grounds for commercially important fisher-
ies (e.g., crabs and rockfish); critical feeding grounds for
migratory waterfowl; and home to furbearers (e.g., muskrat
and nutria).
Areas of Virginia's Eastern Shore are uniquely vulnerable
to sea-level rise because large portions of Northampton and
Accomack counties lie near sea level. Because most of the
land in the two counties is undeveloped or agricultural, the
area also has a high potential for wetland creation relative to
other Virginia shorelines.
Most notably, the bay side of northern Accomack County is
primarily tidal salt marsh, with low-lying lands extending
several kilometers inland. Unprotected marshes are already
migrating inland in response to sea-level rise, creating new
wetlands in agricultural areas at a rate of 16 ha (40 ac) per
year (Strange, 2008e). Given the anticipated lack of shore-
line protection and insufficient sediment input, the seaward
boundaries of these tidal wetlands are likely to continue
retreating (Strange, 2008e, interpreting the findings of Reed
et al., 2008). The upland elevations are higher in southern
than northern Accomack County, however, making wetland
migration more difficult.
The salt marshes of Accomack County support a variety of
species, including rare bird species such as the seaside spar-
row, sharp-tailed sparrow, and peregrine falcon (VA DCR,
undated[a][b]). Growth and survival of these species may
be reduced where shores are hardened, unless alternative
suitable habitat is available nearby. Furthermore, long-term
tidal flooding will decrease the ability of nekton (i.e., free-
swimming finfish and decapod crustaceans such as shrimps
and crabs) to access coastal marshes.
AI.F.2
Chesapeake Bay's watershed has tidal shores in Virginia,
Maryland, the District of Columbia, and Delaware. Because
the shores of Delaware and the District of Columbia account
for a small portion of the total, this subsection focuses on
Virginia and Maryland. (The federal Coastal Zone Manage-
ment Act's definition of "coastal state" excludes the District
of Columbia38.)
Coastal management officials of Maryland have cooperated
with the U.S. EPA since the 1980s in efforts to learn the
ramifications of accelerated sea-level rise for their activities
(AP, 1985). Increased erosion from sea-level rise was one of
the factors cited for the state's decision in 1985 to shift its
erosion control strategy at Ocean City from groins to beach
nourishment (AP, 1985). The state also developed a planning
document for rising sea level (Johnson, 2000), and sea-level
rise was a key factor motivating Maryland to become the
second mid-Atlantic state to obtain lidar elevation data for
the entire coastal f loodplain (after North Carolina).
Neither Maryland nor Virginia has adopted a comprehensive
policy to explicitly address the consequences of rising sea
level. Nevertheless, the policies designed to protect wetlands,
beaches, and private shorefront properties are collectively
an implicit policy. Both states prevent new buildings within
30.5 m (100 ft) of most tidal shores; Maryland also limits the
density of new development in most areas to one home per
8.1 ha (20 ac) within 305 m (1,000 ft) of the shore. Virginia
allows most forms of shore protection. Maryland encour-
ages shore protection39, but discourages new bulkheads in
favor of revetments or nonstructural measures (MD DNR,
2006b). Both states have programs to inform property own-
ers of nonstructural options and have created programs and
educational outreach efforts to train marine contractors on
"living shoreline" design and installation techniques. Both
states work with the federal government to obtain federal
funds for beach nourishment along their respective ocean
37 See .
3816 USC §1453 (4).
39 Code of Maryland Regulations §27.01.04.02.02-03.
225
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Appendix
resorts (Ocean City and Virginia Beach); Virginia also assists
local governments in efforts to nourish public beaches along
Chesapeake Bay and its tributaries. Summaries of these land
use, wetlands, and beach nourishment policies follow.
During 2007, both states established climate change commis-
sions to inform policy makers about options for responding to
sea-level rise and other consequences of changing climate40.
The Maryland Commission on Climate Change (MCCC) is
charged with developing a climate action plan to address both
the causes and consequences of climate change41. Its interim
report (MCCC, 2008) recommends that the state (1) protect
and restore natural shoreline features (e.g., wetlands) and
(2) reduce growth and development in areas vulnerable to
sea-level rise and its ensuing coastal hazards. The Virginia
commission has an Adaptation Subgroup.
AI.F.2.1 USE
The primary state policies related to land use are Maryland's
Chesapeake and Atlantic Coastal Bays Critical Area Protec-
tion Act, Virginia's Chesapeake Bay Preservation Act, and
Virginia's Coastal Primary Sand Dunes & Beaches Act.
Maryland Chesapeake Bay and Atlantic Coastal Bays Criti-
cal Area Protection Act. The Maryland General Assembly
enacted the Chesapeake Bay Critical Area Protection Act in
1984 to reverse the deterioration of the Bay42. (The statute now
applies to Atlantic coastal bays as well; see Section A1.E.2.)
The law seeks to control development in the coastal zone and
preserve a healthy bay ecosystem. The jurisdictional bound-
ary of the Critical Area includes all waters of Chesapeake and
Atlantic Coastal bays, adjacent wetlands43, dry land within
305 m (1,000 ft) of open water44, and in some cases dry land
within 305 m inland of wetlands that are hydraulically con-
nected to the bays45.
The act created a Critical Areas Commission to set criteria
and approve local plans46. The commission has divided land in
the critical area into three classes: intensely developed areas
(IDAs), limited development areas (LDAs), and resource con-
40Maryland Executive Order (01.01.2007.07); Virginia Executive Order
59 (2007).
41 Maryland Executive Order (01.01.2007.07).
42 Chesapeake Bay Critical Areas Protection Act, Maryland Code
Natural Resources §8-1807.
43i.e. all state and private wetlands designated underNatural Resources
Article, Title 9 (now Title 16 of the Environment Article).
44 Maryland Code Natural Resources §8-1807(c)(l)(i)(2).
45 Lands that are less than 305 m (1,000 ft) from these wetlands may
be excluded from jurisdiction if the lands are more than 305 m from
open water, and the wetlands between that land and the open water are
highly functional and able to protect the water from adverse effects
of developing the land. Maryland Code Natural Resources §8-1807(c)
(l)(i)(2) and §8-1807(a)(2).
46 Maryland Code Natural Resources §8-1808.
servation areas (RCAs)47. Within the RCAs, new development
is limited to an average density of one home per 8.1 ha (20
ac)48 and set back at least 61 m (200 ft)49, and the regulations
encourage communities to "consider cluster development,
transfer of development rights, maximum lot size provisions,
and/or additional means to maintain the land area necessary
to support the protective uses"50. The program limits future
intense development activities to lands within the IDAs, and
permits some additional low-intensity development in the
LDAs. However, the statute allows up to 5 percent of the
RCAs in a county to be converted to an IDA51, although a
61-m (200-ft) buffer applies in those locations.
The three categories were originally delineated based on
the land uses of 1985. Areas that were dominated by either
agriculture, forest, or other open space, as well as residential
areas with densities less than one home in 2 ha (5 ac), were
defined as RCAs52. Thus, the greatest preservation occurs in
the areas that had little development when the act was passed,
typically lands that are far from population centers and major
transportation corridors—particularly along tributaries (as
opposed to the Bay itself). The boundary of the critical area
was based on wetland maps created in 1972. MCCC (2008)
pointed out that rising sea level and shoreline erosion had
made that boundary obsolete in some locations. As a result,
the Legislature directed the Critical Areas Commission to
update the maps based on 2007 to 2008 imagery, and there-
after at least once every 12 years53.
The Critical Areas Program also established a 30.5 m (100-
ft) natural buffer adjacent to tidal waters, which applies to
all three land categories54. No new development activities
are allowed within the buffer55, except water-dependent fa-
cilities. By limiting development in the buffer, the program
prevents additional infrastructure from being located in
the areas most vulnerable to sea-level rise. In some cases,
the 30.5-m buffer provides a first line of defense against
coastal erosion and flooding induced by sea-level rise. But
the regulations also encourage property owners to halt shore
erosion56. Nonstructural measures are preferred, followed by
structural measures57, with an eroding shore the least prefer-
able (Titus, 1998).
47 Code of Maryland Regulations §27.01.02.02(A).
48 Code of Maryland Regulations §27.01.02.05(C)(4).
49 Maryland Code Natural Resources §8-1808.10 The required setback
is only 100 ft for new construction on pre-existing lots.
50 Code of Maryland Regulations §27.01.02.05(C)(4).
51 Code of Maryland Regulations §27.01.02.06.
52 Code of Maryland Regulations §27.01.02.05.
53 Maryland House Bill 1253 (2008) §3.
54 Code of Maryland Regulations §27.01.00.01 (C)(l).
55 Code of Maryland Regulations §27.01.00.01 (C)(2).
56 Code of Maryland Regulations§27.01.04.02. 02.
57 Code of Maryland Regulations§27.01.04.02. 03.
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A Focus on the Mid-Atlantic Region
Virginia Chesapeake Bay Preservation Act. The Chesapeake
Bay Preservation Act58 seeks to limit runoff into the bay by
creating a class of land known as Chesapeake Bay Preserva-
tion Areas. The act also created the Chesapeake Bay Local
Assistance Board to implement59 and enforce60 its provisions.
Although the act defers most site-specific development deci-
sions to local governments61, it lays out the broad framework
for the preservation areas62 and provides the Board with
rulemaking authority to set overall criteria63. The Board has
issued regulations64 defining the programs that local govern-
ments must develop to comply with the act65.
All localities must create maps that define the locations of the
preservation areas, which are subdivided into resource man-
agement areas66 and resource protection areas (RPAs)67. RPAs
include areas flooded by the tides, as well as a 30. m (100-ft)
buffer inland of the tidal shores and wetlands68. Within the buf-
fer, development is generally limited to water dependent uses,
redevelopment, and some water management facilities. Roads
may be allowed if there is no practical alternative. Similarly,
for lots subdivided before 2002, new buildings may encroach
into the 30.5 m buffer if necessary to preserve the owner's
right to build; but any building must still be at least 15.2 m
(50 ft) from the shore69. Property owners, however, may still
construct shoreline defense structures within the RPA. The
type of shoreline defense installed is not regulated (beyond
certain engineering considerations). Consequently, hard struc-
tures can be installed anywhere along Virginia's shoreline.
Virginia Coastal Primary Sand Dunes & Beaches Act.
Virginia's Dunes and Beaches Act preserves and protects
coastal primary sand dunes while accommodating shoreline
development70. The act identifies 29 counties, 17 independent
58 Code VA §10.1-2100 et seq. As of August 8, 2003, the Act was posted
on the Virginia Legislative Information System website as part of the
Code of Virginia at: .
59 Code VA §10.1-2102.
60 Code VA §10.1-2104.
"Code VA §10.1-2109.
62 Code VA §10.1-2107(8).
63 Code VA §10.1-2107(A).
64 Chesapeake Bay Preservation Area Designation and Management
Regulations (9 VAC 10-20-10 et. seq.).
65 9 Virginia Administrative Code §10-20-50.
66 Resource Management Areas (RMAs) are lands that, if improperly
used or developed, have the potential to diminish the functional value
of RPAs (9 Virginia Administrative Code §10-20-90). Areas in which
development is concentrated or redevelopment efforts are taking place
may be designated as Intensely Developed Areas (IDAs) and become
subject to certain performance criteria for redevelopment (9 Virginia
Administrative Code §10-20-100). Private landowners are free to
develop IDA and RMA lands, but must undergo a permitting process
to prove that these actions will not harm the RPAs.
67 9 Virginia Administrative Code §10-20-70.
68 9 Virginia Administrative Code §10-20-80 (B).
69 9 Virginia Administrative Code §10-20-130 (4).
70 Virginia Administrative Code §28.2-1400 et seq.
cities, and one town (Cape Charles) that can adopt a coastal
primary sand dune zoning ordinance, somewhat analogous to
a Tidal Wetlands ordinance71. The act defines beaches as (1)
the shoreline zone of unconsolidated sandy material; (2) the
land extending from mean low water landward to a marked
change in material composition or in physiographic form
(e.g., a dune, marsh, or bluff); and (3) if a marked change
does not occur, then a line of woody vegetation or the near-
est seawall, revetment, bulkhead or other similar structure.
Al.l .2.2 WETLANDS AND EROSION CONTROL PERMITS
Virginia. The Tidal Wetlands Act seeks to "...preserve and
prevent the despoliation and destruction of wetlands while
acmmodating necessary economic development in a manner
consistent with wetlands preservation" (VA Code 28.2-1302).
It provides for a Wetlands Zoning ordinance that any county,
city, or town in Virginia may adopt to regulate the use and
development of local wetlands. Under the ordinance, locali-
ties create a wetlands board consisting of five to seven citizen
volunteers. The jurisdiction of these local boards extends
from mean low water (the Marine Resources Commission has
jurisdiction over bottom lands seaward of mean low water)
to mean high water where no emergent vegetation exists, and
slightly above spring high water72 where marsh is present.
The board grants or denies permits for shoreline alterations
within their jurisdiction (Trono, 2003). The Virginia Marine
Resources Commission has jurisdiction over the permitting
of projects within state-owned subaqueous lands and reviews
projects in localities that have no local wetlands board by
virtue of not having adopted a wetland zoning ordinance73.
Maryland. The Wetlands and Riparian Rights Act74 gives
the owner of land bounding on navigable water the right
to protect their property from the effects of shore erosion.
For example, property owners who erect an erosion control
structure in Maryland can obtain a permit to fill vegetated
wetlands75 and fill beaches and tidal waters up to 3 m (10 ft)
seaward of mean high water76. In addition, Maryland's statute
allows anyone whose property has eroded to fill wetlands and
other tidal waters to reclaim any land that the owner has lost
since the early 1970s77. (USAGE has delegated most wetland
71 Virginia Administrative Code §28.2-1403.
72 The act grants jurisdiction to an elevation equal to 1.5 times the mean
tide range, above mean low water.
73 Virginia Administrative Code §28.2.
74Maryland Environmental Code §16-101 to §16-503.
