Environmentally Sensitive Maintenance 

for Dirt and Gravel Roads

October 2007 

Reissue

• Better Roads

• Better 

Environment

• Better

Community

• Less 

Maintenance 

From 

this....

.

To 

this!

Ver: 1.1
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. 
 Technical Report Documentation Page

1. Report No. 

USEPA-PA-2005- 

2. Government Accession No. 3. Recipient’s Catalog No. 

5. Report Date 

February 2006 

4. Title and Subtitle 

Environmentally Sensitive Maintenance for Dirt and Gravel Roads 

6. Performing Organization Code 

7. Compiled by: 

Alan L. Gesford, P.E. and John A. Anderson, Ph.D. 

8. Performing Organization Report No. 

9. Performing Organizations Name and Address 10. Work Unit No. (TRAIS) 

Administration & Leadership Institute of State and Regional 

 Studies – Research & Training Center Affairs 

Indiana University of Pennsylvania Pennsylvania State University 

Dixon University Center, South Hall 777 West Harrisburg Pike 

2986 North Second Street Middletown, PA 17057-4898 

Harrisburg, PA 17110 

11. Grant Assistance I.D. No. 

CP-83043501-0

13. Type of Report and Period Covered 

Technical Reference Manual 

 

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, 6th Floor 

Harrisburg, PA 17120-0064 

 

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. Key Words 

Unpaved road maintenance 

Dirt and gravel roads maintenance 

Environmentally sensitive maintenance

18. Distribution Statement 

No Restrictions 

19. Security Classif. (of this report) 

Unclassified 

20. Security Classif. (of this page) 

Unclassified 

21. No. of Pages 22. Price 

 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized 
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 

 

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. 
Acknowledgements: 

Funding for the compilation of this manual was supplied under Grant Assistance I.D. No. CP83043501-0 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 Corman, who championed 

the Pennsylvania program through funding [Section 9106 of the Pennsylvania Motor Vehicle 

i 
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. 
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.
ii

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

A1.1 Pennsylvania’s Dirt and Gravel Roads ..................................................1-11 

A1.2 Program Origin: A Problem Recognized................................................1-11 

A1.3 Program Origin: A Problem Substantiated .............................................1-12 

A1.4 A Solution ...............................................................................................1-13 

A1.5 The Legislation .......................................................................................1-13 

A1.6 Program Organization.............................................................................1-13 

A1.7 Program Goal ..........................................................................................1-14 

A1.8 Program Training ....................................................................................1-14 

A1.9 Further Program Development................................................................1-15 

A1.10 Program Results ....................................................................................1-16 
iii

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 
iv

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 
v

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 

4.4.5.1. 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 
vi

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 
vii

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 
viii

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 

6.4.2.4. 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 
ix

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 
x

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 
xi

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. 
xii

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. 
1-1

1 - 01 Our roads are part of our total environment. 

Environmentally Sensitive Maintenance 

For 

Dirt and Gravel Roads 

1 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. 

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. 
1-2

1 - 02 Roads exist as unnatural structures in the 

natural environment. 

1 - 03 

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. 

1.2 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 
1-3

1 – 04 Historical development dictated the close 

proximity of roads and streams.

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. 
1-4

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 

life of our roads 

(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. If the 

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. 
1-5

1 – 05 Dirt and gravel roads are a major source of 

erosion and sediment. 

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 RoadEnvironment 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. 
1-6

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.”

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 
1-7

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 
1-8

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 
1-9

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. 
1-10

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 1 is a description 

of the program development and implementation, with a discussion of the essential 

criteria for a successful program. 
1-11

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. 

A1.1 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
1-12

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 A1-

1). The Task Force set out to 

substantiate the extent of the 

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 A1-2). 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 A1-2), 

substantiated the problem. 

 
1-13

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 

Corman 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 
1-14

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 onepage 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 
1-15

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 A1-4). 
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 
2006 - DIRT AND GRAVEL ROAD PROGRAM SUMMARY DATA 

-------All Data is CUMULATIVE Based on District Reports as of January 15, 2007------- 

FINANCIAL SUMMARY TO DATE

Total Allocated to Districts - $35,187,000 includes 10 years of funding

Spent on administration - $2,203,000 (6.3% of total allocated) limit of 10% 

Spent on education - $594,000 (1.7% of total allocated) limit of 5%

Spent on completed contracts (1,608)-$25,381,000 (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 = a steam bank 5 feet high and 9.4 miles long 

 6.7 Acres Drainage Outlets Stabilized = 2,918 outlets, each 10’ x 10’ 

 68 Acres Vegetative Management = an area 10 feet wide 56 miles long 

 67 Acres Eroded Road Bank Stabilized = a road bank 5 feet high and 110 miles long

 71 Acres Eroded Road Ditch Stabilized = a ditch 5 feet wide and 117 miles long

 117 Acres Separation Fabric Used = 54 miles of fabric placed 18 feet wide

 773 Acres Road Surface Stabilized = 354 miles of road 18 feet wide 

 4,610 Crosspipes Installed = 5.6 pipes per mile of project 

 178,400 Feet of Crosspipes Installed = 34 miles of pipe; average crosspipe length is 39’

 581,700 Cubic Yards of Road Base Added = 1 acre of ground covered to a depth of 360 feet 

 

YEAR 

#

Contracts 

Complete 

Money Spent 

on Completed 

Projects* 

Average 

Spent per 

Contract* 

1998-2003 1,156 $ 16,198,000 $ 14,012

2004 173 $ 3,253,000 $ 18,803

2005 136 $ 3,255,000 $23,934 

2006 143 $ 2,675,000 $ 18,706

TOTAL 1,608 $25,381,000 $ 15,784

 

YEAR 

# of 

Trainings 

Municipalities Trained Counties 

Represented 

Total 

Attendees

1998-2002 115 na all 3208

2004 8 142 53 294

2005 13 220 56 574

2006 12 254 57 465

TOTAL 148 na all 4541

Document produced by: Penn State University – Center for Dirt and Gravel Road Studies

 866-668-6683 www.dirtandgravelroads.org

WORKSITE: a section of 

unpaved road that is a 

verified source of pollution 

to an adjacent stream.

