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Best Management PracticesField Guide

LOW-VOLUME ROADSENGINEERING

Gordon Keller&

James Sherar

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Best Management PracticesField Guide

By

Gordon Keller, PEGeotechnical EngineerUSDA, Forest Service

Plumas National Forest, California

and

James Sherar, PELogging Engineer

USDA, Forest ServiceNational Forests of North Carolina

Produced forUS Agency for International Development (USAID)

In Cooperation withUSDA, Forest Service, International Programs

&Conservation Management Institute,

Virginia Polytechnic Institute and State University

July 2003

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photo here

Information contained in this document has been developed for the guidance of road builders,road managers, and resource specialists in most geographic areas to help build better, more cost-effective roads, and roads that minimize adverse environmental impacts and protect water quality.The U.S. Department of Agriculture (USDA) or U.S. Agency for International Development(USAID) assumes no responsibility for the interpretation or use of this information. The use oftrade, firm, or corporation names is for the information and convenience of the reader. Such usedoes not constitute an official evaluation, conclusion, recommendation, endorsement, or approvalof any product or service to the exclusion of others that may be suitable.

The U.S. Department of Agriculture and U.S. Agency for International Development prohibitdiscrimination in all their programs and activities on the basis of race, color, national origin, sex,religion, age, disability, political beliefs, sexual orientation, or marital or family status. (Not allprohibited bases apply to all programs.) Persons with disabilities who require alternative means forcommunication of program information (braille, large print, audiotape, etc.) should contact USDA’sTARGET Center at (202)-720-2600 (voice and TDD).

To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326-W, Whitten Building, 1400 Independence Avenue, SW, Washington, D.C. 20250-9410, or call(202) 720-5964 (voice and TDD). USDA is an equal opportunity provider and employer.

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LOW-VOLUME ROADS ENGINEERINGBest Management Practices Field Guide

FOREWORD

The Conservation Management Institute (CMI) in the College of Natural Resources atVirginia Tech is dedicated to helping apply sound scientific principles to the managementof renewable natural resources around the world. Access is an important consideration

in many settings — not only to facilitate utilization of natural resources, but also to enable peopleto reach markets for their products and health services. However, it is vital that roads con-structed provide adequate access while following sound practices for environmental protectionwherever possible. Improperly constructed roads can negatively impact everything from terres-trial plant populations and soil conservation efforts to water quality and populations of aquaticorganisms in receiving waters.

This manual was originally published in Spanish as “Practicas Mejoradas de CaminosForestales” by the U.S. Agency for International Development (USAID) for use throughoutLatin America, and has proven valuable in helping to protect forest-based resources. It becameclear that the practical advice offered in this manual could be of value to resource managersthroughout the world. So, to reach this broader audience and inspired by the original Spanishwork, CMI and the USDA Forest Service have collaborated to produce this updated version inEnglish. We hope that the materials presented here are useful to you.

This project grew from our collaboration with Gerald Bauer, of the US Forest Service, onnatural resource education programs in Latin America. Mr. Bauer was a contributor to theoriginal manual and found the publication in great demand. This collaboration exemplifies ourinvolvement with USAID and the Forest Service on many natural resource projects. Weencourage you to contact USFS or CMI if we can be of assistance in your conservation efforts.Finally, we acknowledge the notable efforts of Julie McClafferty of CMI, who was instrumentalin preparing this manual for publication.

