Environmentally Sensitive Maintenance
for Dirt and Gravel Roads
• Better Roads
• Better
Environment
• Better
Community
• Less
Maintenance
October 2007
Reissue
Ver: 1.1
PENNSTATE
Center for Dirt and Gravel Road Studies
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NOTICE
This publication was developed under Assistance
Agreement No. CP-83043501-0 awarded by the U.S.
Environmental Protection Agency. It has not been
formally reviewed by EPA. The views expressed in this
document are solely those of the authors and EPA
does not endorse any products or commercial services
mentioned in this publication.
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Technical Report Documentation Page
1. Report No.
USEPA-PA-2005-
2. Government Accession No.
4. Title and Subtitle
Environmentally Sensitive Maintenance for Dirt and Gravel Roads
7. Compiled by:
Alan L. Gesford, P.E. and John A. Anderson, Ph.D.
9. Performing Organizations Name and Adc
Administration & Leadership
Studies - Research & Training Center
Indiana University of Pennsylvania
Dixon University Center, South Hall
2986 North Second Street
Harrisburg, PA 17110
ress
Institute of State and Regional
Affairs
Pennsylvania State University
777 West Harrisburg Pike
Middletown, PA 17057-4898
12. Sponsoring Agency Name and Address
Commonwealth of Pennsylvania
The Pennsylvania Department of Transportation
Bureau of Maintenance and Operations
Commonwealth Keystone Building
400 North Street, 6* Floor
Harrisburg, PA 17120-0064
3. Recipient's Catalog No.
5. Report Date
February 2006
6. Performing Organization Code
8. Performing Organization Report No.
10. Work Unit No. (TRAIS)
11. Grant Assistance ID. No.
CP-83043501-0
1 3 . Type of Report and Period Covered
Technical Reference Manual
14. Sponsoring Agency Code
15. Supplementary Notes
Funding Assistance provided by the U. S. Environmental Protection agency
16. Abstract
This is a nonpoint source pollution project that identifies, documents, and encourages the use of
environmentally sensitive maintenance of dirt and gravel roads. Specifically, this project involved the
development of a reference manual and related technical information sheets on Environmentally Sensitive
Maintenance of Dirt and Gravel Roads for national use.
The manual will provide insight into using natural systems and innovative technologies to reduce erosion,
sediment and dust pollution while more effectively and efficiently maintaining dirt and gravel roads. The
manual will address the environment of forests, mountainous terrain, and rolling hills. Various states
already employ some of the more common practices, particularly forestry departments. These states and
their local governments are prime targets for deploying the additional practices to be addressed in the
manual. The manual will give the users a 'tool box' full of environmentally sensitive maintenance 'tools' or
practices, recognizing that not one tool can fit every situation or site or solve all their problems in
maintaining their dirt and gravel roads and protecting the environment.
17. KeyWords 18. Distribution Statement
Unpaved road maintenance No Restrictions
Dirt and gravel roads maintenance
Environmentally sensitive maintenance
19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price
Unclassified Unclassified
Form DOT F 1700.7 (8-72)
Reproduction of completed page authorized
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Environmentally Sensitive Maintenance
For
Dirt and Gravel Roads
A Manual to provide guidance
using natural systems and innovative technologies to reduce erosion,
sediment and dust pollution while more effectively and efficiently
maintaining dirt and gravel roads.
Compiled by
John A. Anderson, Ph.D.
Alan L. Gesford, P.E.
Sponsored by the
Pennsylvania Department of Transportation
with Funding Assistance from the
U.S. Environmental Protection Agency
This manual is based on information and training products developed by
Pennsylvania State Conservation Commission
& the Penn State Center for Study of Dirt & Gravel Roads
Center far Dirt and Gravel Road Studies
December, 2007
The contents of this report reflect the views of the authors, who are responsible for the facts and the
accuracy of the data presented herein. The contents do not necessarily reflect the official views of either the
Pennsylvania Department of Transportation or the U. S. Environmental Protection Agency. This report
does not constitute a standard, specification, or regulation.
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Acknowledgements:
Funding for the compilation of this manual was supplied under Grant Assistance I.D. No. CP-
83043501-0 sponsored jointly by the U.S. EPA and PennDOT.
We would like to recognize Rod Frederick, Robert Goo, and Chris Solloway from the US EPA
for their support, reviews and encouragement throughout the manual development. Our
appreciation also goes to the Pennsylvania Department of Transportation, especially to Bob Peda,
Bureau of Maintenance and Operations, who initially championed this manual project in
cooperation with the US EPA.
Major Manual Contributors:
This manual has resulted from the initial two-year effort at the Pennsylvania Transportation
Institute at Penn State and the Dirt and Gravel Roads Task Force, funded through the State
Conservation Commission, which assemble materials for a 2-day ESM training program. Under
the direction of the Center for Dirt and Gravel Road Studies, the training program has
subsequently followed a path of continued quality improvements over the next seven years which
has resulted in two comprehensive revisions to the original document. This manual owes its
success to the contributions provided by:
John Anderson, IUP
Steve Bloser, CD&GS/PSU
Woodrow Cobert, SCC [retired]
Dave Creamer, CD&GS/PSU
Alan, Gesford, PSU
Dave Shearer, CD&GS/PSU
The re-issue of this manual has been done to provide formal recognition to the Center for Dirt
and Gravel Road Studies, which is part of the Penn State Institutes of Energy and the
Environment at The Pennsylvania State University, for their major contributions to the continued
development of the ESM practices and training materials from the onset of the Center in 1999 to
the present. It is the Center's activities and ongoing Environmentally Sensitive Maintenance for
Dirt And Gravel Roads Training upon which most of this manual is based. In addition to the
contributors from the Center cited above, we want to acknowledge the Center staff for their
support:
Barry E. Scheetz, Center Director
Tim Zeigler, Field Operations Specialist
Kathy Moir, Administrative Assistant
We also gratefully acknowledge the major contribution of the Pennsylvania State Conservation
Commission, as the lead Commonwealth agency for Pennsylvania's Dirt and Gravel Roads
Program which provides funding, administration and program guidance, with special thanks to:
Karl Brown, Executive Director
Michael J. Klimkos, Program Coordinator
Special recognition needs to be made to former State Senator Doyle Gorman, who championed
the Pennsylvania program through funding [Section 9106 of the Pennsylvania Motor Vehicle
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Code] which established the 2-day training course and is responsible for its long-term
continuation..
A special acknowledgement needs to be made to Woodrow "Woody" Colbert whose
vision shaped the focus of the program to 'natural systems' and whose guidance kept the
direction of the program focused on the local level where the program would be
implemented. Without his efforts, the D&G program and this manual would never have
existed.
In addition, although they are no longer part of the PA program, a special appreciation has to go
to, Morris Perot, Kate Thompson, Denise Wardrup, Phil Dux, Joe Kisic, Shelly Stoffels and Eric
Brown for their early work and shared experiences with the Pennsylvania Program.
We also have to thank PA Trout Unlimited and the efforts of Ed Bellis, Bud Byron and Wayne
Kober, whose many members and chapters contributed untold hours of volunteer work who
conducted the initial field surveys to establish the Dirt And Gravel Roads Program.
We are also grateful for the contributions and assistance from our Pennsylvania Department of
Environmental Protection and our Pennsylvania Department of Conservation and Natural
Resources, the Pennsylvania Game Commission, the Pennsylvania Fish and Boat Commission,
the Pennsylvania Association of Township Supervisors, and the USDA National Resource
Conservation Service.
We would like to acknowledge the National LTAP Program and all the state centers for continual
sharing of information and technology , and particularly the Pennsylvania LTAP funded through
PennDOT and the Federal Highway Administration and administered by the Pennsylvania
Transportation Institute of Penn State University, which provided the basis for the original
Pennsylvania dirt and gravel road training program. (Note: Both John Anderson and Alan
Gesford were actively involved in the Pennsylvania LTAP, providing program administration,
along with road maintenance training, training development, and technical assistance to
Pennsylvania's municipalities.)
Our sincere thanks to the South Dakota Local Transportation Assistance Program (SD LTAP)
(Ken Skorseth and Ali Selim, Ph.D., P.E), for allowing unlimited use of material from their
Gravel Roads Maintenance and Design Manual., a product that has become an essential standard
resource for gravel road maintenance personnel across the United States.
Our thanks to the national Rural Roads Group comprised of individuals from the US
Environmental Protection Agency, Forest Service (US Department of Agriculture), Federal
Highway Administration, Bureau of Indian Affairs (US Department of the Interior), Bureau of
Land Management (US Department of the Interior), National Association of County Engineers
(NACE), National Association of Counties, National Transportation Library, National Local
Technology Assistance Program Association, the APWA LTAP Clearinghouse, and particularly
to Tony Giancola, Executive Director of NACE, and associates, for their valuable reviews and
critiques of this manual throughout the development task.
Special thanks goes to Albert Davenport, Davenport Communications, for editing services.
Also thanks to Penn State's Institute of State and Regional Affairs Director Michael Behney with
special thanks to Stacey Faircloth for all her work in final electronic formatting.
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Lastly, thanks to the County Conservation Districts, local municipal governments and various
organizations and entities for allowing use of graphics and photos for the enhancement of this
manual resource.
John A. Anderson, Ph.D.
Alan L. Gesford, P.E.
Barry E. Scheetz, Ph.D.
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Table of Contents
Acknowledgements i
Table of Contents ii
Foreword xi
1. Introduction 1-1
1.1. Manual Mission & Scope 1-1
1.1.1. The Mission 1-1
1.1.2. Scope 1-1
1.2. The Importance of Dirt and Gravel Roads 1-2
1.3. The Problem: Roads and the Environment 1-3
1.3.1. A Historical Perspective 1-3
1.3.2. The Connection 1-4
1.3.2.1.Factors Affecting Roads 1-4
1.3.2.2.Factors Affecting the Environment 1-4
1.3.2.3.The Road - Environment Relationship 1-5
1.3.3. Traditional Maintenance Practices 1-6
1.3.4. Combining Goals 1-7
1.3.5. Road Safety 1-7
1.4. The Manual: Philosophy, Objectives and Contents 1-7
1.4.1. The Manual Philosophy 1-7
1.4.2. The Manual Objectives 1-8
1.4.3. The Manual Contents 1-9
1.5. Essential Programs 1-10
Appendix 1. Case Study: The Pennsylvania Dirt and
Gravel Roads Program 1-11
Al.l Pennsylvania's Dirt and Gravel Roads 1-11
A1.2 Program Origin: AProblem Recognized 1-11
A1.3 Program Origin: AProblem Substantiated 1-12
A1.4 A Solution 1-13
A 1.5 The Legislation 1-13
A1.6 Program Organization 1-13
Al.7 Program Goal 1-14
A1.8 Program Training 1-14
A1.9 Further Program Development 1-15
A 1.10 Program Results 1-16
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2. Geology, Rocks, and Soils 2-1
2.1. Introduction 2-1
2.2. Geology and Natural Forces 2-1
2.2.1. Geologic Time 2-2
2.2.2. Types of Binding Forces 2-2
2.2.3. Natural Physical Forces 2-3
2.3. Rocks 2-7
2.3.1. Rock Families 2-7
2.3.2. Geological Provinces 2-7
2.3.3. Rock as a Road Material 2-9
2.4. Soils 2-11
2.4.1. Soil Formation 2-11
2.4.2. Soil Particles 2-12
2.4.3. Soil Layers 2-13
2.4.4. Topsoil Versus Subsoil 2-15
2.5. Summary of Geology, Rocks, and Soils 2-16
Appendix 2. Case Study: Pennsylvania's Geology 2-17
A2.1 Central Lowland Province 2-18
A2.2 Appalachian Plateaus Province 2-18
A2.3 Ridge and Valley Province 2-19
A2.4 Blue Ridge Province 2-19
A2.5 New England Province 2-19
A2.6 Piedmont Province 2-20
A2.7 Atlantic Coastal Plain Province 2-20
A2.8 What Pennsylvania Has to Work With 2-20
3. Water, Erosion, Drainage and Road Basics 3-1
3.1. Introduction 3-1
3.2. Water and Erosion 3-1
3.2.1. Principles of Erosion 3-1
3.2.2. Accelerated Erosion 3-2
3.3. Water and the Importance of Road Drainage 3-2
3.3.1. The Importance of Drainage 3-2
3.3.2. Characteristics of Water 3-3
3.3.3. How Water Enters Our Roads 3-4
3.4. Road Drainage 3-5
3.4.1. Drainage Systems 3-5
3.4.2. Surface Drainage 3-5
3.4.2.1. Road Crown and Cross Slope 3-5
3.4.2.2. Road Shoulders 3-7
3.4.2.3. Road Structure (Cross Section) 3-8
3.4.3. Subsurface Drainage 3-8
in
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3.5. Road Materials 3-9
3.5.1. Quality Aggregates 3-9
3.5.1.1. Surface Aggregate versus Other Uses 3-10
3.5.1.2. Road Aggregate Specifications 3-11
3.5.1.3. Recycled Asphalt 3-12
3.5.2. Sampling and Testing Aggregates 3-13
3.5.3. Pit/Quarry Operations 3-14
3.6. Basic Road Maintenance Practices 3-16
3.6.1. Basic Techniques 3-16
3.6.1.1. Blading or Smoothing 3-17
3.6.1.2. Regrading or Reshaping 3-18
3.6.1.3. Adding New Material 3-19
3.6.2. Transitions 3-19
3.6.2.1. Road Intersections 3-19
3.6.2.2. Driveways 3-19
3.6.2.3. Curves 3-20
3.6.2.4. Railroad Crossings 3-20
3.6.2.5. Bridges 3-20
3.6.3. Frequency of Maintenance Operations 3-21
3.7. Summary 3-22
Appendix 3. Sample Aggregate Specifications 3-23
A3.1 Pennsylvania's Driving Surface Aggregate 3-23
A3.2 Illinois DOT Specifications 3-25
A3.3 Michigan DOT Specifications 3-27
A3.4 New York DOT Specifications 3-29
4. Basics of Natural Systems 4-1
4.1. Introduction 4-1
4.2. Ecology, Ecoregions and Ecosystems 4-2
4.3. The Stream Ecosystem (Community) 4-4
4.3.1. Introduction 4-4
4.3.2. Basics of Stream Ecology 4-4
4.3.2.1. Watersheds 4-4
4.3.2.2. Stream Systems 4-6
4.3.2.3. Hydrology 4-7
4.3.2.4. Water Quality 4-9
4.3.2.5. Stream Life 4-10
4.3.2.6. Stream Food Webs 4-10
4.3.2.7. Outside Inputs 4-11
4.3.2.8. Stream Habitat 4-12
4.3.3. Stream Management and Protection Goals 4-13
4.3.3.1. Indicator Species and Community Composition 4-13
4.3.3.2. Stream Evaluation 4-15
IV
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4.3.4. Impact of Erosion and Sediment on Streams 4-16
4.3.4.1. Suspended Sediment (Turbidity) 4-17
4.3.4.2. Sedimentation (Embeddedness) 4-17
4.3.4.3. Attached Contaminants 4-18
4.3.5. Fish Constituency 4-18
4.3.6. Stream Ecosystem Summary 4-19
4.4. The Wetland Ecosystem (Community) 4-19
4.4.1. Introduction 4-19
4.4.2. Definition of a Wetland 4-20
4.4.3. Wetland Basics 4-20
4.4.4. Wetland Management 4-21
4.4.4.1. Wetland Loss 4-22
4.4.4.2. Regulatory Protection 4-22
4.4.5. Wetland Benefits 4-23
4.4.5.l.Floodwater Storage 4-24
4.4.5.2. Bank Stabilization (Shoreline Protection) 4-25
4.4.5.3. Energy Dissipation 4-25
4.4.5.4. Sediment Trapping 4-25
4.4.5.5. Water Quality Improvement 4-26
4.4.5.6. Ecological Benefits 4-27
4.4.5.7. Economic and Social Benefits 4-28
4.4.6. Types of Wetlands 4-29
4.4.7. Wetlands and Road Maintenance 4-31
4.4.7.1. Recognizing Wetland Areas 4-31
4.4.7.2. Wetland Characteristics 4-31
4.4.7.3. Encountering Wetlands 4-35
4.4.7.4. Wetland Strategy 4-36
4.4.7.5. Working with Regulatory Agencies 4-37
4.4.8. Wetland Ecosystem Summary 4-37
4.5. The Upland/Forest Ecosystem (Community) 4-38
4.5.1. Introduction 4-38
4.5.2. Plant Basics 4-38
4.5.2.1. Plant Growth & Photosynthesis 4-38
4.5.2.2. Vegetative Groupings 4-39
4.5.2.3. Plant Life Cycles 4-40
4.5.2.4. Root Structures 4-40
4.5.2.5. Plant Ecology 4-41
4.5.3. Understanding Trees 4-43
4.5.3.1. Tree Growth 4-43
4.5.3.2. Tree Injury 4-44
4.5.3.3. Tree Reaction to Injury 4-45
4.5.3.4. Proper Pruning 4-46
4.5.4. Plant Establishment and Succession 4-46
4.5.4.1. Colonizer Species 4-47
4.5.4.2. Intermediate and Climax Species 4-48
4.5.4.3. Significance of Plant Succession for Roadside Maintenance 4-49
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4.5.5. The Importance of Plants 4-49
4.5.5.1. Ground Cover and Erosion Prevention 4-49
4.5.5.2. Air Conditioning 4-50
4.5.5.3. Air Purification 4-50
4.5.5.4. Water Purification 4-50
4.5.5.5. Aesthetics and Economics 4-51
4.5.6. Upland Ecosystem Summary 4-51
4.6. Summary of Natural Systems 4-51
Appendix 4. Case Study: Pennsylvania's Ecology 4-53
A4.1 Ecoregions and Geological Provinces 4-53
A4.2 Pennsylvania's Stream Ecosystems 4-53
A4.3 Pennsylvania's Wetland Ecosystems 4-55
A4.4 Pennsylvania's Upland Ecosystems 4-56
5. Environmentally Sensitive Maintenance Practices:
Roads and Road Drainage 5-1
5.1. Introduction 5-1
5.2. Erosion Prevention and Sediment Control 5-1
5.2.1. Managing Your Erosion Prevention and
Sediment Control Systems 5-2
5.2.2. Temporary and Permanent Erosion Prevention and
Sediment Control Measures 5-2
5.2.3. Basic Temporary Practices 5-3
5.2.3.1. Straw Bale Barriers 5-3
5.2.3.2. Silt Fence Barrier 5-4
5.3. Environmentally Sensitive Maintenance Practices 5-6
5.3.1. Practices Related to Road Profile 5-6
5.3.1.1. Insloping 5-6
5.3.1.2. Outsloping 5-8
5.3.2. Practices Related to Roadside Ditches 5-9
5.3.2.1. To Ditch or Not To Ditch? 5-9
5.3.2.2. Ditch Shape 5-9
5.3.2.3. Ditch Slope 5-11
5.3.2.4. Alternative Ditch Cleaning Practices 5-12
5.3.2.5. Ditch Widening and Slope Flattening 5-12
5.3.2.6. Reuse of Topsoil and Vegetative Root Mats 5-12
5.3.2.7. Ditch/Channel Linings 5-13
5.3.2.8. Ditch Turnouts and Vegetative Filter Strips 5-16
5.3.3. Practices Related to Ditches and Road Profile 5-18
5.3.3.1. Broad Based Dips 5-18
5.3.3.2. Grade Breaks 5-20
VI
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5.3.4. Practices Related to Driveways 5-21
5.3.4.1. Proper Profile 5-21
5.3.4.2. Driveways Over Deep Ditches 5-22
5.3.4.3. Driveways Over Shallow Ditches 5-24
5.3.5. Practices Related to Culverts 5-25
5.3.5.1.Shallow Culvert Installations 5-27
5.3.5.2. Fords on Perennial Streams 5-29
5.3.5.3. Culvert End Structures 5-30
5.3.5.4. Aprons at Culvert Outlets 5-31
5.3.5.5. Through Drains 5-33
5.3.5.6. Large Culverts in Perennial Streams 5-34
5.3.6. Combination Practices 5-35
5.3.6.1. The Stream Saver System 5-35
5.3.6.2. Multiple Culverts 5-37
5.3.7. Major Reconstruction: Raising the Road 5-37
5.3.7.1. Raising the Entrenched Road 5-39
5.3.7.2. Raising the Road and Moving Away from a Stream 5-41
5.3.8. Practices Related to Bridges 5-41
5.3.8.1. The Stream Saver Bridge System 5-42
5.3.8.2. Gravel Bar Removal 5-43
5.3.8.3. Bridge Decks 5-43
5.4. Summary 5-44
Appendix 5. Worksites in Focus 5-45
A5-1 Worksite #1: Red Rose Road, Hungtington County, PA 5-46
A5-2. Worksite #2: Horseshoe Road, Potter County, PA 5-54
A5-3. Worksite #3: Dutch Corner Road, Fulton County, PA 5-56
6. Environmentally sensitive Maintenance Practices:
Roadsides and Streams 6-1
6.1. Introduction 6-1
6.2. Expectations of a Finished Product 6-2
6.3. Practices Related to Roadsides 6-3
6.3.1. Vegetation Management 6-3
6.3.2. Equipment and Methods 6-3
6.3.3. Roadside Clearing 6-4
6.3.3.1. Shading, Good or Bad? 6-5
6.3.3.2. Problems with Traditional Clearing Techniques 6-6
6.3.3.3. Alternative Techniques 6-8
6.3.3.4. Adjacent Residents and Off Right-of-Way Work 6-9
6.3.3.5. Advantages of Using the Forest System 6-10
6.3.3.6. A Common Pitfall in Tree Removal 6-10
6.3.3.7. Tree Leaves 6-11
6.3.4. Using Other Plants for the Roadside 6-12
Vll
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6.3.5. Clearing Stream Banks at Cross Pipes 6-14
6.3.5.1. Common Practice and Associated Problems 6-14
6.3.5.2. Alternative Practices 6-15
6.3.5.3. Benefits of a New Approach 6-15
6.4. Practices Related to Road and Stream Banks 6-16
6.4.1. Initial Site Visit 6-17
6.4.2. Proven Techniques for Banks 6-21
6.4.2.1. Diversion Swales 6-21
6.4.2.2. Slope Geometry 6-22
6.4.2.3. Benching 6-23
6.4.2A. Seeding and Mulching 6-24
6.4.3. Bioengineering Techniques 6-26
6.4.3.1. Live Stakes 6-27
6.4.3.2. Live Fascines 6-29
6.5. Summary 6-30
Appendix 6 6-32
Appendix 6A. Soil Identification in the Field 6-33
Appendix 6B. Additional Worksite in Focus 6-35
A6B-1 Worksite #4: Fall Brook Road, Tioga County, PA 6-36
7. Environmentally Sensitive Maintenance Practices:
Additional Maintenance Techniques 7-1
7.1. Introduction 7-1
7.2. Dust Control 7-1
7.2.1. What is Dust? and Where Does It Come From? 7-2
7.2.2. The Necessity of Dust Control 7-2
7.2.3. Benefits of a Dust Control Program 7-3
7.2.4. Dust Control Options 7-4
7.2.5. Evaluation of Dust Suppressant Materials 7-5
7.2.6. Common Dust Suppressants 7-6
7.2.6.1. Water 7-6
7.2.6.2. Sodium Chloride 7-7
7.2.6.3. Calcium and Magnesium Chlorides 7-7
7.2.6.4. Brines 7-7
7.2.6.5. Lignin Derivatives 7-7
7.2.6.6. Asphalt Emulsions and Cutbacks 7-8
7.2.6.7. Resins and Other Materials 7-9
7.2.7. Use and Application of Dust Suppressants 7-9
7.2.7.1. Environmentally Sensitive Materials 7-10
7.2.7.2. Application Process 7-10
7.3. Road Stabilization 7-11
7.3.1. What is Road Stabilization? 7-11
7.3.2. Advantages of Stabilization 7-11
7.3.3. Stabilization Additives 7-12
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7.3.4. The Stabilization Process 7-12
7.4. Geosynthetics 7-15
7.4.1. Why Use Geosynthetics? 7-16
7.4.2. Functions and Applications 7-16
7.4.3. Geotextile Fabrics 7-16
7.4.4. Geosynthetic Applications in Road Maintenance 7-17
7.4.4.1. Drainage/Infiltration Fabrics 7-17
7.4.4.2. Prefabricated Subdrains 7-19
7.4.4.3. Subdrain Outlets 7-19
7.4.4.4. Erosion and Sediment Control 7-19
7.4.4.5. Embankment Soil Reinforcement 7-21
7.4.4.6. Separation Fabrics 7-21
7.4.4.7. French Mattress 7-24
7.4.4.8. Geocells & Geowebs 7-25
7.4.4.8.1. Road Stabilization 7-25
7.4.4.8.2. Retaining Walls 7-26
7.4.4.8.3. Low Water Road Crossing 7-26
7.4.4.8.4. Road Stream Ford Crossing 7-27
7.4.4.9.Prefabricated Geosynthetic Pipe Endwalls 7-28
7.5. Summary 7-29
Appendix 7 7-31
Appendix 7A. Pennsylvania's Testing and Approval Program
for Dust Suppressants and Road Stabilizers 7-31
Appendix 7B. Worksites in Focus 7-33
A7B-1 Worksite #1: Miltenberger Road, Adams County, PA 7-34
A7B-2. Worksite #2: Powdermill Nature Reserve,
Westmoreland County, PA 7-36
A7B-3. Worksite #3: Hell Hollow Road, Monroe County, PA 7-38
Glossary 8-1
References 9-1
Technical Information Sheets 10-1
ESMP-01 Insloping 10-2
ESMP-02 Outsloping 10-4
ESMP-03 Ditch Turnouts & Vegetative Filter Strips 10-6
ESMP-04 Broad Based Dips 10-9
ESMP-05 Grade Breaks 10-12
ESMP-06 Driveways 10-15
ESMP-07 Culvert End Structures 10-18
ESMP-08 Culvert Aprons 10-21
ESMP-09 Shallow Culvert Installations 10-23
ESMP-10 Through Drains 10-26
ESMP-11 Stream Saver System 10-28
IX
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ESMP-12 Raising the Entrenched Road 10-31
ESMP-13 Slope Geometry, Benching and Diversion Swales 10-35
ESMP-14 Roadside Trees - Using the Forest System to
Reduce Maintenance 10-39
ESMP-15 Road Separation Fabrics 10-44
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Foreword
This manual was written for Road Maintenance Personnel.
To use this manual, do the following two things:
1. Review the underlying basis, mission and major objectives for this
manual:
Basis of the Manual: The following facts are the driving force behind development
of this manual:
1. Over 1.6 million miles of dirt and gravel roads exist within the United States, and they
provide a vital service as part of the nation's transportation system.
2. Dirt and gravel roads will remain important and significant in mileage and use into the
future.
3. The depositing of unwanted sediments into our streams and waterways represents one
of the largest pollution problems in North America, and improperly maintained dirt and
gravel roads are major contributors to this problem.
The Manual's Mission:
The mission of this manual is to address this pollution problem affecting our streams and
stemming from our dirt and gravel roads in the form of erosion, sediment and dust.
Major Objectives to Accomplish the Mission:
1. Provide users with an understanding that our road system is part of our overall
environment, that a vital connection exists between the two, and that this
connection needs to be considered in whatever actions we take in regards to
constructing and maintaining our road system. In doing so, we will be able to
preserve our environment and more effectively and efficiently prolong the life of
our transportation system.
2. Give users a 'tool box' full of environmentally sensitive maintenance 'tools' or
practices that support both good roads and a good environment by offering a
variety of simple, practical environmentally sensitive maintenance practices and
by providing a means for using these practices in routine road maintenance.
The practices presented in this manual are inclined toward use for dirt and gravel roads in
forested areas. The user may find, however, that many of the concepts and practices
could prove applicable in various types of environments, and possibly require only minor
research and development efforts.
XI
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2. Look at the Chapter Titles to determine how to effectively use the
information presented:
Chapter:
1. Introduction
2. Geology, Rocks and Soils
3. Water, Erosion, Drainage and Road Basics
4. Basics of Natural Systems
5. Environmentally Sensitive Maintenance Practices: Roads and Road Drainage
6. Environmentally Sensitive Maintenance Practices: Roadsides and Streams
7. Environmentally Sensitive Maintenance Practices: Additional Techniques
By looking at the Chapter titles, we see that the maintenance "guts" of this manual are
contained in Chapters 5, 6, and 7 on "Environmentally Sensitive Maintenance Practices".
These are the chapters that you may want to read all the way through and then use this
information with the accompanying "Technical Information Sheets" in implementing
these practices for better roads and a better environment.
If this is all you do, however, you will not have a full understanding of why you are doing
a particular practice a particular way or how these practices really work to better the road
and the environment. This path is the traditional philosophy of telling someone what to
do without any explanation of why it works or the reasons or factors upon which the
practice is based. Without a full understanding of "why and how it works," the wrong
reasoning for doing any work may prevail - "this is the way we always did it." On the
other hand, if we fully understand the "why and how it works," we become confident in
doing it right and can use this knowledge to actually improve upon the practice and its
use in maintaining our roads.
This is where Chapters 1, 2, 3, and 4 become most important. These chapters give
background information that enables an understanding of "how and why it works." We
feel that it is important for road personnel to have "the whole story" or all the information
behind the practices. This will enable them to implement the proper practice when needed
or desired. Road personnel should know why and what they are doing, and why and how
it benefits both the roads and the environment.
Xll
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Environmentally Sensitive Maintenance
For
Dirt and Gravel Roads
Chapter 1: Introduction
1.1 Manual Mission & Scope
1.1.1 The Mission. The
development of our national road
system and the need to sustain it
dictated governmental ownership
from the start. Today, our state and
local governments maintain the vast
majority of roads. But our roads are
part of our total environment, and just
as we are the governmental trustees
of our road system, we are also the
trustees of our environment and all its
resources.
1-01 Our roads are part of our total environment.
Beyond this trusteeship lies a greater calling: to be responsible stewards of our
environment. The environment is under assault on many fronts, and many of those battles
must be fought at the national and international level. But roads and their relationship to
the environment are perhaps the one area where state and local governments can make a
difference.
Unwanted sediments choke many streams and waterways, representing one of the
largest pollution problems in North America. The culprits in many cases are dirt and
gravel roads. Our mission, then, is to present proven methods of maintaining our dirt and
gravel roads that reduce the erosion, sediment and dust that pollute our streams.
1.1.2 Scope. This manual's mission and philosophy are rooted in the
Pennsylvania Program on "Environmentally Sensitive Maintenance for Dirt and Gravel
Roads." (This Commonwealth program provides funding, training, and technical
assistance and is highlighted as a case study for "Essential Programs" in Appendix 1 at
the end of this chapter.)
Based on the Pennsylvania model, the practices presented in this manual focus on
dirt and gravel roads in forested areas, recognizing that, with only minor research and
development, many of the concepts and practices can be applied in various types of
environments.
1-1
-------
This manual will show that our
road system is part of our overall
environment, that there is a vital
connection between the two, and
that this connection needs to be
considered when we construct and
maintain our dirt and gravel roads.
By doing so, we will be able to
preserve our environment and
prolong the life of our
transportation system.
Roads exist as unnatural
structures in the natural
environment. Natural forces
continually take their toll on our
roads, often resulting in degraded
roads and environmental damage. The challenge rests in simultaneously preserving our
roads and streams in a safe and cost-effective manner. Using a combination of natural
systems and road maintenance principles, environmentally sensitive maintenance
practices can be integrated into an effective and efficient approach benefiting both the
environment and our road transportation system.
Although this manual addresses environmentally sensitive maintenance for dirt
and gravel roads, many of the practices, particularly in terms of drainage and vegetation,
can be transferred to paved roads and result in benefits to both the paved road and the
environment.
1-02 Roads exist as unnatural structures in the
natural environment.
1.2 The Importance of Dirt and Gravel Roads
Over 1.6 million
miles of dirt and gravel
roads criss-cross rural
areas of the United States,
providing a vital service
as part of the nation's
transportation system. In
many cases, our unpaved
roads are the main access
for major industries.
Unpaved roads provide
essential market access for
farms, foresters depend on
dirt and gravel roads to
remove timber from the
Dirt & Gravel Roads
Providing Vital Service to Residents and Industries:
1-03
1-2
-------
forest, and the mining industry could not get minerals out of the mines without these
valuable pathways.
In many areas, dirt and gravel roads play a major part in tourism, adding to the
economic wealth of the region. Dirt and gravel roads also directly serve millions of rural
residents living along them.
Many of our dirt and gravel roads remain unpaved for economic reasons, but, in
many areas, residents do not want paved roads, desiring to preserve the rural nature of
their area. Dirt and gravel roads are considered the lowest service level in any functional
road classification system, usually serving the lowest volumes of traffic. But even as their
numbers decline, giving way to more and more paved roads, dirt and gravel roads
continue to be a significant part of our road system.
In fact, traffic on dirt and gravel roads is increasing. Further, the vehicles and
equipment using these roads are getting larger, meaning the most safe, effective and
efficient maintenance practices must be employed to keep pace with the stress these
larger vehicles place on the roads.
1.3 The Problem: Roads and the Environment
1.3.1 A Historical
Perspective. Read our country's
history books and the accounts of
our discoverers, trailblazers,
pioneers, and early settlements and
it becomes clear that roads and
streams are connected by their
imminent proximity.
Early settlements were
built next to streams that became
the essential water source for
drinking, washing, domestic
animals, crops, and power
generation for sawmills or
gristmills. Streams were also used
as transportation corridors to haul
goods between homesteads.
Footpaths developed along these
streams to connect the settlements by land. Streamside terrain offered relatively easy
slopes for construction and subsequent use by horses and wagons. These footpaths
became the roads, many of which survive today as our dirt and gravel roads. This close
proximity of roads and streams, dictated by historical development, began the conflict of
erosion and sediment degradation affecting both roads and streams.
1-04 Historical development dictated the close
proximity of roads and streams.
1-3
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1.3.2 The Connection. Erosion is a natural occurrence in the environment. When
roads are constructed, however, they create an interference with the natural systems and
collect water, increasing its volume and velocity, resulting in accelerated erosion.
1.3.2.1 Factors Affecting Roads. When we look at all the factors affecting the
i^^^^^^^^^^_ life of our roads
Figure 1-1
Factors Affecting
Your Road
Traffic Load
Environment
(Climate)
Vegetation
Water
Subgrade Quality
Road Structure (Age)
Quality of Road
Materials
Maintenance
Practices
What Can You
Control?
(Figure 1-1), water
has to top the list.
Alone or combined
with other factors,
water can be
disastrous. The
subgrade of the road
is what it is built on,
the soils. If this
foundation is poor,
the road's life will be
significantly
reduced.Ifthe
subgrade is water
saturated, the
condition will be
worse.
Most maintained dirt and gravel roads are quite old. Current maintenance crews
were not involved in the construction. If poor quality materials were used or the
workmanship was substandard, maintenance crews inherit numerous headaches with the
road. And even when materials and workmanship are up to standards, the road may not
have been built to handle today's heavier traffic loads. Traffic volumes and weights have
both increased substantially in the last 20 years. The combination of water and increased
traffic loads is potentially disastrous for our roads. That is why maintenance practices are
so important. Poor maintenance equals poor roads. If there are drainage problems,
however, even the best maintenance is doomed unless drainage problems are taken care
of first.
The environment and climate also affect road conditions. The environment, as
defined here, refers to vegetation, soil, sand, rocks, drainage conditions, and the overall
stability of the area. Climate dictates the local weather conditions. Weather includes rain,
freeze-thaw cycles, and hot sun that can dry out soils and road materials.
Looking at all these factors affecting roads, we should ask ourselves "What can
we control?"
1.3.2.2 Factors Affecting the Environment. The same factors that affect the
road affect the environment. Water feeds vegetation and streams and creates habitats, but
also causes erosion, flooding, and sedimentation.
1-4
-------
Figure 1-2
Factors Affecting the Environment
Traffic Water
Climate
Vegetation
Roads
>Subgrade
>Structure
>Materials
Maintenance
Practices
What Can You
Control?
Our roads certainly
affect the environment along
with our maintenance
practices. Poor road structure
and material quality, increased
traffic levels, and proximity to
waterways lead to erosion,
sediment and dust pollution
problems.
Again, we should ask,
"What can we control?"
1.3.2.3 The Road-
Environment Relationship.
Road conditions are deeply
intertwined with the surrounding environment. Concentrated water flows accelerate
erosion, overloading natural systems. Excess sediment clogs our streams. Dust becomes
sediment in our streams, generates complaints from residents and harms plants, animals,
people and equipment. Chemical contamination complicates the picture even more
because oils, nutrients, pesticides, herbicides, and other toxic substances bind to dust and
sediment and go along for the ride to pollute our streams and waterways.
Dirt and gravel roads are a
major potential source of these
pollutants. Many roads have
unstable surfaces and bases. Roads
act like dams, concentrating flows
that accelerate erosion of road
materials and roadsides. Both
unstable surfaces and accelerated
erosion then lead to sediment and
dust.
The close proximity of
roads and streams thus establishes
the connection. Because road
systems are situated close to
streams within the natural
environment, they affect the
natural systems as they are in turn affected by the natural processes that take place there.
The two systems - roads and the environment - are interrelated. Thus, in order to fix road
problems, we must understand some things regarding each system to find a solution
beneficial to both our roads and the environment.
1-05 Dirt and gravel roads are a major source of
erosion and sediment.
1-5
-------
In addition, not only is there a relationship between the roads and the
environment, but both the roads and the environment also have an effect on the overall
quality of life within your region. John Muir, who has been called the father of our
National Park system, summed it up in this statement: "When we try to pick out
anything by itself, we find it hitched to everything else in the universe."
Roads
Quality of Life
Figure 1-3: Relationship & Effect
1.3.3 Traditional
Maintenance Practices. Even
though the goal of road
maintenance personnel is to
maintain good roads, accepted
maintenance practices do not
always adequately address the
road's relationship to the
environment.
Why do we do what we do?
Because we've always done it that
way? There are many things that
we do that may not be the best way for the environment or the road. In fact, many
existing practices cause damaging sediment pollution, impacting both the road and the
environment.
Vegetation management is a major example where many existing practices become
counterproductive. Traditional "daylighting" exposes bare soil, disrupts ecological
succession and eliminates soil-stabilizing roots, all of which increase erosion and
sedimentation, damaging both the road and the environment. In addition, excessive
sunlight can dry the roadbed, leading to excessive dust generation. Maybe we should
consider leaving existing root structures undisturbed, thinning canopy cover to allow
moderate sunlight, and avoid clearing banks just because they are there. Using nature's
patterns and forces can result in better roads, less erosion and sediment pollution and
lower maintenance costs.
Bank cutting and undercutting results in extensive sediment runoff, blocked
ditches, and increased cyclical maintenance. On the other hand, refraining from cutting
the toe of slopes, using headwalls to reduce pipe inlet and bank erosion, and using
diversion or intercepting swales preserve both road quality and the environment.
Conveying road and ditch runoff to the nearest stream using the most direct route
possible has long been an established practice. Any type or amount of sediment being
carried by that runoff is also dumped directly into the stream. But directing culvert and
ditch outlets (turnouts, bleeders) into a vegetative filtering area will help filter out the
sediment, allow water infiltration and groundwater recharge, and protect the stream
ecology.
Road aggregate quality directly impacts both the survival of the road and the
environment. Covering the road with poor 'low-bid' material that may wash away is
1-6
-------
another way of paying for sediment pollution, not to mention increased road aggregate
replacement costs. Using a good road material that remains in place and prolongs road
life will also benefit the total environment.
Undersizing and oversizing water channels, bank armoring, and flow redirection
can disrupt stream energy, increasing maintenance costs and causing environmental
harm. Understanding stream flows and the natural forces can help to establish better
practices to again protect both the road and the environment.
Clearly, many traditional practices are counterproductive. They should be
replaced with more productive measures that incorporate our knowledge of roads and
natural systems. The result will be better roads, less sediment pollution, and lower
maintenance costs.
1.3.4 Combining Goals. The goal of road maintenance personnel has always
been good roads through proper maintenance at the lowest cost. We want to keep this
goal, but expand our vision. We need to take a different look at our roads and see the total
environment in which our roads are contained. This environment affects the life of our
roads just as the road affects the environment.
If our goal within this project is to protect the environment through reduction of
erosion, sediment and dust pollution, then let's combine our goals. Let's use additional
and improved maintenance techniques and practices that benefit both the roads and the
environment.
1.3.5 Road Safety. Any effective road maintenance program needs to consider
and address safety. A safe transportation system is essential and remains part of our
overall goal. Maintaining our roads and environment, however, need not come at the
expense of safety. In fact, roads maintained in an environmentally friendly way have
more structural strength, suffer less deterioration, and have fewer defects, and, thereby,
are also safer. The goals of low-cost, environmentally sensitive maintenance and
improved road safety can be combined seamlessly.
1.4 The Manual: Philosophy, Objectives and Contents
1.4.1 The Manual Philosophy. This manual is titled Environmentally Sensitive
Maintenance for Dirt and Gravel Roads. The mission, as stated, is to address the
pollution problem of erosion, sediment and dust stemming from our dirt and gravel roads
and affecting our streams. To meet this mission, the manual centers on an important
philosophy or rationale.
To municipal road maintenance personnel, the road has been "sacred." Everything
they have been taught about road maintenance has centered on what is good for the road,
which has proven at times not to be correct. We need to initiate a change in this thinking.
We can no longer afford to think only about the road. We need to understand the
relationship between the road and the environment, that everything is interconnected, and
1-7
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that there are practices that can be implemented that are not only good for the road, but
also good for the environment. In addition, we need to make the connection that both
good roads and a good environment are important to the welfare of local governments
and their residents.
Only when this thinking changes can it be converted into action. In presenting
"environmentally sensitive practices," this manual will illustrate to the users how easy
these practices are to use and how useful and beneficial they become in prolonging the
life of the road and protecting the environment. To accomplish this, however, the
practices need to be simple, practical, and easy to incorporate into a routine road
maintenance program.
The manual will give the users a "tool box" full of environmentally sensitive
maintenance 'tools' or practices, recognizing that no one tool or practice can fit every
situation or site or solve all their problems. Because every road and every site along that
road is different, we need a toolbox from which we can select the appropriate tool or
tools to help solve whatever situation we encounter.
1.4.2 The Manual Objectives. To meet the mission and put "punch" into our
philosophy, we set our objectives as follows:
1. Enable the user to recognize the connection between road maintenance and
the environment and the importance of good roads and a good environment
for good government.
2. Enable the user to recognize sources of erosion, sediment and dust pollution
associated with roads and the importance of preventing these pollution
sources.
3. Enable the user to recognize that standards cannot fit every situation and that
sound decisions require proper knowledge of basic principles and practices.
(Most standards, although often dictated as requirements, should be presented
as only guidelines that need to be adjusted or revised to fit each particular site
or problem area in the field. To know, however, what "tool" to use or what
adjustment is needed, one needs to recognize basic principles and practices
not only related to road maintenance but also to the natural systems that
influence these roads, leading to our 4th objective.)
4. Arm the user with knowledge on basic principles of nature and natural
systems as applied to road maintenance and a healthy environment and on
basic road maintenance materials and techniques. (The user needs to know the
basics of nature and the natural forces, and how they can be applied to help
establish good roads and protect the environment. In addition, to make sure
we are "on the same road"; we want to cover the road basics of good materials
and techniques.)
5. Arm the user with knowledge on environmentally sensitive maintenance
practices and the effective use of these practices in road maintenance. (This is
where we provide the "tools" for their toolbox - a variety of simple, practical
environmentally sensitive maintenance practices and the means of using these
1-8
-------
practices in routine road maintenance to keep both good roads and a good
environment.)
1.4.3 The Manual Contents. To accomplish this comprehensive list of
objectives, the manual contains 7 chapters.
Chapter 1 - Introduction: Chapter 1 is simply an introduction to the manual. The
mission and scope of the manual is introduced, followed by a discussion on the
importance of dirt and gravel roads. We then start to make the connection between roads
and the environment and discuss the shortcomings of traditional road maintenance
practices. The chapter then shows the value of combining the goals of good roads and a
good environment. The manual philosophy is then discussed, followed by the objectives
and this description of contents. To close, the need for essential programs is covered,
with an appendix to describe the Pennsylvania program as a case study.
Chapter 2 - Geology and Soils: This chapter discusses geologic time and
relentless natural forces, looking at geological regions, topography, weather, rocks and
soils. The chapter demonstrates how geology and natural forces give us what we have to
work with and the conditions under which we have to work. Geology dictates the
aggregates available for road materials and the soils available to support the natural
vegetation.
Chapter 3 - Water, Erosion, Drainage and Road Basics: This chapter starts with
basic principles of erosion and how roads cause accelerated erosion and increased
sediment and the importance of preventing this pollution, showing the connection
between roads and the environment. This module hits hard on the importance of good
drainage, discussing the characteristics and effects of water on roads. Discussion then
turns to road materials, what's being used and what we need to be concerned with. We
then review basic road maintenance techniques for dirt and gravel roads - basic grading
operations, road crown, etc. - and end with a discussion on winter maintenance
operations.
Chapter 4 - Basics of Natural Systems: This chapter sets the basics on the natural
side, presenting guiding principles by defining ecology and discussing three distinct
ecosystems: the streams, wetlands, and forests or uplands. We stress the important
benefits of these areas and set the stage to discuss, in a later module, how we can use
these systems to help in road maintenance. This is unfamiliar area to most road
maintenance personnel. The user should read this chapter with an eye to relating roads
and road maintenance to natural systems.
Chapter 5 - Environmentally Sensitive Maintenance Practices: Having set the
basics for both roads and the natural systems, this chapter presents the environmentally
sensitive maintenance practices, with emphasis on road profiles, ditches, culverts, and
bridges. Simple, straightforward, easy to implement practices are presented - some of
which may already be familiar, or some that may be just tweaking something already in
use. Others may be new, but still simple and easy to implement.
1-9
-------
We start to fill the user's toolbox with the tools, emphasizing that not one tool or
practice or technique will solve all their problems, but a toolbox full of tools will help
greatly.
Chapter 6 - Roadsides and Streams: This chapter discusses the value of roadside
vegetation management and the important factors affecting bank stability. The chapter
then builds on this discussion to show how we can use the forests and natural systems to
help reduce road maintenance, introducing more environmentally sensitive maintenance
practices. We review common practices and the associated problems that can be
detrimental in the long term for both roads and the environment, followed by alternative
methods to improve or enhance the existing conditions (e.g., traditional clearcutting
practices, stream channel clearing practices). This leads to more environmentally
sensitive maintenance practices for vegetation management and bank stabilization,
ending with an introduction to a variety of bioengineering techniques for stream banks.
Chapter 7 - Additional Maintenance Techniques: Chapter 7 continues to add tools
to the toolbox, discussing three specific areas: dust control, road stabilization (full-depth
reclamation), and the world of geosynthetics. The geosynthetics section emphasizes
geotextile separation fabrics along with other geosynthetics used in actual road projects
including a drainage pipe project case study, demonstrating the variety of functions and
uses that geosynthetics play in road maintenance.
1.5 Essential Programs
To successfully fulfill our mission of addressing the national problem of erosion
and sediment pollution from our dirt and gravel road system affecting our streams, there
is a need not only for a manual but also for comprehensive state programs providing
funds, education and training, and technical assistance to the nation's road maintenance
personnel.
No change in our environment will occur without a change in thinking. Roads do
not exist in isolation. They are an integral part of the environment. A change to the road
changes the environment. An environmental shift has consequences for the road. Until
those performing maintenance on our roads understand this relationship, both the roads
and the environment will continue to suffer.
The way to change thinking is through training and technical assistance, coupled
with funding. The message must be clear, simple, and easy to administer. It must be
targeted at local and regional road maintenance managers.
As a case study, Appendix 1 presents Pennsylvania's Program as a successful
model and resource for other states in meeting this mission. Appendix lisa description
of the program development and implementation, with a discussion of the essential
criteria for a successful program.
1-10
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APPENDIX 1
Case Study: The Pennsylvania Dirt and Gravel Roads Program
In 1997, Pennsylvania introduced a program that provides an annual $5 million
appropriation for "Environmentally Sensitive Maintenance" for our nearly 20,000 miles
(38,180 km) of dirt and gravel roads. The program addresses three critical components:
Thought and Attitude, Cost Effective Best Management Practices, and Technology
Transfer. In developing an understanding of the problem, the program team, spearheaded
by the State Conservation Commission, developed a philosophy that simplifies
administration, holds the stream sacred, and strives for better roads and reduced
maintenance. This exemplifies a major change in "thinking and doing" for road
maintenance personnel, where traditionally the road had priority. The program leads them
to consider both the road and the environment as important and how natural systems can
help with overall road maintenance.
Al.l Pennsylvania's Dirt and Gravel Roads. Pennsylvania has over 117,000
total miles (188,253 km) of public roads, including both paved and unpaved. Local
municipal governments own and maintain two thirds of that total mileage. Of that total
mileage, nearly 20,000 miles (32,180 km) are unpaved dirt and gravel roads.
Local municipal governments own and maintain the majority of dirt and gravel
roads with over 17,000 miles (27,353 km).The PA Department of Conservation and
Natural Resources (DCNR), Bureau of Forestry owns and maintains over 2500 miles
(4023 km). The PA Department of Transportation (PENNDOT) has less than 500 miles
(805 km). This number continues to decline due to PENNDOT's Turnback Program
(PENNDOT pays $2500 per mile as an annual sum added to a municipality's liquid fuels
funds for any state roads "turned back" to the municipality to own and maintain). Other
agencies having nominal mileage are the DCNR Bureau of State Parks, the PA Fish and
Boat Commission, and the PA State Game Commission. Dirt and gravel road mileage
continues to decline as development and traffic volumes increase and more and more
roads become paved, but dirt and gravel roads will remain a significant part of
Pennsylvania road mileage into the future.
Pennsylvania's dirt and gravel roads play an important role for the
commonwealth. They provide vital direct access for over 3.6 million PA residents,
although probably used by almost all of PA's 12 million people. They also provide vital
access to Pennsylvania's industry, namely our top industries of agriculture, forestry,
mining and tourism. In fact, tourism is projected to become our state's number one
industry, a position that has been held by agriculture. To emphasize, Pennsylvania's dirt
and gravel roads have always played an important role, are still playing that role, and will
remain playing that role into the future.
A1.2 Program Origin: A Problem Recognized. In January 1991, a man by the
name of James "Bud" Byron, active in Trout Unlimited, instigated a Northcentral
Pennsylvania Conference of parties interested in protecting streams from sediment
1-11
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Figure Al-1
PA Task Force on Dirt
and Gravel Roads
pollution associated with dirt and gravel roads. The results and publicity of that meeting
held in Pleasant Gap, PA, sowed the seeds of the program.
A1.3 Program Origin: A Problem Substantiated. Lead by Trout Unlimited,
various individuals, organizations and agencies became active in addressing this problem
on a statewide basis. In 1993,
they formed the Dirt and Gravel
Road Task Force, (Figure Al- [F J% H
1). The Task Force set out to !^£M (LjftJ I
substantiate the extent of the •^•Hl
problem. They began by
conducting field surveys of
roads and streams to identify
actual conditions in the affected
watersheds. Using volunteers
(no funding was available), they
zeroed in on protected
watersheds identified as
Exceptional Value and High
Quality. Just surveying these
areas was a huge undertaking
(Figure Al-2). A great number of volunteers were needed, and Trout Unlimited, with its
55 PA chapters, provided most of the manpower. A simplified manual card system was
developed to record actual field conditions. The volunteers received onsite training to
help ensure consistent results. These surveys identified actual "trouble spots" of sediment
pollution into streams throughout the commonwealth. These pollution trouble spots
became the initial worksites and, when viewed plotted on a map (Figure Al-2),
substantiated the problem.
Figure Al-2: Result - A Problem Substantiated
• Initial Worksites
PENNSTATE
9
v~— I—^
High Quality Watersheds
Exceptional Value Watersheds
1-12
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A1.4 A Solution. With the problem substantiated, the Task Force needed to look
at a solution. Who was maintaining these dirt and gravel roads? Why were the problems
of erosion and sediment occurring? What did they need to do to correct the problems?
Municipal governments owned the roads, so the Task Force looked to existing road
maintenance. They found that even though the goal was to maintain good roads, existing
accepted maintenance practices did not always adequately address environmental
concerns. To solve the existing and continually occurring pollution problems required
maintenance managers to change their thinking to see the road as part of the environment.
This change in thinking had to lead to changes in procedures. Improved maintenance
techniques that were good for both the roads and the environment had to be used. To
initiate this change, the task force recognized two major needs - training and money.
Legislation was necessary to meet these needs. Pennsylvania Senator Doyle
Gorman became the program champion and drafted legislation, which became part of the
PA Transportation Revenue Bill, signed into law as PA Act 3 of 1997. Section 9106 was
added to the PA Motor Vehicle Code, initiating the Dirt and Gravel Road Program.
A1.5 The Legislation. Section 9106 created an annual, non-lapsing $5 million
appropriation for Dirt and Gravel Road Maintenance to address the pollution problems of
erosion, sediment and dust. Section 9106 took effect July 1, 1997. The legislation
provides that $1 million go directly to the Bureau of Forestry for their roads and that the
other $4 million go to the State Conservation Commission, the lead agency for the
program. This annual $4 million was to be used as grants for environmentally sensitive
maintenance projects on dirt and gravel roads.
The legislation stated that the identified "trouble spots" would be the top priority,
recognizing the significance of the volunteer work that substantiated the problem and led
to the legislation.
The legislation also required grant recipients to receive training as a
prerequisite to applying for grant funds.
A1.6 Program
Organization. The PA State
Conservation Commission
serves as the lead agency for
the program (Figure A1-3).
They allocate the money to
the County Conservation
Districts who are responsible
for administering the program
at the local level. Each County
Conservation District is
required to implement a
Quality Assurance Board
(QAB) who reviews and
Figure Al-3: Program Administratio
State Conservation Commission
County Conservation District
Quality Assurance Board (QAB)
Grant Recipients
(Municipalities, State Agencies)
1-13
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prioritizes grant applications and provides assurance of project completion in accordance
with the applications. This board provides recommendations back to the County
Conservation District for formal approval. To benefit from a variety of background and
experiences, the QAB is comprised of four members: a chairman from the County
Conservation District (non-voting) and three voting members, one appointed by the
County Conservation District, one appointed by the PA Fish and Boat Commission, and
one appointed by the National Resource Conservation Service (NRCS).
Grant recipients are the local municipalities or state agencies that own and
maintain dirt and gravel roads.
Two major points emphasized through the program legislation are simplicity and
local control. The program organization meets these points with a requirement of a one-
page grant application form and with the charge given to the County Conservation
Districts to implement the program. What better way to keep it simple and have the
program handled at the local level?
A1.7 Program Goal. The program's major goal is to reduce the pollution due to
erosion, sedimentation, and dust associated with dirt and gravel roads in the
commonwealth. To meet this goal, a strong program basis to protect the dirt and gravel
roads was formulated. Several decisions were made by the program initiators and agreed
upon through the legislation.
First, the program supports maintaining dirt and gravel roads as dirt and gravel.
The program will not fund paving these roads. Second, to minimize road maintenance
and stretch limited resources, cost effective maintenance practices that are not only good
for prolonging road life but also for protecting the environment are essential.
This program goal and basis led to the required training with its own rationale and
objectives.
A1.8 Program Training. The Pennsylvania State University, through the
Pennsylvania Transportation Institute and the Environmental Resources Research
Institute, were originally charged with development and delivery of the training
associated with the Dirt and Gravel Road Maintenance Program. Since then, a Center for
Dirt and Gravel Road Studies, in conjunction with Penn State University, was funded
through contract with the PA State Conservation Commission. This Center now
administers the education, training and technical assistance aspects of the program.
The major purpose of the training was simple - to meet the requirements of the
legislation which required anyone who applies for program funding to attend a training
course as a prerequisite.
The course was simply titled, following the legislation, "Environmentally
Sensitive Maintenance for Dirt and Gravel Roads." The program goal, as stated, is to
reduce erosion, sediment, and dust pollution relating to dirt and gravel roads. To meet
1-14
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this major goal, the training centers on the philosophy and rationale as discussed above in
Section 1.4.1 for this manual.
To meet the main program goal, objectives similar to the ones outlined above in
Section 1.4.2 for this manual were adopted along with an additional objective to provide
the trainee with information on associated laws and regulations and with the information
on grant funding procedures.
The training gives them a "tool box" full of environmentally sensitive
maintenance "tools" or practices, recognizing that not one tool or practice can fit every
situation or site or solve all their problems. These practices are mostly simple, practical,
cost effective techniques that can be easily implemented. Municipal road crews with
available equipment resources can perform most of the practices, incorporating them into
their normal routine road maintenance program. Not all practices will apply to any one
municipality's roads, but having a full toolbox from which to choose the best tool or tools
to address the problem or concern encountered tends toward a more successful solution.
Many of these practices can be used in combination and will apply to most dirt and gravel
roads in general
The training is a two-day course and consists of classroom training only. The
possibilities of field trips to nearby roads were discussed, but weather and the logistics of
coordinating transportation to the site does not lend to the feasibility. The time factor also
comes to play an important deterrent.
The training uses PowerPoint® presentations with an LCD projector and
projection screen. The PowerPoint® presentations contain all the digitized photos and
several video clips to enhance, clarify, or show examples. Trainers also use various
samples of products, particularly geosynthetic products.
Training evaluation sheets are distributed at each session. Results have been
overwhelmingly favorable on all aspects of the training. Acceptance by municipal road
personnel of the many practices presented has been greater than expected. This is a
testament to the dedication and concern of local municipal government road personnel.
A1.9 Further Program Development. A new inventory and assessment of PA's
dirt and gravel roads were completed with the establishment of the new Center for Dirt
and Gravel Roads. County Conservation Districts worked with the local governments to
verify unpaved roads via municipal and county maps. All identified roads then received
field assessments by the County Conservation Districts for pollution problems affecting
streams. This new assessment identified over 11, 000 new sites across the commonwealth
which then became eligible for program funding (Figure Al-4).
1-15
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Figure Al-4: Assessment Phase II Results
County Conservation Districts inspected the roads and
identified worksites
A1.10 Program Results. The program has been and continues to be a success.
Projects undertaken and completed with program funds have been evaluated. A
computerized GIS system is used for project tracking and central reporting with minimal
paperwork. An implemented quality assurance/quality control (QA/QC) process
continually monitors and evaluates completed projects, verifying that all but one project
has met or exceeded expectations.
The following page is the 2006 Program Report reflecting a summary of the
program data showing 1608 projects completed by the close of 2006. The summary gives
a breakdown of program funding, completed project costs and major work items, and a
training summary of sessions and attendees. It should be interesting to note the amount of
in-kind contributions, which are the materials and services donated to the projects by the
local government grantees. Although contributions are not required and the projects are
100% fundable with program grant monies within the prescribed parameters, the in-kind
contributions have averaged 36%. Comparing this to the many federal and state grant
programs that require 10 to 25% matching funds, we can see the substantial voluntary
commitment made by the Pennsylvania local governments. This factor again speaks to
the acceptance and success of the program.
1-16
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2006 - DIRT AND GRAVEL ROAD PROGRAM SUMMARY DATA
-All Data is CUMULATIVE Based on District Reports as of January 15, 2007-
Total Allocated to Districts -
Spent on administration -
Spent on education -
FINANCIAL SUMMARY TO DATE
$35,187,000 includes 10 years of funding
$2,203,000 (6.3% of total allocated) limit of 10%
$594,000 (1.7% of total allocated) limit of 5%
WORKSITE: a section of
unpaved road that is a
verified source of pollution
to an adjacent stream.
Spent on completed contracts (1,608)-$25,3 81,000 (72% of total allocated) (In-kind not included)
Current contract commitments (196)- $3,796,000 (11% of total allocated) (Partially completed project included here)
TOTAL SPENT/COMMITTED - $31,974,000 (91% of total allocated)
*****In-Kind Contributions - $9,147,000 (donated goods/services from participants) (Avg 36? per $1 spent) ****
COMPLETED PROJECT COST SUMMARY
note that some worksites have multiple contracts complete
Contracts complete - 1,608 Length of contracts complete - 826 miles
BREAKDOWN of $25,381,000 Program funds spent on completed contracts:
$20,340,000 for materials (80%), $3,725,000 for equipment (15%), $1,316,000 for labor (5%)
BREAKDOWN of $9,147,000 In-kind contributions for completed contracts:
$ 1,451,000 materials (16%), $4,045,000 equipment (44%), $3,262,000 labor (36%), $389,000 other (4%)
COMPLETED PROJECT WORK SUMMARY
5.7 Acres Eroded Stream Bank Stabilized
6.7 Acres Drainage Outlets Stabilized
68 Acres Vegetative Management
67 Acres Eroded Road Bank Stabilized
71 Acres Eroded Road Ditch Stabilized
117 Acres Separation Fabric Used
773 Acres Road Surface Stabilized
4,610 Crosspipes Installed
178,400 Feet of Crosspipes Installed
581,700 Cubic Yards of Road Base Added
= a steam bank 5 feet high and 9.4 miles long
= 2,918 outlets, each 10' x 10'
= an area 10 feet wide 56 miles long
= a road bank 5 feet high and 110 miles long
= a ditch 5 feet wide and 117 miles long
= 54 miles of fabric placed 18 feet wide
= 354 miles of road 18 feet wide
= 5.6 pipes per mile of project
= 34 miles of pipe; average crosspipe length is 39'
= 1 acre of ground covered to a depth of 360 feet
COMPLETED PROJECTS
2-DAY TOWNSHIP TRAINING SUMMARY:
YEAR
1998-2003
2004
2005
2006
TOTAL
#
Contracts
Complete
1,156
173
136
143
1,608
Money Spent
on Completed
Projects*
$ 16,198,000
$ 3,253,000
$ 3,255,000
$ 2,675,000
$25,381,000
Average
Spent per
Contract*
$ 14,012
$ 18,803
$23,934
$ 18,706
$ 15,784
YEAR
1998-2002
2004
2005
2006
TOTAL
#of
Trainings
115
8
13
12
148
Municipal-
ities Trained
na
142
220
254
na
Counties
Represented
all
53
56
57
all
Total
Attendees
3208
294
574
465
4541
*in-kind not included
Document produced by: Penn State University - Center for Dirt and Gravel Road Studies
866-668-6683 www.dirtandgravelroads. org
PENNSTATE
Center for Dirt and Gravel Road Studies
-------
The PA Dirt and Gravel Road Program is well established and continues to meet
its goal of pollution reduction. The training is constantly under review and changes as
more program work projects are completed. The program uses new experiences to
develop new practices and test new materials. Environmentally Sensitive Maintenance
Practices have been accepted and are being put to use, many of which apply to paved
roads as well as unpaved gravel roads. This acceptance, as mentioned before, attests to
the dedication and desire to do things better on the part of municipal road personnel. It is
best put by one long-time Township Roadmaster who stated: "I wish I would have known
these things 30 years ago!"
Resource: The Center for Dirt and Gravel Road Studies
The Pennsylvania State University
207 Research Unit D
University Park, PA 16802
Tel: 814-865-5355
Fax: 814-863-6787
Toll-free: 866-NO-TO-MUD (866-668-6683)
Email: dirtandgravel(ajpsu.edu
Website: www.dirtandgravelroads.org
1-18
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Environmentally Sensitive Maintenance
For
Dirt and Gravel Roads
Chapter 2: Geology, Rocks and Soils
2.1 Introduction ^^^^^^* %.-
The term "geology" is used to
describe the study of the planet earth,
specifically the materials that make up the
earth, the processes that affect these
materials, the products formed, and the
history of the planet. Geology, therefore,
with its history, processes, and materials, 2-01 Geology sets the stage
becomes important in the operation and
maintenance of our roads. Geology helps
explain the physical setting in which roads are situated as well as the local road materials
that are available for use in road building, for example, why limestone may be a prime
road aggregate in one area and granite the prime material in another area.
As solid rock breaks down into smaller particles from geological processes,
natural forces, and weather, often mixing with decomposing plant and animal matter, it
forms soil. Soils are also important in the operation and maintenance of our roads. As the
type of soils varies from area to area due to the varying geology of the area, the influence
on our road system will vary in different aspects. Roads are typically built directly on top
of soils covering the underlying bedrock. The type of soil over which roads are built will
influence the design, construction, and maintenance of the overlying portion of the road.
In addition, the stability of roadside banks, both upslope and downslope, and the road
drainage network are dependent upon the inherent behavior of the soils and vegetation
that covers them. The vegetation is also directly dependent on the soil's characteristics as
to its type and growth.
In this module, our goal is to focus on geology, soils, and the natural forces that
shape the surface of our land and give us the rocks, soils, and vegetation that make up the
environment in which our roads exists and, therefore, influence many aspects of design,
operation, and maintenance of our total road system.
2.2 Geology and Natural Forces
As mentioned above, geology is important to the construction and maintenance of
roads because it defines the physical setting in which roads are situated and the road
materials that are locally available. In other words, geology gives us what we have to
work with.
2-1
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The geologic history of the earth is complex and spans a period of approximately
4.5 billion years. This complex history has included processes that have drastically
changed the characteristics of our planet. Different regions of the United States have very
different geologic histories and consequently vary greatly in road conditions, materials,
and construction and maintenance methods.
Geologists have divided the United States into different physiographic provinces.
These provinces are areas of different geologic history based on the way the different
types of rocks and landscapes were formed. The significance of physiographic provinces
will be discussed in Section 2.3.2.
2.2.1 Geologic Time. It is
important to note that many of the
geological processes that shape the earth
occur at an extremely slow rate. Because
our frame of reference only covers an
average of a 70-to 80-year life span, it is
often extremely difficult to notice or even
comprehend the changes that take place
over thousands, millions, or even billions
of years. This is geologic time. The
gradual erosion of the Alleghanian
Mountains, a grand mountain range that
2-02 Pennsylvania Ridge and Valley Province
once stood 2 Va miles high over the ridge and
valley province of Pennsylvania (Photo 2-
02), is a good example of an erosion process
that occurs over geologic time. The erosion
of this mountain range, which continues
today, is not likely to be noticed without
careful observation and measurement over
several decades. On the other hand, some
geologic events happen relatively quickly.
Volcanoes in Hawaii, the explosion of Mount
St. Helens (Photo 2-03), or major landslides
are geologic events that drastically change
the landscape over a sufficiently short period
of time, and humans are able to perceive the
changes.
2.2.2 Types of Binding Forces. To
provide background information that will
assist in understanding some of the
geological processes discussed later in this
I
2 - 03 Mount St. Helens
2-2
-------
chapter, we will introduce three types of binding forces that act to hold rock and soil
particles together: chemical, physical, and electrical.
Elements are the basic building blocks with which everything is formed. There
are approximately 110 different known elements, including things such as oxygen,
carbon, hydrogen, sulfur, iron, potassium, nitrogen, gold, silver, and uranium. While we
can see many of these elements with the naked eye, they are made up of tiny, individual
particles called atoms. For example, a gold ring is an element. It is, however, made up of
many minute gold atoms. The atom, in turn, is made up of smaller particles. Although the
names of these sub-atomic particles are not important for this discussion, it is important
to note that these particles influence the way atoms interact with each other.
When different elements are joined together through a chemical reaction, they
form a separate and distinctly different compound composed of two or more elements.
