FsEPA
            United States
            Environmental Protection
            Agency
             Office of Policy
             Planning and Evaluation
             Washington, DC 20460
May 1986
EPA 230-10-85-014
Potential Impacts of
Sea Level Rise On
Wetlands Around Charleston,
South Carolina
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Library of Congress Cataloging-in-Publication Data
Kana, Timothy W., 1949-
   Potential Impacts of sea level rise on wetlands
around Charleston, South Carolina.

   Bibliography: p.
   1. Wetland conservation—South Carolina—Charleston.
2.  Wetlands—South Carolina—Charleston.  3. Sea Level—
South Carolina—Charleston. 4. Greenhouse effect, Atmospheric.
I. Baca, Bart J.  II. Willliams, Mark L.  III.  Title.
QH76.5.S67K36  1986   333.91'815'09757915   86-29309

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   POTENTIAL IMPACTS OF SEA  LEVEL  RISE ON WETLANDS
          AROUND CHARLESTON,  SOUTH CAROLINA
                        Prepared by
               Timothy W. Kana, Bart J. Baca
                   and Mark L. Williams

             Coastal Science & Engineering,  Inc.
                        P.O.  Box 8056
              Columbia, South Carolina  29202
This document  has been reviewed in accordance with the U.S.
Environmental  Protection Agency's peer and administrative
review policies  and approved for publication.  Mention of
trade names  or commercial products does not constitute
endorsement  or recommendation for use.   Please send comments
to James G.  Titus (PM-220), Strategic Studies Staff, U.S.
Environmental  Protection Agency, Washington, B.C.  20460.

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                                  11
                              SUMMARY

    Recent reports by the National Academy of Sciences (NAS)  and others have
concluded that increasing concentrations  of carbon dioxide and other gases
released by human activities are likely to warm the earth a few degrees
Celsius in the next century.  Such a warming could raise sea  level by
expanding ocean water, melting mountain glaciers,  and eventually causing polar
glaciers to slide into the oceans.  Unfortunately, it is not  yet possible to
accurately predict future sea level.  Estimates for the year  2025 range from
five to twenty-one inches above current sea level, while estimates of the rise
by 2100 range from two to eleven feet.  While the  timing and  magnitude of the
future rise in sea level is uncertain, there is an emerging scientific
consensus that a significant rise is likely.

    Several issues must be resolved for society to rationally address the
possibility of a significant rise in sea level.  Officials in coastal areas
making decisions about near-term projects with long lifetimes must determine
whether the risk of sea level rise justifies a shift to strategies that can
more successfully accommodate a rise in sea level.  The research community
needs to decide whether to accelerate studies to more accurately project
future sea level.  These decisions require assessments of the adequacy of
existing projections and of the value of developing better estimates and the
prospects for doing so.

    These decisions also require an understanding of the consequences of sea
level rise and of the potential costs and benefits of adopting measures that
can forestall those consequences.  To further this understanding, EPA has
initiated studies of the impacts of sea level rise on economic development in
Charleston, South Carolina, and Galveston, Texas;  on municipal drainage
facilities; on salinity of surface and ground water; and on beach erosion on
coastal barrier islands.

    This study examines the potential impact of alternative sea level rise
scenarios on wetlands in the area of Charleston, South Carolina.  Because
economic development in coastal areas can have long-term impacts on the
viability of wetland ecosystems, and because sea level rise would cause these
ecosystems to migrate inland, wetland protection strategies constitute a class
of decisions that may depend on sea level rise.  The purpose of this report is
to enhance our knowledge of the possible impacts of the rise in sea level
projected by previous reports.  Because of the uncertainty associated with
these forecasts, additional analysis will be needed to determine what changes
in existing wetland protection strategies,  if any, may be appropriate.

    In this report, a team of wetland scientists describes surveys of twelve
wetland transects in the Charleston area and presents estimates of the ability
of these wetlands to keep pace with rising  sea level.  Also presented are
estimates of the shifts in wetland communities and of the net  loss of marsh
acreage associated with three possible scenarios of sea level  rise for the
year 2075, all of which are well within the range of  estimates reported in
previous studies:   (1) current trends of 1  foot per century along the Atlantic
Coast;  (2) the NAS estimate of a  2-1/3 foot global rise in sea level; and  (3)
a high scenario of a 4-1/2  foot global rise.  Because sea level is rising
about 8 inches per century more rapidly along the Atlantic coast than
worldwide, these scenarios  imply  rises of 2.9 and 5.2 feet, respectively, by
2075 in the Charleston area.

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                                 Ill
                            CONCLUSIONS
 1.  Sea level rise could become a significant cause of wetland loss in the
    Charleston area.  If current trends continue for the next century,
    economic development will destroy less than 0.5 percent of the area's
    wetlands, and those losses would be more than offset by natural creation
    of wetlands.  Projected sea level rise, however, could result in the loss
    of between 50 and 90 percent of the area's marsh in the next century.

 2.  The National Academy of Sciences' estimate of sea level rise (2.9 feet)
    implies that Charleston could lose 50 percent of its marsh by 2075.  The
    area of high marsh would decline from 2300 to 700 acres, while the area of
    low marsh would decline from 5400 to 3200 acres.

 3.  The high scenario (5.2 feet) implies that Charleston could lose 80
    percent of its marsh by 2075 if human activities do not interfere.  As
    with the NAS estimate, the high marsh would decline from 2300 to 700
    acres; low marsh, however, would decline from 5400 to 900 acres.

 4.  The impact of sea level rise on coastal wetlands will ultimately depend
    on whether developed areas immediately inland of the marsh are protected
    from rising sea level by levees and bulkheads.   The above estimates are
    based on the assumption that new wetlands will be created as inland areas
    are flooded.  However, new wetlands can only be created if areas just
    inland of the marsh are undeveloped.  If these areas are developed and
    protected with levees and bulkheads as the sea rises, no additional
    wetlands will be created; thus, the net loss will be greater.  The high
    scenario (5.2 feet)  would imply a loss of all high marsh and all but 750
    acres of low marsh.   Because development in the Charleston area is
    generally at least three feet above the high marsh,  constructing these
    barriers would not increase the loss of marsh by 2075 for the NAS scenario
    (2.9 feet),  although some transition wetlands would be lost.

5.  Factors not  considered in this report could increase or decrease the
    vulnerability of wetlands to a rise in sea level.   The estimates in this
    report are based on the assumptions that the rate of vertical marsh growth
    and the shape and position of marsh profiles remain unchanged.   More
    extensive study could improve upon these assumptions and take into account
    such factors as impacts of global warming on peat formation,  reworking of
    sediment, and oxidation of peat due to marsh drowning.

6.   Other communities with similar types of marsh can obtain inexpensive
    first-order  estimates of future wetland loss.   The data in this  report,
    along with information on tidal ranges,  can be  used by those  who need only
    a rough indication of the vulnerability of wetlands  to rising sea level.

7.   Assessments  should be undertaken of how to mitigate  loss of wetlands from
    sea level rise.   Although the most substantial  losses of wetlands  are at
    least  50 years  away,  today's coastal development may largely  determine the
    success with which wetlands  adjust to rising sea level  in the future.

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                                   IV
                          ACKNOWLEDGMENTS
    The authors wish to express  their appreciation  to  several  people who
provided assistance to this study.

    The research was completed with the assistance  of  several  people at
Coastal Science and Engineering,  Inc.,  including S.  Jonathan Siah,  who
prepared the tide probability analysis; Bill  Eiser,  Mark Jordana,  and Mike
Bise, who assisted in the field;  and Tom Ballouy, who  helped identify the
marsh species.   Graphics for the report were  prepared  under  the  supervision of
Starnell Perez with the assistance  of Jerry Cole, Steve Loy, Harriet
Gilkerson, and Cindi Fehrs.

    Report production services were provided  by staff  at EPA,  RPI,  Inc., and
IGF Incorporated:  Joan O'Callaghan of EPA and Susan MacMillan of  ICF provided
editing contributions; and finally, the manuscript  was prepared  by Diana
Sangster of RPI and Margo Brown  of  ICF Incorporated.

    Discussions with Miles 0. Hayes, President of RPI, Inc., were  beneficial
to the authors in preparing this report.  David Flemer, Alan Hirsch, Howard
Marshall, and Gregory Peck of the Environmental Protection Agency  reviewed  the
draft and provided substantive comments.  Carroll Cordes and Edward Pendleton
of the U.S. Fish and Wildlife Service's National Coastal Ecosystems Team and
Joy Zedler of San Diego State University also made  useful suggestions.
Finally, James G. Titus of EPA provided overall guidance for the study  and
wrote portions of the final report.

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                         TABLE OF CONTENTS


                                                                         Page

INTRODUCTION 	    1

FUTURE SEA LEVEL RISE AND ITS IMPLICATIONS 	    2

    Global Warming and a Rising Sea 	    2
    Ecological Balance of Wetlands 	    3
    Potential Transformation of Wetlands 	    7

COASTAL HABITATS OF THE CHARLESTON STUDY AREA 	    8

WETLANDS TRANSECTS:   METHOD AND RESULTS 	    17

    Data Collection and Analysis 	    17
    Results of Individual Transects 	    19
    Composite Transect 	    21
    Area Estimates 	    24

WETLAND SCENARIOS FOR THE CHARLESTON AREA:  MODELING AND RESULTS 	    25

    Scenario Modeling 	    26
    Scenario Results 	    31

RECOMMENDATIONS FOR FURTHER STUDY 	    35

    Normalized Elevations 	    36
    Conclusion 	    39

REFERENCES 	    41

APPENDIX A:  WETLANDS TRANSECTS AND DISTRIBUTIONS OF SPECIES 	    45

APPENDIX B:  TIDE ELEVATION PROBABILITY DISTRIBUTION FOR CHARLESTON,
             SOUTH CAROLINA 	    59

APPENDIX C:  AREA DISTRIBUTION BY ELEVATION ZONE FOR EACH OF THE
             FIVE PRINCIPAL LAND DIVISIONS IN THE CHARLESTON STUDY
             AREA 	    63

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       VI
LIST OF FIGURES

Figure 1 .
Figure 2.
Figure 3.

Figure 4.
Figure 5.
Figure 6.
Figure 7 .
Figure 8.
Figure 9 .

Figure 10.
Figure 11.

Figure 12.

Charleston Study Area 	
Coastal Wetland Habitats 	
Back Barrier Wetlands and Tidal Creek Near Kiawah
Island 	
Transition from Highland to Marsh: Kiawah Island 	
Marsh Tidal Flat System Behind Isle of Palms 	
Transition from Marsh to Oyster Flat 	
A Developed South Carolina Coastal Barrier 	
Locations of Study Area and Twelve Transects 	
Composite Wetlands Transect for Charleston
Illustrating Modal Elevations and Key Species 	
Marsh Loss Due to Bulkheads 	
Conceptual Model of the Shift in Wetlands Zonation
along a Shoreline Profile 	
Tide-Probability Curves 	
Page
9
11

12
13
14
15
16
18

23
29

33
37

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                                   Vll
                           LIST OF TABLES


                                                                         Page

Table 1.    Scenarios of Future Sea Level Rise:   1980-2100  	    4

Table 2.    Modal Elevations and Percentage of Transect Covered
            by Principal Species 	    20

Table 3.    Summary Statistics for Elevations of Marsh Plant  Species  ..    22

Table 4.    Sea Level Rise Scenarios to the Year 2075  	    27

Table 5.    Shore-Protection Scenarios 	    30

Table 6.    Acreage of Principal Habitat in 1980 and 2075  	    32

Table 7.    Net Change in Acres for Principal Wetland  Habitats:
            1980-2075 	    32

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                                   -1-
                             INTRODUCTION






    Increasing atmospheric concentrations of carbon dioxide, methane, and




other "greenhouse" gases are expected to raise the earth's average temperature




a few degrees centigrade in the next century.   Such a warming could cause sea




level to rise a few feet by expanding ocean waters, melting mountain glaciers,




and perhaps causing polar glaciers to melt or slide into the oceans.  Because




most coastal wetlands are within a few feet of mean sea level, a rise in water




levels could cause a major loss of these ecosystems.