75 See MD. CODE ANN, ENVIR. §16-201 (1996); see Baltimore District
(1996), app. at 1-24,1-31. Along sheltered waters, the state encourages
property owners to control erosion by planting vegetation. For this
purpose, one can fill up to 10.7 m (35 ft) seaward of mean high water.
See MD. CODE ANN, ENVIR. §16-202(c)(3)(iii) (Supp. 1997).
Along Chesapeake Bay and other waters with significant waves, hard
structures are generally employed.
76MD. CODE ANN, ENVIR. §16-202(c)(2).
77 MD. CODE ANN, ENVIR. §16-201.
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The U.S. Climate Change Science Program
Appendix I
Table Al.3. Selected State Funded Beach Nourishment Projects Along
Estuarine Shores in Maryland and Virginia
$Cost
Location
• City or County
7 ' (Millions)
North Beach
Sandy Point
Point Lookout State Park
Choptank River Fishing Pier
Jefferson Island
Tanners Creek
Bay Ridge
Hart and Millers Island
Rock Hall Town Park
Claiborne Landing
Terrapin Beach
Jefferson Island Club - St Catherine Island
Elms Power Plant Site
Calvert
Anne Arundel
St. Mary's
Talbot
St. Mary's
St. Mary's
Anne Arundel
Baltimore County
Kent
Talbot
Queen Anne's
St. Mary's
St. Mary's
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Virginia (1995 to 2005)
Bay Shore
Parks along James River
Buckroe Beach
Cape Charles
Colonial Beach
Aquia Landing
Norfolk
Newport News
Hampton
Northampton
Westmoreland
Stafford
5.0
1.0
1.3
0.3
0.3
0.2
Sources: Maryland Department of Natural Resources; Virginia Board on Conservation
and Development of Public Beaches
permit approval to the state78.) Although the state has long
discouraged bulkheads, much of the shore has been armored
with stone revetments (Titus, 1998).
Shore protection structures tend to be initially constructed
landward of mean high water, but neither Virginia nor Mary-
land79 require their removal once the shore erodes to the point
where the structures are flooded by the tides. Nor has either
state prevented construction of replacement bulkheads within
state waters, although Maryland encourages revetments.
For the last several years, Maryland has encouraged the
"living shorelines" approach to halting erosion (e.g., marsh
planting and beach nourishment) over hard structures and
revetments over bulkheads80. Few new bulkheads are built
for erosion control, and existing bulkheads are often replaced
with revetments. Nevertheless, obtaining permits for struc-
tural options has often been easier (NRC, 2007; Johnson and
78 See Baltimore District (1996) §§1-5.
19 The Maryland/Virginia border along the Potomac River is the low
water mark. Courts have not ruled whether Maryland or Virginia
environmental rules would govern a structure in Maryland waters
attached to Virginia land.
!0 Baltimore District (1996).
Luscher, 2004). For example, in the aftermath of Hurricane
Isabel, many property owners sought expedited permits to
replace shore protection structures that had been destroyed
during the storm. Maryland wanted to make obtaining a per-
mit to replace a destroyed bulkhead with a living shoreline
as easy as obtaining a permit to rebuild the bulkhead; but
the state was unable to obtain federal approval. The permits
issued by USAGE authorized replacement of the damaged
structures with new structures of the same kind, but they did
not authorize owners to replace lost revetments and bulkheads
with living shorelines, or even to replace lost bulkheads with
revetments (Johnson and Luscher, 2004).
Recognizing the environmental consequences of contin-
ued shoreline armoring, the General Assembly enacted
the Living Shoreline Protection Act of 200881. Under the
act, the Department of Environment will designate cer-
tain areas as appropriate for structural shoreline measures
(e.g., bulkheads and revetments)82. Outside of those ar-
eas, only nonstructural measures (e.g., marsh creation,
beach nourishment) will be allowed unless the prop-
81 MD H.B. 973 (2008).
82 MD Code Environment §16-201(c)(l)(i).
228
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erty owner can demonstrate that nonstructural measures
are infeasible83.
AI.F.2.3 BEACH NOURISHMENT AND OTHER SHORE
PROTECTION ACTIVITIES
Virginia. Until 2003, the Board on Conservation and Develop-
ment of Public Beaches promoted maintenance, access, and
development along the public beaches of Virginia. The largest
beach nourishment projects have been along the 21 km (13 mi)
of public beach along the Atlantic Ocean in Virginia Beach.
During the last 50 years, the state has provided 3 percent of
the funding for beach nourishment at Virginia Beach, with
the local and federal shares being 67 percent and 30 percent,
respectively (VA PBB, 2000).
Virginia has made substantial efforts to promote beach
nourishment (and public use of beaches) along Chesapeake
Bay and its tributaries. Norfolk's four guarded beaches serve
160,000 visitors each summer (VA PBB, 2000). When shore
erosion threatened property, the tourist economy, and local
recreation, the Beach Board helped the city construct a series
of breakwaters with beachfill and a terminal groin at a cost
of $5 million (VA PBB, 2000). State and local partnerships
have also promoted beach restoration projects in several other
locations along Chesapeake Bay and the Potomac and York
rivers (see Table A1.3).
Maryland. Maryland's primary effort to protect shores along
the bay is through the Department of Natural Resource's
Shore Erosion Control Program. Until 2008, the program
provided interest-free loans and technical assistance to Mary-
land property owners to resolve erosion problems through
the use of both structural and nonstructural shore erosion
control projects; the program is now limited to "living shore-
line" (see Box 6.3 in Chapter 6) approaches. The program
provides contractor and homeowner training to support the
installation of "living shorelines". The Department of Natural
Resources has been involved in several beach nourishment
projects along Chesapeake Bay (see Table A1.3), many of
which include breakwaters or groins to retain sand within
the area nourished.
The Maryland Port Administration and the USAGE have
also used dredge spoils to restore Poplar and Smith islands
(USAGE, 200Ib). Preliminary examinations are underway to
see if dredged materials can be used to restore other Chesa-
peake Bay islands such as James and Barren islands (USAGE,
2006c), or to protect valuable environmental resources such
as the eroding lands of the U.S. Fish and Wildlife Service
(USFWS) Blackwater National Wildlife Refuge (USFWS,
2008).
to
A Focus on the Mid-Atlantic Region
- -
• "
North Carolina's coastline is outlined by a barrier island
system, with approximately 500 km (300 mi) of shoreline
along the Atlantic Ocean. North Carolina's winding estuarine
shorelines extend a total of approximately 10,000 linear km
(6,000 mi) (Feldman, 2008). There are three well-known
capes along the coastline: Cape Hatteras, Cape Lookout, and
Cape Fear, in order from north to south. The "Outer Banks"
of North Carolina include the barrier islands and barrier spits
from Cape Lookout north to the Virginia state line. Much of
this land is owned by the federal government, including Cape
Lookout National Seashore, Cape Hatteras National Seashore,
Pea Island National Wildlife Refuge, and Currituck National
Wildlife Refuge. The Outer Banks also include several towns,
including Kitty Hawk, Nags Head, Rodanthe, and Ocracoke
(see Section Al.G.4.2). North and east of Cape Lookout,
four rivers empty into the Albemarle and Pamlico Sounds.
Albemarle Sound, Pamlico Sound, and their tidal tributaries,
sometimes collectively called the Albemarle-Pamlico Estua-
rine System, comprise the second largest estuarine system in
the United States (after the Chesapeake Bay estuary).
Previous assessments of North Carolina's estuarine regions
have divided the state's coastal regions into two principal
provinces (geological zones), each with different character-
istics (e.g., Riggs and Ames, 2003). The zone northeast of a
line drawn between Cape Lookout and Raleigh (located about
260 km [160 mi] northwest of the cape) is called the Northern
Coastal Province, and includes the Outer Banks and most of
the land bordering the Albemarle and Pamlico Sounds. It has
gentle slopes, three major and three minor inlets, and long
barrier islands with a moderately low sediment supply, com-
pared to barrier islands worldwide (Riggs and Ames, 2003).
The rest of the state's coastal zone—the Southern Coastal
Province—has steeper slopes, an even lower sediment supply,
short barrier islands, and many inlets.
The Albemarle-Pamlico Peninsula is the land between Al-
bemarle and Pamlico sounds, to the west of Roanoke Island.
The potential vulnerability of this 5,500 sq km (2,100 sq mi)
peninsula (Henman and Poulter, 2008) is described in Box
A1.8. The majority of Dare and Hyde counties are less than 1
m (3 ft) above sea level, as is a large portion of Tyrell County
(Poulter and Halpin, 2007). Along the estuarine shorelines
of North Carolina, wetlands are widespread, particularly in
Hyde, Tyrell, and Dare counties. North Carolina's Division
of Coastal Management mapped a total of more than 11,000
sq km (4,400 sq mi) of wetlands in the 20 coastal counties in
North Carolina (Sutler, 1999). Wetland types present include
marshes, swamps, forested wetlands, pocosins (where ever-
' MD Code Environment §16-201(c)(l)(ii).
229
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I
Vulnerability to sea-level rise on the diverse Albemarle-Pamlico Peninsula is very high: about two-thirds of the
peninsula is less than 1.5 meters (m) (5 feet [ft]) above sea level (Heath, 1975), and approximately 30 percent is less
than I m (3 ft) above sea level (Poulter, 2005). Shoreline retreat rates in parts of the peninsula are already high, up
to about 8 m (25 ft) per year (Riggs and Ames, 2003). The ecosystems of the Albemarle-Pamlico Peninsula have long
been recognized for their biological and ecological value. The peninsula is home to four national wildlife refuges, the
first of which was established in 1932. In all, about one-third of the peninsula has been set aside for conservation
purposes.
The Albemarle-Pamlico Peninsula is among North Carolina's poorest areas. Four of its five counties are classified
as economically distressed by the state, with high unemployment rates and low average household incomes (NC
Department of Commerce, 2008). However, now that undeveloped waterfront property on the Outer Banks is
very expensive and scarce, developers have discovered the small fishing villages on the peninsula and begun acquir-
ing property in several areas—including Columbia (Tyrrell County), Engelhard (Hyde County), and Bath (Beaufort
County). The peninsula is being marketed as the "Inner Banks" (Washington County, 2008). Communities across
the peninsula are planning infrastructure, including wastewater treatment facilities and desalination plants for drink-
ing water, to enable new development. Columbia and Plymouth (Washington County) have become demonstra-
tion sites in the North Carolina Rural Economic Development Center's STEP (Small Towns Economic Prosperity)
Program, which is designed to support revitalization and provide information vital to developing public policies that
support long-term investment in small towns (NC REDC, 2006).
There are already signs that sea-level rise is causing ecosystems on the Albemarle-Pamlico Peninsula to change.
For example, at the Buckridge Coastal Reserve, a 7,547-hectare (ha) (18,650-acre [ac]) area owned by the North
Carolina Division of Coastal Management, dieback is occurring in several areas of Atlantic white cedar. Other parts
of the cedar community are beginning to show signs of stress. Initial investigations suggest the dieback is associated
with altered hydrologic conditions, due to canals and ditches serving as conduits that bring salt and brackish water
into the peat soils where cedar usually grows. Storms have pushed estuarine water into areas that are naturally
fresh, affecting water chemistry, peatland soils, and vegetation intolerant of saline conditions (Poulter and Pederson,
2006). There is growing awareness on the part of residents and local officials about potential vulnerabilities across
the landscape (Poulter, et a/., 2009). Some farmers acknowledge that saltwater intrusion and sea-level rise are af-
fecting their fields (Moorhead and Brinson, 1995). Researchers at North Carolina State University are using Hyde
County farms to experiment with the development of new varieties of salt-tolerant soybeans (Lee et a/., 2004).
Hyde County is building a dike around Swan Quarter, the county seat (Hyde County, 2008).
A variety of evidence has suggested to some stakeholders that the risks to the Albemarle-Pamlico Peninsula merit
special management responses. In fact, because so much of the landscape across the peninsula has been transformed
by humans, some have expressed concern that the ecosystem may be less resilient and less likely to be able to
adapt when exposed to mounting stresses (Pearsall et a/., 2005). Thus far, no comprehensive long-term response
to the effects of sea-level rise on the Peninsula has been proposed. In 2007, The Nature Conservancy, U.S. Fish and
Wildlife Service, National Audubon Society, Environmental Defense, Ducks Unlimited, the North Carolina Coastal
Federation, and others began working to build an Albemarle-Pamlico Conservation and Communities Collaborative
(AP3C) to develop a long-term strategic vision for the peninsula. Although this initiative is only in its infancy, sea-
level rise will be one of the first and most important issues the partnership will address (TNC, 2008).
The Nature Conservancy and other stakeholders have already identified several adaptive responses to sea-level rise
on the Peninsula. Many of these approaches require community participation in conservation efforts, land protec-
tion, and adaptive management (Pearsall and Poulter, 2005). Specific management strategies that The Nature Con-
servancy and others have recommended include: plugging drainage ditches and installing tide gates in agricultural
fields so that sea water does not flow inland through them, establishing cypress trees where land has been cleared
in areas that are expected to become wetlands in the future, reestablishing brackish marshes in hospitable areas
that are likely to become wetlands in the future, creating conservation corridors that run from the shoreline inland
to facilitate habitat migration, reducing habitat fragmentation, banning or restricting hardened structures along the
estuarine shoreline, and establishing oyster reefs and submerged aquatic vegetation beds offshore to help buffer
shorelines (Pearsall and DeBlieu, 2005; Pearsall and Poulter, 2005).
230
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to
A Focus on the Mid-Atlantic Region
green shrubs and wetland trees occupy peat deposits), and
many other types (Sutler, 1999).
Where the land is flat, areas a few meters above sea level
drain slowly—so slowly that most of the lowest land is non-
tidal wetland (Richardson, 2003). Because rising sea level
decreases the average slope between nearby coastal areas and
the sea, it slows the speed at which these areas drain. Some of
the dry land within a few meters above the tides could convert
to wetland from even a small rise in sea level; and nontidal
wetlands at these elevations would be saturated more of the
time (McFadden et al., 2007; Moorhead and Brinson, 1995).