This type of bonding is referred to as chemical bonding. The joining of different elements
in various proportions and combinations has produced an almost infinite number of
compounds. For instance, compounds like our deicing rock salt, which is chemically
referred to as sodium chloride, is formed via chemical bonds between sodium and
chlorine atoms. The term "molecule" may be familiar to many, and it simply refers to the
smallest unit of a compound that can exist. For example, a water molecule is made up of
two parts of hydrogen and one part oxygen, H2O. A bucket of water contains millions of
water molecules.
In a geological setting, particles of different compounds may be physically bound
together. When this physical bonding occurs, the identities of the original compounds are
retained in the new bound material. Sandstone is an example of physical bonding, and
you can see the individual grains of sand that are cemented together to form the rock.
The third type of bond, electrical bonding, occurs when particles of one kind
"stick" to the surface of another kind of particle. The static electricity that causes pet hair
to stick to clothes is an example of electrical bonds. With electrical bonds, the sub-atomic
particles act like magnets and cause different elements and compounds to be stuck
together. Many of the interesting properties associated with clay are a result of the
electrical bonds that hold clay particles together. Because of the electrical bonds, clay
particles are strongly attracted to each other, making clay "sticky." These bonds are
somewhat flexible or elastic, which also allows for some stretching between the clay
particles, causing some clays to be highly plastic and flexible, as well as able to absorb
water and expand when wetted.
Electrical bonding also comes into play when other substances attach themselves
to sediment particles. These other substances can be toxic substances from chemicals or
other materials that can substantially increase pollution when sediment washes into our
streams.
2.2.3 Natural Physical Forces. At the same time binding forces are acting to hold
things together as elements or compounds, other forces are acting to move or even tear
20
-3
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these bonds apart. Naturally occurring forces, such as wind, water, frost action, heat,
gravity, etc. are constantly working to change the surface of the earth. Frequently these
forces work very slowly to change the landscape. They are relentless, however, and the
cumulative effect of billions of years of activity has worn down mountains, carved rivers
and filled inland seas. Although these processes may act too slowly for us to see their
effects, they are ongoing and continue to affect the earth's surface.
These processes not only shape the
surface of the earth, but the habitat that
humans need to survive. For example,
many productive agricultural areas are
dependent upon nutrients that are
deposited when sediment-laden
floodwaters spill onto adjacent
floodplains. Many of these floodplains are
used for farming and the deposited
sediments act as natural fertilizers for the
farmers. Roads are also a necessary part of
our human habitat and the effect of the
natural forces on our roads creates the
need for road maintenance activities on a
routine basis. As discussed in greater
detail later, these gradual processes and
forces are so intricately related to other natural systems that they act to sustain all life on
earth.
2-04 The relentless force of gravity causes
bank failures, downed trees, loss of road gravel
and water erosion.
2-05 Gravity along with water,
acting as a lubricant, causes slip
planes.
On the other hand, acts of mankind
frequently disrupt these natural processes and
forces and thereby accelerate rates of erosion. This
increased rate of erosion is faster than naturally
occurring rates and is referred to as accelerated
erosion. This manual, with its proposed practices,
is intended to eliminate or at best alleviate
accelerated erosion. Understanding these processes
and forces is the key to learning how to use them
to reduce pollution and improve the stability of our
roads.
Gravity, water lubrication, erosion, water
currents and frost action are among the wide range
of naturally occurring forces most frequently
impacting our road systems. Gravity is the force
that causes objects to fall or water to flow
downhill. It is one of the most important natural
forces because it influences many of the other
forces. It is also an important maintenance factor
2-4
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because it causes road bank failure, downed trees, loss of gravel from road surfaces and
water erosion.
When water gets between rocks or soil particles, it acts as a lubricant to help
particles slide and roll about. When gravity enters into the picture, the slope of the
material may be steep enough that the material may begin sliding along a slip plane. A
slip plane is the movement of material in different directions along a plane of weakness,
and is similar to the sliding that takes place between individual playing cards when
stacked and slanted, (Photo 2-05). It is also common for hillside roads to contribute to
their own failure by creating a dam to natural water flow, trapping and absorbing
downhill flowing water, adding greatly to the weight of soil and causing the bank to slip
or slump along a plane of weakness. Banks can fail slowly by creeping downhill
(sloughing) or catastrophically, such as a landslide.
Erosion is defined as a wearing away and most often occurs with wind or water.
The effects of winds can be seen in the phenomenon of shifting sands. At Cape Cod, for
instance, the sands thrown ashore by the sea are driven inland by the winds, advancing
upon the cultivated lands, burying them and destroying their fertility. The sands from the
beach on the Pacific coast near San Francisco are driven inland in a similar manner again
encroaching upon the more fertile soils. In the fairly dry regions of the interior of our
country, high winds, laden with sand and gravel, are a powerful agent in sculpting the
rocks into the fantastic forms so often found there.
Erosion due to water ranges from the impact of raindrops to water currents
picking up particles and carrying them away from their original location. Erosion due to
the movement of surface water is one of the major physical forces that have shaped our
country's landscape. Water, in the form of rain or other precipitation, falls to the earth's
surface and either soaks into or runs across that surface. Water, percolating through the
earth, slowly disintegrates the hardest rocks initiating the work of soil-making, which we
will address later in this chapter. A large portion of rainwater, however, never soaks into
the earth, but runs off the surface.
Erosion is all about energy - soil
and rock particles do not move unless a
force or process has enough energy to pick
up and carry the particle away. The ability
of water to erode soil and rock materials
depends on four factors:
1. Force of the raindrop
impact;
2. Soil resistance;
3. Volume of accumulated
water; and
4. Velocity (speed) of flow.
2-06 Impact of each raindrop on bare soil
initiates the erosion process.
2-5
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Vegetation plays a key role in erosion prevention. This will be discussed in detail
in Chapter 4. Briefly, vegetation facilitates soil resistance by breaking the impact force of
raindrops, disrupting and slowing the flow of water across the soil surface, and
reinforcing the soil with root structures to hold the soil in place.
While soil resistance helps prevent erosion, the remaining three factors lead to
erosion. A single raindrop falling from the
sky on bare soil creates a mini-explosion
to dislodge and scatter soil particles,
initiating the erosion process. Once on the
ground, water from these raindrops
collects and starts to flow downhill,
growing in volume and velocity, forming
rills and rivulets and producing furrows
and gullies. The accumulated water has
lots of energy to erode particles. The
rivulets join to form torrents, creating
ravines and gorges, and further uniting to
form rivers that in turn deposit their load
2-07 Flowing water picks up volume and
velocity causing further erosion.
partly in their course and partly into the
sea. As the accumulated water flows downhill, steeper slopes cause greater speed,
increasing the energy and erosive capacity of the flowing water.
While each of these factors can cause erosion, the impact from a combination of
these factors can be great, causing everything from washouts and bank failures to
flooding and complete roadbed failure. The width and depth of the Grand Canyon, which
has been carved over millions of years by the Colorado River, is testament to the
tremendous erosive power of water.
Our landscape is continuously
being altered by water and erosion with
material eroded from one location being
transported and eventually deposited
somewhere else. In this fashion, the
landscape is altered in two locations, the
point of original soil erosion and the
location where the material is deposited as
sediment.
Frost action, or the freeze-thaw
process, has also helped to change the face
of the earth. When water freezes, it
expands and exerts pressure on anything
that contains it - like the soda can that was
stuck in the freezer and "exploded" when it froze. When water gets into the small cracks
in rocks, the expanding ice can split the rock. Bear in mind that a large part of our climate
2-08 Deposition of sediment alters the
landscape.
2-6
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has drastically changed, swinging from temperate to near-arctic conditions during the
advance and retreat of glaciers over several periods of time. As will be discussed in
Chapter 3, this freeze-thaw process also causes rocks to move upward through the road
base and surface; causes potholes to form; and causes posts, poles and structural
foundations to shift or tilt.
2.3 Rocks
2.3.1 Rock Families. In their study of the earth's history, geologists have
identified three basic rock families: igneous, sedimentary, and metamorphic. What family
a rock belongs to is determined by the way in which the rock was formed.
Igneous rocks form when molten rock (magma) cools and hardens. Lava is a form
of magma that erupts from volcanoes, and when it hardens, forms volcanic rock. Hawaii
and Iceland, both volcanic islands, are primarily made of volcanic igneous rocks. Other
types of igneous rocks also form beneath the surface of the earth when magma oozes and
intrudes between layers of existing rock. Igneous rocks are usually our older rocks
underlying the stratified sedimentary rocks forming the great mass of the earth's interior
and forming the axes and peaks of our
great mountain ranges, such as the Sierras
and the various Colorado ranges.
Examples of igneous rocks include granite
and diabase.
Sedimentary rocks form when the
elements (sun, wind, water temperature,
etc.) wear away rock and soil and the
eroded particles wash into low-lying
depressions where they are deposited.
Over time, these sediments may become
fused together by natural cementing,
compression, or other methods, forming
sedimentary rocks. Common examples of
sedimentary rocks include shale,
sandstone, conglomerate, and limestone.
2-09 Sedimentary limestone layers.
Metamorphic rocks make up the third family. These rocks have been changed
from their original form by heat, pressure, or chemically active fluids to produce new
rocks with different minerals and texture. These heat, pressure, or chemical processes
may act on any of the three families of rock to produce a new metamorphic rock.
Examples of metamorphic rocks include slate, schist, gneiss, quartzite, and marble. Shale
often serves as a parent material that is metamorphosed into slate, while sandstone may
become quartzite and limestone may become marble.
2.3.2 Geological Provinces. As mentioned in Section 2.2, geologists have divided
the United States into physiographic provinces. Each province has a vastly different
2-7
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geological history that has influenced the local geology and the shape of the landscape.
Geological processes and natural forces take place on a number of different scales that
range from individual hillsides to entire regions. Consequently, geologic conditions are
not uniform across a province or their immediate subdivisions, geologic sections. Site
conditions may even vary between locations within the same local government limits.
Surface water erosion has played an important role in shaping the landscape in all
the physiographic provinces. Surface water draining from the landscape has eroded and
carved many, if not all, of the river and stream valleys that we see today. In many
locations, this erosion was tremendous and considerably increased the difference in
elevation between the highest and lowest points. The stream erosion process will be
discussed further in Chapter 4.
Several periods of glaciation occurred across the northern part of our continent in
which large masses of ice in the form of glaciers altered the landscape with their passage.
These glaciers were part of a continental ice sheet that covered most of Canada and the
northern part of the United States. These glaciers shaped the landscape by grinding away
and lowering the tops of hills, producing rounded uplands and broad, flat-floored valleys.
The first glaciers advanced approximately 800,000 years ago with the most recent
glaciers advancing only 24,000 years ago.
Glaciers form when snow
accumulates to a depth of many feet,
compressing the snow at the bottom of the
pile into ice. When snow accumulates on
top of the glacial ice, the additional weight
causes the glacier to slowly move
downhill. Glaciers act like huge belt
sanders and conveyor belts. Large
quantities of rock and smaller fragments
become frozen and trapped in the ice.
These rocks frozen in the ice of the
advancing glacier scrape, grind, and gouge
across the landscape, carrying soil and
eroding the underlying bedrock as the ice mass slowly slips downhill. This erosion is
particularly effective when the underlying rock is as soft as many of the shales and
limestones. When glacial ice melts, it leaves behind deposits made of till and outwash
that can sometimes be greater than 100 feet in depth.
Till is an unsorted mixture of clay, silt, sand, gravel, and larger particles that was
left in piles at the edges or beneath glaciers. Outwash, as the name implies, is composed
of well-sorted gravel and sand sediments deposited by streams running away from the
ice. Outwash often filled the bottoms of valleys leading away from the glaciers, leaving
behind relatively shallow, broad, and level valley bottoms. These outwash deposits
frequently serve as a source of low-cost bank run gravel for use on roads. This material,
2-10 Glaciers shaped much of the landscape
across the northern United States.
2-8
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however, is usually not good road material and can be a major source of sediment and
dust pollution.
Local government road managers should become familiar with their state and
local geology in order to gain a better understanding of their site conditions and the
driving forces shaping those conditions. Additionally, they should have a good working
knowledge of the types of rocks and materials available for road maintenance. As we
shall see in future chapters, the geological provinces not only define the local topography
and the existing rocks and soils, but also relate to other natural systems such as
ecoregions, vegetation, and forest types that impact the way we maintain our local road
system. Many states have Web sites showing the physiographic provinces contained
within their state with a description of the provinces and rock formations that are
predominant for the region. Appendix 2 maps Pennsylvania's physiographic provinces,
showing the rock types and topography of each province. Other sources of information on
local geology include local libraries, universities, agricultural extension offices, county
farm service centers, and the U.S. Department of Agriculture (USDA), Natural Resources
Conservation Service (formerly the Soil Conservation Service).
2.3.3 Rock as a Road Material. As previously discussed, the geological history
of an area determines the characteristics of an area's underlying rock structure.
Consequently, the characteristics of the locally available materials determine the
suitability for road materials as well as the potential for creating environmental problems.
Three important major material characteristics that often help determine the structural
and environmental suitability for road use are hardness, durability, and the pH.
A gravel road surface material is directly subjected to vehicles traveling on the
road, unlike a base or subbase material under a paved asphalt or cement concrete
pavement. In this respect, the hardness of the surface material becomes important to
withstand the constant grinding by vehicle tires. A material's hardness can be measured
in comparison to a diamond. In roadwork, the Los Angeles Abrasion Test method can be
used to measure the aggregate's hardness
or abrasion resistance. This test measures
the percent weight of material loss or
abraded away by tumbling a specific
sample of sized material in a drum with
steel ball bearings at a fixed speed and for
a fixed time (Photo 2-11). Results are
abbreviated as LA-xx where xx is the
relative hardness. For example, a type of
rock with a LA-22 is abrasion resistant
since it has only lost 22% of its weight,
while another rock with a LA-70 is softer
and less resistant to abrasion because 70% 2' n Los An§eles Abrasion Test Drum.
was worn away from the sample.
2-9
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The hardness of a material is an important factor when selecting road material
because it determines how easily the material will be physically broken down and worn
away. Road materials are broken down by both vehicle traffic and environmental
conditions, resulting in successively finer particles. These fine particles are then removed
from the road as sediment or dust, which can negatively impact the surrounding natural
systems. The removal of fine particles as dust and sediment also means that road material
is being lost.
Another measure of a rock's performance as road material is durability, a term
used to express a rock's resistance to frost action. Durability can be measured by repeated
saturation in a salt (sulfate) solution. Crystallization of the salt in cracks in the rock
causes the rock to split. When the test results of a sulfate test are received, remember it is
really expressing the reaction to frost. Because this characteristic is critical when
aggregates are bound in cement or asphalt, the levels for these applications are more
stringent (e.g., durability factor of 10) than those used where the aggregates are not
bound (e.g., durability of 20).
The third characteristic is the pH of the rock used as a road material. Chemical
tests for pH measures the acidity or alkalinity of a material, with the pH scale ranging
from 0 to 14.0. values of less than 7.0 are acidic, while values greater than 7.0 are basic
or alkaline, with a value of 7.0 being neutral. For the purposes of this manual, the pH
measures the ability of a material to increase or decrease the acidity of soil and water.
Fine particles worn from the road have chemical characteristics, and when this dust or
sediment settle, the particles can change the pH of the surrounding soil or water. For
instance, dust from crushed aggregate having a low pH can be washed into an adjacent
trout stream. The acidic particles then mix with the water and increase the acidity of the
stream. Because plants and animals can only tolerate a certain range of pH conditions,
this increased acidity may decrease or eliminate the productivity of the trout stream. The
health and productivity of terrestrial plants and animals can also be negatively impacted
by changes in pH. Particles with a different pH may affect soils, thereby impacting
plants, crops, and organisms utilizing these soils.
The harmful effects of acid rain is one of the major reasons why we must be
careful not to further alter the natural pH of our rivers, streams, wetlands, and soils with
road materials. Acid rain is caused when moisture (raindrops, snow, fog, clouds) in the
atmosphere is exposed to gaseous and particulate air pollutants that come from our
vehicles, factories, and power plants. Normal rainwater is, by nature, slightly acidic, and
exposure to these pollutants alters the chemistry of the moisture, causing it to become
even more acidic. When the acidified moisture falls as precipitation, it brings the acid
with it, where it can impact the natural pH of the soil and water. In many cases, acid rain
is so harsh that numerous streams and lakes have become so acidic that they are devoid of
almost all life. This form of environmental pollution is everywhere, but some areas are
stressed more than others. Since many natural systems are already stressed by acid rain,
the environmental impacts of even slight changes in pH caused by eroded road materials
may be great.
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Our ability to be environmentally conscious is based on attention to local
conditions. The variety of both land and water communities necessitates choosing the
right road material for each situation. There are roads in areas where rare, acid-loving
plant species grow. Placing limestone on those roads could raise the pH of those areas,
destroying the habitat that those species require for survival. Conversely, placing acidic
shale on a road that is upslope from a clover field could drive the pH of the field's soil
down below tolerable levels. It is critical for us to be aware of the potential impacts that
our road maintenance activities have on our natural environment.
Local government road personnel should also be aware of threatened and
endangered species living within their jurisdiction. These plant and animal species are not
only protected by federal and state laws, but they also deserve every official's and
citizen's protection so that they survive for their own benefit and for that of future
generations. Just one thing such as changing the pH of their required habitat by not
paying attention to discharges from road operations and maintenance activities, cannot be
justified because both the liability and ethical concerns of such actions are tremendous.
The value of a good road aggregate along with other important road aggregate
characteristics and specifications will be further discussed in Chapter 3 with an appendix
of example state specifications.
2.4 Soils
Soils play an important role in the construction, maintenance and operation of dirt
and gravel roads because most of these roads are built directly on soil. Characteristics of
these soils, such as particle size, type, and combinations, influence the properties of the
soil. These soil properties, which can include things like drainage, erodability, suitability
as a road sub grade material, and use as a growth medium, influence many of our
necessary road maintenance activities discussed in this manual as well as those activities
currently being performed.
2.4.1 Soil Formation. Soil formation is a component of the larger geologic cycle,
and the rocks making up the local geology commonly serve as parent material for a
region's soils. Parent material is the raw, intact rock that eventually breaks down into
finer and finer pieces which, when combined, are called soil. This process of soil
formation can take from 10 to 10,000 years. Soil formation also includes the addition of
decomposing plant and animal matter brought by organisms living within the soil, which
adds fertility to the newly formed soil.
Chemical and physical weathering are two types of mechanisms that transform
parent material into soil. Chemical weathering is the decomposition, or chemical
breakdown, of geological materials. Rainwater acts as the most important agent of the
chemical weathering process because it is, by nature, mildly acidic. Rainwater, however,
also contains other acids obtained from gases in the atmosphere (i.e., acid rain),
vegetation, and from microorganisms, which boost the rainwater's ability to dissolve the
chemical bonds that hold rocks and minerals together. As these bonds dissolve, fractures
2-11
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form along zones of weakness. Limestone is dramatically impacted by chemical
weathering, forming sinkholes and solution channels for underground streams.
Physical weathering can be thought of as the disintegration, or crumbling, of
larger particles into smaller particles. Water also plays a large role in the disintegration
process and the frost action discussed before is a common example of physical
weathering.
These weathering processes often work hand in hand with one type of weathering
occurring along zones of weakness created by the other type. Weathering typically occurs
at or near the surface of the earth, with fractures in the rock allowing these weathering
processes to penetrate to limited depths. The degree of weathering usually decreases with
depth below the ground surface. The depth of weathering, however, may vary from area
to area, and geological studies in the Piedmont physiographic province discovered
weathered granite approximately 100 feet below the ground surface. Historical and recent
climatic conditions also influence the degree of each type of weathering. During periods
of glaciation, intense frost action near the glacial margins physically fractured many
subsurface sedimentary rock formations. Currently, moderate chemical weathering with
frost action is common.
Because of local geology's history and characteristics, parent material varies from
one location to the next. This variation in parent materials, in conjunction with local
weathering conditions, has resulted in the development of many different types of soils
within a small area. The USDA Natural Resources Conservation Service has compiled
county soil survey maps that contain information on the location and types of each
county's soils.
2.4.2 Soil Particles. As rocks weather, they break down into smaller particles,
forming sand, silt, and clay-sized particles. When physical weathering occurs, these
particles are simply smaller-sized pieces of the parent material, while chemical
weathering alters the nature of the parent material in the decomposition process. The
following Table 2-1 contains information on the actual size of the different particles.
Table 2-1: Soil Particle Sizes
Particle Size
Clay
Silt
Sand
Diameter (mm)
Less than 0.002
0.002 to 0.05
0.05 to 2.0
Field Test
Feels sticky
Feels like flour
Feels gritty
The size difference between these particles is also significant for a number of
reasons that will be discussed later. To put the particle sizes into perspective, if a clay
particle were considered to be the size of the head of a pin, then a silt particle would be
the size of a kernel of corn, and a sand particle the size of a basketball.
Clay has unique properties that frequently cause it to impact road construction and
maintenance activities. Clay particles have a flat, plate-like structure that is unlike the
irregular and more rounded structure of silt and sand, respectively. This flat shape gives
2-12
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clay particles greater surface area for electrical bonding to take place between individual
clay minerals. These electrical bonds give clay its tenacious, sticky properties. The shape
and electrical bonds of clay are also responsible for many of clay's other interesting
properties, including its ability to absorb water and swell, sometimes to great extents; be
flexible; be slippery; and hold more nutrients than other particles types.
The different particle sizes and the type of material that make up those particles
influence a number of important properties. The likelihood that a material will erode is
affected by shape of the particles as well as the degree of bonding, or cohesion, between
particles. For example, Table 2-2 below indicates that rounded sand particles are likely to
erode, while sticky clay particles are not. Particle properties also influence how well it
serves as a growth medium for vegetation. While clay holds nutrients, many of these
nutrients are bound to the clay and not available for plants. Silt has the most nutrients
available, and sand is relatively nutrient poor. Road managers are probably more familiar
with the suitability of these types of materials for road stability and drainage purposes as
shown in Table 2-2.
Table 2-2: Soil Type Properties
Clay
Silt
Sand
Erodability
Stable
Moderately stable
Unstable
Growth Medium
Holds nutrients
Rich
Poor
Road Stability
Soft, slippery
Soft
Poor compaction
Drainage
Holds water
Moderately drained
Well drained
It is important to note that none of the individual particle sizes or types makes a
good, stable road material. Particle combinations are key! Soils are formed from
combinations of these different particles, and the relative proportions of sand, silt, and
clay-sized particles determines soil types. The combination of different particle sizes and
types, and their properties, influence the overall characteristics of the soils they form.
Knowledge of these combinations and properties can aid decisions regarding
management of dirt and gravel roads, and especially the stability of banks and ditches.
Appendix 6A, Soil Identification in the Field, gives a guide that allows road
personnel to determine soil particle types in the field.
2.4.3 Soil Layers. Because soils are formed from parent material via weathering
processes, they typically develop from the surface downward. Soil development forms
layers in the soil, which are called soil horizons, and may be observed when a trench cuts
through soils that have not been disturbed by agriculture or construction. Figure 2-1, Soil
Horizons, shows an example of these horizons, though not all of these horizons may be
represented in every given soil profile.
2-13
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Figure 2-1: Generalized Soil Horizons in Undisturbed Soil Profile
-, £'' ,
,O Horizon — humus/organic matter just
below the surface
A Horizon — rich in organic matter
B Horizon — accumulated materials
washed down from A horizon
C Horizon — partially weathered parent
material
R Horizon — unaltered parent material
Topsoil
•Subsoil
Note: a. Not all horizons may be represented in a given soil profile
b. The degree of weathering decreases with depth
•Bedrock
The horizons develop hand in hand with the soils, frequently taking several
hundred to several thousand years to become well developed. Changes in environmental
conditions can lead to changes in the development of both the soils and the horizons
within those soils. For example, soils that develop under the saturated conditions found in
wetlands produce unique soil conditions, as will be discussed in Chapter 4.
The upper layers of the soil are
commonly referred to as topsoil. Topsoil
is made up of the O and A horizons (refer
to Figure 2-1). The O horizon consists of a
collection of organic materials resting on
the surface, including seeds, leaves,
branches, vegetation, bacteria, insects,
animal wastes, and deteriorating plant and
animal remains. This organic matter serves
as a valuable source of nutrients for the
underlying soils.
2-12 Earthworms live in the A Horizon, the
first layer of "dirt."
The A horizon is the first layer of "dirt" and is made up of varying proportions of
sand, silt, and clay mineral materials, along with a substantial amount of organic matter.
Much of this matter has been washed down through the soil from the overlying O
horizon. Plants utilize this layer for the germination of their seeds and the development of
root networks for support and gathering food and water. Creatures such as insects,
earthworms, fungi, and other microorganisms live within the A horizon and provide
several vital functions. These insects, molds, fungi and bacteria help encourage the
rotting of wood and leaves, thereby breaking down the organic matter into more usable
forms. The insects and earthworms burrow through the ground, aerating the soil so that
plant roots can breathe. The burrows of these creatures also help water to infiltrate the
2-14
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soil. Infiltrating water can help plants grow, but it also helps recharge groundwater
supplies.
The layer of soil beneath the topsoil is commonly referred to as subsoil. This layer
of soil can be broken into the B and C horizons, as shown in Figure 2-1. In the B horizon,
the parent material has been completely weathered, so few rocks are present. The B
horizon lacks the organic matter that the A horizon has, but does contain extra silt and
clay particles that have washed out of the overlying horizons by water percolating down
through the soil profile. The C horizon is typically very rocky and consists of partially
weathered parent material. The R horizon is the bottommost horizon and consists of hard
bedrock that underlies the soil. Because these subsoil layers do not have organic matter
and biological organisms that the A horizon does, they are not as suitable a growth
medium for plants. Some plants, however, do send roots down into the subsoil layers to
gather water and nutrients that have accumulated in these deeper soils. It is critical to
understand that bank and ditch stability is aided by the plants and their root structures.
Plants are dependent on the soil and thrive best when a natural soil profile is maintained.
Mechanical removal of even leaf litter decreases a plant's chances of holding the bank or
ditch together. The common practice of removing all topsoil materials and exposing
subsoils is difficult to justify in light of the following valuable insights.
2.4.4 Topsoil Versus
Subsoil. Plants normally grow in
topsoil, and because of this, topsoil
can be used to help road
maintenance projects in several
ways. Topsoil contains many of the
nutrients that plants require for
healthy and quick growth. The
organic content of the topsoil also
helps to retain soil moisture as well
as the vital nutrients, which is then
'opsoil provides the nutrients needed for plant
available for plant uptake. Many
sro ' kinds of seeds lay dormant in the
topsoil, where they wait for an opportunity to sprout and grow. These dormant seeds
often are the first to sprout when topsoil is disturbed by equipment. All of these things
help new vegetation to become established quickly. As will be discussed in several other
portions of this manual, established vegetation not only looks better, but also prevents
erosion of both the road banks and ditches.
In addition, subsoil cannot develop overnight into a suitable growth medium for
bankside vegetation. It requires a geological time scale to develop into topsoil. For these
reasons, it is important to retain topsoil when performing ditch and other road
maintenance activities so that it can be reused to revegetate the site at the completion of
the work. Chapter 6 will cover this concept in more detail.
2-15
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When we consider road construction and maintenance, however, subsoil for road
subgrades becomes the material of choice. We do not need all the vital nutrients to
support vegetation, but we do need a structurally sound material containing the proper
combination of particles to properly drain water away from the road.
It all boils down to the fact that what makes a good garden makes a poor road
and what makes a good road makes a poor garden.
2.5 Summary of Geology, Rocks, and Soils
The construction and maintenance of roads is closely tied into the local geology.
Each region's geologic history has influenced the rocks and soils underlying and
surrounding its roads. These underlying materials determine the road's design and
maintenance requirements, and the surrounding materials determine the roadside's design
and maintenance, affecting vegetation type and growth, bank and slope stability, and
drainage. Geology also explains why some road materials are locally available and others
are not.
Environmental and road problems stem primarily from several relentless, natural
physical forces acting to change the landscape. These forces include gravity, water
lubrication, water currents, erosion, and frost action. Many human activities have greatly
influenced the effects of these natural forces, often resulting in accelerated rates of
erosion and sediment. By understanding and limiting our influence on these natural
forces and processes, we can slow this accelerated erosion and minimize our impact on
the natural environment.
Igneous, metamorphic, and sedimentary rocks are formed over long periods of
time by a number of different geological processes. These processes produce varying
conditions that geologists identify as physiographic provinces. Each province has its own
unique combination of geologic materials, topography, drainage, and overall character.
We have identified hardness, durability and pH as three important characteristics used to
determine the suitability of rocks for use as road materials and their potential for
environmental problems.
Rocks are subjected to physical and chemical weathering processes that break
them down into finer sand, silt, and clay-sized particles. These three particle sizes
combine to form soil. The various combinations of particles size and type influence the
physical characteristics of soil, which then affects the soil's erosion and drainage
characteristics, as well as its suitability as a growth medium and road sub grade material.
Topsoil contains decomposing vegetation and animal materials and other vitals for plant
establishment and growth, while the "dead" subsoil is better suited to road subgrades.
Rocks and soils form over geological time scales of many thousands of years.
Because our roads are situated within the context of the natural environment, they are not
only subjected to the same physical and weathering forces, but also often act to accelerate
and increase the effects of these forces. As such, it is important to be knowledgeable
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about, respect, and consider the interactions between roads and natural systems in order
to minimize disturbances to both systems.
When road managers understand their local geology, rocks and soils, they can
develop appropriate maintenance techniques. The best maintenance techniques minimize
disturbances while striving to retain the functions of the natural systems and facilitate the
long-term stability of the road and its surrounding environment.
2-14 Understanding geology helps to develop good road maintenance practices.
APPENDIX 2. Case Study: Pennsylvania's Geology
Geologists have divided Pennsylvania into seven physiographic provinces (see
Figure A2-1). Each province has a vastly different geological history that has influenced
the local geology and shaped the landscape. In general, older rocks (more than 570
million years old) are found in southeastern Pennsylvania while younger rocks (less than
290 million years old) are found in the northwest parts of the state.
Thus, most of the igneous rocks in Pennsylvania are found in the southeastern
corner of the state and are of the intrusive type igneous rock. Sedimentary rocks are the
CENTRAL LOWLAND
Figure A2-1 Physiographic Provinces of PA
APPAUACHI
LAjni&
ATLANTIC
COASTAL PLAIN
BLUE RIDGE
PROVINCE
2-17
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most common type of rock in Pennsylvania and cover approximately 85 to 90% of the
state. Metamorphic rocks are again present predominantly in the southeastern portion of
the state.
Surface water was a major factor in shaping the landscape in all seven provinces,
eroding and carving most of the river and stream valleys that can be seen today. The
periods of glaciation occurring in northern Pennsylvania also altered the landscape. The
following province descriptions provide a basic overview of Pennsylvania's landscape
and its geologic history.
A2.1 Central Lowland Province. This is the northern most province in
Pennsylvania, and is found along the Lake Erie shoreline in Erie County. This is only a
small portion of the Central Lowland Province as it extends from northwestern
Pennsylvania and western New York, northwestward to Minnesota and southwestward to
Texas. The portion of the province located in Pennsylvania consists of a series of sand
and gravel beach ridges that run parallel to Lake Erie. These ridges were formed by the
lake during the last period of glaciation in the area, from approximately 24,000 to 18,000
years ago. As the glaciers retreated and melted, water levels in Lake Erie were higher
than they are today. Waves piled up sands and gravels, forming these beach ridges at the
then current water levels. As the lake's water levels declined, these beach ridges became
inactive, with vegetation becoming established and stabilizing the mobile sand ridges.
The ridges can now be viewed as the gently rolling land that is characteristic of the area.
Additional wave erosion and relatively steady water levels have caused the more recent
formation of a bluff along the Lake Erie shoreline. Surface water drains towards the lake
in this area, forming steep-sided, narrow valleys that cut across the ridges and into the
underlying shales and siltstones. Rocks in this province include gray and black shale, red
sandstone, limestone, and chert.
A2.2 Appalachian Plateaus Province. This province covers the greatest part of
Pennsylvania, approximately 60% of the state, including 42 counties and extends from
Greene, Somerset, and Fayette counties in the southwest to Erie in the northwest and
northeastward across the northern part of the state to Wayne and Pike counties. The
province was covered by a series of salt and fresh water seas in which sedimentation
occurred. Sediments laid down by these seas became cemented together, forming the
250- to 405-million-year-old sedimentary rocks that underlie this area. During periods
when the land was not submerged, vast swamps and bogs developed. Dead vegetation
from these swamps and bogs accumulated and formed thick beds of peat. Some of these
peat beds were later covered by new layers of sediment which compressed the peat and
caused it to metamorphose into coal, forming the vast coal deposits that have played an
essential part in Pennsylvania's history. Surface water erosion has deeply carved an
extensive drainage network across this province. Glaciers covered a large portion of the
northern corners of the sate, where they dramatically reshaped the landscape. Rocks in
this province include red, gray and black shale, red and gray sandstone, limestone,
conglomerate, coal, and chert.
2-18
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A2.3 Ridge and Valley Province. The Ridge and Valley Province of central
Pennsylvania is characterized by long, narrow mountain ridges separated by valleys of
varying widths. This province encompasses approximately a quarter of the state and
extends northeastward into New Jersey and southwestward through Maryland. The
province is underlain by the many of same sedimentary rocks that underlie the
Appalachian Plateaus Province and are approximately 290 to 570 million years old. The
subsequent geological events, however, warrant separation of this area into a new
physiographic province.
The earth's continental plates drift around the surface of the earth at a rate of
about an inch per year, and about 290 million years ago, North America collided with
Africa. This collision resulted in a period of mountain building as the two continents
pushed together. The massive forces involved with this collision caused the relatively flat
rocks within the province to wrinkle and become folded much like a carpet does when the
ends are pushed together. This geologic upheaval resulted in the formation of a mountain
range that was 150 miles wide and at least 2.5 miles high that is referred to as the
Alleghanian Mountains. Approximately 250 million years ago, the Alleghenian
Mountains began to erode away. Because some rocks are more susceptible to erosion
than others, erosion rates differ. Extensive erosion of these mountains has since formed
valleys in areas of soft rock (shales and siltstones) and left erosion-resistant ridges
comprised of very tough sandstone. The ridges and valleys presently cutting across the
state are all that remain of this former mountain range. Rocks in this province include
gray and black shale, siltstone, red and gray sandstone, limestone, chert conglomerate,
quartzite, and dolomite.
As with the Appalachian Plateaus Province, surface water erosion has played a
major role in shaping the current topography of the province. The Susquehanna River,
which cuts through many of the ridges of the province, is evidence of the impact of
surface water erosion on shaping the landscape. The Susquehanna River was able to
erode sufficient material to maintain its course while the underlying land was being
uplifted by the collision of the continental plates. Glaciers have also acted on small
portions of the province, primarily in Northampton, Carbon, Monroe, Luzerne, Columbia,
Sullivan and Lycoming counties.
A2.4 Blue Ridge Province. The Blue Ridge Province is represented in south-
central Pennsylvania in portions of Cumberland, York, Adams, and Franklin counties.
Known locally as South Mountain, this mountain ridge extends southwestward into
Maryland and Virginia, where it is known as the Blue Ridge Mountains. The quartzite
and metamorphic volcanic rocks that make up this highland province are erosion resistant
and more than 500 million years old. Rocks in this province include shale, sandstone,
limestone, quartzite, dolomite, gneiss, granite, marble, and other metamorphic rocks.
A2.5 New England Province. The portion of this province extends
southwestward into portions of Northampton, Bucks, Lehigh, Berks, Lancaster, and
Lebanon counties in southeastern Pennsylvania. This portion of the province is known as
the Reading Prong section, which consists of highly distorted metamorphic rocks that are
2-19
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significantly more resistant to erosion than the surrounding sedimentary rocks. Rocks in
this province include gneiss, marble, other metamorphic rocks, and granite.
A2.6 Piedmont Province. The Piedmont Province is located in Southeastern
Pennsylvania and covers approximately 15% of the state. This area was influenced
tremendously by the same collision of continental plates previously discussed and again
formed the Alleghanian Mountains in this area. This mountain building process created
metamorphic rocks that are least 430 million years old. Younger sedimentary rocks
containing intrusions of igneous rock formed in the northern portions of the province
approximately 140 to 250 million years ago during the separation of the two continental
plates. As with the Ridge and Valley Province, millions of years of surface water erosion
has worn down the grand Alleghanian mountains to form the current topography
characterized by broad valleys and gently rolling hills. Rocks in this province include
quartzite, schist, slate, marble, serpentine, gneiss, other metamorphic rocks, red
sandstone, shale conglomerate, limestone, dolomite, diabase, and granite.
A2.7 Atlantic Coastal Plain Province. This province is located in the extreme
southeastern part of Pennsylvania, including almost all of Philadelphia County and
southeastern portions of Bucks and Delaware counties. This province extends from
Massachusetts to Florida, and includes most of Delaware and all of southern New Jersey.
In higher elevations within this province (maximum elevation is about 200 feet above sea
level), sand and gravels approximately 2 to 67 million years old overlie older
metamorphic rocks. In lower elevations along the Delaware River, floodplain deposits of
sand, gravel, silt, and clay are less than 2 million years old. In general, the geologic
history of the province has produced rather flat lands with sandy soils. Many of the sand,
gravel, silt, and clay deposits remain unconsolidated, as they have not had sufficient time
to become cemented together.
A2.8 What Pennsylvania Has to Work With. These previous descriptions of
Pennsylvania's geologic history with its physiographic provinces show what the local
governments have to work with as far as rocks, soils and road materials. Comparing the
province map with the geology map and a soils map shows the similar patterns (Figure
A2-2 and Figure A2-3). And, of course, the soils will dictate types and growth of
vegetation and the environment in which the roads exist. It explains why many unpaved
roads through most of Pennsylvania use limestone as the aggregate road material
available from local quarries. It also explains the lack of limestone across the north
central part of the state where only softer shales are available, creating more problems of
erosion and dust along with increased road maintenance. Geologic history shows how the
steep hills and deep valleys in some sections were formed. Roads and banks in these
sections are difficult to stabilize because they must fight gravity's relentless force.
Pennsylvania still has approximately 20,000 miles of unpaved roads. Sediment and
erosion from these roads represent major environmental problems. Part of Pennsylvania's
rich geological legacy is its vast resources of coal. But this bounty has come at a price.
Acid mine drainage into the streams costs taxpayers millions of dollars each year in
cleanup expenses.
2-20
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Figure A2-2: What do you have to work with?
GEOLOGIC MAP OF PENNSYLVANIA „, «"
:
SCALE \-,Z.OOO.tXK
c ti SB y> ->o so MI
t Ol RfSOLtRCtS MANAGEMENT
RAPI HC AND CtOLOClC SURVEY
o af
-------
Environmentally Sensitive Maintenance
for
Dirt and Gravel Roads
3-01 Never underestimate the force of water.
Chapter 3: Water, Erosion, Drainage and Road Basics
3.1 Introduction
Water is essential for all life on
earth. Water, however, can also cause
devastation through erosion and flooding.
In the first chapter, we detailed the
historical relationship between roads and
streams, the interrelationship of our roads
and the environment, and the importance
of good roads and a good environment for
a good municipality. In Chapter 2, we
discussed the relentless forces shaping the
earth, specifically gravity and water. Now
we need to discuss water, accelerated
erosion and the importance of proper
drainage in maintaining our roads and the
environment.
We will cover basic road maintenance
materials and techniques to ensure an
understanding of accepted and proven practices in
maintaining dirt and gravel roads and establish a
basis for our environmentally sensitive
maintenance practices.
3.2 Water and Erosion
3.2.1 Principles of Erosion. Never
underestimate the force of a drop of rainwater. To
recap what was discussed in Chapter 2, it is that
water drop exploding when it impacts bare soil
that starts the erosion process. Water's eroding
force increases with its volume and flow velocity
(how fast it is flowing).
How resistant soil is to erosion depends on
several factors. First, soil type and particle size
are important. Soil stability will depend on the
3-02 Stability depends on percentages
of rock, sand, silt, and clay.
3-1
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percentages of rock, sand, silt, and clay in the soil. A rock bank such as seen in the photo
is stable with little erosion taking place.
A second factor is soil cover,
specifically vegetation. Vegetation breaks
the raindrop's fall, dissipating its
destructive energy before it hits the soil.
Vegetation also slows down surface water
flow, keeping velocities low and
minimizing erosion.
Plant roots constitute the third
factor. Never underestimate the value of
root systems as soil reinforcement. Plant
roots provide additional stability by
removing water from the soil. The
importance of plant roots and root systems
3-04 Roads interfere with natural systems,
causing accelerated erosion
3-03 Vegetation provides many advantages in
erosion control.
will be discussed more thoroughly in
Chapter 4.
3.2.2 Accelerated Erosion.
Remember, the greater the velocity, the
greater the erosive force. Erosion is a
natural occurrence in nature. When roads
are constructed, however, they interfere
with natural systems and concentrate
water, increasing its volume and velocity,
causing accelerated erosion It is this
accelerated erosion that causes severe
problems for both our roads and the
environment.
3.3 Water and the Importance of Road Drainage
3.3.1 The Importance of Drainage. Although water may be the life-giving liquid
of our planet, it has long been recognized as the archenemy of our roads. Road literature
provides a rich history of the disastrous effect water has on roads.
In 1820, the great Scottish road builder of the 19th Century, John Loudon
McAdam, stated ".. .experience having shown that if water passes through a road and fills
the native soil, the road, whatever may be its thickness, loses its support and goes to
pieces." In 1909, Connecticut State Highway Commissioner, James H. MacDonald,
remarked, "If there is no drainage, there will be no road, no matter what the material may
be." In 1912, John Nathaniel Mackall in his Drainage, the Fundamental Principle of Road
Construction discussed his conclusion after a seven-year study by stating, "Lay out your
road with the object of draining it and never lose sight of this point. It is the ABC of road
3-2
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building and maintenance." A New Hampshire Highway Department Handbook in 1916
stated it this way: "Always remember and apply this most important rule: Keep water
OFF your road, OUT of your road, and AWAY from your road."
These statements are just as true today! Good road drainage and proper
maintenance is the best way to combat water's damaging influence - keeping water off,
out of, and away from the road. Proper drainage cannot be over-emphasized in road
maintenance and construction. Water affects all aspects of road serviceability.
3.3.2 Characteristics of Water. To
understand water and its effects, we must
understand water's three key characteristics that
concern us in road maintenance:
1. Water acts as a lubricant
2. Water expands upon freezing
3. Water runs downhill
Remember these factors as related to those
relentless physical forces back in Chapter 2. A
more detailed discussion of these characteristics is
required to determine the concern for roads.
Water acts as a lubricant. Water's
presence allows materials to move more freely by
decreasing the friction between particles. Photo 3-
05 shows a well-lubricated road. When a road
gets wet, aggregates are more likely to move or
become displaced under traffic loads. This in turn
causes surface depressions that collect more water
and result in even more weakened areas and soft
spots.
3-05 Water acts as a lubricant,
allowing material to move more freely.
Figure 3-1: Ice Lens Formation and Capillary Rise
Frost Heave
If water is within the road structure and freezes, it expands and forms ice lenses as
shown in Figure 3-1. This freezing process starts at the road surface and moves
downward into the road
structure. As the freezing
takes place, more water is
drawn up from the soils
below. Thus, the road
structure becomes
supersaturated. The ice
lenses formed from the
expanded frozen water
causes pressure in limited
spaces - a pressure that is
usually transmitted
3-3
-------
upwards, deflecting the road surface, causing frost heaves or frost boils. As the first step
in controlling this frost damage, we must recognize the three conditions required for frost
damage to occur: freezing temperatures, frost-susceptible soils, and water. The
elimination of any one of these three conditions will prevent frost damage.
Since the power to control temperature is beyond us, we can concentrate on the
remaining two. Some soils are more susceptible to frost heave, such as fine-grained clay
soils, as was described in Chapter 2, Geology and Soils. It may not be feasible to remove
frost-susceptible soils depending on the extent of the problem. Small localized areas can
be considered for removal while larger areas may use alternate treatments with
geosynthetics. Geosynthetics, their properties and uses will be discussed in Chapter 7. A
combined strategy of proper drainage and the use of geosynthetics is usually the most
feasible and cost effective method.
Springtime and thawing brings
additional problems. During the spring
thaw, ice lenses melt, releasing excess
water to the base and sub grade. The
problem is compounded since melting will
occur from the top down, trapping water
from draining downward. This excess
water, if it cannot drain off laterally, acts
as a lubricant, softening our roads and
killing their load-bearing capacity.
Springtime, often referred to as "mud
season," can be a very trying for road
maintenance crews.
The simplest and most obvious
characteristic of water is that it runs down-
hill, subject to the relentless force of
gravity. But we do not maintain our roads with this in mind. How many roads have
ponding problems on the surface? We ignore this obvious characteristic at our roads'
peril. Like gravity, water's
devastating effects are
relentless.
3-06 Spring, "Mud Season," can be a trying
time for road maintenance crews.
Figure 3-2: Ways in which Water Enters the Road
Through Permeable Surface
I * * I
Lateral Flow
from Roadside
I I I
Capillary Flow
Seepage from
High Ground
I
Water Table
3.3.3 How Water
Enters Our Roads. Figure
3-2 shows the many ways
water can seep into our
road structure. Road
surfaces are not impervious
to water, so water can seep
through the surface. The
longer water lays on the
3-4
-------
surface, the more seepage takes place. Water may enter as lateral flow from the roadside
or high ground. The water table may rise and enter the road base. If the water table is at a
level higher than the road base, then we have to look at ways to lower the water table in
the vicinity of the roadway structure using underdrain systems (discussed in a later
section). Even if the water table is low, you may still get water into your road by
"capillary flow" through the soil. The soil acts like a wick in a kerosene heater, drawing
the water upward and into the road. This capillary flow also aids the freezing process as
additional water is drawn up from below. Capillary rise can be quite substantial
depending on soil type, as the following table illustrates.
Height of Capillary Rise through
Soil Type
Small Gravel
Coarse Sand
Fine Sand
Silt
Clay
Soils
Height of Rise (feet)
0.1-0.4
0.5
1-3
3-30
30-90
Given water's destructive effect on our roads, good drainage must be our highest
priority. Further, unless drainage issues are addressed first, all other maintenance work
will not last as long as it should, resulting in a waste of time and money.
3.4 Road Drainage
3.4.1 Drainage Systems. There are two major road drainage systems: surface
drainage and subsurface drainage. The surface drainage system controls surface water
caused by direct rainfall, melted snow, or surface runoff. The subsurface drainage system
drains subsurface water from in our roads or from the subsurface areas surrounding our
roads.
3.4.2 Surface Drainage. Surface drainage involves collecting the water from the
road surface, road shoulders or berms, side slopes and adjacent areas and carrying it away
via downhill slopes, roadside ditches and pipes. More complex surface drainage practices
will be presented in later chapters;
here we concentrate on road basics
emphasizing the road and shoulder
profile and the road cross-section or
actual structure of the road.
3.4.2.1 Road Crown and
Cross Slope. The road surface acts as
our first line of defense against water,
and the first component of a good
surface drainage system is the road
crown. The road crown means the
center of the road is higher than the
outer edges of the road, as shown in
3-07A good road crown is our first line of
defense against water.
3-5
-------
Figure 3-3. The crown should be a flat "A" shape with a cross slope or drop from the
center to the edge of Va" to %" per foot or a 4-inch to 6-inch drop for an 8-foot lane.
The crown must be
maintained to allow water
to flow off the road.
Problems develop quickly
when a gravel road has no
crown, as evident in photo
3-08. Water will quickly
collect on the road surface
during a rain, softening the
surface crust. This will lead
to rutting, which can
become severe if the
Figure 3-3 Road Crown
(flat A shape)
Dirt & Gravel: 1/2" - 3/4" per foot (5-7.5
inches in 10 feet)
subgrade also begins to soften. Even if the
subgrade remains firm, traffic will quickly
pound out smaller depressions in the road
where water collects, and the road will
develop potholes. A dirt and gravel road
must have crown.
A crown's ideal shape is a straight
line from the centerline down to each road
edge, the flat "A" shape already mentioned.
This shape can sometimes become
rounded. The term for this is "parabolic
crown," and it is virtually always a
problem. The middle portion of the road
will have considerably less crown than the
outer portions. This center area is somewhat flat, and water will collect and not drain
from the middle adequately. Traffic will form potholes and ruts. A parabolic crown is
often caused by a worn grader blade. Grader blades, which are worn down through the
center portion of the blade, should be replaced or cut straight with a torch.
3-08 Water quickly collects when the road
crown is lost.
With curves, we
need to slope the road from
one side to the other to
"bank" the curve. This
banking of the curve, called
superelevation, provides
for vehicle safety in
traveling around the curve,
as shown in Figure 3-4.
Figure 3-4 Superelevated Roadway
(Curves)
Dirt & Gravel: 1/2" - 3/4" min. per foot
3-6
-------
The sloped surface still provides
for proper drainage, getting the water off
the road. The cross slope of the
superelevated section should be a
minimum of Vi" to 3/T per foot. Sharper
curves may demand steeper cross slopes
for safety. Of course, the steeper we bank
the curve, the faster the vehicles will go.
3.4.2.2 Road Shoulders. Most of
our dirt and gravel roads do not have
defined shoulders. But shoulders provide
some key advantages.
3-09 Banked (superelevated) curve.
If you have shoulders or a berm area, keep it flush with the road edge with a
slightly steeper cross slope, avoiding "shoulder drop-off," which becomes a safety hazard
for the motorist. A vertical drop-off can cause a serious accident. The errant driver leaves
the road's travel way and drops to the shoulder area. When he attempts to return the
wheel will catch on this "lip," and the driver will end up over-steering, allowing the
vehicle to jump the lip, taking the vehicle into the adjacent lane of oncoming traffic.
Roads without a properly
sloped shoulder or berm area often
develop a "secondary ditch" that
will not allow the water to drain
off and away from the road. This
secondary ditch develops when
road material moves toward the
edge of the road and catches in the
vegetation, forming a barrier to
road drainage, as shown in Photo
3-10. Improper grading techniques
can also leave a windrow of road
material along the edge that acts as
a dam, keeping water on the
roadway.
3-10 When water cannot drain off the road, the result is
a "secondarv ditch."
A shoulder or berm area also supports the road structure, preventing road edge
breakdown. Look at a road where the roadside slope drops immediately from the road
edge into the adjacent road ditch, and you will probably find road edge deterioration.
Shoulders also allow the water to flow further away from the road, maintaining better
drainage, getting the water off and away more effectively.
And finally, shoulders make the road safer by providing a more defined visible
roadway for the motorist and more room for erratic vehicle maneuvers or pull-offs. With
3-7
-------
all these advantages, developing and maintaining shoulders along our dirt and gravel
roads, where feasible, should become a high priority in our road maintenance program.
3.4.2.3 Road Structure (Cross Section). The crown and cross slope are not only
important for the road surface and shoulders, but also are important for the road base and
subgrade, or the soil on which the road is built. The configuration in Figure 3-5a supports
good drainage.
Road Structure for Drainage
The old
"trench
construction"
method for building
a road consisted of
digging a trench
with a flat bottom
and then building
your road, depicted
in Figure 3-5b.
Depending on
geology and soil
types, this
procedure could
actually trap water
within the road
structure.
Figure 3-5a
Supports Good Drainage
Surface Material
Base
Subgrade
Figure 3-5b
Can Cause Drainage Problems
Surface Material
Base
Subgrade
Proper construction maintains a cross slope for each layer including the subgrade
and also carries the base materials through to the ditch slope to provide proper drainage
of the road structure.
Notice in the figure that the bottom, or flow line, of the ditch is below the
subgrade of the road. If a roadside ditch is required, this configuration with a 4:1
foreslope from the road into the ditch is the ideal ditch to drain the road surface and base
properly and provide a safety factor for errant vehicles leaving the road. This
construction, however, is not always feasible because of roadside terrain and right-of-way
limitations often found on our dirt and gravel roads. Ditches will be discussed more
thoroughly in Chapter 5 where we address ditch shapes and slopes and look at a variety
of practices that can help us in maintaining our roads and ditches.
3.4.3 Subsurface Drainage. Surface drainage is only part of the overall drainage
picture. We must drain the road subsurface as well. The free draining base of the road
with a proper cross slope is a major component of the subsurface drainage system to
drain the road structure, either into the roadside ditch or subdrain system. The ideal road
structure would have a free draining base material topped with a good wearing course
material, particularly in those areas where subsurface water is a concern.
3-8
-------
Figure 3-6 Subdrains
Road
Shoulder.
Subdrain
Cut or Fill
Sections
Free-draining aggregate
Perforated Pipe
The second
major component of
a subsurface
drainage system is
an underground
collector system,
usually referred to
as a subdrain. A
typical subdrain, as
shown in the Figure
3-6, consists of a
trench parallel to
the road with a free
draining aggregate and a perforated pipe to carry the water to an outlet and away from the
road. All subdrains should have an outlet. Whether or not adequate ditching exists,
subdrains may be necessary to remove the water from the road structure and the
surrounding area and/or to lower the water table.
But subdrains are subject to clogging over time. Soil fines, carried into the
perforated pipe, can build up sediment eventually blocking water flow and causing the
system to malfunction. Some perforated pipes have perforations halfway around the pipe.
These pipes should be installed with the perforations on the down side to prevent fine
particles from falling through the holes and clogging the system. Water will find its way
into the pipe (the path of least resistance) and keep the bottom flushed more effectively,
prolonging the life of the system. Traditionally, roofing paper has been placed over the
free draining aggregate in the trench to reduce the amount of fine particles migrating into
the pipe.
Chapter 7 will discuss the use of geotextiles and geosynthetic pre-fabricated
subdrains as cost effective alternatives that prolong system life.
3.5 Road Materials
Road materials play an important part in a road's structural stability. Additionally,
good quality road materials reduce erosion, sediment and dust pollution. Road material is
normally sorted by type, size, shape, and gradation. In addition, as discussed in Chapter
2, we need to be concerned about other factors such as hardness, soundness, pH, and
plasticity (cohesiveness/stickiness) to adequately protect both the road and the
environment.
3.5.1 Quality Aggregates. What do we mean by quality road aggregates? The
answer to this question will vary depending on location (remember geology and the
physiographic provinces), aggregate availability, intended aggregate use, and other
factors. Some regions do not have good aggregate sources. Common available materials
may include:
• granite
• quartzite
3-9
-------
• limestone
• sandstone
• shale
• glacial deposits of stone, sand, silt and clay or
• river run gravels. One thing to remember - using the best material
available will prolong the road's life, decrease required maintenance
work, and further protect the area's natural environment.
3.5.1.1 Surface Aggregate versus Other Uses. Many times surface aggregate
used for our dirt and gravel roads comes from stockpiles processed for other uses. For
example, the aggregate may have
been produced for use as a base or
subbase material beneath a paved
road surface. But there are major
differences between surface
aggregates and base course
aggregates. Base course aggregate
is not designed to withstand traffic
and the constant, direct grinding of
wheels. A base aggregate may
have larger sized stone and less
fines than what is required for a
good surface aggregate. Base 3~n Road Aggregates
aggregate may not be suited to
developing a hard crust surface and remaining bound and stable under traffic. A free-
draining fill aggregate may be great as fill material for building sites, but the high sand
content that allows for good drainage will remain loose and unstable as a surface
aggregate on an unpaved road. A good surface road aggregate needs a fine binding
material having more plasticity or stickiness than subbase aggregate.
There are still many local governments that use their State Department of
Transportation (DOT) specifications for their road aggregates. But many states only have
base/subbase course aggregate specifications and do not have an actual unpaved road
surface aggregate specification. Aggregate meeting base material specifications will
probably not meet unpaved road surface requirements.
3-10
-------
3-12 A good road surface aggregate will be well graded from fine to coarse.
3.5.1.2 Road Aggregate Specifications. Dirt and gravel road aggregate must be a
granular, well-graded, crushed (irregular) material. Well-graded means the aggregate has
a variety of sizes from a maximum coarse material down to a fine material and
everything in between. The fine material (passing a #200 sieve) fills all the voids between
the larger particles and locks everything together in place. The fines hold the road
together, obtaining good density and a hard crust surface to shed water. Most
specifications will have a required content of 8% to 15% fines.
Another characteristic of good road fines is their plasticity, or binding quality.
Although fines are needed to fill the voids between the large aggregate, a percentage of
good plastic fines, such as natural clay, is needed to bind the material together and
maintain a tight surface to shed water and prevent dust. A plasticity index (PI) of 4 to 12
is a common specification requirement.
Please note that we are describing a gravel road "surface" material. The amount
and plasticity of this fine material determines how effectively it locks in place to form a
tight surface that will shed water and provide a smooth driving surface.
Road "base" material plays a different role in effective drainage. This role dictates
that base material contain less fines and have a plasticity index of down to 0% to allow
water to drain from the road structure. Large quantities of plastic fines in the road base
will clog drainage channels in the base material and prevent proper drainage. A poorly
drained road will lose strength and stability and ultimately fail.
We have discussed several times how common maintenance techniques can spell
disaster for dirt and gravel roads. This is another example. Maintenance crews will
commonly use only one type of material for both the road surface and the road base. But
that results in either a weak road surface or a poorly drained road base. The best
approach, particularly in those areas of poor drainage, would be to specify two types of
road aggregates, one for the road surface and one for the road base.
3-11
-------
The aggregate should also be angular or irregular in shape. In some regions, it is
common to use material directly dredged from streams or by simply loading material
from a site onto trucks without processing - hence the terms "river run" gravel or "bank
run" gravel. These natural deposits will most likely not meet gradation requirements and
will contain rounded natural shape material that will not lock up for stability. Have you
ever tried to stabilize a hand full of marbles?
The benefits of processing the material by crushing cannot be overstated.
Crushing insures that a good percentage of the stone will be fractured. This crushed,
fractured material will lock together for better strength and stability under traffic loads.
Quarried aggregates will be composed of virtually all fractured particles, resulting in the
best specified road material.
The aggregate must be free of any other debris or contaminants such as soil,
vegetation, or trash. Any contaminant material will only interfere in obtaining good
consolidation and long-term stability.
The importance of additional material considerations of hardness, durability, and
pH were discussed in Chapter 2, Section 2.3.3 in relation to not only the road's structural
stability, but also to the surrounding environment.
Quality road aggregate with good gradation, shape, plasticity, hardness,
durability, and proper pH will compact well, developing a tightly bound surface to
withstand traffic loads, and reduce washboarding, rutting, erosion, sediment, and
dust for less maintenance and a better environment.
Appendix A for this chapter contains several state specifications for unpaved road
surface aggregate material. Notice the great similarities and the relatively minor
differences in the various parameters. Some titles such as Pennsylvania's "Driving
Surface Aggregate" say it all. In addition, the Pennsylvania specification reflects the
environmental/structural combination qualities of hardness and pH.
3.5.1.3 Recycled Asphalt. As our paved roads wear out, the asphalt pavement
materials can be recycled. Although there are various recycling methods to restore the
asphalt paved road, this recycled material is many times used for gravel roads. Milling
the old asphalt pavement is a common method used in the recycling process. The asphalt
pavement can also be removed and then processed through crushing. This milled or
crushed recycled asphalt material can create a good gravel road surface. The asphalt in
this material, however, is still the binder, and depending on the age and oxidation
(brittleness) of the material, can still form the characteristic asphalt pavement. This
means that the road will be hard to maintain as a gravel road as far as blading or grading
operations and may develop cracking, potholes and other typical asphalt pavement
distresses. If the asphalt is still somewhat viscous and not hard and brittle, virgin
aggregate can be mixed with the asphalt to overcome some of the asphalt binding quality
and to provide a material that will still remain workable for blading and grading
operations. A commonly used mix would have 50% virgin aggregate.
3-12
-------
3.5.2 Sampling and Testing Aggregates. Aggregates can differ substantially
from one area to another or from one quarry to another. Aggregates can also differ
substantially within the same quarry and may depend on geology, or quarry operations
and procedures in the handling and processing of the material.
Road maintenance managers need to understand the necessity of sampling and
testing aggregates to insure that they are getting a road material that meets the
specifications and makes for a well-structured road. A visual inspection can tell very little
about the quality of the aggregate.
3-13 Mechanical Sieves
National standards for aggregate sampling require a representative sample of the
aggregate you intend to use. Using a representative sample helps to ensure reliable test
results. A sieve analysis for the proper gradation blend along with other tests for the
specified parameters (plasticity, hardness, pH) is essential to insure the quality of the
aggregate.
Testing costs, when compared to the benefits of a structurally strong road, are
nominal. Using quality aggregates greatly reduces overall maintenance costs and protects
the environment.
3-14 Quarry Visit
Check parent material
-------
3.5.3 Pit / Quarry Operations. As mentioned, handling and processing at the
quarry has a significant influence on the aggregate quality. Road maintenance managers
would be wise to visit the quarry and talk to the operator. Take a look at the parent
material and check the pile. Observe the equipment operators as they remove the gravel
3-15 Check Moisture Content And Fines
from the face of the quarry pit, process the piles and mix and load the aggregate. As they
remove material, are they getting a good blend? Is segregation of the aggregate visible on
the belt loaders or on the surface of the piles?
Check the moisture content of the material. Grab a handful and compress into a
ball. If the material sticks together when you open your hand, you've got a good moisture
level. If it falls apart, it's too dry. If water runs out between your fingers, it's too wet.
Some separation of aggregate in a pile is normal. Coarse material will tend to end
up on the surface. A good loader operator will view the pile and then work it
appropriately to obtain a good blend of aggregate.
3-16 Aggregate Separation In A Pile Is Normal
Contamination of the aggregate can also become a problem. Has all the topsoil
and vegetation been cleared from the top of the removal site? Are the stockpile sites well
maintained, with an uncontaminated level working area? Does the loader operator start
with a lowered bucket too far in advance of the pile, picking up soil or other contaminate
material?
3-14
-------
Figure 3-7 Using Aggregate Piles Without
Mixing When Loading
n
11
- Good Mixture
- Large Stone
In The Pile
Loading and
hauling of the
material, even a
good gravel road
material, can affect
the quality of the
road.If the loader
operator does not
work the pile and
obtain a good mix
of material from the
pile, normal
aggregate
separation will
produce undesirable
results on the road.
This is depicted in
Figure 3-7.
Long distance hauls can also cause problems. The continual vibrations created by
hauling, especially over longer haul times, can cause aggregate settling in the truck bed
producing a surface of larger stones, as depicted in Figure 3-8.
Effect on the Road
Figure 3-8 Vibratory Settling of Aggregate
During Transportation
£.'.•'•'-
i
•
1
- Good Mixture
- Large Stone
In The Truck
Effect on the Road
3-15
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3-17 Talk To The Quarry Operator
Establish The Spirit Of Cooperation
Quarry visits, including
observations and discussions with the
operators, can establish good working
relationships with the proper spirit of
cooperation and can result in quality
aggregate, good handling practices,
and a stronger, longer-lasting road.
3.6 Basic Road Maintenance
Practices
We will primarily discuss the
use of the motorgrader for dirt and
gravel road maintenance. We
recognize, however, that other equipment can work just as well. Front-or rear-mounted
grading attachments for tractors, road rakes, and road drags of various designs are often
used effectively. No matter what equipment is used, the principles of basic road
maintenance remain the same.
Basic road maintenance
practices are designed to produce a
structurally sound road capable of
supporting traffic with a good hard
crust surface and proper crown for
good drainage. Good road surfaces
vary in appearance depending on
the type and gradation of the
aggregate material being used, as
can be seen in the photos. This manual is not a basic gravel road surface maintenance
manual. However, it does discuss effective maintenance techniques that ensure road
stability. Further, the manual emphasizes the importance of proper basic road surface
maintenance in protecting the environment. One of the best resources for gravel road
maintenance is the Gravel Roads Maintenance and Design Manual, developed by the
South Dakota Local Transportation Assistance Program (SD LTAP) in conjunction with
the Federal Highway Administration (FHWA), November 2000. This manual provides
valuable information for road maintenance personnel on gravel road materials and routine
maintenance operations. The following section, Section 3.6, will provide brief coverage
of the basics with several references from the South Dakota manual.
3.6.1 Basic Techniques. First, no matter what work is being done on the road, it
should be planned when there is adequate moisture. This usually means that all work
should be done after a rainfall unless there is an available water truck and water source.
Adequate moisture is needed not only to achieve proper compaction for structural
integrity and strength, but also to avoid dust.
3-18 Good road surfaces differ in appearance
depending on aggregate type and gradation.
3-16
-------
Dirt and gravel roads are usually maintained through three basic practices:
blading or smoothing, reshaping or regrading, and adding new material. Gravel road
deterioration, like any paved road, will develop in stages. Low severity surface distresses
such as roughness, loose gravel, and minor ripples appear first. Bidding or smoothing the
road surface frequently to correct these distresses will result in less intense efforts of
reshaping or adding new material. When the road loses crown and more severe
distresses appear, a reshaping or regrading to re-establish proper crown is required. The
more frequently we reshape using existing road material, the less often we will need to
add new material. Sooner or later, however, the road loses crown and enough material
has been lost off the roadside or by way of erosion and dust that there is not enough
remaining material to simply regrade the road. Then we must add new material in order
to re-establish the crown and have an effective road profile.
3.6.1.1 Blading or Smoothing. As
described above, blading a road is needed
when surface distresses appear but the
road still has a good crown. We need to
blade the road to smooth the rough surface
to restore good rideability and prevent
further more extensive distress.
When using the motorgrader, the
moldboard angle and pitch is critical to
doing good maintenance. The moldboard
should be angled somewhere between 30
and 45 degrees, tilted forward, with light
down pressure. A 10 to 15 degree tilt on
the front wheels will help oppose the
resisting forces and stabilize the
operations. A speed of 3 to 5 miles per
hour is considered average, but there are many conditions or variables that may require
slower speeds for effective operations. With the blading or reshaping operations,
compaction of the material is often left to traffic.
3-19 Blading or smoothing a rough surface
restores rideability and prevents further more
extensive deterioration.
3-17
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Aggressive Cutting
Light Blading
©
Sketches from South Dakota Manual
Operating with proper pitch or tilt of the moldboard is important. Moldboard pitch
or tilt refers to how much the moldboard is tipped forward or backward. The following
excerpts and sketch are taken from the South Dakota LTAP Gravel Roads Maintenance
and Design Manual:
3.6.1.2 Regrading or Reshaping. As stated above, when the road loses crown
and more severe distresses appear, a reshaping or regrading to re-establish proper crown
is required. With the moldboard tilted slightly backward and sufficient down pressure to
produce a cutting action, the road is reshaped to restore proper crown and cross-slope for
good drainage. A minimum of four passes may be required, with a first pass in each
direction to cut and windrow the material to the road center and then a second pass in
each direction to spread the material back across each lane. The cutting action should be
deep enough to cut to the bottom of all existing distresses such as corrugations, ruts, and
potholes or soft spots.
Since this operation is being
performed to restore proper crown and
cross slope, check the resulting cross slope
to insure it meets the half inch to three
quarters inch drop from the center of the
road with the flat "A" shape.
This operation should include a
compaction effort. Using rollers for proper
compaction of the disturbed material will
result in a stronger road for a longer
period of time.
3-20 Checking Cross Slope to insure proper
drainage.
3-18
-------
3.6.1.3 Adding New Material. If there is not sufficient material remaining to
regrade and restore proper crown and cross slope at the proper elevation, additional road
material will have to be added. Prior to adding new material, the road should be in good
shape with all other maintenance work performed. All distresses, such as corrugations
and rutting, should be repaired and the
road brought into the proper condition and
shape to receive the new material. If the
existing road surface is smooth or has a
hard crust, the surface should be lightly
scarified to loosen surface material to
provide a good bond between the road
surface and layer of new material.