    This study examines the potential impact of future sea level rise on




coastal wetlands in the area of Charleston, South Carolina, for the year




2075.  The report builds upon previous EPA studies that had assessed the




potential physical and economic impacts of sea level rise on the Charleston




area.  We surveyed twelve wetland transects to determine elevations of




particular parts of the marsh, frequency of flooding, and vegetation at




various elevations.  From these transects, we developed a composite transect




representing an average profile of the area.  Using this information and




estimates of the sediment provided by nearby rivers, we then estimated the




shifts in wetland communities and net loss of marsh acreage associated with




three possible scenarios of sea level rise for the year 2075:  (1) the current




trend, which implies a rise of 24 cm (0.8 ft); (2) the National Academy of




Sciences estimate, which implies a rise of 87 cm (2.9 ft); and (3) a high




scenario rise of 159 cm (5.2 ft).




    This report presents background information concerning global warming and




future sea level rise, the ecological balance of coastal wetlands; and the




potential transformation of these ecosystems as sea level rises.  Next, it




examines the wetlands in the Charleston study area and describes a field study

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                                   -2-
in which we developed wetland transects.   Finally,  it  discusses  the potential




impact of future sea level rise on Charleston's  wetlands,  and  suggests ways to




improve our ability to predict the impact of sea level rise  on other  coastal




wetlands.








             FUTURE SEA LEVEL RISE AND ITS IMPLICATIONS






Global Warming  and a Rising Sea




    A planet's temperature is determined by the  amount of  sunlight it




receives, the amount of sunlight it reflects, and the  extent to  which its




atmosphere retains heat.  When sunlight strikes  the earth, it  warms the




surface, which then radiates the heat as infrared radiation.  However, water




vapor, carbon dioxide, and other gases in the atmosphere absorb  some  of  the




energy, rather than allowing it to pass undeterred through the atmosphere  to




space.  Because the atmosphere traps heat and warms the earth  in a manner




somewhat analogous to the glass panels of a greenhouse, this phenomenon  is




generally known as the "greenhouse effect."



    Since the industrial revolution, the combustion of fossil  fuels,



deforestation, and cement manufacture have released enough CCL into the



atmosphere to raise C0_ concentrations by 20 percent  (Keeling, Bacastow, and




Whorf  1982).  Review panels of the National Academy of Sciences  have concluded




that a doubling of atmospheric CO- expected in the next century, would warm




the earth  1.5°-4.5°C  (3°-8°F).  Increasing concentrations of methane,




chlorofluorocarbons, nitrous oxide, and other trace gases could roughly  double




the warming  from CO- alone  (Lacis et al.  1981; Ramanathan et al.  1985).




    A  global warming of a few degrees could be expected to  raise  sea level for




several  reasons.   Increasing atmospheric  temperatures would cause seawater to

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                                   -3-
warm and expand.  Mountain glaciers, which have retreated in the last century,




could melt more rapidly.  Glaciers in Antarctica and Greenland could melt




along the fringes, and portions of them could slide into the oceans.  Although




a complete disintegration of the West Antarctic Ice Sheet would raise sea




level six meters, it is unlikely to occur in the next century (Meier et al.




1985).




    In 1983, two independent reports estimated sea level rise in the next




century.  The National Academy of Sciences report Changing Climate estimates




that worldwide sea level will rise 70 cm (2-1/3 ft) in the next century,




ignoring the impact of the global warming on Antarctica (Revelle 1983).  The




Environmental Protection Agency report Projecting Future Sea Level Rise




states that the uncertainties regarding the factors that could influence sea




level rise are so numerous that a single estimate of sea level rise is




impossible (Hoffman, Keyes,  and Titus, 1983).  Instead, it specified high and




low estimates for all the factors that could influence sea level and estimates




resulting high, medium, and low scenarios.  As Table 1 shows, the EPA report




estimates that sea level will rise between 38 and 212 cm by 2075, with the




likely range falling between 91 and 136 cm (3 and 5 ft), compared with a




global rise of 10 to 15 cm (4 to 6 in) in the last century.  Because most of




the coast is subsiding, sea level rise along the Atlantic coast has been 15 to




20 cm per century higher than the worldwide average; this subsidence trend is




expected to continue into the future.









Ecological Balance of Wetlands




    Recent attention concerning rising sea level has been focused on the fate




of economic development in coastal areas.  However, the area facing the most

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                                   -4-
                                TABLE 1

            SCENARIOS OF  FUTURE  SEA LEVEL RISE:   1980-2100
                               (centimeters)
                    2000
2025
2050
2075
2080
Current Trends in
  High
  Mid-range high
  Mid-range low
  Low

NAS Estimate
(Global Sea
Level Rise--
excluding
Antarctic
cont r ibut ion)
17.1
13.2
8.8
4.8
54.9
39.3
26.2
13.0
116.7
78.9
52.6
23.0
211.5
136.8
91.2
38.0
                               70.0
2100
Sea Level Rise
Global 2.0-3.0 4.5-6.8 7.0-10.5 9.5-14.3
East Coast 6 13.5 21 28.5
EPA Scenarios -
(Global Sea
Level Rise)
10-15 12.0-18.0
30 36
                                        345.0
                                        216.6
                                        144.4
                                         56.2
SOURCES:  (1) John S. Hoffman,  D.  Keyes,  and J.G.  Titus,  Projecting Future Sea
          Level Rise. U.S.  EPA, 1983;  (2) R.  Revelle,  "Probable Future Change
          in Sea Level Resulting from Increased Atmospheric Carbon Dioxide,"
          in Changing Climate,  Washington, D.C.:   National Academy Press,
          1983; (3) Hicks,  S.D., H.A.  DeBaugh,  and L.E. Hickman,  Sea  Level
          Variations for the United States 1855-1980,  Rockville,  Maryland:
          National Ocean Service,  1983.
immediate consequences would be intertidal wetlands.   Lying between the  sea

and the land, this zone will experience the direct effects  of changing sea

levels, tidal inundation, and storm surges.

    The intertidal wetlands contain productive habitats,  including marshes,

tidal flats, and beaches, which are essential to estuarine  food webs.  The

distribution of the wetlands is sensitively balanced for  existing tidal

conditions, wave energy, daily flooding duration, sedimentation rates  (and

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                                   -5-
types), and climate.  Their elevation in relation to mean sea  level is




critical to determining the boundaries of a habitat and the plants within  it,




because elevation affects the frequency, depth, and duration of flooding and




soil salinity.  For example, some marsh plants require frequent (daily)




flooding, while others adapt to irregular or infrequent flooding  (Teal 1958).




Along the U.S. East Coast, the terms "low marsh" and "high marsh" are often




used to distinguish between zones (Teal 1958; Odum and Fanning 1973) that  are




flooded at least daily and zones flooded less than daily but at least every 15




days.  Areas flooded monthly or less are known as transition wetlands.




    Regularly flooded marsh in the southeast United States is dominated by




stands of smooth cordgrass (Spartina alterniflora), which may at first




appear to lack zoning.  However, work by Teal (1958), Valiela, Teal, and




Deuser (1978), and others indicates total biomass varies considerably within




the low marsh, ranging from zones of tall S. alterniflora along active creek




banks to stunted or short S. alterniflora stands away from creeks and




drainage channels.  The tall S. alterniflora may be caused by a combination




of factors, including more nutrients, a higher tolerance for the reductions in




oxygen that result from subtle increases in elevation along levees (DeLaune,




Smith, and Patrick, 1983); and differences in drainage created by variations




in the porosity of sediment.  The zone where S.  alterniflora grows is thought




by many to be limited in elevation to mean high water.   This is probably too




broad a simplification according to Redfield (1972), who emphasized that the




upper boundary of the low marsh is,  at best, indistinct.




    High marsh,  in contrast, consists of a variety of species.  These include




Salicornia spp.  (glassworts),  Distichlis spicata (spikegrass), Juncus spp.




(black needlerush), Spartina patens  (salt-marsh hay),  and Borrichia

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                                   -6-
frutescens (sea ox-eye).  Teal (1958) reports that Juncus marsh tends to be




found at a slightly higher elevation than the  Salicornia/Distichlis marsh.




    The high marsh can also be distinguished from low marsh on the basis of




sediment type, compaction, and water content.  High-marsh substrate tends to




be firmer and dryer and to have a higher sand content.  Low-marsh substrate




seldom has more than 10 percent sand (except where barrier-island washover




deposits introduce an "artificial" supply) and is often composed of very soft




mud.  Infrequent flooding, prolonged drying conditions, and irregular rainfall




within the high marsh also produce wide variations in salinity.  In some




cases, salt pannes form, creating barren zones.  But at the other extreme,




frequent freshwater runoff may allow less salt-tolerant species, such as




cattails, to flourish close to the salt-tolerant vegetation.  These factors




contribute to species diversity in the transition zone that lies between S_^




alterniflora and terrestrial vegetation.




    By most reports, low marsh dominates the intertidal areas along the




southeast (Turner 1976), but the exact breakdown can vary considerably from




place to place.  Wilson (1962) reported S. alterniflora composes up to 28




percent of the marsh in North Carolina, whereas Gallagher, Reimold, and




Thompson (1972) report for one estuary in Georgia that the same species covers




94 percent of the "marsh" area.  Low marsh is thought by many to have a




substantially higher rate of primary productivity than high marsh (Turner




1976).  Data presented in Odum and Fanning (1973) for Georgia marshes support




this notion.  However, Nixon (1982) presents data for New England marshes that




indicate above-ground biomass production in high marshes comparable to that of




low marshes.  Some data from Gulf Coast marshes also support this view




(Pendleton 1984).

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                                   -7-
Potential Transformation of Wetlands




    The late Holocene (last several thousand years) trend has been one of




gradual infilling and loss of water areas (Schubel 1972).  During the past




century, however, sedimentation and peat formation have kept pace with rising




sea level over much of the East Coast (e.g., Ward and Domeracki 1978; Due




1981; Boesch et al. 1983).  Thus, apart from the filling necessary to build




the city of Charleston, the zonation of wetland habitats has remained fairly




constant.  Changes in the rate of sea level rise or sedimentation, however,




would disrupt the present ecological balance.




    If sediment is deposited more rapidly, low marsh will flood less




frequently and become high marsh or upper transition wetlands, which seems to




be occurring at the mouths of some estuaries where sediment is plentiful.  The




subtropical climate of the southeastern United States produces high weathering




rates, which provide large fluxes of sediment to the coastal area.  Excess




supplies of sediment trapped in estuaries have virtually buried wetlands




around portions of the Chesapeake, such as the Gunpowder River, where a




colonial port is now landlocked.




    If sea level rises more rapidly in the future, increased flooding may




cause marginal zones close to present low tide to be under water too long each




day to allow marshes to flourish.  To maintain the distribution of their




habitats, wetlands must shift along the coastal profile--moving upward, to




keep pace with rising sea levels (unless sedimentation rates are high).  Total




marsh acreage can only remain constant if slopes and substrate are uniform




above and below the wetlands, and inundation is unimpeded by human activities




such as the construction of bulkheads.  Titus, Henderson, and Teal (1984),




however, point out that there is generally less land immediately above wetland

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                                   -8-
elevation than at wetland elevation.   Therefore,  significant  changes  in  the

habitats and a reduction in the area  they cover will  generally  occur  with

accelerated sea level rise.  Moreover, increasing development along the  coast

is likely to block much of the natural adjustment in  some  areas.