B. R. Murphy, PhD., Director, CMI ([email protected])A.L. Hammett, PhD., Faculty Fellow, CMI and Coordinator of International Programs, College

of Natural Resources ([email protected])Gordon Keller, PE, Geotechnical Engineer, USFS ([email protected])James Sherar, PE, Logging Engineer, USFS ([email protected])

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ACKNOWLEDGMENTS

ALARGE NUMBER OF INDIVIDUALS have been involved in the developmentof the MinimumImpact Low-Volume Roads Manual and this subsequent Low-Volume RoadsEngineering Best Management Practices Field Guide. These individuals have had the

vision and commitment to preserving and enhancing the quality of our environment, while alsorecognizing the need for good roads. Futhermore, they recognize the planning, design, mainte-nance, and overall management necessary to have good roads. Funding for this project hasprincipally been provided by the US Agency for International Development (USAID), theGlobal Bureau, and the Forestry Team, with contributions from the USDA, Forest Ser-vice, Office of International Programs, the Pacific Southwest Region, and the PlumasNational Forest.

The original Spanish version of this document was produced with the help of Ramon Alvarez,Roberto Medina, and Atilio Ortiz with USAID, Honduras. The authors are particularly grateful forthe support of Jerry Bauer, Alex Moad, and Michelle Zweede with the International Programsoffice of the U.S. Forest Service; Jim Padgett and Nelson Hernandez from the Washington Office,USFS; Scott Lampman, Paul DesRosiers, and Mike Benge with the U.S. Agency for InternationalDevelopment; and the steadfast support from our Plumas National Forest colleagues.

The drawings presented in this document come from a variety of sources, as indicated, and mosthave been redrawn or adapted with the artistic talent of Jim Balkovek, Illustrator, and Paul Karr,a retired Forest Service Engineer. Scanning, labeling, and computer manipulation of figures for thisfield guide have been accomplished with the skill and patience of Lori Reynolds of ReynoldsGraphics in Quincy, California. Translation of portions of this Field Guide and the original Mini-mum Impact Low-Volume Roads Manual was skillfully accomplished by Alejandra Medina of theVirginia Tech Transportation Institute.

A sincere thanks to the many professionals and laymen who gave their time in reviewing and editingthe document, as well as making valuable suggestions regarding the form and content of this FieldGuide. Particular thanks to Jill Herrick, U.S. Forest Service, for her valuable contributions andassistance with editing this guide, assistance with the Definition of Terms and References, andoverall content review, as well as to Michael Furniss, Charlie Carter, Jerry Short, Tim Dembosz,and Ozzie Cummins for their numerous suggestions and ideas on drainage and other issues. Thanksto Richard Wiest, author of “A Landowner’s Guide to Building Forest Access Roads”, for hisinspiration and ideas on format and layout. Other individuals involved in review and editing includeLeslie Lingley of Leslie Geological Services; Marty Mitchell of Clear Water West; Alfred Logiewith the International Programs office of the Federal Highway Administration (FHWA); MikeBenge and Eric Peterson with U. S. Agency for International Development; Dr John Metcalf fromLSU/PIARC World Roads Association; Dr. Francis Greulich, Forest Engineer at the University ofWashington; Dr. Allen Hathaway, Geologic Engineer at the University of Missouri-Rolla; David

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Orr, PE with the Cornell University Local Roads Program; Prof. Raymond Charles, University ofWest Indes; Art Klassen, Tropical Forestry Foundation; James Schenck and Wilson Castaneda,Cooperative Housing Foundation-Guatemala; Harold Tarver with Africare; Wes Fisher with TellusInstitute; and Sandra Wilson-Musser, Corky Lazzarino, Armando Garza, Gary Campbell, KenHeffner, Terry Benoit, Allen King, John Heibel, William Vischer, and Greg Watkins, U.S. ForestService employees dedicated to watershed protection and building good roads.

Most of the photos used in this manual either belong to the authors, Gordon Keller and JamesSherar, or to Jerry Bauer, co-author on the “Minimum Impact Low-Volume Roads” Manual.Others belong to individuals as indicated on the specific photo. The retaining wall photo on thecover was provided by Michael Burke.

Finally, the authors wish to give special thanks to Tom Hammett at Virginia Tech for his connec-tions and facilitation of this project and Julie McClafferty of the Conservation Management Insti-tute and Patty Fuller of Poplar Hill Studios in Blacksburg, Virginia, for their magic in layout andpublication of this guide and making it look the way it does. Last, and by no means least, a big hugto our wives, Jeanette and Julie, and families for their patience and support during this project!