Compaction is again required to provide
the proper density for structural strength
and durability.
3-21 Adding new material.
3.6.2 Transitions. There are
always those areas where we have to
transition from our normal road crown to
meet other profiles. Transitions are required at road intersections, driveways, road curves,
railroad crossings, and bridges.
3.6.2.1 Road Intersections. When two unpaved roads intersect, we need to
gradually eliminate the crown as we approach the intersection. This transition from
normal crown to a flat profile at the
intersection should be made within
approximately one hundred (100) feet,
resulting in a smooth gradual transition.
The shoulder or berm area of the road
should still maintain a slope for proper
drainage of the road.
When a gravel road meets a paved
road, we need to transition the crown into
the existing edge elevation of the paved
road. As we grade out toward the paved
road, backdragging may be required in
order to avoid leaving aggregate on the paved road. Depending on traffic conditions and
safety or operations, working parallel to the paved road can be an advantage in tying into
the edge of the paved road.
3.6.2.2 Driveways. Driveways will also cause a need for transitioning. We will be
discussing driveways in more detail in later chapters as we look at environmentally
sensitive maintenance practices. For now, the basic rules are that we need to grade the
driveway, keeping the low point at the ditchline and not leaving a windrow of material
3-22 Working parallel to a paved road has
advantages.
3-19
-------
across the driveway. The low point at the ditch line insures drainage off of and away
from the road.
100ft
50ft
25ft
Figure 3-9 Transitioning into and out of a curve.
3.6.2.3 Curves
Back in Section 3.4.2.1, we
discussed superelevation or
banking the curve, sloping
the entire road surface from
one side to the other for
vehicle safety in
transversing the curve.
Here again, we need to
transition from the normal
crown to the banked slope
of the curve and then
transition from the banked
slope of the curve back to the normal crown. This should be accomplished within about
100 feet on each end of the curve, as shown in Figure 3-9.
3.6.2.4 Railroad Crossings.
Railroad crossings also require gradual
elimination of the road crown as we
approach the rails. It is important that our
operations leave the rails clean, keeping
aggregate off of the tracks and being
careful not to damage the rails or the
moldboard. Handwork could be required
using a shovel and broom in order to
insure a safe railroad crossing for both
vehicles and trains.
3-23 Keeping rails clean of road material is
essential for safety.
3.6.2.5 Bridges. At bridges, we
need to transition into the existing bridge
deck profile. Many bridges on unpaved
roads have flat decks that will require the
gradual elimination of the road crown. If
the bridge deck is crowned, the task will
be to transition the road crown gradually
into the bridge crown.
Although we will be discussing
practices for better bridges in Chapter 5,
good bridge maintenance dictates keeping
3-24 Road crowns must transition into the
existing bridge deck
3-20
-------
all road material off the bridge and keeping the bridge drainage facilities clear and open.
Road material buildup on the bridge deck will only retain water or moisture that is
detrimental to the bridge deck and structure no matter whether the bridge is constructed
of metal, concrete or wood.
Bridges need to have good
drainage. Usually drainage openings are
provided in the deck, called scuppers,
which drain directly to the stream below.
Keeping the deck clean is imperative not
only for good drainage and longer bridge
life, but also for prevention of sediment
into the stream.
One of the more troublesome areas
at bridges is the approach area where the
road aggregate meets the deck. This
approach area demands special attention
and probably more maintenance. When
3-25 Drainage openings (scuppers) in bridge
decks must be kept cleaned.
traffic moves from a rigid bridge deck to a
more flexible dirt and gravel road surface,
the impact forces of those vehicles can
cause problems, resulting in significantly
more maintenance for the approach areas.
3.6.3. Frequency of Maintenance
Operations. No matter when operations
are being performed, remember that the
presence of moisture will avoid dust and
aid in proper compaction. If a water truck
or water source is not available, work
should be planned after a rainfall if at all
possible.
3-26 Bridge approach areas demand special
attention and usually more maintenance.
That brings us to the question of "how frequently do we blade or smooth the
road?" We have already discussed the fact that the more we blade or smooth, the less
often we will regrade or reshape, and the less often we will add new material. In other
words, keeping the road in good condition by blading and smoothing prolongs the road's
life while cutting maintenance costs.
So maintenance operations are performed "as needed" depending on a number of
variables such as road type and condition, drainage conditions, the weather, and traffic
volumes. How many storms have occurred since the last maintenance was performed?
How severe was the storm? What's the traffic volume? Do we have a lot of truck traffic?
3-21
-------
Special events may dictate needs, requiring maintenance work in preparation
before the event to put the roads in good shape, or after the event to repair damage.
If we accept the "as needed" scenario, we must inspect the roads frequently.
Routine inspections, supplemented by special inspections after major storm events, are
essential to determining road needs and performing the required maintenance at the right
time.
Equipment operators play key roles in road inspection. The operator can also take
note of other existing problems on the road or roadside, such as damaged drainage pipes
or broken delineators, while he is working on the roads. Operators should keep a notepad
and jot down problems with location details so they can be taken care of later, but in a
timely fashion to prevent any major problems or costs.
_^_ ~&r-.?lm
'.-• r f-t'.Jf:-: '.: , -;••'- , ("•• » •., JI
CX^W"
^>-tm
3-27 Operators should note existing problems.
Look at the photos in 3-27. These are samples of what an operator could notice
and jot down a note so that maintenance repairs can be planned and the problems taken
care of.
On a last note, Photo 3-28 depicts
the "sign" of a professional equipment
operator. He carries a shovel and is not
afraid to use it.
3.7 Summary
We have seen how the dirt and
gravel roads and their surrounding
environment are deeply entangled with
one another. We have also seen how
poorly maintained roads contribute to
erosion, pollution, and dust. By using
appropriate materials and techniques,
local governments can reduce pollution and maintenance costs at the same time.
3-28 Using a shovel is the sign of a
"professional operator."
3-22
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APPENDIX 3. Sample Aggregates Specifications
Following are sample specifications for gravel road aggregate surface courses from
several different states. Road personnel should check with their State Department of
Transportation or their Local Technical Assistance Program / Technology Transfer (T2)
Center for specifications being used in their own state. Many state DOTs have their
specifications readily available via their Web sites.
A3.1 Pennsylvania's Driving Surface Aggregate
Material Specifications: All Driving Surface Aggregate (DSA) is to be derived from
natural stone formations. Stone is defined as rock that has been crushed; rock is defined
as consolidated mineral matter. For use in this program, both are restricted to that which
has been mined or quarried from existing geologic bedrock formations.
All components of the aggregate mix are to be derived from crushed parent rock material
that meets program specifications for abrasion resistance, pH and freedom from
contaminants. Ninety-eight percent (98%) of fines passing the #200 sieve must be parent
rock material. No clay or silt soil may be added. The amount of particles passing the
#200 sieve shall be determined using the washing procedures specified in PTM No. 100.
Size: The required amounts and allowed
ranges, determined by percent weight, for
various size particles are shown in Table 1.
LA Abrasion: The acceptable limit as
measured by weight loss is "less than 40%
loss." Los Angeles Abrasion test, AASHTO
T-96 [ASTM C 131] shall be used to
determine this property. Existing data
obtained from tests made for and approved by
PENNDOT will be accepted.
Passing sieve
I 1A inches
3/4 inches
#4
#16
#200
Lower %
100
65
30
15
10
High%
90
65
30
20
Table 1. DSA Gradation
Sulfate Test: Soundness or resistance to freeze/thaw [i.e., sulfate test] is not specified
for this application because a gravel road driving surface aggregate is not bound within
a concrete or asphalt mix.
pH: Aggregate must be in the range of pH 6 to pH 12.45 as measured by EPA 9045C.
Optimum Moisture: Material is to be delivered and placed at optimum moisture content
as determined for that particular source. The optimum percentage moisture is to be
identified by the supplier in the bid/purchasing documents.
Transport: Tarps are to be used to cover 100% of the load's exposed surface from the
time of loading until immediately before dumping. This requirement includes standing
time waiting to dump.
Aggregate producers are required by the program to certify that the aggregate they
deliver conforms to the program specifications.
-------
Road Surface Preparation: Driving Surface Aggregate will reflect the shape of the
surface to which it is applied; therefore, all road surface preparation work is to be
completed before delivery and placement of the aggregate.
1. Prepare underdrainage, including drain tile, French drains (porous fill) and crosspipes.
2. Address surface drainage features such as broad-based dips, grade breaks, crown, and
side-slope.
3. Establish proper cross-slope in existing base (Fig. 1). Recommended crown or slope is
!/2 to 3/4 inch rise per horizontal foot. Proper shape may be a flat "A" crown profile, an in-
slope or out-slope. If exposed bedrock or insufficient material prevents proper shaping of
the road base, additional base material may be needed.
4. To bind aggregate with the road base, scarify impermeable smooth surfaces such as oil
and chip, exposed bedrock or smooth tight aggregate. Do not loosen coarse aggregate or
chinked stone roadbeds rough enough to permit binding with Driving Surface Aggregate.
5. If required, separation fabric should be placed according to manufacturer's
recommendations.
Placement: An un-compacted uniform depth of 8 inches of DSA is to be used to
establish the driving surface. Placement is to be in a single 8-inch lift. The preferred
method of application is through a paver. Set the paver adjustments on application
thickness and width so it is unnecessary to use a grader. The required crown or side slope
is to range from 1A to 3/4 inch rise per horizontal foot. This slope is to be achieved by
properly preparing base and placing aggregate in a uniform lift. When the paver is
applying aggregate, care should be taken to keep the paver at or near capacity at all times.
To fill driving surface areas outside the specified width (e.g., driveway entrances, pull-
offs, and passing lanes), additional DSA is to be added and tapered to grade or butted
against a precut channel of the same depth. If berm or bank edges don't exist to hold the
new DSA surface, then sufficient material is to be placed, tapered and compacted to form
protective edge berms. Material shall be compacted to a final thickness of approximately
6 inches.
DSA CALCULATION FORMULA
DSA Road Road
Needed = Width X Length X 0 042
(tons) (ft) (ft)
Applies to standard 8" lift, compacted to 6"
Compaction Sequence: Verify that moisture is optimum for compaction. If the material
has dried out, re-wet the DSA surface with a water truck. If clumps of aggregate adhere
to the roller drum, the aggregate may be too moist. Allow drying time before rolling. Do
not use the vibratory rolling mode if that action brings water to the surface of the
aggregate.
Only self-powered machines designed specifically for compaction shall be used.
Compaction with truck tires is not acceptable.
1A. Supported Edge: If edge of placed aggregate is supported by an existing bank
3-24
-------
or berm: First pass: Roll slowly in static mode on the outside edge of placed
aggregate.
IB. Unsupported Edge: If the edge of the placed aggregate is not supported:
First Pass: Roll slowly in static mode near but not over unsupported outside
edges. Once that path is firm, move progressively closer to the outside edge
with static passes until unsupported edge is firm.
2. Sequence: As in all rolling operations, compaction is achieved making
overlapping lengthwise passes beginning at the ditch or berm-side and working
toward the crown or the top edge (if it is a side-sloped or super-elevated section
of road). In no case should the roller be run lengthwise on the top of the road
crown.
3 A. Static Roller: The minimum acceptable weight of a static roller is 10 tons.
Repeat the sequence of overlapping passes until desired compaction is achieved.
3B. Vibratory Roller: The minimum striking force of vibratory rollers is 20,000
Ibs. When using a vibratory roller, the initial pass over un-compacted aggregate
should be completed in static mode. All successive passes should be made using
the vibratory mode until the desired level of compaction is achieved. The final pass
over each area should be made in static mode to remove all roller edge marks. The
vibratory roller should be set to deliver between 6 and 17 impacts per linear foot
with the roller moving at the speed at which a person walks on each pass upgrade.
Vibration must be turned off during downgrade passes Vibrating the drum
when rolling downgrade will cause aggregate to flow in "waves" in front of the
roller, resulting in an uneven surface.
4. Desired Compaction: Unless more refined testing equipment is available,
adequate compaction is indicated when no further depressions are created with a
roller or loaded dump tuck. Cracking of larger stones or rocks in the road surface is
another reliable indication of adequate compaction.
A3.2 Illinois DOT Specifications. (excerpts)(www.dot.il.gov)
Section 402. Aggregate Surface Course
402.01 Description. This work shall consist of furnishing and placing one or more course
of aggregate upon a prepared sub grade.
402.02 Materials. Materials shall meet the requirements of Section 1000, Article 1004.04
1004.04 Coarse Aggregate for Aggregate Surface Course.
a. Description. The coarse aggregate shall be pit run gravel, gravel, crushed
gravel, novaculite, crushed stone, crushed concrete, crushed slag or crushed sandstone.
a. Quality. The coarse aggregate shall be Class D Quality or better.
Quality Test
Sodium Sulfate Soundness2 5 cycle,
AASHTO T1041'2, Max % loss
Los Angeles Abrasion
AASHTO T96, Max % loss
Class D
253
45
1 As modified by the Department
2Does not apply to crushed concrete.
3For aggregate surface course, the maximum percent loss shall be 30.
3-25
-------
c.
Gradation.
1. For aggregate surface course Type B, Gradation CA6, CA9,
or CA10 may be used. If approved by the Engineer,
Gradation CA4 or CA12 may be used.
2. For aggregate subbase Type B, Gradation CA6, CA10,
CA12,, or CA19 shall be used. If approved by the Engineer,
Gradation CA2 or CA4 may be used.
3. For aggregate Subbase Type C, Gradation CA7 or combined
size CAS and CA7 shall be used.
4. For granular aggregate courses (base, subbase, and shoulder
except subbase Types B and C), Gradation CA6, or CA10
shall be used. If specified, Gradation CA2 or CA4 For
aggregate surface course Type B, Gradation CA6, CA9, or
CA10 may be used. If approved by the Engineer, Gradation
CA4 or CA12 may be used.
5. Stabilized aggregate courses (base, subbase, and shoulder),
Gradation CA6 or CA10 shall be used. If approved by the
Engineer, Gradation CA2, CA4, or CA12 may be used.
6. For aggregate surface course Type A, Gradation CA6, or
CA10 shall be used. If approved by the Engineer, Gradation
CA2, CA4, CA9, or CA12 may be used.
Plasticity. All material shall comply with the plasticity index
requirements listed below.
Type of construction
Aggregate Subbase
Type A or B
Aggregate Base Course
Type A or B
Aggregate Surface Course
Type A or B2
Stabilized Aggregate Material
Plasticity Index - Percent1
Gravel
Oto9
Oto6
2 to 9
Oto9
Crushed Gravel, Stone, Slag
Oto4
Oto9
Elasticity index shall be determined by the method given in AASHTO T90. Where shale in any form exists
in the producing ledges, crushed stone samples shall be soaked a minimum of 18 hours before processing
for plasticity index or minus #40 material. When clay material is added to adjust plasticity index, the clay
material shall be a minus #4 sieve size.
2When Gradation CA9 is used, the plasticity index requirement will not apply.
402.03 Equipment shall meet the requirements of the following Articles of Section 1100:
a. Tamping Roller 1101.01
d. Pneumatic-Tired Roller 1101.01
e. Three-Wheel Roller (Note 1)....1101.01
f. Tandem Roller (Note 1) 1101.01
g. Spreader 1101.01
h. Vibratory Machine (Note 2) 1101.04
Note 1. Three-wheel or tandem rollers shall weigh 6 to 10 tons and shall weigh
not less than 2001b/in nor more than325 Ib/in of width of the roller.
3-26
-------
Note 2. The vibratory machine shall meet the approval of the Engineer.
Construction Requirements
402.04 Subgrade. The subgrade shall be prepared according to Section 301 except that
Article 301.06 will not apply.
402.05 Type A Requirements. Aggregate surface course, Type A shall be constructed
according to Article 351.05(a) and (b) except the bearing ratio requirements shall not
apply.
402.07 Type B Requirements. Any one or two gradations of the material specified in
Article 1004.04 shall be used except where two gradations of material are used, the
change shall not be made at more than one location on the section.
The surfacing material shall be deposited on the subgrade by means of a spreader.
The equipment used shall be such that the required amount of material will be deposited
uniformly along the central portion of the roadbed.
The material which has been deposited shall be spread immediately to the plan cross
section. Hauling shall be routed over the spread material so it will cover the entire width
of surface. If the equipment used in hauling operations causes ruts extending through the
spread material and into the subgrade, and the subgrade material is being mixed with the
surface material, the equipment shall be removed from the work or the rutting otherwise
prevented as directed by the Engineer.
The Contractor shall keep the surface smooth by dragging or blading as many times each
day as the engineer may direct.
Holes, waves, and undulations which develop and which are not filled by blading shall be
filled by adding more material.
A3.3 Michigan DOT Specifications (excerpts) (www.mdot.state.mi.us)
Section 306. Aggregate Surface Course
306.01 Description. Construct an aggregate surface course on a prepared subgrade or an
existing aggregate surface.
306.02 Materials. Use materials meeting the following:
Dense-graded Aggregate 21AA, 21 A, 23 A 902
Use aggregate 21 AA or 21A if the aggregate surface course will later receive a hot mix
asphalt (HMA) surface. Use aggregate 23 A if the aggregate surface course is to be
constructed without an HMA surface. Use dense-graded aggregate 22A, 23 A for
temporary maintenance gravel.
902.06 Dense-Graded Aggregates for Base Course, Surface Course, Shoulders,
Approaches and Patching. Michigan Class 21AA, 21A, 22A and 23A dense-graded
aggregates will consist of natural aggregate, iron blast furnace slag, reverberatory furnace
slag, or crushed concrete, in combination with fine aggregate as necessary to meet the
gradation requirements in Table 902-1, the physical requirements in Table 902-2, and the
following:
A. Dense-graded aggregates produced by crushing Portland cement concrete will
not contain building rubble as evidenced by the presence of more than 5.0%,
by particle count, building brick, wood, plaster, or similar materials. Sporadic
pieces of steel reinforcement may be present provided they pass the maximum
grading sieve size without hand manipulation.
3-27
-------
B. Class 21AA, 21 A, and 22A dense-graded aggregates produced from Portland
cement concrete will not be used to construct either an aggregate base or
aggregate separation layer when either of the following conditions apply:
1. When there is a geotextile liner or membrane present with
permeability requirements.
2. In a pavement structure with an underdrain, unless there is a
filter material between crushed concrete and the underdrain.
The filter material will be either a minimum of 12 inches of
granular material or a geotextile liner or blocking membrane
that will be a barrier to leachate.
C. Class 23 A dense-graded aggregate may be produced from steel furnace slag,
but only for use as an unbound aggregate surface course or as an unbound
aggregate shoulder.
Table 902-1 Grading Requirements for Dense-Graded Aggregates
Class
21AA,
21A
22A
23A
Sieve Analysis (MTM 109) Total Percent Passing (b)
1.5 in.
100
lin.
85-100
100
100
3/4in
90-100
!/2in
50-75
3/8 in
65-85
60-85
#8
20-45
30-50
25-60
Loss by Washing
(MTM 108)
% Passing #200
4-8 (e)(f)
4-8(e)(f)
9-16(f)
(b) Based on dry weights
(e) When used for aggregate base courses, surface courses, shoulders and approaches and the
material is produced entirely by crushing rock, boulders, cobbles, slag, or concrete, the maximum
limit for Loss by Washing will not exceed 10%.
(f) The limits for Loss by Washing of dense-graded aggregates are significant to the nearest whole
percent.
Table 902-2 Physical Requirements for Dense-Graded Aggregates
Class (j)
21AA
21A
22A
23A
Crushed Material, % min.
(MTM 110, 117)
95
25
25
25
Loss, % max,
102)
Los Angeles Abrasion (MTM
50
50
50
50
(j) Quarried carbonate (limestone or dolomite) aggregate will not contain over 10% insoluble
residue finer than Number 200 sieve when tested in accordance with MTM 103.
306.03 Construction.
A. Preparation of Base. When required, blade, or scarify and blade, the existing aggregate
surface to remove irregularities in the grade.
B. Placing and Compacting. Provide a uniform aggregate mixture compacted in place with
uniform density full depth. Provide a completed surface course conforming to the line, grade
or plan cross section.
Place maintenance gravel to provide a flush transition between shoulders, driveways and other
areas where traffic is maintained. Maintenance gravel may remain permanently as part of the
work, if approved by the Engineer.
Do not place aggregate when the base is unstable. Maintain the aggregate in a smooth, stable
condition and provide dust control until removed or surfaced.
C. Use of additives. Use of additives to facilitate compaction and for dust control of the
aggregate is acceptable.
3-28
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A3.4 New York DOT Specifications (excerpts) (www.dot.state.ny.us)
Section 667 - Local Road Gravel Surface, Base, and Subbase Courses
667-1.02 Material Types. Provide materials as specified by the following options.
Type A. Surface quality material with a maximum particle size of 25mm.
Type B. Base quality material with a maximum particle size of 50 mm.
Type C. Subbase quality material with a maximum particle size of 75mm.
667-2.02 Material Requirements. Provide materials for road gravel surface, base and
subbase courses that consist of Sand and Gravel, approved Blast Furnace Slag or Stone
that meet the requirements contained herein. Provide materials well graded from coarse
to fine, and free from organic or other deleterious materials. Any gravel material will be
rejected if it is determined to contain any unsound or deleterious materials.
B. Gradation, Perform sieve analysis in accordance with AASHTO procedures
T27, T88 or T311. Provide materials meeting the gradation limits from Table
667-1.
C. Soundness. Material will be accepted on the basis of Magnesium sulfate.
Soundness Loss after four cycles performed according to NYSDOT
procedures and Table 667-2.
D. Plasticity. Determine plasticity using either of the following methods:
1. Plasticity Index. The Plasticity Index of the material passing
the #40 mesh sieve shall meet the values in Table 667-2.
Determine plasticity using AASHTO tests T89 and T90.
2. Sand Equivalent. The sand equivalence of the granular
material shall meet the values in Table 667-2. Determine
sand equivalence using AASHTO test T176.
Table 667-1 : Percent passing by Weight of Gravel Material
Sieve (US Sieve)
3"
2"
1.5"
1"
3/4"
!/4"
#40
#200
A (Surface)
100
85-100
50-75
15-35
8-15
B (Base)
100
85-100
-
-
30-50
5-20
0-5
C (subbase)
100
-
70-100
-
-
30-55
5-25
0-8
Table 667-2: Test and control Limits of Gravel Materials
Material Properties
Maximum Soundness loss (%)
Plasticity Index
Sand Equivalent
A (Surface)
20
2-9
>25
B (Base)
20
0-5
>40
C (subbase)
25
0-8
>35
Elongated Particles Not more than 30%, by weight, of the particles retained on
a l/2" sieve shall consist of flat or elongated particles. A flat or elongated
particle is defined herein as one which has its greatest dimension more than 3
times its least dimension. Acceptance for this requirement will normally be
3-29
-------
based on a visual inspection. When the municipality elects to test for this
requirement, material with a percentage greater than 30 will be rejected.
F. Fractured faces. When the municipality elects to test for this requirement,
Type A material shall have at least two fractured faces on 50% of the stone
particles larger than Va" or at least one fractured face on 75% of the particles
larger than Va". Type B material shall have at least one fractured face on 50%
of the stone particles larger than l/2\
667-3.02 Placement.
A. Place the upper course material on the grade in a manner to minimize
segregation, using equipment and procedures approved by the municipality.
Do not perform uncontrolled spreading from piles dumped on the ground.
B. B. / The maximum compacted layer thickness is 15" or as shown on the plans.
In confined areas as defined by the municipality, the maximum compacted
layer thickness is 6". The minimum loose lift thickness is 1.5 times the
maximum particle size.
667-3.03 Compaction. When the moisture content is within the limits for proper
compaction, compact the material in accordance with the requirements of Section 203-
3.12, compaction. Density tests are not required for the acceptance of these courses.
3-30
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Environmentally Sensitive Maintenance
for
Dirt and Gravel Roads
4-01 Many roads were built without regard to
natural systems.
Chapter 4: Basics of Natural Systems
4.1 Introduction
Today, road managers must
operate and maintain public roads in a
broad context that considers multiple
social, political, and environmental
objectives. This tough task is made more
difficult by the fact that most roads were
built within a much narrower context that
focused only on short-term purposes such
as engineering, cost, and convenience.
Through construction, our
transportation systems were traditionally
laid down across the entire fabric of the
landscape. Nearly all roads were built without regard for the function of the natural
systems that evolved in these locations. Roads built adjacent to and across streams,
through wetlands, farms, and forests inevitably disrupted both surface and subsurface
drainage, vegetation patterns, and native animal communities.
Potholes, ruts, road washouts, bank
failures, ditch blockages, and fallen trees
bear witness to our disturbance and
disruption of natural systems. In addition,
typical environmental problems also
appeared, such as muddy streams,
deteriorated habitat, and changes in the
number and type of both plant and animal
communities. But efforts to address these
problems without understanding their
causes have often been a waste of money.
As previously stated, road
management is an increasingly complex
task where managers must balance human
expectations against intricate natural
systems. This chapter will introduce some
basic guiding principals of natural systems
4-02 Environmental problems bear witness to
our disturbance and disruption of natural
systems.
4-1
-------
so road managers can better understand the relationship between the roads and the
environment. These basic guiding principles will focus on the three pertinent natural
systems: streams, wetlands, and forest/upland areas.
Chapter 4 starts with an introduction to ecology and ecosystems. It will then
provide more specific information on the three common ecosystems or communities:
streams, wetlands, and forests/uplands, respectively. This information supports our
objective to "arm the user with knowledge on basic principles of nature and natural
systems..." so that we can apply that knowledge to our road maintenance programs
through environmentally sensitive practices, resulting in better roads and a better
environment.
4.2 Ecology, Ecoregions and Ecosystems
The term ecology stems from the
Greek word "oikos," which means
"house." Ecology can be defined as the
study of interactions of organisms
between one another and the physical and
chemical environment. As indicated by the
definition, all living organisms (plants,
animals, fungi, and micro-organisms, such
as bacteria and viruses) are dependent
upon conditions present where they live
(in their "house"). This range of ecological
conditions, which describes where an
organism lives, is termed "habitat." Habitat is defined by a wide variety of physical and
biological factors. Physical factors, such as local geology (elevation, slope, drainage, rock
type, etc.), soil (nutrients, stability, etc.), hydrology (precipitation, runoff, soil, moisture,
evaporation, etc.), and climate (temperature, sunlight, day length, etc.), shape the setting
in which biological organisms live. Biological factors, such as competition for food
sources and mates, predation, disease, and social interaction, determines how well
organisms survive and reproduce within the physical setting.
Ecologists have studied many of the interactions that take place between
biological and physical systems, and based upon their findings, divided the landscape into
ecoregions or areas with similar characteristics. These ecoregions reflect the physical
factors (geology, soil, hydrology, climate) that help define their respective habitats, and
in turn determine the type of animals and plants that live in that habitat. Geological
provinces and ecoregions are closely linked. The comparison of geological and
ecoregions maps demonstrates the boundary similarities. (Appendix 4. Case Study:
Pennsylvania's Ecology illustrates this comparison in Figure A4-1 using the geology
province map and an ecoregion map of Pennsylvania.)
Vegetation is heavily dependent upon the area's elevation, slope, drainage,
stability, and nutrient availability conditions, in essence, the geology and soils. If plants
4-03 Physical factors such as geology, soil,
hydrology, and climate shape the 'habitat'.
4-2
-------
4-04 Plants develop and evolve under the
physical conditions of their ecoregion.
from one ecoregion are planted within another ecoregion, they will most likely not do as
well as they would have in their own ecoregion. This is because plants (and animals)
have developed and evolved under a certain set of physical conditions characteristic of
their ecoregion, and if these conditions are not met, then they will have a difficult time
surviving. In some instance, road locations and maintenance practices create conditions
unnatural to that ecoregion, causing
survival failures in otherwise viable
animals or plants.
This ecoregion concept is critically
important for "environmentally sensitive
maintenance for dirt and gravel roads."
Road managers must understand natural
systems to adopt effective road
maintenance practices that provide
sustainable roads without hurting the
environment.
One key is to use nearby natural
systems as an example of what our project
sites should look like and how they should
function. Projects, whether construction or maintenance, will be more successful if they
are modeled after nearby natural systems because nature has already done the research
for us. These natural systems can be used to determine what slopes are sustainable for
road and stream banks, as well as what plants grow well in a specific location. The
relative size of local drainage features serve as a guide for sizing drainage structures for
the roadway system. Projects modeled after natural systems will also look more natural
and aesthetic compared to
more sterile engineering
designs. And, as we shall
see, we can learn how to
use these natural systems to
actually aid us in more
effective and efficient road
maintenance
Ecoregions are
broad areas that cover
many different types of
habitat, and because of this,
ecoregions are often broken
down into smaller units.
Within each ecoregion,
there are typically three
types of ecosystems, or
communities: streams,
Wetlands
4-05 Ecosystems (Communities)
Uplands
4-3
-------
wetlands, and forests/uplands. The term upland commonly refers to areas of higher
elevation that are well drained, covered with forests or cleared for farming or have
reverted to meadows.
Each one of these ecosystems relate differently to maintaining dirt and gravel
roads. In the stream ecosystem, sediments and their effect on stream life are a major
concern. Sensitive plants and animals are a major concern with wetlands, in addition to
other major benefits, such as flood storage. Strict laws and regulations govern roads built
through and near wetlands so we can continue to receive these benefits. Finally, in
forested or upland areas, improper trimming and clearing of vegetation associated with
road maintenance causes a major concern and unwarranted expense.
4.3 The Stream Ecosystem (Community)
4.3.1 Introduction: According to
EPA's National Water Quality inventory,
there are 3,692,830 miles of rivers and
streams within the United States. This vast
network of streams is a tremendous
natural resource. There are a number of
important interactions between our dirt
and gravel roads and our stream networks.
Precisely because our roads and streams
are so closely linked, road managers must
be extremely sensitive to the well-being of
the stream.
4-06 There are 3,692,830 miles of rivers and
streams within the United States.
4.3.2 Basics of Stream Ecology:
Stream ecosystems, or communities, are
dependent upon a wide range of both physical and biological factors, as reviewed
previously. These factors, how they are connected, and their importance to the stream
will be discussed in the following sections.
4.3.2.1 Watersheds:
Streams are situated in the bottom
of their valleys, draining water
from the surrounding higher
landscape. This area drained by the
stream is referred to by several
interchangeable terms: watershed,
drainage basin, or catchment area.
Although we typically perceive
streams starting where sufficient
water has accumulated to form a
channel, streams actually begin at
the highest points within their
Watershed
boundary^
Small headwater
sir fill i is
Mains tern of riv>
'' Mouth of the river
—*"^& water shed outlet
eadwaters of
the watershed
Tributary to the
mains tern
Figure 4-1 Watershed Features
4-4
-------
watersheds, the point where precipitation first contacts the ground. Once precipitation
hits the ground, gravity causes the water to flow downhill, first as a very thin sheet of
water similar to a sheet of water flowing over a paved road. Irregularities in the ground
surface break up this smooth flow, causing the water to accumulate in increasingly
greater quantities. This water accumulation begins to cut a channel, first forming small
rills, then gullies, and then becoming small streams. Small streams are formed in the
headwaters portion of the watershed, as shown in Figure 4-1. Small streams join each
other, accumulating more water until the flow eventually becomes a river.
Because streams obtain water from their watershed, activities that take place in
the watershed can negatively affect the quality of the water entering the stream. If the
stream receives polluted water, then the life in the stream will also be impacted. The
pollution of our nation's waterways and water quality issues over the past 100 years has
created much public resentment. In response to this pollution, laws were passed to protect
our water resources as early as the Federal Rivers and Harbors Acts of 1890 and 1899.
Pollution, and our knowledge of its impacts, has increased since these early laws, and
additional regulations govern activities along streams in an effort to protect and preserve
stream systems and the benefits that they provide. It is important to know about and work
within these necessary legal restrictions when conducting road maintenance work.
Traditional management
divisions (e.g., township, county
these jurisdictional
boundaries, making
management and protection of
this valuable resource
difficult. Effective
management must involve the
challenging task of
coordinating efforts between
multiple political
jurisdictions. One of the best
ways to make the
management of our water
resources easier and more
effective is to manage it on a
watershed or catchment area
basis. Because planning at the
local level is often at too small
a scale to address watershed
size resource problems, local
governments are strongly
encouraged to communicate and
coordinate control efforts with
neighboring municipalities and
county agencies.
of our water resources has been based on political
, state boundary lines). Water, however, flows across
u
.^
u.
O eo CL
»
00
1000
100
£
I
10
1.0
Erosion
N velocity Erosion
Sedimentation
Fall velocity
I
I
l
0.001 0.01 0.1 1.0 1O 100 1000
Figure 4-2 Average water velocities to erode, transport and
deposit uniformly sorted particle sizes. Velocities between the
dotted lines and higher will erode the indicated particle sizes.
When velocities drop below the fall velocity line, there is
insufficient energy to keep particles suspended in the water, so
sedimentation occurs. Erosion velocities differ depending on the
shape and bonding characteristics of the particles.
4-5
-------
4.3.2.2 Stream Systems. As mentioned in our discussion of watersheds, streams
are formed when water flowing downhill concentrates and forms a channel. The volume
of water, the velocity, or speed, of water flow, and the characteristics of the underlying
material influence the size, shape, and path of the channel. Although the information in
this section refers specifically to streams and stream channels, these processes also
explain and describe the interactions between water and sediment in drainage ditches.
Flowing water picks up (erodes) material from the bottom (bed) and sides (banks)
of the stream channel. This eroded material is called sediment. The water's velocity
determines how much material will be picked up, as larger sized particles, in general,
require greater amounts of energy to erode or move them. Figure 4-2 shows the velocities
necessary to erode, transport, and deposit uniformly sorted particle sizes. This figure also
shows that clay sized particles require more velocity to erode than do larger, sand-sized
particles. This is because electrical bonds associated with the clay particles help to hold
them together, thus requiring more energy to pull this sticky material apart than to pick
up the loose grains of the larger-sized sand.
The material that is eroded and carried by the water current is called suspended
sediment. If the material is too large to be fully suspended in the water, it may either
bounce (saltation load) or roll
along the bottom (bed load),
as depicted in Figure 4-3.
When water velocities slow
(e.g., when a mountain
stream leaves a hilly area and
starts across a valley floor),
larger, heavier particles are
the first to drop out of
suspension and are deposited
on the bottom of the stream.
As water velocities continue
to slow, there is less energy
to suspend particles, and finer
and finer particles continue
settling to the bottom. This
process is called
sedimentation. Because clay is the smallest and lightest particle, once the stickiness is
overcome and the particles are suspended, they remain in suspension longer and travel
further than any of the other particle sizes. It can even take several days or weeks for clay
particles to settle from perfectly still water.
Stream channels are dynamic because erosion and deposition processes change
their form and shape (morphology) over time. They change both their cross-sectional
profile (width, depth, and slope) as well as their 'plan-view' path. It is important to note
that stream paths are not fixed in place; stream channels often migrate sideways, either
incrementally by eroding their banks or by carving whole new channels through low-
CURRENT
WATER SURFACE
_ v
• . • *•'•'••'•*• °
.'••.'•'•• SUSPENSION • .
T(SIIT & CLAY SIZE) '•
SALTATION
(SAND SIZE)
(ROCKS,
GRAVEL)
4-3; Water transport various sized par tides in various ways.
4-6
-------
4-07 Streams are constantly eroding,
transporting, and depositing materials.
lying areas. These changes in the shape of the stream channel occur both site specifically
as well as throughout the whole stream system.
Natural channels are constantly
eroding, transporting, and depositing
materials. Normal daily flows tend to
redistribute small amounts of materials
within streams. Storm events, however,
introduce large volumes of water in to the
stream system, which can significantly
alter the morphology of a river or stream
by cutting new channels, eroding whole
banks, and gouging out shallow river beds.
Sediment generated during flooding from
major storm events is often carried out of
the channel by flooding waters, where it is
deposited and stored on the floodplain.
These sediments enrich floodplain soils with nutrients, which enable plants to grow well
in a floodplain environment. The plants and their roots also help to trap and hold the fine
sediments in place. Over time, however, rainwater washing over the floodplain may
erode and return some of this sediment to the stream.
As streams continue to erode, transport, and deposit materials, human activities
anywhere within the watershed can interfere with these natural processes, creating
conditions that alter habitat and disrupt the aquatic life that lives in the stream. For
example, poor maintenance of a dirt or gravel road may cause excess sediment to wash
into an adjacent stream. Excess sediments will be carried downstream until the water
velocity slows and sedimentation occurs.
Individual streams are part of a network of channels that extend the whole length
of a watershed. Because networks extend from the top (highest elevation) of a watershed
to its outlet (lowest elevation), changes in the headwaters of a stream can affect the entire
network. For example, logging a hillside in the headwaters of a watershed can cause more
storm water runoff to reach the stream at a faster rate than it ever has before (trees block
water flow across the ground and help the water sink into the ground). This extra flow is
added to the existing water and can lead to problems downstream. Suddenly the 24-inch
culvert that you installed last year is no longer large enough to handle the extra volume of
water, resulting in water backing up and flooding out the road. This extra volume of
water can also cause additional bank erosion and the redistribution of sediments that
destroy habitat and clog drainage facilities and bridges.
4.3.2.3 Hydrology. A major factor influencing stream systems is their source of
water and its movements within the watershed. Hydrology is simply the study of water
distribution or movement within the watershed. Precipitation landing within a watershed
can enter the streams by two different pathways. The most obvious pathway is when
surface runoff flows across the landscape directly into the stream system. The less
4-7
-------
obvious route is when it seeps (infiltrates) into the ground, where it becomes
groundwater. Groundwater flows through the pore spaces between soil and rock particles,
and shallow groundwater near the surface may eventually drain into a stream channel.
Water may also follow a combination of these pathways. For example, precipitation may
flow as surface runoff down a hillside where it settles into a depression. In the
depression, it may infiltrate into the ground and flow as groundwater into a stream.
The speed at which water flows through a watershed and enters a stream system
helps shape the channel and the habitat found within the stream. Surface runoff,
especially after large storm events or when the ground is frozen, flows quickly over the
land surface and enters the stream. This causes large amounts of water to enter the stream
system within a short time period, exceeding the channel's capacity and resulting in
flooding. Streams that receive a large portion of their water supply from surface runoff
are susceptible to widely fluctuating water flows and levels. These fluctuating flows
create a highly variable, stressful environment in which only specially adapted plants and
animals may live.
Groundwater-fed streams have
more stable flows and environments than
surface fed streams. They fill slowly,
accumulating groundwater as it makes it
way through the tiny pore spaces in soil
and rock. When large amounts of
precipitation infiltrate into the ground and
become groundwater, the surface runoff
from the storm is drastically reduced. This
water still may enter the stream system,
but because it flows slowly through the
ground, possible taking days, weeks, or
months to reach the stream, stream flows
become more stable. More stable stream
flows tend to result in more stable channel conditions and in turn, offers habitat for plant
and animals that are adapted to these stable conditions.
Several landscape factors influence water flow across and through the landscape.
As will be discussed further in our sections on wetlands and upland communities, a
watershed's vegetation usually slows the rate and decreases the volume of surface runoff
by aiding infiltration of water into the ground. Plants are also able to diminish
groundwater supplies by up taking water through their roots. Roads also influence water
flow and can have a major impact on watershed hydrology. By cutting across the
landscape, roads block, constrict, and divert both surface and subsurface drainage
patterns, artificially acting to collect and concentrate flows. These artificially
concentrated flows cause many of our familiar road maintenance problems, including
washouts, rutting, and flooding. Alterations in subsurface hydrology can also lead to soft
spots in roads where additional concentrated water raises groundwater levels and
4-08 Concentrated water flows cause many
familiar maintenance problems.
-------
4-09 As turbidity increases, light penetration
decreases.
groundwater flow is blocked. These problems and others are discussed further and
addressed elsewhere in this manual.
4.3.2.4 Water Quality. Water in
natural environments is not just pure
water. As mentioned in the previous
discussion on watersheds, precipitation
falls to earth where it moves over and
beneath the ground's surface, down
through the watershed and into the stream
system. As the water moves through the
watershed, it picks up materials and
transports these materials into the stream
environment. Materials may be
transported as suspended sediment or may
become dissolved in the water and carried
as dissolved load. The type and quantity of
materials entering the stream system from
the watershed influence the overall quality of the water. This water quality is often
evaluated by testing the water for specific chemical and physical characteristics, such as
nitrogen, phosphorus, pH, dissolved oxygen, temperature, color, and turbidity. Turbidity
is the degree to which the passage of light through water is blocked by suspended
sediment, the cloudiness of the water.
Both the geology and the land use influence water quality. The rocks and soil in
the underlying geology of a watershed have always influenced a basin's water. Rocks and
soils add nutrients and minerals as well as filter excess materials from groundwater and
surface runoff. The type of natural vegetated cover and human uses of the land also
influence a watershed's water quality. Land uses such as roads, farming, construction,
homes, industrial facilities, and urban areas have caused excessive materials to enter and
harm stream systems. In particular, massive amounts of sediment have been eroded due
to changes in land use over the past 200 years. These materials may either wash directly
into the stream system or become bound to sediment particles and carried into the stream
while attached to the sediment. Both natural and artificial materials that wash into
streams may include sediment, fertilizers (nitrogen, phosphorus), animal wastes, human
sewage, road salts, pesticides, herbicides, other chemicals, oil, and gasoline. The large
number of roads crossing streams, unfortunately, has also provided opportunities to dump
garbage, tires, appliances, and all sorts of other solid waste into our streams.
Water temperature is an especially important component of water quality for
headwater streams. The temperature of the water in these headwater streams is largely
influenced by the source of water. Groundwater-fed streams are fed by a relatively
constant supply of cold water. Surface runoff-fed streams are fed by intermittent flows of
water following storm events where the water flows across hot land in the summer and
the cold (frozen) earth in the winter. These surface runoff streams have an irregular
supply of water whose temperatures varies widely with ambient temperatures. Vegetation
4-9
-------
along streams is also an important temperature influence because it helps to moderate
water temperatures. In the summer, shading of streams by adjacent vegetation prevents
warming, and in the winter months, forests can trap warmer air in valleys to delay
cooling.
4-10 Life in a Stream
4.3.2.5 Stream Life. There are a
wide variety (diversity) of organisms that
utilize stream habitats, and each stream
contains a mix of different species. This
mix of species makes up the stream
community. Types of organisms include
plants, insects, crayfish, mollusks, fish,
reptiles, amphibians, spiders, birds, and
f£jl|U!GUU9^^^H Aft' '
cMnQB| mammals. Some aquatic plants are
, • V microscopic and include things such as
plankton and algae. Larger aquatic plants
are very diverse, with some spending their
life floating in the water, while others live
by attaching to soil, rocks, or plants. Many
different insects spend at least part of their
life cycle underwater (the larvae stage), including dragonflies, mayflies, stoneflies,
caddisflies, beetles, and true flies (e.g., gnats, midges, black flies, horse flies, and crane
flies). For example, mayflies live in the bottom of streams for a year before emerging as
adults to reproduce and die within 2 to 3 days. Although numbers are swiftly declining,
freshwater clams and mussels are important stream organisms. Streams can contain a
wide diversity offish, including minnows, sculpins, perch, trout, bass, and sunfish.
Turtles (reptiles) and frogs (amphibians) are also found living in and near streams. Birds,
such as herons, ducks, and hawks, frequently live along streams. Streams also provide
habitat for mammals such as river otters, raccoons, deer, and beaver.
4.3.2.6 Stream Food Webs. All living organisms need a source of energy (food)
to survive. In general, plants get their energy from the sun and produce their own food.
Animals, on the other hand, get their energy from three different sources. One group of
animals, the herbivores, gets their energy or food from the plants they eat. The second
group of animals, the predators, eats other animals for their food energy. The third group
are the decomposers, who get their energy from plant and animal remains. In stream
systems, aquatic plants utilize sunlight and nutrients absorbed from the surrounding water
and soil to help them grow. The energy found in aquatic plants, and sometimes more
importantly energy from bank-side and upland vegetation (outside inputs), provides food
for aquatic insects and some fish. While some fish and insects use plant material for food,
many others are predators and gain their energy by eating other animals. This concept of
who eats what and whom was originally known as a food chain, but biologists have
realized that it is more complex than a simple chain of events. The interactions between
who eats what is extremely interconnected and is more like a food web than a chain.
4-10
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4-11 "Outside Inputs" are essential to a
stream.
Outside inputs in the form of plant
and plant material falling into the stream
form the base of the stream food web in
headwater streams. The stream's
inhabitants break down this plant material
and process it in a number of ways.
Bacteria and fungi attack this plant
material initiating the decomposition
process by beginning to break down the
plant material, and freeing nutrients for
other organisms within the stream system.
Algae and plankton within the
stream utilize nutrients, fungi and sunlight
to grow. In turn, these plants provide food
for other organisms, such as aquatic insects. Aquatic insects play a very large and
important role in the aquatic food web. These insects are generally in their larvae stage of
development. One group of insect larvae are grazers and wander around grazing and
scraping algae and bacteria growing on the rocks and decomposing plant materials.
Another group are shredders, tearing up and eating leaves and other plant material that
has fallen into the stream. The filtering group strain small particles of suspended debris
from the moving water. And finally, there
are the predators (both larvae and adults)
who eat other insects and small fish.
Fish are also important in the
aquatic food web. Like the insects, fish
have also become adapted to certain diets.
Most stream fishes, like the trout, eat a
variety of aquatic insects, while others,
such as the northern pike, prey upon
smaller fish for their survival. Other types
offish obtain their food from plants,
decomposing material from the stream
bottom, or are parasitic to other fish. All
of this interaction of the various organisms illustrates the complexity of a stream food
web.
4-12 Fish are an important part of the aquatic
food web.
Stream systems also play an essential role in many terrestrial food webs. They
provide vital habitat for creatures to catch food and obtain water. Many important, game
and non-game species are directly dependent on the use of streams and the organisms
within for survival. And we cannot forget that streams play a role in the human food web,
as attested to by many anglers.
4.3.2.7 Outside Inputs. We need to further emphasize the importance of outside
inputs. Upper elevation streams are usually small, steep-sloped, fast moving streams.
4-11
-------
These smaller headwater streams are less dependent upon materials generated within the
stream and more dependent upon the outside source of nutrients and food to support
aquatic life. Overhanging branches and bank-side vegetation serve as their primary
source of nutrients. Leaves, branches, twigs, roots, and fruit fall into and are washed into
the water and, as mentioned previously, become the basis for a food web in the stream.
Thus, these outside inputs become vital to the health of the stream. The overhanging
vegetation along the stream edges also shades the water so algae dependent on sunlight
does not grow and is therefore not readily available as a food source for aquatic life.
Shading also helps to moderate swings in temperature, which is an important benefit
during hot summer days.
Human activities can interfere with
this critical component of the food web by
clearing vegetation from along the stream
banks. Unfortunately, clearing stream
banks has been a traditional form of
stream bank maintenance. This practice
was thought to be beneficial for a number
of reasons, including that it cleared the
floodway, improved drainage, was easy to
maintain, and looked cleaner.
4-13 Clearing stream hanks has many negative
effects on streams.
We now realize, however, that
there are a number of problems associated
with this traditional practice. These clean stream banks in fact shortchange the start of the
food web, starving the entire system. In addition, without the vegetation to shade the
stream, water temperature increases, and native organisms may not be able to tolerate this
increased temperature. Clearing stream banks reduces the number of places for aquatic
organisms to live because there are fewer roots and branches that extend over and into the
stream. The bank side vegetation also helps slow the velocity of surface water and
prevent erosion of the banks into the stream. Finally, without the vegetation along the
stream to dissipate energy, trap sediment and floating branches and debris, this material
can end up collecting and blocking openings of culverts and bridges or other drainage
facilities. We will discuss alternative practices to the traditional stream bank cleaning in
Chapter 6.
This manual focuses predominantly on these headwater types of streams as they
are the most likely streams to interact with dirt and gravel roads. Impacts to these
streams, however, which serve as a source of water, sediments, nutrients and biological
organisms for the stream system, can and will impact the larger downhill streams into
which they run.
4.3.2.8 Stream Habitat. Each plant and animal species needs a certain set of
physical and biological conditions to survive. The area within the stream where these
conditions are present is the organism's habitat. Stream organisms have adapted to these
conditions and subsequently have become dependent upon these habitat conditions for
4-12
-------
survival. If one or more of these factors are missing, then the organisms dependent on
those factors will have a harder time surviving. If the change is too great, the organism
will die.
The suitability of the habitat also influences the abundance of a species.
Abundance is critical because organisms need to be able to find mates to reproduce. If
members of the same species are not abundant, fewer offspring will be produced, starting
a downward population spiral. A decline of a species is significant for two reasons. First,
as a living organism each individual and species has an inherent value. Second, declining
populations of a species may upset delicate food webs by creating shortages for other
species dependent on them for food, creating an imbalance in those populations, further
disrupting the entire stream ecosystem.
4.3.3 Stream Management and Protection Goals. Streams are viewed as a
public natural resource and, as such, are protected under various federal, state, and local
laws and regulations in addition to many state constitutions. This protection covers the
purity (quality) of the water as well as the organisms living in the stream. To this end,
one of the primary goals of managing and protecting streams is to maintain a healthy and
naturally producing fish community. Natural reproduction offish is an important goal,
and fish are dependent upon a clean, healthy stream environment in which to live. The
lack of a naturally reproducing fish community is often an indication that conditions
within the stream have degraded.
4.3.3.1 Indicator Species and Community Composition. Effective stream
systems management requires some kind of indicator to help managers measure
conditions within the stream. Although stream biologists have a wide range of tools and
tests that can be performed to help measure stream health, stream ecology is a complex
science. Stream ecologists have a strong understanding of the processes and interactions
that take place in streams, but there is still much to be learned about these systems.
Biologists have learned that instead of trying to monitor all the conditions that organisms
require to survive, they can monitor the population of certain existing species and the
community composition within the stream environment. These indicator species are
sensitive to changes within the stream system, and if one of their habitat and resource
needs is impacted, then changes in species
abundance will indicate to biologists that
something is wrong within the stream.
Thus, indicator species are analyzed in the
context of the overall abundance of
organisms in assessing the condition of the
aquatic system.
Trout are frequently used as an
indicator species within headwater streams
because, as a top predator, their survival is
dependent upon a broad range of stream
components. Some of the habitat needs of
4-14 Trout is a water quality indicator species.
(Photo courtesy of Trout Unlimited)
4-13
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trout include cool, clean, well-oxygenated water, suitable invertebrate food sources, cover
to hide from other predators and to rest, and spawning sites with gravel beds.
The life cycle of trout is important for their selection as an indicator species. If we
look at the brook trout as a common primary species, these trout use their tails to dig
nests in gravel streambeds in October and November of each year. The eggs are
deposited and then fertilized before they are covered over with loose gravel. These nests
need large amounts of cool, clear water flowing through the gravel as it supplies the eggs
with oxygen dissolved in the water and carries away waste products produced by the
developing eggs, as illustrated in Figure 4-4. This is a critical period for the new trout
population because sediment deposition at this point can smother and kill the entire year-
class offish. If all goes well, these eggs will then hatch in March and April.
[FLOW THRU| NEEDED
Once the eggs
hatch, the trout are initially
called sac-fry because they
carry their first month's
supply of food in an
attached yolk sac. At first,
this yolk sac is quite large
in relation to the size of the
fish, which limits the ability
of the sac-fry to move
about and escape predation.
The yolk sac is gradually
absorbed during the first
month of the fish's life. After the yolk sac has been absorbed, the trout are then called
fingerlings. These fingerlings are increasingly mobile and look for minute particles of
food. Fingerlings will grow as juvenile trout until they reach sexual maturity at about one
to three years of age. Maturity typically corresponds to about 8 inches in length, but
depends on environmental factors such as food supply and stress.
Figure 4-4: Trout eggs need clean flowing water for oxygen
Hatching trout fry are
typically abundant, but because of
the harsh competitive stream
environment, less than one percent
of the hatched fry will live longer
than one year. As will be further
discussed, sediment is one of the
major environmental factors that
decimate the newly hatched young
of the year's trout population. Once
past this one-year milestone, the
death rate of young trout declines
sharply because the older and larger
trout are better equipped to survive.
Trout's Life Cycle
Trout spawn: Oct-Nov
Eggs hatch: Mar-April into
Sac Fry
Newly hatched
Sac Fry are
very immobile
Sac absorbed & fry become
Fingerlings, can now swim
around
4-15 A Trout's Life Cycle
4-14
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If done improperly, the initial grading of dirt and gravel roads in the spring time
with the possible resulting sediment can totally wipe out an entire one year's population
of newly hatched sac-fry trout for a nearby stream.
4-16 The stonefly larva is another indicator
species.
Other useful indicator species of
stream health are the "macroinvertebrates"
such as stoneflies, mayflies, and
caddisflies. Some of the stonefly species
are particularly sensitive to changes in
water quality and methods have been
developed to use these insects to evaluate
stream health. In general, the public is less
aware of the importance of stoneflies and
other macroinvertebrates as indicator
species for a healthy stream because they
are harder to identify and are definitely
less charismatic and less tasty than trout.
4.3.3.2 Stream Evaluation. State environmental agencies routinely monitor
streams to ensure water quality and overall stream health. These agencies conduct
biological and chemical surveys in an attempt to measure habitat conditions and see what
pieces of the food web are present. This generally involves various techniques such as the
use of electro-fishing gear to shock and temporarily stun fish, which are then collected,
identified, measured, weighed, counted, and released. Various methods are used to
collect, count, and identify invertebrates living in the streambed, floating in the water,
and hiding in the vegetation. Data collected from these surveys are then analyzed and
used to make management decisions.
Stream Management &
Protection requires routine
Evaluation Surveys
4-17
4-15
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4-18 Excessive sediment causes distress for the
stream's inhabitants.
4.3.4 Impact of Erosion and Sediment on Streams. Excessive erosion impacts
streams in a number of ways. Many of the physical effects, such as bank erosion and
channel migration, have been discussed in Section 4.3.2. Sediment generated from this
excess erosion, however, critically harms the stream system as will be discussed here.
As we stated earlier, sediment in
stream systems occurs naturally. Although
these natural occurrences can be
devastating, stream channels and stream
life are more adapted to these natural
influxes of sediment and can usually
recover appropriately. It is the excessive
amounts of sediment and selective particle
types and sizes (commonly fine silt and
clay) that end up in stream systems as a
result of human activities that disrupt the
stream ecosystem beyond their ability to
recover. These disruptions can cause the
original habitat to become unsustainable
for the native organisms. These organisms
will either die off or move to more suitable habitat. As the former occupants vacate this
new habitat, new organisms that prefer the altered habitat will take over. The original
nature and character of the stream will have been altered, perhaps changing the stream
from a high-quality trout stream to a less valuable and productive stream polluted with
what sportsmen call "trash" fish.
Timing of sediment and erosion events is not spread evenly over the course of a
year. These events are highly seasonal, with heavy rains and stream flows coinciding
with spring construction and road maintenance activities. This combination of events
leads to a large percentage of the year's total sediment ending up in stream systems
within a short time period during these spring months. During other times of the year,
generally drier weather conditions and better established vegetation that is able to hold
soils in place or filter sediment from runoff, result in less erosion and sediment into the
streams. Although not always practical, shifting human activities (ditch and bank repair)
from the spring to the summer or fall months can significantly reduce the sediment
pollution entering streams.
However, even modest amounts of sediment entering streams during periods of
drought or low-flows may cause problems. During drier periods, many streams are
subject to low-flow conditions, with water only present in the deepest part of the stream
channel. Summer storms can cause flash flooding and sudden influxes of sediment from
disturbed earth into the stream. These floodwaters can quickly recede, leaving water
levels low, with much of the sediment recently being left behind in the deeper parts of the
channel. These sediments remain for longer periods and reduce living space for aquatic
organisms. This can be a real problem because it occurs at a time when water
temperatures and other conditions are also very stressful.
4-16
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4.3.4.1 Suspended Sediment (Turbidity). Earlier in this chapter we talked about
suspended sediment and the fact that fine particles stay suspended for much longer
periods of time than larger particles, and clay can stay suspended for days and weeks in
still water. Once sediment is suspended in
the water, it interferes with the habitat
needs of both plants and animals. For
plants, the sediment particles suspended in
the water increase the turbidity of the
water, blocking light as well as decreasing
the depth to which light penetrates.
Decreasing light, the source of energy for
plants, results in less food production for
plants and less plant growth. With less
plant growth, there is less food available at
the bottom levels of the food web. This
food shortage can cascade through the
food web, resulting in less food for top
predators like the trout.
4-19 Suspended sediment interferes with both
plants and animals within the stream.
Suspended sediment also impacts the aquatic insects and fish directly. Many fish
and insects rely on their vision to detect prey and help avoid predators. As the suspended
sediment decreases the visibility through the water, organisms will find less food and
have a decreased ability to avoid being eaten. Fish and many types of insects breathe
underwater by using gills to gather dissolved oxygen from the water. Gills are sensitive
organs and suspended sediment can clog them, making it harder for the fish to breathe.
Gills are also subject to abrasion from sediment particles. Sediments are particularly
harmful to the relatively immobile sac-fry.
These physical impacts to aquatic
organisms are likely to make it harder for
the individuals to find food, eat, and grow
normally. With abnormal growth,
organisms do not have the energy to fight
off disease or to reproduce.
•
4.3.4.2 Sedimentation
(Embeddedness). As water velocities slow
within the stream environment,
sedimentation occurs. The primary impact
of excess sediment in the channel is the
altering of habitat. The sediment settles
down into the nooks and crannies between
the gravel and rock substrate. Insects and
small fish need these spaces to graze algae,
hide from predators, hunt prey, and as
shelter from the faster flowing currents
above. Filling in these spaces with
4-20 Embeddedness refers to the sediment
filling in all the nooks and crannies in the
streambed.
4-17
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4-21 Contaminants attached to sediment
particles further degrades water quality.
sediment reduces the amount of living
space available. Some plants and animals
may also be buried and suffocate.
Sedimentation is particularly harmful to
trout reproduction because it kills the eggs
while they are incubating in the gravel
nests over the winter months.
This filling in of the nooks and
crannies in a gravel streambed by
sediment is referred to as embeddedness.
A typical trout stream is usually about
30% embedded, while one that is
completely buried by sediment would be
described as being 100% embedded.
4.3.4.3 Attached Contaminants: Another impact of sediment on streams stems
from the materials such as road salt, fertilizers, pesticides, oils, greases, and other toxic
compounds that are often attached to the sediment particles. Once in the water, these
attached compounds may degrade water quality.
4.3.5
Fish Constituency: Fish, unlike many other organisms in the stream
environment, are unique in that they have
advocates who represent them - the sport
fishermen. Angler groups have organized at
the local, state, and national levels, where
they effectively lobby for government
action. These groups, such as Trout
Unlimited and B.A.S.S. (Bass Angler
Sportsmen's Society), act as watchdogs to
protect their fishing interests and aquatic
resources. These groups can be a source of
positive support for local governments or
can make life difficult if inappropriate
actions threaten our aquatic resources.
4-22 Anglers are avid fish advocates and can
be a positive resource.
Anglers, however, do not always
have a positive impact on the stream
ecosystem. In their efforts to pursue their
interests, they frequently create and use stream access points, footpaths, and car pull-offs.
These places can often become a source of erosion and sediment or even interfere with
erosion control measures that local governments have already put in place.
4-18
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Just as when dealing with any group of stakeholders, whether they are
landowners, businesses, environmental groups, or
angler organizations, the most effective approach is to
collaborate, or work together. Collaboration between
local governments and angler groups offers tremendous
potential. If these stakeholders are included in the
decision-making processes, they may be able to add
constructive and helpful suggestions, provide resources
to aid projects in the form of funds, materials or people,
and positively influence other groups, agencies or
elected officials as needed. Many of these groups have
vast volunteer resources that can be tapped for
construction and maintenance projects. It is also an
additional opportunity for the community to become
more knowledgeable about road maintenance concerns,
activities and budgetary limitations.
4.3.6 Stream Ecosystem Summary. Streams
are an important natural resource. Stream communities
are dependent upon the types of physical and biological
habitat present within the stream system. Stream flows
and water quality conditions shape this habitat and are
strongly influenced by both the watershed's underlying
geology and land use. Trout and macroinvertebrates,
such as stoneflies, are considered good indicators of the
4-23 Anglers can also have negative effects
on stream ecology as stream access points,
car pull-offs, and footpaths become
erosion sources.
health and quality of our headwater streams, as they are sensitive species dependent upon
a number of factors that are likely to be impacted by adverse conditions within the stream
system. Human activities, such as road maintenance, construction, logging, agriculture,
development, and industry, can threaten the health of our streams and the organisms that
live there. Excessive erosion and sediment from dirt and gravel roads is one of the
primary threats to our streams, altering the entire stream ecosystem. Collaboration with
stakeholders, such as anglers, farmers, and landowners, can help alleviate some of the
problems and benefit local government in a variety of ways, especially in helping in the
planning, construction, and maintenance of environmentally sensitive practices and
projects.
4.4 The Wetland Ecosystem
(Community)
4.4.1 Introduction: The wetland
ecosystem or community is an important
one, with wetlands currently covering over
one hundred million acres of land in the
lower 48 states. Although the word
"wetland" seems to conjure up visions of
wasteland swamps inhabited by undesirable
4-24 Wetlands are important ecosystems.
4-19
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creatures or fears of stifling regulations, wetlands provide valuable services and functions
that are beneficial to both humans and the environment. This section will define and
describe wetlands, discuss the history of management, regulations and wetland loss,
introduce the valuable benefits derived from wetlands, and help road managers recognize
wetland areas in order to avoid conflicts with existing regulations.
4.4.2 Definition of a Wetland: Under the Federal Clean Water Act, a wetland is
defined as "those areas that are inundated or saturated by surface or ground water at a
frequency and duration sufficient to support, and that under normal circumstances do
support, a prevalence of vegetation typically adapted for life in saturated soil conditions."
Simply put, a wetland
is an area that meets a certain
set of soil, plant, and
moisture requirements. So
there are three basic
characteristics common to all
wetlands:
a) For at least part of the
year, water must be
present at or near the
ground's surface.
b) Plants must be
adapted for wet soil
conditions.
c) Soil types must have
developed under
saturated conditions.
Wetlands are often the transitional area between the deep water and the uplands
and can include permanently flooded areas to periodically flooded areas to permanently
saturated areas to periodically saturated areas, as depicted in Figure 4-5.
4.4.3 Wetland Basics. A number of environmental factors affect these three
wetland characteristics. For example, the amount of water found within a wetland can be
influenced by either surface water or groundwater. The source of water plays an
important role in providing outside nutrients to wetland systems. The underlying geology
and topography of the landscape can influence the location and formation of wetlands.
Geology also dictates the rock types that serve as parent material for the initial wetland
soils. These mineral soils, however, are often buried under thick layers of organic peat
and muck common to many types of wetlands. These moisture and soil factors, in
addition to climate characteristics, directly influence the types of vegetation that are
present within the wetland. The water in a wetland is directly responsible for forming the
hydric soils.
Deep Water -
Lakes & Streams
Per looi cally
Saturated (near
Upland
4-20
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A hydric soil forms when soil is saturated with water for extended time periods.
There are a number of biological and chemical processes that take place in soil that
influence its formation and the types of plants that it is able to support. In drier soils,
oxygen is typically abundant and leads to the formation of upland soils. When soils are
saturated, however, natural processes deplete oxygen from the soil and produce very
different wetland soils. Many wetland soils also have a much higher percentage of
organic matter (decaying plant and animal life, etc.) than do upland soils, a factor that
greatly increases the availability of nutrients and food for many wetland plants and
animals. These hydric soils also have visible characteristics making them readily
identifiable. Hydric soils mark wetlands: recognize the soil and you identify a wetland.
The details of wetland recognition will be discussed later.
Wetland plants are those plants that have adapted to life under wet conditions.
These plants have taken on a wide range of forms, from pond lilies to trees, in order to
take advantage of the many different types of wet habitat. The major difference between
these wet habitats is the variation in the amount or depth of water, which changes along
an elevation and moisture gradient. For example, pond lilies can only grow in three to
four feet of water, while red maples only tolerate periodic saturation. The moisture
conditions within each of these habitats fluctuate according to seasons and weather
patterns from year to year, with some locations wetter during the winter and spring
months than during the warmer months. This variation in moisture or water levels is
important because many of the wetland plants, especially grasses and herbs, require drier
periods to produce seeds and germinate. Additionally, just as with stream systems, the
variability of conditions within each habitat helps maintain a broader mix (diversity) of
plant and animal species.
The presence of wetlands is dependent upon a delicate balance between the right
soil, water, and vegetation characteristics. While natural variation within a wetland is
normal and desirable, human induced disturbances can disrupt wetlands beyond their
ability to recover. Human activities near wetlands may alter the flow of water into and
out of wetlands, and/or lead to excessive inputs of sediment nutrients, and chemicals.
Care should be taken while conducting road construction and maintenance activities to
prevent both short- and long-term impacts to these delicate ecosystems. It is important to
note that wetland ecosystems are protected by stringent state and federal laws that restrict
activities in and around these areas, as will be discussed in Subsection 4.4.4.2.
4.4.4 Wetland Management. Historically, as mentioned, wetland areas have
received a bad reputation as dismal, disease-ridden, unproductive wastelands. As early as
the Swamp Land Act of 1849, Congress encouraged draining and filling wetlands for
development. Since then, in the name of progress, amazing efforts were put forth to drain
and fill vast marshes and swamps to give these lands a purpose. These former wetlands
were converted for residential, agricultural, and industrial uses.
These negative attitudes towards wetlands, however, have begun to change over
the last several decades. We now realize that wetlands provide many physical,
mechanical, and biological benefits that are useful not only to the natural environment,
4-21
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but to humans as well. Consequently, we have begun to protect wetlands and even
replace some of the ones that have been lost to development. So the management of
wetlands has come full circle over the last century. Undisturbed wetlands are now viewed
as very productive, valuable natural resources for many reasons as will be reviewed in
Subsection 4.4.5.
4.4.4.1 Wetland Loss.
Over half of our original wetlands
in the United States have been
drained and converted to other
uses. Major wetland losses
occurred from the mid 1950s to the
mid 1970s, with the rate of loss
decreasing since then. Various
factors have contributed toward
this decline in wetland loss
including the adoption of wetland
protection laws and regulations.
"Public education and outreach
about the value and functions of wetlands, private land initiatives, coastal monitoring and
protection programs, and wetland restoration and creation actions have also helped
reduce overall wetland losses," according to the U.S. Environmental Protection Agency.
We now understand that wetlands provide many beneficial services and host the
most productive habitats on earth. Wetlands, however, can be harmed by many different
human activities including draining, dredging, stream channelization, filling, diking and
damming, logging, mining, tilling for crops, and miscellaneous pollution discharges. The
conversion of wetlands for development and agricultural purposes has probably resulted
in the largest loss of wetlands. The loss of wetlands results in a loss of all the benefits
derived from them. And all wetlands are important, no matter what size, location, or
quality.
4.4.4.2 Regulatory Protection. The regulatory protection of wetlands began early
in the 1900s when people began to recognize their value as breeding and fishing habitat
for waterfowl. One of the early protection measures was the establishment of many
National Wildlife Refuges in which wetland habitat was protected and enhanced for
waterfowl and other water birds. During the years since this initial recognition of the
wildlife value of wetlands, scientists, policy makers, and the public have also realized
that wetlands provide society with many other benefits.