    Louisiana is an extreme example.   Human interference with natural sediment

processes and relative sea level rise are resulting in the drowning of 100 sq

km of wetlands every year (Gagliano,  Meyer Arendt,  and Wicker 1981; Nummedal

1982).  There is virtually no ground  to which the wetlands can  migrate.   Thus,

wetlands are converting to open water; high-marsh zones are being replaced by

low marsh, or tidal flats; and saltwater intrusion is converting  freshwater

swamps and marsh to brackish marsh and open water.



           COASTAL HABITATS  OF  THE CHARLESTON STUDY AREA



    As shown in Figure 1, the case study area, stretching  across  45,500  acres,

is separated by the three major tidal rivers that converge at the port city:

the Ashley, Cooper, and Wando Rivers.  In addition, it covers five land areas:

        •   West Ashley, which is primarily a low-density
            residential area with expansive boundary marsh;

        •   Charleston Peninsula, which contains  the bulkheaded
            historic district built partly on landfill;

        •   Daniel Island, which is an artificially embanked
            dredge spoil island;

        •   Mount Pleasant, which derives geologically from
            ancient barrier island deposits oriented parallel to the
            coast; and

        •   Sullivans Island, which is an accreting barrier
            island at the harbor entrance.

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              -9-




            FIGURE 1


      CHARLESTON STUDY AREA
                     -•.-.:•  MT. PLEASANT
CHARLESTO
   eninsula

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                                   -10-
    Six discrete habitats are found in the Charleston area,  distinguished by

their elevation in relation to sea level and,  thus,  by how often they are

flooded (Figure 2):

        highland             -   flooded rarely (47  percent  of study
                                 area)

        transition wetlands  -   flooding may range  from biweekly to
                                 annually (3 percent)

        high marshes         -   flooding may range  from daily to
                                 biweekly (5 percent)

        low marshes          -   flooded once or twice daily (12
                                 percent)

        tidal flats          -   flooded up to half  of the day (16
                                 percent)

        water                -   flooded more than half of the day
                                 (27 percent)

    This flooding, in turn, controls the kinds of plant species that can

survive in an area.  In Charleston, the present upper limit of salt-tolerant

plants is approximately 1.8-2.0 m (6.0-6.5 ft) above mean sea level (Scott,

Thebeau, and Kana 1981).  This elevation also represents the effective lower

limit of human development, except in areas where wetlands have been

destroyed.  The zone below this elevation (delineated on the basis of

vegetation types) is referred to as a critical area  under South Carolina

Coastal Zone Management laws and is strictly regulated (U.S. Department of

Commerce 1979).

    The distribution of coastal environments around  Charleston is balanced for

tides occurring twice each day.  However, the actual upper limit of

salt-tolerant species is considerably above mean high water.  Because of the

lunar cycle and other astronomic or climatic events, higher tides than average

occur periodically.  Spring tides occur approximately fortnightly in

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                                                    FIGURE 2

                                          COASTAL  WETLAND  HABITATS
+TO-

 +8-



 +4-
U.
-
>  -2-
uu    ^
UJ  -4-
VERTICAL EXAG 1:100
                                                                                              WATER 27%
                                                                                                       _ 10 YR STORM
                     TRANSI- (HIGH MARSH 5%
                     TION 3%
                                                    PEAK YEARLY TIDE

                                                    SPRING HIGH WATER
                                                    MEAN HIGH WATER
                                                    NEAP HIGH WATER
                                                                                                     . MEAN LOW WATER
                                                                                                     • SPRING LOW WATER
                                                                                                                       -*»
                                                                                                                       -o Q
                                                                                                                        •-8

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                                   -12-
conjunction with the new and full moons.  The statistical average of these,




referred to as mean spring high water, has an elevation of 1.0 m (3.1 ft)




above mean sea level in Charleston  (U.S. Department of Commerce 1981).




    Less frequent tidal flooding occurs annually at even higher elevations




ranging upwards of 1.5  m (5.0 ft) above mean sea level.  In a South Carolina




marsh near the case study area, the  flooding of marginal highland occurred at




elevations of 4-6 ft above mean sea  level  (approximately 2.0-2.5 ft above




normal).  The peak astronomic tide that was responsible for the flooding




included an estimated wind setup of  0.5-1.0 ft under 7-9 m/s (13-17 mph)




northeast winds.




    The Charleston area has a complex morphology.  Besides the three tidal




rivers that converge in the area, numerous channels dissect it, exhibiting




dendritic drainage patterns typical  of drowned coastal plain shorelines.




    To help provide an  understanding of these ecosystems, Figures 3-6




illustrate various marshes in South  Carolina.  Figure 3 is an oblique aerial




                               FIGURE 3




      BACK BARRIER  WETLANDS AND TIDAL CREEK NEAR KIAWAH  ISLAND
                             Photo by M.O.  Hayes.

-------
                                   -13-
photograph of a back-barrier,  tidal creek/marsh/mud-flat  system near Kiawah




Island, approximately 20 km south of Charleston.   It  shows  a  typical drainage




pattern and a recently abandoned, horseshoe-shaped infilling  with mud.




    Throughout the area, highlands are typically  less than  5  m (16  ft) above




mean sea level.  With a mean tidal tange of  1.6 m (5.2 ft), a broad area along




the coastal edge is flooded twice each day.  The  natural  portions of




Charleston Harbor are dominated by fringing  salt  marshes  from several meters




to over one kilometer wide.




    The upper limit of the marsh can usually be distinguished by an abrupt




transition from upland vegetation to marsh species tolerant of occasional




salt-water flooding.   On topographic maps of Charleston,  this break is often




about 1.5 m (+5 ft) above mean sea level.  The ground photo in Figure 4 shows




                                FIGURE 4




          TRANSITION  FROM  HIGHLAND TO MARSH:   KIAWAH ISLAND
                    Photo by M.L. Williams, May 16, 1984.

-------
                                   -14-
such an abrupt transition along  the back side of Kiawah Island, just south of




the case study area.   Highland terrestrial vegetation appears on the left side




of the photo and the  marsh is on the  right.  The detritus seen in the




foreground has been washed up by extreme high tide.




    The photos in Figures 5 and  6 illustrate typical horizontal and vertical




division of these intertidal environments.  The most extensive intertidal mud




flats around Charleston generally occur in the sheltered zone directly behind




the barrier islands.   They are thought to represent areas with lower




sedimentation rates (Hayes and Kana 1976) away from major tidal channels or




sediment sources.   Looking seaward, Figure 5 is an oblique aerial photo of the








                                FIGURE 5




            MARSH TIDAL FLAT SYSTEM BEHIND  ISLE OF  PALMS
                      Photo by T.W. Kana, February 1981.

-------
                                   -15-
marsh/tidal-flat system behind Isle of Palms (upper right)  and Dewees  Island,




just outside of the Charleston study area.   The inlet shown is Dewees  Inlet.




Note the mud flat and circular oyster mounds in the foreground near  marsh  and




tidal channels.




    The photo in Figure 6 was taken at low tide.   It shows  the vertical




transition from marsh to oyster flats along a tidal creek in the  Charleston








                                FIGURE 6




                TRANSITION  FROM MARSH  TO OYSTER  FLAT
                      Photo by L.C.  Thebeau, April  1981.
case study area.   Where the waterfront  is  developed  (Figure 7), the transition




from marsh or tidal creeks to highland  can be very distinct because of the




presence of shore-protection structures, such as vertical bulkheads and




riprap.  This aerial view was taken 50  km  (31 mi) north of the case study area.

-------
                                   -16-
                                FIGURE 7



             A DEVELOPED  SOUTH CAROLINA  COASTAL BARRIER
                      Photo by T.W. Kana, February  1981.






    Much of the Charleston shoreline  has accreted (advanced seaward and




upward) during the past 40 years  (Kana  et al.  1984).  Marshes accrete through




the settling of fine-grained sediment on the marsh  surface, as cordgrass




(Spartina alterniflora) and other species baffle the  flow adjacent to tidal




creeks.  Marsh sedimentation has  generally been able  to keep up with or exceed




recent sea level rises along this area  of the  eastern U.S. shoreline (Ward and




Domeracki 1978).   Much of the sediment  into the Charleston area has derived




from suspended sediment originating primarily  from  the Cooper River, which




carries the diverted flow of the  Santee River  (U.S. Army Corps of Engineers,




unpublished general design memorandum).  However, the recent rediversion will




reduce sediment input, which could slow the rate of marsh accretion in the




future.

-------
                                   -17-
              WETLANDS TRANSECTS:  METHOD AND  RESULTS






    To determine how an accelerated rise in sea level would  affect the




wetlands of Charleston, one needs to know the portions  of  land  at particular




elevations and the plant species found at those elevations.  To characterize




the study area, we randomly selected and analyzed twelve transects (sample




cross sections, each running along a line extending from the upland to the




water).  This section explains how the data from each transect  was collected




and analyzed, presents the  results from each transect,  and shows how we




created a composite transect based on those results.








Data Collection and Analysis




    For budgetary and logistical reasons,  we had to use representative




transects near, but not necessarily within,  the study area.  For example, a




limiting criterion was nearness to convenient places where reliable




elevations, or benchmarks,  had already been established.   The marshes behind




Kiawah Island and Isle of Palms are similar to the  marshes behind Sullivans




Island, but are more accessible.   As Figure 8 shows, all the transects were



within 20 km (12 mi) of the study area.




    Each transect began at  a benchmark located on high  ground near a marsh's



boundary, and ended at a tidal creek or mud flat, or after covering 300 m




(1,000 ft)--whichever came  first.   The length of the transects  was limited




because of the difficulty of wading through very soft muds.  Although this




procedure may have biased the sample somewhat,  logistics prevented a more



rigorous survey.

-------
                                  -18-
                               FIGURE 8

           LOCATIONS OF STUDY AREA AND  TWELVE TRANSECTS
    / V
                                                           SCALE
                                                        150  1   2 3.
                                                                    mites
    For each transect, we measured elevation and distance from a benchmark

using a rod and  level.  Data points were surveyed wherever there was a

noticeable break in slope or change in species.  The average distance between

points was about 7.5 m (25 ft).  Along each transect we collected and tagged

samples of species for laboratory typing and verification, noting such

information as the elevation of the boundaries between different species.   By

-------
                                    -19-
measuring the  length of the transect that a species covered and dividing  it by




the transect's total length, we computed percentages for the distribution of




each species along a transect.




    National Geodetic Vertical Datum (NGVD) is the reference level we used for




all transects.  This datum, derived from the so called 1929 measure of mean




sea level, is  about 13 cm  (0.4 ft) lower than the mean sea level of Charleston




today  (Ebersole 1982) and  therefore does not include sea level rise during the




past 50 years.  We used the 1929 mean sea level because it is the most widely




applied measure of sea level and is used on most published maps.  In addition,




there  is no agreement on an absolute measure of today's sea level since it has




to be  computed after a period of tidal records become available for analysis.








Results of Individual Transects




    Table 2 summarizes the results of the twelve transects.  It presents the




principal species observed along each transect, their "modal"--or most




common--elevations, the percentage of each transect they covered, and the




length of each transect.   For example,  in transect number 6,  Borrichia




frutescens was found at a modal elevation of 118 cm (3.86 ft) above mean sea




level and covered 40 percent of the transect,  or about 37 m (120 ft).