Wetland loss could occur if dikes and drainage systems are
built to prevent dry land from becoming wet (McFadden et
al, 2007).
The very low tide range in some of the sounds is another
possible source of vulnerability. Albemarle Sound, Currituck
Sound, and much of Pamlico Sound have a very small tide
range because inlets to the ocean are few and far between
(NOAA, 2008b). Some of the inlets are narrow and shallow
as well. Although Oregon and Ocracoke inlets are more than
10 m (over 30 ft) deep, the inlets are characterized by exten-
sive shoals on both the ebb and flood sides, and the channels
do not maintain depth for long distances before they break
into shallower finger channels. Like narrow channels, this
configuration limits the flow of water between the ocean
and sounds (NOAA, 2008c). Thus, although the astronomic
tide range at the ocean entrances is approximately 90 cm (3
ft), it decreases to 30 cm (1 ft) just inside the inlets and a few
centimeters in the centers of the estuaries. It is possible that
rising sea level combined with storm-induced erosion will
cause more, wider, and/or deeper inlets in the future (Riggs
and Ames, 2003; see Chapter 3 of this Product). If greater tide
ranges resulted, more lands would be tidally inundated.
The configuration of the few inlets within the Northern
Coastal Province reduces tidal flushing and keeps salinity
levels relatively low in most of the estuaries in this area (Riggs
and Ames, 2003). Salinity is relatively high at the inlets, but
declines as one proceeds upstream or away from the inlets.
Also, there can be a strong seasonal variation with lower
salinities during the periods of maximum river discharge and
higher salinities during periods of drought (Buzzelli et al.,
2003). The salinity in Albemarle-Pamlico Sound generally
ranges from 0 to 20 parts per thousand (ppt), with the upper
reaches of the Neuse and Pamlico rivers, Albemarle Sound,
and Currituck Sound having salinities usually below 5 ppt
(Caldwell, 2001; Tenore, 1972). (The typical salinity of the
ocean is 35 ppt [Caldwell, 2001].) Some tidal marshes (which
are irregularly flooded by the winds rather than regularly
flooded by astronomical tides) are thus unable to tolerate
salt water (Bridgham and Richardson, 1993; Poulter, 2005;
Titus and Wang, 2008). In some areas, the flow of shallow
groundwater to the sea is also fresh, so the soils are unac-
customed to salt water, and hence potentially vulnerable to
increased salinity.
More than other areas in the Mid-Atlantic, the Albemarle -
Pamlico Sound region appears to be potentially vulnerable
to the possibility that several impacts of sea-level rise might
compound to produce an impact larger than the sum of the
individual effects (Poulter and Halpin, 2007; Poulter et al.,
2008). If a major inlet opened, increasing the tide range and
salinity levels, it is possible that some freshwater wetlands
that are otherwise able to keep pace with rising sea level
would be poisoned by excessive salinity and convert to open
water. Similarly, if a pulse of salt water penetrated into the
groundwater, sulfate reduction of the organic-rich soil and
peat that underlies parts of the region could cause the land
surfaces to subside (Hackney and Yelverton, 1990; Henman
and Poulter, 2008; Mitsch and Gosselink, 2000; Portnoy and
Giblin, 1997). Moreover, a substantial acceleration in the rate
of sea-level rise or high-intensity hurricanes or winter storms
could cause barrier islands to be breached (see Chapter 3 and
AI.G.2). Pamlico Sound (and potentially Albemarle Sound)
could be transformed from a protected estuary into a semi-
open embayment with saltier waters, regular astronomical
tides, and larger waves (Riggs and Ames, 2003).
AI.G.2 Sli • I
AI.G.2.1 ' i i j COASTS
North Carolina receives the highest wave energy along the
entire East Coast of the United States and the northwest At-
lantic margin (Riggs and Ames, 2003). The coast of North
Carolina has shifted significantly over time due to storms,
waves, tides, currents, rising sea level, and other natural and
human activities. These factors have caused variable sediment
transport, erosion, and accretion, along with the opening and
closing of inlets (see, e.g., Everts et al., 1983).
The North Carolina Division of Coastal Management
(NCDCM) has calculated long-term erosion rates along the
coastline adjacent to the ocean by comparing the location of
shorelines in 1998 with the oldest available maps of shoreline
location, mostly from the 1940s. The average erosion rate
was 0.8 m (2.6 ft) per year. Approximately 18 percent of the
ocean coastline retreated by more than 1.5 m (5 ft) per year,
20 percent eroded at an annual rate of 0.6 to 1.5m (2 to 5 ft)
per year, and 30 percent of the coastaline eroded by 0.6 m
(2 ft) per year or less. However, 32 percent of the coastline
accreted (NC DCM, 2003). The NCDCM recalculates long-
term erosion rates about every five years to better track the
dynamic shoreline trends and establish the setback line that
231
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I
Table AI.4 Estuarine Shoreline Erosion Rates (by shoreline type and the percent
of total shoreline for each type). From Riggs and Ames (2003).
[-'^^v.u^^-'^'-y' ,'•;••
.'.!.! ^L.,:,:.L:::'Li.^^
Sediment Bank
Low Bank
Bluff/high bank
Back-barrier strandplain
beach
Organic Shoreline
Mainland marsh
Back-barrier marsh
Swamp forest
Human modified
Weighted averageb
^', '' <"%i j" ' '. K< ^(
i^V'1','*-'' '•''•:•';'*•
38
30
8
<\
62
55
<\
7
Unknown
?^;V;'j/f^v
2.7
8.0
0.6
5.6
5.8
1.8
2.0
\,"y' ' i1''.'1-''' '* ">'''"*• i ' ••"''
fer.vy?;:
1.0
0.8
-0.2a
0.9
0.4
0.7
0.2
2.7
"The negative erosion rate listed refers to this shoreline type, on average, accreting.
bThis weighted average excludes strandplain beaches and human-modified shorelines.
determines where structures may be permitted on the ocean-
front (NC DCM, 2005).
An analysis of shoreline change between approximately 1850
and 1980 in the area between the northern border of North
Carolina and the point 8 km (5 mi) west of Cape Hatteras has
been published. Data were averaged over 2 km (1.2 mi) reach-
es (stretches of coastline). Across the areas where data were
available during this time period, approximately 68 percent
of the ocean shoreline retreated towards the mainland, while
approximately 28 percent advanced (or accreted) away from
the mainland, and 4 percent did not change position (Everts
et al., 1983). On average, the parts of the coastline between
Ocracoke Inlet and Cape Hatteras eroded an average of 4.5
m (14.8 ft) per year over 1852 to 1917, 8.3 m (27.2 ft) per year
over 1917 to 1949, and 2.0 m (6.6 ft) per year over 1949 to
1980. The average erosion rate over the study period along
the parts of the coastline facing east (between Cape Hatteras
and Cape Henry, in Virginia) was 0.8 m (2.6 ft) per year.
However, the study indicates that the coastline from Cape
Hatteras to Oregon Inlet accreted slightly (an average of 0.4
m [1.3 ft] peryear) over 1852 to 1917, eroded an average of 2.9
m (9.5 ft) per year over 1917 to 1949, and eroded an average
of 1.3 m (4.3 ft) per year over 1949 to 1980. North of Oregon
Inlet, the coastline was stable on average over 1852 to 1917;
however, there was an average of 1.2 m (3.9 ft) per year of
erosion over 1917 to 1949 and an average of 0.3 m (1.0 ft) per
year of erosion in 1949 to 1980 (Everts et al., 1983).
The Everts et al. report cautions against predicting future
shoreline change based on the limited data available from
surveys conducted since 1850. The authors observe that
shoreline change can be influenced by local features, such
as inlets, capes, and shoals (Everts etal, 1983). For example,
shorelines north of the ridges of three offshore shoals inter-
secting North Carolina's ocean coast have retreated, whereas
shorelines south of the ridges have generally advanced (Everts
et al., 1983). Everts et al. also point out that while geologi-
cal evidence indicates that the barrier islands have migrated
landward over thousands of years, the islands are presently
narrowing from both sides, in part because overwash pro-
cesses cannot carry sand to the estuarine side due to island
width and development (Everts et al., 1983).
More recently, researchers have used models to predict the
amount of shoreline change that might result from future
sea-level rise, above and beyond the shoreline change caused
by other factors. For example, one analysis of statewide ero-
sion rates over the past 100 years led researchers to estimate
that a 1-m sea-level rise would cause the shore to retreat an
average of 88 m (289 ft), in addition to the erosion caused by
other factors (excluding inlets) (Leatherman et al., 2000a).
Another study estimated that a rise in sea level of 0.52 m
between 1996 and 2050 would cause the shoreline at Nags
Head to retreat between 33 and 43 m, or between 108 and
144 ft (Daniels, 1996).
Some researchers are concerned that the barrier islands
themselves may be in jeopardy if sea-level rise accelerates.
According to Riggs and Ames (2003), about 40 km (25 mi)
of the Outer Banks are so sediment-starved that they are
already in the process of "collapsing". Within a few decades,
they estimate, portions of Cape Hatteras National Seashore
could be destroyed by: (1) sea-level rise (at current rates
or higher); (2) storms of the magnitude experienced in the
1990s; or (3) one or more category 4 or 5 hurricanes hitting
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to
A Focus on the Mid-Atlantic Region
the Outer Banks (Riggs and Ames, 2003). Most of the Outer
Banks between Nags Head and Ocracoke is vulnerable to
barrier island segmentation and disintegration over the next
century if the rate of sea-level rise accelerates by 2 mm per
year—and portions may be vulnerable even at the current
trend (see Chapter 3).
,3
Some wetland systems are already at the limit of their abil-
ity to vertically keep pace with rising sea level, such as the
remnants of the tidal marshes that connected Roanoke Island
to the mainland of Dare County until the nineteenth century.
The pocosin wetlands can vertically accrete by about 1 to 2
mm per year with or without rising sea level—when they are
in their natural state (Craft and Richardson, 1998; Moorhead
and Brinson, 1995). The human-altered drainage patterns,
however, appear to be limiting their vertical accretion—and
saltwater intrusion could cause subsidence and conversion to
open water (Pearsall and Poulter, 2005).
AI.G.3.1 ESTUARINE SHORELINE RETREAT
Pamlico Sound, Albemarle Sound, the smaller sounds in the
state, and the lower reaches of the Chowan, Roanoke, Tar, and
Neuse rivers are all affected by rising sea level (Brinson et al.,
1985). Rising sea level is not the primary cause of shoreline
retreat along estuarine shores in North Carolina. Storm waves
cause shorelines to recede whether or not the sea is rising. A
study of 21 sites estimated that shoreline retreat—caused by
"the intimately coupled processes of wave action and rising
sea level"—is already eliminating wetlands at a rate of about
3 sq km (800 ac) per year, mostly in zones of brackish marsh
habitat, such as on the Albemarle-Pamlico Peninsula (Riggs
and Ames, 2003).
Riggs and Ames (2003) compiled data collected across North
Carolina shorelines, both those that are adjacent to wetlands
and those that are not. These data show that the vast major-
ity of estuarine shores in the region are eroding, except for
the sound sides of barrier islands (which one might expect to
advance toward the mainland). Data spanning up to 30 years
indicate that the weighted average estuarine retreat rate along
the northeastern North Carolina coast is 0.8 m (less than 3
ft) per year, and the average retreat rate observed along the
Outer Pamlico River and the Albemarle-Pamlico Sounds
was just over 1 m (more than 3 ft). Annual averages for most
shoreline types are less than 1 m per year (Table A1.4), but
annual maxima exceed the average many-fold and can reach
8 m (26 ft) per year where the shoreline is characterized by
sediment bluffs or high banks. One or a few individual storm
events contribute disproportionately to average annual shore-
line recession rates (Riggs and Ames, 2003).
An analysis of estuarine shoreline change is also included in
Everts et al. (1983). The authors calculated average erosion
rates for the periods around 1850 to 1915 and 1915 to 1980.
Between Nags Head and Oregon Inlet, the estuarine points
analyzed between 1850 and 1915 showed both advance rates
greater than 4 m (13 ft) per year and retreat rates of close to
3 m (10 ft) per year. However, between 1915 and 1980, the
estuarine points analyzed in this region showed a range of
approximately 1 m per year of retreat to less than 1 m per
year of advance. Study authors did not analyze the area ad-
jacent to Oregon Inlet or along most of Pea Island. Just north
of Rodanthe, the earlier dataset shows dramatic shoreline
advance averaging 4 m per year, but the later dataset shows a
relatively stable shoreline. Just south of Rodanthe, there was
slow advance during the earlier period and slow retreat (of ap-
proximately 1 m per year or less) in the later period. Between
Avon and Salvo, both datasets show shoreline retreat at rates
not exceeding 2 m per year, with a slightly higher average
rate of retreat in the later period than the earlier period (taken
from Figure 34 in Everts et al., 1983).
The study indicates that the average retreat rate across all
the estuarine points analyzed from 1852 to 1980 was 0.1 m
(4 in) per year. However, this average masks an important
trend seen both north and south of Oregon Inlet. The rate of
shoreline change gradually changed from shoreline advance
(movement towards the sounds) to shore retreat. The rate of
advance was almost2.0mperyearfrom 1852 to 1917. Shores
were generally stable from 1917 to 1949, but they retreated
over the period from 1949 to 1980. Erosion was greater along
estuarine shores facing west (an average of 1.2 m peryear over
1852 to 1980) than those facing north or south (averaging 0.1
m per year over 1852 to 1980). The authors observed that these
data indicate that the North Carolina barrier islands in the
study region did not appear to be migrating landward during
the study period, but instead they narrowed from both sides.
The present rate of island narrowing averages 0.9 m (3.0 ft)
per year. Available data indicate that sand washed over the
barrier islands to the estuarine side of islands (overwash) did
not significantly affect shoreline change along the estuary,
particularly after the artificial dunes were constructed, a pro-
cess that might itself have caused erosion from the sound side
because it removed sand from the estuarine system (Everts et
al., 1983). Away from the inlets connecting the Albemarle-
Pamlico Estuarine System to the ocean, the authors conclude
that the retreat of the estuarine shoreline "can be accounted
for mostly by sea-level rise" (Everts et al., 1983).