In the 1960s and 1970s, both the federal and state governments began to enact
laws that protected wetlands. There are a number of federal agencies that work to protect
our wetland resources, including the Army Corp of Engineers, the U.S. Environmental
Protection Agency, the U.S. Fish and Wildlife Service, the U.S. D.A. Natural Resources
Conservation Service, along with the corresponding state and local agencies. This list of
agencies represents a broad spectrum of program areas, ranging from navigation to water
4-22
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quality and from wildlife management to soil conservation. This spectrum thus represents
the complex array of issues associated with the protection of wetlands and each agency is
responsible for portions of our federal and states wetland regulations.
The regulatory environment at the time these wetland laws were enacted utilized
the permitting process as a major tool to protect wetlands. This system of permits remains
in place today. The permitting process is not intended to stop work activities; rather, it is
designed to help people learn about wetland benefits as well as methods to lessen the
impact of their activities on these important natural resources. In essence, permits are
agreements between regulatory agencies and applicants governing work activities in and
near wetland areas and outline necessary protection measures. Permits limit the loss of
wetland area and help protect existing wetlands from excessive erosion and
sedimentation, disruption of wetland hydrology, and pollution from sources such as mine
acid drainage, toxic substances, and nutrient runoff. When necessary, permits also
provide regulatory agencies with a basis for levying fines and forcing remedial action
against those who have failed to live up to the permit's terms.
These regulatory agencies also have procedures for dealing with people who
either intentionally or unintentionally harm these valuable natural resources. Local
governments and road managers cannot afford to be ignorant about the value of these
resources, since ignorance is not a defense against the penalties that may be imposed. The
replacement, or mitigation, of wetlands is an expensive prospect, with engineering, land
purchases, construction, and operational costs reaching into many thousands of dollars
per acre.
Wetlands are also protected by many private groups. Conservation groups acquire
land and provide education and volunteers at local, state, and national levels. Several
major conservation organizations include The Nature Conservancy, Ducks Unlimited, the
National Audubon Society, and the National Wildlife Federation. While these groups do
not have the authority to develop their own regulations, they are considered "watchdog"
groups and actively advise regulatory agencies of possible violations. Many of these
groups also purchase property to protect and preserve sensitive habitat and /or species.
Litigation is likely to be a possible response in a case where one of these properties is
threatened by off-site sources of disturbance.
4.4.5 Wetland Benefits. Many valuable benefits are associated with wetlands. It
is important, therefore, to become familiar with these benefits so that we can take a
common sense approach when dealing with roads and wetlands. The following
subsections describe the major benefits derived from our wetlands.
4-23
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4.4.5.1 Floodwater
Storage. A significant wetland
benefit is the role that they play in
floodwater storage. Since many
wetlands form in low-lying areas,
they are often the first areas to
receive water when surface water
runoff fills the streams to overflow
their banks. The vegetation in
these wetland areas slows the
movement of the floodwaters,
which are temporarily adsorbed, or
held back, by the wetland. The
wetland acts like a sponge, holding
the excess storm water. As time
passes, water is slowly released
4-25 Wetland Hood
storage, a definite
benefit
Higher flood &
higher flows
With Wetlands
Lower flood crest '••-...
& lower flows
•-.No Wetlands
•a.
•s
Time
Figure 4-7 Hydrograph
from its temporary storage within the
wetland and drains either into the
ground to become groundwater or
back into the stream network. An
engineer's "hydrograph" shown in
Figure 4-7, which depicts the amount
of flow during a storm time period,
illustrates the flood storage benefit of
wetlands. The wetlands spread out
the flow of water into the stream over
a longer period, decreasing flood
flows and the peak flood flow that
would occur without the wetland.
Thus, with less water to overwhelm
the stream channel, the height of
floodwaters and the area flooded will
be reduced.
The Charles River in Massachusetts serves as a good example of the beneficial
use of wetlands for floodwater storage. The Charles River watershed has approximately
8,400 acres (13 square miles) of wetlands located in the river's floodplain. The lower
portion of the river flows right through Boston, posing a serious flood threat to the city.
In the early 1970's, the U.S. Army corps of Engineers studied flood control options to
protect Boston. The Corps found that the wetlands were so effective at storing floodwater
that the best flood protection option was to purchase the floodplain wetlands instead of
building structural flood controls, such as levees and detention basins, saving millions of
dollars in construction over and above the purchase of the wetlands.
Wetland preservation can thus provide a level of flood control which would
otherwise have to be provided by expensive structural facilities and/or dredging
4-24
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operations. As another example, the bottomland hardwood-riparian wetlands along the
Mississippi River once stored at least 60 days of floodwater, but, because of wetland loss
due to filling and draining, they now only store 12 days' worth. (U.S. EPA)
4.4.5.2 Bank Stabilization
(Shoreline Protection). Wetland
plants typically help stabilize
stream banks and shorelines. Both
emergent plants, which grow up
out of the water, and woody
wetland vegetation have a complex
root system that helps hold the
plants in place in the soft, wet
soils. This extensive root structure
also helps to keep the soils in
place. In areas where shoreline
vegetation has been removed,
water currents can swiftly erode
the exposed soils. Once eroded,
fe*
4-26 Bank stabilization/ shoreline protection - another
wetland benefit.
these soils can significantly impact
stream systems, as discussed in the
previous section on The Stream
Ecosystem.
4.4.5.3 Energy Dissipation.
Wetland vegetation also helps reduce
erosion by providing resistance to
moving water currents and waves. The
vegetation slows the flow of water as it is
spread out over the wetland and
dissipates its energy. Although vegetation
is not able to stop all of the erosion
associated with water currents, it can
drastically reduce the impact by reducing
the velocity of the water by up to 90%.
4-27 Sediment study being conducted in a
wetland.
4.4.5.4 Sediment Trapping.
Many wetlands, especially those
located along the edges of rivers and
streams, act as natural sediment traps.
As the water slows from spreading
out over the wetlands and meeting the
flow resistance of vegetation, the flow
energy becomes insufficient to carry
the suspended sediment and the
larger and heavier particles begin to
4-28 Do NOT use wetlands as sediment traps!
4-25
-------
settle out. The accumulation of sediment within wetlands is a naturally occurring process,
and each wetland has its own sedimentation rate. For, example, one particular wetland
may have two inches of sediment deposited each year, while another wetland may
typically receive only a quarter of that amount. Studies are conducted to determine the
amount of sediment received by wetlands.
This natural sediment trapping wetland function does not mean that wetlands
should be used as sediment collection basins. Human activities can seriously increase the
natural sedimentation rate and when wetlands fill in, many of the associated benefits are
lost.
4.4.5.5 Water Quality Improvement. Wetlands play an important role in
improving and maintaining water quality. As mentioned previously, vegetation helps to
filter sediments from the water, making the water cleaner and better able to transmit light
to underwater plants. These sediments are often nutrient rich, which supports the growth
of wetland plants. Materials dissolved in the water also provide a source of nutrients for
wetland plants, as well as microorganisms within the soil.
Unfortunately, just as with stream systems, the water quality associated with
wetlands is frequently harmed by excess nutrients and chemicals from agricultural and
urban runoff and other human activities. These compounds can be dissolved in the runoff
or attached to the sediment particles in the runoff. Many of these compounds are filtered
from the water by wetlands plants and are even transformed from toxic compounds into
harmless compounds. Many wetlands, however, must still process the materials that
naturally end up within their boundaries, and excessive materials coming from human
sources can easily overwhelm a wetland's ability to improve the water quality.
Wetlands also serve as "riparian
buffers" for streams and rivers. The term
riparian refers to the portion of the
landscape that is located immediately
beside the stream or river, while the term
buffer refers to a type of filter or barrier.
Simply stated, a riparian buffer is any strip
of vegetation left intact along a stream or
river that can filter out excess sediment
nutrients and chemicals from runoff
before the runoff enters the stream.
It is important to note that not all
riparian buffers are wetlands because
buffers can be constructed in upland areas
and contain non-wetland plants. One type of buffer, vegetated filter strips, will be
covered in Chapter 5.
4-29 Wetlands serve as "riparian buffers'
4-26
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4.4.5.6 Ecological Benefits. Wetlands possess a unique combination of physical
and chemical conditions that
provide ideal habitat for a diverse
mix of plants and animals. Many of
these wetland organisms have
adapted to the unique conditions
within wetlands: and if the wetlands
are lost, then so are the dependent
species that may not be able to
survive in any other type of habitat.
More than one third of the
threatened and endangered species
in the United States live only in
wetlands. Additionally, many other
animals and plants depend on
wetlands for survival.
4-30 Wetlands provide vital habitat for a diverse mix of
plants, including threatened and endangered species.
Wetlands offer numerous habitat benefits to insects, amphibians, fish, and birds
alike. The thick wetland vegetation provides shelter from the elements as well as cover to
hide from predators. Wetlands provide habitat for reproduction and developing young for
many different terrestrial and aquatic species. The plant material within the wetland also
serves as building material for nests and other types of homes. Wetlands provide required
habitat for one third of the resident bird population in the United States. Wetlands
provide vital habitat for amphibians such as frogs and salamanders, particularly the small
forested wetlands, which
are only wet during the
spring months.
Wetlands also play
an important role in the
food web. Wetland
vegetation serves as a
source of plant material that
is eaten by insects, fish,
birds, and mammals. These
animals, in turn, provide
food for the predators.
When wetland plants and
animals die, their remains
break down and decompose, where their nutrients replenish the wetland soils and provide
nourishment for additional plant growth.
4 31 Wetlands provide Wildlife Habitat: Fish, amphibians, birds, animals. 1/3
U.S. resident bird species dependent on wetlands, especially important for
waterfowl.
4-27
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4.4.5.7 Economic and Social Benefits. Many of the plant and wildlife species
that utilize wetlands are
economically valuable.
Wetlands are home for
many commercially
important plant species,
such as blueberries and
cranberries. Bass and other
game fish grow and hunt
among the wetland
vegetation, which also
provides critical nesting
habitat for most of our
waterfowl.
Wetlands
provide
many
social and
economic
benefits
•Education
•Recreation
•Bird Watching
•Hunting
•Fishing
•Photography
•Painting
Groups such as
Ducks Unlimited were
among the first to
recognize the importance of
wetland habitat to ducks and geese. Because of this group's efforts, many thousands of
wetlands acres have been protected and restored.
One of the most important benefits of wetland habitat is their use by migratory
species. Migratory animals, such as fish, waterfowl and other birds, and insects, use
wetlands as places to temporarily rest and replenish food reserves on their long journeys.
Many of the wetlands used by migratory animals are relatively small in size, but not in
their importance to serve as sanctuaries in our increasingly developed landscape. Because
many of these wetland sanctuaries are not large or easily identified, there is a danger that
little patches of wetlands will be lost as a result of road maintenance practices and
decisions.
Wetlands provide a number of social benefits and opportunities to those who live
in and near communities with wetlands. These benefits are largely social in nature,
however; just as with stream systems, many of these social benefits also help to support
local economies. These economic benefits stem, either directly through creating demand
for education or recreation related jobs and services, or indirectly through related
spending for gas, lodging, and meals.
Wetlands provide great locations to educate children and adults on a number of
different topics. Wetlands provide space that can be used as outdoor classrooms for
teaching biology, ecology, natural history, photography, bird watching, painting, arts and
crafts, hunting, fishing, trapping, and many other topics and activities.
4-28
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4.4.6 Types of Wetlands.
There are several systems for
classifying wetland types, and each
has its own merits. For our
purposes, and ease of recognition
in the field, we will discuss a
system that divides wetlands into
three different categories or types.
These three types are classified
based upon where they are located
in the landscape and are more
closely associated with the road
environments in the forested areas
that are the focus of this manual.
Some wetlands form in
depressions, some form on slopes,
while others form along
floodplains.
Figure 4-8: Depression Wetland
Depression wetlands form
in low lying, bowl-shaped areas. Water enters these wetlands from surface water sources
and sometimes ground water sources as
well. Figure 4-8 illustrates that these
wetlands can have a permanent pool, but
in many cases will have various
fluctuating water levels depending on
precipitation and actually become dry on
the surface in times of little or no
precipitation. Typically, these wetlands do
not have streams or other obvious exits, so
water in these wetlands must exit either by
evaporation, plant uptake, or by draining
4-33 Depression Wetland (Vernal Pool)
into the soil. In forested areas, these "vernal
pools" are a prime habitat for a diverse
population of amphibians.
Wetlands that form in these depressions
are often the most vulnerable to sedimentation
caused by human activities because it is
difficult for the sediment to be flushed out of
the depression. When excessive sediments
Figure 4-9: Slope Wetland
4-29
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accumulate in these depressions, it buries plants and animals and can quickly fill in the
entire wetland area. This can cause the moisture and soil conditions to change, forcing the
plant community to rapidly transition to a more upland mix of species. The wetland
plants are then lost along with the wetland and associated benefits.
Sloped wetlands are those wetlands that form on the side of hills and gentle
grades. These wetlands typically develop on
slopes that have about a 3% grade. This is a
common type of wetland found in forested
areas where the ground water emerges at the
surface of a slope to supply the wetland, as
shown in Figure 4-9. Streams may also enter
and leave these wetlands and carry excess
sediments during periods of high flows out
of the wetland area to locations downhill
and downstream. Although still vulnerable
to impacts from excess sediment this ability
to remove sediments means that these
wetlands are less vulnerable to filling than
depression-type wetlands.
„. . . . Ai 1 c 11 4-34 Slope (Seepage) Wetland
Floodplam wetlands are round along
the fringes of lakes, rivers, and streams.
This wetland type includes vegetation
that is commonly submerged by
water, as well as vegetation that is
temporarily covered with water
during periods of high water. This is
the most easily recognized and
common type of wetland in most
areas, as depicted in Figure 4-10.
Fluctuating water levels brought
about by periodic flooding are critical
to the continued survival of these
wetlands. Flooding generally occurs
during spring months; however, these
wetlands can be either dry during
much of the year or fairly wet.
Sometimes floodplain wetlands also
receive water from groundwater
sources, and these wetlands tend to be
wetter over longer periods. Although
all wetlands can be impacted by
excessive sediment, sediment and
other pollutants in floodplain, wetlands are often only temporarily stored until the next
storm event flushes them out.
Figure 4-10: Floodplain (Riverine) Wetland
4-30
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4-35 Floodplain (Riverine) Wetland
4.4.7. Wetlands and Road
Maintenance. Now that we have discussed
the major benefits and regulatory issues
regarding wetlands, it is important to provide
some tools to help road personnel recognize
wetland areas and provide guidance on what
to do when these sensitive areas are
encountered during road maintenance
activities.
4.4.7.1 Recognizing Wetland Areas.
When you hear the word wetland, an image
of a marsh with cattails might come to mind.
Wetlands, however, are not created equally
and they vary in size, shape, position in
landscape, amount of water present, mix of
plants and animals, appearance, and benefits.
While cattail marshes are one kind of
wetland, there are many other kinds. Many of
the wetlands in forested areas are referred to
as forested or shrub wetlands. Although there
are a variety of wetland types, several
relatively easy clues are available to aid in
their identification. These clues are based
upon the three criteria for wetlands
previously discussed: hydrology (drainage),
soils, and vegetation. These clues can be used
to help road managers know which portions
of their jurisdiction might contain wetlands,
as well as identify specific areas that
regulatory agencies consider wetlands.
4-36 Wetland Indicators
4.4.7.2 Wetland Characteristics:
Although each of the wetland types
discussed previously is different, they share
similar characteristics. Based on the
regulatory definition of wetlands
previously discussed, each wetland must be
wet during part of the year, must have soils
that are saturated with water, and contain
4-37 Wetland Indicators
4-31
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plants that are adapted to wet
conditions. These factors - hydrology,
soils, and vegetation - provide
characteristics and clues that we can
recognize while we are in the field.
Although the presence of
standing or flowing water is an
obvious indicator of a wetland, many
wetlands are only wet during part of
the year. There are, however, telltale
signs that water has been there. High
water leaves silt lines on tree trunks,
4-38 Wetland Indicators
similar to a ring around a dirty
bathtub. These high water marks are
a good indicator that you may have
a wetland. Fine sediment particles
suspended in water frequently settle
and are deposited on vegetation,
leaving silt-covered or silt-stained
leaves, another wetland indicator.
When water flows through
wetlands, especially floodplain
wetlands, floating debris tends to
4-39 Wetland Indicators
pile up against trees and rocks, forming wrack
lines. These wrack lines indicate water once
covered this area and again cold indicate a
wetland.
4-41 Wetland Indicators
4-40 Wetland Indicators
The roots of trees and plants
living in the area provide another clue.
Many wetland plants have shallow
roots because the roots need oxygen.
Soils that are saturated by a high water
table do not supply this much-needed
oxygen, so the roots remain closer to or
4-32
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4-42 Wetland Indicators
at the surface to get the oxygen they need.
Wet soils are also very soft and do not
provide much support for large trees. Some
wetland trees thereby adapt by developing
large bases or buttressed trunks and root
systems that provide better support. These
buttressed trunks indicate soft, saturated
soils that may be a wetland.
The second characteristic of
wetlands is saturated soils. Interesting
things happen to soils when they become
saturated with water. Saturation causes
oxygen levels to become depleted, resulting in changes to the soil's normal chemical
reactions. In submerged or very saturated conditions, the decomposition of dead
vegetation is practically halted because there is little oxygen available to support
decomposing organisms and reactions. Without decomposition, partially decomposed
plant material accumulates into thick layers of organic soils called peat. This peat is
similar to the peat that is dried and sold in stores for use in our gardens. Other wetland
soils do not have as much organic matter present and consist mainly of mineral soils
derived from parent material. These saturated mineral soils are referred to as hydric soils
and sometimes produce gleyed soils that are greenish or blue-gray in color. If these
mineral soils form in a seasonal wetland, where the area is alternately wet and dry, metals
such as iron and manganese react with oxygen to form oxides (rust) and becomes a
mottled soil with orange/reddish brown or dark reddish brown/ black spots in the
otherwise gray or greenish gleyed soils. The familiar rather unpleasant rotten egg odor
that is sometimes given off by wetlands is caused by the release of hydrogen sulfide gas
when wetland soils and sediments are disturbed.
4-43 Wetland Indicators: Common Wetland Plants
4-44 Wetland Indicators: Common Wetland Plants
The third wetland characteristic is the vegetation. Most plants cannot tolerate the
wet conditions within wetlands. Some species, however, have adapted to wet habitats.
These water-loving wetland plants are referred to as hydrophytes and based on their
tolerance for standing water can be further lumped into three groups:
4-33
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1. Those that are dependent
upon permanent water for their
survival such as cattails, water lilies,
skunk cabbage, buttonbush, and
arrowhead. This group includes those
plants that most of us would associate
with wetlands.
2. Those that can live in
standing water but prefer moist soils
such as black ash, cinnamon fern, joe-
pye weed, jewel weed, cardinal
flower, pin oak, and pussy willow.
4-45 Common Wetland Indicator Plants
3. Those that do best in moist to somewhat dry soils such as red maple, catalpa,
slippery elm, and arrowwood viburnum.
Wetland scientists
and regulatory personnel use
this differentiation of plants
to identify and map wetland
areas.
It is important to
note that not all wetland
plants are beneficial. The
invasion of purple
loosestrife is an example.
Just as we are gaining an
appreciation for the qualities
and benefits provided by
wetlands, a terrible foreign
invasive plant is destroying
our wetlands. Purple
loosestrife is a wetland plant
with pretty purple flowers
that was imported from
Europe and Asia. This plant spreads rapidly and, when established, completely out-
competes and takes over the wetland within a year. This invasive species became a real
problem in New England and quickly spread south and west into many other states.
4-46 Less Known Wetland Indicator Plants
4-34
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4^47 Purple Loosestrife
Aggressive,
invasive
species
Purple loosestrife
establishes dense,
impenetrable stands that are
unsuitable as cover, feed, or
nesting sites for many
wetland animals, including
ducks, geese, rails, bitterns,
muskrats, frogs, toads and
turtles. It also drives out
endangered and rare plant
species. Purple loosestrife
frequently establishes on
moist soils that are disturbed
by construction activities.
Once established, it is very
difficult to remove because
each plant can dispense 2 million seeds per year. The plant is also able to resprout from
roots and broken stems that fall onto the ground or into water. Mowing purple loosestrife
often makes the problem worse because it spreads the seeds and scatters bits of plants,
which resprout.
4.4.7.3 Encountering Wetlands. Because many of our roads were built along
streams and through low-lying areas, it is very likely that wetlands will be a concern for
many road managers. It is probably
not a question of "if' you
encounter wetlands in your work
but "when" you encounter
wetlands.
competes
native plant
species
; Listed on many states'
Noxious Weed Lists
Useless to
wildlife
4-48 Mandate by Federal Government
As mentioned, there are
federal and state laws and
regulations governing the
protection of wetlands. In many
cases, compliance with these laws
requires biological and engineering
studies and permits with any
encroachment onto a wetland. If
roadwork interferes with a
wetland, the result can be major costs, delays, and potentials for litigation.
A real opportunity exists, however, for local road officials in the realm of wetland
regulation. Currently routine maintenance work is usually not a point of enforcement
emphasis and, to some degree, permits are waived for such routine items as ditch
cleaning. The opportunity is for local road officials to take the information presented here
to heart and through their daily maintenance activities prove that no further regulation or
increased enforcement is needed in this area. While these opportunities exist, it is critical
4-35
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to remember the possibility of severe penalties for those that do not follow these wetland
protection rules.
4.4.7.4 Wetland Strategy
We hope that a strategy of "avoid,
minimize, and mitigate" will help
road managers as they attempt to
work through encounters with
wetlands. This strategy involves, in
order, avoiding impacts to
wetlands wherever possible,
minimizing those impacts that
cannot be avoided, and mitigating
damages where they occur.
Avoid. The ideal way to
deal with wetlands is to identify
Wetland Strategy:
> Avoid
jfc" Minimize
Mitigate
4-49 Adopt a Wetland Strategy
them in advance and then plan
improvements and maintenance
activities that will avoid impacting
these sensitive areas. Traditionally we probably would have drained a whole hillside into
a single culvert that discharges water directly into a wetland or stream, dumping more
water, sediment road fines, and chemicals into a wetland than it is capable of handling.
Using a combination of the tools presented in this manual, however, we can avoid
discharging these excesses into wetlands. For example, stabilizing banks, maintaining
vegetated ditches, and installing turnouts and broad-based dips at frequent intervals could
prevent significant amounts of sediment and quantities of water from accumulating and
carrying material into the wetland. Many tools or practices will be described in
subsequent chapters.
Minimize. We recognize the fact that it is not always feasible to avoid impacting
wetlands near our roads. In these instances, it is best to minimize those impacts as much
as possible. Continuing with the hillside and single culvert illustration used in our
discussion of avoiding impacts, we can use a combination of tools to minimize disruption
and damages to wetlands. We can set the culvert discharge back from the lowest point
and divert water through a vegetated filter strip of grass or other vegetation, thereby
trapping excess sediment before it gets to the wetland. Sediment traps can also be used in
place of filter strips, but they need to be inspected and cleaned out on a routine basis.
Although only temporary, practices such as the use of silt fences can also provide
significant short-term benefits. Straw bale barriers have also been used, but their
effectiveness is questionable and are not recommended by the U.S. Environmental
Protection Agency. These materials should only be used for short-term activities and
must be maintained and cleaned out regularly until the work site is stabilized. These
practices and proper use will also be described in more detail in Chapter 5.
4-36
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Mitigate. Mitigation involves the creation of artificial wetlands in order to replace
the lost function and habitat of a natural wetland. This is often an expensive prospect and
should only be used as a last resort when avoidance and minimization techniques are
insufficient to prevent the destruction of an existing wetland. The biological and
engineering studies and design and required permits, along with site acquisition and
actual construction, all lend to the extreme costs and time required for mitigation
projects. Given the scale and scope of the projects that are likely to be carried out under
maintenance activities, it is unlikely that mitigation will be a necessary and/or a viable
option.
4.4.7.5 Working with Regulatory Agencies. This section on wetlands is not
intended to turn road experts into wetland experts. Rather, its intent is to provide
background information on wetlands and help road managers recognize the importance
and value of these sensitive habitats. Using the clues discussed above, road managers
should be able to recognize areas that might be considered as wetlands. When these
potential wetlands are encountered during road maintenance activities, it is highly
recommended that local governments contact their local county or state agencies for
further guidance on appropriate actions. Local county conservation agencies are familiar
with the local conditions and they are familiar with state and federal environmental
regulations and agencies, and will be able to help you directly or help you direct inquiries
to the appropriate agency.
4.4.8 Wetland Ecosystem Summary. Wetlands are an important natural resource
located between full aquatic and upland environments. For an area to be considered a
wetland, it must be saturated with water at least part of the year, have soils that have
developed under saturated conditions, and contain plants that are adapted to those wet
conditions. Many different types of landscape features meet these conditions, of which
three were discussed - depression wetlands, slope wetlands, and floodplain wetlands.
Most of these areas are relatively easy to recognize using the hydrology (drainage), soils
and vegetation clues as potential indicators for a wetland area.
Wetlands benefit natural systems by providing habitat for fish and wildlife and
supporting the food web. They also provide important benefits in terms of floodwater
storage, bank and shoreline stabilization, sediment trapping, water quality improvements,
and opportunities for education and recreation activities. Linked to many of these values
are economic benefits as well. Unfortunately, we have been slow to recognize all these
benefits and have lost over 50% of our wetlands. Our federal, state, and local
environmental regulatory agencies have reacted to this loss and enacted strict measures to
protect the remaining wetlands and the benefits they provide. Road managers are advised
to adopt a strategy of avoiding wetlands or minimizing the impact and using mitigation
only as a last resort as they encounter wetlands in their road maintenance activities.
4-37
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4.5 The Upland / Forest Ecosystem (Community)
4.5.1 Introduction. As the third
ecosystem or community , the uplands
present drier conditions and different
challenges for road managers. In upland
areas, nature's purposes may conflict with
road maintenance just as they do in stream
and wetland areas. Because significant
portions of local government budgets are
spent maintaining roadside vegetation,
road managers need a more complete
understanding of plants. A better
understanding of the natural reaction
4-50 Uplands produce different challenges for plants have toward outside impacts such
road managers. as their reaction to injury can help road
managers develop a strategy to deal with vegetation that takes advantage of nature and
natural systems instead of trying to overpower these forces. Trying to overpower nature is
unrealistic, costly, and temporary at best.
4.5.2 Plant Basics. In order to effectively manage roadside plants, it is important
to understand some basic information including the way plants grow, their life cycles,
root structures, and general plant ecology.
4.5.2.1 Plant Growth and
Photosynthesis. Unlike animals, which
gather energy by eating other plants and
animals, plants are able to produce their
own food through a complex process
called "photosynthesis." If we can recall
from the high school science class where
we were introduced to this "big word,"
photosynthesis is the process by which
plants convert sunlight, carbon dioxide
from the atmosphere, water, and
nutrients into sugars. Plants then use
these sugars as food, and extra sugar is
stored throughout the plant. A familiar
example of this energy storage is the
sugar maple. The sugar maple stores excess sugar developed during the summer in its
roots. As the plant begins to grow in early spring, the sap containing these dissolved
sugars is transported to the buds. "Tapping" holes in the trunk of the sugar maple allows
collection of this sap, which can be boiled to evaporate the water and concentrate the
sugar into maple syrup. This is how the sugar maple got its name, because of the sap's
particularly high concentration of sugar.
4-51 Plants use the sun's energy (light) with
carbon dioxide from the air combined with
water and nutrients to produce sugars (food)
through the process of "Photosynthesis."
4-38
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Herbaceous Grasses
Herbaceous Broadleaf
4-52 Plant Groupings
4.5.2.2 Vegetation
Groupings: There are
many different types of
vegetation. As road
managers, we will look at
three groupings: woody
plants, herbaceous plants,
and seedless plants, with a
brief discussion of each.
Woody plants
contain hard, ligneous
fibers in their trunk, stem,
and root tissues, which
collectively are called
wood. Trees (beech birch,
maple, oak, white pine,
hemlock, etc), shrubs
(mountain laurel,
rhododendron, low bush
blueberry, etc), and many vines (honeysuckle, grape, etc.) are classified as woody plants.
Herbaceous plants are seed-bearing plants that have fleshy stems instead of
woody ones. These plants are typically shorter than woody plants and include broadleaf
species and grasses. Common herbaceous plants include goldenrod, milkweed, grasses,
daylilies, and skunk cabbage. The life span of herbaceous plants varies by species. A
discussion of plant life cycles follows in the next subsection.
Grasses are herbaceous plants that have some unique adaptations that make them
of special interest to road managers. Unlike other plants that grow at the tips, the growing
point of grasses is located at the base, or ground surface; so as new tissue is added, the
plant extends itself upward. Many grasses also reproduce in multiple ways. Grasses do
flower and produce seeds for sexual reproduction, but many grasses also reproduce and
spread by extending horizontal tillers called rhizomes (underground) and stolons (above
ground), which act to fill in the spaces between plants, as new grass shoots extend forth
from these tillers, as
depicted in Figure 4-11. mj \^ Flower Cluster
The ability of grass to
reproduce in this fashion
makes it very valuable as a
roadside plant since the
frequent mowing of grassy
roadsides removes the
flowers/seed structures, but
not the growing points. The
rhizomes and stolons also
Blade
Sheath
Stem or Culm
Fibrous Roots
Stolon (above ground)
Rhizome (underground)
\
Ground Surface ^"Growing Point
Figure 4-11 Grasses
4-39
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create a fibrous root system, which holds the soil in place and reduces water runoff
velocity.
Seedless plants reproduce by tiny spores that drift on the wind, settle on a surface,
and begin to grow. Common seedless plants include mosses, ferns, and puffballs. Mosses
are often one of the first plants to become established on barren soil. Ferns are very
common roadside plants, and many have deep roots that provide good soil anchorage.
4.5.2.3 Plant Life Cycles. In general, herbaceous plants can be grouped in terms
of three basic life cycles. The plant life cycle begins with the germination of a seed and is
the time required for the plant to grow, mature, produce seeds, and die. One type of plant
has an annual cycle because they complete their seed-to-seed life cycle within a year.
Some annuals, called summer annuals, sprout from seeds in the spring, flower, produce
seeds by the end of the fall, and then die. Winter annuals sprout in the late summer, lay
dormant over the winter, flower, produce seeds in the early summer, and then die.
Biennial plants require two years to produce seeds and complete their life cycle.
Typically, they germinate in the spring or early summer, grow until fall, and then go
dormant for the winter. The following spring, a second growing season begins and the
plant grows to maturity, flowers, produces seeds, and then dies during its second fall.
Canada thistle is a common biennial plant. If this thistle is continually mowed to prevent
flowering and seed production, the plants will die in two years with no replacements to
contend with.
Perennial plants live for an indeterminate number of years. Daylilies and skunk
cabbage are common perennial plants. These plants keep coming back year after year,
typically going dormant in the winter months.
4-53 Root structures
• Tap
• Fibrous
• Sod
• Bulbous
4.5.2.4 Root
Structures. Roots provide
anchorage for plants and act as
a collection system for water
and nutrients from soil. The
structure of plant roots varies
from species to species. Some
plants have a large main
taproot that penetrates deep
into the ground. Tap rooted
trees like hickory also have
fine feeder roots near the
surface of the soil where
oxygen is more abundant.
Taproots act like reinforcing bars and can be very effective in stabilizing banks that are
seasonally saturated and potentially unstable.
4-40
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Some plants have a fibrous root system. Maple trees are prime examples of plants
with fibrous roots. Fibrous root systems provide excellent soil reinforcement.
Some grasses form thick, matted roots called sod, while other grasses grow from a
central point and form clumps. Turf type sod grasses act as a natural erosion control
fabric by holding soil in place, trapping soil moisture, slowing runoff and increasing
infiltration. Grasses that grow in clumps, like tall fescue, tend to hold soil closer and
more securely to the plants' center. With clump type grasses, surface erosion tends to
remove soil from between clumps while plant growth builds the clump higher. Clump
grasses are thereby not as effective at retarding soil erosion as turf type grasses unless
they are seeded densely and are well maintained.
Other plants have a bulbous root system of bulbs or tubers. Daylilies are a
bulbous root plant and can be great roadside bank stabilizers without interfering with the
road.
4.5.2.5 Plant Ecology. Plants have characteristics that cause them to act very
different from animals. These differences involve the way plants gather resources,
develop, and grow. We already discussed photosynthesis, the process with which plants
produce their own food. In addition, plants are strongly influenced by their stationary,
rooted nature. Plants cannot move. They can only react to the environment that exists
where they are growing. Animals, by comparison, can simply seek the environment that
they like best.
The growth of plants is affected by soil, light moisture, and climatic/weather
conditions. Plants require a certain mixture of these factors to thrive, depending on the
plant species. While some plants prefer or even require full sunlight to do well, others
prefer partial sunlight or shady conditions. Similarly, some plants require lots of water
and others prefer drier conditions. For example, the vegetation found along dry, hot ridge
tops is very different than the low-lying, lush vegetation found in wetlands. Topography,
or the shape of the landscape, is a major factor in plant growth because of its influence on
light and moisture conditions. Flat land receives direct sunlight while slopes receive more
or less sunlight according to their orientation to the sun. Sloped areas also dry faster
because precipitation runs off quickly, with less infiltration into the ground.
Since light, soil and moisture conditions vary across regions, plant species are not
uniformly distributed. In areas where the right combination of conditions exist, species
that favor those conditions will dominate the landscape. Forest types are commonly
named for the species predominant within them. The significant point is that plants grow
and thrive in direct relation to the amount of light, quality of soil, quantity of water and
type of weather conditions. Where the conditions are similar across the landscape, similar
plants will dominate.
Plants are very dependent upon the underlying soil for a number of their critical
needs. Although plants' water requirements vary by species, no plant can survive without
water. Moisture stored in the soil serves as a steady supply of this vital requirement. Soils
4-41
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also provide nutrients that are necessary for plant growth. Water collected by the roots
carries these soil nutrients up into the leaves, where together with sunlight and carbon
dioxide, they enable the plant to transform these materials through photosynthesis into
sugars for food.
Soils also provide anchorage for plants. By providing support, roots and soil work
together to allow plants to grow vertically. By increasing in height, which varies by
species, plants can collect more sunlight for greater food production.
As stated, the ability of plants to collect resources and grow is limited by their
location since they cannot move. Plants aid themselves in this limitation through
recycling. Leaves, branches, and bark fall in close proximity to the plant, where insects,
worms, bacteria, and fungi digest them. The decay of this fallen organic matter creates an
excellent growth medium. By providing habitat for other creatures, plants also attract
nutrients and growth enhancers in the form of animal wastes to their location.
Since plants cannot move like
animals, they cannot flee from danger. If
they could, there would be a lot fewer trees
along our roads with cavities that result
from road grader injury. Plants have
developed numerous adaptations to deter
and prevent insect, animal, and physical
damage and even intrusion of other plants.
These adaptations range from physical
factors, such as fire resistant bark, sticky
sap, thorns, and very hard seeds, to
chemical factors, such as bad tasting
leaves, strong and offensive odors, and
toxins released to soil. Some plants, such
as ferns, black walnut trees, goldenrod and
a few grasses, release toxins into the soil, a
process called alleopathy. These toxins released into the soil discourage competing plant
species from germinating and growing nearby.
4-54 Plants cannot move, cannot flee from
danger.
Earlier it was mentioned that plants form the foundation of a stream's food web.
This lead role is carried through to the whole earth's food webs. The ability of plants to
effectively transform the sun's energy into another form of energy (i.e., sugar) is one of
the basic building blocks of life. Sunlight is the key ingredient, supplying an
inexhaustible supply of energy, while the other necessary raw materials for
photosynthesis are found practically everywhere in the environment. The availability and
abundance of these raw materials explains why plants are so widespread across the
planet. Consequently, plants serve as a ready and almost limitless source of food for
plant-eating insects and animals, forming the foundation of our earth's food webs.
4-42
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4.5.3 Understanding Trees. Trees are present along many roadsides. Efforts to
manage roadside vegetation consume fantastic amounts of money and effort. In order that
road managers might better integrate their vegetation management programs with the
natural and relentless growth of vegetation, a better understanding of trees is necessary. A
discussion of tree growth and their reaction to injury follows.
4.5.3.1 Tree Growth. Trees grow in diameter by adding a new layer of wood
each year. This new wood forms in the cambium layer immediately behind the inner
bark. These annual layers of new growth form the "rings" that most all of us have seen on
tree stumps. These rings of growth, if examined closely, can be counted to determine the
age of the tree. In addition, the width of the ring indicates the condition of the growing
season, a wider ring meaning more growth from a good growing season with plenty of
moisture and positive conditions.
The outermost layer of the tree is the bark. Similar to our skin, bark is a protective
layer of tissue on the outside of the tree that stabilizes temperature and forestalls insects
and disease from damaging the more delicate, actively growing layers beneath it. Bark is
adapted to allow the annual increase in diameter of the tree. Some species of trees have
bark that can be described as striped or occurring in vertical rows. On trees with this type
of bark (e.g., chestnut, oak) the bark accommodates the annual increase in trunk diameter
by expanding between the ridges. Other species of trees have smooth bark that actually
stretches as the tree expands in diameter. This bark is then replenished in late summer
during a period of less vigorous growth. The point here is that bark is very valuable to the
tree. It is a highly adapted tissue that performs numerous functions critical to the tree's
survival. We need to be aware of the value of bark so that we can avoid damaging it with
our maintenance activities.
When trees grow, they increase their height by extending new tissue at the end of
branches. This is why a barbed-wire fence nailed to trees does not become higher off the
ground with each year of tree growth. The base of the tree is simply growing outward, not
upward. The annual increase in diameter is how objects become embedded in trees.
Although all trees add new tissue in the same manner, they do not all look alike.
While each tree species has its own growth patterns, individual plants adapt to their
surrounding conditions. The oak trees in Figure 4-12 have all taken on different forms
based on their specific site conditions. The field grown oak standing alone in full sunlight
grows to a different shape than a forest grown oak The field oak must withstand the wind
and elements all by itself and therefore needs a lot more structural root support than the
forest oak that is sheltered from the wind by surrounding trees. Forest trees grow upwards
in an attempt to gather sunlight, resulting in taller trees with fewer low branches. When
trees are cut down, some will resprout new growth from the newly cut stumps. These
stump sprouts grow in clusters, which result in yet another growth shape. Trees grown
under utility wires continuously have their tops removed, producing an unnatural tree
shape that is structurally unsound.
4-43
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Figure 4-12: Plants are affected by their environment.
The same acorn <&& could grow into any of these trees!
Field Grown
Oak
Forest Grown
Oak
Sprouted Plantation Utility
Oak Oak RO.W.'Oak
4.5.3.2 Tree Injury. As we discussed earlier, bark is the protective layer of tissue
on the outside of the tree. When bark is damaged, the tree is permanently wounded.
Trees do not heal, they seal. Many things can damage the bark of trees. Fire, animals,
and equipment are common causes of tree wounds.
Fire is an enemy of some trees and a friend to others. The heat of fire is an
obvious enemy to most trees. Some trees, however, require the heat of a forest fire to
open pinecones, expose mineral soil, initiate seed germination, or stimulate new growth.
Some species, such as scrub oak, have a high oil content, which cause them to catch fire
quickly and generate very high temperatures. The hot fires generated when these species
burn kills other
species, reducing
competition. This
suppression of species
intolerant of fire is an
important component
in maintaining the
diversity and function
of many ecosystems.
Animals are a
major source of injury
to trees. Insects
burrow under the bark 4-55 Trees do not heal, they seal!
4-44
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which cuts the trees' lifelines and can allow pathogens
into the tree. Insects, like the tent caterpillar, can strip the
tree of its leaves, resulting in severe injury or death since
the tree cannot process food without green leaves. Birds,
such as woodpeckers, peck holes in trees to get bugs and
suck sap. Beavers cut trees down for food and building
materials, porcupines munch on trees, and deer rub their
antlers on trees, damaging the bark.
Road maintenance activities can also cause
significant damage to trees. Trees are frequently wounded
when heavy equipment bangs into them, ripping sections
of bark loose or disturbing the roots. In addition to the
physical damage caused by cutting and tearing of the
roots, filling and compaction of soils damages roots by
cutting off some of their oxygen supply. Any activity that
disturbs the tree bark is injurious. Vegetation control
measures, which result in indiscriminate injury to roadside
trees cause permanent injury. The natural reaction plants
have to injury may cause more problems for road
managers than the temporary benefit realized by
indiscriminant cutting.
4.5.3.3 Tree Reaction to Injury. When trees are
wounded, they are not able to heal from the inside as
people do. As already mentioned, the growing tissue of the
tree is immediately beneath the bark. When a tree is
wounded and the growing tissue under the bark is exposed
to air, the tissue dries out and dies. Trees attempt to seal these wounds by forming new
wood around the edges where bark remains intact. This gradual sealing, or growth of the
cambium layer, causes the characteristic callusing around a wound's edges. This sealing
process can take years depending on the size of the wound.
As soon as the tree is damaged, natural
pathogens attack the exposed tissue. Bacteria
and fungi begin to infect and digest the wood.
Larger animals like birds and bears dig into the
tree to eat the insects that live in the decaying
wood. The way trees grow creates ready
avenues for rot to spread. When rot invades the
tree, it spreads in three directions: radially
outwards from the center, vertically up and
down, and circularly. The tree rots from the
inside out, thus the hollow trees that finally die
and always seem to fall onto the road.
4-56 Fungi attacking
wounded tree.
4-57 What's happening inside?
4-45
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4-58 Once rotted, another natural force causes
additional damage: freeze cracks.
Even after a tree has sealed the
wound, the internal rot does not stop.
Rotting wood attracts water. In freezing
weather, this saturated wood freezes,
expands, and cracks outward, breaking the
seal and re-injuring the tree. These frost
cracks can extend deep into the center of
the tree and, with repeated freeze-thaw
cycles, the tree's seal is continuously
broken, exposing the new tissue to
additional bacteria and fungi.
4.5.3.4 Proper Pruning. While pruning trees is a necessary maintenance activity,
it also wounds a tree by creating openings in the protective bark layer. By understanding
the way tress grow and react to injury, we can minimize the unintended damage
frequently done by ill-advised and improperly executed pruning. Proper pruning of trees
becomes one of our environmentally sensitive maintenance practices that will be
discussed in Chapter 6.
4.5.4 Plant Establishment and Succession. In our discussion of geology, we
talked about geological time scales because natural processes and forces act to change the
surface of the landscape over time. The composition of plant communities (i.e., types of
species present) also changes over time and is referred to as ecological succession.
Ecological succession takes place in a much shorter time frame than geological
processes. Like most things in nature, ecological succession is a complex process. There
are some basic principles, however, that are important for road managers to understand.
Once understood, these natural principles can be utilized to make roadside vegetation
management efforts more successful and less costly.
In ecological succession, the composition of a plant community changes as
physical and biological processes act to alter the condition of the habitat. As habitat
conditions change, plant communities change. Plant succession can be defined as the
gradual and orderly process of ecosystem development brought about by change in the
community composition and the production of a climax characteristic of a particular
geographic region. In other words, plant succession starts with bare earth and, over time,
transitions towards mature forest.
4-46
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Rates of succession vary depending on site conditions. Succession proceeds most
slowly in bare, unshaded, nutrient-poor rock and subsoil conditions. On the other hand,
disturbed areas where the topsoil is not removed or is saved and re-used are able to
revegetate quickly. This is why old strip mines remain barren for so long, while
abandoned pasture is quickly vegetated and often quickly forested.
Figure 4-13: Plant Succession
For road managers, roadside trees become a major item within the realm of
roadside vegetation management. The following sections describe tree characteristics as
they relate to both new and mature successional stages.
4-59 Colonizer or Pioneer Species
4.5.4.1 Colonizer
Species. Succession begins
with bare soil. The trees that
are best adapted to
conditions of full sun and
nutrient-poor subsoil are
called colonizer or pioneer
species. Common pioneer
species familiar to road
managers may include
aspen, locust, sumac, grey
birch and black locust.
These types of trees have
certain characteristics for
adaptation to the conditions
described.
Generally, colonizer species produce massive quantities of lightweight seeds.
Although colonizer seeds are not durable, the massive quantities produced and their
ability to be transported by the wind assures that some seeds will find barren ground in
full sun and germinate. Since they are shade intolerant, roadside banks laid bare during
construction and maintenance activities are classic examples of sites prime for
colonization.
Structurally
weak & short-
lived
Fast growing
Early maturity
Shade
intolerant
EXAMPLES:
Sumac
Multaflora rose
Aspen
Birch
Locust
4-47
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Although colonizer species are very valuable plants, serving as nature's pioneers,
colonizing the harshest environments, and paving the way for successional changes
towards intermediate and climax species, they can be problematic for road managers.
These trees are fast growing, reaching an early maturity. Thus, they are structurally weak
and short-lived. As roadside trees, these factors tend to make them a recurring
maintenance problem. These are the trees that will lean out over the road due to their
weak structure and end up falling onto the road as wind and storms take their toll or as
the trees reach maturity and start to age and die.
4-60 Intermediate/Climax Species
Structurally strong
& long lived
Slow growing
Long term for seed
production
Shade tolerant
EXAMPLES:
Oak
Hickory
Maple
Dogwood
Redbud
Servicebeny
4.5.4.2 Intermediate and
Climax Species. Ecological
succession is a process that never
ends. The modification of the soil
by the colonizing species results in
an environment that is more
attractive to sturdier and longer-
lived species, causing better suited
plants to gradually take over. This
rate of transition between species
groups and plant communities
varies over time. As slow growing,
long-lived species become
established, the process of succession slows down. As the rate of change slows and
stabilizes, we describe it as an intermediate successional stage. Intermediate plant
communities offer greater stability for roadside trees. Intermediate stages are typically
followed by climax stages, although in many areas few climax forests are found because
they were cut down for lumber and have not had sufficient time to progress from
intermediate forests to the climax stage. Examples of intermediate/climax trees include
oak, hickory, beech, dogwood, redbud, and serviceberry.
Intermediate and climax species typically produce heavy seeds, like oak and
hickory, which remain relatively close to their parents. This is an advantage, since the
seeds from these species prefer soils that are shaded and rich in organic material. These
ideal conditions are typically found underneath the intermediate/climax trees because
they shade the ground, trap moisture, and their fallen leaves, branches, and bark
reproduce large quantities of organic material.
The slow-growing, strong structure of these intermediate and climax trees make
them better roadside plants. Hemlock, beech, and sugar maple all have these
characteristics. Because they are stronger than colonizers, they are less apt to lean out
over the road or snap under a heavy snow load. The slow growth of these long-lived
species also means that they do not need to be trimmed as frequently as the faster
growing colonizers.
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4.5.4.3 Significance of Plant Succession for Roadside Maintenance. As
succession continues and intermediate species become established, the modifications to
the soil and environment continue, thereby promoting and encouraging additional
intermediate species. As more and more intermediate species establish, the particular site
becomes less and less attractive to the colonizer species. This natural process can be used
to reduce roadside vegetation maintenance workload by shading out the fast growing,
light-dependent colonizers.
Soil laid bare by grading, daylighting and other common maintenance activities is
always going to be subject to the natural process of succession. Road managers need to
be aware of this process because the natural reaction to many of their maintenance
activities creates colonizer growth. In addition, traditional maintenance activities to
control the growth of these colonizers typically encourage its re-growth, effectively
resetting the clock on an endless cycle of cutting and re-growing.
Although succession proceeds at varying rates, it is ongoing. Even the modest
efforts at encouraging the establishment and growth of properly adapted plants along our
roadsides can pay large dividends. Properly selecting the plants you remove, the plants
you leave, and the species planted can control and accelerate the revegetation of our
disturbed roadsides.
The goal for roadside vegetation management should be stability with as little
maintenance as possible. A road built through an intermediate or climax plant community
can be less costly to maintain if we learn how to use the forest system to our advantage.
The use of the forest system to benefit road maintenance will be further discussed in
Chapters 5 and 6.
4.5.5 The Importance of Plants. The fact that plants form the basis of the earth's
food webs was already mentioned. In addition to food, plants provide valuable habitat for
wildlife. Plants also provide numerous other benefits to human society as part of their
role in ecology. These benefits are widespread and occur wherever plants grow, whether
in forests, fields, or along our roadways. Many of the benefits have been discussed
previously, so the following descriptions will both summarize and add to the benefits that
plants provide.
4.5.5.1 Ground Cover and Erosion Prevention. Plants act as groundcover and
prevent erosion in several ways. The foliage and physical structure of the plant reduces
the direct impact of raindrops on the soil. Plants hold soil in place with their network of
roots. Plants also act to slow surface flow, decreasing erosion energy, trapping sediment
and allowing more infiltration into the soils. The shaded or partially shaded soils under
plants are cooler and more moist than more exposed soils and therefore more permeable
to rainfall. Obviously, the more water that soaks into the ground, the less that runs off and
causes erosion problems.
Plants also soak up water out of the soil. This process dries the soil and decreases
the lubricating effect of water and again decreases the amount of runoff and erosion.
4-49
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4.5.5.2 Air Conditioning. The water drawn up from the soil and into and
throughout the plant carries the nutrients for plant food production. Excess water is then
evaporated from the leaves and released into the atmosphere. This release process, called
transpiration, cools the leaves and the surrounding atmosphere. Just as perspiration cools
us, transpiration cools the plants, adding humidity and cooling the air. Trees are nature's
air conditioners, which is a great advantage to humans. Where would you rather be on a
hot summer day: a paved parking lot at the mall or sitting on a park bench under a giant
oak tree?
water travels
through plant
water absorbed
by roots_
water evaporates
Plants also provide shade that f from )Mf surface
cools the area by reducing sunlight and
the drying effect that it has on soil. In
this way, plants act to modify the
environment to their own benefit, too.
4.5.5.3 Air Purification. The
air cleaning characteristics of plants
improves the quality of air. As part of
the process of photosynthesis, plants
take carbon dioxide from the air as a
raw material and give off oxygen as a
natural by-product. Animals, including
humans, require oxygen to live. When
animals inhale, their lungs extract the
oxygen from the air and exhale the
carbon dioxide. By using the by-
products of each other's life processes,
plants and animals are fundamentally tied to one another, with each providing a critical,
life-giving element for the other.
Plants can also provide physical cleaning of the air. Airborne particles are filtered
out as air drifts through vegetation. The leaves act to slow the air velocity down, which
allows dust to settle. This is why leaves on roadside trees are commonly coated with dust
(until it rains and the dust is transported as sediment to the nearest stream or wetland).
4.5.5.4 Water Purification. The value of wetland plants in water quality was
discussed in the section on the Wetland Community. Plants soak up water along with any
chemicals and other contaminants that may be dissolved in the water, thereby having a
cleansing effect.
Figure 4-14 Transpiration
4-50
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4-61 Value of Plants: Aesthetics and Economics
4.5.5.5 Aesthetics and
Economics. The first impression
visitors get of a community is what
they see along the roads. Nicely
vegetated and diverse roadsides
give an impression of comfort and
relaxation. Management of roadside
vegetation in harmony with nature
benefits us visually and
economically. It looks good (better
for tourism), and it is easier on the
local government budget than an
unending cycle of invasive growth
and removal.
4.5.6 Upland Ecosystem Summary. The management of roadside vegetation is
traditionally an expensive and time-consuming task. A general understanding of the way
plants grow and react to our maintenance efforts can help road managers to utilize natural
processes to reduce the frequency and cost of vegetation management efforts.
In this section, we talked about plant basics, their growth factors and the process
of photosynthesis that allows plant to produce their own food. We discussed different
groupings of plants and their characteristics, along with the different plant life cycles. We
looked at plant root systems and their importance in soil stabilization. We then looked at
plant ecology and how plants are influenced by light, soil, water, and climate, factors that
vary from site to site. Changing any of these primary influencing factors can have a
dramatic effect on the plant community. We discussed how plants react to injury,
particularly roadside trees. We covered plant succession, differentiating between the
colonizer or pioneer plants that are high maintenance items and the intermediate and
climax species that can reduce maintenance.
Finally, we discussed the overall importance of plants, noting their value for soil
reinforcement and erosion prevention, as air cleaners and conditioners, as water cleaners,
and for general roadside aesthetics.
As road managers, the more we know about plants and natural systems, the more
we can use this knowledge toward a more efficient and effective roadside vegetation
management program.
4.6 Summary of Natural Systems
Because dirt and gravel roads are located amidst natural biological systems, the
stream, wetland, and upland/forest communities that these roads pass through are likely
to interact with the daily maintenance and operation of these roads. These interactions
can affect both the road and the natural systems. Therefore, if road managers are to
provide better roads while complying with today's complex environmental regulations, it
4-51
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is important for them to understand the importance of these natural systems and some of
the major processes that take place.
This chapter contains a significant amount of information on natural biological
systems. This information should be useful as we move into the remaining chapters and
begin to discuss environmentally sensitive maintenance practices that will benefit both
the road and the environment and help prevent erosion, sediment and dust pollution. We
will spend less money and do less environmental harm if we understand and work with,
not against, nature and the natural systems.
These natural systems have been discussed and summarized individually, but it is
critical to note that these systems do not exist individually. Just as they interact with
roads, these natural systems interact and depend on each other, with processes and
functions blending across the boundaries between each system, making up the total
environment in which we live and work. Remember, as John Muir put it, "When we try
to pick out anything by itself, we find it hitched to everything else in the universe."
4-52
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PA Geological Pro
PA Ecoregions
APPENDIX 4. Case Study: Pennsylvania's Ecology
A4.1 Ecoregions
and Geological Provinces.
The Commonwealth of
Pennsylvania encompasses
a whole range of ecological
conditions or habitats. As
discussed, ecoregions
reflect the physical factors
that help define the type of
habitat present and in turn
determines the type of
animals and plants that live
and survive in that habitat.
For example, vegetation is
heavily dependent upon the
area's elevation, slope,
drainage, stability, and
nutrient availability, in
essence, the geology and
soils. Comparing geology
and ecoregion maps and
noting the similarity of
boundaries demonstrates
this association. Figure A4-
1 illustrates this
comparison using the
geology province map and
an ecoregion map of
Pennsylvania. The ecoregion map shows that there are eight ecoregions in Pennsylvania.
These ecoregions have been delineated primarily according to vegetation types - each
ecoregion contains similar types of vegetation. This is because plants (and animals) have
developed and evolved under a certain set of physical conditions characteristic of their
ecoregion. The three typical community types or ecosystems within each ecoregion -
streams, wetlands, and uplands - are all represented in Pennsylvania.
A4.2 Pennsylvania's Stream Ecosystems. The commonwealth has
approximately 83,260 miles of streams. Streams systems have played a very large role in
shaping the landscape of Pennsylvania, primarily through erosion and deposition of
sediments. Much of this activity takes place at a rate that spans thousands to hundreds of
thousands of years or geologic time as discussed in Chapter 2, and these processes
continue today. For example, approximately 290 million years ago, much of western and
northern Pennsylvania was relatively flat and covered with lake-bottom sediments, which
later hardened into sedimentary rock. Since that time, erosion has carved numerous
stream valleys through these former lake-bottom sediments that are sometimes more than
Figure A4-1 Comparing Ecoregions
and Geological Provinces
-------
1000 feet below the level of the surrounding terrain. The process of landscape
modification continues today as sediments eroded from a watershed are transported until
the water velocities slow and sedimentation occurs as bars in the middle and along the
edges of the streams. Sediments are also deposited when floodwaters transport particles
outside of the stream channel, depositing them on the floodplain, where they replenish
soils along the stream margins.
Pennsylvania derives a number of significant recreation and economic benefits
associated with its stream systems. Streams and rivers provide places and opportunities
for numerous recreation activities such as fishing, tubing, canoeing, Whitewater rafting,
bird watching, hunting, and outdoor education. In turn, people who participate in these
activities must spend money for gas, lodging, food, sporting equipment, licenses, guides,
and many other associated costs. This demand helps provide jobs for local residents.
Since many participants live outside the community where the activities take place, there
is a significant influx of outside money to the local economies. However, there are costs
associated with this tourism, especially their impact on a local government's road system.
The timing of tourist activities may be unfortunate - muddy dirt and gravel roads during
hunting season can cause tremendous maintenance challenges. The number of tourists
viewing the autumn colors may also overwhelm the capacity of less traveled roads. Thus,
the condition of a local governments' transportation system can be a great influence -
advantage or disadvantage - to the economic growth of the area.
Streams are viewed as a public natural resource in the commonwealth, and, as
such, are protected under Pennsylvania's Constitution. To this end, one of the primary
goals of managing and protecting streams in Pennsylvania is to maintain a healthy and
naturally reproducing fish community. As we have learned, natural reproduction offish is
an important goal because fish are dependent upon a clean, healthy stream environment
in which to live. The lack of a naturally reproducing fish community is often an
indication that conditions within the stream are degrading.
Pennsylvania has targeted two types of water bodies and their watersheds for
"special protection" in
order to maintain their
existing quality. These two
watershed types are
described as "Exceptional
Value" and "High Quality."
They are delineated on a
PA map in Figure A4-2. An
Exceptional Value (EV)
water body is considered to
have outstanding water
quality, and no degradation
of the water is permitted.
This is the most stringent
protection within the
S^ Figure A4-2 PA Protected Watersheds
High Quality
Exceptional Value
4-54
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commonwealth. High Quality (HQ) water bodies are considered to be relatively
unaffected by humans. No degradation of the water is allowed unless the PA Department
of Environmental Protection (PA DEP) agrees that the project's social and economic
benefits justify lowering the quality of the water. HQ protection is slightly less stringent
then the EV protection status.
Streams designated as EV or HQ are primarily located in the headwater portions
of many Pennsylvania streams. Natural reproduction within these streams is a vital
function in order to maintain fish populations and trout is the especially good indicator
species. As discussed back in Chapter 1 as a historical perspective, many of the state's
roads were laid down next to streams in order to take advantage of the gentle gradient and
existing routes of travel. The location of these roads often results in erosion and sediment
impacts to the adjacent streams, and resulted in the development and implementation
Pennsylvania's Dirt and Gravel Road Program.
Pennsylvania's streams are evaluated by the PA DEP's Bureau of Watershed
Conservation, whose focus is maintaining water quality and overall health, and the PA
Fish and Boat Commission, who manage the state's recreational fishery. These agencies
conduct biological and chemical surveys in their evaluation of the streams and rivers.
Data collected from these surveys are then analyzed and used to make management
decisions.
A4.3 Pennsylvania's Wetland Ecosystems. The wetland community is an
important component of Pennsylvania's ecoregions, with wetlands currently covering
approximately !/2 million acres, or two percent of the commonwealth. These wetlands
provide many valuable services and functions that are beneficial to humans and wildlife,
as described in Section 4-4 above.
At the time of European settlement in the late 1700's, there were an estimated
1.127 million acres of wetlands within Pennsylvania, or 4.5% of the state. Back then, as
mentioned under Section 4.4, these wetlands were looked upon as wasteland and
unproductive land. A great
deal of wetlands has been
lost in Pennsylvania, with
conversion of
approximately 56% of the
pre-settlement wetlands to
human land uses.
Typically, wetlands have
been converted through
dredging, draining, and
filling, for a number of
different human uses. The
conversion of wetlands for
agricultural purposes has
probably resulted in the
LI Agriculture
D Urban
HI Open Water
0 Other
Figure A4-3 PA Freshwater Wetlands Conversion
(mid 1950s to 1970s, thousands of acres)
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largest loss. Figure A4-3 shows that wetlands in Pennsylvania have also been converted
for urban development, creation of ponds, reservoirs, and lakes, and other forms of
development. The loss of wetlands has resulted in a loss of all of the various benefits that
they provide.
These valuable natural resources are not evenly distributed across Pennsylvania.
The northeastern and northwestern corners contain almost half of the state's wetlands.
These relatively small portions of the state contain a large concentration of wetlands
primarily because of the impact of glaciers on the underlying geology, topography, and
soils. Floodplain wetlands, as previously described, are found along the fringes of lakes,
rivers, and streams. This is the most common wetland type in Pennsylvania.
Along with the federal agencies, Pennsylvania has a number of state and local
agencies that work to protect the wetland resources, including the PA Department of
Environmental Protection, the PA Department of Conservation and Natural Resources,
the PA Fish and Boat Commission, and the PA County Conservation Districts.
A4.4 Pennsylvania's Upland Ecosystems. The vast majority of Pennsylvania is
uplands. As discussed throughout Chapter 4, plants have physical resource requirements
needed to grow and survive. Each species has its own climate, light, moisture, and soil
needs. As these conditions vary across the state, plant species are not uniformly
distributed. Forest types are commonly named for the species predominant within them.
Figure A4-4 shows the
forest types of
Pennsylvania. Notice the
similarity to the previous
maps in figure A4-1
showing the geological
provinces and ecoregions.
Trees are the rule, rather
than the exception, along
the dirt and gravel roads in
Pennsylvania. Management
of the forest systems
becomes a predominant factor in dirt and gravel road maintenance for Pennsylvania's
road managers. Selective tree trimming and limiting shading as described in Chapter 6
are a major component of environmentally sensitive maintenance practices taught
through the Pennsylvania Dirt and Gravel Road Program.
Figure A4-4 Forest Types
Map - Location by species groups
I Appalachian Oak
Northern Hardwood
Beech/Maple
I Mixed Mesop hylic
| Oak/Hickory/Pine
Atlas of Penna., 1989
4-56
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Environmentally Sensitive Maintenance
for
Dirt and Gravel Roads
Chapter 5: Environmentally Sensitive Maintenance
Practices: Roads and Road Drainage
5.1 Introduction
Like when building a good road, we started with a sound foundation. We
described the pollution problem from a historical perspective, discussed traditional road
maintenance practices, and defined our goals and objectives. We then discussed geology,
rocks, and soils as raw materials (giving you what you have to work with) for road
maintenance, and continued building on that foundation with road maintenance and
natural systems basics. Now, combining and using all that information, we are ready to
examine good, sound, specific "Environmentally Sensitive Maintenance Practices" that
will benefit both the road and the environment.
Once adopted, these practices will become commonly used tools in your road
maintenance toolbox. In some cases, you may already be using the practice we discuss. In
others, you may just need to tweak the practice to make it more sensitive to the
environment, but still be effective for the road. Some practices may be new, but may fit a
need or a particular site.
As with all maintenance and maintenance projects, we need to make that field
inspection, evaluate the conditions and decide what needs to be done. The more practices
or "tools" available in our toolbox, the better we will be able to perform the required
tasks to prevent pollution and prolong the life of the road. Not one tool or practice will
solve all your problems, but with a full toolbox, you will be able to select the most
appropriate tool or tools for the job.
5.2 Erosion Prevention and Sediment Control
When we talk about erosion and
sediment, we should emphasize erosion
prevention. If we prevent erosion from
happening in the first place, there is no
sediment to pollute. Erosion prevention
becomes our first line of defense. Look at
the badly eroded road in Photo 5-01.
Notice the banks on each side of the road.
At what elevation do you think the road
surface was forty years ago? The road
5-01 Typical entrenched eroded road.
5-1
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5-02 Once erosion takes place, the sediment
needs to be addressed.
would not have been built at the present elevation. If the road surface was originally at
the top of the banks, where did all the material go? This is only one small section of road.
We have many miles of forested roads with similar profiles. From this photo, we can see
why sedimentation, by volume, is the largest pollutant of our streams. Typically, roads
with higher banks on each side cause can be improved by filling the road cross section.
This technique, although involving major fill work, will be discussed in Section 5.3.7,
along with all its advantages.
When erosion does take place, for
whatever reasons, then we have to control
the resulting sediment. Otherwise, we can
end up polluting our streams and have
serious problems both for our roads and the
environment.
5.2.1 Managing Your Erosion
Prevention and Sediment Control
Systems. Whether temporary or permanent
controls, managing your control systems is
important. Periodic inspections of your
roads, drainage facilities and work sites
allow you to keep an eye on potential problem areas and identify problems when they
first start. For example, a vulnerable spot around a culvert is a danger sign. If ignored, it
could create major road problems, damage the environment, and escalate costs. The
following sections include sound practices that can make your control systems more
effective and efficient.
5.2.2 Temporary and Permanent Erosion Prevention and Sediment Control
Measures. Road managers have a wide variety of control methods or practices at their
disposal to combat erosion and sedimentation. They range from the simple to the
complex. In some cases, it may be as simple as widening a ditch or flattening a slope to
reduce water velocity.
Erosion prevention and sediment control can be broken into two areas or
conditions that we have mentioned before:
Temporary Practices. Practices used before or during construction or
maintenance work to prevent and control only for those activities. These include
emergency work situations. Some practices serve as either temporary or
permanent solutions. Other temporary practices can be used during maintenance
and construction activities and become permanent after the work is completed.
Permanent Practices. Practices uses as long-term prevention controls, often
requiring little or low maintenance. These practices may be simple or complex in
construction and costs.
5-2
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5.2.3 Basic Temporary Practices. Two of the most common temporary controls
are straw bales and filter fabric fence (silt fence). Unfortunately they are also the most
improperly used techniques on road construction and maintenance work sites. Although
the use of bales has traditionally been a popular method of sediment control from work
sites, the fact remains that they are relatively ineffective. Straw (or hay) bales are not
recommended for use. Bale barriers have more failures than successes and are
expensive to install and maintain. The Federal Environmental Protection Agency (EPA)
does not recognize bale barriers as an appropriate control method. Since straw bale
barriers are still being used in many areas, the most effective installation practices are
described below, followed by the recommended commonly used silt fence (fabric filter
fence) barrier.
5.2.3.1 Straw Bale Barriers (not recommended by EPA) Straw bales are for
temporary use only. Bales should not be used for more than 3 months. They should not be
used in concentrated flow conditions. They should only be used for sheet or shallow
flows.
5-03 Improper bale installations doomed to fail!
Proper installation is essential as shown in Figure 5-1.
Bale
2" x 2" x 36" Stakes
Bale Bi
J~
Compacted
Backfill
.Slope
fffff-fm ffff f- f; ffff ff ffff m-fffffm-f ff ff ffff •
• • V • % • S • S • V • S • % •N • "m • S • % ••••>••. • V • \ • •» • V • \ • % • % i
i J. .- . J . / . J . J « fm .'m f- fm fm fm fm fm fm fm fm fm fm fm fm .
Figure 5-1 Proper Straw Bale Barrier Installation
5-3
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They should be placed in an
excavated area approximately four (4)
inches below the ground surface and the
excavated soil compacted on the upslope
side of the bales. Each bale should be
anchored securely by 2 support stakes with
straw being wedged between the bales.
Notice in the figure that the bale bindings
are horizontal, not vertical, where they
would be in contact with the ground and
susceptible to rot or degradation. Photo 5-
04 shows a proper installation immediately
prior to a major construction project.
They need to be inspected at regular
intervals and cleaned or replaced as
needed. Cleaning should take place when
the sediment reaches 1/3 above the ground
height of the barrier.
5-04 Proper bale installation prior to start of a
major construction project. (Note: Bale barriers
not recommended by EPA.)
5.2.3.2 Silt Fence Barrier. Silt fence or filter fabric fence is a geosynthetic, or
specifically a geotextile fabric, designed for the filtration function needed in sediment
control. Again, this fabric is for temporary use only and should not be used for
concentrated flow conditions, as can be seen in the photos. Silt fence is normally used at
the toe of slopes for sheet sediment flows.
5-05 Improper silt fence installations.
Proper installation is essential, as shown in Figure 5-2. The fence needs to be
anchored by digging a small trench and burying the toe of the fabric as shown. Wood or
metal stakes need to be place on the downslope side of the fabric to properly support the
installation against the load.