    Because species often overlapped,  the sums of the percentages exceed 100.




In addition,  to omit any marginal plants that  exist at transition zones, a




modal elevation differs slightly from the arithmetic or weighted mean.




    Appendix A contains plots of the profiles  of each transect,  showing the




modal elevations of the substrate and zonation of plant species  found there.

-------
                                                                         TABLE  2

                                        MODAL ELEVATIONS AND PERCENTAGE OF TRANSECT COVERED BY PRINCIPAL SPECIES
                                                               (in  feet  at  mean sea level)
                                                                      Nodal Elevations (percent of transect covered)
SPECIES
Batis maritime
Borrichia frutescens
Distichlis spicata
Juncus roemerianus
Limonium carol in ianum
Polygonum setaceum
Salicornia virginica
Spartina alterniflora
Spartina patens
Spartina cynosuroides
Suaeda linear^s

Transect Length (in
1

3.90(1)
-
3.40(1)
3.27(80)
-
3.42(1)
3.27(1)
-
-
-

189
2

4.34(33)
-
_
-
-
3.38(31)
2.12(75)
-
-
-

51
3
3.13(4)
4.98(3)
-
-
3.07(1)
-
3.06(9)
2.45(99)
5.35(1)
-
-

440
4
.
3.48(7)
-
5.34(5)
3.76(1)
-
3.49(37)
2. 05( 85)
-
2.51(72)
-

353
5
3.20(61)
3.60(14)
3.52(10)
3.63(2)
3.14(68)
-
3.12(77)
2.55(78)
-
-
-

933
6
3.04(14)
3.86(40)
-
3.48(7)
3.04(14)
-
3.30(34)
-(11)
-
-
3.61(34)

300
7
_
3.17(6)
3.20(4)
-
3.01(4)
-
3.10(9)
1.95(62)
-
-
3.11(4)

421
8
_
3.82(27)
3.70(23)
-
3.89(28)
-
3.30(18)
2.79(57)
-
-
4.00(7)

387
9
_
3.54(29)
3.29(15)
-
4.35(1)
-
3.14(31)
2.71(70)
-
-
3. 22( 5)

232
10
_
4.94(1)
3.80(9)
—
-
5.72(1)
-
3.50(99)
-
-
-

700
11
_
4.10(9)
3.95(35)
5.45(1)
-
5.45(1)
-
3.40(97)
—
-
—

588
12
_
-
3.54(7)
-
-
3.32(7)
-
2.65(97)
—
-
—

402










1
lo
0
1

feet)

-------
                                   -21-
Composite Transect




    To model the scenarios of future sea level rise, we had to develop a




composite transect from the data in Table 2.  Thus, for each species, one




modal elevation was estimated from the various elevations in Table 2.




Similarly, the percent of each transect covered by an individual species was




used to estimate an average percent coverage for all transects (Table 3).




    This information allowed us to choose for our composite the five species




that dominated the high and low marshes in all the transects:  Spartina




alterniflora, Salicornia virginica, Limonium carolinium, Distichlis




spicata, and Borrichia frutescens.  We call these the indicator species.




Figure 9 shows the modal elevations for these five species, for two other




salt-tolerant plants found in the transects (Juncus roemerianus and Spartina




patens), and for a species found in tidal flats and under water (Crassotrea




virginica).  The primary zone where each species occurs is indicated by the




shaded area; occasional species occurrence outside the primary zone is




indicated by the unshaded, dashed-line boxes.  Figure 9 also outlines the




boundaries for the six habitats and indicates the estimated percentage of the




study area that each covers.




    While this profile is by no means precise, it gives some insight into the




expected habitat for a given elevation and the tolerances various species have




for flooding.  For example, it establishes the general lower limit of marsh




for Charleston, where it is presumed that too frequent flooding kills




low-marsh species and transforms the marsh to unvegetated mud flats.




    The low-marsh plant Spartina alterniflora was the most dominant species,




making up 69 percent of the composite transect.   Its modal elevation was 75 cm




(2.45 ft) above mean sea level (MSL), or 5 cm (0.15 ft) below mean high water

-------
                                -22-
                                TABLE 3

                   SUMMARY STATISTICS FOR ELEVATIONS
                       OF MARSH  PLANT  SPECIES


SPECIES
Batis maritima
Borrichia frutescens
Distichlis spicata
Juncus roemerianus
Limonium carolinianum
Polygonum setaceum
Salicornia virginica
Spartina alterniflora
Spartina patens
Spartina cynosuroides
Sueada linear is
Weighted Mean
( feet above
mean sea level)
—
3.76
3.71
-
3.38
-
3.18
2.59
-
-
-
Standard
Deviation
(+ ft)
—
.53
.27
-
.46
-
.20
.59
-
-
-

Modal
Elevation*
3.17
3.16**
3.71**
4.17
3 . 38**
3.32
3 . 16**
2.45**
5.35
2.51
3.59
Percent
Occurrence
Composite
7
14**
9**
1
16**
1
21**
69**
> 1
6
4
     * Excludes anomalous values in some cases and observations covering  less
than 2 percent of transect.

    ** Recommended indicator species.

-------
                           ELEVATION (FT)-MSL
    IB
    C
    VO
ft fl> O
-> = O
fl> Q.3
3   T3
Cf> 3 O
(D O (A
o a —
ft 0> ft
01 — (D


'  •$
Z(0 ft

3 09 0)
O ft 3
-, _.a
  o o>
V) 3
•O   ft


(D   0>
(A 3T»
   3 O
  O.T
or —
WOO
(D 0) 31
3 ft 0>
.0-1
O -5 —
3  (D
— (A CA
rfO ft
ft a o
CO O 3

   '
  o c
  T en
    ft
  ft 3
  ttlO
  ft
  B» ft

  aa
  09
  T5
  a-o
   3 X


   31
   «B ft
   C <0

   ftTJ
    -* -1 H ^ =5
^ m m m H Q
m * JO 2 R1 m
a 3
1 I ! I ! ! ! ! i
                           ELEVATION (FT)-MSL

-------
                                   -24-
as measured from the 1929 MSL datum.  Thus, it would be reasonable to assume




that today's low-marsh S. alterniflora prefers elevations close to the limit




of the neap tide.  For Charleston, this is about 15 cm (0.5 ft) below mean




high water.  Figure 9 shows that S. alterniflora extends beyond the limits of




low marsh into both high marsh and tidal flat; however, this species occurs




primarily at low-marsh elevations.




    The other indicator species are generally considered to be high-marsh




species.  These include Distichlis spicata, Borrichia frutescens, Limonium




carolinianum and Salicornia virginica.  Spartina patens, while having been




found to coexist with Distichlis spicata in Maryland and North Carolina




marshes (E.G. Pendleton, personal communication, December 1984), is uncommon




at elevations less than 122 cm (4 ft) above mean sea level in Charleston




(Scott, Thebeau, and Kana 1981).  The variance in these observations may be




related to the significant difference in tidal range between central South




Carolina and North Carolina.




    As illustrated in Figure 5 in the previous section, large portions of the




back-barrier environments of Charleston consist of tidal flats at lower




elevations than the surrounding marsh.  Oyster mounds were found at a wide




range of elevations along tidal creek bands, but over tidal flats most were




common at 30-46 cm (1.0-1.5 ft) above mean sea level.









Area  Estimates




    Two sources of information were available for land area estimates:  United




States Geological Survey (USGS) 7.5-minute quadrangles and digitized computer




maps prepared in an earlier EPA-sponsored case study (Kana et al. 1984).




Using topographic and contour maps, we estimated the number of acres of each

-------
                                   -25-
habitat in each of the divisions of the Charleston area  (see Figure  1).  For

budgetary reasons, we could not rigorously calculate areas using a

computerized planimeter.  This level of precision would  be questionable

anyway, in light of the imprecision of USGS topographic  maps in delineating

marshes and tidal flats near mean water levels.

    Our results were graphically determined and  spot-checked by a second

investigator to ensure they were consistent to within +15 percent for each

measurement.  Thus, the error limits for the overall study area are  estimated

to be a maximum of +15 percent by subenvironment.   (Because the standard

error of a sum is less than the sum of individual standard errors, the errors

are likely to be less.  Unfortunately, we had no way of  rigorously testing

these results within the time and budget constraints of  the project.)

    Tidal-flat areas were estimated using aerial photos  and shaded patterns

shown on USGS topographic sheets.   The marsh was initially lumped together

(high and low marsh) to determine representative areas for each Charleston

community.  The total number of acres for this zone was  divided into high- and

low-marsh areas by applying the typical percentage of each along the composite

transect (70 percent low marsh and 30 percent high marsh).  The transition

zone areas were estimated from the digitized computer maps.



             WETLAND SCENARIOS  FOR  THE  CHARLESTON AREA:
                        MODELING AND RESULTS


    After establishing the basic relationships among elevation, wetland

habitats,  and occurrence of species  for Charleston,  the  next steps in our

analysis were to develop a conceptual model for  changes  in saltwater wetlands

-------
                                   -26-
under an accelerated rise in sea level and to apply the model to the case

study area.



Scenario Modeling

    Based on an earlier study sponsored by EPA (Earth and Titus 1984), we

chose three scenarios of future sea level rise:

        •   a baseline scenario, with an average annual rise of
            2.5 mm (.1 in), based on current sea-level trends in the
            Charleston area (Hicks, DeBaugh, and Hickman 1983);

        •   a low scenario with  an average annual rise of 9.2 mm
            (.36 in), based on the National Academy of Sciences
            estimate of a worldwide rise of 70 cm (2.3 ft) in the
            next century and the EPA mid-low scenario; because sea
            level is rising faster in Charleston than globally, this
            scenario implies a rise in the Charleston area of 87 cm
            (2.9 ft) by 2075;

        •   a high scenario, with an average annual rise of 17.0
            mm (.67 in), based on EPA's mid-range high scenario;
            because of local subsidence trends, this scenario
            implies a rise of 159 cm (5.2 ft) by 2075 in the
            Charleston area.

To be consistent with the previous study, we projected the scenarios to the

year 2075--95 years after the baseline date of 1980 used to determine

"present" conditions.

    The model for future wetland zonation also accounted for sedimentation and

peat formation, which partially offset the  impact of sea level rise by raising

the land surface.  Sedimentation rates are highly variable within East Coast

marsh/tidal-flat systems, with published values ranging from 2 to 18 mm  (.08

to  .71 in) per year  (Redfield 1972; Hatton, DeLaune, and Patrick 1983).  Ward

and Domeracki (1978) established markers in an intertidal marsh 20 km  (12 mi)

south of the Charleston case study area and measured sedimentation rates of

4-6 mm (.16-.24 in) per year.  Hatton, DeLaune, and Patrick  (1983) reported

-------
                                   -27-
comparable values (3-5 mm per year)  for Georgia marshes.   Although the  rate  of

marsh accretion will depend on proximity to tidal channels (sediment  sources)

and density of plants (baffling effect and detritus),  we  believe the  published

rate of 4-6 mm per year is reasonably representative for  the  case study area

(Ward and Domeracki 1978).  Thus,  for purposes of modeling, we assumed  a

sedimentation rate of 5 mm per year.   Obviously, the actual rate will vary

across any wetland transect, so this  assumed value represents an average.

Lacking sufficient quantitative data  and considering the  broad application of

our model, we found it was more feasible to apply a constant  rate for the

entire study area.