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PREFACE

THE AUTHORS ARE GRATEFUL for the opportunity to develop this guide for the US Agency forInternational Development (USAID) with the cooperation of the USDA, the Forest Service,the Office of International Programs, and the International Programs Department at Virginia

Polytechnic Institute and State University. The original development of this Roads Best ManagementPractices (BMP) Field Guide was funded by USAID/Honduras, in support of their ForestryDevelopment Program (FDP) and their National Forestry School (ESNACIFOR). It has sincebeen revised and expanded to be consistent with and complement the training manual titled“Minimum Impact Low-Volume Roads” for roads work in developing regions.

This Low-Volume Roads Engineering Best Management Practices Field Guide is intended toprovide an overview of the key planning, location, design, construction, and maintenance aspectsof roads that can cause adverse environmental impacts and to list key ways to prevent thoseimpacts. Best Management Practices are general techniques or design practices that, whenapplied and adapted to fit site specific conditions, will prevent or reduce pollution and maintainwater quality. BMPs for roads have been developed by many agencies since roads often have amajor adverse impact on water quality, and most of those impacts are preventable with goodengineering and management practices. Roads that are not well planned or located, not properlydesigned or constructed, not well maintained, or not made with durable materials often have nega-tive effects on water quality and the environment.

This Guide presents many of those desirable practices. Fortunately, most of these “Best Manage-ment Practices” are also sound engineering practices and ones that are cost-effective by prevent-ing failures and reducing maintenance needs and repair costs. Also keep in mind that “best” isrelative and so appropriate practices depend to some degree upon the location or country, degreeof need for improvements, and upon local laws and regulations. Best practices are also constantlyevolving with time.

This guide tries to address most basic roads issues in as simple a manner as possible. Complexissues should be addressed by experienced engineers and specialists. Included are key “DO’s”(RECOMMENDED PRACTICES) and “DON’Ts” (PRACTICES TO AVOID) in low-volume roads activities, along with some relevant basic design information. These fundamentalpractices apply to roads worldwide and for a wide range of road uses and standards. Oftenrecommended practices have to be adapted to fit local conditions and available materials. Addi-tional information on how to do the work is found in other Selected References, such as the“Minimum Impact Low-Volume Roads Manual”.

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Most practices apply to a wide range of road standards, from native surfaced, single-lane roads todouble-lane paved roads. Desirable general practices include good road planning and location,performing environmental analysis, recognizing the need for positive surface drainage, ensuringadequately sized drainage crossing structures, using stable cut and fill slopes, using erosion controlmeasures, developing good materials sources, and reclaiming sites once work has been com-pleted.

Certain design practices, such as use of rolling dips, outsloped roads, or low-water stream cross-ings, are very cost-effective and practical but typically apply to low-volume, low-speed roadsbecause of safety concerns, vertical alignment issues, or unacceptable traffic delays. Other issues,such as the use of log stringer bridges, are very desirable for stream crossings in developingregions to avoid driving through the water, yet their use is now discouraged by some agencies,such as the U.S. Forest Service, because of their short design life and potentially unpredictableperformance. Thus the information presented herein must be considered in terms of local condi-tions, available materials, road standards, project or resource priorities, and then applied in amanner that is practical and safe.

Local rules, agency policies or regulations, or laws may conflict with some of this information ormay include more specific information than that included herein. Thus, good judgment should beused in the application of the information presented in this guide, and local regulations and lawsshould be followed or modified as needed.

You may reproduce or copy any portion of this Guide. However, please acknowledge this Guideas the source of information.

Reproduction Of This Field Guide is Encouraged!