5-4
-------
Wood or Steel
Support Stake
Existing
Fabric Fence
Compacted Backfill
Ground
:f:f:f:f!f:f:f:f:fif:f:f:f:f;f:f:f;f:f;t:f:f:f:t:f:f:f:f:f:f:i:f:f:f:f:t:f:f:f:'fif:f:f:f:f:f,
Figure 5-2 Proper Silt Fence Barrier Installation
5-06 This installation will not control
be cleaned when the sediment
reaches one-half the height of the
barrier.
Like straw bales, frequent
inspections followed by proper
cleaning or repairs are necessary
for proper performance. Filter
fabric fence is much more
effective and has a much longer
life than straw bale barriers but
still must be installed properly,
inspected regularly and properly
maintained.
.,.-><}. - . V-
SVS*- .
much sediment!
Photo 5-06 shows an
improper installation with the
bottom of the fabric above ground
level (this will last a long time but
won't control much sediment).
Photo 5-07 shows a good installation
in a new paved road subdivision that
has not been maintained. Although
this photo shows the strength of a
silt fence barrier, the risk of a system
failure is imminent, and the
consequences of pollution and
cleanup required could be quite
substantial. Filter fabric fence should
5-07 Cleaning is required when sediment reaches one-
half the height of the fence.
5-5
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5.3 Environmentally Sensitive Maintenance Practices
Let's turn our attention to more permanent practices that both prolong road life
and are good for the environment. Specifically we will look at environmentally sensitive
practices involving the road profile, driveways, drainage ditches, culverts, end structures,
stream crossings, and bridges. Roadsides and banks will be specifically addressed in
Chapter 6.
These practices, as stated before, are mostly simple, practical techniques that can
be easily implemented. Local government road crews can perform most of the practices
with available equipment resources, incorporating them into their normal routine road
maintenance program. Not all practices will apply to any one road or one road system,
but having a full toolbox to address any problem encountered lowers overall costs. Many
of these practices can be used in combination and will apply to most dirt and gravel roads
in general. And many practices are also useful on paved roads.
As we discuss these practices, keep in mind that proper drainage is absolutely
essential to prolonging road life and protecting the environment. Drainage means
handling flowing water. Greater volume and greater velocity (speed) of that water result
in greater erosion and sedimentation. In other words, if we can limit the volume of water
and slow it down, we diminish the energy and erosion potential of the flow. Many of the
practices to be discussed are based on this "divide and conquer" premise. By limiting the
drainage area contributing to the flow, we reduce water volume, thus allowing smaller
sized drainage facilities (ditches, pipes, etc.). This reduced area also reduces the flowing
water's ability to pick up speed, reducing energy and the likelihood of erosion.
Common practices will be mentioned without elaborate detail but with some
explanation of the rationale for inclusion. Other more uncommon practices will include a
short description and associated sketches as necessary for clarification. For discussion
purposes, the practices are organized into related groups.
5.3.1 Practices Related to Road Profile. In Chapter 3, we discussed the
importance of road crown and cross slope, road shoulders, good road materials, and
proper road drainage. Following those basic practices will result in a better road and
promote a better environment. But beyond those basics, we now introduce several
alternate road profile practices.
5.3.1.1 Insloping. "Insloping" of the road can be applied when the road runs
along a steep bank. With a steep uphill bank on one side and a steep downhill bank on the
other, common practice is to install a normal crown (see Figure 5-3a). This practice
concentrates the water volume and flow, causing erosion with the possibility of a severe
washout down over the bank and normally into the adjacent stream below. Sometimes a
berm dam is installed along the edge of the road at the top of slope. The berm dam can
also cause a secondary ditch with poor road drainage and a build-up of water volume and
flow that could result again in a severe washout.
5-6
-------
Sbfely?
Create berm dam'
along road edge at
top of slope
a. Road Profile: Common
practice for roads along steep
banks
Slopec 1/2" - 3/4" mill, per foot
b. Alternate Road Profile: hsloping
Figure 5-3
Insloping the road using normal cross slopes may take care of this problem (see
Figure 5-3b).The entire road is sloped toward the uphill side, eliminating flow over the
steep downhill slope and the possible erosion and washout into the stream. The only
water reaching this downhill slope will be the rain that falls directly onto the surface. The
water draining from the road and the uphill slope still should be collected via a ditch on
the uphill side and carried to a cross culvert. The only additional water, however, that is
draining into this ditch is from the other half of the roadway surface. This limited
additional water volume will not require changes in ditch and culvert sizes. Culverts can
be placed strategically with outlet flow protection as needed. The berm on the downhill
side can still be built up if desired for safety of vehicles.
Photo 5-08 depicts the typical
conditions for insloping. We can prevent
water from flowing over the face of the
downhill slope by sloping the entire
roadway toward the uphill embankment
on the left side of the photo. We need to
collect this water into a side ditch and to
a cross pipe to outlet away from the road.
In this photo, we can see how the stream
meanders close to and then away from
the road. The cross pipes can be
strategically located where the vegetative
grass strips are the widest to filter out any
potential sediment prior to entering the
stream. At this particular site, a cross pipe can be installed further down the road where
its outlet would be at a flat rock outcrop. This rock configuration will spread the flow,
acting as an energy dissipater prior to a grass filtering strip and the stream.
5-08 Road candidate for insloping.
5-7
-------
Vehicular safety has to be considered in this approach. Keeping the cross slope at
a minimum and considering low traffic volumes, we can still maintain a berm dam on the
downhill side for extra safety perception since everything is draining away from that side.
5.3.1.2 Outsloping. "Outsloping" of the road can be applied when the road
crosses a gentle sloping terrain. Common practice is to install a crown with side ditches.
This configuration (see Figure 5-4a) creates a dam and concentrates the overland sheet
flow with possible erosion of ditches and ditch outlets. This profile also requires cross
pipes to outlet the uphill side ditch with the potential clogging and flooding concerns.
The volume of water to be handled can become substantial.
Safety?
Roadside ditches
a. Road Profile: Common
practice for roads crossing
gentle sloping terrain
Slope: 1/2" - 3/4" min. per foot
b. Alternate Road Profile: Outsloping
Figure 54
With outsloping, we slope the entire road with a normal cross slope from one side
to the other, similar to superelevation on a curve, but with no ditching. With this
outsloping of the road, as shown in Figure 5-4b, and blending it into the surrounding
terrain, concentrated flows are eliminated with no ditches or cross pipes required. The
existing general slope sheet flow continues across the road with no interference. This
technique should be used with gentle sloping terrain and low overland sheet flow
conditions. Low traffic flow (low APT) should also be a prerequisite.
Photo 5-09 shows a
typical outsloped road. The
terrain is gentle with low sheet
flows, which are carried across
the outsloped road blending into
the natural drainage. This will
eliminate concentrating the water
flow in ditches and cross pipes
and the maintenance of these
facilities. Site selection for this
practice is critical. A heavy storm
may require road maintenance
afterward if the flows are
substantial enough to cause road
surface degradation.
5-09 Outsloping this road proved beneficial,
eliminating ditches and cross pipes.
5-8
-------
Again, safety should be a concern. Normal cross slopes can be used, alleviating
the concern of vehicle safety. Depending on the road surface and amount of flow along
with the temperature conditions for the area, however, icing of the road surface may
become a problem. This has not happened on the various sites where outsloping has been
implemented, but the concern should be recognized and conditions monitored during the
winter months.
5.3.2 Practices Related to Roadside Ditches. Ditches drain water away from the road,
but often cause various erosion and sediment problems. A typical ditch sketch is shown
in Figure 5-5 with common ditch terms of foreslope, backslope, and flowline. In
discussing ditches, there are several environmentally sensitive maintenance practices that
can be considered.
Roadway
A
Shoulder
(Eterm Area)
Backslope
Foreslope
Figure 5-5 Roadside Ditches
5.3.2.1 To Ditch or Not To Ditch? The first question in ditching should always
be "Do we need a ditch?" If the road surface drainage can continue to sheet flow away
from the road without causing any problems, then a ditch only becomes an impediment,
concentrating the sheet flow and compelling further handling through ditches and/or
pipes to an outlet along with all the required maintenance. If we can let the road drain
naturally by sheet flow into a vegetated area, flows are spread out and thereby slowed
down, resulting in the least erosion and sediment potential. At many sites, however, this
natural sheet flow drainage conditions is
not possible, and ditching is still going to
remain the option of choice.
5.3.2.2 Ditch Shape Ditches
should be shaped and sloped to prevent
standing water and must have an outlet.
Safety for errant vehicles should also be a
consideration. There are many ditch shapes,
with common shapes shown in Figure 5-6
with different advantages and
disadvantages. For purposes of erosion
5-10 Trapezoidal shaped ditch.
5-9
-------
prevention and the environment, ditch cross sections with a trapezoidal or parabolic
shape are desired. These shapes tend to spread water flow and slow it down, which will
reduce the erosion potential and subsequent sediment.
"V" shaped
Figure 5-6 Ditch Shapes (*Preferred)
V-shaped ditches are common due to motor grader use in dirt and gravel road
maintenance and may not be a problem. A
deep V-shape, however, concentrates
water flow, increasing its velocity,
possibly eroding the ditch's bottom. Deep
sharp V-shaped ditches are more prone to
this bottom erosion and should be
inspected regularly. If water flows and
velocity are starting to cause erosion, the
ditch can simply be flattened to a wider V-
shape. This will again spread the water out
and slow it down, diminishing the energy
and thereby the erosion potential. Photo 5-
11 shows a good grass-lined, v-shape
ditch. On close inspection, however, the
bottom of the ditch is showing signs of
initial erosion. The erosion may not get
any worse, but the ditch needs to be
watched. If the erosion continues and gets
worse, a possible solution may be a simple
flattening of the ditch, which would
spread the water and slow it down,
decreasing energy and erosion potential.
Rectangular shapes give a vertical
surface prone to destabilization and
5-11 Grass-lined, V-shaped ditch.
5-10
-------
erosion without a more substantial surface protection. Rectangular-shaped ditches may
also pose a vehicular safety hazard and are not recommended for use.
5.3.2.3 Ditch Slope. Ditch side slopes often dictate the amount of maintenance
due to instability and resulting erosion and sediment. The recommended side slope is 4 to
1 (4 foot horizontal to every 1 foot vertical drop). This slope provides greater stability,
better support for the road, and is easier to maintain. In addition, this 4:1 slope is a
forgiving shape for safety. A vehicle running off the road onto a 4:1 slope will not turn
over and has a better chance to recover control without a serious accident.
On many existing roadsides, the terrain or right-of-way limitations do not allow
for a proper slope and ditch. We need to keep in mind, however, that the steeper slopes
mean greater instability, less road support, harder maintenance, and lower safety levels
(see Figure 5-7).
Forgiving Shape for Safety (4:1)
Road safety & liability!
Road
problems 4:1 (14°)
maintenanc§Pg£
slight problems 3:1 (18°)
moderate problems 2:1 (30°)
Figure 5-7 Roadside Slopes
Steeper slopes - more problems
slope stability!
severe problems 1:1
road edge support!
unstable 1:2 (60°)
Ditches should have minimum
longitudinal slopes of 1% or 1-foot drop in
100 feet of ditch. For proper drainage, we
need to keep ditch water flowing to an outlet
away from the road. Standing ditch water
will only result in additional road
maintenance. The water will seep back into
the road structure, creating the road softening
lubricating effect described in Chapter 3
along with freezing and frost heave
problems.
5-12 Standing water can only lead to
problems.
Flatter slopes slow the water,
decreasing ditch erosion while steeper slopes increase velocity, raising ditch erosion
potential. On the other hand, flatter slopes will allow sediment accumulation resulting in
5-11
-------
increased ditch cleaning, but, remember, if there is no erosion, there is no sediment. Find
the source of the erosion, fix the erosion problem, and eliminate the sediment.
5.3.2.4 Alternative Ditch Cleaning Practices. By tweaking traditional practices,
ditches can be cleaned in an environmentally sensitive way that benefits the road as well.
Again, please note that these practices may not be entirely new, but just a modification of
something we are already doing.
Watch Weather Conditions. You can avoid potential devastating erosion and
sediment events by only cleaning ditches when no substantial rain or storms are
predicted.
Conduct Erosion and Sediment Control During Maintenance. Temporary
erosion prevention and sediment control practices (refer to Section 5.2.3 for common
basic practices) should be used as necessary during the maintenance operation and until
vegetation is completely reestablished. Vegetation reestablishment is critical - including
seeding and soil supplements and mulching. Seeding for re-vegetation and other
vegetative stabilization practices will be thoroughly covered in Chapter 6.
Sectional Cleaning. Common practice is to clean the entire ditch along the entire
section of road right to the outlet and directly to a stream. We will look at that direct
outlet to the stream and better alternatives, such as outletting into a vegetative filter strip
below. However, we will now look at some alternative cleaning practices that can be used
in combination with other practices. For example, cleaning upgrade sections first and
leaving the last section before the outlet until later avoids excessive erosion. Similarly,
cleaning alternating sections of long ditches accomplishes the same result, and if erosion
does take place prior to re-establishment of vegetation, the sediment will be trapped in
the uncleaned sections that can be cleaned later.
5.3.2.5 Ditch Widening and Slope Flattening. Preventing ditch erosion may be
as simple as widening the ditch to spread water flow and slow velocity or flattening the
ditch side slopes to slow water velocity entering the ditch. Remember, the slower the
water, the less erosive force it has with less potential for sediment pollution. These
practices go right back to the parabolic or trapezoidal shapes discussed before.
5.3.2.6. Reuse of Topsoil and Vegetative Root Mats In ditch cleaning, ditch
widening and slope flattening operations, we usually clean out the established vegetation
and end up with subsoil conditions. In Chapter 2 we saw that "dead" subsoil poses a
problem for reseeding to establish vegetation. Ditch work can strip existing vegetation
and topsoil, which is usually hauled away and discarded. With a little more work and
effort, this material could be reused, and re-vegetation will become easier and more
timely. Depending on the natural conditions and the equipment used, the existing
vegetative root mass can be stripped, laid aside while subsoil is removed to the proper
elevations, and then the root mass reused on the newly constructed surface. This root
mass, with proper moisture, will re-establish and may need no other seeding or soil
supplements added, thus saving additional maintenance work for revegetation and repair
5-12
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of eroded areas. This practice will be further discussed in Chapter 6 when we look at
roadside banks.
5.3.2.7 Ditch / Channel Linings. The water volumes and velocities of ditch and
channel flows may necessitate different stabilization methods using different
ditch/channel linings. Higher velocities usually dictate a more substantial ditch lining.
Each site has to be analyzed to determine what may be required. Charts showing
maximum velocities for different linings are available and are good guidelines. A typical
chart for natural soil, vegetation and several "paved" linings with the maximum velocities
sustained by these linings is shown in Figure 5-8.
Figure 5-8 Maximum Velocities for Various
Typ es of Ditch/Channel Linings
Natural Soil Linings
- Clean gravel
- Silty gravel
- Clean sand
- Silty sand, clay
- Ckyeysand,silt
Vegetative Linings
- Avg. turf, erosion resistant soil
- Avg. turf, easily eroded soil
Max Velocity (fp s)
6-7
2-5
1-2
2-3
3-4
Max Velocity (fps)
4-5
3-4
- Dense turf, erosion resistant soil 6 - 8
- Gravel bottom, brushy sides 4-5
- Dense weeds 5 -6
Paved Linings Max Velocity (fps)
- Gravel bottom, concrete sides 8-10
- Rip-rap side s& bottom 15-13
- Concrete or asphalt IS -20
As velocities increase, more substantial linings are required to prevent erosion.
Remember, however, to keep in mind that if we can spread the water out by widening the
ditch/channel and flatten the
ditch/channel grade, we can slow the
water (reduce the velocity) and possibly
negate the need for a more substantial
paved lining. Vegetative linings are less
costly over the long run when compared
to paved linings. Vegetative linings also
provide for infiltration and better
aesthetics.
5-13 Seeding and mulching may be sufficient to
revegetate the ditch.
5-13
-------
legradable netting will prevent
erosion until vegetation is established.
For stabilizing new or disturbed
roadside ditches with vegetation,
practices can range from seeding and
mulching only or in combination with
biodegradable mats, netting or blankets,
to geosynthetics. These materials provide
erosion prevention until the vegetation
becomes re-established. They usually
come in rolls with directions for pinning
or anchoring. Many different products are
available with many different designs
depending on soil characteristics and
water flow conditions. They allow
vegetation to grow while providing the
necessary erosion protection either
temporary as for the biodegradable types
to more permanent reinforcement
provided by the geosynthetics. Keep in
mind that geosynthetics are not
biodegradable and will remain for an
indefinite period of time.
The type of lining is selected
based on the steepest grade of the channel
or ditch. Velocity and volume of water in
5-15 Many geosynthetic products are available for erosion prevention.
the ditch and the potential for sediment also need to be considered. If the flow is too
slow, sedimentation is the major factor; if the flow is too fast, erosion of the ditch and
lining material is the major factor.
5-14
-------
5-16 Good netting installation, but problems at
pipe outlet need to be addressed.
Of course, any lining should be
installed properly. Photo 5-16 shows a
biodegradable netting installation. But
look at the erosion behind and around the
culvert with sediment on top of the
netting. We need to make sure we
examine the entire area and stabilize
accordingly.
Vegetation lined ditches offer
several advantages including low-cost
maintenance. (Refer back to Figure 5-8 for
maximum allowable velocities for
different types of vegetation-lined
ditches.) Vegetation not only protects the soil from erosion by covering the surface and
slowing the water flow with the root structure reinforcing the soil layers, but it also
removes silts and fines and attached chemicals from storm water allowing infiltration for
ground water replenishment. Keeping suspended solids in side ditches improves water
quality.
We must keep ditches from filling
with sediment. Always look to the source
of the erosion and sediment to determine
what corrective measures can be taken.
Higher water velocities may
demand more substantial linings such as
riprap, as seen in the chart. Reducing water
velocity should always be a priority. For
instance, widening the ditch allows you to
use a less expensive lining.
5-17 Use caution when deciding to line ditches
with rock riprap.
Here is one word of caution. Riprap is
not a good ditch/channel lining choice if further
erosion and sediment is likely. The rock riprap
will fill with sediment resulting in major cleanup
problems. Most likely, the riprap will have to be
removed and replaced at considerable expense.
This type of operation can strain limited local
government budgets. When considering riprap
for ditch linings, factor in future maintenance
costs as well. Photo 5-18 shows a typical rock
riprap use as ditch lining placed during
construction. If this area is not stabilized
immediately, the riprap will end up filled with
sediment during the first rainstorm. Keep future
5-18 Riprap placed during construction—
looking at the sediment potential, was this a
good idea?
5-15
-------
maintenance in mind when
considering any materials or
practices at any given site.
5.3.2.8 Ditch Turnouts and
Vegetative Filter Strips. Do not
outlet ditches directly to streams.
Photo 5-19 shows a common
situation with ditch outlets. They
carry water along with any sediment
directly to the stream, which is the
low point on the road. We need to
change our way of thinking and
doing in this regard. We need to
consider turning the ditch out prior to that low point or that stream into a vegetative
filtering area or "filter strip."
Ditch turnouts and vegetative filter strips should automatically go together.
Vegetation filter strips spread the water flow, slow velocity, decrease erosive force, and
filter out sediment. The slower water allows sediment to settle. Other pollutants that may
have attached to the sediment will also be contained and may break down and dissipate,
as described in Chapter 4.
5-19 Do not outlet ditch directly to stream—use
turnouts into vegetative filter strips!
Road
Ditch
In addition, more
turnouts should always be
an option. Limiting the
length of the ditch to a
turnout will reduce the
amount of water and flow in
the ditch, keeping ditch size
nominal and reducing water
velocity and erosion
potential (remember "divide
and conquer"). Numerous
turnouts may be the answer
to the private property
flooding/wet area problem
created by one long ditch
with one turnout at that
location. Dumping a huge
volume of water with possibly a high velocity from a long downhill ditch can cause
erosion and flooding problems on private property. Installation of additional turnouts will
break the volume of water into smaller quantities, reducing velocity and erosion and
flood potential.
Turnout
Figure 5-9
Vegetative Filtering
Area
5-16
-------
As in other techniques, there are no exact spacing or size requirements for
turnouts. Charts are available but usually are based on only one condition such as the
longitudinal grade of the ditch. They do not take into consideration the many variables
that are different from site to site. Other factors to consider are water volume, ditch slope,
right-of-way conditions, and ownership. Water volume can vary considerably depending
on the terrain - does the ditch just drain the road surface or the road surface plus the
entire hillside adjacent to the road?
Photo 5-20 shows a simple turnout of nominal dimensions and a large turnout that
apparently takes a lot of water. In the case of this large turnout, the terrain and off right-
of-way conditions created no problems or concerns. But every site will be different. We
need to remember that more turnouts mean less water, less erosion, and fewer ponding or
flooding problems, meaning less future maintenance.
5-20 Multiple small turnouts mean less water, less velocity, less erosion potential.
Working with Residents. Do you have a problem concerning drainage and private
property and dealing with residents? Working with property owners is always a
requirement for road maintenance personnel. Most people will respond better if they are
approached beforehand with a thorough explanation of the work or project to be
completed. A resident whose lawn is saturated from a ditch turnout may not be too
enthused about putting in additional turnouts. But if approached prior to the work with a
positive attitude and explanation of the benefits, the resident may be willing to at least try
the solution to see how it works. The additional turnouts may solve the problem by
dissipating the water in smaller amounts over a greater area with no adverse effects
anywhere. Maintenance workers should promise to reestablished original conditions if
the situation does not improve. Establishing good relationships with residents enhances
the road department's ability to implement new practices to get the job done.
5-17
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5.3.3 Practices Related to Ditches and Road Profile
Original fOad grade:
3% rrin.outslope
Gradual, shallow, skewed dip. May need to use select
aggregate & geotextile fabric for crossing area
Figure 5-10 Broad Based Dip
5.3.3.1 Broad Based Dips "Broad
based dips" are shallow gradual dips
skewed across the road in the direction of
water flow, as depicted in Figure 5-10.
"Broad based dips" are used when there is
a high embankment on one side of the
road with a downhill grade. The high
embankment does not allow for ditch
outlets and would normally require a cross
pipe to carry the water to the other side
and then to an outlet. These cross pipes
are expensive to maintain because of their
great potential for blockage and other
problems to occur. Without "Broad Based
Dips," the water is carried all the way to
the bottom of the downhill grade in large
volumes at high velocity. The only way to deal with it then is to build large-sized ditches.
But this approach creates erosion and sediment-ladened flows that usually outlet directly
into a stream. Water also tends to drain down the road surface, building in volume and
velocity, producing severe surface erosion.
("Water bars" may be a familiar term and are similar to broad based dips, but with
a significant difference. Water bars are short, abrupt drainage ways to get water across a
road without using a cross pipe. They eliminate water from flowing down the road and
can be used to actually block traffic use of the road. They have been most often used on
retired logging roads to block traffic and divert water away from the road. Broad based
dips can be thought of as water bars stretched out into gradual slopes in order not to
interfere with vehicles using the road.)
5-21 Severely eroded road - ideal conditions
for broad based dips.
5-18
-------
Ideal location for
a broad based dip
5-22 Broad based dips can be used in lieu of cross-
pipes.
On very low traffic volume
roads, broad based dips present an
alternative to the costly cross pipes
without creating large erosion
producing flows. Used only for
ditch flows, broad based dips
should not be used for perennial
streams with permanent or
intermittent flows. Broad based
dips allow the ditch water to flow
to the other side joining that ditch
flow to a joint outlet or turnout to
a vegetative filter strip. The "dip"
channel is skewed in the direction
of water flow, and the crown of
the road is eliminated within this area. The use of multiple broad based dips on a long
downhill stretch of road also allows a smaller ditch size to carry the limited volume of
water from a shorter section of road, which will not build in volume or velocity within
the area between these crossings. This limited water volume and flow should not be
substantial enough to do any damage to the reinforced road surface crossing.
Broad based dips can be graded
into the road rather easily with existing
road materials. Depending on road
materials and conditions, an hour of
grading and shaping time should be
sufficient to complete a broad based dip.
For general guidelines, water volume
must be contained in the channel with no
overtopping the dip, longitudinal road
slopes must be gradual to prevent
vehicles from dragging. The best way to
test the safe traverse of a broad based dip
is to drive the road after installation. If
the bounce is too great or dragging is experienced, it may be necessary to reshape the
skewed dip.
5-23 Broad based dip reinforced with large
aggregate.
The dip may have to be reinforced or stabilized with a select aggregate and
geotextile separation fabric, since we have water and traffic crossing perpendicular to one
another. The need for this reinforcement/stabilization will depend on water volume and
flow and the type of existing road material. These fabrics will be discussed in Chapter 7.
Broad based dip spacing and size will vary from site to site depending on road
and ditch slopes, volume of water, traffic, terrain, etc. Experienced road personnel know
the roads and the water conditions encountered from storms. Their knowledge of the site
should be sufficient to establish size and spacing required for broad based dips.
5-19
-------
Remember, a greater number of dips decreases the length of road being drained and
thereby decreases the volume and the velocity of the water to be handled within each
broad based dip.
Road grader operators have to be aware of the broad based dip installations so that
they do not think they are washouts or problem areas and reshape the road back to a
normal crown. In addition, winter plow operators should be aware of these installations
for proper and safe plowing operations.
5.3.3.2 Grade Breaks. "Grade Breaks" are long, gradual breaks in grade on a
road with a relatively gradual downhill slope. Grade breaks retain the road crown and
require appropriately placed cross pipes. Grade breaks limit water flow by decreasing
concentration and velocity from a reduced area of road section, resulting in limited ditch
and cross pipe size. This reduction in water volume and flow in turn helps alleviate
problems at the pipe outlet. Grade breaks also limit the length of flow and thus velocity
down the road surface, eliminating potential surface erosion gullies and rutting.
Nav centediiu
gride
Original rc> id eeniedme gride
Figure 5-11 Grade Break
Photo 5-24 depicts typical grade
breaks on a road with a long downhill slope.
Like broad base dips, there are no exact
formulas for spacing or size, again
depending on slopes, traffic, volume of
water, terrain, etc. Although the photo
shows cross pipes at the road low points,
cross pipes can be strategically placed and
can actually be used to create the grade
break. A cross pipe can be installed to
effectively meet the ditch gradient, as shown
in Figure 5-11, and the road would be built
up and over the pipe to create a grade break.
Otherwise, cross culverts would have to be
installed at a much deeper elevation than
the road ditch, resulting in additional
potential for pipe blockage, road flooding,
or road and ditch erosion. Pipe outlet areas
should be continually monitored and erosion protection established as needed.
Alternative erosion prevention measures at pipe outlets will be discussed in a later
section.
5-24 Grade breaks result in short road
sections with reduced water volume and flow
velocity.
5-20
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5.3.4 Practices Related to Driveways. Driveways can only be controlled through
an ordinance or regulations and a permit system. Each local government should adopt
policies and procedures appropriate to their particular situation and resources. Many local
governments provide for a cost sharing arrangement with the property owner. The local
government may pay for and supply a cross pipe to continue ditch flow, or may do the
pipe installation at no cost to the owner. Options as to who does what work and who pays
vary considerably from one local government to the next one, but the decision must be set
by ordinance or regulation. The main factor is "to have control" so road personnel are
free to review the site and determine the best approach to protect both road and
environment while providing safe ingress and egress for the property owner and a safe
roadway for the motorist.
Edge of roadway
Improper
Blocked
drainage ditch
Figure5-12 Common driveway c distinction without control
5.3.4.1 Proper Profile.
Although driveways should not
interfere with normal road and
shoulder profile, driveway profiles
pose additional problems for proper
road drainage. The worst condition
results when the driveway slopes
downward toward the road and is
constructed right to the road edge
obliterating the roadside ditch (see
Figure 5-12). Even if a pipe is
installed to maintain ditch flow, the
water draining from the driveway
flows onto the road, deteriorating the
road surface and causing possible
hydroplaning in the summer and icing
5-25 Improperly constructed driveways create
recurring road maintenance problems.
5-21
-------
in the winter. Continuing ditch flow to drain the road while properly draining the
driveway is imperative to ensure vehicle safety, prolong the life of the road and protect
the environment. Uncontrolled driveway construction can result in high levels of
maintenance, costs, liability, and frustrations, as seen in Photo 5-25. The low point
should be over the ditch line and the ditch flow maintained.
5.3.4.2 Driveways Over Deep Ditches. There are several options for maintaining
good drainage. The most common practice is to install a pipe to carry the ditch flow
under the driveway. With the low point remaining over the ditch line, the road and the
driveway will both drain to the ditch off either side of the drive (see Figure 5-13).
Edge of roadway
Ro
Proper
Figure 5-13 Proper driveway construction with deep ditch
An alternate method for medium-depth ditches is to use an open-top culvert or a
box with an open grate (see Figure 5-14). These can be pre-fabricated items or
homemade. The photo inset in the figure pictures two types of pre-fabricated units, one
all-plastic type with a choice of colored grates. Pre-fabricated units are built to withstand
truck traffic when installed following the respective manufacturer's requirements.
5-22
-------
Edge of roadway
Box with Grate
or
Open-Top Culvert
Figure5-14 Alternate driveway
construction with medium-deep ditch
Several cautions should be noted in using these alternatives. First for safety,
consider animals and bicycles in determining the appropriate sized openings for drainage
in homemade installations. Secondly, although these are definitely beneficial in paved
road and driveway conditions, they can be applied for paved driveways to unpaved roads.
Water coming off an unpaved driveway may cause problems with clogging the openings
or drainage way with eroded driveway material. A paved driveway usually does not
present this problem. Photo 5-26 shows an ideal condition for an open-top grate across
the drive to collect any water without having to alter the driveway grade.
5-26 Open-top grates may be used on paved driveways.
5-23
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5.3.4.3 Driveways Over Shallow Ditches. Of course, if ditches are shallow and
water flow is not substantial, the ditch may be continued across the drive, as shown in
Figure 5-15.
Edge of roadway
Proper
Continue water flow in ditch across
driveway, may need to stabilize crossing
with proper aggregate and geotextile
Figure 5-15 Driveway omsfiiution with shallow ditch
Carrying only ditch flows during storm events, the shallow ditch should be no
problem for vehicles to traverse. This area may need to be stabilized with proper
aggregate and a geotextile separation fabric for crossing traffic. Geotextile separation
fabrics will be discussed in Chapter 7. Photo 5-27 shows a newly constructed access
driveway to a gas facility. The driveway was graded to drain away from the road and
5-27 Gas facility access driveway designed to drain away from road.
5-24
-------
away from the gas facility to a low point on the driveway and then off into the wooded
area (vegetative filter area) on either side.
Of course, every road and
driveway site will have different
conditions with different problems.
Sometimes good solutions are hard
to find, as shown in Photo 5-28.
Each site should be evaluated and
designed for the best drainage and
greatest safety.
5.3.5 Practices Related to
Culverts. Culverts or pipes are
enclosed channels designed to
direct stream or ditch water away
from the roadway. Culverts come
in various materials and shapes.
Selection depends on specific
applications or particular needs such as durability, strength, cost, corrosion resistance,
abrasion resistance, flow characteristics, and installation requirements.
.
5-28 Sometimes good solutions are hard to find!
5-29 Common Pipe Materials
The three common materials available are concrete pipe, corrugated metal pipe,
and plastic pipe, as shown in the photos. Whatever the shape or material, the culvert has
to have adequate strength for support of both fill material and traffic loads. Deep
installations have to support the fill material above the pipe. Traffic loads are a minor
concern with deep installations. However, with shallow installations traffic is the major
concern.
First, we need to understand how vehicle loads are distributed to the road. All
vehicle weight is transferred to the road through the tires. But the area where the tire
contacts the road is small. The pounds per square inch over these tire contact areas are at
the maximum. However, the load is distributed out over a greater area as it is transmitted
down into the road structure, as depicted in Figure 5-16. The greater the road structure
5-25
-------
depth, the less pounds per square inch loading occurs because the same amount of load is
distributed over a larger area.
Vehicle Tire
Road surface
Figure 5-16 Vehicle Load Distribution
In addition to load distribution, it is also important to understand the impact of
moving traffic. Traffic exerts a vertical force due to weight and a horizontal force due to
motion. These two forces combine to produce an impact force hitting the road surface.
The more shallow the pipe, the greater the traffic impact force. It is important to keep a
minimum of twelve (12) inches cover over the pipe below the subgrade of the road to
minimize the effect of this impact factor. Pipes larger than 24-inch diameter may need
additional cover.
Concrete pipe is considered a rigid pipe while corrugated metal and plastic pipes
are considered flexible. Rigid concrete pipe cannot flex, and the pipe itself carries most of
the load, but it is important that the pipe be given uniform support throughout its entire
length to develop its maximum strength. The load-carrying capacity of flexible pipe
depends on the support it gets from the surrounding earth. Proper compaction of the
backfill material in layers is critical to develop maximum strength. Many pipe failures
Fi gur e 5-17 Pip e L o -\
-------
occur due to improper backfill material compaction. Traffic loads, particularly in shallow
installations, will cause the pipe to flex, causing cavities to form around the pipe,
eventually undermining the whole installation. Properly compacted backfill provides the
necessary support to limit flexing movement and possible resultant failure. Figure 5-17
depicts the pipe load support characteristics of rigid and flexible pipes.
Culverts can be a primary cause of erosion and sediment. Culverts normally
restrict water flow as it enters the culvert, increasing velocity, causing turbulence, and
increasing energy at the outlets. Shallow installations across the road can also cause
continual road maintenance work. With a little understanding and consideration, these
problems can be alleviated.
5.3.5.1 Shallow Culvert Installations. Most cross road shallow culvert
installations are dictated by the surrounding conditions and terrain. But when the culvert
is too shallow, heavy traffic can cause problems. As discussed above, flexible type pipe
tends to deflect under traffic, causing road materials to shift and eventual road
deterioration to occur. Cross-pipes of 24-inch diameter or less need that minimum of one
foot of cover material over the pipe beneath the structure of the road. This will protect the
pipe from the impact forces of moving traffic.
5-30 Shallow pipe installations can cause continual road deterioration.
When adequate cover cannot be maintained, there are alternatives. A rigid pipe
(concrete, cast iron, steel) will not deflect to the detriment of the road. A "squash pipe" or
elliptical pipe will allow for proper flow capacity but will give additional cover for
protection. An equivalent 18-inch diameter corrugated metal "squash pipe" is 15 inches
in height. This extra three inches of cover can be significant when it comes to traffic
loads and resulting road degradation. Rigid concrete pipe does come in an elliptical
shape, giving a double advantage of pipe rigidity and extra cover.
5-27
-------
5-31 Shallow installations: use rigid pipe, squash pipe, or elliptical concrete (rigid) pipe.
Another consideration is the
use of multiple pipes of smaller
diameter, allowing more cover but
still providing adequate flow
capacity. To use multiple pipes, there
are a few rules to keep in mind. Flow
capacity is directly related to the area
of the pipe opening. This means that
two 12-inch diameter pipes do not
equal the flow capacity of one 24-
inch diameter pipe. (Remember back
in high school mathematics, the area
of a circle is Tir2 or 3.14 times the
radius squared.) Another rule is to
make sure the pipes are installed far
enough apart to enable adequate
compacting of the backfill material
between the pipes.
5-32 Shallow installation: Use multiple pipes of smaller
diameter, allowing more cover with same capacity.
The use of multiple pipes
usually brings comments regarding
clogging. Any pipe can clog. One of the simplest solutions, particularly with metal or
plastic pipe, is to cut the inlet end of the pipe on a slant or bevel. Any debris flowing
toward the pipe will tend to ride up the slant, and water will continue to flow through the
pipe. If multiple pipes are used, staggering the inlet ends so that they are not parallel in
one line perpendicular to flow will reduce the probability of clogging. Each pipe inlet end
is extended a little further (offset) than the pipe beside it. When large debris, such as tree
5-28
-------
limbs, comes down stream, it will be forced to an angle that is skewed across the pipes,
allowing water to continue flow through the pipes (see Figure 5-18).
fiftff>fififtf,
VfeJUuuhJtAJ
Water flow
Water Bow
A. Cutpipe inlet end on
a h evel or angle (single
or multiple pipes)
f^flflff^fl.
K K ^ „ -->. j. J
B. Offistpye inlets on multiple pye
mstaHations
Figure 5-18 Recommendations to Help Eliminate Pipe Clogs
5.3.5.2 Fords on Perennial streams. Ford crossings eliminate the need for a
pipe. Several states have numerous existing fords along with related erosion and
sedimentation problems. If there is a ford crossing, and it is to remain, the crossing needs
to be stabilized and area drainage altered to flow away from the site. Stabilization can be
accomplished with select aggregate and geosynthetics with several variations being
available (e.g., aggregate and geotextile separation fabric, perforated geoweb filled with
aggregate - discussed in Chapter 7).
5-33 Existing fords should be stabilized to prevent erosion and stream degradation.
5-29
-------
Figure 5-19 Flow characteristics
at pipe ends
5.3.5.3 Culvert End Structures. Here are some ideas to reduce future
maintenance problems. As mentioned above, when water flows into a pipe, it normally is
restricted, as shown in Figure 5-
19. This restriction increases the
velocity of the water and its
erosive force. When water flows
out of the pipe, eddy currents
develop, swirling water back
around at the sides of the pipe,
as also shown in Figure 5-19,
causing erosion and scour.
Straight, smooth transitions into
and out of the pipe reduce
turbulence and erosion at
culvert ends.
Straight transitions in
and out of the pipe, however,
are not always possible.
Roadside ditch water flowing
parallel to the road must be
turned to flow through a cross
pipe. Even in straight
restricted flew
, *c our
• I I • •! \\-fimm jjjf mm
\ \
of Road \ _\
\ \
_\, ^
Figure 5-20 Roadside ditch flows need to turn through
the cross-pipe - end structures protect against erosion
5-30
-------
transitions, circumstances may cause erosion problems on either pipe end. Culvert inlet
and outlet protection is important in the prevention of erosion in these areas.
Inlet and outlet structures not only protect the embankment from undercutting
water currents and eddies, but also help anchor the culvert and help prevent crushing of
the pipe ends from heavy traffic or equipment, A variety of materials can be used for end
structures, from prefabricated units and gabions to cement concrete and flagstone to
native stone that may be available on site. Native stone not only becomes cost effective
but also is environmentally aesthetic, blending in with the natural conditions. The series
of photos show different types of end structures.
5-34 Various materials can be used for end structures.
5.3.5.4. Aprons at Culvert Outlets. Culvert outlets, even with an end structure,
may still pose a problem with the flow discharge energy. It may be necessary to create a
conveyance channel to establish a stable discharge point. For example, a simple pre-
5-35 Typical flared end sections.
5-31
-------
fabricated flared end section (concrete, metal, plastic), as shown in Photo 5-35, provides
an apron to spread the water flow and dissipate energy. Photo 5-36 shows a metal flared
end section on plastic pipe.
Rock riprap can also be used at
culvert outlets effectively. The first photo
is a new installation with seeding and
mulching around the rip-rap. The
vegetation, once established will enhance
the area aesthetics. The size of rock and
the dimensions of an apron will depend on
pipe size, discharge volume and velocity,
and slope of the outlet channel or terrain.
Charts providing guidelines are available.
Using riprap for an apron, however,
should not be so technically challenging.
Experienced road personnel know the
water flow amounts and the potential
5-36 Metal flared end section on plastic pipe.
5-37 Rock rip-rap at pipe outlets spreads flow and dissipates energy.
problems at each specific pipe outlet site.
They can size the apron based on their
past experience. Then, road personnel
should follow up with field inspections
during and after the next several
rainstorms. If erosion is evident past the
riprap limits, expand the apron and inspect
again. In Photo 5-38, rip-rap was placed
from the pipe outlet down the slope as an
energy-dissipating channel.
5-38 Using rip-rap for erosion prevention at
culvert outlet.
5-32
-------
Size of rock & dimensions
of Apron depends upon
pipe size, discharge
velocity, & slope (terrain)
Figure 5-21 Aprons at Culvert Outlets
Although native stone may be the aesthetic choice
of material, depending on location, even brush and tree
stumps can be effective in dissipating flow energy of
water.
5.3.5.5 "Through Drains." Through drains are
cross culverts installed strategically to handle springs or
spring seeps flowing perpendicular to the road. These
drains carry the flow under (through) the road to the other
side. Through drains allow water to continue down the
path it traveled before the road was built. Because this
usually clean water never enters the ditch, it stays clean.
The photos depict typical through drain placements. The
drains prevent roads from intercepting native ground
water flows. If we establish a through drain to allow this
natural flow to continue without entering the road ditch,
we solve several problems. In addition to keeping the
spring water clean, we do not have to handle the water via
the road ditch. This reduces ditch flow and potential
erosion problems in the ditch and at the ditch outlet. With
reduced flow we also may be able to reduce the size of the
roadside ditch.
5-39 Brush, tree stumps, etc. can be
effective energy dissipaters.
5-33
-------
Through-p j» e carries
clean water under road
Road drainage
carried over pjie
5-40 Through drains keep springs and spring
seeps out of road drainage facilities.
If the spring flowing into the ditch has
existed for a number of years, the spring's natural
downhill channel may no longer exist. This
channel may have to be reestablished, keeping
proper erosion prevention in mind.
Through-pipe carries
clean water under road
Road drainage
carried over pipe
5-41 Through drains keep water clean.
5.3.5.6 Large Culverts in Perennial Streams. Large culverts in perennial
(continual flow) streams provide a prime opportunity to enhance the natural stream
environment. With new or replacement installations, a pipe culvert or box culvert can be
sized to accommodate both flow and the natural streambed. Observe the existing
streambed grade and average surface elevation. Set the bottom of the culvert at the
required depth to establish a natural streambed through the culvert. Add stream-like
material in type and size to minimize disturbance.
Another option is to use a metal
plate arch without a bottom. The arch
spans the stream, resting on footers at
each side. This practice maintains the
stream ecosystem and still provides the
necessary conveyance for proper
drainage. This option also enhances
protection against undermining of the
culvert due to seepage around the pipe
(don't underestimate those little crayfish
"critters" from burrowing alongside a
culvert in their attempt to move up
stream, creating water channels along the
outside of the culvert that can initiate an
undermining process).
5-42 Over sizing culverts to allow natural
streambed conditions through the culvert
maintains the stream ecosystem.
5-34
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5.3.6 Combination Practices. The next two practices combine new techniques
with practices described previously. The use of any of the various practices in
combination will depend on analysis of the existing site conditions.
5.3.6.1 The Stream Saver System. Commonly, a road's low point is directly
over the stream. For many years, this condition seemed to be the most practical and
effective way of draining the road. Roadside ditches could be carried directly to the low
point and outletted directly to the stream with a cross culvert carrying the stream under
the road.
Water on road and in side ditches drainsto lowpoint and then
directlyinto stream creating road deterioration, erosion, and
sediment pollution.
Existing Road Profile
Existing Cross
Culvert
Figure 5-22 Common Practice — Low Point
Stream Crossing on Existing Road
But this concept centered on the road only. An analysis of its total impact
revealed some problems. First, everything drains directly to the stream, including any and
all sediment and other pollutants. A deeper look revealed it wasn't really all that good for
the road, either. Under the scenario illustrated in Figure 5-22, if the stream flow exceeds
the culvert capacity and overflows the road, we have created a v-shaped channel,
although flat, to concentrate the flow and increase the erosive energy. This condition can
cause erosion of the road material and continual road maintenance with every major
storm.
5-35
-------
Figure 5-23 Stream Saver System
New Road Profile
Old Road Profile
Existing Cross Culvert
> Reiise the road over the stream crossing.
> Keep road grade level over stream area for sheet
flow during flooding conditions
> Use broad based dips and turnouts to vegetative
filter strips for road and ditch flows on each approach
The solution is to implement a
"Stream Saver System." Raise the road
over the stream crossing, creating a level
area extending away from the stream on
both sides. This level road grade will
allow sheet flow during flooding
conditions, if the cross pipe cannot
handle the flow. Using broad based dips
and turnouts to vegetative filter strips for
the road and ditch drainage on each
approach as conditions warrant will avoid
direct sediment input into the stream and
alleviate some flood flow. If pipe
capacity is severely limited, a flood flow
relief crossing can be established away from the stream depending on the existing terrain
and land uses. This crossing can be stabilized as a low water crossing (refer to Chapter 7
for a description of a stabilized low water crossing using geosynthetics).
In raising the road, additional smaller cross pipes could be installed at higher
elevations than the flood flow relief cross pipes. Depending on depth of new material to
raise the road, these pipes may need only to be laid on the existing road surface or
partially excavated into the existing surface. In certain storms, these pipes would handle
the additional flow without overtopping the road. Although additional pipes mean more
maintenance, these flood relief pipes will only come into use when substantial storms
exceed the capacity of the main cross pipe and will keep the road intact.
5-43 Stream Saver System - raised level road
with ditch turnouts to vegetative filters.
5-36
-------
Figure 5-24 Stream Saver System with
Flood Relief Pipes
New Road Profile
New Flood f ~\*-^~ EM sting Cross Culviert
Relief Pipes
Use smaller diameter p yes at higher elevations for flood relief flow
5.3.6.2 Multiple Culverts. Under certain conditions, multiple culverts at various
elevations may be the answer. As an example, an existing road traversing a wetland area
had existing cross culverts to carry the perennial flow from the naturally formed
channels. Both sides of the road, however, had substantial wetland areas abutting the road
embankment. Under normal conditions, the pipes handled flow adequately. The
watershed, however, being quite extensive, guaranteed that almost any storm would
overtop the road, causing some washout of road material into the stream and wetland. A
stream saver system was implemented. The installation of smaller pipes at higher
elevations and at locations across the extent of the adjacent wetlands gave an additional
benefit to the wetlands. As the water level rose during storm conditions, the additional
pipes handled flow and kept velocities and currents to a minimum, maintaining a more
stabilizing effect on the wetland habitat.
5.3.7 Major Reconstruction:
Raising the Road. Raising the road
involves major filling of the road cross
section between high banks. Before we get
into the details for this work, we should
understand the reason and basis for the
road being in this condition. Referring
back to the beginning of this chapter in
Section 5.2, we mentioned the typical
cross section of many roads depicts a low
road surface with high roadside banks on
each side. This is particularly the case in
forested areas. In almost all cases, this
condition is the result of years of
traditional road maintenance.
5-44 Remember this photo? Look at the banks
on either side of the road.
Routine road maintenance practices (road grading, snow removal, shoulder
cutting, ditch cleaning, etc.) combined with the wear and tear of traffic and natural
erosive forces have the cumulative effect of lowering the road elevation in relation to the
surrounding terrain. As the road profile drops, or becomes entrenched, water draining to
the road is trapped and concentrated in parallel ditches, and the road begins to function as
5-37
-------
a channel for water flow. This entrenched road profile makes installation of crosspipes,
turnouts, and other drainage features to get the water away from the road increasingly
challenging. Raising the road can eliminate the persistent maintenance difficulties
associated with this entrenched condition.
Looking at
the sequence of
photos in Figure 5-
25, one can view the
lowering of the road
surface through the
years establishing
those high banks on
either side. The new
road (#1) starts to
show surface rutting
(#2). The ruts get
worse (#3) until
grading operations
re-establish the
profile and attempt
to create a better
ditch gouging into
the bank for
drainage (#4). The
banks' vertical
surfaces start to fall
in, and, along with
the eroded road
materials, create the
need for ditch
cleaning . Repeated
maintenance
operations of blading and grading along with ditch cleaning (#5-8) finally results in a
need (#9) for additional material as the road crown is lost. Material is added (#10) and the
process starts again. This repeated maintenance over the years as more material is lost
causes the road to become more and more entrenched (#11-16). Snow removal becomes a
problem with the snow being piled along the banks, aggravating the problem (#17). This
entrenchment causes the road to act as the drainage conveyance channel, resulting in
enhanced erosion of the road and banks and sediment-laden ditches. This, of course, leads
to greater road maintenance as the road becomes deeper and wider year after year (#18-
25).
rt W in -iff/ W ^
Figure 5-25 The Sequence of Road Entrenchment
5-38
-------
5.3.7.1 Raising the Entrenched Road We can break this cycle We need to
restore the road to its original surface elevation. This could mean substantial fill and a
major work effort. Fill material becomes a prime cost in this practice. There are local
governments, however, that can obtain free fill and can load and haul the material with
their own equipment. Free fill and use of in-house equipment reduces the cost although it
will still be a major work effort. Photo 5-45 shows two roads that would be ideal
candidates for road raising. Both of these roads have severe drainage, erosion, and
sedimentation problems requiring substantial and continual maintenance. But returning
11 I ' '• ; ll i
5-45 Good candidates for "raising the road."
these roads to their original elevation could significantly cut maintenance costs. Many
roads could be raised to eliminate the banks on both sides, providing excellent road
drainage conditions with much less erosion and sediment pollution.
Figure 5-26A shows
a typical existing entrenched
roadway. Figure 5-26B
shows the filled roadway,
completely eliminating a
bank on one side and
reducing the height of the
bank on the other side.
Depending on terrain, etc,
drainage could be sheet-
flowed off the road without
a ditch on the one side. The
road no longer serves as the
drainage channel and will
experience far less surface
erosion, rutting or other
degradation. Snow removal
no longer becomes a
problem since we now have
a place to plow it.
5-39
Figure 5-26 Raising the Road.
-------
The series of photos shows Red Rose Road in Huntington County, Pennsylvania.
The road was raised with free fill shale from a nearby pit. This road then received a final
road surface aggregate. (Refer to Appendix 5, Worksites in Focus, to review this
Pennsylvania Dirt and Gravel Road Program Project.) Raising the road improves
drainage resulting in less erosion and road degradation and thus less road maintenance
and a better environment. Winter snows can now be plowed totally off and away from the
road, providing better protection from melting snow water seeping back into the road
structure.
5-46 Red Rose Road, Huntington County, PA
Before, an entrenched road
During placement of shale fill
Ideal Elevation Achieved
After finishing the shale
Final road with driving surface aggregate
Use of Recycled Material. Commonly used fill materials include native rock and
mining spoil. Other fill material such as concrete or demolition waste, tire shreds, ground
glass, spent sandblasting sand, and coal combustion waste has also been used to aid in
recycling programs. Select fill material carefully. Some materials may need special use
permits or require special handling. Work closely with your local conservation agencies
and state environmental agencies.
5-40
-------
adjacent tost rea
5.3.7.2 Raising the
Road and Moving Away
from a Stream. Figure 5-27
shows a road raising
variation where the road has
a high embankment on one
side and falls steeply off
directly to a stream on the
other side. The road is
entrenched with side ditches.
The road is raised upslope
away from the stream. We
eliminate the entrenchment
on the stream side, allowing
for sheet flow across
additional vegetated area.
On the other side, we reduce
the embankment height for
better stability and drainage
control. Depending on the
various conditions, insloping could be combined with raising the road, providing
additional benefits.
5.3.8 Practices Related to Bridges. Although bridge replacement is neither
simple nor inexpensive, sometimes there is simply no alternative. But there are several
environmentally sensitive techniques available that will protect the environment and
prolong bridge life. Common practice, once more, places the bridge at the low point of
the road grade across the stream. The road drains directly onto the bridge, carrying road
material and sediment that then drains directly into the stream through the bridge
"scuppers" or drainage openings. In addition, abutments built to support the bridge are
placed so as to constrict the water flow to the main channel. This scenario poses several
maintenance problems. Scour and erosion at bridge abutments shorten bridge life.
Further, the constricted water flow frequently results in gravel bars that must be
continually removed.
Figure 5-27: Raising the road and moving away from the
stream.
Bridge at the low point of road
Road debris washes
onto bridge deck
Normal stream channel
Figure 5-28 C ommoii Practice - Existing Bridges
Abutments constrict
st rea m f I o w cau si n g
bars
5-41
-------
5.3.8.1 The Stream Saver Bridge System. The Stream Saver Bridge System
reduces maintenance by raising the bridge and sloping the road away from it. Roadside
ditches are then turned out into vegetative Filter strips well away from the bridge
approaches.
Normal stream channel
Stream flood corridor
+ Keep bridge high, slope road to low points away from bridge, draining
ditches through vegetativief iIter strips
+ Bridge should span entire natural stream channel, no nestrictionsto
natural flows, no gravel bars, no abutment scour
Figure 5-29 Better Ridges Ideally, the
stream saver bridge
spans the entire
natural stream flood
flow channel.
Spanning the natural
stream corridor
reduces interference
in stream flows,
eliminating abutment
scour and gravel bar
problems. This system better protects both the environmental stream ecosystem and the
bridge structure.
Raising the bridge also allows better drainage off and away from the bridge
structure prolonging its life. Bridge drainage can also be carried away from the stream to
the same ditch turnout through a vegetative filter strip. Bridge drainage scuppers
(openings in the bridge deck - remember the photo from Chapter 3) normally empty the
flow directly to the stream along with all
the accumulated sediment on the bridge
deck. A raised bridge surface that drains
off the bridge longitudinally keeps
sediment and debris from washing onto the
bridge and the bridge surface drainage
water clean. This clean water will be much
less detrimental to the stream if the bridge
has scuppers draining directly into the
stream.
5-47 Eliminate this maintenance and
environmental problem with Stream Saver
Bridges.
5-42
-------
5-48 Gravel Bar Removal is a costly
maintenance task.
5.3.8.2 Gravel Bar Removal.
Gravel bars normally occur because the
bridge structure interferes with the natural
conditions of stream flow, but can occur
naturally anywhere along the stream. At
bridge structures, however, gravel bars
mean additional maintenance. The bars
must be removed to maintain proper flows
for flood control and to prevent damage to
the bridge.
Sometimes the removed gravel is
used for road material. If we refer back to
Chapter 3 to the discussion of road
material, this "gravel" does not meet the specifications for good road material. It
commonly has a rounded shape with little fines and does not lock together to stay in
place.
Gravel bar removal also poses several problems other than the cost of removal.
Operations cause stream disturbance with resultant turbidity and sediment downstream.
This can also result in 100% embeddedness, as described in Chapter 4, to the detriment of
stream life. This turbidity and sediment continues for an extended period of time until
natural conditions can re-establish the equilibrium.
If gravel bar removal is necessary,
there are a few factors to be aware of. Do
not use the removed gravel for road
material. Keep stream disturbance at a
minimum by working in low flow
conditions and keeping equipment tires
and tracks "dry." Work with your
conservation agencies to secure the
necessary permits.
If gravel bars are extensive and
form rapidly after each removal
operation, this material has to be coming
from somewhere. Look at the stream
flow and upstream terrain conditions to
determine the source and what may be causing the material deposition, and see if there is
a remedy that can prevent future gravel bars from forming.
5.3.8.3 Bridge Decks. Crowning the bridge deck similar to the road will also
enhance bridge drainage. Many of our rural bridges have flat decks that aggravate the
problem of water and debris on the deck, particularly when the road approaches on either
side drain directly to the bridge.
5-49 Gravel bar removal causes turbidity and
sediment for extended time periods
detrimental to the stream ecology. Would you
want to fish here?
5-43
-------
Figure 5-30 Better Bridges
a
Crown the bridge deck
for proper drainage
Incorporating these techniques
allows for longer bridge life by
providing better drainage of the bridge
deck and away from the total bridge
structure. It also reduces maintenance
costs because less material accumulates
on the bridge, drainage scuppers are not
blocked, less choking sediment flows
into the stream, and no gravel bars have
to be removed. Just as importantly, the
whole stream ecosystem is not affected
by these activities, leaving a better environment.
5.4 Summary
This chapter started to fill your toolbox with many various tools or practices that
are environmentally sensitive and good for your roads. These practices, for the most part,
are simple, practical techniques that can easily be adopted as part of your daily routine
maintenance work. Of course, the more major practices of raising the road and replacing
bridges can also reap major benefits for your road system and the environment.
Many of these practices, particularly concerning proper drainage, can be adopted
for paved roads and will prove to be just as beneficial as they are for unpaved gravel
roads.
As you begin to use these practices, you will begin to see the long-range continual
benefits for your roads and your environment and thereby for your community.
The following Appendix 5 reviews actual projects in which a combination of
practices has been used to solve erosion and sediment pollution problems stemming from
dirt and gravel roads.
5-44
-------
APPENDIX 5. Worksites in Focus
This appendix reviews several actual projects funded through the Pennsylvania
Dirt and Gravel Road Program, as described in Appendix A-l. The first worksite on Red
Rose Road was a Demonstration Project for the Pennsylvania Dirt and Gravel Road
Program that became the "Drive Thru Classroom Self-Guided Tour" Project to
demonstrate various environmentally sensitive maintenance practices being taught to
local governments under the program. The next two worksites were actual projects
undertaken by Pennsylvania local governments with major funding through the
Pennsylvania Dirt and Gravel Road Program. At each local government worksite, the
problem(s) is identified, with objectives, considerations, and solutions, followed by a cost
summary for the project. The accompanying photos give an insight into the before and
after conditions at each site, demonstrating the benefits of using environmentally
sensitive maintenance practices to the road and the environment and to the overall
aesthetics and to a better community.
5-45
-------
raising the road profile
before, during & after
Please contact the center with any questions:
toll free: 1-866-668-6683
e-mail: dirtandgravel@psu.edu
For more information visit:
www.dirtandgravelroads.org
Center for Dirt and
tudles
environmentally
sensitive
maintenance
ose
road
Drive-T1
Self-'
The Problem:
Because the road was lower tftan the surrounding
terrain, rainfall and runoff were captured and con-
centrated in the roadway, gaining energy and erod-
ing road surface and bank materials. This concen-
trated flow exited the road with tremendous force,
directly into the stream. The stream, consistently
inundated with a high-velocity input of sediment-laden
water, was eventually incised to the point that it was
totally disconnected from its floodplain.
The Solution:
The road profile was raised to elimimate ditches and
allow road runoff to flow gently from the road sur-
face into the surrounding porous forest soils. One
particularly problematic section of road was shifted
uphill, away from the stream, to protect an already
damaged and fragile stream reach from further
harm. Selective thinning of the tree canopy allows
the road to dry out while promoting healthy forest
growth patterns.
How to enjoy the outdoor classroom:
Follow along with this brochure
Look for matching numbered signs
The icon indicates picture
location and direction)
Stop and have a look around
-------
rose
road
Site Location
& Directions
rose
road
Site Map
DIRECTIONS
RED ROSE ROAD is located in Huntingdon
County 10 miles south of State College. From
the north, take Rte. 26 south from State College.
Red Rose Road is on the right 3.5 miles past the
summit of Tussey Mountain. From the south, take
Rte. 26 north from Huntingdon approximately 19
miles. Red Rose Road is the first road on the
left after passing the entrance to Whipple Dam
State Park.
State College
10 miles
f/F\\V ^^V/J
;iB^l
Tributary to
Shaver's Creek
-------
ENTRENCHED ROAD
BEHAVES LIKE A DITCH
Years of wear and tear, machine maintenance
and erosion caused the road surface to become en-
trenched below its banks. This captures all water
from surface and near-surface drainage. The cap-
tured water gains energy as it flows down the road
causing it to erode the road surface and side ditches.
Road banks collapse into ditches mandating more
machine work, which further lowers the road. Ob-
serve how the natural surface drainage has been
restored by filling the road back to it original eleva-
tion and stopping the endless cycle of erosion and
repair.
ERODED BANK & SHADE
In addition to the sunken road surface, no-
tice the density of vegetation shown in this photo.
The shade is so dense, plants whose roots could
have held the bank's soil in place did not have enough
light to grow. Also, look at how the treetops lean
over the road shading it. Individual trees, which were
not structurally sound or vigorous were removed. If
not disrupted by deer browsing, vigorous strong
young plants will now grow with more full light and
provide protection for the soil. Trees growing close
to the road will receive light from both sides and de-
velop even crowns.
CONTRASTING
DRAINAGE TURNOUTS
Road drainage constructed without concern
for increasing environmental harm and maintenance
costs frequently cuts banks vertically and makes
steep drainage patterns. The maintenance practice
at this location was to dig excess material out of the
turnout and pile it beside the drainage course, con-
stricting the width of flow causing the water to move
faster and be more erosive. Now, observe how drain-
age from the restored road height does not require a
ditch, and how flow is dispersed over a wide area at
a shallow angle.
-------
before
NATURAL ENERGY MANAGEMENT
In a natural landscape it is difficult for water
to concentrate. Organic material, including branches
and logs, and rocks disrupt and slow the water's flow.
Porous forest soils reduce the amount of surface
runoff by allowing water to infiltrate.
The natural pattern of organic debris was
successfully emulated at the discharge end of this
pipe. This simple use of organic materials not only
dissipates the energy of the pipeflow but also pro-
vides life-supporting food for plant roots and the mi-
crobes living in conjunction with them. The roots, in
turn, further stabilize the soil and increase infiltra-
tion.
MAINTAINABLE ROAD SURFACES
The bank-run shale used on the previous road
surface had pieces in it that were too large for avail-
able grading machines to work into a drivable sur-
face. Left un-graded, the road deteriorated. Shale
has two other disadvantages. It "slacks," or breaks
down into silt or clay soil particles when exposed to
air, and it does not resist the abrasion of traffic well
enough to be rated as a suitable road surface mate-
rial. Clay and silt are the soil types most prone to
make dust and sediment. The Driving Surface Ag-
gregate visible now is a specially formulated mixture
of abrasion resistant limestone. Contrast this sur-
face with that of nearby off-site locations.
GRADE BREAK
The pipe here was installed at an elevation
high enough to allow the pipeflow to discharge at
natural ground level. In order to get the required 12"
of cover over the plastic pipe, a grade break was
constructed. Grade breaks are inexpensive to build,
easy to maintain, and serve several purposes. The
additional road material used to construct the grade
break provides cover for the pipe, slows traffic, and
acts to divert water flowing down the road surface
into the road ditch. This disruption of water flow pre-
vents road deterioration from water movement on
steep road grades and lengthens maintenance
cycles.
-------
before
HIGH-CAPACITY DITCH
The picture shows evidence of fast moving
water. Tangled brush mattresses and large rocks
washed clean indicate a strong erosive force gener-
ated by concentrated swift flow. Contrast how wide
and deep the pictured ditch is compared to the
present ditch.
Large rocks were placed in the ditch before
the road was filled in. Known as a "French Drain", it
serves to conduct clear sub-surface water downgrade
without forcing it to come to the surface, where soil
particles can be carried as unwanted sediment to
the stream. To some extent, sub-drains help keep
the road base drained, and therefore stronger.
BANK WASHOUT OVERLOADED DITCH
Concentrated flow washed out the road bank
at this location sending a plume of sediment to the
stream. Over time, that concentrated flow further
eroded 400 ft. of ditchline discharging even more
sediment directly into the stream.
A non-corroding cross-pipe was added un-
der the road to harmlessly direct this flow to the for-
est floor on the other side of the road. The pipe
entrance was raised to lessen the energy the water
gained by falling into the pipe. On the other side,
the pipe discharges at natural ground elevation. Dis-
persed there in a natural pattern, the water can infil-
trate into the ground as if the road had never been
built.
A STREAM AND ITS FLOODPLAIN
A stream will naturally form a channel with
the width and depth to contain average flows while
allowing naturally-occurring high flows to spill over
its bank and onto its floodplain. By spreading high
flows out over the floodplain, the excess energy and
force of the water is released. Compare the size and
shape of the stream channel here to that below the
road crossing. The concentrated volumes and ve-
locities of the road drainage have cut a deep gully-
shaped channel disconnecting the stream from its
floodplain thereby preventing energy dissipation.
When all the energy of high flow events is confined
within the channel, the cycle of repeated "down cut-
ting" results.
-------
RAISING THE ROAD PROFILE
Excavated shale and limestone from the
abandoned pit was trucked and spread on the en-
trenched road. A D-8 bulldozer crushed, spread and
compacted the fill material.
Work sequence was as follows:
• Dump and spread stone of all sizes;
• Track over and crush material to 12" & less;
• Blade resistant larger stone to ditch line to cre-
ate a subsurface French drain along road;
• Blade forward fines in approximate 8" lifts;
• Track compact and build surface shape into
road with each lift, repeat until natural drain-
age is restored.
NEW ROAD LOCATION
Sediment from the original road, indicated on
the photo at right, flowed directly to the adjacent
stream reach. The road base would eventually have
failed as storm flows continued to erode the stream
banks. This is a very common problem wherever
roads are located too close to streams.
The road was relocated to demonstrate the
value of respecting and using the forces of nature to
correct long-term environmental problems. The pit
was reclaimed, surface drainage was restored to its
original pattern and a buffer zone was created be-
tween the road and the stream.
READY FOR NATURE TO ADOPT
Pictured here shortly after project completion
is the newly created buffer area immediately after
seeding and mulching. Note the naturalized uneven
surface with stump, log and rock obstructions to over-
land water flow. High stumps were placed near the
road to provide a visual marker of the road edge.
Contrast during your visit how growth patterns
are influenced by water and leaves trapped upslope
of the obstructions. As organic matter builds up from
leaf litter, more water will be retained over these dry
soils. In turn, the numbers of microbes and small
creatures like earthworms will increase. As they do,
growth capacity of this abandoned shale pit will in-
crease.
-------
DESTRUCTIVE IMPACT ON STREAM
This section of stream channel should look
similar to the stream channel above the road which
is generally very stable, producing only small amounts
of sediment from the bed and bank materials (# 9).
The channel shape, characterized by a series of cas-
cades and irregularly spaced scour pools, is normally
12-15 times wider than it is deep.
In contrast, the stream channel immediately
below the road reflects the long-term effects of con-
centrated road drainage. Notice the severe down cut-
ting that causes the channel to be deeper than it is
wide and the complete physical separation of the
stream from its floodplain.
LOOKING EAST AT SHALE PIT
The road at its new alignment and elevation
shows several features that prevent pollution. Com-
pare this to previous photos.
In the right foreground see the bank bench
(1) and how it intercepts and redirects water toward
the camera at a nearly level slope. On the left, the
extra space between the road and the stream acts
as an effective buffer. In the background, notice the
ditch to the left (2) is located farther from the road
preventing the bank drainage from mixing with road
material.
AGGREGATE PLACEMENT
Drainage patterns such as crown and grade
breaks, visible in the surface of the road, are reflected
in every layer of fill to enhance subsurface water
movement under the road base.The top layer is Driv-
ing Surface Aggregate (DSA), a specially formulated
abrasion resistant mixture of crushed limestone. DSA
has a carefully blended size distribution from 11/4"
stone to fine particles small enough to pass a screen
with 200 holes per square inch. The fines act to fill
all voids and create strength from increased density.
Placement through a paving machine to a uniform
8" depth enables compaction with fines in place. This
placement method avoids aggregate separation.
-------
LOOKING EAST AT SHALE PIT
Easily available shale was periodically re-
moved in uneven patterns, extending back over 120'
to the right. It was taken from around the underlying
hard limestone protrusions, shown here near the
road. The road at this spot curved around the end of
the abandoned pit, immediately adjacent to the
stream (by the people in the photograph).
Contrast this "BEFORE" image with photos
#12 and #14 showing the new road at its higher el-
evation and alignment. The actual point from which
this photo (#16) was taken is now under 6' of fill and
would be on the bank closest to the stream.
LOOKING EAST AT SHALE PIT
The steep bank on the right, shown being
cleared of trees, is now under the left edge of the
road. This bank was partially lowered, and the road
was built at a steeper angle allowing it to pass over
the old bank at a higher elevation.
These actions prevent the creation of a typi-
cal 1:1 uphill road bank or "cut" slope and the ero-
sion consistently associated with such steep road
banks. When native vegetation is thoroughly estab-
lished, this more natural land shape will blend in with
the beauty of the surrounding forests even better
than pictured in photo #12.