    As shown in Table 4, the combined sea level rise scenarios and

sedimentation rates yield a positive  change in substrate  elevation for  the

baseline and a negative change for the low and high scenarios.  The positive

change for baseline conditions follows the recent trend of marsh accretion in

Charleston.

                                 TABLE 4

              SEA LEVEL RISE  SCENARIOS TO THE YEAR 2075

                                                       Annual      Annual Net
                                        Average       Sedimen-     Substrate
Scenario    Sea Level Rise by 2075    Annual Rise    tation Rate     Change

Baseline      +23.8 cm (0.78 ft)         2.5mm        5mm          +2.5 mm
Low           +87.0 cm (2.85 ft)         9.2mm        5mm          -4.2mm
High         +159.2 cm (5.22 ft)        17.0 mm        5 mm          -12.0 mm


    For each of these three scenarios, we considered four alternatives  for

protecting against the rising sea: no protection, complete protection,  and

two intermediate protection options.   Protective options  consist of bulkheads,

dikes, or seawalls constructed at  the upper limit of wetlands (S.C. Coastal

-------
                                   -28-
Council critical area line).   Figure 10 illustrates the various options.  If




all property above today's wetlands are protected with a wall, for example,




the wetlands will be squeezed between the wall and the sea.   Table 5




illustrates the intermediate protection options, whose economic implications




were estimated by Gibbs (1984).




    For our modeling, we used the composite habitat elevations we derived from




the twelve transects (see Figure 9).  The cutoff elevation for highland around




Charleston was assumed to be 200 cm (6.5 ft) above mean sea level.  In




general, land above this elevation around Charleston is free of yearly




flooding dominated by terrestrial (freshwater) vegetation.  Although




terrestrial vegetation occurs at lower elevations that are impounded between




dikes or ridges, this information is less relevant for sea level rise




modeling.  The zone of concern is the area bordering tidal waterways, where




slopes are assumed to rise continuously without intermediate depressions.




    The transition zone is defined as a salt-tolerant area between




predominant, high-marsh species and terrestrial vegetation.   This area is




above the limit of fortnightly (spring) tides but is generally subject to




tidal and minor-storm flooding several times each year.  If storm frequency




remains constant, it is reasonable to assume that storm tides will shift




upward by the amount of sea level rise (Titus et al. 1984).   However, most




climatologists expect the greenhouse warming to alter storm patterns




significantly.  Nevertheless, because no predictions are available, we assumed




that storm patterns will remain the same.

-------
                                -29-
      NO
 PROTECTION
                                                           2075 +6.5
1980+6.5
 PROTECTION
   AT 2020
 PROTECTION
  AT 1980
                -NO WETLANDS
                    2075
FIGURE 10.  If people build walls  to protect property  from rising sea level,
           the marsh will be squeezed between the wall and the sea.  Sketches
           show only the upper part of the wetlands which would be affected
           by shore-protection structures.  Mean sea  level is off the diagram
           to the right.

-------
                                   -30-
           Area
            TABLE 5

SHORE-PROTECTION SCENARIOS

         Without Anticipating
            Sea Level Rise
Low Scenario
  Peninsula
  West Ashley/James Island

  Mt. Pleasant
  Sullivans Island

High Scenario

  Peninsula
  West Ashley/James Island

  Mt. Pleasant
  Sullivans Island
         Protection after 2050
         Protectjon after 2050

         None
         None
         Protection after 2020
         Protection after 2020

         Protection after 2050
         None
  With Anticipating
   Sea Level Rise
Protection after 2030
Protect half of area
after 2050
Protection after 1990
None
Protection after 2010
Protect half of area
after 2030
Protection after 1990
None
Note:  In West Ashley/James Island,  less protection is necessary if sea level
       rise is anticipated, because  more of the low-lying areas are subject to
       an orderly abandonment.   Our  high scenario was called "medium" by Gibbs.

Source:  Gibbs 1984.
    High marsh is defined here by a narrow elevation range of 90 to 120 cm (3

to 4 ft) above mean sea level, and low marsh ranges from 45 to 90 cm (1.5 to

3.0 ft) above mean sea level.   This delineation follows the results of

surveyed transects and species zonation described earlier.   The lower limit of

the marsh was estimated from the typical transition to mud flats.  Sheltered

tidal flats actually occur between mean low water and mean high water but were

found to be more common in Charleston in the elevation range of 0-46 cm (0-1.5

ft) above mean sea level.  This somewhat arbitrary division was also based on

the contours available on USGS maps, which enabled estimates of zone areas

within the case study region.

-------
                                   -31-
Scenario Results



    Based on the shore-protection alternatives for the five suburbs around




Charleston, we computed area distributions under the baseline, low, and high




scenarios.  Figure 10 illustrates shore-protection scenarios and their effects




on the wetland transect.  Our basic assumption was that the wetland habitats'




advance toward land ends at 200 cm (6.5 ft) above mean sea level.  Dikes or




bulkheads would be constructed under certain protection scenarios at that




elevation on the date in question to prevent further inundation.




    Because the results are fairly detailed for the five separate subareas and




four protection scenarios within the Charleston case study area, we have only




listed the overall changes in Tables 6 and 7 (complete protection and no




protection).  Results by subarea for all four protection scenarios, given in




Appendix C, illustrate the variability of land, water, and wetland acreage




from one subarea to another.  For example, the peninsula currently has a much




lower percentage of low marsh than all other areas.  Tidal flat distribution




was also variable, ranging from 3.2 percent of the Mt. Pleasant zone to 8.6




percent of the Sullivans Island zone.  The summary percentages given in Table




6 are appropriately weighted for the five subareas within the study area.



    Table 6 lists the number of acres for each elevation zone in 1980



(existing) and for the baseline, low, and high scenarios with and without



structural protection by the year 2075.  The percentage of the total study




area that a habitat covers is given in parentheses in Table 6 and graphically




presented in Figure 11.  Table 6 indicates losses under all scenarios with no




protection for the four upper habitats and gains in area for tidal flats and




water areas.  For example, without protection, highland would decrease from




46.6 percent of the total area in 1980 to 41.7 percent in 2075 under the

-------
                            TABLE 6



         ACREAGE  OF PRINCIPAL HABITAT  IN 1980  AND  2075
Habitat
Highland
Transit ion
High Marsh
Low Marsh
Tidal Flat
Water
TOTALS



Exi sting
1980
Acres (%)
2 1 , 200
1,500
2,300
5,400
2,600
12.500
45,500



(46.6)
(3.3)
(5.1)
(M. 9)
(5.7)
(27.4)
( 100.0)



Basel ine
2075
Acres (%)
2 1 , 700
2,820
3,320
3,910
2,600
".150
45,500



(47.7)
(6.2)
(7.3)
(8.6)
(5.7)
(24.5)
( 100.0)



Low Scenario - 2075
No Protection
Acres (%)
20,445
1,355
690
3,235
5,020
"».755
45,500



(44.9)
(3.0)
(1.5)
(7.1)
( 'I. 0)
(32.5)
( 100.0)



Protection
Acres (%)
21,195
605
690
3,235
5,020
14.755
45,500



(46.6)
(1.3)
(1.5)
(7.1)
(II. 0)
(32.4)
( 100.0)



Hi ah Scenario - 2075
No Protection
Acres (%)
18,990
1,420
675
860
1,425
22.130
45,500



(41.7)
(3.1)
(1.5)
(1.9)
(3.1)
(48.7)
(100.0)



Protect ion
Acres (%)
21, 195
0
0
750
1,425
22. 130
45,500



(46.6)
(0)
(0)
(1.7)
(3.1)
(48.6)
( 100.0)










i
w
ro
                           TABLE 7



NET CHANGE IN ACRES FOR PRINCIPAL WETLAND HABITATS:   1980-2075
Habitat
Highland
Transit ion
High Marsh
Low Ma rsh
Tidal Flats
Water
Basel ine
Acres (%)
500
1,320
1,020
- 1 , 490
0
- 1 , 350
(+2.4)
(+88)
(+44)
(-28)
(0)
(-10.8)
Low Scenario - 2075
Without Protection With Protection
Acres (%) Acres (%)
-744
-144
-1,610
-2,165
+2,420
+2,255
(U)
(10)
(70)
(40)
(+93)
( + 18)
0
-895
-1,610
-2,165
+2,420
+2,255
(0)
(60)
(70)
(40)
(+93)
( + 18)
High Scenario - 2075
Without Protection With Protection
Acres (%) Acres (%)
-2,210
-80
-1,625
-4,540
- 1 , 1 75
+9,630
(10)
(5)
(71)
(84)
(45)
(+77)

-1,
-2,
-4,
-1,
+9,
0
500
300
650
175
630
(0)
(100)
(100)
(86)
(45)
(+77)

-------
+8-

+6-

+4-
-2-
-4-
WATER
 2O75
 33%
                       2O75 MSL
                       LOW SCENARIO

                       1980 MSL
                       EXISTING
         HIGHLAND
           1980
           47%
                                        i
                                       U5
                                       03
      Figure  II.  Conceptual model of the  shift  in wetlands  zonation along a shoreline profile  if sea  level
                  rise exceeds  sedimentation  rates.   In  general,  the response will be a landward shift and
                  altered areal distribution  of  each  habitat because of variable slopes at each elevation
                  interval.

-------
                                   -34-
high scenario.  This represents a loss of over 2,200 acres or 10 percent of




the present highland area.  Land that is now terrestrial would be transformed




into transition-zone or high-marsh habitats a century from now.  Under the




2075 high scenario with no protection, high and low marsh, combined, would




decrease from 7,700 acres to 1,535 acres--a reduction of almost 80 percent.




While highland and marsh areas would decrease under the no-protection




scenarios, water areas would increase dramatically—from 27.4 percent to as




much as 48.7 percent--under the high scenario of 2075.




    With structural protection implemented at different times for each




community (see Table 5), highland areas would be maintained at a constant




acreage, but transition and high-marsh habitats would be completely eliminated




by 2075 under the high scenario (because of the lack of area to accommodate a




landward shift).  Total marsh acreage would decrease from 7,700 acres to 3,925




acres (2075 low scenario), or 750 acres (2075 high scenario), under the




assumed mitigation in Table 5.




    The net change in areas under the various scenarios listed in Table 7




indicates that all habitats would undergo significant alteration.  Even under




the baseline scenario, which assumes historical rates of sea level rise, 20-35




percent losses of representative marsh areas are expected by 2075.  Protection




under the low scenario (as outlined by Gibbs 1984) would have virtually no




effect on high or low marsh coverage; but it would cause a substantially




increased loss of transition wetlands.  Under the high scenario with




protection, highland would be saved at the expense of all transition and high




marsh areas and almost 90 percent of the low marsh.  Even under the low




scenario, sea level rise, would become the dominant cause of wetland loss in




the Charleston area.  Although a substantial amount of marsh was filled as the

-------
                                   -35-
city was built, destruction of coastal wetlands came to a virtual halt with




the creation of the South Carolina Coastal Council.   Since 1977,  the entire




state has only lost 35 of its 500,000 acres of wetlands to dry lands (South




Carolina Coastal Council 1985).  Approximately 100 acres have been flooded by




artificial impoundments (U.S. Fish and Wildlife Services, Charleston Office;




personal communication).  Thus, without the impact of sea level rise, one




would expect the Charleston area to lose less than 0.5 percent of its wetlands




in the next century.






                 RECOMMENDATIONS FOR FURTHER STUDY




    This study is a first attempt at determining the potential impact of




accelerated sea level rise on wetlands.  The experience gained in the




Charleston area should be built upon with case studies in other estuaries.