Disclaimer

This Field Guide does not constitute a standard, specification, or regulation from or bound on anyprofessional group, agency, or political entity. It is intended only as a guide for good roads engi-neering and sound environmental management in developing countries based upon the profes-sional judgment and experience of the authors.

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LOW-VOLUME ROADS ENGINEERINGBest Management Practices Field Guide

TABLE OF CONTENTS

Foreword iii

Acknowledgments v

Preface vii

Definition of Terms xi

Chapter 1 Introduction 1

Chapter 2 Environmental Analysis 5

Chapter 3 Planning Issues and Special Applications 11Key Road IssuesReducing Vulnerability of Roads to Natural DisastersStreamside Management ZonesTimber Harvesting

Chapter 4 Low-Volume Roads Engineering 21Road PlanningRoad LocationRoad Survey, Design, and ConstructionRoad CostsRoad MaintenanceRoad Closure

Chapter 5 Hydrology for Drainage Crossing Design 37

Chapter 6 Tools for Hydraulic and Road Design 43

Chapter 7 Drainage of Low-Volume Roads 53Roadway Surface Drainage ControlControl at Inlets and Outlets of Cross-Drains and DitchesNatural Stream CrossingsWet Areas and Meadow Crossings, Use of Underdrains

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Chapter 8 Culvert Use, Installation, and Sizing 75

Chapter 9 Fords and Low-Water Crossings 91

Chapter 10 Bridges 97

Chapter 11 Slope Stabilization and Stability of Cuts and Fills 103

Chapter 12 Roadway Materials and Material Sources 115

Chapter 13 Erosion Control 129

Chapter 14 Stabilization of Gullies 141

Selected References 147

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I. ROAD COMPONENTS

Figure (I.1): Terms Used to Define Low-Volume Roads

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Arranged by Topic:Section I Road Components ixSection II Road Structural Section and Materials xiiSection III Surface Drainage xiiiSection IV Culverts and Drainage Crossings xvSection V Fords and Low Water Crossings xviiSection VI Erosion Control xviiiSection VII Miscellaneous Terms xx

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Figure (I.2) Terms Used to Define Low-Volume Roads (Cross-Section)

Base Course - See Section II below.

Berm - A ridge of rock, soil, or asphalt, typically along the outside edge of the road shoulder, used to controlsurface water. It directs surface runoff to specific locations where water can be removed from the road surfacewithout causing erosion.

Buttress - A structure designed to resist lateral forces. It is typically constructed of large riprap rock, gabions,or drained soil to support the toe of a slope in an unstable area.

Cross-Section - A drawing depicting a section of the road sliced across the whole width of the road (SeeFigure I.2 above). Can also apply to a stream, a slope, or a slide.

Cut Slope (Back Slope or Cut Bank) - The artificial face or slope cut into soil or rock along the inside edgeof the road.

Cut-and-fill - A method of road construction in which a road is built by cutting into the hillside and spreadingthe spoil materials in adjacent low spots and as compacted or side-cast fill slope material along the route. A“balanced cut-and-fill” utilizes all of the “cut” material to generate the “fill”. In a balanced cut-and-fill designthere is no excess waste material and there is no need for hauling additional fill material. Thus cost is minimized.

Ditch (Side Drain) - A channel or shallow canal along the road intended to collect water from the road andadjacent land for transport to a suitable point of disposal. It is commonly along the inside edge of the road. Italso can be along the outside edge or along both sides of the road.End Haul - The removal and transportation of excavated material off-site to a stable waste area (rather thanplacing the fill material near the location of excavation).

Embankment (Fill) - Excavated material placed on a prepared ground surface to construct the road subgradeand roadbed template.

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Fill Slope (Embankment Slope) - The inclined slope extending from the outside edge of the road shoulder tothe toe (bottom) of the fill. This is the surface formed where material is deposited to build the road.

Full Bench Cut and End Haul - A method of road construction in which a road is built entirely by cutting awaythe slope, and the excess material is hauled away (end hauled) to an off-site disposal area.