WORK IN PIT
Excavating material from the abandoned pit
produced fill to raise the road and correct the en-
trenched drainage pattern. By removing shale from
the pit, a less steep and therefore less erodible pro-
file was created. The more naturally appearing shape
was formed with machinery normally used in road-
work.
A D-8 bulldozer with ripping teeth and "U"
blade loosened the shale and limestone domes left
behind by the smaller machinery used to originally
excavate the pit. A track hoe was used to load trucks,
shape the final grade and set the stumps.
-------
Worksite
in Focus
Potter County
Horseshoe Road
6/10/04
Problem Identification
Routine maintenance operations and the
wear and tear of traffic had the
cumulative effect of lowering the road
elevation in relation to the surrounding
terrain (see photo). The resulting
entrenched road trapped road drainage.
Confined by the road, this water
concentrated in parallel ditches and
gained velocity. As the volume and
velocity increased, more and more
valuable road material was washed
away, polluting nearby Pine Creek.
Project Objectives
1. Prevent direct discharge of sediment-
laden road drainage to Pine Creek.
2. Reduce concentrated drainage from
parallel ditches.
3. Filter road runoff using existing
roadside vegetation.
Project Considerations
Off right-of-way (ROW) drainage input
from an adjacent driveway compounded
the problems on Horseshoe Road.
Existing drainage structures (ditches and
crosspipes) were inadequate to handle
flow volumes.
Spring seeps in the road bank drained
directly onto the road surface resulting in
a soft road base and observable
ditchflow year-round.
Adequately addressing drainage on
Horseshoe Road required an additional
drainage outlet, installation of under-
drain, and elevation of the road itself.
Project Statistics
Potter County -
Ulysses
Township
Coudersport
Ulysses
Horseshoe
Road*
•^Galeton
Road:
Road Owner:
Affected Watershed:
Project Length:
Cost:
Date Completed:
Horseshoe Road
Ulysses Township
Pine Creek
1600ft
$53,829
September 2002
Before: The entrenched road trapped road drainage resulting
in fast-moving concentrated ditchflow. This water eroded
road material and deposited it directly into Pine Creek.
The publishers of this publication gratefully acknowledge the financial support of the Pennsylvania State
Conservation Commission. For additional information or assistance, contact: Center for Dirt & Gravel
Roads Studies, Penn State University, 207 Research Unit D, University Park, PA 16802 (Toll-Free
Phone: 1-866-668-6683, Fax: 814-863-6787, Email: dirtandgravel@psu.edu). Additional copies
available on our website at: www.dirtandgravelroads.org
Center Tor Dirt and Gravel Road Studies
-------
Project Solutions
Adding a cross-pipe: Installing a new cross-
pipe on the road provided an extra drainage
outlet and shortened the flow length of
parallel road drainage. By minimzing the
distance water has to travel before it is
removed from the road corridor, the velocity
and erosivity of the water are reduced.
Adding perforated underdrain: Underdrain,
or drain tile, was added in the ditch to
collect water flowing from spring seeps.
This eliminated perennial ditchflow and
corrected the soft road base problem.
Filling the road: The elevation of the road
was raised by filling the road profile. The
added elevation eliminated the need for
parallel ditches and allowed drainage to
sheet flow into the surrounding terrain
through vegetated buffers, removing
sediment-laden surface flow to Pine Creek.
Adequate Culvert Size: A hydrologic &
hydraulic analysis was used to determine
the proper size of the culvert needed for the
stream crossing. The existing 30" round
concrete pipe was replaced by a 77"x 52"
squash pipe. The road was raised to
ensure proper cover over the new pipe.
Cost Summary
Total Project Value: $53,829
District Funding: $31,769
Materials $28,428
Contracted Work $3,341
In-Kind from twp: $22,060
Materials $3,837
Labor & Equip. $18,223
For More Information
After: The road profile was raised eliminating
ditchflow on the downslope side of the road.
Drainage that was trapped on the entrenched
road can now sheet flow freely off the road into
surrounding vegetation. Because the water
does not have the opportunity to gain velocity,
its erosive potential is greatly reduced.
After: The pipe was re-sized and the road raised
for proper cover over the new installation.
The Center for Dirt and Gravel Road Studies
(814) 865-5355
www.dirtandgravelroads.org
Potter County Conservation District
Eric Potter
(814)274-8411
* Directions to Horseshoe Road worksite: From Coudersport: Take U.S. Route 6 east approximately 13 miles to State Highway 449.
Follow 449 north to Brookland; just past Brookland veer right at the Y-junction onto SR 1001 . Horseshoe Road (T450) is 4/10 of a mile
ahead on the left. The project begins at the intersection with SR 1001 and continues for 1600'.
This publication is available in alternative media upon request. The Pennsylvania State University is committed to the policy that all persons shall have equal access to
programs, facilities, admission, and employment without regard to personal characteristics not related to ability, performance, or qualification as determined by
University policy or by state or federal authorities. The Pennsylvania State University does not discriminate against any person because of age, ancestry, color,
disability or handicap, national origin, race, religious creed, sex, sexual orientation, or veteran status. Direct all affirmative action inquiries to the Affirmative Action
Office, The Pennsylvania State University, 201 Willard Building, University Park, PA 16802-2801; tel. (814) 863-0471; TDD (814) 865-3175. U.Ed #RES-01-50.
-------
Worksite
in Focus
Problem Identification
Fulton County
Dutch Corner Road
Dutch Corner Road contributed concentrated, sediment-laden water to Patterson Run, a tributary of
Licking Creek. Three primary issues caused this impairment: steep road slopes, deeply entrenched
road segments, and significant off right-of-way (ROW) water inputs. Long steep road segments
bordered by high banks on either side served to trap stormwater water increasing its volume and
velocity thus making it highly erosive. Off ROW inputs from driveways and connecting paved roads
contributed more water to already concentrated erosive flows.
Project Objectives
1. Minimize the entrenchment of the road.
2. Separate off ROW drainage and prevent it
from flowing onto the road.
3. Divide and minimize concentrated water flow
on steep road segments.
Project Considerations
The deep road entrenchment made raising the
road elevation to the height of the surrounding
landscape impractical and expensive. The
topography lent itself on the steep entrenched
road segments to pipe installation through the
road banks at a slope of 2% and discharging
road drainage on the other side of the bank.
Drainage routed in this way is directed into
adjacent vegetation where it encounters
resistance, can release energy and infiltrate
slowly.
Project Statistics
Fulton County
Breezewood
Licking Creek
Township
Dutch
Corner
Road*
McConnellsburg
Road: Dutch Corner Rd
Road Owner: Licking Creek Township
Length: 4,835ft
Date Completed: November 2003
Legend*
Pipe Replacement
New Pipe
Pipe through
Pipes not drawn to scale
Raising the road elevation to the elevation of the
surrounding landscape was impractical because
of the amount of material required (above).
The publishers of this publication gratefully acknowledge the financial support of the Pennsylvania State
Conservation Commission. For additional information or assistance, contact: Center for Dirt & Gravel
Roads Studies, Penn State University, 207 Research Unit D, University Park, PA 16802 (Toll-Free
Phone: 1-866-668-6683, Fax: 814-863-6787, Email: dirtandgravel@psu.edu). Additional copies
available on our website at: www.dirtandgravelroads.org
Center for Din and Gravel Road Studies
-------
Before and After Shale Placement. Before, severely entrenched road slopes steeply to steam at the bottom of the hill. After,
cross-pipes are added to divide drainage and reduce concentrated flow and the road elevation is raised 2' to cover the new pipes.
Project Solutions
Road profile. Shale was placed on
steep entrenched areas to a
maximum depth of 2 feet to obtain
adequate cover on new crosspipes.
Road surface was topped with
Driving Surface Aggregate (DSA) for
improved performance.
Adding crosspipes and installing
pipes through the bank. 3 existing
crosspipes were replaced and 9 new
drainage pipes were added. 3 of the
9 were installed through the bank.
Increased road drainage capacity
minimizes concentrated flow before
sufficient volume and velocity can
build to strong erosive force.
Re-profiling driveways.
Driveways were re-shaped at the
point where they entered the
roadway to eliminate any direct
discharge to the road.
Grade breaks and broad-based
dips. On steep driveways at
points of concentrated flow, grade
breaks and broad-based dips were
installed to direct drainage off the
driveway surface into surrounding
vegetation for infiltration.
* Directions: From U.S. 30: Take Breezy Point Road north 0.4 miles, turn right on Dutch Corner Road. Dutch Corner Road is located
12 miles east of Breezewood, 6 miles west of the intersection of U.S. 522 and U.S. 30 north of McConnellsburg.
Pipes Through the Bank. Note the depth of the trench during construction.
After construction the pipe has been covered and stabilized with vegetation.
Cost Summary
Total Project Value: $70,962
District Funding:
Materials
Contracted Work
& Equipment
In-Kind from twp:
Materials
Labor &
Equipment
$63,712
$46,970
$16,742
$7,250
$4000
$3250
For More Information
The Center for Dirt
and Gravel Road Studies
(814) 865-5355
www.dirtandgravelroads.org
Fulton County
Conservation District
(717) 485-3547
This publication is available in alternative media upon request. The Pennsylvania State University is committed to the policy that all persons shall have equal access to
programs, facilities, admission, and employment without regard to personal characteristics not related to ability, performance, or qualification as determined by
University policy or by state or federal authorities. The Pennsylvania State University does not discriminate against any person because of age, ancestry, color,
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Office, The Pennsylvania State University, 201 Willard Building, University Park, PA 16802-2801; tel. (814) 863-0471; TDD (814) 865-3175. U.Ed #RES-01-50.
PENNSTATE
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Environmentally Sensitive Maintenance Practices
for
Dirt and Gravel Roads
Chapter 6: Environmentally Sensitive Maintenance
Practices: Roadsides and Streams
6.1 Introduction
Throughout the previous
discussions of natural systems and road
maintenance, we have shown how the
road and environment are deeply
intertwined. That is particularly true of the
relationship between roadsides and
streams. Traditional road maintenance
activities for shoulder, ditch, and
roadsides frequently include undercutting
stable slopes, removing valuable
vegetative cover from roadside banks, and
a failure to re-stabilize unprotected soil.
The greatest failing of traditional
maintenance practices is in the underlying
belief of many road managers that
roadside vegetation is unwelcome. When
road maintenance activities leave bare
soil, the resultant erosion and deposition
of sediment into critical drainage facilities
creates the need for more frequent
maintenance cycles. This becomes a self-
perpetuating cycle of maintenance and
pollution with unacceptable costs to local
governments and unacceptable detrimental results to the environment.
As our machinery has become larger and more powerful, in many cases, we have
lost touch with basic principles of nature and natural systems; we have fallen into a belief
that we can work to set standards, forcing nature to comply to our will. Often the natural
consequence of our actions is in direct conflict with our maintenance goal.
Environmentally sensitive maintenance practices take into account road maintenance
goals and natural principles to provide cost effective longer-term solutions to traditional
cyclical maintenance activities.
6-01 Typical roadside erosion problems.
6-1
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In this chapter, environmentally sensitive maintenance practices will be presented to
deal with the necessary activities of roadside vegetation management and bank
stabilization. A short discussion of stream bank maintenance around cross pipes and
bridges for stream crossings is also included.
6.2 Expectations of a Finished Product
Even without an understanding of natural systems, road managers usually are well
aware of the roads in their network that require less maintenance. Roads requiring less
maintenance frequently are working in harmony with natural principles. The road
manager would be wise to "read" these roads, comparing them with their problem roads
with excessive maintenance.
In this section we want to step out of the box of traditional standards and
expectations. Roads that look like they are in harmony with nature, require less money to
maintain, pollute less, and offer the additional benefit of being beautiful.
Most of us have been around long enough to witness the incredible advances in
machinery over the last forty years. Although some local governments move forward
faster than others, most counties and townships are vastly better equipped today than they
were twenty-five years ago. As our equipment has gotten better, so too have our projects
gotten larger. Generally, local governments have effectively updated their dirt and gravel
road networks that so well serve the citizens and industries of their communities.
The development of our state and federal highway systems has in many ways
provided guidance and expectations to local governments and citizens for how their roads
should look. We as local officials and road managers, however, need to look at and
develop guidelines for our roads that fit the use and needs of our own communities.
These local roads provide a very different link in our national highway system.
A natural systems approach to road
maintenance requires changing
expectations and behaviors. When a road is
working well within the environment,
minimal maintenance should be required. A
road that requires continual maintenance
attention is probably working against
natural principles. Simply asking the
question, "Does it look right?" can provide
terrific insight. However, the "right" that
forms the comparison must be a road that is
in harmony with nature. Herein lies a
problem if we try to use standards and
practices developed for superhighways and
interstates.
6-02 When a road is working well within the
environment, minimal maintenance will be
required.
6-2
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6.3 Practices Related to Roadsides
6.3.1 Vegetation Management. Tree trimming and removal, brushing, brush
cutting, right-of-way clearing are all terms for vegetation management. These activities
are common, and road managers may need to perform these activities for a variety of
reasons. We need to look at these common practices and reasons and determine what is
best for our roads and our municipality.
Roadside vegetation plays an important part in our road maintenance program.
Understanding the natural systems allows us to use these systems to help in more
effective road maintenance.
6.3.2 Equipment and Methods. First, let's examine typical roadside maintenance
equipment and methods and evaluate their effectiveness in all areas of road maintenance,
the environment, and community relations.
The normal methods used
to trim trees, remove brush and
cut vegetation along roadsides
include manual methods with
manual equipment such as
chainsaws, string trimmers, and
hand pruners; mechanical
methods with mowers and brush
cutters; and chemical methods
with chemical application
equipment and herbicides. All of
these methods and equipment
have their place in an integrated
vegetation management program
and can be used effectively. There
are some cautions, however, that
should be noted.
6-03 Roadside Vegetation Management Options.
In an environmentally
sensitive maintenance program, chemical methods using herbicides are certainly the first
concern. There are many potential problems associated with the use of herbicides. As a
result, numerous federal laws and regulations govern their use. States have also adopted
regulations, patterned after the federal laws, regarding the use of chemicals for vegetation
control. These regulations require local government applicators to become certified
through testing. Environmentally sensitive maintenance does not promote the use of
herbicides. If you do use herbicides, you need to become familiar with the laws and
follow all the requirements and regulations associated with herbicides use.
6-3
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Because roadside vegetation management is labor-intensive, boom mowers have
become increasingly popular. The boom mower, properly used, is a labor saver and can
be safer than other equipment such as chainsaws. However, one only has to travel down a
road on which a boom mower was used to
totally destroy the roadside vegetation,
leaving a hurricane-aftermath look, to
realize that the use of this equipment can
get out of hand. Damage to large tree limbs
can eventually kill the total tree. Refer to
the discussion in Chapter 4 on
understanding your trees and the effects of
wounds.
Boom mowers also raise some
roadside safety issues. Using a boom
mower to cut down young saplings, leaving
those "spikes" behind, can result in a very
unsafe condition. Motorcyclists or
bicyclists who may skid off the road and
upset can be impaled on these "spikes,"
causing severe injury or death, not to
mention the resulting tort liability claims.
Boom mowers and their resulting
destruction can also be a public relations
headache. Many complaints have been
lodged against both state and local
governments about the "butchering" of
roadside vegetation.
6-04 Boom mower impalers!
6.3.3 Roadside Clearing. Traditional right-of-way clearing, or "daylighting"
practice, often creates problems for roadside vegetation for our dirt and gravel roads.
These practices may have their place on the interstates and superhighways, but often they
cause increased maintenance work on gravel roads in forested areas.
Common accepted reasons for clearing the roadside of trees and bushes are:
1. Eliminate shade
2. Improve roadside visibility
3. Establish a safety "clear zone"
4. Reduce routine trimming.
All of these reasons have some merit and may apply for some roads, but a more
thorough understanding of the conditions encountered on dirt and gravel roads, and the
consequences of inappropriate roadside clearing, is necessary to make effective decisions.
6-4
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6.3.3.1 Shading, Good or Bad? Brush cutting, trimming, and tree removal for the
purpose of eliminating or reducing shading is probably the most common roadside
management practice, other than roadside mowing of grass. A great deal of money is
invested in vegetation management for shade reduction each year. The goal of improved
public safety is universal and laudable. On low traffic dirt and gravel roads, however,
excess tree removal can have the dire consequences of increasing speeds to unsafe limits.
6-05 The disadvantages of shade: retains moisture to promote icing, reduces visibility.
Why should we eliminate shading? Here are the reasons:
1. Shading retains road moisture, promoting unsafe conditions such as
icing in the winter.
2. Shading also reduces visibility and limits the "clear zone," again
affecting safety.
An abrupt transition from bright
sunlight to dense shade or vice versa can
be a great safety hazard. Extreme changes
in light can have a devastating effect on
the motorists' visibility and be a direct
cause of accidents. Extreme changes in
light conditions should be avoided.
Shading, however, also has
advantages. Shading:
6-06 Bright sunlight to dense shade or vice
versa - major visibility safety hazard - should
be avoided.
1. helps retain road
moisture, reducing
dust:
2. reduces growth of colonizer plant species and encourages desirable
herbaceous plant growth (discussed below);
3. is more aesthetically pleasing, contributing to tourism and the
economy.
6-5
-------
With this information, we may want
to look at shading with a new perspective.
A limited amount of shading may be more
effective and efficient for our road
maintenance and the environment.
6.3.3.2 Problems with Traditional
Clearing Techniques. Traditional clearing
techniques involve total removal of brush
and vegetation along the roadside from
right-of-way line to right-of-way line,
typically resulting in vastly increased
sunlight along the edge of the road. So, if
increased sunlight is the goal, what is the
problem?
If we could view time-lapse photos
of the road and its surrounding environment
following a traditional roadside clearing
before doing it, we would see it is not the
best or most effective practice. If the
roadside is wooded or forested and the road
well shaded and we automatically go in and
cut everything down, as shown in Figure 6-
la to Ib, on each side of the road for
whatever distance we consider necessary,
let's observe what happens.
The forest trees, by nature, have
grown structurally as a forest, meaning that
each tree can depend on surrounding trees
for protection against the elements. When a
section of trees is cut down, the remaining
trees along the cut edge are open to storms and wind and may not be structurally strong
enough to withstand these conditions. Wind damage, broken branches, and even
uprooting can result, as shown in Figure 6-2a.
^reduces colonizer growth
encouraging desirable
erbaceous plants
6-07 The advantages of shade.
Traditional clearing practice for a shaded road would be from right-of-way line to right-of-way line
Figure 6-1
6-6
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Common reaction of previously protected trees Dense weak colonizer growth, which can threaten
exposed by clear cutting - broken stems, wind roadway & recreate shade, appears surprisingly
damage, uprooting fast
Figure 6-2
Additional problems with common clearing practices include the rapid regrowth
of the removed trees through stump sprouting. These stump sprouts are weak in structure
and can become a continual maintenance problem.
When large quantities of trees and vegetation are removed, previously protected
plants, now exposed to full sun, begin to fail. A formerly shaded roadside with low
growing, broad-leafed ground cover vegetation becomes a completely different
ecosystem when exposed to full sun. Exposing low growing, broad-leafed, shade-tolerant
plants to full sunlight typically kills them, with the potential of soil erosion.
Unfortunately, when the roadside,
which was previously shaded, receive full
sunlight, nature produces vigorous growth,
as depicted in Figure 6-2b. This vigorous
growth is due to the invasion of colonizer
species that are most attracted to this
environment, but are the worst possible
roadside plants. Colonizer species, which
we described in Chapter 4, Section 4.5.4
on succession, are fast-growing, weak
growth types. Colonizer trees can threaten
the roadway safety and recreate shade.
These colonizer trees then become
6-08 You do not need fast-growing weak-
structured colonizer-type roadside trees!
extremely high maintenance roadside
plants. In many cases the plants we most
want to remove are the plants most encouraged by our efforts. This creates the need to
mow and trim in increasingly frequent cycles.
So in this scenario, the mowing/removal of trees and brush in the interest of safety
and visibility, have the opposite effect, starting an endless cycle of cutting and re-cutting
of this colonizer growth.
6-7
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6.3.3.3
Alternative
Techniques. The
solution is to use
the forest system to
reduce
maintenance. By
taking advantage of
natural principles, it
is possible to create
safe clearances,
provide enough
shade to control
dust and invasive
species, and
eliminate the
invasive rapid re-
growth of colonizer
species and frequent mowing cycles. We need to develop a strategy following some basic
guidelines.
Selective trimming retains some shading to protect roadside
soils and forest edge & still allow drying of roadbed
Figure 6-3
6-09 Remove dead, diseased, unstable, or dying
trees first.
Be selective! When doing roadside
trimming and tree removal, remember to
remove the dead, dying, unstable, or
damaged trees first. Trees that have been
damaged by previous maintenance
activities, automobile accidents, etc. will
eventually die and become hazards.
The second priority should be to
remove the existing colonizer trees. These
trees, even if they are healthy, are not
good roadside trees. They are very rapid
growers and have weak wood and short
lives. They commonly fall onto the road
or drop limbs, which create maintenance
and hazards.
After removing the damaged trees
and the colonizers, it is advisable to look
the situation over and evaluate the rest of
the trees. Maintaining strong, slow-growing, deep-rooted climax species should be an
objective (refer to chapter 4, Section 4.5.4). Avoid straight-line cutting, however,
favoring instead an irregular edge. Traffic will tend to travel more slowly on a road with
an irregular edge. Speed has always been a major safety problem for our dirt and gravel
-------
6-10 Pockets of deep shade can create irregular
winter icing conditions.
roads. Clearing the roadside completely
or cutting back on a straight line parallel
to the road gives the motorist the safe
illusion to increase speed.
Maintaining a uniform level of
shading is best. One of the greatest
dangers from shading comes from winter
conditions where pockets of deep shade
create irregular icing conditions. The
objective should be to thin the canopy to
achieve the desired shade density.
Sometimes it is necessary to thin back off
the edge of the right-of-way, as the
desired sunlight may only be available
from the side, not from above. Obviously it is necessary to discuss any plans and
objectives with property owners to receive permission to work off the right-of-way.
6.3.3.4 Adjacent Residents and Off Right-of-Way Work. Local governments
must have a public relations strategy. Road managers should meet with the property
owners where brush cutting/trimming is proposed. This local government representative
should discuss the plan to do brush cutting with the property owner, offering to walk the
roadside and specifically discuss the goal of the project and to take into consideration the
property owner's concerns. This one-on-one contact with the property owner prior to the
actual cutting of brush or trees is critical. It establishes a level of respect for the property
owner, something that is commonly overlooked. It is especially helpful to walk the road
with the property owner. When a tree is infringing on the travel-way or an obvious threat
of falling into the roadway, it is easier to recognize the problem when both parties are
standing right there looking at it. Listening to the property owner's concerns and
developing a plan that meets both parties' needs is vital to the success of a roadside
management plan.
6-9
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6-11 Before and after look at selective tree trimming during a road project - letting in more
sunlight with less shade - striking a balance.
6.3.3.5 Advantages of Using the Forest System. In a situation where a dirt and
gravel road is heavily lined with trees or passes through forested areas, a vegetation
management program that uses the forest system to take advantage of natural principles
can save time and money in several ways.
1. Moisture is nature's stabilizing agent. Allowing enough shade to hold
some moisture on dirt and gravel roads helps to hold the surface together and
reduce dust. Although few road managers would readily identify moisture
retention as a benefit of shaded roads, they will almost always tell you they use
less dust control in shaded areas.
2. Maintaining shade
along our roads reduces the
establishment of colonizer species
(aspen, birch, poplar, sumac,
striped maple, etc.). These rapidly
growing, weak-wooded trees
create the biggest maintenance
problems, especially during
winter maintenance operations.
(They lean out in the roadways
with snow load.)
6-12 Would anyone want to plow this road?
3. The trees that are removed are less likely to return as stump sprouts if
shade is retained. All of us have witnessed the rapid return of vegetation under
new power line cuts. This is usually a combination of stump sprouts and colonizer
species. This scenario can be avoided by simply allowing the road to remain
partially shaded.
6.3.3.6 A Common Pitfall in Tree Removal. All of these techniques will reduce
the frequency and cost of roadside vegetation maintenance. Importantly, at no time in our
discussion of vegetation management has a diameter or size been mentioned as a criterion
6-10
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for what to remove and what to leave. Herein lies one of the biggest problems with boom
mowers. Boom mower operators are frequently instructed to cut "everything you can
reach and everything small enough that you can cut." This direction and practice will
ultimately have, as its consequence, roadsides vegetated only by large trees. If these trees
are the right species and are in good health, this might be a defendable practice.
Boom mowers may be effective in maintaining right-of-way, but great care should
be exercised when using them to re-establish those long neglected rights-of-way. When
decisions are based solely on size, damaged and potentially hazardous trees are left while
the potentially stronger, healthier replacement trees are removed. Often this leaves a
roadside stimulated into vigorous growth by excessive sunlight. In the case of boom
mowers, what is perceived as the "easiest way" may actually be the most expensive.
Additionally, some of the most beautiful, slow-growing, strong, wildlife-friendly
trees along the roads are being systematically removed because they have the misfortune
of being small. Dogwood trees and serviceberry trees are some of nature's finest work
and are frequently chosen as roadside trees by planners. Yet they are often removed by
boom mower operations just because of their size. Would it not have been better to
remove the big old damaged or dead trees and save those small dogwoods? The dogwood
makes an excellent roadside tree with the
added value of blossoms to beautify the
roadside in the spring.
6.3.3.7 Tree Leaves. What road
maintenance person hasn't uttered
unmentionable language concerning leaf
problems? Leaves in ditches, leaves on
the road - leaves! leaves! leaves! Fall can
be a beautiful time of the year with the
diverse coloration of the landscape from
the changing of the leaves. This seasonal
occurrence concludes, however, with the
leaves falling to the ground and filling
ditches and covering roadways. If we are adding road material, the layer of leaves can
become a problem if not removed. If the layer is substantial, the slow composition of the
leaves can result in a slip plane for road material to slide. In addition, leaves fill the
roadside ditches and interfere with proper drainage, clogging ditches and crosspipes when
the rains come.
6-13 Dogwoods are a good roadside tree with
the added value of spring blossoms.
6-11
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Leaf removal can be labor intensive and burdensome to the road maintenance
crews. Backpack blowers or wheeled walk-behind power blowers are often used to blow
leaves off the road prior to aggregate placement. Leaf cleaning in the ditches can be
accomplished by the usual grading of ditches, removing the leaves and possibly the
existing vegetation lining that may not have time to re-establish prior to winter.
6-14 Leaf Blowers to Clean Ditches and the Roadway
The job can be made easier with a three-point hitch leaf blower. These are the
same machines used by many golf courses. By using this type of blower, we can save
time and effort. The machine is easy to use and relatively inexpensive considering the
amount of leaf blowing needed on many road systems.
Blowing the leaves off the road and out of the ditches and leaving them to
decompose in the natural roadside environment is definitely environmentally sensitive. In
addition, we reap the benefit of not losing soil and existing vegetation through a ditch
grading operation, which would open the potential for additional erosion and sediment.
6.3.4 Using Other Plants for the Roadside. In addition to maintaining limited
shading, there are many low maintenance plants that readily grow on roadsides. Deciding
what plants to encourage on a given site involves many factors. Often maintenance
practice, such as mowing, can be timed to encourage some plants while discouraging
others. Plants such as day lilies and ferns are examples of low maintenance plants that do
a terrific job of holding soil in place and limiting growth of invasive species. Day lilies
and ferns do not benefit from mowing. Wherever possible, care should be taken to leave
these plants intact during a mowing cycle. Unless they create a visibility problem, there is
no benefit to mowing these plants. If invasion of woody plants into fern or day lilies is a
concern, time mowing operations for the dormant seasons of the year. Visibility is better
at this time also.
6-12
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Day Lilies
6-15 Day lilies or ferns are good roadside plants - low maintenance, aesthetically pleasing
When doing shoulder cutting or ditch cleaning, if the berm or spoil material is full
of sod with day lilies or ferns, we should use this material to our advantage. Pick a bank
where there have been problems holding the soil in place and coat it with six inches or
more of dirt full of sod and weeds and lilies and whatever else. In no time at all these
plants will become established on the new soil. Obviously care should be taken to
provide some type of temporary erosion control for the time it takes the plants to become
established. It is a lot easier to vegetate soil, which is naturally full of plants, than to get
plants to grow from seed on hand-polished subsoil. Remember our discussions in Chapter
2 on topsoil and subsoil.
Grass, of course, is a wonderful
roadside plant. Because of how it grows,
(refer to Chapter 4, section 4.5.2 Plant
Basics) grass is usually not affected by
mowing. Grass holds soil in place and
helps slow the speed of surface runoff.
Grass also traps sediment that is moving
with the water. The benefits of grass from
an environmental point of view are
obvious. The benefit of grass from the
perspective of a road manager should also
be obvious, but frequently it is
unrecognized.
6-16 Grasses make good roadside plants,
establishing surface erosion protection
Other vegetation can be used to reduce maintenance in many roadside situations.
By encouraging appropriate plants for the location and terrain, maintenance can be
minimized and the environment enhanced. Deep-rooted species can be used for soil
reinforcement. Ground covers can be used for surface erosion prevention. Species
selection for these applications should consider low or no maintenance.
6-13
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Working with our local and state conservation agencies on appropriate plants for
specific sites is always a good idea. We'll be discussing site evaluation in a little more
detail below.
6.3.5 Clearing Stream Banks at Cross Pipes. In Chapter 2, we discussed the
historical aspects of how so many roads were built close to streams. With so many roads
adjacent to streams, we have many stream crossings with associated culvert pipes and
bridges. Maintenance around these structures consumes great quantities of time and
money for local governments. As science has learned more about water and how it
behaves around restrictions in flow, better bridges and culverts have been designed and
built. The stream saver system along with the section on better bridges described in
Chapter 5 is a great step forward in reducing maintenance and pollution at stream
crossings.
6.3.5.1 Common Practice and Associated Problems. We need to zero in on the
specific maintenance operation of clearing brush and trees from stream or channel banks
adjacent to these crossings. Traditionally, common practice has been to clear stream
banks upstream and downstream from a roadway cross culvert or bridge to clear the
floodway and improve drainage. Doing so left the crossing with a clearner look and
presumably easier maintenance. But are these assumptions really valid?
6-17 Clearing stream banks for a road crosspipe replacement can have devastating effects on the
stream and future maintenance.
Although taken during different seasons of the year, look at the before and after,
Photo 6-17, of a crosspipe replacement project and consider some of the potential
problems. Referring back to Chapter 4, the stream shading is reduced, affecting stream
temperature, which in turn affects the stream habitat. Outside inputs of vegetation debris
vital to stream life are eliminated, and the streamside habitat is reduced. Look at the
stream width upstream of the work area and within the work area. Would fisherman fish
this area, or would they go upstream to find the natural shady 'holes'? These are all
environmentally related.
6-14
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Widening the stream causes the water flow to spread out and slow down, resulting
in deposition of material immediately prior to the new crosspipe. It should also be
apparent that any debris coming down the stream will be deposited at the road culvert or
bridge, with possible blockage of drainage openings and subsequent flooding damage at
the road or bridge.
Clearing the floodway to improve drainage could also have the unintended
consequence of causing flooding downstream. The fact is that improved drainage usually
means faster water. Faster drainage of a watershed means more water at one time with
potential flooding downstream.
6.3.5.2 Alternative Practices. The alternative technique, or environmentally
sensitive maintenance practice for stream bank/stream crossing vegetation is very easy:
"DO NOTHING!" The natural stream channel will have less influence on the road
crossing and cause less maintenance. The "before" Photo 6-17 emphasizes the fact that
any large debris will get hung up long before it gets to the crosspipe.
Sometimes it is impossible to do nothing; some streams produce so much debris
that large pieces upstream from the road have to be removed. Common sense dictates that
some vegetation maintenance such as selective thinning may be required. The message is
to look at what is being done and ask if it is necessary or it has any benefit. The less we
disturb streams and stream bank vegetation around our pipes and bridges, the better for
the environment and reduced future maintenance. If vegetation has to be removed at the
immediate worksite for room to work, trim to the ground. The vegetation will grow back
and again create a more natural low-maintenance site. So the solution is to either do
nothing (avoid) or do only what is absolutely necessary (minimize).
6.3.5.3 Benefits of a New Approach. Vegetation in the floodway catches a lot of
the debris in high water flows, spreads and slows the water flow, allowing gradual escape
or release of water without letting the debris clog the drainage pipe or bridge opening
There are other benefits of woody type vegetation around pipes and bridges.
Although grass has roots and does act as an erosion preventer by holding soil in place,
these roots are shallow surface roots. Woody vegetation commonly has deeper roots and
offers greater soil reinforcement around stream and road banks. This extra reinforcement
is especially needed at bridges and pipes where water is forced to change direction or
speed, causing much more turbulence and the potential for erosion and scour.
Streamside vegetation also shades the stream. The stream ecosystem is very
temperature sensitive. Raising the water temperature can have dire consequences for
species living in the stream. Additionally, vegetation along streams provides habitat for
numerous species critical to the aquatic ecosystem along with those important outside
inputs vital as the food link in the aquatic food web.
6-15
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All of these benefits result in a better environment, less maintenance in keeping
the banks cleaned or mowed and the pipes clear and open, and less potential of flooding
at the site or downstream.
Although this section dealt with clearing of stream or channel banks at a roadway
cross pipe, the next section deals with the stabilization of road and stream banks.
6.4 Practices Related to Road and Stream Banks
In discussing roadsides, roadside banks and stream banks are always a large issue.
Our road and streams banks are constant sources of erosion. Road banks, in particular,
are constantly being disturbed and stripped of ground cover, waiting for erosion to occur.
Erosion from these bare soil road banks creates ongoing maintenance headaches by
filling drainage ditches and clogging pipes.
There are a few general factors that should be noted in re-establishing a stabilized
bank, be it a road bank or a stream bank. Large, obvious sites with bank erosion can be
easily targeted and are commonly the only ones that get taken care of. There are,
however, numerous small sites of unstable eroding banks that are left unattended. An
effort should be made to do a bank restoration program and include all of these small
sites. When we began to add up all the existing small sites across our own local road
system and then add those to all of the other sites in other local road systems, we realize
that even the small ones can add up to significantly contribute sediment pollution. In
addition, these small sites will only continue to get worse with time if left unattended and
will eventually become the large site.
6-18 Eroded roadside banks are common sights, but add up to a large erosion and sediment
pollution problem affecting both roads and the environment.
6-16
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The type and physical structure of the soil is the first obstacle of plant
establishment. We have already discussed the advantages of topsoil over subsoil. We also
need to note that the use of heavy equipment should be limited to avoid excessive
packing of the soil. Soil compaction can affect the amount of water penetration versus
runoff and the ability of roadside vegetation to survive. Remember, when we reseed an
area of our lawn, it is always recommended that we till the soil, breaking up the hard
surface. Roadsides tend to have very compacted soils due to vehicles and equipment and
construction and maintenance activities for the road.
6.4.1 Initial Site Visit. To initiate environmentally sensitive maintenance
practices for bank stabilization, a thorough investigation of the site is required. When we
think about what makes a bank stable, there are several conditions that we need to
determine. First, what type of material and slope do we have? Second, what is the
drainage condition? And third, what is the existing vegetation, if any? These important
characteristics are all interrelated and should be considered during an initial site visit.
At this initial site visit, we need to ask ourselves the specific questions listed
below. Look at each of the following sets of photographs. Do these banks look familiar?
Soils:
1. What soil types are present?
2. What is the degree of slope?
3. Is the bank stable?
4. Are there existing slip planes undercutting the surface?
What's the
degree of
6-19
6-17
-------
Is Hie bank
stable?
Are there
existing slip
6-20
Hydrology:
1. Is the slope wet or dry?
2. Is there seepage or over the bank flow?
3. What is the condition of nearby banks?
4. What is the surrounding terrain?
6-21
6-18
-------
What s the
condition of
nearby
bunks?
6-22
Vegetation:
1. What is the existing vegetation?
2. What vegetation occurs naturally in the area?
3. Are tree roots reinforcing the bank?
4. Is it shady or sunny?
What's the
existing
vegetation?
What
vegetation
occurs
natmallv'
6-23
Are tree roots
reinforcing
the bank?
6-24
6-19
-------
In pursuing
this initial site
evaluation for road
and stream banks, it
is wise to observe
and follow the
natural patterns and
not disturb a stable
bank. One of the
most common
problems is "bank
gouging" during
grading operations
or ditch cleaning.
The grader operator
cuts into a stable
bank and creates a
vertical surface at
the toe of the bank
as shown in Figure
6-4. This vertical
bank is unstable and
will slough off as
the bank tries to
return to a stable
angle. As this occurs, the ditch is filled back in and the whole process starts over again
with the next grading operation. Photos 6-25 show to what extremes this operation can
lead and clearly indicate that, as these banks collapse, grading operations will again be
required - the recurring maintenance in an endless cycle.
Bank will try to
re-stabilize
Figure 6-4: Bank Gouging
6-25 Unstable vertical bank will collapse.
6-20
-------
Keep in mind that tree
removal can result in bank failure.
The soil reinforcing roots will no
longer be effective. Tree roots are
mother nature's reinforcing bars,
as discussed in Chapter 4, Section
4.5.2.4
6-26 Tree Roots: Mother Nature's Rebar.
6.4.2 Proven Techniques for Banks. Once the site investigation is complete,
then the selected technique or techniques can be effectively implemented. Always keep in
mind the possibility of using a combination of practices. Several of these practices are
commonly known and used but are still worth mentioning as good "tools" to protect both
the road and the environment.
6.4.2.1 Diversion Swales. Diversion or interceptor swales divert upslope surface
water before it washes over the top of the road bank and into the road's drainage ditch.
Diversion swales reduce the volume of water to be handled by the road ditch, decreasing
the size of the road ditch and potential erosion problems. They also stop the erosive
forces on the face of the bank.
Diversion Swale
stops surface
water from
reaching road
Diversion swales must be stable,
with a level longitudinal grade for
infiltration back into the soil or sloped to
an adequate discharge area. They must
contain the overland flow and not be
overtopped. Diversion ditches are
effective for draining low gradual
vegetative slopes. Referring to Photo 6-
27, this would be the ideal location to
6-27 Ideal Location for a Diversion Swale.
6-21
-------
6-28 Diversion Swale: Wider swales and gradual slopes result in
more infiltration and less water volume to handle.
create a diversion swale. The surface runoff from the entire upward slope could be
drained into a swale at the top
Road BJ of the road embankment. The
road bank would then be
protected against the erosion
gullies that are now present.
Diversion swales are
usually outside the right-of-
way but need not interfere
with agriculture. The wider
and more gradual the
sideslopes and longitudinal
slope, the more infiltration and
less accumulation of flows
will result. By eliminating
washouts and erosion gullies
that form down over the road bank and start to "eat" back into the hillside, the swale can
actually improve drainage of the landowner's property.
6.4.2.2 Slope Geometry. Slope geometry is an important aspect of bank
stabilization. Flattening the slopes gives greater stability and less erosion by spreading
water flows out and slowing the flow velocity, in much the same way as flattening
roadside ditches reduces flow velocity, as discussed in Chapter 5.
Observing and following existing natural patterns can be beneficial. Do not
disturb stable areas if at all possible. And remember the value of tree roots in maintaining
a stable slope. Look at the two photos. The first one shows a patchy, vegetated road bank.
Vegetation has already started, but is having difficulty establishing on dead subsoil.
Notice the flush of growth in the ditch area. Perhaps with a little topsoil, seed, and mulch,
this area could flourish. No need for any grader work. If cleaning the ditch, make sure to
clean only to the toe of slope and not to cut into that toe of slope. The second photo
shows a stable revegetated bank. Here, a "Do not disturb" technique is needed.
A little help is needed!
"Do not disturb!"
6-29
6-22
-------
Roughening, grooving, or tracking slopes have distinct advantages. First,
however, we need to change our perception of what a "well-dressed" bank should look
like. We need to think in terms of existing natural banks. Natural banks are not regular or
consistent as to surface and slope, and they are not polished and shiny. A natural
appearing slope as shown in Figure 6-6, offers numerous advantages. The shined bank
offers none.
Organic Debris
Figure 6-6: Roughening, grooving, or tracking slopes have
many advantages
As stated above, roughening, grooving, or tracking of slopes have many
advantages:
1. Catching rain water
2. Slowing surface water flow
3. Reducing erosion
4. Increasing filtration
5. Trapping sediment
6. Holding water, seeds, and mulch for enhanced vegetative growth.
These techniques require light
equipment in order to prevent packing the
soil to the detriment of plant growth.
Track equipment should be used up and
down the slope, not across, so the grooves
catch water and hold seeds and mulch.
6.4.2.3 Benching. Benching,
commonly used effectively on long, steep
slopes, provides the same benefits as
roughening the sloped surface. The top of
the bank may have to be moved back and
may be off the right-of-way. A good
working relationship with property owners
is required.
6-30 Tracking the newly constructed banks.
6-23
-------
Figure 6-7: Benching is commonly used on steep slopes
To be effective, the bench must collect water. The outside edge must be higher
than the inner edge to prevent over the bank flow, as shown in Figure 6-7. The bench
then should have a gradient to drain the bench to a proper outlet. Some benches can be
gradually run out to the road ditch grade for drainage. Do not overlook the use of smaller
multiple benches or steps and keeping some irregularity for a more natural appearance, if
appropriate, for the site. Photo 6-31 shows some newly constructed low-gradient bank
benches.
6.4.2.4 Seeding and Mulching. In all these practices, proper seeding is essential.
Seeding requires:
1. An initial site evaluation (physical condition, soil tests)
2. Soil preparation (tilling & soil supplements)
3. Selection of species (temporary and permanent cover)
4. Timing of seeding (spring, fall
preferred)
5. Establishment procedures
(seeding methods, mulching).
The purpose of the initial site
evaluation is to determine all site factors,
both physical and chemical, which may
limit the adaptability of various plant
species to the site - moisture, temperature
conditions, deficiency of vital soil
nutrients, and any materials in the soil
which are toxic to plants.
6-31 Newly constructed low-gradient bank
benches.
6-24
-------
6-32 Soil: Grab a handful, squeeze; does your hand stay "dirty"?
Soil tests determine a majority of this information. You can also get an idea about
the soils by getting your hands dirty. Grab a handful, squeeze to check for moisture and
clay content. Does it stick together? Does your hand stay "dirty" due to clay? (Refer to
Appendix 6A: Soil Identification in the Field.) The optimum condition would be to work
lime and fertilizer into the top 12 inches of soil for planting. The soil does need to be
loosened by tilling with proper supplements added for good plant growth.
Selection of species is also important. In most applications, a seed mix of fast-
growing nurse grass and the desired long-term plants will work well. Nurse grasses, such
as rye grass, rye grain, and redtop, grow fast, binding the soil and sheltering slower
germinating seeds, and give a good first impression of re-vegetation.
Legumes are a good component of the seed mixture. Legumes fertilize the soil by
adding nitrogen to the soil, aiding the other plant types. Examples of legumes would be
clover, flat pea, and bird's foot trefoil.
Time of seeding varies on geographical location. Generally, prior to mid-June and
from mid-August to mid-September are the best times. This is somewhat a function of
soil temperature, so summer can work, but make sure enough water is added with a good
layer of mulch.
Establishment procedures refer to seeding methods and mulching. Broadcast
spreaders are commonly used for road banks and the scale of most projects. Seeds can be
sown by hand or a cyclone spreader as well. Hydroseeding is a spray mix of water, seed
and fertilizer onto the bank. Hydromulching takes the above mixture and adds mulch.
Mulching is a requirement to hold and protect the seed. After mulching, the ground
should not be visible. More mulch should be used in the summer and fall to protect from
heat and frost, respectively. As another rule of thumb, if using hay or straw bales and the
job requires more than thirty bales, get (rent) a power mulcher. Anyone who has shaken
bales for mulching will gladly accept this rule of thumb.
6-25
-------
6-33 Rolled seed-impregnated straw blankets
can be pinned to steep slopes for re-
establishment of vegetation.
Straw is cleaner than hay (no seeds) and provides good coverage with a mulcher.
Hay is loaded with seeds and is easier spread by hand. Hydromulching, usually green in
color, put in the hydroseed mix, may also be used.
The photo shows a vertical slope
that has been seeded and mulched. This
is a drainage inlet construction site where
the bank had to be removed for inlet
installation. The terrain and other
conditions such as trees and a driveway
directly above dictated the vertical slope.
But it was not left bare to erode away
with the first rainstorm. This is actually a
straw mat, straw stitched into a flat mat
and manufactured in rolls, and pinned to
the bank. Wet down the mat, sprinkle
seeds on it and then pin it to the bank.
There are mats that are already
impregnated with seed that can be used
effectively. Leaving bare soil will only result in erosion and sediment and additional
maintenance work and cost.
Started plants can be used, but are normally limited to small sites where it is hard
to get plants to grow from seed. Started plants include pachysandra, day lilies, and
periwinkle and are commonly available.
Although this was only a quick overview of seed mixtures and seeding, there are
some valuable resources and expertise available. Working closely with the local and state
conservation agencies, Departments of Agriculture, College/University Extension Offices
is necessary for most local road departments, since road personnel do not generally have
expertise in this area. As an additional advantage to consulting the experts, some species
are invasive and should not be used.
6.4.3 Bioengineering Techniques. Bioengineering techniques are being used
effectively in restoration of many stream and upland banks. Bioengineering combines the
biological elements of using live plants with engineering design concepts for slope
protection and erosion reduction. Although not the solution to all slope failure and
surface erosion problems, many bioengineering techniques can be used in combination
with other techniques and practices.
Bioengineering takes a holistic approach, gauging factors such as environmental
compatibility, use for difficult sites, cost effectiveness, and the biotechnical strengths of
the systems. Many bioengineering practices can be used in wet areas with minor
disturbance to the site, enhancing the environmental sensitivity benefit. Hand labor is
usually a necessity, but this becomes a benefit for those difficult sites where the use of
machinery may not be feasible. That same labor lends again to the cost effectiveness
6-26
-------
where labor rates are reasonable. The cost effectiveness of these practices really stems
from the resulting low/no maintenance conditions when the work is completed. As the
vegetation becomes established, the initial biotechnical strength of these systems only
enhances. Growing roots reinforce the soils and extract excess moisture, while the foliage
breaks raindrop impact, reduces surface water velocity, and prevents surface erosion.
Bioengineering makes use of
local vegetation. Local vegetation is
already suited to the climate, soil, and
moisture conditions. Installation is
accomplished during the dormant season,
making the plants easier to handle. A few
of the more common plant materials are
bank willows and shrub dogwoods,
which have been very successful in these
installations. Willows would serve well
in the practices described below.
6-34 Bank willows are commonly used in
bioengineering practices.
Common techniques are live
stakes, live fascines, brushlayers, branchpacking, and joint planting. These are the more
simple techniques that lend themselves to volunteer labor. These techniques and others
are thoroughly described in the U.S. Department of Agriculture, Natural Resources
Conservation Service (NRCS), Engineering Field Handbook, Chapter 16,
Streambank and Shoreline Protection, and Chapter 18, Bioengineering for Upland
Slope Protection and Erosion Reduction. This handbook provides the data and details
on many bioengineering practices. In addition, NRCS personnel can be quite helpful in
providing advice and assistance in these techniques for any site or project being
contemplated.
To clarify the use of these techniques and show the advantages and benefits, we
will discuss a few of the more common practices accompanied by several photos.
6.4.3.1 Live Stakes. This
practice consists of inserting and
tamping live, rootable vegetative
cuttings into the ground, as shown
in Figure 6-8. Once the dormant
stakes begin to grow, they create
a living root mat and foliage. The
primary function of this technique
is to reduce soil erosion by
slowing water velocities and by
reinforcing the soil with root
masses. Construction can be
inexpensive and accomplished in
a short time frame.
Figure 6-8: Live Stakes
6-27
-------
6.35 Cutting the stakes and Preparing the site.
The live stakes are cut to the required length. The site is prepared. The project site
depicted in the photo shows some riprap armoring at the water edge and rolled
biodegradable erosion protection matting being laid. The tops of the live stakes are then
driven into the ground.
6-36 Driving the Stakes.
The top of the stake
is usually the slightly
smaller diameter end and
will make driving it into the
ground a little easier. The
plant will produce roots and
foliage appropriate to its
orientation. A pilot hole can
be made and a dead blow
hammer can be used to
reduce damage to the
cutting. If the end of the
stake is damaged (flattened
6.37 Completed site and after one season's growth.
6-28
-------
and splayed), simply cut off the damaged part. The final photos show a completed site
and one after a season's growth.
6.4.3.2 Live Fascines. Live fascines are long bundles of branch cuttings bound
together and placed in shallow contour trenches on the slope. The function is to protect
the slope from shallow slides and reduce surface erosion. This technique is suited to
steep, rocky slopes where digging is difficult.
6.38 Tying the bundles and digging the trench.
The branches are cut and the cuttings tied together to form long fascine bundles.
Beginning at the base of the slope, a trench is dug on the contour of the slope. The
fascine bundle is placed in the trench and staked. Live stakes can be used in combination
with this technique.
6.39 Placing the fascine and backfilling.
6-29
-------
The live stakes are placed
on the downslope side of the
bundle as shown in Figure
6-9. Backfill soil is then
used to fill around the
bundles keeping the top of
the fascine slightly exposed.
The last photo shows a
completed spring site after a
summer's growth.
As with many of the
bioengineering practices,
this technique lends itself to
volunteer labor, as one can
see in the above photos.
These projects seem
particularly desirable to
many different groups with
the volunteers receiving
substantial satisfaction from
a job well done and the
continued satisfaction of the
continual site enhancement.
! TO, I---.! I.. II
Top of fascine slightly exposed
Dead anchor stake
Live fascine bundle
jFigure] 6-9: Live Fascines
Media publicity can also be a positive
factor in promoting the volunteer group
and the project. From Boy Scouts and Girl
Scouts to 4H Clubs, from service
organizations (Rotary International,
Kiwanis, etc) to watershed and
conservation groups, volunteers are a great
resource for accomplishing these projects.
6.5 Summary
6-40 Fascines after one season's growth.
Throughout this chapter, the
importance of roadside vegetation was
emphasized. Roadside vegetation prevents erosion and sedimentation pollution and
results in lower road maintenance costs. Additionally, a well-vegetated roadside is
naturally beautiful and can be a draw for tourists.
We not only discussed the importance of roadside vegetation, but we
demonstrated how we can effectively use vegetation to our advantage in reducing
maintenance and costs and prolonging road life. We can actually use the forest system
and other plants to create benefits for the environment, the roadway, and local
governments.
6-30
-------
We covered various proven techniques that can be utilized, particularly for bank
stabilization. We pointed out that if all the eroded banks along our roads would be
revegetated, both the large and small sites, a substantial reduction in pollution and
associated road maintenance would result. We mentioned easy to use bioengineering
techniques that can be accomplished with in-house crews or volunteer work from the
many available groups and organizations.
We talked about seeding and the important steps in the revegetation process. And
particularly in this area, we emphasized using the available valuable resources in your
respective geographical location.
To again see these practices used in actual projects, we refer back to Appendix 5,
Section 5A-1 for Worksite #1, Red Rose Road, Huntington County, PA. Adding to that
site, Appendix 6B provides an additional project site utilizing vegetation practices. As in
Appendix 5, this "Worksite in Focus" reviews an actual Pennsylvania worksite in which a
combination of practices has been used to solve the erosion and sediment pollution
problems.
We also need to re-emphasize that all of these practices can be adopted for paved
roads and will prove to be just as beneficial as they are for unpaved gravel roads. And by
using these practices, you will again see the long-range continual benefits for your roads
and your environment and thereby for your community.
6-31
-------
APPENDIX 6.
Appendix 6A: Soil Identification in the Field
6-32
-------
Distinguishing Soil Types
in the Field
When laboratory facilities are not available, some
simple field tests can help you distinguish soil types
and determine gradation, plasticity and dispersion:
Gradation
To judge gradation of dry soil, spread a sample
on a flat surface. Separate the larger and smaller
particles with a piece of stiff paper or cardboard.
Estimate the percentage of particles larger than 1/4
in. (6mm) and the percentage of fines - individual
grains too small for you to see with the unaided eye.
Finally, gauge whether the larger particles are
uniform in size (poorly graded) or have an assortment
of sizes (well graded).
Figure 1 - Gradation Test
If the soil is wet, break a lump apart. Estimate
the percentage of large particles as in the dry soil
method. To find the percentage of fines, put just
enough water in a clear glass to cover the bottom and
fill the glass 1/4 full with soil. Then add enough
water to just cover the soil and mark this level with a
rubber band.
Figure 2 - Percent of Fines
of Fines
Water
»_ Original Mark
-»- Settlement Mark
Now add water to the 3/4 mark and stir the
mixture vigorously. After it settles for a minute and a
half, mark the height of soil that has settled out. The
difference between the two marks as a portion of the
height of the upper mark approximates the percentage
of fines.
Plasticity
Here are four field tests for estimating a soil's
plasticity.
The Shaking Test: Knead a sample of the soil to
work out as many large grained particles as possible.
Add water gradually and knead the soil until it begins
to get sticky.
Figure 3 - Shaking Test
Then hold the ball in one hand and tap the back
of the hand with the other. If the ball becomes wet
and shiny, it is mostly fine sand or silt. No reaction
suggests clay.
The Toughness Test: Use the ball from the
shaking test. Knead about half of it until it's dry.
Then roll the soil sample into a 1/8 in. (3mm) thread
or "worm". If you can't form a worm, the soil is sand
or silt or fine sand (low plasticity).
Highly plastic soils take a long time to dry and
become hard and waxy. You have to exert a lot of
pressure to form a worm that breaks at about 1/8 in.
diameter.
Figure 4 - Toughness Test
The Dry Strength Test: Knead the other half of
the sample into a ball and let it air dry. Then break it
apart and select a jagged, pointy fragment. Try to
crush this fragment between your thumb and
forefinger. A silt will turn to powder with little
effort. A clay will be hard and almost impossible to
crush.
-------
Hand Washing: After handling silts and sands,
your fingers will feel dusty. Rubbing them together
will almost clean them. Gently flowing water will
rinse them.
If you've been handling clay, you'll find a crust
on your fingers you cannot rub off. Water will not
rinse it off. You have to rub your hands together
under water to cleanse them.
Figure 5 - Dispersion Test
Color May Be Tan, Grey '
or Black
Color Will Be Tan to
Dark Brown Depending
on Particle Size
Color Will Be White to
Light Tan, Grey, Blue or
Bluish Green
Settles Instantly
to l'/2 Minutes
— ^_ Sand
Silt
-£. Sand
Clay
Silt
Sand
Dispersion
Use a dispersion test to support your gradation
estimates. It will also give you an idea of how
difficult the soil will be to compact. First fill a glass
1/4 to 1/3 full with soil and then add water to within
1/2 in. (13mm) of the top. Stir the mixture well and
set it aside.
The mixture will settle in three layers: sand at
the bottom, silt in the middle and clay at the top.
Besides showing the relative amounts of the three
soils, the results will indicate whether the soil is well
or poorly graded.
Although silt and clay particles are smaller than
the eye can see, gradation difference will show up as
color differences. Also, the longer it takes a layer to
settle, the smaller the particles. Usually, a single
particle size (poor gradation) and a small particle size
mean more difficult compaction than a mix with good
gradation.
Summary of Identifying Clues
To summarize how various soil types react to
the field tests:
• Clay - No reaction to the shaking test; a tough
worm that dries out slowly; a crusty dry
residue that is hard to remove from the hands.
• Silts - Rapid reaction to the shaking test; a
weak or crumbly worm; powdery residue that
is easily wiped or washed off the hands.
• Silt and Clay Mixtures - Intermediate or
conflicting reactions to hand tests.
• Sand or Gravel with a few Fine Clays -
Enough clay to soil the hand when you
knead a wet sample, but not enough to form
a lump.
• Sand or Gravel with Silt Fines - Dusty
or gritty fines.
• Clean Sands and Gravels - Added water
sinks in immediately without making
mud.
Soil Test Checklist
Watch for these possible reactions when you
are using in-field do-it-yourself soil tests.
1. No reaction to the shaking test, a tough
worm that dries slowly, and a crusty
residue that is hard to remove from your
hands indicates the soil is clay.
2. Rapid reaction to the shaking test, a weak
or crumbly worm, and powdery residue that
washes easily from your hands indicates
silt.
3. Intermediate or conflicting reaction to hand
tests indicate silt as well as clay mixtures.
4. Enough clay to soil your hands when you
knead a sample, but not enough to form a
lump indicates sand or gravel with a few
fine clays.
5. Dusty or gritty fines indicates sand or gravel
with silt fines.
6. When added water sinks in immediately
without making mud, you will have clean
sands and gravels.
The above article and graphics were reprinted from
Caterpillar Inc. and are available from Caterpillar
Dealers. Ask for their "Compaction Manual," Form No.
TECB8081© Caterpillar or see Better Roads, May 1991.
The "Soil Test Check-list" was reprinted from Michigan
Technological University's publication, "The Bridge,"
Vol. 6, No. 2, Winter 1992.
-------
Appendix 6B: Additional Worksite in Focus
The follow ing worksite is an additional project undertaken by a Pennsylvania
local township with major funding through the Pennsylvania Dirt and Gravel Road
Program. This worksite reused berm and ditch dirt to provide the needed topsoil cover
for coalmine spoil to form a new wide vegetated buffer roadside area. The area was then
fertilized and seeded. Although additional road and drainage work were part of the
combination of practices used, the new, well-vegetated roadside buffer area reduces dust
generation and keeps sediment out of nearby Fall Brook stream.
In addition, please refer back to Appendix 5 to the first Worksite on Red Rose
Road in Huntington County, PA, to view the selected tree removal and bank stabilization
practices utilized on that project.
6-35
-------
Worksite
in Focus
Tioga County
Fall Brook Road
4/13/05
Project Background
Fall Brook Road was used as a coalmining
operations haul road until the early 1980's.
Constructed of coalmine spoil, the road width, in
some places, exceeded 60' wide. When coal
trucks quit using the road, Ward Township was
left with a problem road that could not maintain
crown and had constant potholes. The road
surface of coalmine spoil was very acidic, very
soft and fine, holding and pumping water.
Additionally, the coalmine spoil would not
support vegetation, so the berms, ditches and
banks were barren and a constant source of
erosion. The road had inadequate cross pipes,
groundwater in the road, and direct sediment
discharges into Fall Brook.
Project Considerations
This segment of road has 2 stream crossings.
One of these crossings, inadequate for flood
flows, saw high water bypass the existing
stream crossing and spill across the road about
300' away.
Project Facts
Project:
Project Owner:
Affected Watershed:
Project Length:
Date Completed:
Cost Summary
Fall Brook Road
Ward Township
Fall Brook, Tioga River
1100ft
September 2001
Total Project Value: $24,960
District Funding: $21,185
Materials ' $17,070
Equipment $3,965
Labor $150
In-Kind Contributions: $3,775
Labor $3,775
For More Information
The Center for Dirt and Gravel Road Studies
(814)865-5355
www.dirtandgravelroads.org
Tioga County Conservation District
Ralph Brugger
(570)724-1801
Before: Fall Brook Road
was so wide, the township
could not keep the road
crowned. The road surface
of coalmine spoil held water
and was full of potholes
during wet periods and was
a constant source of dust in
the summer. High flows
sent water flooding across
the road eroding the surface
material directly into Fall
Brook. Although already
impacted by acid mine
drainage, Fall Brook did not
need an additional source
of impairment.
The publishers of this publication gratefully acknowledge the financial support of the Pennsylvania State
Conservation Commission. For additional information or assistance, contact: Center for Dirt & Gravel
Roads Studies, Penn State University, 207 Research Unit D, University Park, PA 16802 (Toll-Free
Phone: 1-866-668-6683, Fax: 814-863-6787, Email: dirtandgravel@psu.edu). Additional copies available
on our website at: www.dirtandgravelroads.org
Center for Din and Gravel Road Studies
-------
Project Solutions
Construct new road base: To
solve the problem of the wide flat
road, the township used the existing
road surface of coalmine spoil to
construct a new crowned road base.
Re-surface the road: The centerline of
the new roadway was laid out and a 20-
foot wide layer of limestone Driving
Surface Aggregate (DSA) was placed
and compacted. The newly crowned
road surface sheds water to either side
as sheet flow.
Vegetate road berms: With the extra
width to work with, the township hauled
berm and ditch dirt from other roads in
the township and covered the coalmine
spoil with 6" of topsoil, forming wide
buffer areas (see photo at right). Buffer
areas, banks and ditches were limed
fertilized and seeded.
Stabilize stream crossings: One of the
two stream crossings on this project needed
to be replaced. A new pipe and head- and
endwalls were installed. The township
poured its own 2'x2'x4' concrete blocks to
construct the headwalls (see photo at right).
Additional cross pipes were added to direct
ditch water to the vegetated buffer,
removing a direct discharge to the stream.
At the other crossing, high flows flooded the
road 300' away. Where high water crossed
the road, the road and road base were
armored with R5 rip-rap to allow water to
flow over the road without major damage.
Project Results
Previously, Fall Brook Road required
frequent regular maintenance and
emergency maintenance following high
water flooding. Since project completion
in 2001, the township has only had to
grade twice. The road itself has a new
durable driving surface. Well-vegetated
buffer areas reduce dust generation and
keep sediment out of Fall Brook.
new 20' wide
crowned road
surface
Site Map & Directions
From U.S. Route 6, turn left
on to State Route 2029 in
Mainesburg. State Route
2029 turns into State Route
2022, then into Fall Brook
Road. The project begins
approximately 3 miles down
Fall Brook Road at the
intersection of the road with
Fall Brook.
This publication is available in alternative media upon request. The Pennsylvania State University is committed to the policy that all persons shall have equal access
to programs, facilities, admission, and employment without regard to personal characteristics not related to ability, performance, or qualification as determined by
University policy or by state or federal authorities. The Pennsylvania State University does not discriminate against any person because of age, ancestry, color,
disability or handicap, national origin, race, religious creed, sex, sexual orientation, or veteran status. Direct all affirmative action inquiries to the Affirmative Action
Office, The Pennsylvania State University, 201 Willard Building, University Park, PA 16802-2801; tel. (814) 863-0471; TDD (814) 865-3175. U.Ed #RES-01-50.
PENNSWE
9
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Environmentally Sensitive Maintenance
for
Dirt and Gravel Roads
Chapter 7: Environmentally Sensitive Maintenance
Practices: Additional Maintenance Techniques
7.1 Introduction
In the two previous chapters we introduced numerous maintenance practices as
tools for the toolbox. In this chapter, we provide additional tools relating to three major
topics:
Dust Control: We will define road dust and learn about its effects on roads and the
environment. Armed with this information, we will then discuss dust control materials
and methods.
Road Stabilization: We will define road stabilization and introduce the materials
and techniques most commonly used. Many dust control materials can also be used as
additives in road stabilization.
Geosynthetics: We will then introduce the world of geosynthetics and their many
various functions and uses in environmentally sensitive road maintenance.
7.2 Dust Control
Unpaved roads are considered the
largest source of particulate air pollution
in the country. According to the
Environmental Protection Agency,
unpaved roads produce almost five times
as much particulate matter as construction
activities and wind erosion, which are the
next two largest sources, combined.
Many local governments do some
sort of dust control. This maintenance task
is usually performed as a result of public
complaints, and the resultant work
7-01 Unpaved roads are the largest source of
dust pollution in the country.
consists of doing some sort of dust control in front of residences. This action typifies the
common thoughts of dust as a nuisance. Dust however, is much more than a nuisance.
We need to understand exactly what dust is and how it originates.
7-1
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7.2.1 What is Dust and Where Does It Come From? First, look at a commonly
accepted statement about dust:
"One car making one pass on one mile of dirt or gravel
road one time each day for one year creates one ton of
dust."
What is this dust? Where does this
dust come from? This dust is part of the
road, it's the fines being ground down by
traffic and blowing off in the wind.
Recalling earlier discussions about road
materials, we wanted a well-graded
aggregate with fines to lock everything
together and keep it in place. If we lose
the fines, we lose the road. The above
statement translates to losing 50 tons of
fine road material a year for each mile of
road with an average of 50 vehicles per
day.
7-02 Just what is dust? Where does it come
from?
When these fines are lost as dust, it deteriorates the gravel surface. Larger
aggregate pieces become exposed and are then scattered by vehicles or washed away. The
unstable road surface becomes rough, developing potholes and washboarding. These
distresses hold water that infiltrates and damages the base. In addition, the eroded
material damages ditches and drainage systems. Repairs and maintenance can be frequent
and costly.
Dust indicates the road is deteriorating, and the dust, as it settles out and becomes
additional sediment in the streams or blankets the vegetation, causes deterioration to the
environment. Thus, dust causes excess road maintenance and environmental pollution.
7.2.2 The Necessity of Dust Control. Successful treatment can significantly
reduce dust conditions and help preserve road surfaces. Various studies show that control
measures can reduce dust by 30% to 80% and cut aggregate loss by 25% to 75%. Such
treatments, however, will not last forever, and repeated applications may be necessary.
We must view dust control as a necessary routine maintenance item for all
unpaved roads - not only to prolong road life, but also to protect the environment. Dust
control means that the roads will stay intact; the fines will remain interlocked with the
larger aggregates and keep everything in place. Similar to the cut in aggregate loss,
studies report that one can expect a 25% to 75% cost reduction in blading, regarding, and
re-graveling by implementing a dust control program.
How often we do dust control and to what extent will depend on many variables.
What are the road surface materials? What is the road condition? What is the drainage
7-2
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condition? What are the environmental conditions - severe storms, rain, droughts, etc.?
What is the volume and speed of traffic? What are the objectives or goals for dust
control?
Without traffic, dust is not a problem. According to commonly accepted
"guidelines," roads with an average daily traffic (APT) between 15 and 500 vehicles per
day are good candidates for dust control. With fewer than 15 vehicles per day, there is
probably not a substantial dust problem. Conditions on these roads, however, must be
evaluated on an individual basis to determine the potential for dust-related problems.
Generally speaking, roads carrying more than 500 vehicles per day will require multiple
treatments. In these cases, options range from a more substantial surface treatment to an
actual asphalt pavement. Again, each road must be evaluated individually based on
specific road and roadside conditions.
7.2.3 Benefits of a Dust Control
Program. Let's look at the benefits of a
dust control program. The first two major
benefits are what we have already
discussed above - prolonged road life with
less maintenance and less particulate matter
polluting our streams.
But there are many other benefits to
a dust control program, such as reduced
respiratory and associated health problems,
not only from the dust itself, but also
possibly from other organisms attached to
the dust particles through electrostatic
forces.
Dust on plants can hamper their
growth and development. When the farmer
calls and wants something done about the
dust because it is affecting his crops, that is
a valid complaint. Dust shades necessary
light from plants, hindering photosynthesis
(plants producing their own food), resulting
in stunted plant growth.
In general, a good dust control 7-03 Dust can affect crops.
program reduces cleaning costs associated
with homes, clothes, and vehicles. Dust control can mean a better quality of life and
higher property values for those living and working adjacent to your roads.
7-3
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Dust poses road safety hazards as well because it reduces visibility for motorists.
Dust control can mean reduced vehicle
accidents and improved road safety. If the
driver cannot see properly, it is unsafe to
drive.
A good dust control program can
also reduce vehicle maintenance costs. Dust
plays total havoc on moving parts.