Louisiana provides a present-day analog for the effect of rapid sea level rise




on wetlands because of high subsidence rates along the Mississippi Delta (see




Gagliano 1984).  Additional studies in that part of the coast should attempt




to document the temporal rate of transformation from marsh to submerged




wetlands.




    Accurate wetland transects with controlled elevations are required to




determine the preferred substrate elevations for predominant wetland species.




With better criteria for elevation and vegetation, we can use remote-sensing




techniques and aerial photography to delineate wetland contours on the basis




of vegetation.  Scenario modeling can then proceed using computer-enhanced




images of wetlands and surrounding areas, for more accurate delineation of




marsh habitats.  Using historical aerial photos, it may also be possible to




infer sedimentation rates by changes in plant coverage or species type, which

-------
                                   -36-
could be related to elevation using some of the criteria provided in this



report.




    Another problem that remains with this type of study is the frame of




reference for mean sea level.  For practical reasons, mean sea level for a




standard period (20 years generally) cannot be computed until after the period




ends.  Therefore, earlier mean sea levels, such as the NGVD of 1929, are




used.  But sea level has risen about 15 cm since then.  If everyone uses the




same reference plane for present and future conditions, the problem may be




minor.  But it does not allow us to determine modal elevations with respect to




today's sea level.  The transects surveyed for the present study suggest that




S. alterniflora (low marsh) grows optimally at an elevation of 2.45 ft above




mean sea level, close to mean high water (U.S. Department of Commerce 1981).




Compared with today's mean sea level in Charleston, S. alterniflora probably




prefers to grow as much as 0.5 ft below actual mean high water, which may




confuse the reader who forgets that the report uses 1929 sea level.




    The basic criteria for delineating elevations of various wetland habitats




in this study can be easily tested in other areas.  By applying normalized



flood probabilities (similar to those depicted in Figure 12), it will be




possible to measure marsh transects in other tide-range areas and relate them



to the results for Charleston.








Normalized Elevations




    The absolute modal elevation for each species is site-specific for




Charleston.   Presuming that the zonation is controlled primarily by tidal




inundation,  it is possible to normalize the data for other tide ranges based




on frequency curves for each water level.   Figure 12 contains two such "tide

-------
                                     -37-,
        CHARLESTON TIDES
    e.oo
    4.00
 co
 '   2.00
 o
   0.00
 III
 _)
 Ul
 o
   -2.00'
   -4.00
   -•.00
MSHW
MHW
      0.00   1.00   1.00  3.00   4.00
             PROBABILITY (%)
                                         B
                                                  NORMALIZED TIDE RANGE VS.
                                                     WETLANDS SPECIES
                                                       So Ml«m (trunnion)
                                                            (tin* irarth)
                                                                          M«L
                                                                          MLW
                                               0.00   20.00  40.00  SO.OO  SO.OO   100.0O
                                                    CUMULATIVE PROBABILITY («)
Figure  12.   Tide-probability curves based on  statistics for Charleston given
             in Ebersole  (1982).

             (A)  Probability distribution for the range of astronomic tides.

             (B)  "Normalized" cumulative probability distribution,  indicating
                  the preferential elevation for  various wetland  species.

             Abbreviations:   MSHW (mean spring high .water); MHW  (mean high
             water); MSL  (mean sea level); MLW (mean low water);  MSLW (mean
             spring low water).

-------
                                   -38-
probability" curves, based on detailed statistics of Atlantic Coast water




levels given in Ebersole (1982) and summarized in Appendix B.  The graph of




Figure 12A gives the probability of various water levels for Charleston.  In




Figure 12B, the data have been normalized for the mean tide range of 5.2 ft in




Charleston and given as a cumulative probability distribution.  These graphs




are applicable to much of the southeastern U.S.  coast by substituting




different tide ranges.  Each graph provides a measure of the duration of time




over the year that various wetland elevations are under water.




    In the case of Salicornia virginica (+3.16 ft MSL for Charleston), the




cumulative frequency of flooding is approximately 4 percent (Figure 12B and




Appendix B).  If one wanted to apply these results for an area with a




different tide range but similar species occurrence, such as Sapelo Island




(Georgia), the flooding frequency for S. virginica could be used to estimate




its modal elevation at the locality.  With a mean tide range of 8.5 ft at




Sapelo, S. virginica is likely to occur around +5.3 ft MSL (based on




substitution of the tide range in Figure 12B).  This procedure can be applied




for other southeastern U.S. marshes as a preliminary estimate of local modal




elevations.




    We do not consider elevation results for the transects to be definitive




because of the relatively small sample size.  However, the results are




sufficiently indicative of actual trends to allow scenario modeling.  With the




tide-probability curves presented, it should be possible to check these




results against other areas with similar climatic patterns, but different tide




ranges.

-------
                                    -39-
 Conclusion




    Wetlands  in the Charleston area have been able to keep pace with the




 recent historical rise  in sea level of one foot per century.  However, a




 three- to five-foot rise in the next century resulting from the greenhouse




 effect would  almost certainly upset these ecosystems in a fashion similar to




 that occurring in Louisiana, which every year loses over one hundred square




 kilometers  (fifty square miles) to the sea.




    The success with which coastal wetlands adjust to rising sea in the future




 will depend upon whether human activities prevent new marsh from forming as




 inland areas  are flooded.  If human activities do not interfere, a three-foot




 rise in sea level would result in a net loss of about 50 percent of the marsh




 in the Charleston area.  A five-foot rise would result in an 80 percent loss.




    To the extent that levees, seawalls, and bulkheads are built to prevent




 areas from being flooded as the sea rises, the formation of new marsh will be




 prevented.  We estimate that 90 percent of the marsh in Charleston—including




 all of the high marsh—would be destroyed if sea level rises five feet and



 walls are built to protect existing development.




    This study represents only a first investigation into an area that



 requires substantial additional research.   The methods developed here can be




 applied to estimate marsh loss in similar areas with different tidal ranges




without major additional field work.   Nevertheless,  more field surveys and



 analysis will be necessary to estimate probable impacts of future sea level



rise on other types of wetlands.




    In spite of the preliminary nature of this investigation,  it appears




reasonable to conclude that  a three-  to five-foot rise in sea level could




seriously threaten coastal wetlands  in the United States,  if human activities

-------
                                   -40-
prevent natural adaptation to that rise.  Because of the long-range nature of




the issue, it may be possible to avoid adverse environmental impacts through




low-cost nonregulatory measures and market incentives.  Future studies should




not only focus on the loss of wetlands caused by sea level rise, but on




possible measures to avoid those losses.




    The assumptions used to predict future sea level rise and the resulting




impacts on wetland loss must be refined considerably so that we can have more




confidence in any policy responses that are based on these predictions.  The




substantial environmental and economic resources that can be saved if better




predictions become available soon will easily justify the cost (though




substantial) of developing them (Titus et al. 1984).  However, deferring




policy planning until all remaining uncertainties are resolved is unwise.




    The knowledge that has accumulated in the last twenty-five years has




provided a solid foundation for expecting sea level to rise in the future.




Nevertheless, most environmental policies assume that wetland ecosystems are




static.  Incorporating into our environmental research the notion that




ecosystems are dynamic need not wait until the day when we can accurately




predict the magnitude of the future changes.

-------
                                   -41-
                              REFERENCES
Earth, M.C., and J.G. Titus (Eds.)» 1984.  Greenhouse Effect and Sea Level
    Rise.  Van Nostrand Reinhold Co., New York, N.Y., 325 pp.

Boesch, D.F., D. Levin, D. Nununedal, and K. Bowles, 1983.  Subsidence in
    Coastal Louisiana:  Cases, Rates and Effects on Wetlands.  U.S. Fish and
    Wildlife Serv., Washington, D.C., FWS/OBS-83/26, 30 pp.

DeLaune, R.D., C.J. Smith, and W.H. Patrick, Jr., 1983.  "Relationship of
    marsh elevation, redox potential, and sulfide to Spartina alterniflora
    productivity."  Soil Science Amer. Jour., Vol. 47, pp. 930-935.

Due, A.W., 1981.  "Back barrier stratigraphy of Kiawah Island, South Carolina."
    Ph.D. Dissertation, Geol.  Dept., University of South Carolina, Columbia,
    253 pp.

Ebersole, B.A., 1982.  Atlantic Coast Water-level Climate.  WES Rept. 7, U.S.
    Army Corps of Engineers, Waterways Experiment Station, Vicksburg, Miss.,
    498 pp.

Gagliano, S.M., 1984.  Independent reviews (comments of Sherwood Gagliano).
    In M.C. Barth and J.G. Titus (Eds.), Greenhouse Effect and Sea Level
    Rise.  Van Nostrand Reinhold Co., New York, N.Y., Chap. 10, pp. 296-300.

Gagliano, S.M., K.J. Meyer Arendt, and K.M. Wicker, 1981.  "Land loss in the
    Mississippi deltaic plain."  In Trans. 31st Ann. Mtg., Gulf Coast Assoc.
    Geol. Soc. (GCAGS), Corpus Christi, Texas, pp. 293-300.

Gallagher, J.L., R.J. Reimold, and D.E. Thompson, 1972.  "Remote sensing and
    salt marsh productivity."  In Proc. 38th Ann. Mtg. Amer. Soc.
    Photogrammetry.  Washington, D.C., pp. 477-488.

Gibbs, M.J., 1984.  "Economic analysis of sea level rise:  methods and
    results."  In M.C. Barth and J.G. Titus (Eds.), Greenhouse Effect and Sea
    Level Rise.  Van Nostrand Reinhold Co., New York, N.Y., Chap. 7, pp.
    215-251.

Hatton, R.S., R.D. DeLaune, and W.H. Patrick, 1983.  "Sedimentation, accretion
    and subsidence in marshes of Barataria Basin, Louisiana."  Limnol.  and
    Oceanogr., Vol. 28, pp. 494-502.

Hayes, M.O., and T.W. Kana (Eds.), 1976.  Terrigenous Clastic Depositional
    Environments,  Tech. Rept. NO. 11-CRD.  Coastal Research Division,  Dept.
    Geol., Univ. South Carolina, 306 pp.

Hicks, S.D., H.A. DeBaugh, and L.E. Hickman, 1983.  Sea Level Variations for
    the United States 1855-1980.  National Ocean Service, U.S. Department of
    Commerce, Rockville, Maryland.

-------
                                   -42-
Hoffman, J.S., D. Keyes, and J.G.  Titus, 1983.   Projecting Future Sea Level
    Rise:  Methodology, Estimates  To The Year 2100,  and Research Needs.   U.S.
    EPA, Washington, D.C., 121 pp.

Kana, T.W., J. Michel, M.O. Hayes, and J.R.  Jensen,  1984.   "The physical impact
    of sea level rise in the area  of Charleston, South Carolina.  In M.C.
    Earth and J.G. Titus (Eds.), Greenhouse Effect and Sea Level Rise.  Van
    Nostrand Reinhold Co., New York, N.Y., Chap. 4,  pp. 105-150.

Keeling, C.D., R. Bacastow, and T.G. Whorf,  1982.  "Measurements of the
    concentrations of carbon dioxide at Mauna Loa Observatory, Hawaii."  In
    Clarke (Ed.), Carbon Dioxide Review:  1982.  Clarendon Press, Boulder, CO.

Lacis, A., J.E. Hansen, P. Lee, T. Mitchell and S. Lebedeff, 1981.
    "Greenhouse effect of trace gases, 1970-80."  Geophys.  Res.  Lett., Vol.
    8, p. 1035-1038.

Meier, M.F., et al., 1985.  Glaciers, Ice Sheets, and Sea Level.  Washington,
    B.C.:  National Academy Press.