AI.G.3.2 POTENTIAL FOR WETLANDS TO PACE WITH
RISING SEA LEVEL
Sections 4.3, 4.4, and 4.6 in Chapter 4 discuss wetland verti-
cal and horizontal development. In North Carolina, vertical
accretion rates have, for the most part, matched the rate of
233
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ix I
sea-level rise (see Section 4.6.2 in Chapter 4; Gaboon, 2003;
Erlich, 1980; Riggs et al., 2000). Vertical accretion rates as
high as 2.4 to 3.6 mm per year have been measured, but the
maximum rate at which wetlands can accrete is not well un-
derstood (Craft Qt al., 1993). Further, relative sea-level rise
in North Carolina in recent years has ranged from approxi-
mately 1.8 to 4.3 mm per year at different points along the
North Carolina coast (Zervas, 2004). As discussed in Section
4.6.2.2 in Chapter 4, wetland drowning could result in some
areas if rates of global sea-level rise increase by 2 mm per
year and is likely if rates increase by 7 mm per year. Day et al.
(2005) suggest that brackish marshes in the Mississippi Delta
region cannot survive 10 mm per year of relative sea-level
rise. Under this scenario, fringe wetlands of North Carolina's
lower coastal plain would drown. However, swamp forest
wetlands along the piedmont-draining rivers are likely to
sustain themselves where there is an abundant supply of min-
eral sediments (e.g., river floodplains, but not river mouths)
(Kuhn and Mendelssohn, 1999). As sea level rises further and
waters with higher salt content reach the Albemarle-Pamlico
peninsula, the ability of peat-based wetlands to keep up is
doubtful, where the peat, root map, and vegetation would
first be killed by brackish water (Poulter, 2005; Portnoy and
Giblin, 1997; Pearsall and Poulter, 2005).
Finally, as described in Chapter 3, in a scenario where there
are high rates of sea-level rise, more inlets would likely be
created and segmentation or disintegration of some of the
barrier islands is possible. This would cause a state change
from a non-tidal to tidal regime as additional inlets open,
causing the Albemarle and Pamlico Sounds to have a signifi-
cant tide range and increased salinity, which would greatly
disrupt current ecosystems. In this scenario, wave activity in
the sounds could change erosion patterns and could impact
wetlands (Riggs and Ames, 2003).
AI.G.3.3 IMPLICATIONS OF
PROTECTION
Ecological/habitat processes and patterns. Some wetland
functions are proportional to size. Other functions depend on
the wetland's edges, that is, the borders between open water
and wetland. Many irregularly flooded marshes in coastal
North Carolina are quite large. In the absence of tidal creeks
and astronomical tidal currents, pathways for fish and inver-
tebrate movement are severely restricted, except when wind
tides are unusually high or during storm events. By contrast,
the twice-daily inundation of tidal marshes by astronomical
tides increases connections across the aquatic-wetland edge,
as does the presence of tidal creeks, which allow fish and
aquatic invertebrates to exploit intertidal areas (Kneib and
Wagner, 1994). Mobility across ecosystem boundaries is less
prevalent in irregularly flooded marshes, where some fish
species become marsh "residents" because of the long dis-
tances required to navigate from marshes to subtidal habitats
(Marraro et al., 1991). Where irregularly flooded marshes
are inundated for weeks at a time, little is known about how
resident species adapt. These include, among other species,
several types offish (e.g., killifish and mummichogs), brown
water snakes, crustaceans (various species of crabs), birds
(yellowthroat, marsh wren, harrier, swamp sparrow, and five
species of rails), and several species of mammals (nutria, cot-
ton rat, and raccoon). North Carolina's coastal marshes are
also home to a reintroduced population of red wolves, and
sea-level rise could affect this population (see Box A1.9).
Effects of human activities. Levees associated with waterfowl
impoundments have isolated large marsh areas in the southern
Pamlico Sound from any connection with estuarine waters.
Impoundments were built to create a freshwater environment
conducive to migratory duck populations and thus eliminated
most other habitat functions mentioned above for brackish
marshes. Further, isolation from sea level influences has
likely disconnected the impoundments from pre-existing
hydrologic gradients that would promote vertical accretion
of marsh soil. If the impoundments were opened to an estua-
rine connection after decades of isolation, they would likely
become shallow, open-water areas incapable of reverting to
wetlands (Day etal, 1990).
Drainage ditches, installed to drain land so that it would be
suitable for agriculture and timber harvesting, are prevalent
in North Carolina. By the 1970s, on the Albemarle-Pamlico
Peninsula, there were an estimated 32 km (20 mi) of streams
and artificial drainage channels per square mile of land, while
the ratio in other parts of North Carolina ranged from 1.4:1
to 2.8:1 (Heath, 1975). InDare County, there are currently an
estimated 4 km (2.5 mi) of drainage ditchfeatures per square
kilometer (Poulter et al., 2008). In many cases, ditches, some
of which were dug more than a century ago to drain farmland
(Lilly, 1981), now serve to transport brackish water landward,
a problem that could become increasingly prevalent as sea
level rises. Saltwater intrusion into agricultural soils and peat
collapse are major consequences of this process.
A number of tide gates have been installed on the Albemarle-
Pamlico Peninsula to reduce brackish water intrusion, but
these will serve their purpose only temporarily, given contin-
ued sea-level rise. One analysis indicates that plugging ditches
in selected places to reduce saltwater flow inland would be
effective for local stakeholders. Another option is to install
new water control structures, such as tide gates, in selected
locations (Poulter et al., 2008). Plugging ditches would also
help restore natural drainage patterns to the marshes.
234
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
BOX AI.9: Reintroduced Population of Red Wolves in North Carolina
Habitat:
The red wolf (Canis rufus) is federally listed as endangered
and was formerly extinct in the wild. Red wolves were
hunted and trapped aggressively in the early 1900s as
the Southeast became increasingly developed, and the
remaining wolf populations then suffered further declines
with the extensive clearing of forest and hardwood river
bottoms that formed much of the prime red wolf habitat
(USFWS, 1993, 2004c). The last wild red wolves were
found in coastal prairie and marsh habitat, having been
pushed to the edges of their range in Louisiana and
Texas. The red wolf is elusive and most active at dawn
and dusk. It lives in packs of five to eight animals, and it
feeds on white-tailed deer, raccoon, rabbit, nutria, and
other rodents. In addition to food and water in a large
home range area (65 to 130 sq km, or 25 to 50 sq mi), red
wolves require heavy vegetation cover (USFWS, 1993).
Photo source: Barren Crawford, USFWS, Red Wolf Re-
covery Project.
Locations:
Through a captive breeding program and reintroduction of the species, there are now an estimated total of
100 red wolves living in the wild in coastal areas of North Carolina. In the wild, the red wolf currently occupies
approximately 690,000 ha (1.7 million ac) on three national wildlife refuges and other public and private
lands in eastern North Carolina. Principal among these areas is the Alligator River National Wildlife Refuge
(NWR), the site of the red wolfs reintroduction to the wild in 1987 (USFWS, 2006). This low-lying refuge is
surrounded on three sides by coastal waters and connected to the mainland by a largely developed area. Red
wolves have also been reintroduced to the Pocosin Lakes NWR, slightly inland from Alligator River NWR,
and are occasionally sighted on the Mattamuskeet NWR. The last wild red wolves were found in Louisiana
and Texas coastal marsh areas, but their historic range extended from southern Pennsylvania throughout the
Southeast and west as far as central Texas (USFWS, 2004c). Despite their potential for survival in numerous
habitat types throughout the southeastern United States, the small current population could face serious
threats from sea-level rise.
Impact of Sea-Level Rise:
In a 2006 report, the Defenders of Wildlife (an environmental advocacy organization) characterized Alligator
River NWR, the red wolfs primary population center, as one of the ten NWRs most gravely at risk due to
sea-level rise. The effects of sea-level rise can already be seen on the habitat in Alligator River NWR, where
pond pine forest has transitioned into a sawgrass marsh in one area, and the peat soils of canal banks are
eroding near the sounds (Stewart, 2006). Areas of hardwood forest and pocosin will be replaced by expanding
grass-dominated freshwater marshes currently occupying the edges of the sounds. Bald cypress and swamp
tupelo forests will also replace the hardwood areas (USFWS, 2006). While it is too early to be certain, the
Alligator River NWR biologist projects that the red wolf is not likely to adapt to the marsh habitat given the
rate at which habitat conversion is already taking place (Stewart, 2006). Ultimately, the low-lying refuge risks
being flooded by sea-level rise, in addition to its forests being converted to marsh. Furthermore, developed
areas inland of the peninsular refuge limit habitat migration potential.
235
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I
• •' I', ill • "•
- , .• " ll
AI.G.4.1 STATEWIDE POLK i ' • .111 - r
Several North Carolina laws and regulations have an impact
on response to sea-level rise within the state. First, setback
rules encourage retreat by requiring buildings being con-
structed or reconstructed to be set back a certain distance
from where the shoreline is located when construction
permits are issued. Second, North Carolina does not allow
"hard" shoreline armoring84 such as seawalls and revetments
on oceanfront shorelines85, preventing property owners from
employing one possible method of holding back the sea to
protect property86. Along estuarine shores, however, shoreline
armoring is allowed landward of any wetlands. The North
Carolina Coastal Resources Commission (CRC) is preparing
new state regulations for the location and type of estuarine
shoreline stabilization structures to help encourage alterna-
tives to bulkheads (NC CRC, 2008b; Feldman, 2008). The
goals are similar to the "living shorelines" legislation recently
enacted in Maryland (see Section Al.F.2.2). Adding sand to
beaches (i.e., beach nourishment) is the preferred method
in North Carolina to protect buildings and roads along the
ocean coastline.
The state's Coastal Area Management Act (CAMA) has fos-
tered land-use planning in the 20 coastal counties to which it
applies. Regulations authorized by CAMA require local land
use plans to "[d]evelop policies that minimize threats to life,
property, and natural resources resulting from development
located in or adjacent to hazard areas, such as those subject to
erosion, high winds, storm surge, flowing, or sea-level rise".
However, the state's technical manual for coastal land-use
planning (NC DCM, 2002) does not mention sea-level rise.
Accordingly, local land-use plans either do not mention sea-
level rise at all, mention it only in passing, or explicitly defer
decisions about vulnerable areas until more information is
available in the future (Feldman, 2008; Poulter et al, 2009).
Nevertheless, the regulatory requirement to consider sea-level
rise may eventually encourage local jurisdictions to consider
how the communities most vulnerable to sea-level rise should
prepare and respond (Feldman, 2008). Land-use plans are
updated regularly and are an important tool for increasing
public awareness about coastal hazards.
84 See Chapter 6 for an explanation of various shore protection
options.
8515ANCAC07H.0101.
86 Some hard structures exist along North Carolina's oceanfront
shoreline (e.g., adjacent to inlets). Many were built before 1985
when the statute was enacted to ban new hard structures, or were
covered by exception in the rules. The Legislature regularly considers
additional exceptions, such as terminal groins for beach nourishment
projects and jetties for stabilizing inlets, e.g., North Carolina SB599
(2007-2008).
North Carolina's CAMA and the state's Dredge and Fill Law
authorize the CRC to regulate certain aspects of development
within North Carolina's 20 coastal counties. For example, the
CRC issues permits for development and classifies certain
regions as Areas of Environmental Concern (AECs, e.g.,
ocean hazard zones and coastal wetlands) where special rules
governing development apply. Land use plans are binding in
AECs. In response to the threat of damage to coastal struc-
tures from the waves, since 1980 North Carolina has required
new development to be set back from the oceanfront. The
setbacks are measured from the first line of stable natural
vegetation87. Single-family homes of any size—as well as
multi-family homes and non-residential structures with less
than 464 sqm(5,000 sqft) of floor area—must be set back by
18.3 m (60 ft) or 30 times the long-term rate of erosion as cal-
culated by the state, whichever is greater. Larger multi-family
homes and non-residential structures must be set back by 36.6
m (120 ft) or the erosion-based setback distance, whichever is
greater. The setback distance for these larger structures is set
as either 60 times the annual erosion rate or 32 m (105 ft) plus
30 times the erosion rate, whichever is less88. North Carolina
is considering changes to its oceanfront setback rules, includ-
ing progressively larger setback factors for buildings with 929
sq m (10,000 sq ft) of floor area or more (NC CRC, 2008a).
Along estuarine shorelines, North Carolina has a 9.1-m (30-
ft) setback89 and restricts development between 9.1 and 22.9
m (30 and 75 ft) from the shore90. As the shore moves inland,
these setback lines move inland as well.
As of 2000, the U.S. Army Corps of Engineers participated
in beach nourishment projects along more than 51 km (32
mi) of North Carolina's shoreline (including some nourish-
ment projects that occurred as a result of nearby dredging
projects), and nourishment along an additional 137 km (85 mi)
of coastline had been proposed (USAGE, 2000)91. If neces-
sary, property owners can place large geotextile sandbags in
front of buildings to attempt to protect them from the waves.
Standards apply to the placement of sandbags, which is sup-
posed to be temporary (to protect structures during and after
a major storm or other short-term event that causes erosion,
87 Local governments can request that an alternative vegetation line be
established under certain conditions. Additional rules also apply when
there is a sand dune between the home and the shoreline, to protect
the integrity of the dune.
8815ANCAC 07H.0305-0306.
8915ANCAC07H.0306.
9015ANCAC07H.0209.
91 Although beach nourishment has been a common response to sea-
level rise in many areas along the coast, there has been a decline in
the availability of suitable sand sources for nourishment, particularly
along portions of the coast (Bruun, 2002; Finkl et al., 2007). In
addition, the availability of substantial federal funds allocated for
beach nourishment has become increasingly questionable in certain
areas, particularly in Dare County (Dare County, 2007; Coastal
Science and Engineering, 2004).