Maintaining a vehicle that drives an
average of 40 mph exclusively on gravel
roads costs 40% more than maintaining the
same vehicle traveling the same speed on
paved roads.
7-04 Dust creates visibility problems for the
motorists.
If the road fines are lost, the coarse aggregate ravels and loosens and can be
kicked up by vehicles, causing windshield breakage and vehicle damage. Good dust
control means less vehicle damage.
And, of course, there is the public and public relations. What municipal official
has not received the phone call from the irate resident demanding, "You have to do
something about this dust!"
A good dust control program means a better road, a better environment, and thus a
better community.
7.2.4 Dust Control Options. Road
managers have several dust control
options available to them depending on
specific road conditions. Traffic creates
dust. Limiting traffic volumes, however, is
really not feasible. After all, that is what
the road is there for. Limiting traffic speed
could have an effect. But erecting speed
limit signs does not always slow traffic
down, and no matter what the speed is,
traffic will still create dust. Heavy truck
traffic creates more dust, but limiting
traffic weight is not an efficient dust
control alternative. Usually weight
restrictions are imposed on roads that are incapable of supporting heavy traffic without
significant road deterioration especially in the spring "mud season."
Although paving the road is the only permanent solution to dust problems, using
effective controls can significantly reduce dust and cut required maintenance. That leaves
7-05 Traffic weight and speed increase dust.
7-4
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us with dust suppressants and a few other more substantial methods using road
stabilization and geosynthetics, both of which can help in alleviating the dust problem.
Dust suppressants are classified as routine dust control maintenance items. Of
course, different materials will provide different service intervals depending on many
variables. We also need to be concerned with the environmental effects of the materials
used.
7.2.5 Evaluation of Dust Suppressant Materials. Before we discuss dust
suppressant materials, we need to talk about evaluation of the materials to be used. What
should you know? What do you need to consider?
The following list provides the basic considerations:
Environmentally compatible
Effective at controlling dust
Easily applied with common road maintenance equipment
Workable and responsive to maintenance
Not degrading to ride quality
Relatively harmless to vehicles using the road
Posing little hazard or inconvenience to adjacent residents
Cost competitive
There are several information sources available to help in evaluation of dust
suppressants.
Every chemical has to have a Material Safety Data Sheet (MSDS). Right-to-Know
Laws, originating at the federal level and adopted at the state level, require all
manufacturers to provide an MSDS for every chemical and require all employers to have
MSDS sheets for each chemical used in the workplace available to employees.
The MSDS deals with safety in handling the material, listing the manufacturer's
name, address, and phone number; the major components of the chemical; its
characteristics such as flammability, volatility, reactivity; safety equipment needed to
handle the chemical; and emergency procedures in case of spills or exposure.
The Federal Clean Water Act along with respective state acts set the requirements
as to toxicity for fish and other aquatic stream life. The material or chemical must meet
all of these requirements. But we also should be concerned with effects on vegetation.
We now realize how important roadside vegetation is and the important part it plays in
erosion and sediment pollution prevention and helping reduce road maintenance. We
certainly do not need chemicals that would harm or destroy our roadside vegetation.
It is imperative that road managers evaluate dust control products in light of all of
these factors. Road managers need to seek out all information on the product, check
referenced users as to their experiences, concerns, and problems, and possibly do trial
7-5
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applications to develop an effective, efficient and safe dust control program that will
protect their roads and the environment.
7.2.6 Common Dust Suppressants. The following list of commonly used dust
suppressants along with their attributes and limitations as to effective dust control and
environmental compatibility will be discussed.
Water
Sodium Chloride (salt)
Calcium Chloride
Magnesium chloride
Brines (natural, semi-processed)
Lignin Derivatives
Asphalt Emulsions & Cutbacks (oils)
Resins
7.2.6.1 Water. Water is a dust suppressant. Water will do the job but it is short-
lived. Road personnel would have to be out there continually each day applying water
during the dry summer weather. Water, however, is readily available and safe for the
environment.
A notice of "caution" is required here concerning the "safe for the environment"
statement. A caution comes with using potable "tap" water from a public water system. A
public water system treats water with chlorine for disinfecting to kill all organisms. There
is always a chlorine residual in the water. If a tankload of this water would be dumped
directly into a stream, you may end up
with a detrimental effect on the fish and
other aquatic life depending on the
volume dumped, the amount of stream
flow, the amount of chlorine residual, and
other conditions.
Water's real limitations relate to
evaporating readily and thereby its short-
term control. This means it becomes very
labor intensive and costly due to the need
for repeated applications for effective
control. Contractors use water trucks on
large construction sites continually to cut
dust during work. Not only do they do
this to ward off complaints from adjacent
residents, but they also know the savings
in equipment maintenance. Water as a
temporary control during construction or
maintenance work does have merit.
7-06 Although environmentally sensitive, water
affords only short-term dust control.
7-6
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7.2.6.2 Sodium Chloride. Sodium chloride is our deicing salt or rock salt used all
over the snow-belt states for paved roads in winter. Salt, however, is not an effective dust
control. It begins to absorb water at 76% relative humidity, reduces the rate of water
evaporation by a factor of 1.3 times, and it does lower the freezing point of water.
However, all of these positive dust control characteristics are not substantial, especially
when compared to other available materials.
There are significant environmental concerns with the use of chlorides. Whether
the chlorides come from sodium chloride or from magnesium or calcium chloride, they
still pose environmental challenges. When these materials are used, the sodium, calcium
or magnesium attach themselves to other materials, but the chlorides become free agents
and are able to leach out of the road and into nearby streams or ground water sources.
Chlorides can cause serious problems. They can be detrimental to animals and
plants, and they are corrosive. With these limitations and the fact that sodium chloride is
not effective as a dust control, we do not recommend using sodium chloride for this
purpose.
7.2.6.3 Calcium and Magnesium Chlorides. Calcium and magnesium chlorides,
on the other hand, can be effective dust suppressants. Calcium chloride begins to absorb
moisture at 29% relative humidity, which is very dry and when we need dust control the
most. It also reduces water evaporation by a factor of 3.4 times and lowers the freezing
temperature of water to -60° F.
Magnesium chloride is very similar and begins to absorb water at a dry 32%
relative humidity, reduces water evaporation by 3.1 times, and lowers the freezing point
of water to-27° F.
Even with these attributes, calcium and magnesium chlorides are still chlorides,
which again can be detrimental to plants and animals and corrosive to metals. Site
conditions, particularly where roads are immediate adjacent to streams, must be evaluated
carefully if chlorides are being considered for use.
7.2.6.4 Brines. Brines are usually a by-product of gas production wells and
consist of a combination of chlorides. Brines, as a by-product, can be less costly than
many other materials. Natural or semi-processed brines should be tested and approved
for use as a dust control agent. The manufacturer should be responsible for testing and
assuring a non-contaminated product.
Brines, being mostly chlorides, give us the same positive attributes and the same
concerns as the other chlorides. Brines can be detrimental to animals and plants, but may
be worse in that they could be contaminated with other materials - oils, heavy metals, etc.
For this reason, brines need to be tested and approved before use.
7.2.6.5 Lignin Derivatives. Lignin derivatives are a by-product of the paper
manufacturing industry. They are highly acidic, usually foul-smelling when spread, and
7-7
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very sticky, clinging to vehicles.
Complaints are common because of these
problems, so be sure to give advance
notice to residents and businesses before
treatment. There is dried processed lignin
sulfonate available commercially, which
does not have these problems. In
addition, certain manufacturing processes
may make them more or less effective in
controlling dust. For example,
ammonium lignin sulfonate refers to the
process and is one of the more effective
agents.
7-07 Lignin derivatives are a by-product of the
,,T. , ,..,.. , , paper manufacturing industry.
With hgnm derivatives, the road
should have a silt/clay content of 4% to 8% for them to take the proper effect in
controlling dust. Lignins are slippery when wet and brittle when dry, which is not really
conducive to good dust control. Rain tends to re-emulsify the material, increasing the
potential for run-off. And, although lignins could be called a natural substance, if they
leach into the stream, they will deplete the oxygen and destroy stream life. Lignins,
because of their acidity, are corrosive. Repeated applications will be needed as lignins
decompose over time.
7.2.6.6 Asphalt Emulsions and Cutbacks. An asphalt emulsion is asphalt and
water with an emulsifying agent (soap) added to allow them to mix. When used, the
water evaporates, leaving asphalt. An asphalt cutback is asphalt thinned with a solvent
such as naphtha or kerosene. When used, the solvent evaporates, leaving asphalt. These
materials act as adhesives and binders that physically glue soil particles together.
They form a hard crust, and repeated applications can develop into a "paved"
road. Depending on the number of applications per year, the road conditions and
maintenance operations between applications, and the number of years used, the road
can start to look and act like a paved asphalt road.
Using emulsions and cutbacks
gives us the asphalt to combine with the
gravel road aggregate, forming a paving-
like condition, which begins to build an
asphalt pavement. Considering that a hot
asphalt mix used to pave roads is just
asphalt and aggregate mixed and heated in
an asphalt plant, one can realize that under
continual use of "asphalt oils," a dirt and
gravel road can become that "pancake"
paved road. Periodic regrading of the road
tends to be more expensive and more
7-08 Asphalt emulsions and cutbacks are still
being used for dust control, but...
7-8
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difficult when it has been treated with these products.
These "oils" provide some dust control. Medium cure cutbacks such as MC30 and
MC70 are commonly used. A significant problem related to health and air pollution is the
volatile organic compounds (VOCs) released by the asphalt cutbacks. Because of this
problem, the use of cutbacks has been limited in many states and will probably
continually decrease in the future.
Although they can be applied to a broad range of soil types and are good at
waterproofing an aggregate surface, tracking can be a problem, particularly if the road
surface has a lot of fines. Tracking can be a real nuisance for vehicle owners and nearby
residents. Another concern during application is the potential for run-off from excessive
application or related to a quick rainstorm.
7-09 With the use of asphalt "oils," tracking and/or run-off can become problems.
7.2.6.7 Resins and Other Materials. Numerous other dust control materials are
available, including various resins and enzymes, some of which are by-products of a
manufacturing process. Vegetable oils including soybean soapstocks and sugar beet
extract are also being used. New products are continually being researched and marketed.
Once again, all products need to be evaluated in terms of effectiveness and safety in light
of site-specific road conditions.
7.2.7 Use and Application of Dust Suppressants. The two main objectives in
dust control, however, remain (1) to develop and implement a program and (2) to
use a dust suppressant that will not only be effective, but also environmentally safe.
7-9
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7.2.7.1 Environmentally Sensitive Materials. When evaluating dust suppressant
materials, road managers must pay particular attention to each material's environmental
impact. Road managers must seek out all information on the product, checking referenced
users as to their experiences, concerns, and problems, and then do trial applications to
develop an effective, efficient and safe dust control program that will protect their roads
and the environment.
The Pennsylvania State Conservation Commission has addressed the issue of dust
suppressants by making it clear to manufacturers and vendors that they are responsible
for determining the acceptability of their materials. Appendix 7A discusses the
Commission's testing protocols and lists the products that have been approved for use in
the Pennsylvania Dirt and Gravel Road Program
7.2.7.2 Application Process. No matter what we are using to control dust, the
product must match the existing road materials. We should not be doing dust control with
any threat or prediction of rainfall. And remember this important statement:
Dust control will not make a bad road good, but will keep a good road good,
This leads right into the three major tasks in application of a dust suppressant.
1. Determine the product to be used and application rate. The product may
depend on the road and type of wearing surface. Application rate depends on
the product; the condition of the road; type, volume and speed of traffic;
degree of dust control required; climatic conditions; frequency of
maintenance; and cost.
2. Perform all required maintenance and repairs to the road. Bring the road to a
good condition with a good crown and cross slope. Repair unstable areas,
remove unsuitable material and replace with select material, make necessary
drainage improvements, clean ditches, grade the road, and restore proper
crown.
3. Apply the dust suppressant. An application in spring followed by another
application in late summer or early fall may give good dust control for the
year. Again, this is dependent on all the variable conditions. Remember,
application should be made when there is no threat or prediction of rain for at
least 36 hours. Most dust control agents can be applied when the road surface
is damp (not wet), except for the asphalt cutbacks, which require a dry
surface.
The following are general application guidelines. Use the recommended
application rates from the manufacturer for the first spring application. You may want to
reduce this rate by half for roads that have been previously treated. With most products,
(asphalt cutbacks are an exception) we can pre-wet the surface with water at rates ranging
from 0.03 to 0.3 gallons per square yard to reduce surface tension, to develop capillary
7-10
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action that allows maximum penetration of the suppressant, and to ensure uniform
application. If a dust coat has already developed on the road, regrade and moisten.
Avoid runoff or puddling when applying liquids. Use several light sprays if the
surface is tight. Follow dry applications with enough water to ensure the pellets or flakes
are completely dissolved. Allow the treated road to cure. Curing may take longer for
roads with finer grained materials.
A second treatment may be required in late summer or early fall. Treat the road a
second time before the first treatment becomes totally ineffective. You may need only
half the application rate as used in the spring application.
7.3 Road Stabilization
7.3.1 What is Road Stabilization? We can define road stabilization as the
uniformly crushing, pulverizing and blending of the road materials, adding a stabilizing
agent, mixing the agent with the blended material, spreading and regrading the road with
proper crown, and compacting. Compaction is a requirement in this process. Stabilization
can also be performed without a stabilizing agent but is more commonly done with an
agent for better strength and stability.
7-10 Road stabilization or full-depth reclamation works well with a stabilizing agent
The newer terminology for road stabilization is "full-depth reclamation."
7.3.2 Advantages of Stabilization. There are numerous advantages to road
stabilization. First, stabilization unifies and strengthens the roadbed, prolonging road life.
Through stabilization, we are actually recycling existing road materials to reconstruct a
new road. The stabilizing materials obtain the desired moisture, increase cohesion by
producing a cementing action, and act as a waterproofing, providing greater road strength
and stability. The road also becomes more resistant to dust. Depending on the agent
added (calcium chloride for example), we can aid in reducing frost action or frost heaves.
Stabilization is nothing new but went by the wayside when asphalt paving and
cement concrete paving were introduced for road surfaces. Now we are again discovering
7-11
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the advantages of stabilization not only for improving our dirt and gravel roads, but also
for stronger bases for paved roads.
7.3.3 Stabilization Additives: The common stabilization additives include many
of the dust suppressants with some additional materials added to the list:
Calcium Chloride
Magnesium Chloride
Resins
Lime
Cement
Asphalt
Fly Ash
Many times these materials are used in combination for stabilization.
Caution: Certain materials may require permits or
approval from state environmental agencies for use as a
road stabilizer. For example, the use of fly ash in
Pennsylvania requires the PA Department of
Environmental Protection approval — source, quality,
quantity, and how it will be used, stemming from the
origin of the fly ash and a potential of unwanted
contaminants such as heavy metals.
The same concerns exist for these materials as for dust control materials,
particularly since we are talking about some of the same materials. We do need to be
concerned with environmental sensitivity and the effectiveness as a road stabilizer. The
same information, testing and evaluation should be a priority, with the manufacturer
being responsible for verification of their product being environmentally sensitive. See
Appendix 7A for Pennsylvania's testing requirements and approved products.
7.3.4 The Stabilization Process. Selecting a stabilizing agent is the first step in
the process. Selection of the proper stabilizing agent requires knowledge of the road soils
or aggregates and of the agent being used. The stabilizing agent must be of the correct
type and used in the correct quantity for satisfactory results.
The stabilization process consists of:
• scarifying and pulverizing the existing road materials;
• adding new material if you need to beef up the road structure;
• mixing in the stabilizing agent; and
• then regrading and shaping the road with the proper crown followed by
good compaction.
7-12
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The process can be accomplished with just a road grader and roller. A good
grader operator can scarify and mix the materials and reprofile the road, which can then
be rolled for compaction.
7-11 Stabilization can be accomplished with a road grader - scarifying the road, mixing in a
stabilizing agent, regrading and shaping.
Another viable option is a "reclaimer." A "reclaimer" has a drum with carbide
teeth and a down-cutting action for pulverizing and proper sizing of the material.
Stabilizing agents come in liquid or solid form, and are either sprayed using a tank truck
or spread using various methods and equipment. The same equipment, such as the
reclaimer, can then be used for mixing the stabilizer uniformly with the road material.
7-12 The "reclaimer" has a down-cutting drum with carbide teeth.
With newer systems, a tanker truck connected by a hose to the reclaimer,
introduces the liquid stabilizer agent directly into the roadbed material as it is being
pulverized. The reclaimer has a computer-controlled liquid injection system, which is
capable of accurately regulating additive application rates.
A road grader can then be used to regrade and restore a proper crown and a roller
for compaction. Compaction is a requirement in this process.
7-13
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Stabilization or full-depth
reclamation can be an effective tool to
reconstruct a poorly maintained road. The
end result is a uniform road material
strengthened by the added stabilizer agent
and properly shaped and crowned for
good drainage. Reusing existing road
materials is very cost effective.
Full-depth reclamation is
recommended for roads like the one in
Photo 7-13. The road has a varied look
due to a variety of materials that have
been used over the years. Different
7-14 A sheep's foot roller is used for soil
compaction.
7-13 A mish-mash of road surface materials
lends itself to a full-depth reclamation project.
aggregates, different materials for patching,
different treatments for dust, or sectional
surface treatments all on the same road can
be a continuous maintenance headache for
the road manager. This type of road is an
excellent candidate for full-depth
reclamation.
As a side note on compaction,
different types of compaction equipment are
better suited for different types of materials.
If you are compacting soils, a sheep's foot
compactor, shown in Photo 7-14, is ideal.
This machine compacts the soil from the
bottom up. As the soil becomes compacted,
the roller will "walk" right out.
7-15a A steel grid-type roller fractures large
coarse shale material.
7-15b A rubber tired roller with
environmentally friendly ballast.
7-14
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Large coarse shale materials can be compacted using a grid-type roller, Photo 7-
15a, that will tend to fracture and break the larger pieces, helping to consolidate and
compact the material into a tight mass. Compaction rollers do not have to be fancy. Photo
7-15b shows a trailer-hitch type with natural ballast materials.
7.4 Geosynthetics
The world of geosynthetics continues to expand with new products and uses in all
types of applications. Geosynthetics takes in the whole realm of materials such as
geotextiles, geogrids, geowebs, geocells, and other geocomposites. Many local
governments are using plastic drainage pipe, so they are already into geosynthetics. There
are, however, many other products that could prove useful in a variety of areas associated
with dirt and gravel road maintenance. This section will zero in on geosynthetics for
pipes and subdrains, for soil erosion protection and embankment reinforcement, and for
road separation fabrics.
7-16 The world of geosynthetics and road maintenance.
First, let's examine just what geosynthetics are. The prefix "geo" means relating
to the earth. The word "synthetic" means man-made. So a geosynthetic is a man-made
material used on or under the earth. The concept of earth stabilization using various
materials is not new and can be traced back in history to reed mats in ancient Egypt,
bamboo baskets for rice paddies in Asia, and "corduroy" log roads in England. In the
United States, woven cotton was used for slope stabilization in South Carolina in the
1930s. All of these materials, however, were from natural products and were
biodegradable. Modern geosynthetics began in the 1950s with trials and experiments, but
7-15
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really came into existence in the 1970s with the introduction of certain polymers. Today
the realm of geosynthetics is greatly expanded, using many polymers such as
polypropylene (PP), polyester (PET), polyethylene (PE), polyvinyl chloride (PVC),
nylon, polystyrene, and ethylene interpolymer alloy (EIA), all of which are non-
biodegradable.
7.4.1 Why Use Geosynthetics? Geosynthetics are easy to place because virtually
all installations can be accomplished with in-house crews. Additionally, geosynthetic
materials cost very little. Low installation costs and low material costs means more bang
for the local government buck. Further, geosynthetics may be used in a wide variety of
applications and are durable and long-lasting.
7.4.2 Functions and Applications. Geosynthetics serve a variety of functions in
many useful applications as follows:
Functions
Drainage / Infiltration
Stabilization
Reinforcement
Separation
Erosion Control
Sediment Reduction
Waterproofing
Stress Relief
Applications
Subsurface Drainage
Subgrade Stabilization
Soil Reinforcement
-Embankments
-Steep Slopes
-Vertical Walls
Erosion / Sediment Control
Base Reinforcement
Bridge Deck Waterproofing
Selection of a particular product depends on the function and application. This
becomes extremely important in geotextile fabrics.
7.4.3 Geotextile
Fabrics. There are
numerous fabrics on the
market; each one designed
to perform a specific
function. You cannot tell
one fabric from another by
visual inspection only.
Therefore, it becomes
imperative that the
manufacturer or vendor
know how you are going to
use the fabric or what
function it is supposed to perform.
7-17 Different fabrics are designed to perform various functions
and for various applications.
There are two major fabric types: woven and non-woven. The manufacturing
process of these two types is similar. Plastic polymer beads are melted down and
extruded through dies. For non-woven fabrics, the extruded threads are sprayed in
random patterns, and then thermally bonded in layers and needle punched. They
commonly have high permeability and conformability with high elongation. For woven
7-16
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fabrics, the extruded threads are woven
on machine looms and have a woven
appearance. They have high tensile
strength and low elongation.
There are woven slit-film
fabrics that are melted plastic beads
sprayed in sheet films and then slit into
long narrow strips of varying width.
These strips are then woven together.
They also have high tensile strength
and low elongation.
.-
7-18 Fabrics come in rolls of various widths
Fabrics normally come in rolls of various widths. Widths of twelve, fifteen, and
eighteen feet are common for use as separation fabrics.
7.4.4 Geosynthetic Applications in Road Maintenance. We have already
discussed various geosynthetics - plastic pipe for drainage applications in directing
collected surface flows, perforated plastic pipe for subsurface drainage, erosion control
fabrics for lining ditches or channels, and fabric silt fence for sediment control. We will
expand on those applications as we discuss further drainage applications, erosion and
sediment control, separation fabrics, and some other geosynthetics as used in special
applications.
7.4.4.1
Drainage /
Infiltration Fabrics.
Fabrics can be
specifically used in
conjunction with
subdrains.
Road
Cut or Fill
Sections
Figure 7-1: Subdrain
Free draining aggregate
Perforated Pipe
Recalling the
cross-section sketch
of a subdrain as
again shown in
Figure 7-1, the
typical construction was a trench with well-graded aggregate and a perforated pipe.
Clogging of the system over time has been the major problem with these subdrains, as
shown in Photo 7-19. Looking at the photo, one can imagine how much sediment passed
through this pipe prior to reaching this totally clogged condition? And where did all that
material go? The subdrain probably outletted to a stream, and we ended up with stream
pollution.
7-17
-------
Figure 7-2: (reotextile Fabrics for longer lasting subdrains!
Fine Filter Material Sized
to Retain Natural Soil
Low Permeability
Compacted Backfill1
Coarse Open-Graded
Filter Material Sized
for Max Permeability
• Geotextile Fabric
A. Fabric-Wrapped B. Fabric-Lined Ditch
Pipe Uuderdrain Underdrain
•-
Geotextiles can play a valuable part in
preventing this sediment and the eventual
clogging of the system. You can use a roll of
geotextile drainage/infiltration fabric to line the
trench. We could also wrap the perforated pipe
or purchased pipe already wrapped in a
geotextile sock, as shown in Figure 7-
2. Lining the trench, however, is just
as easy and more effective.
The fabric is designed to let
the water through and into the trench
and pipe and then to the outlet, but it
will not let the fine soils through to
clog the system.
Caution: There have been
some problems in heavy clay soils —
the clay, when wet, becomes very
plastic and sticky and has caused
some problems when fabric is placed
in direct contact with the clay soil.
Lining the trench with fabric
is a simple procedure, as shown in
Figure 7-3 and the accompanying
photos. Dig the trench, roll out the
fabric, place bedding, place the
perforated pipe, backfill with a one-
size aggregate, overlap the fabric on
top, and backfill the trench. The result
is a better subdrain system that will
last a long time.
7-19 Clogged subdrain!
E Figure 7-3:
1 _
Subdrain construction with geotextiles
2 3
7-20 Subdrain construction - dig trench, roll out fabric, add
pipe and aggregate, overlap fabric, backfill.
7-18
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7.4.4.2 Prefabricated
Subdrains. Prefabricated
subdrain systems consist of a
hard plastic perforated core
covered in a geotextile fabric.
The perforated plastic core
becomes the pipe. It is
installed vertically, giving you
a greater area for draining the
road structure. It commonly
comes in 12-, 18-, and 24-inch
heights. All sorts of
connectors are made to
accommodate connections and
installation. In addition, there
are rigid and flexible systems,
the flexible system being
manufactured in rolls.
7-21 Pre-fab Underdrains: Rigid Type
7-23 All subdrains need an outlet.
these applications are usually
manufactured in rolls and are easily
installed with in-house crews,
following manufacturer's
recommendations.
We already mentioned the use
of geosynthetics in this area in Chapter
5 for ditch and channel linings, where
we discussed water flow velocities and
the possible need for stabilizing the
ditch or channel for faster flows. Many
various products are produced for this
type of application.
7-22 Pre-fab Underdrains: Flexible Type
7.4.4.3 Subdrain Outlets. Like any
subdrain system, whether lined with a fabric
or a pre-fabricated, all subdrains must have an
outlet. The pre-fab systems, as mentioned,
have various connectors to allow the outlet to
run in whatever direction is needed.
7.4.4.4 Erosion and Sediment
Control. Geotextiles and other geosynthetics
are used for channel linings and erosion
protection on embankments. Geosynthetics for
Figure "--1: Embankment erosion
protection installation
Up slope Trench:
12 "ditch back-filled
to bury upper edge
of fabric
Overlap: 4" - 6" overlap pinned at 3' - 5' intervals
7-19
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Remember, any type of
geosynthetic is non-biodegradable.
If we use these materials for
temporary erosion prevention until
vegetation is re-established, we
must make sure that they are
compatible with that vegetation
since they will remain in place.
7-24 Installation of an erosion control fabric.
This factor applies to embankment
protection, too. Again, there are many
products on the market for embankment
slope protection against erosion.
Normal installation is depicted in
Figure 7-4 and consists of rolling out the
material, overlapping at seams, pinning,
and anchoring the top of the material in a
small trench. Again, follow the
manufacturer's recommendations for each specific product. Photo 7-24 shows an
extensive erosion control fabric installation, which will be covered with a large-size
aggregate.
7-25 Geotextile silt fence barrier.
Interlocking pre-fab blocks or gabions
Fine aggregate bedding
Figure 7-5: Geosynthetic linings serve as reinforcement
and separation as well as erosion control
Silt fence is
another geosynthetic
used for temporary
erosion control. Silt
fence is discussed in
Section 5.2.3.2 of
Chapter 5, describing
the proper installation
practices and required
maintenance.
Geotextile
fabrics are also used
underneath other types
of channel linings such
as riprap (as in the
above Photo 7-24),
7-20
-------
gabions, or interlocking pre-fabricated blocks, as shown in Figure 7-5. In this installation,
however, they are also serving as
reinforcement and separation fabrics that will
be discussed below.
7.4.4.5 Embankment Soil
Reinforcement. Both geotextiles and
geogrids are used for embankment soil
reinforcement. Geogrids come in many
patterns and have proven their ability to
perform in this type of application.
Reinforcement applications usually entail
embankments in which fabric or geogrids are
place horizontally at designed intervals
during construction, as shown in Figure 7.6.
Alternate layers of fill and rolled-out geogrid
are placed as the embankment is constructed.
7-26 Geogrids come in various patterns
designed for specific applications.
Proposed Shoulder
.Geogrids
Geogrids
(Secondary
Reinforcement)
l^|/2Excavated
1
Coarse Aggregate
Wrapped in Geotextile
6"Drain N 6"Outlet Pipe
Figure 7-6: Design of a geogrid reinforced embankment
The material can be
extended over the face of the
embankment for additional
protection, a method
commonly intrinsic to any
design. Photo 7-27 shows an
actual road construction site
using geogrid for
reinforcement - an extensive
project, but the applicability is
there for any size project.
7.4.4.6 Separation Fabrics. Separation fabrics
are among the most commonly used and cost-effective
type of geotextile fabrics on dirt and gravel roads.
These fabrics separate the subsoil from the road,
provide reinforcement, improve drainage, and reduce
dust.
When roads are built, the subsoil or sub grade is
prepared with a crown, then a specified thickness of
aggregate is laid down and compacted, (Figure 7-7a).
7-27 Construction of a geogrid
reinforced embankment.
Over time, however, depending on conditions (water and traffic), the aggregate
gets pushed down into the soils, and the soils pump up through the aggregate. We end up
7-21
-------
with a transition zone not as strong as the
aggregate, and the road can no longer support
the traffic loads with deterioration as the
result (Figure 7-7b).
With the separation fabrics, we
prepare the sub grade, roll out the fabric, and
build the road on top of the fabric. The
aggregate cannot be pushed into the soil and
the soil cannot pump up into the aggregate.
Everything stays in place, and the road
remains as strong as designed for the traffic
loads (Figure 7-7c).
7-28 Separation fabrics keep the soil and road
aggregate in place.
t
Geotextile Separation Fabric
Figure 7-7: Separation Fabrics
Water can travel either way, but if it gets into the road, it can drain downward or
out laterally due to the crown into side ditches or subdrains. The prevention of soil fines
from pumping up through the aggregate to the road surface eliminates the mud in wet
weather and the dust in dry weather associated with these fines.
4 Rolls of fabric waiting for
installation
Rolling out the fabric
t Backdumping the
aggregate
' Spreading the aggregate * t Compacting the aggregate t f Final grading
7-29 Installation of a Separation Fabric.
7-22
-------
Fabrics come in woven or nonwoven types for this application. The existing road
conditions, particularly the aggregate, rock outcrops, water and saturated subsoils, must
be evaluated when selecting fabric type. Transverse joints should be overlapped a
minimum of 18 inches in the direction of traffic. Fabrics come in standard 12-, 15-, and
18-foot widths (or customized to any width), eliminating the need for longitudinal joints.
Aggregate should be backdumped from the truck to a minimum depth of 6 inches,
preferably 8 inches. Compacting the aggregate along with grading and re-establishing the
crown completes the project. The photos depict fabric installation on a typical dirt and
gravel road. This was a demonstration project where both woven and non-woven
separation fabrics were used along with different road aggregates. In some areas, filling
of the road with shale material to raise the road elevation took place. The different road
materials can be seen in the photos.
If the fabric gets
damaged during
placement, simply patch
with another piece of
fabric making sure that an
18" overlap on all sides is
maintained. Tears can
happen, as shown in Photo
7-30, where the blade of
the dozer caught the fabric
by accident.
[Without Fa brie |
Figure 7-8
Fabrics Separate & Distribute the Load
7-30 If damaged, use a fabric patch with 18" overlap.
Fabrics also help to distribute
traffic loads over a greater area, making
them advantageous to use over soft,
saturated soil conditions. Figure7-8
shows this load distribution effect of the
fabric. Traffic load distribution was
discussed in Chapter 5, Section 5.3.5,
Practices Related to Culverts in regards
to culvert installations.
Many separation fabric
applications are in place throughout the
states and proving effective in
substantial reduction of road
deterioration and the required
maintenance. The use of fabrics for
stabilizing water crossing areas in
conjunction with broad based dips and
driveways was mentioned in Chapter 5.
In these applications, they perform a
reinforcement function and a separation
TTTTTT
With Fabric]
7-23
-------
function to strengthen and keep these areas intact.
The use of separation fabrics, in general, provides us with a number of
advantages. Stabilization
1. Sub grade pumping prevention
2. Drainage improvement
3. Excavation reduction
4. Rutting and pothole reduction
5. Dust reduction
6. Reduced maintenance and costs
7. Longer road life.
The excavation reduction refers to those areas where we find unsuitable saturated
soils for subgrade material. The common practice is to remove the unsuitable material.
This can lead to excavating
several feet depending on MUD
conditions. With a
separation fabric, we can
prepare the subgrade surface
and roll out the fabric over
these soft soil areas and let
the fabric handle the
problem. Would you rather
have a road looking like "a"
or "b" in Photo 7-31? With
separation fabrics, we can
eliminate the sign as seen in
the photo inset.
7.4.4.7 French
Mattress. The French
mattress refers to the old
"French drains" used in
many locations to drain storm water. The French mattress is a mattress-shaped structure
of coarse aggregate wrapped in a geotextile fabric. This structure is placed under the road
and allows water to pass freely through the roadbed without moving soil particles.
The primary purpose of the mattress is to equalize the subsurface water on both
sides the road while providing the needed load support for the road and traffic. Support
strength is provided by the large aggregate in the lower portions of the mattress spreading
the load.
7-31 Before & after fabric installation - let's eliminate the sign!
7-24
-------
7.4.4.8 Geocells and Geowebs.
Geocells or geowebs, as they are also
called, are an innovative geosynthetic
product used in ground stabilization, road
subgrade stabilization, slope erosion
control, embankment reinforcement and
retaining walls, stream crossings, and
channel erosion control. The geocell is a
lightweight, flexible mat with a
honeycombed structure that is spread and
pinned and then filled. A variety of fill
materials can be placed within the cellular
system, such as soil, sand, aggregate,
concrete, etc. The geocell confines the
native or select fill materials, adding to the
structural strength of the system. Geocells
Adjacent cells can
be tied together
Figure 7-9: Geocells
with the appropriate fill material creates various opportunities for economical solutions in
the applications listed above.
i
7-32 Geocells can be filled with a native or
select fill material. (Photo: WebTec, Inc. -
TerraCell®)
JB
7-33 Geocells for road base stabilization. (Photos: WebTec, Inc. -
TerraCell®)
The cells come in various heights
with different cell sizes. They can be solid
wall or perforated to allow flow between
cells. Most manufacturers will also customize
sizes for specific requirements. Anchoring
systems vary according to the manufacturer.
We will look at a few different
applications that could benefit the
maintenance of dirt and gravel roads and
roadsides.
7.4.4.8.1 Road
Stabilization. Geocells have
been used to stabilize road
base aggregates and give
additional structural support
to the road. The geocell is
spread, pinned, and filled
with aggregate, as can be
seen in the photo. Common
practice uses a geotextile
fabric placed on the
subgrade prior to spreading
and pinning the geocell. The
geotextile separation fabric
7-25
-------
prevents fines from pumping up through the geocell and aggregate and to prevent the
aggregate from sinking into the subsoil underneath and to keep a uniform geocell surface
across the road. A final surface aggregate would then be spread over the base aggregate
and geocell system.
7.4.4.8.2 Retaining Walls. Geocells can be stacked to form almost vertical walls
for embankments. As with geogrids, the structural strength of the geocell wall allows for
steeper slopes than most soils would sustain without the geocell confinement system.
Typical wall installations are shown in Photo 7-34. Each layer of geocell is stepped back
from the underlying one.
7-34 Geoweb retaining wall installations (Photos: WebTec, Inc. - TerraCell®)
7-35 Geoweb embankment retaining wall during construction and after vegetation established
(Photos: WebTec, Inc. - TerraCell®)
The cells can be filled with soil and vegetation established to actually conceal the wall
cellular structure. A vegetated geocell wall is shown in Photo 7-35
7.4.4.8.3 Low Water Road Crossing. A low water crossing can be used in lieu of
a cross culvert being installed. This practice should be used on a very low volume road
and will depend on the conditions of the surrounding terrain and the expected flows.
7-26
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A Excavating
trench
+ Placing fabric*
Placing geocell
* Pinning geocell
* Geocell ready*
for fill
Dumping
aggregate fill
Raking fill *
Raising road
elevation
Compacting
7-36 Installation of a low water crossing.
Completed low
water crossing
The series of Photos 7-36 depicts the installation of a typical low water crossing
using a geocell. This site was on a road having less than 10 vehicles a day (<10 APT).
The road was in the watershed of a potable water reservoir. The storm water accumulated
and crossed the road at this point during most storms, causing a great amount of erosion
and road deterioration. The project was designed to raise the elevation of the road but still
allow the water to cross naturally at this point through a stabilized low water crossing. A
cross pipe installation would create major problems due to elevations of the surrounding
terrain. On the downhill side the pipe would have to be extended several hundred feet to
outlet at ground level. A low water crossing allowed the water to cross the road in lieu of
a cross pipe and sheet flow through the wooded vegetated area without the resulting
erosion and road washouts.
A shallow trench excavation is made to install the crossing. As in the road base
reinforcement, a geotextile separation fabric is placed prior to the geocell. The geocell is
then spread and pinned. Large aggregate is dumped into the cell to an elevation slightly
higher then the cell in order that the vehicle wheels do not strike the cell.
7.4.4.8.4 Road Stream Ford Crossing. A geosynthetic reinforced ford crossing
enhances the environmentally sensitivity of an existing crossing in lieu of a costly bridge
construction project. The reinforced crossing provides a stabilized hard aggregate surface
7-27
-------
for vehicles that will not wash out and will not create the continual sediment and
disturbance of the stream that the existing unstabilized crossing causes with each vehicle
crossing.
Presto Products Company Geoweb
7-37 Stream fords cause erosion and sediment, degrading stream habitats. A perforated geoweb
offers a stabilizing solution with proper hydraulic and stream ecology protection.
The existing ford crossing shown in Photo 7-37, depicts the erosion potential with
each vehicle crossing, with the resultant sediment degradation of the stream ecology (the
stream community or ecosystems was discussed in Chapter 4, Section 4.3, and
particularly the effect of erosion and sediment on streams in Section 4.3.4). Using a
perforated geoweb with one-inch holes allows hydraulic equalization and migration of
stream life. The surface of the crossing should match the streambed surface in order not
to cause any disturbance in flow by creating a dam effect across the stream.
7.4.4.9 Prefabricated Geosynthetic Pipe Endwalls. Prefabricated geosynthetic
endwalls consist of polyethylene sections that can be easily installed by road maintenance
crews. The endwalls come
in three preformed
sections with a pipe
adapter for 12", 18", and
24" diameter pipe. One
person can position and
assemble the sections
using a power drill or
screwdriver and
galvanized screws. The
Low Density Polyethylene • Consists of 3 preformed sections sections are filled with
Easy to install + a pipe adapter
7-38 Pre-Fab Geosynthetic Endwall Systems.
7-28
-------
soil, sand, aggregate, or cement and a cap is placed on top. Additional sections can add
height as required. A poured concrete footer is recommended. The geosynthetic end wall
comes in three natural stone colors, and, from the motorists' point of view, look like laid
stone endwalls.
rTM
The photos (HartmanEW System) show an installation sequence for the
endwall.
Prepare site
Position end
section over pipe
Fasten base unit
to pipe
Fill base unit
Install next
section
Fill with dirt,
sand, aggregate
Position cap and
fasten
Finish site work
7-39 Pre-Fab Geosynthetic Endwall Installation.
7.5 Summary
This chapter has discussed the importance of implementing a dust control
program. Since dust is actually the fines in your road that lock everything together should
be reason enough to have a dust control program. A dust control program prolongs road
life, protects the environment, and provides many additional benefits to your community.
We also discussed the importance of evaluation of dust control products as to
their effect on the environment and their effectiveness as a dust control, followed by a
review of common dust suppressants with their advantages and limitations. We
concluded with general application procedures for dust control products.
In the second section, we delved into road stabilization (or full depth reclamation)
and the benefits derived from this technique. Road stabilization can add strength to the
7-29
-------
road, prolonging its life and reducing maintenance. At the same time, keeping the road
intact reduces erosion and dust, thereby helping the environment.
The third section introduced the world of geosynthetics, describing the functions
and applications applicable to dirt and gravel roads. This world is constantly expanding
with new products and applications. But products like the separation fabrics have had
wide use and success in road maintenance.
Appendix 7B continues, as in Appendices 5 and 6, to review actual Pennsylvania
worksites in which a combination of practices has been used, including geosynthetics, to
solve the erosion and sediment pollution problems stemming from dirt and gravel roads.
The first site used pre-fabricated subdrains to collect subsurface water stemming from
spring seeps. The second site was a nature reserve where separation fabrics were used for
driveway re-construction and geogrids provided the structural strength for a bus parking
lane and a French mattress system provided the required subsurface drainage flows. The
third site was a demonstration project where geotextile fabric was used to reinforce and
stabilize a stream crossing having an inadequate crosspipe.
All of these topics and the products and practices discussed are good "tools" for
your toolbox and need to be considered as integral parts of an overall environmentally
sensitive dirt and gravel road maintenance program.
7-30
-------
Appendix 7
Appendix 7A. Pennsylvania's Testing and Approval Program for Dust
Suppressants and Road Stabilizers
The Pennsylvania State Conservation Commission has addressed the issue of dust
suppressants and road stabilizers by making it clear to manufacturers and vendors that
they are responsible for determining the acceptability of their materials in conjunction
with accepted toxicity testing protocols. Before a product can be approved for use in the
PA Dirt and Gravel Road Program, it must undergo toxicity testing according to federal
EPA protocol at a laboratory certified by the EPA. The test results are then interpreted
with the requirements of the PA Clean Streams Law, specifically Title 25, Chapters 16
and 93. That interpretation is the basis of whether or not the product is acceptable to the
Pennsylvania State Conservation Commission.
Tests are required on all commercial products. The tests are to determine toxicity
based on identification, quantity, and behavior of elements and compounds found. The
tests will include the 7-day rainbow trout (Oncorhynchus mykiss) survival and growth
test. Tests with fat head minnows (Pimephales promelas) are not acceptable. The 7-day
cladoceran (Ceriodaphnia dubia) survival and reproduction test is also required.
Guidelines for the tests must use the federal EPA protocols. Each test must produce two
"No Observed Effect Concentrations" (NOEC), one for survival and growth of rainbow
trout and one for survival and reproduction of cladocerans.
In addition, Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand
(COD) values must be obtained for the product. These values are not intended for use in
determination of the environmentally acceptability of the product but are reference values
for use in any potential emergency. (Source: Administrative Manual, Dirt and Gravel
Road Maintenance Program, PA State Conservation Commission, March 3, 2005.)
Under the above criteria, the Pennsylvania State Conservation Commission has
approved nine different products from six different companies for use at approved
application rates in the PA Dirt and Gravel Road Program - four products classified as
petroleum emulsion dust suppressants, two products classified as synthetic fluid dust
suppressants, and three products classified as acrylic polymer dust suppressants. The
products, companies, and approved application rate are as follows:
Petroleum Emulsion Dust Suppressants
PennSuppress "D", American Refining Group, Inc., Bradford, PA
1:4 emulsion to water or more dilute
Ultrabond 2000, JMG Enterprises, Inc., Seward, PA
1:4 emulsion to water or more dilute
Coherex, D&D Emulsions, Inc., Mansfield, OH
1:10 emulsion to water or more dilute
Dust Bond, D&D Emulsions, Inc., Mansfield, OH
1:10 emulsion to water or more dilute
Synthetic Fluid Dust Suppressants
7-31
-------
EK35, Midwest Industrial Supply, Inc., Canton, OH
100% active, no water for application
EnviroKleen, Midwest Industrial Supply, Inc., Canton, OH
100% active, no water for application
Acrylic Polymer Dust Suppressants
Pave-Cyrl Suppress, Rohm & Haas Company, North Andover, MA
As-received (51% solids)
Pave-Cryl Suppress Plus, Rohm & Haas Company, North Andover, MA
As-received (51% solids)
DirtGlue, DirtGlue Enterprises, Wakefield, MA
As-received (>50% solids)
7-32
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APPENDIX 7B. Worksites in Focus
The following worksites are actual projects funded through the Pennsylvania
Dirt and Gravel Road Program. The first site was an entrenched township road with
saturated ditches, surface erosion, and spring seeps. The project raised the road profile
and added pre-fabricated subdrains to collect subsurface water from under the road and
both ditches.
The second site was a Nature Reserve experiencing increased traffic loads from
the increase in visitors. This project added a new driveway and parking areas, including
bus parking reinforced with a geogrid and French mattress construction for two small
drainage ways. The third site was an early demonstration site for the Dirt and Gravel
Roads Program. The spotlight is on one aspect of this site, entailing the resetting of an
existing 3-foot diameter cement concrete drainage pipe.
7-33
-------
Worksite
in Focus
Adams County
Miltenberger Road
7/16/05
Project Facts
Project: Miltenberger Road
Project Owner: Franklin Township
Watershed: Conococheague Creek,
Potomac River
Project Length: 800 ft
Date Completed:June 2005
Problem Identification
Miltenberger Road was an entrenched road
with few outlets for drainage and spring flow
to leave the road area. Water was
concentrated in parallel ditches and directed
1,200' downhill and under State Route 233
into Conocheague Creek. Water entering
the road area had nowhere to go but down
the ditches, gaining velocity and erosive
force. Adding additional drainage outlets
was impossible with the road at an elevation
much lower than that of the surrounding
landscape. The entrenched road profile
also left little room to plow snow (Photol).
Project Objectives
1. Restore natural drainage by raising the road to achieve sheet flow.
2. Reduce stream impact by providing additional outlets for water currently trapped in road ditches.
3. Address maintenance problems such as saturated ditches and lack of space for snow storage.
Project Considerations
Although over 3,000 feet of Miltenberger Road was entrenched, cost limitations only allowed for enough shale
to raise about 800 feet of the roadbed. Spring water entered the road profile as subsurface flow. This excess
water saturated the road and ditches, softening the road base (Photo 1). The land surrounding the road is
owned by the Bureau of Forestry.
Cost Summary
Total Project Value: $15,689
District Funding: $15,689
Materials $670
Equipment $4,292
Shale $10,727
Photo 1. Notice the ice in the middle of the road from a spring seep. The
entrenched road profile made it impossible to get water or snow off of the road.
Photo 2. Pre-fabricated underdrain was used to collect
subsurface water from under the road and both ditches.
The publishers of this publication gratefully acknowledge the financial support of the Pennsylvania State Conservation
Commission. For additional information or assistance, contact: Center for Dirt & Gravel Roads Studies, Penn State University,
207 Research Unit D, University Park, PA 16802 (Toll-Free Phone: 1-866-668-6683, Fax: 814-863-6787, Email:
dirtandgravel@psu.edu). Additional copies available on our website at: www.dirtandgravelroads.org
Center for Dirt and Gravel Road Studies
-------
Miltenberger road was raised an average of 3' using shale
Photo 3. The entrenched road traps water in the road area and
conveys it down to the stream. Note the elevation of the road
relative to the utility pole on the right compared to Photo 4.
Photo 4. The road was elevated to eliminate the ditch on the left and
achieve sheet flow. The added material also provided the necessary
cover to install new crosspipes.
Project Solutions
Install underdrain: Pre-fabricated underdrain (4" perforate pipe wrapped in geotextile fabric) was placed
under the road and ditches to collect subsurface water (Photo 2). The underdrain will keep clean subsurface
water from mixing with road drainage. It will also reduce maintenance by allowing the road and ditches to dry.
Raise the road elevation: Shale was purchased for
use as road fill (Photos 3 & 4). The shale was spread
with a bulldozer and compacted using a vibratory roller
in approximately 8" lifts. The road was filled an average
of 3' over an 800' length and tapered into the existing
road grade on both ends. Filling the road completely
eliminates one ditch, and provides the cover necessary
to install crosspipes to outlet water from the remaining
ditch (Photo 5).
Install crosspipes: Because Miltenberger road was so
severely entrenched, no crosspipes existed on the road
before this project. Crosspipes were needed to divert
drainage into vegetated areas and keep runoff from
entering the stream. The new road elevation provided
the extra cover needed for two shallow crosspipe
installations. These crosspipes were outletted at the
existing ground elevation to avoid creating an "outlet
trench" into the woods. Gradebreaks were constructed
over each crosspipe to obtain adequate pipe cover and
divert water from running down the roadway (photo 5).
Photo 5. One of two new crosspipes installed. Notice the grade-
break in the road over the pipe to get water off the road.
For More Information
The Center for Dirt and Gravel Road Studies
1-866-668-6683 (toll free): www.dirtandgravelroads.org
Adams County Conservation District
(717) 334-0636: user.pa.net/~adamscd/
Site Map & Directions:
From U.S. Route 30 at
Caledonia State Park,
follow State Route 233
north approximately 5.5
miles to Miltenberger
Road. The worksite
begins at the
intersection with State
Route 233 and
continues for 800 feet.
Franklin
County
Adams
County
Caledonia
This publication is available in alternative media upon request. The Pennsylvania State University is committed to the policy that all persons shall have equal access to
programs, facilities, admission, and employment without regard to personal characteristics not related to ability, performance, or qualification as determined by University PENNSjATE
policy or by state or federal authorities. The Pennsylvania State University does not discriminate against any person because of age, ancestry, color, disability or handicap,
national origin, race, religious creed, sex, sexual orientation, or veteran status. Direct all affirmative action inquiries to the Affirmative Action Office, The Pennsylvania State
University, 201 Willard Building, University Park, PA 16802-2801; tel. (814) 863-0471; TDD (814) 865-3175. U.Ed #RES-01-50.
-------
Worksite
in Focus
Westmoreland County
Powdermill Nature Reserve
Project Background
In need of additional parking, Powdermill Nature
Reserve sought an environmentally sensitive
solution that handles increased visitors and related
traffic loads without an ugly scarring of the
surrounding landscape. To accomplish this, the
Reserve added:
• A new driveway with Driving Surface Aggregate*
(DSA-as modified) to improve circulation and
provide second access to Rte. 381;
• 2 new parking areas: a bus parking lane
underlain with Geogrid® (see photo below) and a
pervious grassed automobile lot (60' x 100').
Project Considerations
Where the new driveway crossed two small
drainage ways (see Site Plan below), French
mattresses*, constructed of clean stone wrapped in
non-woven geotextile fabric, were installed. This
low-cost, low-maintenance technique connects the
hydrology on either side of the road allowing water
to percolate through the stone while the fabric
prevents sediment movement.
Above: Construction of the bus parking lane. Geogrid® was used
to add support and tensile strength.
* For more information on DSA and French Mattress construction
please see the DSA Informational Bulletin and the French Mattress
Technical Bulletin available atwww.dirtandgravelroads.org.
11/2/04
Project Facts
Project:
Project Owner:
Affected Watershed:
Project Length:
Date Completed:
Cost Summary
Nimick Nature Center Driveway &
Parking Lot
Powdermill Nature Reserve
Powdermill Run, Youghiogheny River
550ft
October 2003
Project Cost: $35,049
Geoblock® Parking Lot $26,833
Contract $1,980
Materials (geosynthetics) $1,580
Stone $4,056
Tree Removal $600
In-Kind Contributions: $8,300
This project was completed with monies raised by the
Powdermill Nature Reserve.
For More Information
The Center for Dirt and Gravel Road Studies
(814)865-5355
www.dirtandgravelroads.org
Powdermill Nature Reserve
1847 Route 381
Rector, PA 15677
Theresa Gay Rohall
(724) 593-6105
Site Plan
\ B •-»-:; »
Nimick Nature
Center
New Geoblock®
t _Pprous Parking Lot
^*i ,,/
New Bus
Parking Lane
. .
f« FjarkingLojt . Existing Drainages ...,.••"'* Y
"'''' "
b-.-J?"' *4157 \ \STA7F I
, , —
«~- — -
v \^"5 1
• • -
The publishers of this publication gratefully acknowledge the financial support of the Pennsylvania State
Conservation Commission. For additional information or assistance, contact: Center for Dirt & Gravel
Roads Studies, Penn State University, 207 Research Unit D, University Park, PA 16802 (Toll-Free
Phone: 1-866-668-6683, Fax: 814-863-6787, Email: dirtandgravel@psu.edu). Additional copies
available on our website at: www.dirtandgravelroads.org
Center for Dirt and Gravel Road Studies
-------
Driveway Construction Sequence
1. Trees were cleared along the proposed right-of-way
and non-woven geotextile fabric was rolled out.
Additional lengths of fabric were laid perpendicular to
the driveway at two locations to allow construction of
the French mattresses (see photo 1).
2. #3 stone was tailgated on top of fabric along the entire
length of the right-of-way.
3. The perpendicular fabric sections were wrapped over
the #3 stone to create the French mattresses (see
photos 2 & 3).
4. #2b stone was tailgated over the entire length of the
driveway, including the French mattresses. A
modified version of DSA was placed over the #2b
stone and rolled to create the driving surface (see
photo 4).
Project Results
Environmentally sensitive maintenance practices were
employed to minimize cost, reduce future maintenance
demands and expand visitor infrastructure while staying
in tune with natural surroundings. This collaborative
project brought together several diverse partner
organizations to reinforce PowdermiN's environmental
ethic that teaches respect for nature by showcasing how
human handiwork can "lay lightly on the land."
Project Partners
Powdermill Nature Reserve
Center for Dirt & Gravel Road Studies
Westmoreland Conservation District
Sustainable Forestry Initiative of PA
Kennametal Inc
Site Map & Directions
From the PA Turnpike
(Interstate 76), exit at
Donegal/Ligonier/PA711
(#91). Turn left onto Route
31 after the toll booth.
Follow Route 31 to Route
381 north. The Nimick
Nature Center is 6 miles
ahead on the left.
New Stanton
Township
Ligonier
• Powdermill
This publication is available in alternative media upon request. The Pennsylvania State University is committed to the policy that all persons shall have equal access
to programs, facilities, admission, and employment without regard to personal characteristics not related to ability, performance, or qualification as determined by
University policy or by state or federal authorities. The Pennsylvania State University does not discriminate against any person because of age, ancestry, color,
disability or handicap, national origin, race, religious creed, sex, sexual orientation, or veteran status. Direct all affirmative action inquiries to the Affirmative Action
Office, The Pennsylvania State University, 201 Willard Building, University Park, PA 16802-2801; tel. (814) 863-0471; TDD (814) 865-3175. U.Ed #RES-01-50.
PENNSTATE
-------
A7B-3. Worksite #3: Hell
Hollow Road, Monroe County, PA:
This site was a demonstration project for
the Pennsylvania Dirt and Gravel Roads
Program on which various practices were
demonstrated. One of the sub-sites
involved a 36"-diameter cement concrete
pipe installed for a stream crossing Hell
Hollow Road. Viewing the original site,
one can see the voluminous erosion that
had taken place, uncovering the outlet
side of the pipe, which had actually lifted,
causing water to run uphill through the
A7-01Hell Hollow Road Demo Site: Existing
site conditions prior to project.
pipe to the outlet side. The inlet side of
the pipe was at an elevation that caused
water to drop approximately 15" into the
pipe entrance, which was causing
changes in the stream's profile on the
upstream side and thereby affecting the
stream ecology. The pipe was also out of
alignment with the stream flow, causing
tremendous erosion on the downstream
bank, which was in direct line of the pipe
outlet flow.
A7-02 Excavation of existing pipe during dry
conditions.
The pipe could not handle the flows,
particularly during the spring rains, causing
overflow and damage to the road and continual
erosion of the entire site. This township road with
daily traffic of less than 10 cars (<10ADT) was in
the watershed of a potable water reservoir. Building
an adequately sized bridge was not economically
feasible. The solution was to reset the existing pipe
and stabilize the entire area to protect against further
erosion.
A7-03 Geotextile separation fabric laid in
new trench.
7-38
-------
A7-04 Bedding material added
A7-05 New line and grade checked
The pipe was excavated and sections set aside. A new line and grade was
established to better meet the stream flow conditions. Notice from the photos that all
work was done during a dry period with no flow. The new pipe trench was prepared, and
a geotextile separation fabric was then laid in the trench and extended both upstream and
downstream. Bedding material was added,
and the pipe sections were reset. Since the
old pipe joints were not sealed and no
sealing was available, the pipe was
wrapped in a geotextile fabric to prevent
losing fines through the joints with possible
undermining of the material surrounding
the pipe. Duct tape held the fabric in place
for backfilling.
After backfilling, the extended
fabric was brought up and over the pipe
ends, cutting out for the pipe inlet and
outlet, and overlapped on top with a road
separation fabric. Thus the whole pipe and
backfill area was encased in fabric. Water could move through the pipe and through the
A7-06 Fabric wrap covers pipe joints, prevents
fine material from entering.
A7-07 After backfilling, fabric brought up and over pipe ends to encase entire installation.
7-39
-------
surrounding backfill, but the fabric prevented material removal, eliminating the erosion
potential. The pipe end areas received large riprap to face off the embankment and further
protect against erosion.
A7-08 Placing large size riprap at ends of pipe.
The road was leveled for a short
distance on each side of the pipe crossing
using the Stream Saver System discussed
in Chapter 5, Section 5.3.6.1. The project
was completed in the fall of the year.
The following spring brought the
rains, which once more proved too much
for the pipe to handle. The road has
sustained overflows on several occasions
each spring with minimal road damage.
The site remains essentially erosion free.
Road overflows are spread out over the
A7-09 Completed project with a leveled road
stream saver system.
A7-10 Inlet conditions before and after project.
7-40
-------
level road, reducing the velocity and energy of the water. The pipe is better aligned with
the stream flow protecting the downstream banks against erosion. The last photos, A7-10
and A7-11, show before and after conditions at each end of the pipe. The project
demonstrates one innovative use of geotextile fabrics in solving the erosion and
sedimentation pollution at this site.
A7-11 Outlet conditions before and after the project.
7-41
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Glossary
Note: These terms are defined in relation to their use in this manual for environmentally
sensitive maintenance for dirt and gravel roads
ADT: Average Daily Traffic.
Bank Gouging: A problematic practice during grading operations or ditch cleaning where the grader
operator cuts into the toe of a stable bank and creates a vertical surface, destabilizing the bank and creating
erosion and sediment.
Bed Load: Larger particles on the stream bottom that move by sliding, bouncing, or rolling along the
bottom in response to stream flow.
Bench: A step or series of steps cut into and across a steep embankment to catch water and prevent it from
running over the face of the bank, creating erosion and sediment pollution. The bench should be sloped to
prevent over the bank flow and drain to an appropriate outlet.
Bioengineering: Techniques combining the biological elements of using live plants with engineering
design concepts for slope protection and erosion reduction, used effectively in restoration of many stream
and upland banks.
Broad Based Dip: Shallow gradual dips skewed across the road in the direction of water flow, used to
outlet ditch flows to the other side of the road where outletting is prevented by a high embankment on one
side of the road with a downhill grade.
Capillary flow: the percolation or vertical seepage of water through soil. (Fine soils tend to increase
capillary flow, with the soil acting like the wick of a kerosene heater sucking water upward.)
Colonizer Trees: Those species that are shade intolerant and thereby first to grow in cleared areas, having
the characteristics of being fast-growing, short-lived, and weak-structured, making them undesirable
roadside trees, as compared to the intermediate or climax species.
Culvert (pipe, drainage pipe): Enclosed channels of various materials and shapes designed to convey
stream or ditch water away from the roadway.
Daylighting: A traditional practice of removing all trees from the roadside to allow sunlight to penetrate
through to the road surface in order to dry the road to prevent road deterioration from water and to prevent
snow and ice buildup. This practice is also used to improve motorists' sight distance for greater safety.
(Caution: This may not be the best practice for dirt and gravel roads in forested areas - refer to Manual
Chapter 6.)
Ditch Turnout (ditch outlets, tail ditch, bleeders): A formed channel that diverts ditch water away from
the road, usually angled in the direction of water flow and placed at locations to empty into a vegetative
filtering area.
Diversion Swale (diversion channel, interceptor ditch): A water conveyance channel constructed across
the bottom of a slope for the purpose of intercepting surface runoff to minimize erosion and prevent excess
flows into lower lying areas. Most often diversion swales intercept water from an uphill slope and divert it
away from the road and roadside ditch to a stabilized outlet area or infiltration back into the ground.
Dust: Fine road material ground down by traffic and blowing off in the wind, indicating that the road is
deteriorating.
8-1
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Dust Suppressant: Any of the variety of materials used as a successful treatment to significantly reduce
dust conditions on unpaved roads and helps preserve road surfaces.
Ecology: The study of interactions of organisms between one another and the physical and chemical
environment in which the organisms dwell.
Ecoregions: Areas with similar characteristics reflecting the physical factors (geology, soil, hydrology.
climate) that help define respective habitats, and in turn determine the type of animals and plants that live
in that habitat.
Ecosystems: A smaller unit within an ecoregion. Within each ecoregion, there are typically three types of
ecosystems: streams, wetlands, and forests/uplands.
Embeddedness: the degree to which pebbles, cobbles, etc. (the larger pieces of the stream bottom) are
surrounded by fine sediments. Normal embeddedness is about one third; higher degrees of embeddedness
relate to problems such as lack of living space for invertebrates and lack of free-flowing water for fish eggs
in gravel beds.
Endwall, End Structure: A structure placed at a pipe inlet or outlet to prevent erosion and scour around
the pipe, protect the embankment, and help anchor the pipe. Endwall may be constructed from a variety of
materials.
Energy Dissipater: Any device or installation of material used to reduce the energy of flowing water.
Environmentally Sensitive Maintenance: Effective practices that will not only be beneficial in protecting
the natural environment, but also result in less road maintenance and associated costs.
Erosion: the eating away of a surface by water, wind, abrasion, etc.
Flared End Section (pipe end section): A manufactured flared drainage piece that fits on the end of a pipe
to enhance hydraulics (water flow); can be metal, concrete, or plastic.
Flowline: The bottom of the ditch or pipe, the invert of the pipe.
Gabions: Manufactured woven wire baskets filled with stone and tied together to form a structure. Gabions
are used for bank stabilization and armoring, retaining walls, culvert end structures, channel linings (gabion
mattresses), etc.
Geosynthetic: Stemming from "geo" meaning "of the earth" and "synthetic" meaning "man-made";
geosynthetics are man-made materials used on or under the ground, non-biodegradable, for various
purposes ranging from reinforcement and separation to drainage filtration and sediment control.
Geotextile: A geosynthetic fabric or textile manufactured from synthetic plastic polymers, non-
biodegradable, in woven or non-woven types, and used for various purposes ranging from reinforcement
and separation to drainage filtration and sediment control.
Grade Break: A long, gradual break in grade on a road with a relatively gradual downhill slope that
improves drainage. Grade breaks limit water flow by decreasing concentration and velocity from a reduced
area of road section, resulting in limited ditch and cross pipe size.
Gravel Bar: An accumulation of gravel and rock material normally occurring at a bridge structure, which
interferes with the natural conditions of stream flow but can occur naturally anywhere along the stream.
Hydraulics: The mechanics of fluids, primarily water. (Engineers use hydrology to determine the amount
of water that will accumulate at a particular point and then use hydraulics to determine the size of pipe
channel or pipe needed to carry that amount of water.)
8-2
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Hydrology: the science of water and its distribution in the air, on the surface, and underground.
Indicator Species: Certain species that are sensitive to changes within the stream system and can be
analyzed in the context of the overall abundance of organisms in assessing the condition of the aquatic
system.
Insloping: Sloping the entire surface of the road toward the steep uphill bank on one side of the road to
eliminate drainage and erosion over the steep downhill embankment into any adjacent stream.
Intermediate or Climax Trees: Shade tolerant species having characteristics of being slow-growing, long-
lived, and structurally strong, making them more desirable roadside trees for greater roadside stability and
less maintenance.
Macroinvertebrates: Organisms within a stream ecosystem lacking a spinal column (invertebrate) but
large enough to be seen by the naked eye (macro) - usually referring to species such as insect larvae
(stoneflies, caddisflies, mayflies) that are used in evaluation of a stream's health.
Mitigation: The act of reducing or eliminating an adverse environmental impact, such as wetland
mitigation where the destroyed wetland area is replaced with a new wetland of similar size and function.
Morphology: The form and structure or shape, as of a stream or rocks, in relation to the development of
erosional forms or topographic features.
MSDS (Material Safety Data Sheet): A form required for all chemicals, dealing with safety in handling
the material. The MSDS lists the manufacturer's name, address, and phone number; the major components
of the chemical; its characteristics such as flammability and volatility, its reactivity, safety equipment
needed to handle the chemical, and emergency procedures in case of spills or exposure.
Outside Inputs: Streamside vegetation such as leaves, branches, twigs, roots, and fruit that falls into or is
washed into the water and becomes the basis for a food web in the stream.
Outsloping: Sloping the entire surface of the road toward the downhill side with a normal cross slope.
applied when the road crosses a gentle sloping terrain. Outsloping is similar to superelevation or banking of
a curve, but on a straight section of road and with no ditching. The outsloped road blends into the gentle
slope of the terrain with no ditching or cross pipes, allowing the natural sheet flow conditions to prevail.
Photosynthesis: The process by which plants are able to produce their own food, using sunlight and carbon
dioxide from the air with the green chlorophyll of the plant to produce sugars (food) and give off oxygen
back into the air.
Pipe Apron: The area immediately adjacent to a pipe outlet, which may need to be stabilized to prevent
erosion and scour.
Plant Succession: The gradual and orderly process of ecosystem development brought about by change in
the plant community composition and the production of a climax characteristic of a particular geographic
region. In other words, plant succession starts with bare earth and over time transitions towards mature
forest.
Riparian Buffer: A strip of undisturbed vegetation between sensitive areas, such as rivers, streams,
wetlands, ponds, etc., and areas of land disturbance and /or bare ground such as unpaved roads, work sites,
etc.; protecting these sensitive areas from sediments and other pollutants carried by surface runoff.
Wetlands often serve as riparian buffers along streams, protecting the streams from direct sediment input.
Riprap: Stones or rock placed in locations such as ditches, channels, embankments, and pipe outlets, sized
to resist movement and to prevent water erosion and scour of the underlying soils.
-------
Road Cross Slope: The slope of the road surface from the road center to the outer edges, the normal
unpaved road cross slope being Yz'to %" vertical drop for every horizontal foot of road width.
Road Crown: The center of the road being higher than the outer edges, creating a flat A-shape with a
normal cross slope of Yz" to 3/i" per foot for unpaved gravel roads. Road crown serves the major purpose of
drainage the road surface, getting the water off of the road.
Road Stabilization: The process of uniformly crushing, pulverizing, and blending of the road materials,
adding a stabilizing agent, mixing the agent with the blended material, spreading and regrading the road
with proper crown, and compacting.
Runoff: surface drainage due to precipitation or snow melt.
Scuppers: Bridge deck drainage systems, usually openings that allow deck surface runoff to drop directly
into the stream below.
Secondary Ditch: A problematic ditch formed along the edge of the road due to a build-up of material and
vegetation immediately adjacent to the road edge, preventing water from effectively running off the road
surface and into the roadside ditch or swale.
Sediment: Fine particles of inorganic and /or organic matter carried by water.
Sediment Load: The amount of sediment a stream carries under the existing flow conditions.
Sedimentation: The process of deposition of sediment in areas where water velocity is not high enough to
carry the sediment along.
Silt Fence (silt fence barrier, filter fabric fence): A temporary sediment control measure used to intercept
sediment-laden runoff from disturbed earth areas, typically made of a porous geotextile fabric and
supported by wood or metal posts.
Subdrain (subsurface drain, underdrain): A subsurface drainage facility whose prime purpose is to drain
the subsurface water out of and away from the road structure to an outlet. Effective subdrains consist of a
geotextile lined trench with a perforated pipe and well-draining aggregate backfill, or other prefabricated
systems.
Subgrade: The surface or soils upon which the road is constructed, usually shaped with a normal crown
and cross slope.
Superelevation: Sloping or "banking" the curve in the road with a uniform cross slope from one edge of
the travelway to the other to offset centrifugal forces on vehicles for safer travel.
Through Drain: Cross culverts installed strategically to handle springs or spring seeps flowing
perpendicular to the road, carrying the flow under (through) the road to the other side.
Topography: The configuration of a surface (land area) and the position of its physical and natural features
and respective elevations.