Nixon, S.W., 1982.  The Ecology of New England High Salt Marshes:  A Community
    Profile.  U.S. Fish and Wildlife Serv.,  Washington, B.C., FWS/OBS-81/55,
    70 pp.

Nummedal, B., 1982.  "Future sea level changes along the Louisiana coast."  In
    B.F. Boesch  (Ed.), Proc. Conf. Coastal Erosion and Wetland Modfification
    in Louisiana:  Causes, Consequences and Options.  U.S.  Fish and Wildlife
    Serv., Washington, B.C., FWS/OBS-82/59,  pp. 164-176.

Odum, E.P., and M.E. Fanning, 1973.  "Comparisons of the productivity of
    Spartina alterniflora and Spartina cynosuroides in Georgia coastal
    marshes."  Bull. Georgia Acad. Sci., Vol. 31, pp. 1-12.

Pendleton, E.G.,  1984.  Personal communication.  U.S. Fish and Wildlife Serv.,
    National Coastal Ecosystems Team, Slidell, LA.

Ramanathan, V., H.B. Singh, R.J. Cicerone, and J.T. Kiehl, 1985.  "Trace Gas
    Trends and their Potential Role in Climate Change," Journal of
    Geophysical Research  (August).

Redfield, A.C.,  1972.  "Bevelopment of a New England salt marsh."  Ecol.
    Monogr., Vol. 42, pp. 201-237.

Revelle, R., 1983.  "Probable future changes in sea level resulting from
    increased atmospheric carbon dioxide."  In Changing Climate.  National
    Academy Press, Washington, B.C.

Schubel, J.R., 1972.   "The physical and chemical  conditions of the Chesapeake
    Bay."  Jour.  Wash. Acad. Sci.. Vol. 62(2), pp. 56-87.

Scott, G.I., L.C. Thebeau, and T.W. Kana, 1981.   "Ashley River marsh  survey -
    Phase  I."  Prepared for Olde Charleston Partners; RPI, Columbia,  S.C., 43
    pp.

-------
                                   -43-
South Carolina Coastal Council, 1985.  Performance Report of the South
    Carolina Coastal Management Program.   South Carolina Coastal Council,
    Columbia, South Carolina.

Teal, J.M., 1958.  "Energy flow in the salt marsh ecosystem."  In Proc.  Salt
    Marsh Conf., Mar. Inst., Univ. Georgia, pp. 101-107.

Titus, J.G., T.R. Henderson, and J.M. Teal, 1984.  "Sea level rise and wetlands
    loss in the United States.  National Wetlands Newsletter, Environmental
    Law Inst., Washington, B.C., Vol. 6(5).

Titus, J.G., "Sea Level Rise and Wetlands Loss."  In O.T. Magoon (ed.) Coastal
    Zone '85.  American Society of Civil Engineers, New York, New York,  pp.
    1979-1990.

Titus, J.G., M.C. Barth, M.J. Gibbs, J.S. Hoffman, and M. Kenney, 1984.   "An
    overview of the causes and effects of sea level rise."  In M.C. Barth and
    J.G. Titus (Eds.), Greenhouse Effect and Sea Level Rise.  Van Nostrand
    Reinhold Co., New York, N.Y., Chap. 1, pp. 1-56.

Turner, R.E., 1976.  "Geographic variations in salt marsh macrophyle
    production:   a review."  Contributions in Marine Science, Vol. 10, pp.
    47-48.

U.S. Department of Commerce, 1979.  State of South Carolina Coastal Zone
    Management Program and Final Environmental Impact Statement.  Office of
    Coastal Zone Management, National Oceanic and Atmospheric Administration,
    Washington,  B.C.

U.S. Department of Commerce, 1981.  "Tide tables, east coast of North and
    South America."  NOAA, National Ocean Survey, Rockville, MD., 288 pp.

Valiela, I., J.M. Teal, and W.G. Deuser, 1978.  "The nature of growth forms in
    the salt marsh grass Spartina alterniflora."  American Naturalist, Vol.
    112(985), pp. 461-470.

Ward, L.G., and D.D. Domeracki, 1978.  "The stratigraphic significance of
    back-barrier tidal channel migration."  Geol. Soc. Amer., Abs. with
    Programs, Vol. 10(4), p. 201.

Wilson, K.A., 1962.  North Carolina Wetlands:  Their Distribution and
    Management.   North Carolina Wildlife Resources Commission, Raleigh, N.C.

-------
                                 -45-
                          APPENDIX A

         WETLANDS TRANSECTS AND DISTRIBUTION OF SPECIES
    Surveyed wetlands  transects and distribution of species  for 12 profiles  in
the general vicinity of Charleston, South  Carolina (field notes are available
at RPI  Coastal Science & Engineering).

-------
                 RANGE # EPA-1
                  KEY: ••& ^."v
                                                                     EAST SIDE OF MARSH ISLAND PARK BOARDWALK
2U-
(0
? 10-
H
u.
> 0
UJ
UJ



y^ s
*^mm^^m

	 1 	 1 	 1 	 1 	 1 1 	 1 	 1 1 1 1 1 1
                                                                                                                    MHW
                                                                                                                    MLW
       Batis maritima
   Borrichia  frutescenc
     Distichlic  cpicata
   Juncu* roemerianus
Limonium carolinianum
 Polygonum  setaceum
    Salicornia virginica
   Spartina alterniflora
       Spartina patens
 Spartina cynosuroides
       Suaeda  linearis
                              50
100    150    200
250    300    350    400    450    500    550    600    650
   DISTANCE (FT.)
                                                                               3.90(1)

                                                                               3.40(1)
                                                                               3.27(90)

                                                                              .3.42(1)

-------
                                                    RANGE #  EPA-2  BOAT RAMP RD.. WEST OF MARSH ISLAND PARK
                                                      KEY: 16 MAY 1984
                    20-r
                   -10
       Balls maritime
   Borrichia  fruteccens
     Distichlis  spicata
   Juncuc roemerianus
Limonium carolinianum
  Polygonum  cetaceum
    Salicornia virginica
   Spartina  alterniflora
       Spartina patens
 Spartina cynocuroidec
       Suaeda  linearis
                 UJ
                                                                                                                  .MHW
                                                                                                                  _MLW
  	1	t—
50    100    150
                                                 200    250   300    350    400
                                                            DISTANCE  (FT.)
450    500    550    600
H
 650
                                                                                                                            •xj
                                                                                                                            I
                                                                                    .4.34(33)
                                                                                    . 3.38(31)
                                                                                     2.12(75)

-------
RANGE #  EPA-3  LOT 246, END OF SALTGRASS CT.

  KEY: 15 JUNE 1984
4U-
cr
M
? 10-
ik
2j »•
ui
-10-
1
Batif maritima
Borrichia frutescens
Distichlis spicata
Juncus roemerianus
Limonium carolinianum
Polygonum setaceum
Salicornia virginica
Spartina alterniflora
Spartina patens
Spartina cynosuroides
Suaeda linearis
	 MLW
1 50 100 150 200 250 300 350 400 450 500 550 600 650
DISTANCE (FT.)
• 3.13(4)

| 1 _f^ll

• 307(1)

BBfffffBBBBBBB; 3 Qfi,g)
••••••••i^^^HBHHHHHBIHIIIMBBMHI 2.*5(oo)
• 535(1)


                                                    o>
                                                    i

-------
                                                                          RANGE  # EPA-4  LOT  177, MARSH HAWK LANE
                                                                           KEY:  16 MAY 1984
                     20-r
                  W
                     10--
                  >   0--
                  UJ
                  ui
                    -10
       Balis maritima
   Borrichia frutescens
      Distichlis spicata
   Juncus  roemerianus
Limonium carolinianum
  Polygonum setaceum
    Saiicornia virginica
   Spartina alterniflora
       Spartina  patens
 Spartina cynosuroides
       Suaeda linearis
                              50     100    150    200    250    300    350    400
                                                              DISTANCE (FT.)
   MHW
   MLW
-H	1	1	1	1
 450    500    550    600    650
            VD
             I
_ 3.48(7)
_ 5.34(5)
_ 3.76(<1)
_ 3.49(37)
_ 2.05(85)
_ 2.51(72)

-------
                                     RANGE # EPA-5  BETWEEN BtRC TRACT "D" BLOCK "P" AND TRACT "D" BLOCK "Q"
                                       KEY: IS JUN 1984
                  (0
                  5
                     20-r
                    10--
                  >   0 +
                  UJ
                  til
                    -10
  .MHW
  .MLW
       Batis maritima
   Borrichia frutescens
      Distichlis  spicata
   Juncus roemerianus
Limonium carolinianum
 Polygonum  setaceum
    Salicornia virginica
   Spartina alterniflora
       Spartina patens
 Spartina cynosuroides
       Suaeda  linearis
                              50     100    150   200     250    300    350    400    450    500    550    600
                                                             DISTANCE (FT.)
650
  3.20(61)
  3.60(14)
  3.52(10)
  3.63(2)
  3.14(68)

  3.12(77)
  2.55(78)

-------
                                                                    RANGE #  EPA-6   LOT 54. WATERWAY ISLAND  DRIVE
                                                                      KEY: 15 JUNE 1984
                    20-r
                 OT
                    10--
                  >   0--
                  ui
                    -10
       Batis maritima
   BorricfTia frutescens
      Distichlis spicata
   Juncus  roemerianus
Limonium carolinianum
  Polygonum setaceum
    Salicornia virginica
   Spartina alterniflora
       Spartina patens
 Spartina cynosuroides
       Suaeda linearis
                                               TIDAL CHANNEL
                              50
-H	1	1	1	1	1	1—
 100    150    200    250    300   350    400
                          DISTANCE  (FT.)
                               .MHW
                                MLW
450    500     550   600    650
                                          Ln
                                          I-1
                                          I
                               3.04(14)
                               3.86(40)

                               3.48(7)
                               3.04(14)
                              _ 3.30(34)
                              - "(11)
                               3.61(34)

-------
                                                                      RANGE # EPA-7  LOT 57, WATERWAY ISLAND DRIVE
                                                                        KEY: 15 JUNE 1984
                     20-r
       Batic maritima
   Borrichia frutescens
      Distichlis spicata
   Juncus  roemerianus
Limonium carolinianum
  Polygonum setaceum
    Salicornia virginica
   Spartina alterniflora
       Spartina  patens
 Spartina cynosuroides
       Suaeda linearis
                               50
100    150    200
250    300   350    400
    DISTANCE  (FT.)
                                                                                                                         MHW
                                                                                                                         MLW
                                                                                                                                  Ln
                                                                                                                                  S3
450    500     550    600    650
                                                                                 - 3.17(6)
                                                                                 _ 3.20(4)
                                                                                 _ 3.01(4)
                                                                                 _ 3.10(4)
                                                                                 _ 1.95(62)
                                                                                   3.11(4)

-------
                                            RANGE # EPA-8  DEWEES INLET.  NEAR RPI MON. STATION 13. RUNNING WEST
                                             KEY: 16 JUNE 1984
                  CO
                     20-r
                     10 +
       Batis maritima
   Borrichia frutescens
      Distichlis spicata
   Juncus  roemerianus
Limonium carolinianum
  Polygonum setaceum
    Salicornia virginica
   Spartina alterniflora
       Spartina  patens
 Spartina cynosuroides
       Suaeda linearis
                                          TIDAL
                                          CREEK
> 0-
Ul
UJ
-10-
(