Grade (Gradient) - The slope of the road along its alignment. This slope is expressed in percent - the ratio ofelevation change compared to distance traveled. For example, a +4% grade indicates a gain of 4 units ofmeasure in elevation for every 100 units of measure traveled.

Low-Volume Road - A type of transportation system typically constructed to manage or extract resources fromrural or undeveloped areas. These unique systems are designed to accommodate low traffic volumes withpotentially extreme axle loads. They are commonly defined as having less than 400 ADT (Average Daily Traf-fic).

Natural Ground (Original Ground Level) - The natural ground surface of the terrain that existed prior todisturbance and/or road construction.Plan View (Map View) - View seen when looking from the sky towards the ground. A drawing with this viewis similar to what a bird would see when flying over a road.

Reinforced Fill - A fill that has been-provided with tensile reinforcement through frictional contact with thesurrounding soil for the purpose of greater stability and load carrying capacity. Reinforced fills are comprised ofsoil or rock material placed in layers with reinforcing elements to form slopes, walls, embankments, dams orother structures. The reinforcing elements range from simple vegetation to specialized products such as steelstrips, steel grids, polymeric geogrids and geotextiles.Retaining Structure - A structure designed to resist the lateral displacement of soil, water, or any other type ofmaterial. It is commonly used to support a roadway or gain road width on steep terrain. They are often con-structed of gabions, reinforced concrete, timber cribs, or mechanically stabilized earth.Right-of-Way (ROW) - The strip of land over which facilities such as roads, railroads, or power lines are built.Legally, it is an easement that grants the right to pass over the land of another.

Road Center Line - An imaginary line that runs longitudinally along the center of the road.

Roadbed - Width of the road used by vehicles including the shoulders, measured at the top of subgrade.

Roadway (Construction Limits or Formation Width) - Total horizontal width of land affected by the con-struction of the road, from the top of cut slope to the toe of fill or graded area.

Side-Cast Fill - Excavated material pushed on a prepared or unprepared slope next to the excavation toconstruct the roadbed. The material is usually not compacted.

Slope Ratio (Slope) - A way of expressing constructed slopes as a ratio of horizontal distance to vertical rise,such as 3:1 (3 m horizontal for every 1 m vertical rise or fall).

Shoulder - The paved or unpaved strip along the edge of the traveled way of the road. An inside shoulder isadjacent to the cut slope. An outside shoulder is adjacent to an embankment slope.

Subgrade - See Section II below.Surface Course (Surfacing) - See Section II below.

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Traveled Way (Carriageway) - That portion of the road constructed for use by moving vehicles includingtraffic lanes and turnouts (excluding shoulders).

Through Cut - A road cut through a hill slope or, more commonly, a ridge, in which there is a cut slope on bothsides of the road.

Through Fill - Opposite of a through cut, a through fill is a segment of road that is entirely composed of fillmaterial, with fill slopes on both sides of the road.

II. ROAD STRUCTURAL SECTION AND MATERIALS

Figure (II): Road Structural Section

Base Course (Base) - This is the main load-spreading layer of the traveled way. Base course material normallyconsists of crushed stone or gravel or of gravelly soils, decomposed rock, sands and sandy clays stabilized withcement, lime or bitumen.Borrow Pit (Borrow Site) - An area where excavation takes place to produce materials for earthwork, such asa fill material for embankments. It is typically a small area used to mine sand, gravel, rock, or soil without furtherprocessing.Quarry - A site where stone, riprap, aggregate, and other construction materials are extracted. The materialoften has to be excavated with ripping or blasting, and the material typically needs to be processed by crushingor screening to produce the desired gradation of aggregate.Raveling - A process where coarse material on the road surface comes loose and separated from the roadbedbecause of lack of binder or poor gradation of material. The term also applies to a slope where rock or coarsematerial comes loose and falls down the cut or fill slope.Sub-Base - This is the secondary load-spreading layer underlying the base. It normally consists of a materialthat has lower strength and durability than that used in the base, e.g. unprocessed natural gravel, gravel/sand orgravel/sand/clay.Subgrade - The surface of roadbed upon which sub base, base, or surface course are constructed. For roadswithout base course or surface course, this portion of the roadbed becomes the finished wearing surface. Thesubgrade is typically at the level of the in-place material.