COMPLETED PROJECTS 2-DAY TOWNSHIP TRAINING SUMMARY:

*in-kind not included 
 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@psu.edu 

Website: www.dirtandgravelroads.org 

 

1-18 
2-1

2 – 01 Geology sets the stage 

Environmentally Sensitive Maintenance 

For 

Dirt and Gravel Roads 

2 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, 

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. 
2-2

2 – 02 Pennsylvania Ridge and Valley Province 

2 - 03 Mount St. Helens 

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 

once stood 2 1⁄2 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 
2-3

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 
2-4

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. 

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. 

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 
2-5

2 - 06 Impact of each raindrop on bare soil 

initiates the erosion process. 

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. 
2-6

2 - 07 Flowing water picks up volume and 

velocity causing further erosion. 

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 

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. 
2-7

2 - 09 Sedimentary limestone layers. 

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. 

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 
2-8

2 - 10 Glaciers shaped much of the landscape 

across the northern United States. 

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, 
2-9

2 - 11 Los Angeles Abrasion Test Drum. 

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% 

was worn away from the sample. 
2-10

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. 
2-11

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 subgrade 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 
2-12

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 Diameter (mm) Field Test 

Clay Less than 0.002 Feels sticky 

Silt 0.002 to 0.05 Feels like flour 

Sand 0.05 to 2.0 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 
2-13

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

Erodability Growth Medium Road Stability Drainage 

Clay Stable Holds nutrients Soft, slippery Holds water 

Silt Moderately stable Rich Soft Moderately drained 

Sand Unstable Poor Poor compaction 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. 
2-14

2 - 12 Earthworms live in the A Horizon, the 

first layer of “dirt.” 

A Horizon – rich in organic matter

R Horizon – unaltered parent material

O Horizon – humus/organic matter just 

below the surface

B Horizon – accumulated materials 

washed down from A horizon

C Horizon – partially weathered parent 

material

Topsoil

Subsoil

Bedrock

Figure 2-1: Generalized Soil Horizons in Undisturbed Soil Profile 

Note: a. Not all horizons may be represented in a given soil profile

b. The degree of weathering decreases with depth

A Horizon – rich in organic matter

R Horizon – unaltered parent material

O Horizon – humus/organic matter just 

below the surface

B Horizon – accumulated materials 

washed down from A horizon

C Horizon – partially weathered parent 

material

Topsoil

Subsoil

Bedrock

Figure 2-1: Generalized Soil Horizons in Undisturbed Soil Profile 

Note: a. Not all horizons may be represented in a given soil profile

b. The degree of weathering decreases with depth

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. 

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 
2-15

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 

available for plant uptake. Many 

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 - 13 Topsoil provides the nutrients needed for plant 

growth. 
2-16

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 subgrade 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 
2-17

2 – 14 Understanding geology helps to develop good road maintenance practices. 

Figure A2-1 Physiographic Provinces of PA

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. 

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 
2-18

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. 
2-19

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 southcentral 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 
2-20

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. 
2-21

Figure A2-3: What do you have to work with?

SOIL MAP OF PENNSYLVANIA

Figure A2-2: What do you have to work with?
3-1

Environmentally Sensitive Maintenance 

for 

Dirt and Gravel Roads 

3 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 

3-01 Never underestimate the force of water. 

3-02 Stability depends on percentages 

of rock, sand, silt, and clay. 
3-2

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 

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 

3-03 Vegetation provides many advantages in 

erosion control.

3-04 Roads interfere with natural systems, 

causing accelerated erosion 
3-3

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. 

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 

3-05 Water acts as a lubricant, 

allowing material to move more freely.
3-4

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 subgrade. 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 downhill, 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. 

3.3.3 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 

3-06 Spring, “Mud Season,” can be a trying 

time for road maintenance crews. 
3-5

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 Soils

Soil Type Height of Rise (feet) 

 Small Gravel 0.1 - 0.4 

 Coarse Sand 0.5 

 Fine Sand 1 – 3 

 Silt 3 - 30 

 Clay 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.
3-6

Figure 3-3. The crown should be a flat “A” shape with a cross slope or drop from the 

center to the edge of 1⁄2” to 3⁄4” 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 

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. 

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. 

3-08 Water quickly collects when the road 

crown is lost. 
3-7

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 1⁄4” to 3⁄4” 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. 

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. 

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 

3-09 Banked (superelevated) curve. 

3-10 When water cannot drain off the road, the result is 

a “secondary ditch.” 
3-8

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. 

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. 

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. 
3-9

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 
3-10

• 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 

aggregate may not be suited to 

developing a hard crust surface and remaining bound and stable under traffic. A freedraining 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.

3-11 Road Aggregates 
3-11

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. 

3-12 A good road surface aggregate will be well graded from fine to coarse. 
3-12

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. 
3-13

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. 

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. 

3-13 Mechanical Sieves 
3-14

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 

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. 

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? 
3-15

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. 
3-16

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.
3-17

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. Blading 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.
3-18

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.
3-19

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. 

3.6.2 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 

3-21 Adding new material. 

3-22 Working parallel to a paved road has 

advantages.
3-20

across the driveway. The low point at the ditch line insures drainage off of and away 

from the road. 

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. 

3.6.2.5 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 

3-23 Keeping rails clean of road material is 

essential for safety. 

3-24 Road crowns must transition into the 

existing bridge deck.
3-21

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 

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. 

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? 

3-25 Drainage openings (scuppers) in bridge 

decks must be kept cleaned. 

3-26 Bridge approach areas demand special 

attention and usually more maintenance. 
3-22

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. 

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. 

3-27 Operators should note existing problems. 

3-28 Using a shovel is the sign of a 

“professional operator.”
3-23

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. 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. 