) 50
^N/
V)
100 150


200


250


300 350
\~*
i i i
400 450 500
	 1
I i i
I I 1
550 600 650
                                                               DISTANCE  (FT.)
                                                                                                                        MHW
                                                                                                                        MLW
_ 3.82(27)
_ 3.70(23)
_ 3.89(28)
_ 3.30(18)
_ 2.79(57)
_  4.00(7)

-------
                                          RANGE # EPA-9  DEWEES INLET.  NEAR RPI MOM. STATION 13,  RUNNING NORTH
                                            KEY: 16 JUNE 1984
                     20-r
                 G*
                 CO
                 ?  io4-
                 H
                  >   0--
                  UJ
                  LU
                    -10
       Batis maritima
   Borrichia frutescens
      Distichlis spicata
   Juncus  roemerianus
Limonium carolinianum
 Polygonum setaceum
    Salicornia virginica
   Spartina alterniflora
       Spartina patens
 Spartina cynosuroides
       Suaeda linearis
 LEVEE
                                     +
                              50
100    150    200
250    300    350    400
   DISTANCE  (FT.)
                                                            _MHW
                                                            _MLW
450    500     550   600    650
                                                                                 3.54(29)
                                                                                 3.29(15)

                                                                                 4.35«1)

                                                                                 3.14(31)
                                                                                 2.71(70)
                                                                                 3.22(5)
                                                                                           Ui
                                                                                           *~
                                                                                            i

-------
                                                               RANGE #  EPA-10  790 WOODWARD  RD.. RUNNING WEST
                                                                 KEY: 16  JUNE 1984
                 CO
                    20-r
                    10 +
                 >  0--
                 UJ
                 UJ
                    -10
       Batis maritima
   Borrichia frutescens
      Distichlis spicata
   Juncus  roemerianus
Limonium carolinianum
  Polygonum setaceum
    Salicornia virginica
   Spartina alterniflora
       Spartina  patens
 Spartina cynosuroides
        Suaeda  linearis
                              .MHW
                              _MLW
                              50    100    150    200     250    300    350    400
                                                             DISTANCE (FT.)
450    500     550   600     650
                                        Ln
                                        l/i
                                         I
                               4.94(1)
                              . 3.80(9)
                               3.50(99)

-------
                                                               RANGE # EPA-11  790 WOODWARD  ST.. RUNNING SOUTH
                                                                 KEY: 16 JUNE 1984
                    20-r
                 CO
                 >  0  -
                 UJ
                 UJ
                    -10
       Batis maritima
   Borrichia frutescens
     Distichlis spicata
   Juncus roemerianus
Limonium carolinianum
 Polygonum setaceum
    Salicornia virginica
   Spartina  alterniflora
       Spartina patens
 Spartina cynosuroides
       Suaeda linearis
                                                                                 .MHW
                                                                                 _MLW
                              50
100
—I	I—
 150    200
                      +
 +
+
+
250    300    350    400
   DISTANCE  (FT.)
H
450    500     550   600     650
                                                                                           l/l
                                                                                           0\
                                                                                           I
                                                                                 4.10(9)
                                                                                 3.95(31)
                                                                                 5.45(<1)

                                                                                 5.45«1)

                                                                                 3.40(97)

-------
                                                                                RANGE  # EPA-12  END OF OAKDALE ST.
                                                                                  KEY:  16 JUNE 1984
20-i
en
•
u.
> 0-
UJ
UJ
in.


^

-------
                -59-
            APPENDIX B

TIDE ELEVATION PROBABILITY DISTRIBUTION
    FOR CHARLESTON, SOUTH CAROLINA

-------
APPENDIX B.
               -60-

Tide elevation probability  distribution for Charleston  (based
on data given in Ebersole, 1982).
Common
Reference*










MSHW


MHW
















Elevation
(ft)
5.2
5.0
4.8
4.6
4.4
4.2
4.0
3.8
3.6
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
-0.6
Normalized Elev.
(Elevation/
Tidal Range)
1.000
0.962
0.923
0.885
0.846
0.808
0.769
0.731
0.692
0.654
0.615
0.577
0.538
0.500
0.462
0.423
0.385
0.346
0.308
0.269
0.231
0.192
0.154
0.115
0.077
0.038
0.000
-0.038
-0.077
-0.115
Probability
0.00
0.01
0.02
0.03
0.08
0.13
0.26
0.44
0.72
1.01
1.54
2.02
2.55
2.97
3.20
3.40
3.47
3.48
3.22
3.18
2.89
2.76
2.71
2.69
2.66
2.65
2.66
2.67
2.80
2.94
Cumulative
Probability
0.00
0.01
0.03
0.06
0.14
0.27
0.53
0.97
1.69
2.70
4.24
6.26
8.81
11.78
14.98
18.38
21.85
25.33
28.55
31.73
34.62
37.38
40.09
42.78
45.44
48.09
50.75
53.42
56.22
59.16

-------
                              -61-
APPENDIX B.  Continued.
_ Cl .. Normalized Elev.
Common Elevation (Elevation/
Reference* (ft) Tjdal Rgnge)
-0.8
-1.0
-1.2
-1.4
-1.6
-1.8
-2.0
-2.2
-2.4
MLW -2.6
-2.8
-3.0
MSLW -3.2
-3.4
-3.6
-3.8
-4.0
-4.2
-4.4
-4.6
-4.8
-5.0
-5.2
-0.154
-0.192
-0.231
-0.269
-0.308
-0.346
-0.385
-0.423
-0.462
-0.500
-0.538
-0.577
-0.615
-0.654
-0.692
-0.731
-0.769
-0.808
-0.846
-0.885
-0.923
-0.962
-1.00
Probability
r%;
3.13
3.17
3.47
3.64
3.78
3.72
3.77
3.39
3.14
2.54
2.13
1.67
1.16
0.86
0.53
0.35
0.21
0.12
0.03
0.02
0.01
0.00
0.00
Cumulative
Probability
r%;
62.29
65.46
68.93
72.57
76.35
80.07
83.84
87.23
90.37
92.91
95.04
96.71
97.87
98.73
99.26
99.61
99.82
99.94
99.97
99.99
100.00
100.00
100.00
*MHW - mean high water
MLW - mean low water
MSL - mean sea level
MSHW - mean spring high water
MSLW - mean spring low water

-------
                     -63-
                 APPENDIX C

AREA DISTRIBUTION BY ELEVATION ZONE FOR EACH OF THE
      FIVE PRINCIPAL LAND DIVISIONS  IN THE
            CHARLESTON STUDY AREA

-------
APPENDIX C.  Area distribution  (%)  by elevation zone for  each of the five principal communities or land divisions  in  the  Charleston case study area
             under various sea  level  rise and mitigation  scenarios.
NO PROTECTION
ZONE
Existing
(1980)
Basel ine
(2075)
Low
Scenario
(2075)
LOW SCENARIO
With Without
High Anticipation Anticipation
Scenario Protection Protection Protection
(2075) @ 1980 @2030 @2050
CHARLESTON PENINSULA
Highland
Transition
High Marsh
Low Marsh
Tidal Flat
Water
TOTALS
53.4
3.7
1.1
2.5
7.1
32.0
100.0
52.3
3.6
1.4
2.1
4.6
36.0
100.0
51.5
3.1
2.0
1 .9
3.2
38.3
100.0
47.9
3.1
2.1
2.2
2.1
42.6
100.0
53.4
1.2
2.0
1.9
3.2
38.3
100.0
WEST ASHLEY -- 9
Highland
Transition
High Marsh
Low Marsh
Tidal Flat
Water
TOTALS

Highland
Transition
High Marsh
Low Marsh
Tidal Flat
W&ter
TOTALS
29.5
2.1
7.4
16.8
7.4
36.8
100.0

53.3
3.8
7.1
16.7
3.2
15.9
100.0
29.0
1.9
2.2
14.3
12.2
40.4
100.0

52.1
3.8
2.6
13.5
10.4
17.6
100.0
28.6
1 .8
0.9
9.9
15.6
43.2
100.0

51.3
3.7
1 .6
9.8
14.9
18.7
100.0
26.4
2.1
0.9
0.9
3.5
66.2
100.0
MT. PLEASANT:
47.7
3.8
1.5
2.3
3.9
40.8
100.0
29.5
0.9
0.9
9.9
15.6
43.2
100.0
TOTAL
53.3
1 .7
1.6
9.8
14.9
18.7
100.0
— 14,000 ACRES
52.4
2.2
2.0
1 .9
3.2
38.3
100.0
,500 ACRES — %
28.55
1 .85
0.9
9.9
15.6
43.2
100.0
ACRES = 15,750
53.1
1 .9
1.6
9.8
14.9
18.7
100.0
— % AREA @ 2075
51.9
2.7
2.0
1 .9
3.2
38.3
100.0
AREA @ 2075
28.60
1 .80
0.9
9.9
15.6
43.2
100.0
— % AREA @ 2075
51.3
3.7
1.6
9.8
14.9
18.7
100.0
Protection
@1980

53.4
0.0
0.0
1.9
2.1
42.6
100.0

29.5
0.0
0.0
0.8
3.5
66.2
100.0

53.3
0.0
0.0
2.0
3.9
40.8
100.0
HIGH SCENARIO
With
Anticipation
Protection
02010

51.6
0.0
1.5
2.2
2.1
42.6
100.0

27.15
1.35
0.9
0.9
3.5
66.2
100.0

52.7
0.0
0.3
2.3
3.9
40.8
100.0
Without
Anticipa tion
Protection
§2020

51 .0
0.0
2.1
2.2
2.1
42.6
100.0

28.2
0.3
0.9
0.9
3.5
66.2
100.0

49.2
2.3
1.5
2.3
3.9
40.8
100.0

-------
APPENDIX  C.   Continued.
NO PROTECTION
ZONE
Existing
(1980)
Bisel ine
(2075)
Low
Scenario
(2075)
LOW SCENARIO
With Without
High Anticipation Anticipation
Scenario Protection Protection Protection
(2075) @ 1980 02030 @2050

HIGH SCENARIO
With
Anticipation
Protection Protection
@1980 @2010

Without
Anticipa tion
Protection
@2020
SULLIVANS ISLAND: TOTAL ACRES = 1,750
Highland
Transition
High Marsh
Low Marsh
Tidal Flat
Witer
TOTALS
37.1
2.9
7.1
15.7
8.6
28.6
100.0
36.2
2.9
2.3
13.0
12.4
33.2
100.0
35
2
1
9
14
36
100
.6
.8
.2
.6
.7
.1
.0
32
3
0
1
3
57
100
.8
.4
.7
.7
.5
.9
.0
37
1
1
9
14
36
100
.1 NA NA
.3 -
.2 -
.6 -
.7 -
.1 -
.0 -
37
0
0
1
3
57
100
.1 NA
.0
.0
.5
.5
.9
.0
NA
:
-
_
DANIEL ISLAND: TOTAL ACRES = 4,500
Highland
Transition
High Marsh
Low Marsh
Tidal Flat
Water
TOTALS
41.6
2.8
5.0
11.7
5.7
33.2
100.0
40.7
2.8
1.9
9.5
8.9
36.2
100.0
40
2
1
7
10
38
100
.2
.6
.2
.0
.9
.1
.0
37
2
1
1
2
54
100
.5
.8
.1
.7
.8
.1
.0
41
1
1
7
10
38
100
.6 NA NA
.2 -
.2 -
.0 -
.9 -
.1 -
.0 -
41
0
0
1
2
54
100
.6 NA
.0
.0
.5
.8
.1
.0
NA
~
-
-
                                                                                                                                                              I
                                                                                                                                                             ON
                                                                                                                                                             Ui
                                                •&U.S. GOVERNMENT PRINTING OFFICB, 1986-621—73^—00190

-------