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Surface Course (Surfacing) - The top layer of the road surface, also called the wearing course. Rock,cobblestone, crushed aggregate and paving, such as Bituminous Surface Treatments and Asphalt Concrete, aretypes of surfacing used to improve rider comfort, provide structural support, and weatherproof the road surfacefor wet season use.Washboarding (Corrugations) - A series of ridges and depressions across the road caused in soil and aggre-gate road surfaces by the lack of surface cohesion. This is typically a result of the loss of fines in the roadsurface caused by dry conditions or poorly graded material. These conditions worsen with excessive vehiclespeeds and high traffic volumes.Wearing Course (Wearing Surface) –The top layer of the road surface that is driven upon. It should bedurable, may have a high resistance to skidding, and it typically should be impervious to surface water. Wearingsurfaces may be the native soil, aggregate, seal coats, or asphalt.

III. SURFACE DRAINAGE

Figure (III.1): Road Surface Drainage

Armor - Rocks or other material placed on headwalls, on soil, or in ditches to prevent water from eroding andundercutting or scouring the soil.Catch Water Ditch (Intercept Drain) - A flat-bottomed excavation or ditch located above a cut slope that isdesigned to intercept, collect and drain away surface runoff water before it goes over the cut slope, to protectthe cut slope and roadway from erosion.Check Dam (Scour Check, or Dike) - A small dam constructed in a gully or ditch to decrease flow velocity,minimize channel scour, and to trap sediment.Cross-Drain (X-Drain) - Installed or constructed structures such as culverts and rolling dips that move waterfrom one side of the road to the other.

Crown - A crowned surface has the highest elevation at centerline (convex) and slopes down on both sides.Crown is used to facilitate draining water off a wide road surface.Debris - Organic material, rocks and sediment (leaves, brush, wood, rocks, rubble, etc.) often mixed, that isundesirable (in a channel or drainage structure).

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Figure (III.2): Rolling Grade with Rock-Armored Rolling Dips

Drainage Structure - A structure installed to control, divert, or move water off or across a road, including butnot limited to culverts, bridges, ditch drains, fords, and rolling dips.French Drain (Underdrain) - A buried trench, filled with coarse aggregate, and typically placed in the ditchline along the road, which acts to drain subsurface water from a wet area and discharge it a safe and stablelocation. French drains may use variable sizes of rock but do not have a drain pipe in the bottom of the trench.Inside/Outside - Reference to a feature on the inside of the road, which is typically the cutslope (back slope)side of the road/ Reference to a feature on the outside of a road, typically on the fill slope side.Inslope - The inside cross-slope of a road subgrade or surface, typically measured in percentage. Inslope isused to facilitate the draining of water from a road surface to an inside ditch. An insloped road has the highestpoint on the outside edge of the road and slopes downward to the ditch at the toe of the cut slope, along theinside edge of road.Lead-Off Ditches (Turnouts, Outside Ditch, or Mitre Drains) - Excavations designed to divert wateraway from the ditch and roadway (at a point where this doesn’t occur naturally) in order to reduce the volumeand velocity of roadside ditch water.Outslope - The outside cross-slope of a road subgrade or surface, typically measured in percentage. Outslopeis used to facilitate the draining of water from a road directly off the outside edge of the road. An outsloped roadhas the highest point on the uphill or inside of the road and slopes down to the outside edge of the road and thefill slope.Riprap - Well-graded, durable, large rock, ideally with fractured surfaces, sized to resist scour or movement bywater and installed to prevent erosion of native soil material.Rolling Dip (Dip, Broad-Based Dip) - A surface drainage structure, with a constructed break in the roadgrade, specifically designed to drain water from an inside ditch or across the road surface, while vehicles travelspeed is somewhat reduced (see lower photo on the cover of this Guide).Underdrain (Subsurface Drain) - A buried trench, filled with coarse aggregate, coarse sand, or gravel, andtypically placed in the ditch line along the road, which acts to drain subsurface water from a wet area anddischarge it a safe and stable location. Underdrains may use a uniform size of rock, be wrapped in geotextile,and have a perforated drain pipe in the bottom of the trench.