Tracking (grooving, roughening): The practice of creating an irregular surface on a smooth bank by
tracking up and down the bank with a track vehicle or any method of roughening or grooving the surface to
catch rain water, reduce erosion, increase water infiltration, trap sediment, and enhance vegetative growth.
Turbidity: The degree to which suspended sediment interferes with light passage through water, the
cloudiness exhibited by water carrying sediment.
8-4
-------
Upland: Areas of higher elevation that are well drained, covered with forests or cleared for farming or that
have reverted to meadows. One of the three typical ecosystems - uplands, streams, wetlands - within an
ecoregion.
Vegetative Filter Strip: Any vegetated area receiving water flows in order to spread the flow, reduce flow
velocity, and filter out sediment from the flow prior to the water reaching a stream.
Wetland: "Those areas that are inundated or saturated by surface or ground water at a frequency and
duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation
typically adapted for life in saturated soil conditions," as defined by the Federal Clean Water Act.
Water Table: The top surface of the free water in the ground and below is completely saturated.
Watershed (drainage basin, drainage area, catchment area): The area of land that drains all collected
precipitation to a common low point or outlet.
8-5
-------
References
Major Resource References: The following items are highlighted as major resources to
accompany this manual:
Gravel Roads Maintenance and Design Manual, Ken Sorseth & Ali A Selim, Ph.D.,
South Dakota Local Transportation and Assistance Program (SD LTAP), Report No.
LTAP-02-002, April 2005
For bioengineering techniques discussed in Chapter 6, Section 6.4.3
Chapter 16 Streambank and Shoreline Protection, Engineering Field Handbook,
Natural Resources Conservation Service, U.S. Department of Agriculture
Chapter 18 Soil Bioengineering for Upland Slope Protection and Erosion Reduction,
Engineering Field Handbook, Natural Resources Conservation Service, U.S. Department
of Agriculture
Additional References:
Adopt-A-Buffer Toolkit: Monitoring and Maintaining Restoration Projects,
Delaware Riverkeeper Network, September 2003
Alaska Soil Stabilization Design Guide, R Gary Hicks, Alaska Department of
Transportation and Public Facilities, FHWA-AK-RD-01-6B, February, 2002
Best Management Practices for Environmental Issues Related to Highway and
Street Maintenance, A Synthesis of Highway Practice, William A Hyman and Donald
Vary, National Cooperative Highway Research Program (NCHRP) Synthesis 272, 1999
Dust Palliative Selection and Application Guide, Peter Bolander and Alan Yamada,
San Dimas Technology and Development Center, San Dimas, California, USDA Forest
Service Technology and Development Program, November 1999
Ecosystem Road Management, San Dimas Technology and Development Center, San
Dimas, California, USDA Forest Service, November 1997
Erosion Control Handbook for Local Roads, Ann Johnson, P.E., Minnesota Local
Road Research Board, Manual No. 2003-08, 2003
Fabric for Reinforcement and Separation in Unpaved Roads, Julie B. Bearden and
Joseph F. Labuz, University of Minnesota, MN/RC-1999-04, 1998
Guidelines for Geometric Design of Very Low-Volume Roads (ADT<400), American
Association of State Highway Officials, 2001
9-1
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The Nature of Roadsides and the Tools to work with It, J. Baird Callicot and Gary K
Lore, Federal Highway Administration Publication No. FHWA-EP-03-005, 1999
Low Volume Roads Engineering, Best Management Practices Field Guide, Gordon
Keller and James Sherar, U.S. Agency for International Development, 2003 (USDA
Forest Service international Programs)
Massachusetts Unpaved Roads BMP Manual, Berkshire Regional Planning
Commission, Project 98-06/319, 2001
Motor Grader Operator Handbook and Motor Grader Operation Tips and
Techniques, Kansas Local Technical Assistance Program (LTAP), 1999
NACE Action Guide Volume III-5 Stormwater Management and Drainage, National
Association of County Engineers, 2000
Problems Associated with Gravel Roads, Local Technical Assistance Program (LTAP),
Federal Highway Administration, Publication No. FHWA-SA-98-045, 1998
Pruning Ornamental Plants, Special Circular 235, J Robert Nuss, Penn State College
of Agricultural Services Cooperative Extension, 1998
Recommended Practices Manual, A Guide for Maintenance and Service of Unpaved
Roads, Choctawhatchee, Pea and Yellow Rivers Watershed Management Authority,
February 2000
Roadside Use of Native Plants, Bonnie L. Harper-Lore and Maggie Wilson, Federal
Highway Administration, Island Press, 2000
Soil Bioengineering, An Alternative for Roadside Management, Lisa Lewis, UDA
Forest Service, Sam Dimas Technology and Development Center, San Dimas, California,
September 2000
Stream Corridor Restoration: Principles, Processes, and Practices, The Federal
Interagency Stream Restoration Group
Water / Road Interaction Field Guide, USDA Forest Service, San Dimas Technology
and Development Center, San Dimas, California, September 2000
9-2
-------
Technical Information Sheets
10-1
-------
iraw/ifal/y Sensitive MaMeaum lot flirt am/ fime/ to*
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP #01 Insloping
Category: Practices Relating to Road Profile
Refer to: Manual Chapter 5, Section 5.3.1.1
Description: Insloping is applied when the road has been constructed along a steep bank,
with a steep uphill bank on one side and a steep downhill bank on the other side, ending
at the edge of a stream. Insloping means the entire surface of the road slopes toward the
uphill embankment side to eliminate drainage over the steep downhill embankment into
the adjacent stream, as shown in Figure 1.
Create berm dam •
along road edge at
top of slope
Safety?
a Road Profile: Common
practice for roads along steep
banks
Figure 1 Insloping
Slope: 1/2" - 3/4" min. per foot
b. Alternate Road Profile: Insloping
Common Practice and Associated Problems: With a steep uphill bank on one side and
a steep downhill bank on the other, common practice is to install a normal road crown.
This practice concentrates drainage from half of the road toward the downhill side,
causing erosion or severe washouts down over the bank, resulting in sediment into the
stream. Sometimes a berm dam is installed along this edge of the road at the top of the
slope. The berm dam creates a secondary ditch, building up water volume and flow that
will result in a washout over the embankment and again into the stream. The photo shows
a prime candidate for insloping.
10-2
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Installation: The road is sloped entirely toward the uphill side using a normal cross slope
(1/2" per foot). A roadside ditch
collects the water and carries it to a
strategically located cross culvert with
proper outlet protection. Pipe flows
should be directed to a vegetative filter
strip. A berm barrier can be constructed
along the road at the top of the
downhill embankment, if desired, for
vehicle safety. Multiple crosspipes will
lessen the amount of water to be
handled by each pipe, keeping ditch
and pipe sizes to a minimum along with
minimizing the erosion potential at the
pipe outfall.
ESMP#01-01 Road candidate for insloping. Crosspipes
can be strategically placed to outlet into the vegetative
areas between the stream meanders.
Advantages:
• Eliminates flow over the
downhill embankment
• Eliminates erosion on bank and
sediment flow into stream
• Adds only one half of road surface runoff to ditch along uphill bank, eliminating
need to increase size of ditch or cross pipes
• Allows all road drainage to strategically place cross pipes outletting to vegetative
filter strips, filtering out sediment and attached pollutants
• Additional crosspipes minimize volume and velocity of water, minimizing ditch
and pipe size, adding to roadside safety
Safety Considerations: Vehicle safety has to be considered. This practice should be used
on a low volume road with a minimum cross slope. A higher berm along the downhill
side creates an additional safety factor. Attempting to keep shallow ditches on the uphill
side with flattened foreslopes and additional crosspipes will add to safety regarding
vehicles sliding on winter ice.
Related Practices:
ESMP #02 Outsloping
ESMP #11 Stream Saver System
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iraw/ifal/y Sensitive MaMeaum lot flirt am/ fime/ to*
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP#02 Outsloping
Category: Practices Relating to Road Profile
Refer to: Manual Chapter 5, Section 5.3.1.2
Description: Outsloping is applied when the road crosses a gentle sloping terrain.
Outsloping means the entire surface of the road slopes toward the downhill side with a
normal cross slope. Outsloping is similar to superelevation or banking of a curve, but on
a straight section of road and with no ditching. The outsloped road blends into the gentle
slope of the terrain with no ditching or cross pipes, allowing the natural sheet flow
conditions to prevail, as shown in Figure 1. This technique should be used with gentle
sloping terrain and low overland flow conditions.
Road
Safety?
Roadside ditches
a Road Profile: Common
practice for roads crossing
gentle sloping terrain
Figure 1 Outsloping
Slope: 1/2" - 3/4" min. per foot
b. Alternate Road Profile: Outsloping
Common Practice and Associated Problems: Common practice dictates a road with a
normal crown and side ditches. This configuration creates a dam and concentrates the
overland sheet flow, causing potential erosion of ditches and ditch outlets. This profile
also requires cross pipes to outlet the uphill side ditch with the potential clogging and
flooding concerns. The volume of water to be handled can become substantial.
10-4
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Installation: The road is sloped entirely toward the downhill side using a normal cross
slope (1/2" per foot). The outsloped road profile blends into the sloping terrain and there
are no ditches or cross pipes. The
uphill natural sheet flow continues
down across the road and through
lower vegetative filtering areas
(vegetative filter strip).
The photo depicts outsloping of a
road. The wooded area on the
uphill side results in low surface
runoff. This runoff continues to
sheet flow across the road and into
the vegetative area on the other
side. No ditches and no ditch
maintenance required.
ESMP#2-01 Outsloped road showing no ditches and
vegetative filtering areas for overland sheet flows.
Advantages:
• Eliminates concentrating
the natural overland sheet
flow. Eliminates erosion on
bank and sediment flow into stream
• Eliminates ditches and cross pipes, eliminating erosion potential and maintenance
• Allows all road drainage to blend into the natural drainage system
• Has been successfully used for driveways crossing gentle sloping terrain,
eliminating driveway ditch flows onto the main gravel road and ditches
Safety Considerations: Vehicle safety should be considered. Although the use of a
normal cross slope helps in safety, the road surface condition, amount of flows and
temperatures may cause icing of the road surface. Although this has not been the case on
actual sites where outsloping has been constructed, conditions should be monitored
closely during the winter months. In addition, a heavy storm may require road
maintenance afterward if flows are substantial enough to cause road surface degradation.
Again, this practice should be used on a low volume road crossing gentle sloping terrain
with low overland flow conditions.
Related Practices:
ESMP#01 Insloping
ESMP #11 Stream saver system
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fflwrowwte//y Semite Mnteataee tot flirt mi Stavel tads
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP #03 Ditch Turnouts and Vegetative Filter Strips
Category: Practices Relating to Roadside Ditches
Refer to: Manual Chapter 5, Section 5.3.2.8
Description: All roadside ditches should
be outletted to carry the water away from
the road. Otherwise, the water will pond in
the ditch, seeping back into the road
structure, reducing its structural capacity
and leading to road degradation.
Terminology varies from region to region
with various descriptive terms used for
outletting ditches. Ditch outlets, ditch
turnouts, tail ditches, and bleeders are all
commonly used terms. Whatever you call
it, the ditch turnout carries the ditch flow
ESMP#3-01 Standing water can only lead to
problems!
from the ditch, away from the road, and
into a vegetative filter strip. The
vegetative filter strip is an area of vegetation that filters out the sediment laden ditch
water, increases water infiltration into the ground, and permits only clean runoff into a
nearby stream. Ditch turnouts and vegetative filter strips should automatically go
together.
Common Practice and Associated Problems: Do not outlet ditches directly to streams!
Ditches carry surface runoff from the road and from the surrounding terrain along with
any sediment and any contaminants attached to the sediment. Outletting directly to the
stream is common since the stream is usually at the low point of the road. But this allows
sediment and pollution to go directly into the stream, adversely affecting the stream
ecology. Road personnel should turn ditches out prior to that low point into a vegetative
filtering area to prevent stream pollution.
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Installation: Turnouts can be installed during ditch cleaning operations. Turnouts should
be skewed in the direction of water flow into a vegetative area. There are no exact
spacing or size requirements for turnouts. Available charts do not take into consideration
the many variables of specific sites, but may be used as guidelines. Road personnel need
to consider the volume of water and ditch slope and the off right-of-way conditions and
ownership. The volume of water can vary considerably depending on the terrain. The
ditch may just drain the road surface or it may drain the road surface plus a major hillside
area adjacent to the road. Road personnel should use their knowledge and experience
when locating and
constructing turnouts.
It is important to note that
installing more turnouts
limits the length of the
ditch to each individual
turnout. This in turn
reduces the amount of
water and flow within the
ditch reducing water
velocity and erosion
potential and keeping the
size of both the ditch and
the turnout nominal.
Limiting the amount of
water that has to be
handled should always be a
consideration in any
drainage situation. Refer to
ESMP#10 Through Drains,
for reducing water volume in ditches stemming from natural roadside springs.
Ditch turnouts should be strategically located to direct flows to vegetative areas.
Vegetative filters strips will spread the water flow, slow velocity, decrease energy, and
Road
Ditch
Turnout
Vegetative
Filtering Area
Figure 1: Ditch turnout into vegetative filter strip.
ESMP#3-02 Multiple small turnouts mean nominal size ditches with less water, less velocity, less
erosion potential, although large sized turnouts may be the only option on certain sites.
10-7
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filter out the sediment. Other pollutants that may have attached to the sediment will also
be contained and may be broken down physically or chemically by the soil or plants
(refer to Manual, Chapter 4).
Advantages: The combination of ditch turnouts and vegetative filter strips:
• Carries the water away from the road and keeps streams clean
• Multiple turnouts decrease the volume and velocity of the water that the turnout
handles, thereby decreasing the energy and erosion potential and keeping a
nominal size on ditch and turnout
• Vegetative filter strips slow the water, dissipate energy, and filter out sediment
and other attached pollutants
Safety Considerations: Ditch turnouts and vegetative filter strips carry the water away
from the road providing effective road drainage to prevent flooding and road structural
deterioration.
Related Practices:
ESMP #04 Broad Based Dips
ESMP #05 Grade Breaks
ESMP #10 Through Drains
Manual Chapter 5, Section 5.3.2, Practices Relating to Roadside Ditches
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-15
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP #04 Broad Based Dips
Category: Practices Relating to Ditches and Road Profile
Refer to: Manual Chapter 5, Section 5.3.3.1
Description: Broad based dips are shallow, gradual dips skewed across the road in the
direction of water flow, as depicted in Figure 1. This practice is used where there is a
high embankment
on one side of the
road with a
downhill grade. The
high embankment
does not allow for
ditch turnouts and
requires a cross
pipe to carry the
water to the other
Original road gradfe-
3% min. outslope
Gradual, shallow, skewed dip. May need to use select
aggregate & geotextile fabric for crossing area
Figure 1: Broad Based Dip
side and then to an outlet. Broad based dips allow the ditch water to flow to the other side
joining that ditch flow to a joint outlet or turnout to a vegetative filter strip. The "dip"
channel is skewed in the direction of water flow, and the crown of the road is eliminated
within this area.
Broad based dips present an alternative to installing and maintaining cross pipes on very
low traffic volume roads. Broad based dips should be used only for ditch flows and not
for perennial streams with permanent or intermittent flows.
Common Practice and
Associated Problems: Many
roads have long downhill sections
with a steep embankment on the
uphill side, requiring ditches to be
outletted through cross pipes or
run from the top of the grade all
the way to the bottom before they
are outletted. Water volume and
velocity continually increase as the
flows run downhill, necessitating
larger ditches and cross pipes to
outlet the flow. Increased volume
and velocity results in increased
ESMP#3-01 Broad based dips can be used in lieu of
cross-pipes.
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erosion potential and flooding. In addition, water runs down the road surface, again
picking up volume and velocity, and causes erosion gullies and rutting to occur. All of
these factors lead to ever-increasing road maintenance and the associated increased costs.
Installation: Broad based dips can be graded into the road rather easily with the existing
road materials. The bottom of the dip has to pick up the ditch flow, carry it across the
road, and outlet to a vegetative filter strip. Broad based dips eliminate the road crown
within the dip area. Water volume must be contained in the channel with no overtopping,
and longitudinal slopes must be gradual to prevent vehicles from dragging. Proper
transitions must be constructed to blend to
and from the road crown. Test the dip by
driving the road after installation.
There are no exact formulas for spacing or
size for broad based dips. These factors
will depend upon many variables, such as
road grade, traffic, volume of water,
terrain, etc. The use of multiple broad
based dips on a long downhill stretch of
road also allows a smaller ditch size to
carry the limited water volume from a
ESMP#3-02 Broad based dip reinforced with shorter section or road. This limited
large aggregate. volume of water should not haye
substantial flow or velocity to do any damage to the road surface crossing. Steeper road
grades require placing more broad based dips closer together to limit water volume and
velocity. Broad based dips can be easily constructed with a grader or small dozer within a
short time period using the existing road materials.
Select larger sized aggregate to fill the dip. Geotextile separation fabric may be required
to reinforced and stabilize the dip, since we have traffic and water crossing perpendicular
to one another. The need to reinforce the dip depends on water volume and velocity and
the type of road material. (See Manual Chapter 7 and ESMP #15for using geotextile
separation fabrics.)
Road grader operators have to be aware of the broad based dip installations so that they
do not think they are washouts or problem areas and reshape the road back to a normal
crown. In addition, winter plow operators should be aware of these installations for
proper and safe plowing operations.
Advantages:
• Breaks road into smaller sections for better drainage, handling less water with less
velocity
• Allows the ditch to outlet across the road without a cross pipe
• Multiple broad based dips allow use of smaller sized ditches
• Reduces road surface water flows, eliminating damaging erosion gullies and ruts
10-10
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• Outlets smaller volumes of water into vegetative filtering areas, providing for less
erosion and greater sediment control
Safety Considerations: Broad based dips have a calming effect on traffic speed. Broad
based dips also break the downhill momentum of vehicles, reducing the operator's
chance of losing control.
Related Practices:
ESMP #05 Grade Breaks
ESMP #03 Ditch Turnouts and Vegetative Filter Strips
ESMP #15 Road Separation Fabrics
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iraw/ifal/y Sensitive MaMeaum lot flirt am/ fime/ to*
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP #05 Grade Breaks
Category: Practices Relating to Ditches and Road Profile
Refer to: Manual Chapter 5, Section 5.3.3.2
(Adapted from the Pennsylvania Dirt and Gravel Roads Program, Technical
Bulletin, 2/21/04)
Description: Grade breaks are long gradual breaks in the longitudinal grade of a road on
a downhill slope, as depicted in Figure 1, breaking the road into shorter lengths for more
efficient drainage. Grade breaks retain the road crown and require appropriately placed
cross pipes.
Cross pipe
Ditch flovvline guide
Figure 5-11 Grade Break
New centeiline
Grade breaks limit
water flow by
limiting the road
section area to be
drained. A shorter
section of road
decreases
concentration and
velocity, resulting in a smaller ditch cross pipe size. This reduction in water volume and
flow in turn helps alleviate problems at the pipe outlet. Grade breaks also limit the length
of flow and thus velocity down the road surface, eliminating potential surface erosion
gullies and rutting.
Common Practice and Associated Problems: Many roads have long downhill sections
where the ditches run from the top of the grade all the way to the bottom before they are
outletted. Water volume and velocity continually increase as the flows run downhill,
necessitating larger ditches and cross pipes to outlet the flow. Increased volume and
velocity results in increased erosion potential and flooding. Erosion can be combated
with additional ditch armoring, but that is very costly. Large flows through large pipes
cause potential problems at the pipe outlet to dissipate the flow energy. In addition, water
runs down the road surface, again picking up volume and velocity, and causes erosion
gullies and rutting to occur. All of these factors lead to ever-increasing road maintenance
and the associated increased costs.
10-12
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ESMP#5-01
Installation: There are no exact
formulas for spacing or size for
grade breaks. These factors will
depend upon many variables,
such as road grade, traffic,
volume of water, terrain, etc.
Multiple grade breaks keep the
road sections shorter for
effective drainage and less
erosion potential. Steeper road
grades require placing more
grade breaks closer together to
limit water volume and velocity.
Grade breaks can be constructed
with a grader or dozer. It is
important to gradually taper the
grade break back into the road grade. Testing the longitudinal slopes by driving through
the break at a reasonable speed will indicate whether additional work is needed. The
grade break also needs to accommodate snow plowing without road surface damage.
As shown in the above figure, a grade break can be installed at the location of the cross
pipe. This allows the cross pipe to effectively meet the ditch gradient with the road being
built up and over the pipe to create the grade break. This eliminates the need to install the
cross pipe at a much deeper elevation than the road ditch, resulting in additional potential
for pipe blockage and road flooding. Pipe outlet areas need continual monitoring and
erosion protection established as needed.
Road maintenance personnel, specifically the grader operator, must be aware of grade
breaks and their purpose. An uninformed operator may see the grade break as a road
surface deviation or consider the grade break as a source of extra road material to use
elsewhere.
Advantages:
• Breaks road into smaller sections for better drainage, handling less water with less
velocity
• Allows use of smaller sized ditches and cross pipes
• Smaller cross pipes decreases pipe outlet problems
• Eliminates damaging road surface water flows, eliminating gullies and ruts
• Outlets smaller volumes of water into vegetative filtering areas, providing for less
erosion and greater sediment control
Safety Considerations: Grade breaks can actually have a calming effect on traffic speed.
Grade breaks also break the downhill momentum of vehicles, reducing the operator's
chance of losing control.
10-13
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Related Practices:
ESMP #04 Broad Based Dips
ESMP #03 Ditch Turnouts and Vegetative Filter Strips
10-14
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Environmentally Sensitive Maintenance lor Dill and Gravel tods
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP#06 Driveways
Category: Practices Relating to Driveways
Refer to: Manual Chapter 5, Section 5.3.4
Description: Driveways pose several problems or concerns not only for the road user,
but also for road maintenance personnel. Safety for the road user and the property owner
served by the driveway should be a priority. Safe ingress and egress with minimal
interference with other traffic should be a goal in driveway construction. Many states
have regulations regarding driveways entering the state road system. These regulations
are good resources for local governments, since the only way to insure effective driveway
construction and rehabilitation is through the adoption and enforcement of policies and
regulations, necessitating a driveway permit system. This provides the needed control
allowing the road manager to review the site and determine what needs to be done for
proper drainage to protect the road and the environment and provide safe access for the
property owner and a safe road for other
drivers. With that said, this technical
information sheet will deal with the one
specific problem for road maintenance
personnel that also affects road safety and
the environment - Drainage.
Common Practice and Associated
Problems: If property owners are under
no regulations and do not need to obtain a
permit or notify the governing entity, the
end result of driveway construction will
most likely cause continual drainage
problems and road safety hazards.
Roadside ditches will be filled in, and
driveways sloping down to the road will
continue on a down slope right to the road
edge. This condition will drain the driveway onto the road, creating hydroplaning in the
summer and icing in the winter. Blocked drainage ditches, likewise, will flood the road
and again cause these unsafe situations. Water ponding on the roadway and in the
roadside ditch will seep into the road structure and began the degradation that will plague
the road crew and shorten the life of the road.
ESMP#6-01 Improperly constructed driveways
not only cause road drainage and road safety
hazards, but also cause degradation of the
environment through erosion and sediment.
10-15
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Proper
Culvert
Figure 1 Proper driveway construction with deep ditch
Installation: Driveway installation must follow a few rules - the first of which is
maintaining proper road and shoulder and ditch profile. Ditch flow has to be maintained.
For driveways
sloping down
toward the road, the
low point should be
over the ditch line,
allowing both the
road and driveway
to drain into the
ditch off either side
of the driveway, as
shown in Figure 1.
For driveways with
deep ditches, a pipe
under the driveway continues to carry the ditch flow. These driveway drainage pipes may
have nominal cover and have to be strong enough to support the vehicle loads. Refer to
ESMP#09 for alternatives in shallow culvert installations.
For driveways with medium depth ditches, an open-top culvert or a box with an open
grate may suffice, as shown in Figure 2. These units can be prefabricated or homemade.
The photo insert in the figure pictures two types of prefabricated units, one all-plastic and
one of a
combination of
plastic and metal.
This system should
only be employed
for paved
driveways, which
will only drain clean
surface runoff into
the channel without
clogging the grate.
Box with Grate
or
Open-Top Culvert
Figure 2 Alternate driveway
construction with medium-deep ditch
10-16
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In many instances, the roadside ditch will be shallow with nominal flows. In this case the
ditch may continue across the driveway, as shown in Figure 3. Vehicles should not have
any problem
traversing a shallow
ditch carrying only
ditch flows during
storm events. This
area may require
stabilization and
reinforcement
through the use of
Proper
Continue water flow in ditch across
driveway, may need to stabilize crossing
with proper aggregate and geotextile
Figure 3 Driveway construction with shallow ditch
larger aggregate
and/or a geotextile
separation fabric. The need to reinforce the crossing depends on water volume and
velocity and the type of driveway material. Geotextile separation fabrics are discussed in
the Manual, Chapter 7 and ESMP #15.
Advantages:
• Regulations and driveway permits give the road manager the authority to enforce
proper conditions at the driveway site to meet drainage and safety requirements
• Properly constructed driveways:
o Maintain roadside ditch flows, preventing blockage and flooding
o Maintain proper road surface drainage off of the road
o Eliminate water on the road surface which could cause hydroplaning or
icing
o Maintain road structural adequacy by keeping water out of the road
structure.
o Eliminate erosion and sediment from block ditches or road surface
ponding, thereby protecting the environment.
Safety Considerations: These practices maintain proper drainage off, out of and away
from the road, keeping the road safe, eliminating the potential hydroplaning and icy
conditions. The driveway will also be safer due to proper drainage and less degradation.
One safety factor to keep in mind: if a box with grate facility is homemade, use
appropriately sized openings in the grate that will not be a safety hazard to animals or
bicycles.
Related Practices:
ESMP #07 Culvert End Structures
ESMP #08 Aprons at Culvert Outlets
ESMP #09 Shallow Culvert Installations
ESMP #15 Road Separation Fabrics
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fflwrowwte//y Semite Mnteataee tot flirt mi Stavel tads
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP #07 Culvert End Structures
Category: Practices Relating to Culverts
Refer to: Manual Chapter 5, Section 5.3.5.3
Description: A culvert end structure is simply a structure built at a pipe opening, either at
the pipe's entrance or outlet end. The terms headwall and endwall are also used
interchangeably, again referring to end structures for the drainage pipes or culverts.
Common Practice and Associated Problems: Many pipes are installed without any
consideration for end structures. The end areas of roadway cross pipes transporting ditch
water from side of the road to the other are prime targets for erosion and sediment. The
pipe redirects the water flow, turning it through the pipe and across the road. This
redirection of flow causes turbulence resulting in erosion around the pipe opening. Where
there are close roadside embankments, gouging out the bank to install the crosspipe
enhances the erosion potential if bare soil remains, as shown in the photo.
\
..
ESMP#7-01 Typical process of gouging out the roadside bank to install a cross pipe for ditch flow
with no end structure leads to continual erosion and maintenance.
Even when water flows directly into and out of a pipe, these straight transitions are prone
to erosion. Water flow into the pipe is usually restricted by the pipe opening, causing
turbulence and possible erosion around the pipe entrance. Since the pipe restricts flow,
the water travels faster through the pipe and out the other end. As the flow emerges from
the pipe, eddy currents cause swirling flows on each side, leading to erosion around the
pipe, as depicted in Figure 1. End structures can solve the erosion problem and provide
other benefits as well, as described below.
10-18
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Installation: Materials vary from concrete, flagstone or native stone to gabions or
prefabricated units. Consequently, the cost of installation can vary as much as the
material being used. Native stone not only becomes cost effective since it may be
available on site, but it is also environmentally aesthetic, blending into the natural
conditions. Several factors may
influence the choice of materials,
including local availability, skill
and time required for construction,
durability, cost, and volume and
velocity of water to be handled.
The photos show different types of
end structures, including a
geosynthetic, prefabricated unit.
The shape of the end structure is
important to direct water flow,
protect the road and embankments,
and improve drainage. The end
ESMP#7-02 structure should funnel the water
into the pipe while protecting the
surrounding area from erosion. On the inlet side,
end structures direct the flow into the pipe,
reducing turbulence and maximizing the flow
capacity of the pipe. Outlet structures prevent
erosive back eddy currents from undermining the
pipe and road structure.
Figure 1 Flow characteristics at
pipe ends
restricted flow
eddy currents, scour
Cross pipes should be installed on an angle
(skewed - not perpendicular) across the road in
the direction of water flow for smoother flow
transitions into and out of the pipe to further
reduce erosion potential.
Culvert end structures may not be enough to
protect against erosion at the pipe outlet. Further
erosion protection may be needed in this "apron" area past the structure. Culvert aprons
including the use of flared end sections are covered in Technical Information Sheet
ESMP#08 referenced below.
Advantages:
• Prevents erosion from occurring around the pipe opening
• Provides a low-cost, long lasting solution to erosion problems at pipe openings
• Reduces continual maintenance needed to address the erosion and sediment and
clogging of the pipe
• Provides structural support for the road
10-19
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Anchors the culvert providing structural support and preventing crushing of the
pipe end by heavy vehicles
Safety Considerations: Culvert
end structures increase safety by
providing structural support to the
roadway and to the culvert. There
are also many designs to enhance
roadside safety as to errant
vehicles, as well as providing the
other benefits described above. .
One such design is depicted in
Figure 2.
Figure 2: Veliicle safe end structure
for roadside embankment
Related Practices:
ESMP #08 Aprons at Culvert Outlets
ESMP #09 Shallow Culvert Installations
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Environmentally Sensitive Maintenance lor Dill and Gravel tods
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP #08 Aprons at Culvert Outlets
Category: Practices Relating to Culverts
Refer to: Manual Chapter 5, Section 5.3.5.4
Description: Aprons at culvert outlets refer to the immediate area at a pipe outlet.
Culvert outlets, even with an end structure, may still pose a problem with the flow
discharge energy. A conveyance channel may need to be created to a stable discharge
point. A simple flared end section may suffice as an apron to spread the water flow and
dissipate the erosive energy. Other materials, however, can be used as culvert aprons, or
used in conjunction with flared end sections to extend the stabilizing apron area.
Common Practice and Associated
Problems: Many pipes are installed
without any consideration for erosive
energy potential of the exiting water.
Since flow is usually restricted by a pipe,
the water travels faster through the pipe
and out the other end. As the flow
emerges from the pipe, dissipation of the
flow energy is often needed to prevent
erosion. This apron area is often neglected
and can lead to severe erosion and
maintenance headaches, as shown in the
photo.
ESMP#8-01 Severe erosion at a pipe outlet.
Size of rock & dimensions
of Apron depends upon
pipe size, discharge
velocity, & slope (terrain)
Installation: This is one area
where rock riprap can be very
effective. The rip-rap will spread
the water flow, slowing it down
and dissipating energy. Native
stone becomes the cost effective
aesthetic material choice, but,
depending on location, even
brush and tree stumps can be
effective. The size of rock and
the dimensions of the apron
depend on many variables such as pipe size, soil type, the discharge volume and velocity,
Figure 1 Aprons at Culvert Outlets
10-21
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and the slope of the outlet channel or terrain. Although there are charts available that can
be used as guidelines, apron installation should not be technically challenging.
Experienced road personnel know the amount of water flow and the potential problems at
a specific site. They can size the apron based on their past experience. Then, they need to
follow up with field inspections during and after the next several rainstorms. If erosion is
evident past the riprap limits, expand the apron and inspect again.
Flared end sections can be metal, concrete
or plastic. As mentioned, these pre-
fabricated sections may be enough to
transition the flow to a stable discharge, or
may be used in conjunction with other
materials, such as riprap. The flared end
section initiates spreading the flow and
protects against those swirling eddy
currents on each side of the pipe opening,
while the riprap further spreads the flow
and dissipates the flow energy eliminating
the erosion potential. Typical flared end
sections are shown in the photo.
Advantages:
• Prevents erosion from occurring
around the pipe opening, reducing
maintenance
• Provides a low-cost, long lasting solution to erosion problems at pipe openings
• Helps anchors the culvert, providing structural support
ESMP#8-02 Rock riprap makes an effective
apron to dissipate energy and prevent erosion
at the pipe outlet.
Safety Considerations: Culvert aprons prevent erosion of outlet ditches, eliminating the
vehicle drop-off potential in roadside ditches.
Related Practices:
ESMP #07 Culvert End
Structures
ESMP #09 Shallow
Culvert Installations
Metal flared end section
' *. on plastic pipe
»
4flfc .
ESMP#8-03 Typical Flared End Sections.
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Environmentally Sensitive Maintenance lor Dill and Gravel tods
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP #09 Shallow Culvert Installations
Category: Practices Relating to Culverts
Refer to: Manual Chapter 5, Section 5.3.5.1
Description: Roadway cross pipes are subjected to a variety offerees and loads. The
weight of the backfill material above the pipe is a concern in deep installations. Many
drainage cross pipes, however, are placed at a shallow depth to better accommodate the
flow of water from roadside ditches. Vehicle loading due to the weight and movement of
the vehicle is significant in these shallow installations. (See Manual Chapter 5, Section
5.3.5 for a discussion on traffic load distribution.) Road managers should consider
various alternatives in those installations where proper cover cannot be maintained. This
technical information sheet addresses several alternatives for shallow pipe culvert
installations.
Common Practice and Associated Problems: Because of site conditions, depth of
drainage ditches, water flow, etc., many cross pipes are installed without sufficient cover
and with no consideration of the traffic loading. These shallow installations are subject
to failure under traffic loads. In particular, flexible type pipe tends to deflect under traffic
ESMP#9-01 Shallow pipe installations can cause continual road deterioration.
loads, causing road materials to shift resulting in road surface degradation and possible
pipe failure. The more shallow the pipe, the greater the direct force from vehicles, and the
greater the deflection and resulting damage. A minimum of 12 inches of cover material
over the pipe and below the road material minimizes or dissipates the traffic loads. Pipes
larger than 24-inch diameter may need additional cover. The required cover, however,
cannot always be met in many situations, and the pipe becomes a shallow installation. In
10-23
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Figure 1: For shallow installations, use rigid pipe.
pipe arch, or elliptical concrete (rigid) pipe
addition, the road surface area directly above the pipe becomes a maintenance headache
with continual surface degradation.
Installation: There are
several alternatives to
improve shallow
installations:
Rigid Pipe: A rigid
pipe (concrete, cast iron,
steel) has the strength to
resist deflection under the
traffic loads to the
detriment of the road.
Elliptical Pipe or Pipe Arch ("Squash Pipe"): Pipe arch not only allows proper
flow capacity but also allows additional cover. An equivalent 18-inch diameter
corrugated metal pipe arch is only 15 inches in height. That extra three inches of
additional cover is significant in further distribution (reduction) of traffic loads. Rigid
pipe also comes in an elliptical shape allowing extra cover in addition to the extra
strength factor of the pipe itself. See
Figure 1 with accompanying photos.
Multiple Pipes: Multiples
pipes are another alternative. Multiple
pipes of smaller diameter allow more
cover but still provides adequate flow
capacity (see Figure 2). To use
multiple pipes, however, road mangers
must keep a few rules in mind. Flow
capacity is directed related to the area
of the pipe opening. This means that
two 12-inch diameter pipes do not
equal the flow capacity of one 24-inch
diameter pipe. The area of a circle (the
opening of the pipe) is nr2 or 3.14
times the radius squared. A 24-inch
diameter pipe has 452 square inches of
opening (3.14 x 12 x!2). A 12-inch
pipe has 113 square inches, or two 12-inch pipes have a total of 226 square inches of
opening. It would take four 12-inch pipes to equal the flow of one 24-inch pipe (4 x 113
= 452 square inches). Using three 15-inch pipes or two 18-inch pipes would give
additional flow capacity and still maintain greater cover over the pipes.
Another rule for multiple pipes is to make sure they are installed far enough apart to
allow adequate backfill compaction between the pipes for the compaction equipment
being used.
Figure 2: For shallow installations, use
multiple pipes of smaller diameter allowing
more cover with same capacity
10-24
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One of the concerns voiced in multiple pipe use is clogging. Any pipe can clog. One of
the simpler solutions for metal or plastic pipes is cutting the inlet end of the pipe on a
slant or bevel. Any debris flowing toward the pipe will tend to ride up the slant, which
will allow water to continue through the pipe. For multiple pipes, staggering the inlet
ends so that they are not parallel in one line perpendicular to flow will lessen the
probability of clogging. Each pipe inlet end is extended a little further (offset) from the
pipe beside it. When large debris, such as tree limbs or logs, come downstream, they will
either block only one pipe or be forced to an angle, skewing across the pipe entrances, but
allowing water to continue to flow through the pipes (see Figure 3).
r\r^r\rs v vw
Water flow
A. Cut pipe inlet end on
a bevel or angle (single
01 multiple pipes)
WWX^l
AAAMA/
rvwwwv
UulwUuluwtJ
Water flow
B. Offset pipe inlets on multiple pipe
installations
Figure 3 Recommendations to Help Eliminate Pipe Clogs
Advantages:
• The use of rigid pipe diminishes the potential of pipe failure and road surface
degradation.
• Elliptical or pipe arches allow adequate cover over cross pipes to protect the pipe
and the road.
• Multiple pipes allow adequate cover over cross pipes to protect the pipe and the
road.
• Cutting pipe inlet ends on a slant and offsetting multiple pipes reduces potential
clogging and the resulting flooding of the road and environment.
Safety Considerations: Shallow culvert alternatives will keep the road and cross pipe(s)
in good condition, eliminating the safety factors surrounding road degradation or pipe
failures.
Related Practices:
ESMP #07 Culvert End Structures
ESMP #08 Aprons at Culvert Outlets
10-25
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iraw/ifal/y Sensitive MaMeaum lot flirt am/ fime/ to*
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP #10 Through Drains
Category: Practices Relating to Culverts (and Roadside Ditches)
Refer to: Manual Chapter 5, Section 5.3.5.5
Description: Through drains are cross culverts that are strategically placed to handle
natural springs or spring seeps flowing perpendicular to the road and carry them under
(through) the road to the other side to continue in the original channel prior to the road's
existence. Many roads intercept native ground water flows in this manner. The through
drain allows this natural flow to continue without entering the road ditch or interfering
with road drainage, as shown in Figure 1.
Through Drain intercepts clean
Figure 1 Through Drain
Common Practice and Associated Problems: Common practice allows natural springs
of clean water to flow into the road ditch, mix with often sediment-laden ditch flows, and
then flow directly to a stream. The additional flows can be substantial during certain
periods of the year, such as during the spring rains, causing flooding of the road ditch and
road degradation. Even if flooding does not occur, this added volume has to be handled
by oversized ditches, increasing the erosion and sediment potential of the combined ditch
and spring flows. In addition, substantial flows diverted into streams could adversely
affect the stream ecology.
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Installation: Through drains should be installed wherever natural spring flows are
intercepted by the road and are carried by the roadside ditch and the surrounding terrain
and off right-of-way conditions allow installation. The through drain pipes are placed to
pick up the natural spring waters and carry them under the road, outletting on the other
side into the original downhill flow channel. This eliminates the usually clean water from
entering the road ditch, thus
keeping the water clean as it
continues in its original path prior
to the road's existence. The photo
depicts typical placement of a
through drain.
The through drain outlet has to be
stabilized as to flow volume and
energy. If the natural spring waters
have been flowing into the ditch
for a number of years, the natural
channel on the downhill side may
be nonexistent. This channel may
have to be reestablished, providing
proper erosion prevention until the
channel is stabilized.
Through-pipe carries
clean water under road
Road drainage
carried ovei
ESMP#10-01 Through Drains keep springs and spring
seeps out of road drainage facilities.
Advantages:
• Maintains clean natural spring waters as clean water
• Eliminates handling of this water volume via the road ditch, reducing ditch size
• Reduces ditch flow reduces erosion potential and resulting sediment
Safety Considerations: Through drains will decrease ditch size and reduce the flooding
and road degradation potential, keeping the road and roadside safer for vehicles.
Related Practices:
ESMP #07 Culvert End Structures
ESMP #08 Culvert Aprons
10-27
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Eminnmtilli Jw'fire fltataw lor Dirt mi time! Ms
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP #11 Stream Saver System
Category: Combination Practices
Refer to: Manual Chapter 5, Section 5.3.6.1
Description: The Stream Saver System raises the road profile over the low-point stream
crossing; the road surface remains level for an extended area away from the stream on
both sides, as
shown in Figure 1.
If the cross pipe
cannot handle the
flow, this level road
allows sheet flow
Figure 1 Stream Saver System
New Road Profile
Old Road Profile
•Existing Cross Culvert
> Raise the road over the stream crossing.
> Keep road grade level over stream area for sheet
flow during flooding conditions
> Use broad based dips and turnouts to vegetative
filter strips for road and ditch flows on each approach
across the road
during flooding
conditions with less
erosion potential.
Using broad based
dips and turnouts
into vegetative
filtering areas for the road and ditch drainage on each approach as conditions warrant
avoids direct discharge into the stream and alleviates some flood flow. If pipe capacity is
severely limited, a flood relief crossing can be established away from the stream
depending on the existing terrain and land use. This crossing should be a stabilized low
water crossing (refer to Chapter 7, Section 7.4.3.8.3 for a description of a stabilized low
water road crossing using geosynthetics).
In raising the road,
additional pipes
installed at higher
elevations allow for
flood flow relief, as
shown in Figure 2.
Depending on the
depth of material
used to create the
new road profile,
the additional flood
Figure 2 Stream Saver System with Flood
Relief Pipes
New Road Profile
New Flood *" C \+—- Existing Cross Culvert
Relief Pipes
Use smaller diameter pipes at higher elevations for flood relief flow
10-28
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relief pipes can be laid with minimal or no excavation. During major storms, these flood
relief pipes handle the extra flow, minimizing overtopping the road thus preventing road
deterioration.
Common Practice and Associated Problems: Common practices followed the
traditional topographical site conditions where the road's low point was directly over the
stream. This condition seemed to be the most practical way of draining the road.
Roadside ditches could be carried to the low point and outletted directly to the stream
with a cross culvert carrying the steam under the road. In analyzing the existing problems
at these sites, however, this procedure was not the best for the road and definitely not the
best for the environment. When all surface and ditch flows drain directly into the stream,
they carry all of the road's sediment and pollutants with them. When major storms hit,
creating flows beyond the culvert's capacity, the low point of the road became the v-
shaped channel, narrowing the overflow across the road, increasing the flow energy and
causing erosion of the road surface, again directly into the stream.
Installation: Every site will have different
requirements. The installation basics,
however, are the same. Add enough road
material to raise the road over the stream
with a level grade extended in each
direction for 50 to 100 feet. Use ditch
turnouts into vegetative filter strips for
roadside ditches on each approach. Use
broad based dips, grade breaks, or
additional cross culverts as needed on each
approach to break up the surface runoff
from the road and surrounding terrain and
handle effectively prior to the stream. Refer
to the individual technical information
sheets on these additional techniques for
more detailed information.
ESMP#11-01 Stream Saver System - raised
level road with ditch turnouts to vegetative
filters.
Advantages:
• Eliminates surface drainage and any sediment from the road and roadside ditches
directly into the stream, protecting the stream and the environment
• Raises the road to reduce flooding and surface erosion, establishing a level
surface for lower energy sheet flow, with much less road deterioration
• Provides additional flow capacity for flood flows as needed (by installation of
additional flood relief pipes)
Safety Considerations: Stream Saver Systems protects the structural stability of the
road, keeping the road safer. Road deterioration from flooding and surface erosion will be
minimal.
10-29
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Related Practices:
ESMP #03 Ditch Turnouts and Vegetative Filter Strips
ESMP #04 Broad Based Dips
ESMP #05 Grade Breaks
ESMP #07 Culvert End Structures
ESMP #08 Culvert Aprons
ESMP #12 Raising the Entrenched Road
Many other practices can be used in conjunction with the Stream Saver System as
the site conditions may warrant.
10-30
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Environmentally Sensitive Maintenance lor Dill and Gravel tods
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP #12 Raising the Entrenched Road
Category: Major Reconstruction
Refer to: Manual Chapter 5, Section 5.3.7
Description: Raising an entrenched road involves major filling of the road cross section
between high banks, bringing the road surface back up to the original road surface
elevation. When you look at the photo, you see a typical entrenched road in a forested
area. Usually entrenchment results
from years of traditional road
maintenance involving road
grading, shoulder cutting, ditch
cleaning and widening. As the road
profile drops, or becomes
entrenched, water draining to the
road is trapped and the road begins
to function as a channel. Restoring
the road to its original surface
elevation eliminates a multitude of
problems and maintenance
ESMP12-01 A typical entrenched road.
Common Practice and Associated Problems: Although common road maintenance
practices naturally lead to an entrenched condition, we continue year after year making
the situation worse. (Refer to chapter 5, Section 5.3.7, for a detailed description and
photo sequence of road entrenchment over the road's life.) An entrenched road becomes
the stream channel, even as ditch size continues to increase in an attempt to handle the
entrenched flows. Flooding and surface deterioration along with a saturated road structure
create ongoing maintenance to keep the road usable. Snow removal becomes an
increasing problem with the plowed snow piling up against the high banks, adding to the
water problem. As the above photo depicts, these roads have severe drainage, erosion and
sedimentation problems requiring continual maintenance. All these problems can be
eliminated by bringing the road surface back up to the original elevation.
10-31
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Figure 1: Raising the Road
Installation: Installation involves
substantial fill and a major work
effort. Fill material is expensive, but
obtaining free fill material and using
in-house equipment and operators can
offset costs. Various types of fill
material can be used. A new road
with good road material can then be
built on top of the fill material. The
road surface is built back up to its
original elevation, eliminating the
banks on both sides and providing for
excellent road drainage conditions
with much less erosion and sediment
pollution. Figure 1 shows the typical
entrenched roadway before and after
filling, completely eliminating the
bank on one side and reducing the
bank height on the other side.
Drainage can then sheet flow off the
road without a ditch on the one side.
The road will no longer be a drainage channel, experiencing far less road surface
deterioration. Snow removal becomes easier, and the removed snow will not be a future
source of water back into the road.
Figure 2 shows the construction
sequence, beginning at the top with
an entrenched road cross section.
The entrenched road traps road
drainage on the road and in the
parallel ditches. To prepare for
raising the road, proper crown is
needed on the existing road. Then
each lift of material is placed in
uniform 8- to 12-inch lifts with
proper crown of %-inch to %-inch
per foot and compacted.
Compaction is critical. A large
static roller, vibratory roller or
sheep's foot roller should be used
to thoroughly compact each lift of
fill material. Geotextile separation
fabrics or geogrids between lifts will add strength to the road base. (See Chapter 7,
Section 7.4.4.6 and ESMP #15 for using separation fabrics and Section 7.4.4.8 for
geogrids.) The road is then reconstructed on top of the fill using good road aggregates.
Entrenched Road
- First lift offill
Reshape existing road with proper crown and place first
lift of fill material and compact
Second lift of fill
Place second lift with proper crown and compact
Place final road aggregate with proper crown and
compact
Figure 2: Construction Sequence
10-32
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The road material is placed with the proper crown and compacted the same as the fill
material.
The photos show an entrenched road project from the start of the filling operation to the
final road surface being compacted.
ESMP12-02 Raising the entrenched road—step-by-step.
(trenched road^
adjacent to strea,
When the road is immediately next to a stream, the procedure is slightly different. In this
example, the road has a high embankment on one side and falls steeply off directly into
the stream on the other
side. The road is entrenched
with side ditches, as shown
in Figure 3. As also
depicted in the figure, the
road is raised upslope away
from the stream,
eliminating the
entrenchment on the stream
side. This allows for sheet
flow across additional
vegetated area. The high
embankment on the other
side is reduced with better
stability and drainage
control. Depending on site
conditions, the
implementation of
insloping would provide
Figure 3: Raising the Road & moving away
from the stream
additional benefits.
10-33
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Advantages:
• Allows road surface drainage to sheet flow off the road through vegetated areas
reducing erosion and the resultant sediment pollution
• Eliminates ditches and ditch maintenance in terrain where sheet flow can be
established
• Eliminates concentration of water trapped in an entrenchment, prolonging the life
of the road with less maintenance
• Allows for more efficient snow plowing, removing the snow away from the road
and eliminating snow melt back into the road structure
Safety Considerations: Raising the entrenched road helps maintain the road in a safe
condition with no flooding and far less surface erosion and rutting.
Related Practices:
ESMP #11 Stream Saver System
ESMP #15 Road Separation Fabrics
Manual Chapter 7, Section 7.4.4 Geosynthetic Applications in Road Maintenance
Many other practices can be used in conjunction with raising the Entrenched Road
as the site conditions may warrant.
10-34
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Environmentally Sensitive Maintenance lor Dill and Gravel tods
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP #13 Slope Geometry, Benching, and Diversion
Swales
Category: Practices Related to Road and Stream Banks
Refer to: Manual Chapter 6, Sections 6.4.2.1, 6.4.2.2, 6.4.2.3
Description: Slope geometry, benching, and diversion swales are all related to bank
stability. Whether the bank requires stabilization and what practice or practices will be
the most appropriate remedy can only be ascertained from a initial site visit that includes
a thorough review and analysis of conditions. To determine the stability of a bank, we
ESMP#13-01 Eroded roadside banks are common sights, but add up to a large erosion and
sediment pollution problem effecting both roads and the environment. Site investigation and
corrective actions are essential.
must consider the site's topography along with the soils, drainage conditions, and
vegetation (Chapter 6, Section 6.4.1). Based on this site investigation, the selected
practices can be effectively implemented. Diversion swales are used where a vast area
drains down toward the road, adding significant surface drainage flows down over the
road embankment to the roadside ditch. The diversion swale will divert the upslope
surface flow away from the road and roadside ditch. Slope geometry has to do with the
degree or steepness of the bank itself and the bank's surface condition. Flattening slopes
and roughening or grooving the bank surface are practices that alter the slope geometry
for greater stability. Benching is the establishment of a bench or step or multiples steps
across a steep bank to aid in stability. Each practice is described in detail below.
10-35
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Figure 1: Bank Gouging
Common Practice and Associated Problems: Common road maintenance practices
tend toward cutting the toe of slopes (bank gouging), cutting or cleaning banks for better
sight distance, and smoothing the
surface until it "shines,", all of which
can lead to bank instability, resulting in
erosion and sediment pollution, and
eventually to road deterioration as
ditches fill and flood. Cutting the toe of
slope leaves a certain-to-erode vertical
surface, unable to withstand gravity's
relentless force as the bank attempts to
re-stabilize itself. In most maintenance
work involving bank cleaning or cutting
for whatever reasons, the work ends
with bare soil remaining, subject to
erosion from the impact of raindrops
and surface flows, carrying the
sediment into the roadside ditches or
downhill into the adjacent stream.
Reestablishing vegetation is a necessary
part of this work and should not be
overlooked. Bank cutting often results in a smooth bank surface. The equipment
operator's expertise used to be defined by how well the operator could "shine" the bank
surface. Then, if we did try to seed and mulch this extra smooth sloped surface, the
results were much less than desired.
Installation: Diversion swales divert upslope surface water before it washes over the top
of the road bank and into the road's drainage ditch. Diversion swale profiles can vary,
but are normally wide with
gradual side slopes. Swales
must contain the overland
flow and not be
overtopped. Diversion
swales must be stable, with
a level longitudinal grade
for infiltration back into the
soil or sloped to an
adequate discharge area.
Diversion swales
effectively drain, low, gradual vegetative slopes. The surface runoff from the entire
upward slope drains into a swale at the top of the road embankment. The road bank
would then be protected against erosion gullies. The volume of water to be handled by
the road ditch decreases along with the size of the road ditch and potential flooding and
erosion problems. Diversion swales are usually outside the right-of-way but need not
interfere with agriculture. Wider and more gradual, the sideslopes and longitudinal slope
will result in more infiltration and less flow accumulation. By eliminating washouts and
Diversion Swale
stops surface water
from reaching road
Figure 2: Diversion Swale
10-36
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ESMP#13-02 Diversion Swale: Wider swales and
gradual slopes result in more infiltration and less water
volume to handle.
erosion gullies that form down over the road bank and start to "eat" back into the hillside,
the swale can actually improve drainage of the landowner's property.
Begin by examining the slope.
Flattening a steep slope and
roughening or grooving the surface
slows the water flow down the
surface and with properly re-
established vegetation can
eliminate the erosion potential. On
the uphill side, flattening the slope
will move the top of the bank
further away from the road and
possibly beyond the right-of-way
limits. The same may hold for
flattening the slope on the downhill
side as we add material and extend
the toe of the embankment further away from the road. Right-of-way limits, land use,
and property owner expectations all need to be considered.
Roughening, grooving, or
tracking slopes are simply
methods to simulate natural
conditions. We need to
think in terms of existing
natural banks. Natural
banks are not regular or
consistent as to surface and
slope and they are not
polished and shiny. These
techniques require light
equipment in order to prevent packing the soil to the detriment of plant growth. Track
equipment should be used up and down the slope, not across, so the grooves catch water
and hold seeds and mulch. Roughening, grooving, or tracking of slopes catch rainwater,
slow surface water flow, reduce erosion, increase infiltration, and trap sediment. In
addition, by holding water, seeds, and nutrients, the rough surface enhances vegetative
growth.
Benching is commonly used effectively on
long, steep slopes with the same benefits
of holding soil, water, seed, and mulch for
enhanced vegetation growth, as listed
above for roughening the sloped surface.
The top of the bank may have to be moved
back and may be off the right-of-way. A
Figure 3: Roughening, grooving, or tracking slopes have
many advantages in stabilizing banks
ESMP#13-03 Tracking newly constructed
banks.
10-37
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good working relationship with property owners is again required.
The bench needs to collect
water. The outside edge
needs to be higher than the
inner edge to prevent over
the bank flow, as shown in
Figure 4. The bench then
should have a gradient to
drain the bench to a proper
Figure 4: Benching is commonly used on steep slopes Qutlet Some benches can
be gradually run out to the road ditch grade, for drainage. Do not overlook the use of
smaller multiple benches or steps, and keeping some irregularity for a more natural
appearance, if appropriate for the site.
ESMP#13-04 Newly constructed low-gradient bank bench.
Advantages: All of these practices result in improved bank stability, tending to do all of
the following:
• Catching rain water
• Slowing surface water flow
• Reducing erosion
• Increasing filtration
• Trapping sediment
• Holding water, seeds and mulch for enhanced vegetative growth.
Whether diversion swales, flattened slopes, rough surfaces, or benches, there will be less
erosion, less sediment, and less maintenance.
Safety Considerations: Bank stability results in better roadside conditions and less road
deterioration, resulting in safer roads.
Related Practices:
Manual Chapter 6, Section 6.4.1 Initial Site Visit
Manual Chapter 6, Section 6.4.2.4 Seeding and Mulching
Manual Chapter 6, Section 6.4.3 Bioengineering Techniques
10-38
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Environmentally Sensitive Maintenance lor Dill and Gravel tods
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP #14 Roadside Trees - Using the Forest System
to Reduce Maintenance
Category: Practices Related to Roadsides
Refer to: Manual Chapter 6, Sections 6.3
Description: By taking advantage of
natural principles when managing
roadside trees, it is possible to provide
safe clearances, enough shade to control
dust and invasive species and eliminate
the rapid re-growth of colonizer species
and frequent mowing cycles. Roads that
look like they are in harmony with nature,
require less money to maintain, pollute
less, and offer the additional benefit of
being beautiful. We need to develop a
strategy following some basic guidelines
to use the forest system to reduce
maintenance.
ESMP#14-01 Following some guiding natural
principles, we can use the forest system to
reduce maintenance.
Tree trimming and removal, brushing, brush cutting, and right-of-way clearing are all
terms for roadside vegetation management. These activities are common, and road
managers may need to perform these activities for a variety of reasons. We need to look
at these common practices and reasons, however, and determine what is best for our
roads and the environment.
Common Practice and Associated Problems: The normal methods used to trim trees
and remove brush along roadsides include manual methods ranging from chainsaws to
hand pruners; mechanical methods using mowers and brush cutters; and chemical
methods with chemical application equipment and herbicides. All of these methods and
equipment have their place in an integrated vegetation management program and can be
used effectively. There are some cautions, however, that should be noted.
In an environmentally sensitive maintenance program, chemical methods using
herbicides are certainly a concern. Due to the many hazards associated with herbicides,
federal and state governments have adopted various laws and regulations governing their
use. These regulations require local government applicators to become certified through
10-39
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testing. Environmentally sensitive maintenance does not promote the use of herbicides. If
you do use herbicides, you must become familiar with the laws and follow all the
requirements and regulations associated with herbicides use.
Boom mowers bring up an additional caution. Boom mowers, when properly used, can be
labor saving. One only has to travel, however, down a road on which a boom mower was
used, destroying the roadside vegetation and leaving a hurricane-aftermath look, to
realize that the use of this equipment can get out of hand. Damage to large tree limbs can
eventually kill the total tree. Refer back to the discussion in Chapter 4 on understanding
your trees and the effects of wounds. In addition, boom mower operators are frequently
instructed to cut "everything you can reach and everything small enough that you can
cut." This direction and practice will ultimately have, as its consequence, roadsides
vegetated only by large trees. Some of the most beautiful, slow-growing, strong, wildlife-
friendly trees along the roads are being systematically removed because they have the
misfortune of being small. Planners frequently choose trees such as dogwood and
serviceberry as roadside trees. Yet they are
often removed by boom mower operations
just because of their size. Would it not
have been better to remove the big old
damaged or dead trees and save those
small dogwoods? The dogwood makes an
excellent roadside tree with the added
value of blossoms to beautify the roadside
in the spring.
A third caution is the common practice of
traditional right-of-way clearing and its
use for dirt and gravel roads. Traditional ESMP#14-02 Dogwoods are a good roadside
clearing practices may have their place on tree with the added value of aesthetics.
the interstate and superhighways, but they can cause continually more maintenance work
when used on our gravel roads in forested areas. Common accepted reasons for clearing
the roadside of trees and bushes are to eliminate shade, improve visibility, establish a
safety clear zone and reduce routine tree trimming. Although all of these reasons have
some merit and may apply for some roads, we need to look closely at the conditions
created and the need for future maintenance.
Although shading is viewed as negative, it also has advantages. Shading retains road
moisture, cutting dust. Shading reduces the growth of unwanted colonizer trees and
encourages desirable plant growth. A limited amount of shading may be more effective
and efficient for our unpaved road maintenance and the environment.
Regarding visibility, one of the greatest safety hazards results from an abrupt transition
from bright sunlight to dense shade or vice versa. This extreme change in light can have a
devastating effect on the motorists' visibility and be a direct cause of accidents. This type
of extreme change in light conditions should be avoided.
10-40
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Traditional clearing practice for a shaded road would be
from right of-way line to right-of-way line.
Traditional clearing techniques involve total removal of brush and vegetation along the
roadside from right-of-way line to right-of-way line, typically resulting in vastly
increased sunlight along the edge of the road. Looking at the sequence of events in a
traditional cleared roadside, however, this may not be what is desired. If the roadside is
wooded or forested and the road well shaded and we automatically go in and cut
everything down, as
shown in Figure la
to Ib, on each side
of the road for
whatever distance
we consider
necessary, the
results may lead to
increased
maintenance. igure
When a section of trees is cut down, the remaining trees along the cut edge are open to
storms and wind and may not be structurally strong enough to withstand these conditions.
Wind damage, broken branches, and even uprooting can result, as shown in Figure 2a.
Other problems include the rapid regrowth of the removed trees through stump sprouts,
which are structurally weak and can become a continual maintenance problem. In
addition, exposing low growing, broad-leafed, shade-tolerant plants to full sunlight
typically kills them, with the potential of soil erosion.
When the roadsides,
previously shaded,
receive full sunlight,
nature produces
vigorous growth, as
depicted in Figure
2b. This vigorous
Common reaction of previously protected Dense weak colonizer growth, which can ornwtrl i
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So in this scenario, the mowing/removal of trees and brush in the interest of safety and
visibility, have the opposite effect, starting an endless cycle of cutting and re-cutting of
this colonizer growth.
Alternative Practices: The solution is to
use the forest system to reduce
maintenance. Be selective! When doing
roadside trimming and tree removal,
remember to remove the dead, dying,
unstable or damaged trees first. Trees that
have been damaged by previous
maintenance activities, automobile
accidents, etc. will eventually die and
become hazards.
The second priority is to remove the
existing colonizer trees. These trees, even
if they are healthy, are not good roadside
trees. They are very rapid growers, have
weak structures and short lives. They
commonly fall onto the road or drop
limbs, which create maintenance and
ESMP#14-04 Remove dead, diseased, unstable, hazards.
or dying trees first.
After removing the damaged trees and the colonizers, it is advisable to look the situation
over and evaluate the rest of the trees. Maintaining strong, slow-growing, deep-rooted
climax species should be an objective (refer to chapter 4, Section 4.5.4). Avoid straight-
line cutting, however, favoring instead an irregular edge. Traffic will tend to travel more
slowly on a road with an irregular edge. Speed has always been a major safety problem
for our dirt and gravel roads. Clearing the roadside completely or cutting back on a
straight line parallel to the road gives the motorist the safe illusion to increase speed.
Maintaining a uniform level of shading is best. One of the greatest dangers from shading
comes from winter conditions where pockets of deep shade create irregular icing
conditions. Thinning of the canopy to achieve the desired shade density should be the
objective. Remember, deciduous trees will lose all their leaves in the winter, letting more
sunlight penetrate to the road. Sometimes it is necessary to thin back off the edge of the
right-of-way, as the desired sunlight may only be available from the side, not from above.
Obviously it is necessary to discuss your plans and objectives with property owners to
receive permission to work off the right-of-way.
Advantages: In a situation where a dirt and gravel road is heavily lined with trees or
passes through forested areas, a program of vegetation management that seeks to use the
forest system and take advantage of natural principles can save time and money in several
ways.
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ESMP#14-05 A before and after look at selective tree trimming during a road project - using the
forest system to reduce maintenance.
1. Allowing a level of shading helps to retain moisture. Moisture is nature's
stabilizing agent. Allowing enough shade to remain to hold some moisture on dirt and
gravel roads helps to hold the surface together and reduce dust. Although few road
managers would readily identify moisture retainage as a benefit of shaded roads, they will
almost always tell you they use less dust control in shaded areas.
2. Maintaining shade along our roads reduces the establishment of colonizer
species (aspen, birch, poplar, sumac, striped maple, etc.). These rapid growing, weak-
wooded trees are the ones which create the biggest maintenance problems, especially
during winter maintenance operations when they lean out into the road laden with heavy
wet snow.
3. The trees that are removed are less likely to return as stump sprouts. All of us
have witnessed the rapid return of vegetation under new power line cuts. This is usually
a combination of stump sprouts and colonizer species, resulting in increased mowing
cycles. This scenario can be avoided by simply allowing the road to remain partially
shaded.
A well-maintained roadside forest system also adds to the aesthetics, which in turn
enhances tourism.
Safety Considerations: Safety factors were discussed throughout the above. Well-
managed roadsides with structurally strong, deep-rooted, long-lived trees will be safe
roads. These roads will also be easier to keep clear and safe through the winter snows.
And irregular edges have a tendency to reduce traffic speeds for additional safety.
Related Practices:
Manual Chapter 6, Section 6.3.3.7 Tree Leaves
Manual Chapter 6, Section 6.3.4 Using Other Plants for the Roadside
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Environmentally Sensitive Maintenance lor Dill and Gravel tods
Technical Information Sheet
Environmentally Sensitive
Maintenance Practices
(ESMPs)
Practice: ESMP #15 Road Separation Fabrics
Category: Practices Using Geosynthetics
Refer to: Manual Chapter 7, Sections 7.4.4.6
Description: Road separation fabrics are geosynthetic fabrics that separate the subsoil
from the road aggregate, providing improved road stability and reinforcement, improved
drainage, prevention of sub grade pumping of fines, and thereby dust reduction.
a.
How They Work: When roads are built,
the subsoil or subgrade is prepared with a
crown, then a specified thickness of
aggregate is laid down and compacted
(Figure la). Over time, however,
depending on conditions (water and
traffic), the aggregate gets pushed down
into the soils and the soils pump up
through the aggregate (Figure Ib). We
end up with a transition zone not as strong
as the aggregate, and the road can no
longer support the traffic loads with
deterioration as the result.
With the separation fabrics, we prepare the
subgrade, roll out the fabric, and build the
road on top of the fabric (Figure Ic). The
aggregate cannot be pushed into the soil,
and the soil cannot pump up into the
aggregate. Everything stays in place, and
the road remains strong enough as
designed for the traffic loads. Water can
travel either way, but if it gets into the
road, it can drain downward or out
laterally due to the crown into side ditches or subdrains. The prevention of soil fines from
pumping up through the aggregate to the road surface eliminates the mud in wet weather
and the dust in dry weather.
>-o7CK\o:
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Installation: Fabrics come in woven or
non-woven types for this application. The
existing road conditions, particularly the
aggregate, rock outcrops, water and
saturated subsoils, are considered in
selection of the fabric type. Transverse
joints should be overlapped a minimum of
18 inches in the direction of traffic. Fabric
rolls come in standard 12-, 15-, and 18-
foot widths (or customized to any width),
eliminating the need for longitudinal
joints.
ESMP#15-01 Separation fabrics keep the soil
and road aggregate in place.
Installation steps include surface preparation with an established crown, rolling out the
fabric, placing the road aggregate, and compacting. Aggregate should be backdumped
from the truck to a minimum depth of 6 inches, preferably 8 inches. Grading and re-
establishing the crown followed by compaction of the aggregate completes the project, as
depicted in the series of photos. On this project, sections of the road received additional
Rolls of fabric waiting for 4.
installation
t Rolling out the fabric
I Back dumping the t
aggregate
* Spreading the aggregate I tCompacting the aggregate t
ESMP#15-02 Installation of a separation fabric.
Final grading
shale material to raise the road elevation (refer to Tech Sheet #ESMP 12, Raising the
Entrenched Road).
If the fabric gets damaged during placement, simply patch with another piece of fabric
making sure that an 18" overlap on all sides is maintained. Tears can happen, as shown in
the photo, where the blade of the dozer caught the fabric by accident.
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ESMP#15-03 If damaged, use a fabric patch with 18" overlap on all sides.
Advantages: The use of separation fabrics
provides us with a number of advantages:
• Stabilization
• Prevention subgrade pumping
• Drainage improvement
• Rutting and pothole reduction
• Dust reduction
• Reduced maintenance and costs
• Longer road life
Fabrics also help to distribute traffic loads over a
greater area, making them advantageous to use
over soft, saturated soil conditions. Figure 2
shows this load distribution effect of the fabric.
(Traffic load distribution was discussed in
After geofabric installation I. '
ESMP#15-04 Separation fabrics have proven to be
effective.
rffTTTT
Without Fabric
With Fabric
I
Figure 2
Fabrics Separate & Distribute the Load
Chapter 5, Section 5.3.5, Practices
Related to Culverts in regards to
culvert installations.)
Separation fabric applications prove
effective to substantially reduce road
deterioration, resulting in reduction of
road maintenance.
The use of fabrics for stabilizing
water-crossing areas in conjunction
with broad based dips and driveways
was mentioned in Chapter 5. In these
applications, they perform a
reinforcement function and a
separation function to strengthen and
keep these areas intact.
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Safety Considerations: Structurally strong roads that remain in place with minor
maintenance will be safer roads.
Related Practices:
ESMP #04 Broad Based Dips
ESMP #06 Driveways
ESMP #12 Raising the Entrenched Road
ESMP #11 Stream Saver System
Manual Chapter 7, Section 7.4.4 Geosynthetic Applications in Road Maintenance
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