Passing sieve Lower % High% 

1 1⁄2 inches 100 

3⁄4 inches 65 90 

#4 30 65 

#16 15 30 

#200 10 20 
3-24

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 

1⁄2 to 3⁄4 inch rise per horizontal foot. Proper shape may be a flat “A” crown profile, an inslope 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 1⁄2 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, pulloffs, 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. 

 

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 
3-25

or berm: First pass: Roll slowly in static mode on the outside edge of placed 

aggregate. 

1B. 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. 

3A. 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 

lbs. 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 subgrade. 

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 Class D 

Sodium Sulfate Soundness2 5 cycle, 

AASHTO T1041,2, Max % loss 

253

Los Angeles Abrasion 

AASHTO T96, Max % loss 

45 

1

As modified by the Department 

2

Does not apply to crushed concrete. 

3

For aggregate surface course, the maximum percent loss shall be 30. 
3-26

b. 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 CA5 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. 

c. Plasticity. All material shall comply with the plasticity index 

requirements listed below. 

Plasticity Index – Percent1 Type of construction 

Gravel Crushed Gravel, Stone, Slag 

Aggregate Subbase 

Type A or B 0 to 9 - 

Aggregate Base Course 

Type A or B 0 to 6 0 to 4 

Aggregate Surface Course 

Type A or B2 2 to 9 - 

Stabilized Aggregate Material 

0 to 9 0 to 9 1

Plasticity 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. 

2

When 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 200lb/in nor more than325 lb/in of width of the roller. 
3-27

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, 21A, 23A...........902 

Use aggregate 21AA or 21A if the aggregate surface course will later receive a hot mix 

asphalt (HMA) surface. Use aggregate 23A if the aggregate surface course is to be 

constructed without an HMA surface. Use dense-graded aggregate 22A, 23A 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. 
3-28

B. Class 21AA, 21A, 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 23A 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 Sieve Analysis (MTM 109) Total Percent Passing (b) 

1.5 in. 1 in. 3⁄4 in 1⁄2 in 3/8 in # 8 

Loss by Washing 

(MTM 108) 

% Passing #200 

21AA, 

21A 

100 85-100 50-75 20-45 4-8 (e)(f) 

22A 100 90-100 65-85 30-50 4-8(e)(f) 

23A 100 60-85 25-60 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) Crushed Material, % min. 

(MTM 110,117) 

Loss, % max, Los Angeles Abrasion (MTM 

102) 

21AA 95 50 

21A 25 50 

22A 25 50 

23A 25 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. 
3-29

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 Materials 

Sieve (US Sieve) A (Surface) B (Base) C (subbase) 

3” 100 

2” 100 - 

1.5” 85-100 70-100 

1” 100 - - 

3⁄4” 85-100 - - 

1⁄4” 50-75 30-50 30-55 

#40 15-35 5-20 5-25 

#200 8-15 0-5 0-8 

Table 667-2: Test and control Limits of Gravel Materials 

Material Properties A (Surface) B (Base) C (subbase) 

Maximum Soundness loss (%) 20 20 25 

Plasticity Index 2-9 0-5 0-8 

Sand Equivalent >25 >40 >35 

E. Elongated Particles Not more than 30%, by weight, of the particles retained on 

a 1⁄2” 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 
3-30

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 1⁄2” or at least one fractured face on 75% of the particles 

larger than 1⁄2”. Type B material shall have at least one fractured face on 50% 

of the stone particles larger than 1⁄2”. 

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.
4-1

Environmentally Sensitive Maintenance 

for 

Dirt and Gravel Roads 

4 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 

4-01 Many roads were built without regard to 

natural systems.

4-02 Environmental problems bear witness to 

our disturbance and disruption of natural 

systems. 
4-2

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’.
4-3

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, 

4-04 Plants develop and evolve under the 

physical conditions of their ecoregion. 

4-05 Ecosystems (Communities) 
4-4

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.

4.3.2 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 

4-06 There are 3,692,830 miles of rivers and 

streams within the United States. 
4-5

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 of our water resources has been based on political 

divisions (e.g., township, county, state boundary lines). Water, however, flows across 

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. 

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. 
4-6

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-
4-7

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 

4-07 Streams are constantly eroding, 

transporting, and depositing materials.
4-8

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. 
4-9

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 

4-09 As turbidity increases, light penetration 

decreases. 
4-10

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. 

4.3.2.5 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 

mammals. Some aquatic plants are 

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 of fish, 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 Life in a Stream 
4-11

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 

of fish 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. 

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 “Outside Inputs” are essential to a 

stream. 

4-12 Fish are an important part of the aquatic 

food web.
4-12

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. 

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 

4-13 Clearing streambanks has many negative 

effects on streams. 
4-13

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 of fish 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)
4-14

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 yearclass of fish. If all goes well, these eggs will then hatch in March and April. 

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. 

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. 4-15 A Trout’s Life Cycle 
4-15

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. 

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. 

4-16 The stonefly larva is another indicator 

species. 

4-17 
4-16

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. 

4-18 Excessive sediment causes distress for the 

stream’s inhabitants.
4-17

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. 

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 

4-19 Suspended sediment interferes with both 

plants and animals within the stream. 

4-20 Embeddedness refers to the sediment 

filling in all the nooks and crannies in the 

streambed.
4-18

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. 

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. 

4-21 Contaminants attached to sediment 

particles further degrades water quality.

4-22 Anglers are avid fish advocates and can 

be a positive resource. 
4-19

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 

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 

4-23 Anglers can also have negative effects 

on stream ecology as stream access points, 

car pull-offs, and footpaths become 

erosion sources.

4-24 Wetlands are important ecosystems. 
4-20

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. 
4-21

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, 
4-22

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 
4-23

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. 
4-24

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 

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 

Figure 4-7 Hydrograph 
4-25

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, 

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%. 

4.4.5.4 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 

4-26 Bank stabilization/ shoreline protection - another 

wetland benefit. 

4-27 Sediment study being conducted in a 

wetland.

4-28 Do NOT use wetlands as sediment traps! 
4-26

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” 
4-27

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. 

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. 