236
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to
A Focus on the Mid-Atlantic Region
or to allow time for relocation)92. Buildings are supposed to
be moved or removed within two years of becoming "im-
minently threatened" by shoreline changes93.
North Carolina officials are in the process of reassessing
certain state policies in light of the forces of shoreline change
and climate change. Policy considerations have been affected
by numerous studies that researchers have published on the
potential effects of sea-level rise on North Carolina (Poulter
et al, 2009). The state legislature appointed a Legislative
Commission on Global Climate Change to study and report
on potential climate change effects and potential mitigation
strategies, including providing recommendations that address
impacts on the coastal zone94. The Commission's recom-
mendations have not yet been finalized, but an initial draft
version offered such suggestions as creating a mechanism
to purchase land or conservation easements in low-lying
areas at great risk from sea-level rise; providing incentives
for controlling erosion along estuarine shorelines using eco-
logically beneficial methods; creating a commission to study
adaptation to climate change and make recommendations
about controversial issues; and inventorying, mapping, and
monitoring the physical and biological characteristics of the
entire shoreline (Feldman, 2008; Riggs et al., 2007).
The CRC is also considering the potential effects of sea-level
rise and whether to recommend any changes to its rules af-
fecting development in coastal areas (Feldman, 2008). In ad-
dition, NCDCM is developing a Beach and Inlet Management
Plan to define beach and inlet management zones and propose
preliminary management strategies given natural forces,
economic factors, limitations to the supply of beach-quality
sand, and other constraints (Moffatt & Nichol, 2007).
AI.G.4.2 CURRENT LAND USE
Ocean Coast (from north to south). North Carolina's ocean
coast, like the coasts of most states, includes moderate and
densely developed communities, as well as undeveloped
roadless barrier islands. Unlike other mid-Atlantic states,
North Carolina's coast also includes a major lighthouse (at
Cape Hatteras) that has been relocated landward, a roadless
coastal barrier that is nevertheless being developed (described
below), and densely populated areas where storms, erosion,
and sea-level rise have caused homes to become abandoned
or relocated.
The northern 23 km (14 mi) of the state's coastline is a desig-
nated undeveloped coastal barrier under the Coastal Barrier
Resources Act (CBRA) and hence ineligible for most federal
9215ANCAC07H.0308.
9315ANCAC07H.0306(1).
94 See the "North Carolina Global Warming Act", Session Law 2005-
442.
programs (USFWS, undated[c]) This stretch of barrier island
includes two sections of Currituck National Wildlife Refuge,
each about 2 km (1 mi) long, which are both off-limits to
development. Nevertheless, the privately owned areas are
gradually being developed, even though they are accessible
only by boat or four-wheel drive vehicles traveling along
the beach. The CBRA zones are ineligible for federal beach
nourishment and flood insurance (USFWS, undated[c]).
Along the Dare County coast from Kitty Hawk south to Nags
Head, federal legislation has authorized shore protection,
and USAGE (2006b) has concluded that the proposed project
would be cost-effective. In some areas, homes have been lost
to shoreline erosion (Pilkey et al., 1998) (see Figure 12.6 in
Chapter 12). Continued shore erosion has threatened some
of the through streets parallel to the shore, which had been
landward of the lost homes. Given the importance of those
roads to entire communities (see Section 12.2 in Chapter 12)
small sand replenishment projects have been undertaken to
protect the roads (Town of Kitty Hawk, 2005). The planned
beach nourishment project does not extend along the coast
to the north of Kitty Hawk. Those beaches are generally not
open to the public and are currently ineligible for publicly
funded beach nourishment.
From Nags Head to the southwestern end of Hatteras Island,
most of the coast is part of Cape Hatteras National Seashore.
A coastal highway runs the entire length, from which one can
catch a ferry to Ocracoke Island, carrying through traffic to
both Ocracoke and Carteret County. Therefore, the National
Park Service must balance its general commitment to allow-
ing natural shoreline processes to function (see Section 12.1;
NRC 1988) with the needs to manage an important transporta-
tion artery. In most cases, the approach is a managed retreat,
in which shores generally migrate but assets are relocated
rather than simply abandoned to the sea. In 1999, as shore
erosion threatened the Cape Hatteras Lighthouse, Congress
appropriated $9.8 million to move the lighthouse 900 m (2900
ft) to the southwest, leaving it the same distance from the
eastern shore of Hatteras Island (about 450 m, or 1475 ft) as it
had been when it was originally constructed (see Figure 11. la
in Chapter 11). The coastal highway has been relocated inland
in places. Because it is essential infrastructure, its protection
would probably require maintaining the barrier island itself,
for example, by filling inlets after severe storms. A possible
exception is where the highway runs through Pea Island Na-
tional Wildlife Refuge on the northern end of Hatteras Island,
just south of the bridge over Oregon Inlet. The federal and
state governments are considering the possibility that when
a new bridge is built over Oregon Inlet, it would bypass the
National Wildlife Refuge and extend over Pamlico Sound just
west of Hatteras Island as far as Rodanthe (USDOI, 2007).
237
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[Tie U.S. Climate Change Science
Appendix I
The undeveloped Portsmouth Island and Core Banks consti-
tute Cape Lookout National Seashore and lack road access.
Cape Lookout is located on Core Banks. Shackleford Banks,
immediately adjacent to the southwest, is also roadless and
uninhabited. Southwest of Cape Lookout, the coast consists
mostly of developed barrier islands, conservation lands, and
designated "undeveloped coastal barriers" that are never-
theless being developed. Bogue Banks includes five large
communities with high dunes and dense forests (Pilkey et al,
1998). Bogue Banks also receives fill to widen its beaches
regularly.
To the west of Bogue Banks are the barrier islands of Onslow
County and then Fender County. Some islands are only ac-
cessible by boat, and most of these are undeveloped. North
Topsail Beach, on Topsail Island, has been devastated by
multiple hurricanes, in part due to its low elevation and the
island's narrow width. Erosion has forced multiple roads on
the island to be moved. While some parts of North Topsail
Beach are part of a unit under the CBRA system, making
them ineligible for federal subsidies, development has oc-
curred within them nonetheless (Pilkey et al., 1998).
Further to the southwest are the barrier islands of New Ha-
nover County, including Figure Eight Island, which is entirely
privately owned with no public access to the beach, and hence
ineligible for public funding for beach nourishment (see
Chapter 8). Wrightsville Beach, like many other communities
southwest of Cape Lookout, has an inlet on each side. It is the
site of a dispute to protect a hotel from being washed away
due to inlet migration (Pilkey et al, 1998). The US ACE has
made a long-term commitment to regular beach renourish-
ment to maintain the place of the shoreline in Wrightsville
Beach and Carolina Beach (USAGE, 2006a). An exception
to North Carolina's rules forbidding hardened structures has
been granted in Kure Beach, west of Carolina Beach, where
stone revetments have been placed on the oceanfront to pro-
tect Fort Fisher (which dates back to the Civil War). These
structures also protect a highway that provides access to the
area (Pilkey et al., 1998). Most of the beach communities in
New Hanover County are extensively developed.
Some of the barrier islands in Brunswick County, close to the
South Carolina state line, are heavily forested with high eleva-
tions, making them more resilient to coastal hazards (Pilkey
et al., 1998). Holden Beach and Ocean Isle Beach, however,
contain many dredge-and-fill finger canals. Historically, at
least two inlets ran through Holden Beach; and storms could
create new inlets where there are currently canals (Pilkey et
al., 1998).
Estuarine Shores. Significant urbanization was slow to come
to this region for many reasons. Most of the area is farther
from population centers than the Delaware and Chesapeake
Estuaries. The Outer Banks were developed more slowly than
the barrier islands of New Jersey, Delaware, and Maryland.
Most importantly, the land is mostly low and wet.
Unlike the Delaware Estuary, North Carolina does not have a
long history of diking tidal wetlands to reclaim land from the
sea for agricultural purposes95. However, the state is starting
to gain experience with dikes to protect agricultural lands
from flooding. In Tyrrell County, the Gum Neck township
has been protected with a dike for four decades. A dike is
under construction for the town and farms around Swan
Quarter (Allegood, 2007), the county seat of Hyde County
(which includes Ocracoke Island). Hurricanes Fran and Floyd
led to federally-sponsored purchases of thousands of proper-
ties across North Carolina's eastern counties, facilitating the
demolition or relocation of associated structures. Pamlico
County has encouraged people to gradually abandon Goose
Creek Island in the eastern portion of the county, by working
with FEMA to relocate people rather than rebuild damaged
homes and businesses (Barnes, 2001). By contrast, in other
areas (e.g., parts of Carteret County), people took the opposite
approach and elevated homes.
Geography, coastal features, and community characteristics
vary greatly along North Carolina's coast. Thus, one can as-
sume that a variety of different planning and adaptation strat-
egies related to shoreline change and sea-level rise would be
needed, particularly over the long term. Scientists, managers,
and community members in North Carolina have undertaken
a variety of efforts to better understand and begin to address
potential sea-level rise vulnerabilities and impacts. These
research and collaborative efforts may increase awareness,
receptivity, and readiness to make informed coastal manage-
ment decisions in the future (Poulter et al., 2009).
95 Nevertheless, it has had a few short-lived projects, most notably Lake
Matamuskeet.
238
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
fN
X
Q
a.
o_
Basic Approaches for Shoreline Change Projections
Lead Author: Benjamin T. Gutierrez, USGS
Contributing Authors: S. Jeffress Williams, USGS; E. Robert Thieler, USGS
While the factors that influence changes in shoreline
position in response to sea-level rise are well known,
it has been difficult to incorporate this understanding
into quantitative approaches that can be used to assess
land loss over long time periods (e.g., 50 to 100 years).
The validity of some of the more common approaches
discussed in this Appendix has been a source of debate
in the scientific community (see Chapter 3, Section
3.1). This Appendix reviews some basic approaches
that have been applied to evaluate the potential for
shoreline changes over these time scales.
The Bruun Model. One of the most widely known mod-
els developed for predicting shoreline change driven
by sea-level rise on sandy coasts was formulated by
Bruun (1962, 1988). This model is often referred to as
the "Bruun rule" and considers the two-dimensional
shoreline response (vertical and horizontal) to a rise
in sea level. A fundamental assumption
of this model is that over time the cross-
shore shape of the beach, or beach profile,
assumes an equilibrium shape that trans-
lates upward and landward as sea level
rises. Four additional assumptions of this
model are that:
1. The upper beach is eroded due to
landward translation of the profile.
2. The material eroded from the up-
per beach is transported offshore
and deposited such that the volume
eroded from the upper beach equals
the volume deposited seaward of the
shoreline.
3. The rise in the nearshore seabed as a result of depo-
sition is equal to the rise in sea level, maintaining a
constant water depth.
4. Gradients in longshore transport are negligible.
Mathematically, the model is depicted as:
Z*
R= -S (A2.1)
B + h*
where R is the horizontal retreat of the shore, h* is the
depth of closure or depth where sediment exchange
between the shore face and inner shelf is assumed to be
minimal, B is the height of the berm, L, is the length of the
beach profile to h*, and S is the vertical rise in sea level
(Figure A2.1). This relationship can also be evaluated
based on the slope of the shore face, ©, as:
1
R =
tan©
•S
(A2.2)
Beach \
Bottom Profile
After Sr.a Love-
Rise
>-&-!
>
^
Bruun
f
B
t
i
Model
i_»
Sea Level
s After Rise /
\ ^.Initial Bottom
^^ Profile
^^5=
ft
Initial Sea Level
r
Bottom Alter Sea
jf Level Rise
/
Initial Bottom
S = S' Vertical rise in soa-kwoi
b-i-b1 Erosion and offshore transport
o( sand in response to sea-level rise
\
~S
1
h,
-*
j
Limiting Depth Betweet
Predominant Nearshort
and Offshore Material
1
1
Figure A2.I Illustration showing the Bruun Model and the basic dimen-
sions of the shore that are used as model inputs (After Schwartz, 1967 and
Dean and Dalrymple, 2002).
239
-------
The U.S. Climate Change Science Program
Appendix 2
Formost sites, it has beenfound that general values of © andR
are approximately 0.01 to 0.02 and 50-S to 100-S, respectively
(Wright, 1995; Komar, 1998; Zhang, 1998).
A few studies have been conducted to verify the Bruun Model
(Schwartz, 1967; Hands, 1980; also reviewed in SCOR, 1991;
Komar, 1998; and Dean and Dairy mple, 2002). In other cases,
some researchers have advocated that there are several uncer-
tainties with this approach, which limit its use in real-world
applications (Thieler et al., 2000; Cooper and Pilkey, 2004;
also reviewed in Dubois, 2002). Field evaluations have also
shown that the assumption of profile equilibrium can be dif-
ficult to meet (Riggse/ al., 1995; List et al., 1997). Moreover,
the Bruun relationship neglects the contribution of longshore
transport, which is a primary mechanism of sediment trans-
port in the beach environment (Thieler et al., 2000) and there
have been relatively few attempts to incorporate longshore
transport rates into this approach (Everts, 1985).
A number of investigators have expanded upon the Bruun rule
or developed other models that simulate sea-level rise driven
shoreline changes. Dean and Maurmeyer (1983) adapted and
modified the Bruun rule to apply to barrier
islands (e.g., the Generalized Bruun Rule).
Cowell etal. (1992) developed the Shoreline
Translation Model (STM), which incorpo-
rated several parameters that characterize
the influence of the geological framework
into sea-level rise-driven shoreline change
for barrier islands. Stolper et al. (2005) de-
veloped a rules-based geomorphic shoreline
change model (GEOMBEST) that simulates
barrier island evolution in response to sea-
level rise. While these models can achieve
results consistent with the current under-
standing of sea-level rise-driven changes to
barrier island systems, there is still need for
more research and testing against both the
geologic record and present-day observa-
tions to advance scientific understanding
and inform management.