4-30 Wetlands provide vital habitat for a diverse mix of 

plants, including threatened and endangered species. 
4-28

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. 

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. 
4-29

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. 

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 

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 4-8: Depression Wetland 

4-33 Depression Wetland (Vernal Pool) 

Figure 4-9: Slope Wetland 
4-30

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 groundwater 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. 

Floodplain wetlands are found 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. 

4-34 Slope (Seepage) Wetland 

Figure 4-10: Floodplain (Riverine) Wetland 
4-31

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. 

4.4.7.2 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 

4-36 Wetland Indicators 

4-37 Wetland Indicators 

4-35 Floodplain (Riverine) Wetland 
4-32

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, 

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 

pile up against trees and rocks, forming wrack 

lines. These wrack lines indicate water once 

covered this area and again cold indicate a 

wetland. 

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 

4-38 Wetland Indicators 

4-39 Wetland Indicators 

4-40 Wetland Indicators 

4-41 Wetland Indicators 
4-33

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. 

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: 

4-42 Wetland Indicators 

4-43 Wetland Indicators: Common Wetland Plants 4-44 Wetland Indicators: Common Wetland Plants 
4-34

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, joepye weed, jewel weed, cardinal 

flower, pin oak, and pussy willow. 

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 outcompetes 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 

4-45 Common Wetland Indicator Plants 
4-35

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. 

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 

4-48 Mandate by Federal Government 
4-36

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 

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. 

4-49 Adopt a Wetland Strategy 
4-37

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. 
4-38

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 

plants have toward outside impacts such 

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. 

4-50 Uplands produce different challenges for 

road managers. 

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.” 
4-39

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. 

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 

4-52 Plant Groupings 
4-40

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. 

4.5.2.4 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. 
4-41

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 
4-42

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. 

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. 

4-54 Plants cannot move, cannot flee from 

danger. 
4-43

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. 
4-44

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! 
4-45

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? 
4-46

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. 

4-58 Once rotted, another natural force causes 

additional damage: freeze cracks. 
4-47

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. 

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. 

4.5.4.1 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. 

Figure 4-13: Plant Succession 
4-48

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. 

4.5.4.2 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 longerlived 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. 
4-49

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. 
4-50

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? 

Plants also provide shade that 

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 byproducts 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 
4-51

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 

4-61 Value of Plants: Aesthetics and Economics 
4-52

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.” 
4-53

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 
4-54

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 of fish 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 
4-55

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 1⁄2 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 
4-56

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. 
5-1

Environmentally Sensitive Maintenance 

for 

Dirt and Gravel Roads 

5 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. 
5-2

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. 

5-02 Once erosion takes place, the sediment 

needs to be addressed. 
5-3

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. 
5-4

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. 

5.2.3.2 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. 

5-04 Proper bale installation prior to start of a 

major construction project. (Note: Bale barriers 

not recommended by EPA.) 
5-5

5-06 This installation will not control 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 

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. 

5-07 Cleaning is required when sediment reaches onehalf the height of the fence.
5-6

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. 
5-7

5-08 Road candidate for insloping. 

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. 
5-8

5-09 Outsloping this road proved beneficial, 

eliminating ditches and cross pipes.

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. 

 

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 ADT) 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. 
5-9

5-10 Trapezoidal shaped ditch. 

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. 

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

5-11 Grass-lined, V-shaped ditch. 

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 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 Vshape. 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

5-12 Standing water can only lead to 

problems.

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). 

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. 

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 

Forgiving Shape for Safety (4:1) 

few problems 4:1 (14o) 

slight problems 3:1 (18o

) 

moderate problems 2:1 (30o

) 

Road safety & liability! 

maintenance! 

slope stability! 

road edge support! 

Steeper slopes - more problems

severe problems 1:1 

unstable 1:2 (60o

) 

o

Road 

Road 

Road 

Road 

Figure 5-7 Roadside Slopes 
5-12

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 
5-13

5-13 Seeding and mulching may be sufficient to 

revegetate the ditch. 

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. 

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. 
5-14

5-14 A biodegradable netting will prevent 

erosion until vegetation is established.

5-15 Many geosynthetic products are available for erosion prevention. 

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 

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. 
5-15

5-16 Good netting installation, but problems at 

pipe outlet need to be addressed. 

5-17 Use caution when deciding to line ditches 

with rock riprap. 

5-18 Riprap placed during construction—

looking at the sediment potential, was this a 

good idea? 

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. 

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 
5-16

5-19 Do not outlet ditch directly to stream—use 

turnouts into vegetative filter strips!

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. 

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. 
5-17

5-20 Multiple small turnouts mean less water, less velocity, less erosion potential. 

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 rightof-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. 

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. 
5-18

5-21 Severely eroded road – ideal conditions 

for broad based dips.

5.3.3 Practices Related to Ditches and Road Profile 

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.) 
5-19

5-22 Broad based dips can be used in lieu of crosspipes. 

Ideal location for 

a broad based dip

5-23 Broad based dip reinforced with large 

aggregate.

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. 

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. 
5-20

5-24 Grade breaks result in short road 

sections with reduced water volume and flow 

velocity. 

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. 

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. 
5-21

5-25 Improperly constructed driveways create 

recurring road maintenance problems. 

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. 

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 
5-22

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). 

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. 
5-23

5-26 Open-top grates may be used on paved driveways. 

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. 
5-24

5-27 Gas facility access driveway designed to drain away from road. 

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. 

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 
5-25

5-28 Sometimes good solutions are hard to find! 

5-29 Common Pipe Materials 

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. 

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 
5-26

depth, the less pounds per square inch loading occurs because the same amount of load is 

distributed over a larger area. 

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 
5-27

5-30 Shallow pipe installations can cause continual road deterioration. 

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. 

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. 
5-28

5-31 Shallow installations: use rigid pipe, squash pipe, or elliptical concrete (rigid) pipe. 

5-32 Shallow installation: Use multiple pipes of smaller 

diameter, allowing more cover with same capacity.

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 πr

2 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. 

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 
5-29

5-33 Existing fords should be stabilized to prevent erosion and stream degradation. 

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). 

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). 
5-30

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 
5-31

5-34 Various materials can be used for end structures. 

5-35 Typical flared end sections. 

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. 

5.3.5.4. 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-
5-32

5-36 Metal flared end section on plastic pipe. 

5-37 Rock rip-rap at pipe outlets spreads flow and dissipates energy. 

5-38 Using rip-rap for erosion prevention at 

culvert outlet.

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 

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. 
5-33

5-39 Brush, tree stumps, etc. can be 

effective energy dissipaters. 

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. 
5-34

5-42 Over sizing culverts to allow natural 

streambed conditions through the culvert 

maintains the stream ecosystem. 

5-41 Through drains keep water clean. 

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. 

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). 

5-40 Through drains keep springs and spring 

seeps out of road drainage facilities. 
5-35

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. 

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. 
5-36

5-43 Stream Saver System – raised level road 

with ditch turnouts to vegetative filters. 

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. 
5-37

5-44 Remember this photo? Look at the banks 

on either side of the road.

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. 

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 
5-38

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). 
5-39

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 

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 sheetflowed 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. 

Figure 5-26 Raising the Road. 

5-45 Good candidates for “raising the road.” 
5-40

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. 

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. 

Final road with driving surface aggregate 

Before, an entrenched road During placement of shale fill 

After finishing the shale 

5-46 Red Rose Road, Huntington County, PA
5-41

Figure 5-27: Raising the road and moving away from the 

stream. 

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. 
5-42

5-47 Eliminate this maintenance and 

environmental problem with Stream Saver 

Bridges. 

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. 

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. 
5-43

5-49 Gravel bar removal causes turbidity and 

sediment for extended time periods 

detrimental to the stream ecology. Would you 

want to fish here? 

5.3.8.2 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. 

5-48 Gravel Bar Removal is a costly 

maintenance task. 
5-44

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. 
5-45

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-1. 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. 
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

raising the road profile

before, during & after red

rose

road

environmentally

sensitive

maintenance

How to enjoy the outdoor classroom:

The Problem:

Drive-Thru Classroom

Self-Guided Tour

• Follow along with this brochure

• Look for matching numbered signs

( The icon indicates picture

location and direction)

• Stop and have a look around

Because the road was lower than the surrounding

terrain, rainfall and runoff were captured and concentrated in the roadway, gaining energy and eroding road surface and bank materials. This concentrated 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 surface 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.

18
red

rose

road

Site Location

& Directions

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.

Route

26

Interpretive

Sign

Project Site

N

State College

10 miles

Tributary to

Shaver’s Creek

Site Map red

rose

road
ENTRENCHED ROAD

BEHAVES LIKE A DITCH

Years of wear and tear, machine maintenance

and erosion caused the road surface to become entrenched below its banks. This captures all water

from surface and near-surface drainage. The captured 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. Observe how the natural surface drainage has been

restored by filling the road back to it original elevation and stopping the endless cycle of erosion and

repair.

ERODED BANK & SHADE

In addition to the sunken road surface, notice 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 develop 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, constricting the width of flow causing the water to move

faster and be more erosive. Now, observe how drainage from the restored road height does not require a

ditch, and how flow is dispersed over a wide area at

a shallow angle.

 1

 2

 3

before

before

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 provides life-supporting food for plant roots and the microbes living in conjunction with them. The roots, in

turn, further stabilize the soil and increase infiltration.

MAINTAINABLE ROAD SURFACES

The bank-run shale used on the previous road

surface had pieces in it that were too large for available grading machines to work into a drivable surface. 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 material. Clay and silt are the soil types most prone to

make dust and sediment. The Driving Surface Aggregate visible now is a specially formulated mixture

of abrasion resistant limestone. Contrast this surface 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 prevents road deterioration from water movement on

steep road grades and lengthens maintenance

cycles.

 4

 5

 6 after

before

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 generated 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.

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 velocities of the road drainage have cut a deep gullyshaped 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 cutting” results.

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 under the road to harmlessly direct this flow to the forest 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. Dispersed there in a natural pattern, the water can infiltrate into the ground as if the road had never been

built.

 7

 8

 9

before

before

before
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 overland 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 increase.

 RAISING THE ROAD PROFILE

Excavated shale and limestone from the

abandoned pit was trucked and spread on the entrenched 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 create 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 drainage 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 between the road and the stream.

10

11

12

during

during

after

Old Road

Old Road
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 cascades 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 concentrated road drainage. Notice the severe down cutting that causes the channel to be deeper than it is

wide and the complete physical separation of the

stream from its floodplain.

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 Driving Surface Aggregate (DSA), a specially formulated

abrasion resistant mixture of crushed limestone. DSA

has a carefully blended size distribution from 11⁄2”

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

The road at its new alignment and elevation

shows several features that prevent pollution. Compare 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.

13

14

15

before

during

after

2

1
WORK IN PIT

Excavating material from the abandoned pit

produced fill to raise the road and correct the entrenched drainage pattern. By removing shale from

the pit, a less steep and therefore less erodible profile was created. The more naturally appearing shape

was formed with machinery normally used in roadwork.

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.

LOOKING EAST AT SHALE PIT

Easily available shale was periodically removed 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 elevation 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 typical 1:1 uphill road bank or “cut” slope and the erosion consistently associated with such steep road

banks. When native vegetation is thoroughly established, this more natural land shape will blend in with

the beauty of the surrounding forests even better

than pictured in photo #12.

16

17

18

before

during

during
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 sedimentladen 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 underdrain, and elevation of the road itself. 

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

Potter County 

Horseshoe Road

Worksite

in Focus 6/10/04

Project Statistics 

Potter County 

Ulysses 

Township 

Coudersport 

Road: Horseshoe Road 

Road Owner: Ulysses Township 

Affected Watershed: Pine Creek 

Project Length: 1600 ft 

Cost: $53,829 

Date Completed: September 2002 

6 

449

Horseshoe 

Road* 

Galeton

Ulysses

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. 
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 

Project Solutions 

Adding a cross-pipe: Installing a new crosspipe 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.