Historical Trend Extrapolation. Another
commonly used approach to evaluate po-
tential shoreline change in the future relies
on the calculation of shoreline change rates
based on changes in shoreline position over
time. In this approach, a series of shorelines
from different time periods are assembled
from maps for a particular area. In most
cases, these shorelines are derived from
either National Ocean Service T-sheets,
aerial photographs, from Global Positioning
System (GPS) surveys, or lidar surveys (Shalowitz, 1964;
Leatherman, 1983; Dolan et al., 1991; Anders and Byrnes,
1991; Stockdon et al, 2002). The historical shorelines are then
used to estimate rates of change over the time period covered
by the different shorelines (Figure A2.2). Several statistical
methods are used to calculate the shoreline change rates with
the most commonly used being end-point rate calculations or
linear regression (Dolan et al., 1991; Crowell e/a/., 1997). The
shoreline change rates can then be used to extrapolate future
changes in the shoreline by multiplying the observed rate of
change by a specific amount of time, typically in terms of
years (Leatherman, 1990; Crowell etal., 1997). More specific
assumptions can be incorporated that include other factors
such as the rate of sea-level rise or geological characteristics
of an area (Leatherman, 1990; Komar et al., 1999).
Because past shoreline positions are readily available from
maps that have been produced over time, the extrapolation
of historical trends to predict future shoreline position has
been applied widely for coastal management and planning
(Crowell and Leatherman, 1999). In particular, this method
is used to estimate building setbacks (Fenster, 2005). Despite
Calculating Long-Term Shoreline Change Rates:
Fire Island, New York
73'ff 7S"85'
Figure A2.2 Aerial photograph of Fire Island, New York showing former
shoreline positions and how these positions are used to calculate long-term
shoreline change rates using linear regression. The inset box shows the
shoreline positions at several points in time over the last 170 years. From the
change in position with time, an average rate of retreat can be calculated. This
is noted by the slope of the line, m. The red line in the inset box indicates the
best fit line while the dashed lines specify the 95-percent confidence interval
for this fit. Photo source: State of New York GIS.
240
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Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
this, relatively few studies have incorporated
shoreline change rates into long-term shore-
line change predictions to evaluate sea-level
rise impacts, particularly for cases involving
accelerated rates of sea-level rise (Kana et al.,
1984; Leatherman, 1984).
Historical trend analysis has evolved over
the last few decades based on earlier efforts
to investigate shoreline change (described in
Crowell et al., 2005). Since the early 1980s,
computer-based Geographical Information
System (GIS) software has been developed to
digitally catalog shoreline data and facilitate
the quantification of shoreline change rates
(May et al, 1982; Leatherman, 1983; Thieler
et al., 2005). At the same time, thorough re-
view and critique of the procedures that are
employed to make these estimates have been
conducted (Dolan et al., 1991; Crowell et al.,
1991,1993,1997; Douglas et al., 1998; Douglas
and Crowell, 2000; Honeycutte/a/., 2001; Fen-
ster et al, 2001; Ruggiero et al, 2003; Moore
et al, 2006; Genz et al, 2007).
The Coastal Sediment Budget
• Debit (Sediment Loss)
•Credit (Sediment Gain)
1, Cliff Erosion
2. Input From Coastal Rivers
3, Wind Transport
4. Longshore Transport
5, Cross-Shone Exchange
with the Continental Shelf
Coastal
Headland
^
Figure A2.3 Schematic of the coastal sediment budget (modified from Komar,
I996). Using the sediment budget approach, the gains and losses of sediment
from the beach and nearshore regions are evaluated to identify possible underly-
ing causes for shoreline changes. In this schematic the main sediment gains are
from: cliff erosion, coastal rivers, longshore transport, and cross-shore sediment
transport from the continental shelf. The main sediment losses are due to off-
shore transport from the beach to the shelf and wind transport from the beach
to coastal dunes.
Recently, a national scale assessment of shore-
line changes that have occurred over the last century has been
carried out by the U. S. Geological Survey (Gulf Coast: Mor-
ton et al, 2004; southeastern U.S. coast: Morton and Miller,
2005; California coast: Hapke etal., 2006). In addition, efforts
are ongoing to complete similar analyses for the northeastern,
mid-Atlantic, Pacific Northwest, and Alaskan coasts.
The Sediment Budget. Another approach to shoreline change
assessment involves evaluating the sediment mass balance,
or sediment budget, for a given portion of the coast (Bowen
and Inman, 1966; Komar, 1996; List, 2005; Rosati, 2005),
as shown in Figure A2.3. Using this method, the gains and
losses of sediment to a portion of the shore, often referred to
as a control volume, are quantified and evaluated based on
estimates of beach volume change. Changes in the volume of
sand for a particular setting can be identified and evaluated
with respect to adjacent portions of the shore and to changes
in shoreline position over time. One challenge related to this
method is obtaining precise measurements that minimize
error since small vertical changes over these relatively low
gradient shoreline areas can result in large volumes of mate-
rial (NRC, 1987). To apply this approach, accurate measure-
ments of coastal landforms, such as beach profiles, dunes, or
cliff positions, are needed. Collection of such data, especially
those on the underwater portions of the beach profile, is dif-
ficult. In addition, high-density measurements are needed to
evaluate changes from one section of the beach to the next.
While the results can be useful to understand where sedi-
ment volume changes occur, the lack of quality data and the
expense of collecting the data limit the application of this
method in many areas.
The Coastal Vulnerability Index. One approach that has
been developed to evaluate the potential for coastal changes
is through the development of a Coastal Vulnerability Index
(CVI, Gornitz and Kanciruk, 1989; Gornitz, 1990; Gornitz
et al, 1994; Thieler and Hammar-Klose, 1999). Recently,
the U.S. Geological Survey (USGS) used this approach to
evaluate the potential vulnerability of the U.S. coastline
on a national scale (Thieler and Hammar-Klose, 1999) and
on a more detailed scale for the U.S. National Park Service
(Thieler et al, 2002). The USGS approach reduced the index
to include six variables (geomorphology, shoreline change,
coastal slope, relative sea-level change, significant wave
height, and tidal range) which were considered to be the
most important in determining a shoreline's susceptibility to
sea-level rise (Thieler and Hammar-Klose, 1999). The CVI
is calculated as:
(A2.3)
241
-------
The U.S. Climate Change Science Program
Appendix 2
where a is the geomorphology, b is the rate of shoreline
change, c is the coastal slope, d is the relative sea-level
change, e is the mean significant wave height, and/is the
mean tidal range.
The CVI provides a relatively simple numerical basis for
ranking sections of coastline in terms of their potential for
change that can be used by managers to identify regions where
risks may be relatively high. The CVI results are displayed on
maps to highlight regions where the factors that contribute to
shoreline changes may have the greatest potential to contrib-
ute to changes to shoreline retreat (Figure A2.4).
Coastal Variability Index:
Assateague Island National Seashore, Maryland
Coastal
/ulneratjilrtv
WfcM* fWue« lnnS
* lilanj
Vulnerability Ranking
VERY HIGH
[ 1 HWH
] MO06RATE
H LOW
H VERY LOW
0 2.S 5 10km
Short** Ch*no*
Coastal S-ope
4 • R«t*trva Se»4.«val Rise
5 « S«jnificam WBVO Hcighi
6 • Tidal Ranoe
Figure A2.4 Coastal Vulnerability Index (CVI) calculated for Assateague
Island National Seashore in Maryland. The inner most color-coded bar is
the CVI estimate based on the other input factors (I through 6). From
Pendleton et al. (2004).
242
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GO
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oL
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GLOSSARY
100-year flood
the standard used by the National Flood Insurance Pro-
gram (NFIP) for floodplain management purposes and
to determine the need for flood insurance; a structure
located within a special flood hazard area shown on an
NFIP map has a 26 percent chance of suffering flood
damage during the term of a 30-year mortgage
A Zone
areas inundated in a 100-year storm event that experi-
ence conditions of less severity than conditions expe-
rienced in V Zones
access, lateral
the right to walk or otherwise move along a shoreline,
once someone has reached the shore
access, perpendicular
a legally permissible means of reaching the shore from
dry land
access point
a place where anyone may legally gain access to the
shore; usually a park, the end of a public street, or a
public path; a place where perpendicular access (see
access, perpendicular) is provided
accretion
the accumulation of a sedimentary deposit that in-
creases the size of a land area; this increase may be
either lateral or vertical
armoring
the placement of fixed engineering structures, typically
rock or concrete, on or along the shoreline to mitigate
the effects of coastal erosion and protect infrastruc-
ture; such structures include seawalls, revetments,
bulkheads, and riprap
avulsion
a sudden cutting off or separation of land by a flood or
by an abrupt change in the course of a stream; as by a
stream breaking through a meander or a sudden change
in current whereby a stream deserts its old channel for
a new one; OR rapid erosion of the shore by waves
during a storm
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
barrier island
a long, narrow coastal sandy island that is above high
tide and parallel to the shore, and that commonly has
dunes, vegetated zones, and swampy terraces extending
landward from the beach
barrier island rollover
the landward migration or landward transgression of a
barrier island, accomplished primarily over decadal or
longer time scales through the process of storm overwash,
periodic inlet formation, and wind-blown transport of
sand
barrier migration
the movement of an entire barrier island or barrier
spit in response to sea-level rise, changes in sediment
supply, storm surges or waves, or some combination of
these factors
barrier spit
a barrier island that is connected at one end to the
mainland
bathymetry
the measurement of ocean depths and the mapping of the
topography of the seafloor
beach
the unconsolidated material that covers a gently slop-
ing zone extending landward from the low water line
to the place where there is a definite change in material
or physiographic form (such as a cliff), or to the line of
permanent vegetation (usually the effective limit of the
highest storm waves)
beach nourishment
the addition of sand, often dredged from offshore, to an
eroding shoreline to enlarge or create a beach area, of-
fering both temporary shore protection and recreational
opportunities
berm
a commonly occurring, low, impermanent, nearly
horizontal ledge or narrow terrace on the backshore of a
beach, formed of material thrown up and deposited by
storm waves
bluff
a high bank or bold headland with a broad, precipitous,
sometimes rounded cliff face overlooking aplain or body
of water
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Glossary and Acronyms
breakwater
an offshore structure (such as a wall or jetty) that, by break-
ing the force of the waves, protects a harbor, anchorage,
beach or shore area
breach
(n.) a channel through a barrier spit or island typically
formed by storm waves, tidal action, or river flow; breaches
commonly occur during high storm surge cause by a hur-
ricane or extratropical storm', (v.) to cut a deep opening in
a landform
bulkhead
a structure or partition to retain or prevent sliding of the land;
a secondary purpose is to protect uplands against damage
from wave action
coastal plain
any lowland area bordering a sea or ocean, extending in-
land to the nearest elevated land, and sloping very gently
seaward
coastal zone
the area extending from the ocean inland across the region
directly influenced by marine processes
coastline
the line that forms the boundary between the coast and the
shore or the line that forms the boundary between the land
and the water
continental shelf
the gently sloping underwater region at the edge of the con-
tinent that extends from the beach to where the steep conti-
nental slope begins, usually at depths greater than 300 feet
continental margin
the region of the sea floor between the shoreline and the deep
abyssal ocean, see margin, active and margin, passive
contour interval
the difference in elevations of adjacent contours on a topo-
graphic map
current
the horizontal movement patterns in bodies of water; in
coastal areas, currents are influenced by a combination of
tidal (flood and ebb) and nontidal (wind-driven, river flow)
forces
datum
a quantity, or a set of quantities, that serves as a basis for
the calculation of other quantities; in surveying and map-
ping, a datum is a point, line or surface used as a reference
in measuring locations or elevations
delta
a low relief landform composed of sediments deposited at the
mouth of a river that commonly forms a triangular or fan-
shaped plain of considerable area crossed by many channels
from the main river; forms as the result of accumulation of
sediment supplied by the river in such quantity that it is not
removed by tidal or wave-driven currents
DEM (digital elevation model)
the digital representation of the ground surface or terrain
using a set of elevation data
deposition
the laying, placing, or throwing down of any material; typi-
cally refers to sediment
depth of closure
a theoretical depth below which sediment exchange between
the nearshore (beach and shoreface) and the continental shelf
is deemed to be negligible
dike
a wall generally of earthen materials designed to prevent
the permanent submergence of lands below sea level, tidal
flooding of lands between sea level and spring high water,
or storm-surge flooding of the coastal floodplain
discount rate
an assumed interest rate or rate of return used to calculate the
present value of a future payment; in mathematical terms,
the present value of receiving $1 Y years hence is l/(l-r)Y,
where r is the discount rate
downdrift
the location of one section or feature along the coast in re-
lation to another; often used to refer to the direction of net
longshore sediment transport between two or more locations
(i.e., downstream)
dredge and fill
an engineering process by which channels are dredged
through wetlands or uplands to allow small boat navigation,
and dredge spoil is placed on the adjacent land area to raise
the land high enough to allow development; sometimes re-
ferred to as "lagoon development" or "canal estates"; used
extensively before the 1970s
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dune
alow mound, ridge, bank, or hill of loose, wind-blown mate-
rial such as sand; capable of movement from place to place
but typically retaining a characteristic shape; may be either
bare or covered with vegetation
ebb current
the tidal current associated with the decrease in height of
the tide, generally moving seaward or down a tidal river or
estuary, see also flood current
ebb tide delta
a large sand shoal commonly deposited at the mouths of
tidal inlets formed by ebbing tidal currents and modified in
shape by waves, compare with flood tide delta
erosion
the mechanical removal of sedimentary material by gravity,
running water, moving ice, or wind; in the context of coastal
settings erosion refers to the landward retreat of a shoreline
indicator such as the water line, the berm crest, or the vegeta-
tion line; the loss occurs when sediments are entrained into
the water column and transported from the source
erosion-based setback
a setback equal to an estimated annual erosion rate multi-
plied by a number of years set by statute or regulation (e.g.,
30 years)
estuary
a semi-enclosed coastal body of water which has a free
connection with the open sea and within which sea water
is measurably diluted with freshwater from land drainage;
an inlet of the sea reaching into a river valley as far as the
upper limit of tidal rise, usually being divisible into three
sectors; (a) a marine or lower estuary, in free connection
with the open sea; (b) a middle estuary subject to strong salt
and freshwater mixing; and (c) an upper or fluvial estuary,
characterized by fresh water but subject to daily tidal ac-
tion; limits between these sectors are variable, and subject
to constant changes in the river discharge
extratropical storm
a cyclonic weather system, occurring in the middle or high
latitudes (e.g., poleward of the tropics) that is generated by
colliding airmasses; such weather systems often spawn large
storms that occurr between late fall and early spring
fetch
the area of the open ocean where the winds blow over with
constant speed and direction, generating waves
flood current
the tidal current associated with the increase in height of the
tide or the incoming tide, generally moving landward or up
into a tidal river or estuary, see also ebb current
flooding
the temporary submergence of land that is normally dry,
often due to periodic events such as storms, see also inun-
dation
flood tide delta
a large sand shoal commonly deposited on the landward side
of a tidal inlet formed by flooding tidal currents, compare
with ebb tide delta
floodproofing
a set of techniques that are intended to limit the amount
of damage that will occur to a building and/or its contents
during a flood (see also floodproofing, dry andfloodproof-
ing, wet)
floodproofing, dry
a.floodproofing technique in which modifications are made
to allow f loodwaters inside a building while ensuring that
there is minimal damage to either the structure or its con-
tents
floodproofing, wet
afloodproofing technique in which a building is sealed such
that f loodwaters cannot get inside the structure
forcing
to hasten the rate of progress or growth; in this report, forc-
ing generally refers to climate change factors that act to alter
a particular physical, chemical, or biological system (e.g.,
changes in climate such as greenhouse gas concentration,
temperature, sea level, or storm characteristics)
geologic framework
the underlying geological setting, structure, and lithology
(rock/sediment type) in a given area
geomorphology (geomorphic)
the external structure, form, and arrangement of rocks or
sediments in relation to the development of the surface of
the Earth
global sea-level rise
the worldwide average rise in mean sea level; may be due to
a number of different causes, such as the thermal expansion
of sea water and the addition of water to the oceans from the
melting of glaciers, ice caps, and ice sheets; contrast with
relative sea-level rise
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Glossary and Acronyms
groin
an engineering structure oriented perpendicular to the coast,
used to accumulate littoral sand by interrupting longshore
transport processes; often constructed of concrete, timbers,
steel, or rock
high marsh
the part of a marsh that lies between the low marsh and the
marsh's upland border; this area can be expansive, extend-
ing hundreds of yards inland from the low marsh area;
soils here are mostly saturated but only flooded during
higher-than-average astronomical tides (see tides and tides,
astronomical)
high water mark (also called ordinary high water mark
or mean high water mark)
a demarcation between the publicly owned land along the
water and privately owned land which has legal implica-
tions regarding public access to the shore; generally based
on mean high water, the definition varies by state; along
beaches with significant waves, it may be based on the line
of vegetation, the watermark caused by wave runup, surveys
of the elevation of mean high water, or other procedures
hydrodynamic climate
the characteristics of nearshore or continental shelf cur-
rents in an area that typically result from waves, tides, and
weather systems
inlet
a small, narrow opening, recess, indentation, or other en-
trance into a coastline or shore of a lake or river through
which water penetrates landward; commonly refers to a
waterway between two barrier islands that connects the
sea and a lagoon
intertidal
see littoral
inundation
the submergence of land by water, particularly in a coastal
setting, see also flooding
jetty
an engineering structure built at the mouth of a river or tidal
inlet to help stabilize a channel for navigation; designed to
prevent shoaling of a channel by littoral materials and to
direct and confine the stream or tidal flow
lagoon
a shallow coastal body of seawater that is separated form the
open ocean by a barrier or coral reef; the term is commonly
used to define the shore-parallel body of water behind a
barrier island or barrier spit
levee
a wall, generally of earthen materials, designed to prevent
the flooding of a river after periods of exceptional rainfall
lidar (Light Detection And Ranging)
a remote sensing instrument that uses laser light pulses to
measure the elevation of the land surface with a high degree
of accuracy and precision
lithospheric
of or pertaining to the solid portion of the Earth, including
the crust and part of the upper mantle; the region of the Earth
that is studied in plate tectonics
littoral
the zone between high and low tide in coastal waters or the
shoreline of a freshwater lake
littoral cell
a section of coast for which sediment transport processes
can be isolated from the adjacent coast; within each littoral
cell, a sediment budget can be defined that describes sinks,
sources, and internal fluxes
littoral transport
the movement of sediment littoral drift in the littoral zone
by waves and currents; includes movement both parallel and
perpendicular to the shore
littoral zone
the region of the shore that occurs between the high and
low water marks
living shoreline
a shore protection concept where some or all of the environ-
mental characteristics of a natural shoreline are retained as
the position of the shore changes
long-lived infrastructure
infrastructure that is likely to be in service for a long time,
and therefore may benefit from consideration of sea-level rise
and shoreline changes in planning and/or maintenance
longshore current
an ocean current in the littoral zone that moves parallel to
the shoreline; produced by waves approaching at an angle
to the shoreline
longshore transport
the movement of sediment parallel to the shoreline in the surf
zone by wave suspension and the longshore current
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low marsh
the seaward edge of a salt marsh, usually a narrow band
along a creek or ditch which is flooded at every high tide
and exposed at low tide (see also high marsh)
margin, active
a continental margin located where the edges of lithospheric
plates are colliding, resulting in tectonic activity such as
volcanoes and earthquakes; also called a "Pacific margin"
after the Pacific Ocean where such margins are common;
compare with margin, passive
margin, passive
a continental margin located in the middle of a lithospheric
plate (see lithosphere) where tectonic activity is minimal;
also called an "Atlantic margin" after the Atlantic Ocean
where such margins are common; compare with margin,
active
marsh
a frequently or continually inundated wetland characterized
by herbaceous vegetation adapted to saturated soil condi-
tions (see also salt marsh)
mean high water
a tidal datum; the average height of high water levels ob-
served over a 19-year period
mean higher high water
the average of the higher high water height of each tidal day
observed over the national tidal datum epoch (see national
tidal datum epoch
mean sea level (MSL)
the "still water level" (i.e., the level of the sea with high fre-
quency motions such as wind waves averaged out); averaged
over a period of time such as a month or a year, such that
periodic changes in sea level (e.g., due to the tides) are also
averaged out; the values of MSL are measured with respect
to the level of marks on land (called benchmarks)
metadata
a file of information which captures the basic characteristics
of a data or information resource; representing the who,
what, when, where, why and how of the data resource; geo-
spatial metadata are used to document geographic digital
resources such as Geographic Information System (GIS)
files, geospatial databases, and earth imagery
moral hazard
a circumstance in which insurance, lending practices, or
subsidies designed to protect against a specified hazard
induce people to take measures that increase the risk of
that hazard
mudflat
a level area of fine silt and clay along a shore alternately
covered and uncovered by the tide or covered by shallow
water
national geodetic vertical datum of 1929 (NGVD29)
a fixed reference adopted as a standard geodetic datum for
elevations; it was determined by leveling networks across
the United States and sea-level measurements at 26 coastal
tide stations; this reference is now superseded by the North
American vertical datum of 1988 (NAVD88)
national tidal datum epoch (NTDE)
the latest 19-year time period over which NOAA has com-
puted and published official tidal datums and local mean
sea-level elevations from tide station records; currently, the
latest NTDE is 1983-2001
nearshore zone
the zone extending from the shoreline seaward to a short,
but indefinite distance offshore, typically confined to depths
less than 5 meters (16.5 feet)
nontidal wetlands
wetlands that are not exposed to the periodic change in
water level that occurs due to astronomical tides (see tides
and tides, astronomical)
nor'easter (northeaster)
the name given to the strong northeasterly winds associated
with extra-tropical cyclones that occur along East Coast
of the United States and Canada; these storms often cause
beach erosion and structural damage; wind gusts associated
with these storms can approach and sometimes exceed hur-
ricane force in intensity
North American vertical datum of 1988 (NAVD88)
a fixed reference for elevations determined by geodetic lev-
eling, derived from a general adjustment of the first-order
terrestrial leveling networks of the United States, Canada,
and Mexico; NAVD88 supersedes NGVD29
overwash
the sediment that is transported from the beach across a
barrier and is deposited in an apron-like accumulation along
the backside of the barrier; overwash usually occurs during
storms when waves break through the frontal dune ridge and
flow landward toward the marsh or lagoon
outwash plain
a braided stream deposit beyond the margin of a glacier; it
is formed from meltwater flowing away from the glacier,
depositing mostly sand and fine gravel in a broad plain
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Glossary and Acronyms
pocket beach
a small, narrow beach formed between two littoral obstacles,
such as between rocky headlands or promontories that oc-
cur at the shore
Public Trust Doctrine
a legal principle derived from English Common Law which
holds that the waters of a state are a public resource owned
by and available to all citizens, and that these publlic prop-
erty rights are not invalidated by private ownership of the
underlying or adjacent land. In most states, the public trust
rights include the land below mean high water. In five low
water states, the public has an access right to intertidal
land solely for the purpose of hunting, fishing, fowling,
and navigation.
rebound
the uplift of land following deglaciation due to the mass of
ice being removed from the land surface
relative sea-level rise
the rise in sea level measured with respect to a specified ver-
tical datum relative to the land, which may also be changing
elevation over time; typically measured using a tide gauge;
compare with global sea-level rise
retreat
one of three possible responses to sea-level rise, which in-
volves adapting to shoreline change rather than attempting
to prevent it, generally by either preventing construction
in a vulnerable area or removing structures already in the
vulnerable area; the other two responses are various methods
of shore protection orfloodproofing
revetment
a sloped facing of stone, concrete, etc., built to protect a
scarp, embankment, or shore structure against erosion by
wave action or currents
river diversion
a set of engineering approaches used to redirect the flow of
river water from its natural course for a range of purposes;
commonly used to bypass water during dam construction,
for flood control, for navigation, or for wetland and flood-
plain restoration
riprap
loose boulders placed on or along the shoreline as a form
of armoring
rip current
a strong, narrow current of surface water that flows seaward
through the surf into deeper water
rollover
see barrier island rollover
rolling easement
1. an interest in land (by title or interpretation of the Public
Trust Doctrine) in which a property owner's interest in pre-
venting real estate from eroding or being submerged yields
to the public or environmental interest in allowing wetlands
or beaches to migrate inland, usually by prohibiting shore
protection. 2. a government regulation that preserves the
environment and/or the public's access along the coast as
shorelines retreat by requiring the removal of structures once
they are inland of a defined high water mark (e.g. the dune
vegetation line or mean high water)
root mean square error (RMSE)
a measure of statistical error calculated as the square root
of the sum of squared errors, where error is the difference
between an estimate and the actual value; if the mean error
is zero, it also equals the standard deviation of the error
salt marsh
a grassland containing salt-tolerant vegetation established on
sediments bordering saline water bodies where water level
fluctuates either tidally or nontidally (see also marsh)
saltwater intrusion
displacement of fresh or ground water by the advance of
salt water due to its greater density, usually in coastal and
estuarine areas
seawall
a structure, often concrete or stone, built along a portion of
a coast to prevent erosion and other damage by wave action;
often it retains earth against its shoreward face; a seawall
is typically more massive than (and therefore capable of
resisting greater wave forces than) a bulkhead
sediment(s)
solid materials or fragments that originate from the break
up of rock and are transported by air, water or ice, or that
accumulate by other natural agents such as chemical pre-
cipitation or biological secretions; solid materials that have
settled from being suspended, as in moving water or air
sediment supply
the abundance or lack of sediment in a coastal system that
is available to contribute to the maintenance or evolution of
coastal landforms including both exposed features such as
beaches and barrier islands, and underwater features such
as the seabed
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setback
the requirement that construction be located a minimum
distance inland from tidal wetlands, tidal water, the primary
dune line, or some other definition of the shore
shoal
a relatively shallow place in a stream, lake, sea, or other
body of water; a submerged ridge, bank, or bar consisting
of or covered by sand
shore
the narrow strip of land immediately bordering any body
of water, especially a sea or large lake; the zone over which
the ground is alternately exposed and covered by the tides
or waves, or the zone between high and low water
shoreface
the narrow relatively steep surface that extends seaward
from the beach, often to a depth of 30 to 60 feet, at which
point the slope flattens and merges with the continental
shelf
shoreline
the intersection of a specified plane of water with the shore
or beach; on National Ocean Service nautical charts and
surveys, the line representing the shoreline approximates
the mean high water line
shoreline armoring
a method of shore protection that prevents shore erosion
through the use of hardened structures such as seawalls,
bulkheads, and revetments; see also armoring
shore protection
a range of activities that focus on protecting land from in-
undation, erosion, or storm-induced flooding through the
construction of various structures such as jetties, groins,
or seawalls, or the addition of sediments to the shore (for
example, beach nourishment)
significant wave height
the average height of the highest one-third of waves in a
given area
soft shore protection
a method of shore protection that prevents shore erosion
through the use of materials similar to those already found
in a given location, such as adding sand to an eroding beach
or planting vegetation whose roots will retain soils along
the shore
spit
a fingerlike extension of the beach that was formed by
longshore sediment transport; typically, it is a curved or
hook-like sandbar extending into an inlet
spring high water
the average height of the high waters during the semi-
monthly times of spring tides (occurs at the full and new
moons)
storm surge
an abnormal rise in sea level accompanying a hurricane or
other intense storm, whose height is the difference between
the observed level of the sea surface and the level that would
have occurred in the absence of the cyclone
subsidence
the downward settling of the Earth's crust relative to its
surroundings
submergence
a rise of the water level relative to the land, so that areas that
were formerly dry land become inundated; it is the result
either of the sinking of the land or a net rise in sea level
surf zone
the zone of the nearshore region extending from the point
offshore where waves break to the landward limit of wave
run-up, as on a beach
taxa (plural of taxon)
a general term applied to any taxonomic element, population,
or group irrrespective of its classification level
threshold
in climate change studies, a threshold generally refers to
the point at which the climate system begins to change in a
marked way because of increased forcing; crossing a climate
threshold triggers a transition to a new state of the system
at a generally faster rate
tidal currents
the horizontal movement of ocean water caused by gravitia-
tional interactions between the Sun, Moon and Earth; part
of the same general movement of the sea that is manifested
in the vertical rise and fall called the tide; see also ebb cur-
rent and. flood current
tidal datum
a baseline elevation used as a vertical point of reference from
which heights or depths can be reckoned; called a tidal datum
when defined in terms of a certain phase of the tide
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Glossary and Acronyms
tidal freshwater marsh
a marsh along a river or estuary, close enough to the coast-
line to experience significant tides by nonsaline water; the
vegetation is often similar to a nontidal freshwater marsh
tidal inlet
an opening in the shoreline through which water penetrates
the land, thereby providing a connection between the ocean
and bays, lagoons, and marsh and tidal creek systems; the
main channel of a tidal inlet is maintained by tidal cur-
rents
tidal range
the vertical difference between normal high and low tides
often computed as the elevation difference between mean
high water and mean low water; spring tide range is the
elevation difference between spring high water and spring
low water
tidal wetlands
those wetlands that are exposed to the periodic rise and fall
of the astronomical tides (see tides and tides, astronomi-
cal)
tide-dominated
a barrier or coastal area where the morphology is primarily
a product of tidal processes
tide gauge
the geographic location where tidal observations are con-
ducted; consisting of a water level sensor, data collection
and transmission equipment, and local benchmarks that are
routinely surveyed into the sensors
tidelands
those lands that are flooded during times of high water,
and are hence available to the public under the Public Trust
Doctrine
tide(s)
the alternating rise and fall of the surface of the ocean and
connected waters, such as estuaries and gulfs, that results
from the gravitational forces of the Moon and Sun; also
called astronomical tides (see tides, astronomical)
tides, astronomical
the alternating rise and fall of the ocean surface and con-
nected waters, such as estuaries and gulfs, that result from
the gravitational forces of the Moon and Sun
tipping point
a critical point in the evolution of a system that leads to new
and potentially irreversible effects at a rate that can either
be much faster or much slower than forcing
transgression
the spread or extension of the sea over land areas, and the
consequent evidence of such advance; also, any change
such as a rise in sea level that brings offshore deep-water
environments to areas formerly occupied by nearshore,
shallow-water environments or that shifts the boundary
between marine and nonmarine deposition away from deep
water regions
updrift
refers to the location of one section or feature along the coast
in relation to another; often used to refer to the direction
of net longshore sediment transport between two or more
locations (i.e., upstream)
VZone
areas where wave action and/or high velocity water can cause
damage in the 100-year flood, see also .4 Zone
wave-dominated
a barrier or coastal area where the geomorphology is primar-
ily a product of wave processes
wave run-up
the upper levels reached by a wave on a beach or coastal
structure, relative to still-water level
waves
regular or irregular disturbances in or on the surface of a
water body that form characteristic shapes and movement
patterns and a range of sizes; for the purposes of this report,
waves are usually generated by the wind (see fetch) and occur
along the coast or in an estuary
wetlands
those areas that are inundated or saturated by surface or
ground water at a frequency and duration sufficient to sup-
port, and that under normal circumstances do support, a
prevalence of vegetation typically adapted for life in satu-
rated soils; wetlands generally include swamps, marshes,
bogs, and similar areas
wetland accretion
a process by which the surface of wetlands increases in
elevation; see also accretion
wetland migration
a process by which tidal wetlands adjust to rising sea level
by advancing inland into areas previously above the ebb
and flow of the tides
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':, ,"-.