* 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.

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. 

For More Information

The Center for Dirt and Gravel Road Studies Potter County Conservation District

(814) 865-5355 Eric Potter 

www.dirtandgravelroads.org (814) 274-8411 
Problem Identification 

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. 

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

Raising the road elevation to the elevation of the 

surrounding landscape was impractical because 

of the amount of material required (above). 

Fulton County 

Breezewood 

Licking Creek 

Township 

Road: Dutch Corner Rd 

Road Owner: Licking Creek Township 

Length: 4,835 ft 

Date Completed: November 2003

30 

522

Dutch 

Corner 

Road* 

McConnellsburg 

Fulton County 

Dutch Corner Road

Worksite

in Focus

4/13/04

Project Statistics 

Legend* 

Pipe Replacement 

New Pipe Installation 

Pipe through the Bank

*Pipes not drawn to scale.

Dutch Corner Road Site Map

6’ 

25’ 
Cost Summary

Total Project Value: $70,962 

District Funding: $63,712

 Materials $46,970 

Contracted Work 

& Equipment $16,742 

In-Kind from twp: $7,250 

 Materials $4000 

 Labor & 

 Equipment $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 

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.

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.

during after 

Pipes Through the Bank. Note the depth of the trench during construction. 

After construction the pipe has been covered and stabilized with vegetation. 

before after 

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. 
6-1

6-01 Typical roadside erosion problems. 

Environmentally Sensitive Maintenance Practices 

for 

Dirt and Gravel Roads 

6 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 selfperpetuating 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. 
6-2

6-02 When a road is working well within the 

environment, minimal maintenance will be 

required. 

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. 
6-3

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. 

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. 

6-03 Roadside Vegetation Management Options. 
6-4

6-04 Boom mower impalers! 

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. 

6.3.3 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. 
6-5

6-05 The disadvantages of shade: retains moisture to promote icing, reduces visibility. 

6-06 Bright sunlight to dense shade or vice 

versa – major visibility safety hazard – should 

be avoided.

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. 

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: 

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. 
6-6

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-

1a to 1b, 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. 

6-07 The advantages of shade. 
6-7

6-08 You do not need fast-growing weakstructured colonizer-type roadside trees! 

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 

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. 
6-8

6-09 Remove dead, diseased, unstable, or dying 

trees first. 

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 regrowth of colonizer 

species and frequent mowing cycles. We need to develop a strategy following some basic 

guidelines. 

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 
6-9

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. 
6-10

6-11 Before and after look at selective tree trimming during a road project – letting in more 

sunlight with less shade – striking a balance.

6-12 Would anyone want to plow this road? 

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.) 

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 
6-11

6-13 Dogwoods are a good roadside tree with 

the added value of spring blossoms. 

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. 
6-12

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. 

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. 

6-14 Leaf Blowers to Clean Ditches and the Roadway 
6-13

6-16 Grasses make good roadside plants, 

establishing surface erosion protection 

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. 

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. 

6-15 Day lilies or ferns are good roadside plants – low maintenance, aesthetically pleasing 
6-14

6-17 Clearing stream banks for a road crosspipe replacement can have devastating effects on the 

stream and future maintenance. 

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? 

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. 
6-15

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. 
6-16

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.

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. 
6-17

6-19 

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? 
6-18

6-21 

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? 

6-20 
6-19

6-24 

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? 

6-22 

6-23 
6-20

6-25 Unstable vertical bank will collapse. 

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. 
6-21

6-26 Tree Roots: Mother Nature’s Rebar. 

6-27 Ideal Location for a Diversion Swale. 

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

6.4.2 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 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 
6-22

6-28 Diversion Swale: Wider swales and gradual slopes result in 

more infiltration and less water volume to handle.

6-29 

create a diversion swale. The surface runoff from the entire upward slope could be 

drained into a swale at the top 

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-ofway 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. 
6-23

6-30 Tracking the newly constructed banks. 

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. 

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. 
6-24

6-31 Newly constructed low-gradient bank 

benches.

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. 
6-25

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 fastgrowing 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. 
6-26

6-33 Rolled seed-impregnated straw blankets 

can be pinned to steep slopes for reestablishment 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 
6-27

6-34 Bank willows are commonly used in 

bioengineering practices.

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.

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.
6-28

6-36 Driving the Stakes. 

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. 

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 

6.35 Cutting the stakes and Preparing the site. 

6.37 Completed site and after one season’s growth. 
6-29

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. 

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. 

6.38 Tying the bundles and digging the trench. 

6.39 Placing the fascine and backfilling. 
6-30

6-40 Fascines after one season’s growth. 

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. 

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 

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. 
6-31

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. 
6-32

APPENDIX 6. 

Appendix 6A: Soil Identification in the Field
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 

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 

Water 

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. 

% Original Mark

of Fines Settlement Mark
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 Will Be White to 

Light Tan, Grey, Blue or 

Bluish Green 

Sand 

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. Settles Instantly 

Color May Be Tan, Grey to 11⁄2 Minutes

or Black

Sand  Clean Sands and Gravels - Added water 

sinks in immediately without making 

mud. 

Color Will Be Tan to 

Dark Brown Depending 

on Particle Size Silt

Soil Test Checklist 

Watch for these possible reactions when you 

are using in-field do-it-yourself soil tests. 

Clay

Silt 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. 
6-35

Appendix 6B: Additional Worksite in Focus 

The following 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. 
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. 

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

before 

Project Facts 

Project: Fall Brook Road 

Project Owner: Ward Township 

Affected Watershed: Fall Brook, Tioga River 

Project Length: 1100 ft 

Date Completed: September 2001 

Cost Summary

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

Tioga County 

Fall Brook Road

Worksite 

in Focus

4/13/05 

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. 
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.

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.

Tioga 

County 15

Wellsboro

6 

Ward 

Township

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.