A-P Albemarle-Pamlico
ABFE Advisory Base Flood Elevations
AEC Areas of Environmental Concern
ASFPM Association of State Floodplain
Managers
BFE base flood elevation
CAFRA Coastal Facility Review Act
CAMA Coastal Area Management Act
CBRA Coastal Barrier Resources Act
CCMP Comprehensive Coastal
Management Plan
CCSP Climate Change Science Program
CORS continuously operating reference
stations
CRC Coastal Resources Commission
CTP Cooperative Technical
Partnership
CVI Coastal Vulnerability Index
CZM Coastal Zone Management
CZMA Coastal Zone Management Act
DDFW Delaware Division of Fish and
Wildlife
DEC Department of Environmental
Conservation
DEM Digital elevation Model
DFIRM digital flood insurance rate maps
FEMA Federal Emergency Management
Agency
FGDC Federal Geographic Data
Committee
FIRM Flood Insurance Rate Maps
FIS Flood Insurance Studies
GAO General Accounting Office (1982)
GAO General Accountability Office
(2007)
GEOSS Global Earth Observation System
of Systems
GIS geographic information system
GCN greatest conservation need
GPS Global Positioning System
HOWL highest observed water levels
IDA intensely developed area
IOOS Integrated Ocean Observing
System
IPCC Intergovernmental Panel on
Climate Change
IPCC CZMS
LDA
LMSL
MHHW
MHW
MLW
MLLW
MSL
NAI
NAS
NAVD
NCDC
NERRS
NDEP
NED
NFIP
NGVD
NHP
NHS
NLCD
NMAS
NOAA
NFS
NRC
NSSDA
NTDE
NWR
NWS
PORTS
RCA
RMSE
RPA
SAV
SFHA
SRTM
SWFL
TNC
Intergovernmental Panel on
Climate Change Coastal Zone
Management Subgroup
limited development area
local mean sea level
Mean Higher High Water
Mean High Water
Mean Low Water
Mean Lower Low Water
mean sea level
No Adverse Impact
National Academy of Sciences
North American Vertical Datum
National Climatic Data Center
National Estuarine Research
Reserve System
National Digital Elevation
Program
National Elevation Dataset
National Flood Insurance
Program
National Geodetic Vertical Datum
National Heritage Program
National Highway System
National Land Cover Data
National Map Accuracy Standards
National Oceanic and
Atmospheric Administration
National Park Service
National Research Council
National Standard for Spatial Data
Accuracy
National Tidal Datum Epoch
National Wildlife Refuge
National Weather Service
Physical Oceanographic Real-
Time System
resource conservation area
root mean square error
resource protection area
submerged aquatic vegetation
Special Flood Hazard Area
Shuttle Radar Topography
Mission
still water flood level
The Nature Conservancy
251
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Glossary and Acronyms
USACE United States Army Corps of
Engineers
U.S. EPA United States Environmental
Protection Agency
USFWS United States Fish and Wildlife
Service
US DOT United States Department of
Transportation
USGS United States Geological Survey
VA PBB Virginia Public Beach Board
WRCRA Waterfront Revitalization and
Coastal Resources Act
252
-------
Coastal Sensitivity to Sea-Level Rise:
A Focus on the Mid-Atlantic Region
Scientific Names-Chapter Five Species
Common Name
American black duck
American oystercatcher
Atlantic menhaden
Atlantic silverside
bald eagle
bay anchovy
belted kingfisher
black rail
black skimmer
bladderwort
blue crab
bluefish
brant
canvasback duck
carp
catfish
clapper rail
common tern
crappie
diamondback terrapin
eastern mud turtle
elfin skimmer (dragonfly)
fiddler crab
Forster's tern
fourspine stickleback
grass shrimp
great blue heron
gull-billed tern
herring
horseshoe crab
Kemp's ridley sea turtle
laughing gull
Latin Name
Anas rubripes
Haematopus palliatus
Brevoortia tyrannus
Menidia spp.
Haliaeetus leucocephalus
Anchoa mitchilli
Ceryle alcyon
Laterallus jamaicensis
Rynchops niger
Utricularia spp.
Callinectes sapidus
Pomatomus saltatrix
Branta bernida
Aythya valisineria
Family Cyprinidae
Order Siluriformes
Rallus longirostris
Sterna hirundo
Pomoxis spp.
Malaclemys terrapin
Kinosternum subrubrum
Nannothemis bella
Uca spp.
Sterna forsteri
Apeltes quadracus
Hippolyte pleuracanthus
Ardea herodias
Sterna nilotica
Qupea harengus
Limulus polyphemus
Lepidochelys kempii
Larus atridlla
Common Name
least bittern
meadow vole
minnows
mummichog
naked goby
northern pipefish
piping plover
red drum
red knot
red-winged blackbird
ribbed mussel
sand digger
sand flea
sandpiper
sea lettuce
sea trout
shad
sheepshead minnow
shiners
spot
striped anchovy
striped bass
striped killifish
sundew
sunfish
threespine stickleback
tiger beetle
weakfish
white croaker
white perch
widgeon grass
willet
Latin Name
Ixobrychus exilis
Microtus pennsylvanicus
Family Cyprinidae
Fundulus herteroditus
Gobiosoma bosd
Syngnathus fuscus
Charadrius melodus
Sdaenops ocellatus
Calidris canutus
Agelaius phoeniceus
Geukensia demissa
Neohaustorius schmitzi
Talorchestia spp.
Family Scolopaddae
Ulva lactuca
Salvelinus fontinalis
Alosa sapidissima
Cyprinodon variegatus
Family Cyprinidae
Leiostomus xanthurus
Anchoa hepsetus
Morone saxatilis
Fundulus majalis
Drosera spp.
Family Centrarchidae
Gasterosteus aculeatus
Cidndela spp.
Cynosdon regalis
Genyonemus lineatus
Morone americana
Ruppia maritima
Catoptrophorus semipalmatus
253
-------
The U.S. Climate Change Science Program Scientific Names
254
-------
U
z
LU
* Indicates non-peer reviewed scientific literature.
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Cover/Title Page/Table of Contents
(listed in order of appearance)
(Sandbags on coast), ©iStockphotos.com/Meppu
(Wading bird), ©iStockphotos.com/Terrence McArdle Produc-
tions Inc.
(Southeast marsh land), ©iStockphotos.com/Barbara Kraus
(Piping Plover), USFWS, New Jersey Field Office, Gene Niem-
inen, 2006.
(Temporary protection along a retreating shore, northeast of Surf-
side, Texas), ©James G. Titus. Reprinted with permission.
(South Manhattan/Battery Park), ©James G. Titus. Reprinted
with permission.
(The south end of Ocean City, Maryland, looking north), ©2008
Town of Ocean City, Maryland, Tourism Office. Reprinted
with permission.
(Crab shanties at Tangier, VA), NOAA Photo Library
(Optimist-class Regatta in Little Egg Harbor Bay, New Jersey),
©2007 Brant Beach Yacht Club, Long Beach Island, New
Jersey, photographer Scot Elis, reprinted with permission.
(Coastal barrier planting), ©iStockphotos.com/Meppu
(San Felipe de Morro [El Morro]. San Juan, Puerto Rico), photo
by Stephanie Chambers. ©2006 IgoUgo.com. Reprinted with
permission.
(Aerial Katrina flooding), USGS
Executive Summary
Page 7, (Eastern North Carolina wetland), Grant Goodge, STG,
Inc., Oak Ridge, TN
Chapter 1
Page 11, Heading, thumbnails, (Sandbags on coast), ©iStockpho-
tos.com/Meppu
Page 12, (Mid-Atlantic coastal wetlands), ©iStockphotos.com/
Tang's Nature Light Photography
Page 23, (North Carolina beach fencing), ©iStockphotos.com/
Andrew Hyslop
Chapter 2
Page 25, Heading, thumbnails, (Wading bird), ©iStockphotos.
com/Terrence McArdle Productions Inc.
Chapter 3
Page 43, (Outer Banks North Carolina), ©iStockphotos.com/
Florida Stock
Page 46, (North Carolina beach boardwalk), ©iStockphotos.com/
Andrew Hyslop
Chapter 4
Page 57, Heading, thumbnails, (Southeast marsh land), ©iStock-
photos.com/Barbara Kraus
Page 65, (Chesapeake bay), ©iStockphotos.com/Joseph C. Jus-
tice
Chapter 5
Page 73, Heading and thumbnails, (Piping Plover), USFWS, New
Jersey Field Office, Gene Nieminen, 2006.
Chapter 6
Page 87, Heading and thumbnails, (Temporary protection along
a retreating shore, northeast of Surfside, Texas), ©James G.
Titus. Reprinted with permission.
Chapter 7
Page 105, Heading and thumbnails, (South Manhattan/Battery
Park), ©James G. Titus. Reprinted with permission.
Chapter 8
Page 117, Heading and thumbnails, For both photos; (The south
end of Ocean City, Maryland looking north), ©2008 Town
of Ocean City, Maryland, Tourism Office. Reprinted with
permission.
Chapter 9
Page 123, Heading and thumbnails, (Crab shanties at Tangier,
VA), NOAA Photo Library, (Coastal development, Ocean
City, MD), ©iStockphotos.com/Sandy Jones
Chapter 10
Page 141, Heading and thumbnails, (Optimist-class Regatta in
Little Egg Harbor Bay, New Jersey), ©2007 Brant Beach
Yacht Club, Long Beach Island, New Jersey, photographer
Scot Elis, reprinted with permission.
Chapter 11
Page 157, Heading and thumbnails, (Coastal barrier planting),
©iStockphotos.com/Meppu
Chapter 12
Page 163, Heading and thumbnails, (San Felipe de Morro [El
Morro]. San Juan, Puerto Rico), photo by Stephanie Cham-
bers. ©2006 IgoUgo.com. Reprinted with permission.
Page 163, (El Morro from the rear). Source: http://bobj.us/Cruise/
cruise_to_the_caribbean.htm. ©2008, Bob Jones, reprinted
with permission.
Chapter 13
Page 179, Heading and thumbnails, (Aerial Katrina flooding),
USGS
Page 180, (Chesapeake Bay, Baltimore, MD), ©iStockphotos.
com/Jeremy Edward
Page 182, (Caribbean atoll), ©iStockphotos.com/Allister Clark
298
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