Mansfield

after 

vegetated buffer

new 20’ wide 

crowned road 

surface 

after

before 
7-1

7-01 Unpaved roads are the largest source of 

dust pollution in the country. 

Environmentally Sensitive Maintenance 

for 

Dirt and Gravel Roads 

7 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 

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. 
7-2

7-02 Just what is dust? Where does it come 

from?

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. 

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 
7-3

7-03 Dust can affect crops. 

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 (ADT) 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 

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. 
7-4

7-04 Dust creates visibility problems for the 

motorists. 

7-05 Traffic weight and speed increase dust. 

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. 

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 
7-5

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 
7-6

7-06 Although environmentally sensitive, water 

affords only short-term dust control. 

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 shortlived. 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 shortterm 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. 
7-7

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 –60o 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 –27o

 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 
7-8

7-07 Lignin derivatives are a by-product of the 

paper manufacturing industry. 

7-08 Asphalt emulsions and cutbacks are still 

being used for dust control, but... 

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. 

With lignin 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 pavinglike 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 
7-9

7-09 With the use of asphalt “oils,” tracking and/or run-off can become problems. 

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. 

7.2.6.7 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. 
7-10

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 
7-11

7-10 Road stabilization or full-depth reclamation works well with a stabilizing agent 

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. 

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 
7-12

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. 
7-13

7-11 Stabilization can be accomplished with a road grader – scarifying the road, mixing in a 

stabilizing agent, regrading and shaping.

7-12 The “reclaimer” has a down-cutting drum with carbide teeth. 

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. 

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. 

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. 
7-14

7-13 A mish-mash of road surface materials 

lends itself to a full-depth reclamation project.

7-14 A sheep’s foot roller is used for soil 

compaction. 

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 

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. 
7-15

7-16 The world of geosynthetics and road maintenance. 

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. 

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 
7-16

7-17 Different fabrics are designed to perform various functions 

and for various applications.

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 nonbiodegradable. 

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 Applications 

Drainage / Infiltration Subsurface Drainage 

Stabilization Subgrade Stabilization 

Reinforcement 

Separation 

Erosion Control 

Sediment Reduction 

Soil Reinforcement 

-Embankments 

-Steep Slopes 

-Vertical Walls 

Waterproofing Erosion / Sediment Control 

Stress Relief 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. 

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 
7-17

7-18 Fabrics come in rolls of various widths 

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. 

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. 

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. 
7-18

7-19 Clogged subdrain! 

7-20 Subdrain construction - dig trench, roll out fabric, add 

pipe and aggregate, overlap fabric, backfill. 

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 onesize 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

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.

7.4.4.3 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 

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. 

7-23 All subdrains need an outlet. 
7-20

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. 

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. 

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), 

7-24 Installation of an erosion control fabric. 

7-25 Geotextile silt fence barrier. 
7-21

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. 

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 subgrade is 

prepared with a crown, then a specified thickness of 

aggregate is laid down and compacted, (Figure 7-7a). 

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 

7-26 Geogrids come in various patterns 

designed for specific applications. 

7-27 Construction of a geogrid 

reinforced embankment. 
7-22

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 subgrade, 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). 

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. 

7-28 Separation fabrics keep the soil and road 

aggregate in place.

7-29 Installation of a Separation Fabric. 
7-23

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. 

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 

7-30 If damaged, use a fabric patch with 18” overlap. 
7-24

function to strengthen and keep these areas intact. 

The use of separation fabrics, in general, provides us with a number of 

advantages. Stabilization 

1. Subgrade 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 

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! 
7-25

7-33 Geocells for road base stabilization. (Photos: WebTec, Inc. - 

TerraCell®) 

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 

with the appropriate fill material creates various opportunities for economical solutions in 

the applications listed above. 

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 

7-32 Geocells can be filled with a native or 

select fill material. (Photo: WebTec, Inc. - 

TerraCell®)
7-26

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®)

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. 

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. 
7-27

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 ADT). 

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 

7-36 Installation of a low water crossing. 
7-28

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. 

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 

sections are filled with 

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. 

7-38 Pre-Fab Geosynthetic Endwall Systems. 
7-29

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. 

The photos (HartmanEWTM System) show an installation sequence for the 

endwall. 

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 

7-39 Pre-Fab Geosynthetic Endwall Installation. 
7-30

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. 
7-31

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 
7-32

 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) 
7-33

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. 
Adams County

Miltenberger Road

Worksite

in Focus

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 (Photo1).

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

Adams 

County

15 Gettysburg

Franklin

Township

Pine Grove 

Furnace

15

30 30

233

Project Facts

Project: Miltenberger Road

Project Owner: Franklin Township

Watershed: Conococheague Creek, 

Potomac River

Project Length: 800 ft 

Date Completed:June 2005

Cost Summary

Total Project Value: $15,689

District Funding: $15,689

Materials $670

Equipment $4,292

Shale $10,727

7/16/05

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.

before

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.

during

Photo 2. Pre-fabricated underdrain was used to collect 

subsurface water from under the road and both ditches.

spring seep

ice saturated ditch spring
during

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.

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.

before before after

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.

after

Photo 5. One of two new crosspipes installed. Notice the gradebreak in the road over the pipe to get water off the road.

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. 

Adams

County

Franklin

County

Gettysburg 10mi

233

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). 

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/

no ditch!

Miltenberger road was raised an average of 3’ using shale fill.

Pipe outlet

on grade

no ditch!
Nimick Nature 

Center 

Existing 

Parking Lot 

New Bus 

Parking Lane

New Geoblock® 

Porous Parking Lot 

New French 

Mattresses 

Site Plan 

Existing Drainages

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. 

* For more information on DSA and French Mattress construction 

please see the DSA Informational Bulletin and the French Mattress 

Technical Bulletin available at www.dirtandgravelroads.org. 

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

Westmoreland County

Powdermill Nature Reserve

Worksite 

in Focus

11/2/04 

Project Facts 

Project: Nimick Nature Center Driveway & Parking Lot 

Project Owner: Powdermill Nature Reserve 

Affected Watershed: Powdermill Run, Youghiogheny River

Project Length: 550 ft 

Date Completed: October 2003 

Cost Summary

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 Theresa Gay Rohall 

Rector, PA 15677 (724) 593-6105

Above: Construction of the bus parking lane. Geogrid® was used

to add support and tensile strength. 
1 

2 

4 

# 2b 

modified 

DSA 

3 

# 3’s 

Westmoreland

County 

30

New Stanton Powdermill 

70 

76

76

Cook 

Township

Ligonier 

Site Map & Directions 

From the PA Turnpike 

(Interstate 76), exit at 

Donegal/Ligonier/PA 711 

(#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. 

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 Powdermill’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 

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.
7-38

A7-01Hell Hollow Road Demo Site: Existing 

site conditions prior to project. 

A7-02 Excavation of existing pipe during dry 

conditions. 

A7-03 Geotextile separation fabric laid in 

new trench.

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 

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. 

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. 
7-39

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. 
7-40

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. 

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 

A7-08 Placing large size riprap at ends of pipe. 

A7-09 Completed project with a leveled road 

stream saver system.

A7-10 Inlet conditions before and after project. 
7-41

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. 
8-1

8 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. 
8-2

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, nonbiodegradable, 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.) 
8-3

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, longlived, 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. 
8-4

Road Cross Slope: The slope of the road surface from the road center to the outer edges, the normal 

unpaved road cross slope being 1⁄2”to 3⁄4” 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 1⁄2” to 3⁄4” 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. 
8-5

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. 
9-1

9 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 
9-2

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 
10-1

10 Technical Information Sheets 
10-2

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. 

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. 
10-3

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. 

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 

ESMP#01-01 Road candidate for insloping. Crosspipes 

can be strategically placed to outlet into the vegetative 

areas between the stream meanders. 
10-4

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. 

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. 
10-5

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. 

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 

ESMP#2-01 Outsloped road showing no ditches and 

vegetative filtering areas for overland sheet flows. 
10-6

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 

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. 

ESMP#3-01 Standing water can only lead to 

problems!
10-7

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 

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. 
10-8

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 
10-9

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 

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. 
10-10

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 

shorter section or road. This limited 

volume of water should not have 

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 

ESMP#3-02 Broad based dip reinforced with 

large aggregate. 
10-11

• 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 
10-12

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. 

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. 
10-13

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. 

ESMP#5-01 
10-14

Related Practices: 

ESMP #04 Broad Based Dips 

ESMP #03 Ditch Turnouts and Vegetative Filter Strips 
10-15

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. 
10-16

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. 
10-17

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 

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 
10-18

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. 

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. 

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.
10-19

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 

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. 

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 

ESMP#7-02 
10-20

• 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. 

Related Practices: 

ESMP #08 Aprons at Culvert Outlets 

ESMP #09 Shallow Culvert Installations 
10-21

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. 

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, 

ESMP#8-01 Severe erosion at a pipe outlet. 
10-22

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 prefabricated 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 

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 

ESMP#8-02 Rock riprap makes an effective 

apron to dissipate energy and prevent erosion 

at the pipe outlet. 

ESMP#8-03 Typical Flared End Sections. 
10-23

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 of forces 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 

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 

ESMP#9-01 Shallow pipe installations can cause continual road deterioration. 
10-24

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 πr

2 or 3.14 

times the radius squared. A 24-inch 

diameter pipe has 452 square inches of 

opening (3.14 x 12 x12). 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. 
10-25

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). 

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 

 
10-26

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. 

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. 
10-27

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. 

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 

 

ESMP#10-01 Through Drains keep springs and spring 

seeps out of road drainage facilities.
10-28

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

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 
10-29

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 vshaped 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. 

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. 

ESMP#11-01 Stream Saver System – raised 

level road with ditch turnouts to vegetative 

filters.
10-30

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. 
10-31

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 

headaches. 

 

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. 

ESMP12-01 A typical entrenched road. 
10-32

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 1⁄2-inch to 3⁄4-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. 
10-33

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.

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 

additional benefits. 

ESMP12-02 Raising the entrenched road—step-by-step. 
10-34

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. 
10-35

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 

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. 

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. 
10-36

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 
10-37

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 reestablished 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 

ESMP#13-02 Diversion Swale: Wider swales and 

gradual slopes result in more infiltration and less water 

volume to handle. 

ESMP#13-03 Tracking newly constructed 

banks. 
10-38

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 

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. 

 

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 

ESMP#13-04 Newly constructed low-gradient bank bench. 
10-39

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. 

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 

ESMP#14-01 Following some guiding natural 

principles, we can use the forest system to 

reduce maintenance.
10-40

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, wildlifefriendly 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 

clearing practices may have their place on 

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. 

ESMP#14-02 Dogwoods are a good roadside 

tree with the added value of aesthetics. 
10-41

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 1a 

to 1b, on each side 

of the road for 

whatever distance 

we consider 

necessary, the 

results may lead to 

increased 

maintenance. 

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 

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 fastgrowing, weak growth types. Colonizer 

trees can threaten the roadway safety and 

recreate shade. These colonizer trees then 

become 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. 

ESMP#14-03 You do not need fast-growing, 

weak-structured colonizer-type roadside trees!
10-42

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 

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 straightline 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.

ESMP#14-04 Remove dead, diseased, unstable, 

or dying trees first. 
10-43

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, weakwooded 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. Wellmanaged 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 

 

ESMP#14-05 A before and after look at selective tree trimming during a road project – using the 

forest system to reduce maintenance. 
10-44

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 subgrade pumping of fines, and thereby dust reduction.

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 1a). 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 1b). 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 1c). 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. 
10-45

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. 

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 reestablishing 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 

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. 

ESMP#15-01 Separation fabrics keep the soil 

and road aggregate in place. 

ESMP#15-02 Installation of a separation fabric. 
10-46

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 

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. 

ESMP#15-03 If damaged, use a fabric patch with 18” overlap on all sides. 

ESMP#15-04 Separation fabrics have proven to be 

effective. 
10-47

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