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Waterbar - A frequently spaced, constructed drainage device, using soil mounds in the road surface, thatinterrupt the flow of water and that diverts water off the road surface. They may be drivable by high clearancevehicles or impassable.

IV. CULVERTS AND DRAINAGE CROSSINGSFigure (IV.1): Culvert Components

Figure (IV.2): Natural Drainage Crossing with a Culvert

Apron - An extension of the head wall structure built at ground or stream level and designed to protect thestream bottom from high flow velocities and to safely move water away from the drainage structure.

Bankfull Width (Ordinary High Water Width) - The surface width of the stream measured at the bankfullstage. This flow, on average, has a recurrence interval of about 1.5 years. The bankfull stage is the dominantchannel-forming flow, and is typically identified as the normal upper limit of stream channel scour, below whichperennial vegetation does not occur.

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Bedload - Sediment or other material that slides, rolls, or bounces along the streambed or channel bottom dueto flowing water.Catch Basin - The excavated or constructed basin at the inlet of a culvert cross-drain pipe, used to store waterand direct it into the culvert pipe.Culvert - A drainage pipe, usually made of metal, concrete, or plastic, set beneath the road surface, to movewater from the inside of the road to the outside of the road, or under the road. Culverts are used to drainditches, springs, and streams that cross the road. The invert is the floor or the bottom of the structure at itsentrance.Drop Inlet - A masonry or concrete basin, or a vertical riser on a metal culvert inlet, usually of the same diam-eter as the culvert, and often slotted, to allow water to flow into the culvert as water flow rises around theoutside. Drop inlets are often used on ditch relief culverts where sediment or debris would plug the pipe. A dropinlet also helps control the elevation of the ditch.Flood Plain - A level or gently sloping area on either side of a river or stream active (main) channel that issubmerged at times during high water or periods of flooding. Silt and sand are deposited and accumulate in thisarea along the main channel.Freeboard - The additional height of a structure above design high water level to prevent overflow or overtop-ping. Also freeboard, at any given time, is the vertical distance between the water level and the bottom of thebridge slab, girders, or structure.Headwall - A concrete, gabion, masonry, or timber wall built around the inlet or outlet of a drainage pipe orstructure to increase inlet flow capacity, reduce risk of debris damage, retain the fill material and minimize scouraround the structure.High Water Mark - The line on a bank or shore established by the highest level of the water. This is usuallyidentified by physical evidence such as a natural impression (small bench) on the bank, changes in the characterof soil, destruction of most vegetation, or presence of litter and debris.Inlet - The opening in a drainage structure or pipe where the water first enters the structure.Metal End Section - A manufactured headwall/wing wall, usually made from the same type of metal as theculvert, to enhance inlet flow capacity.Outlet - The opening in a drainage structure or pipe where the water leaves the structure. The outlet is usuallylower than the inlet to ensure that water flows through the structure.Outlet Protection - Devices or material, such as a headwall or riprap, placed at the outlet of pipes or drainagestructures to dissipate the energy of flowing water, reduce its flow velocity, and prevent channel or bank scour.Perennial Stream - A stream that typically has running water all year long.Piping - The movement of fine soil under a pipe, embankment, or structure, caused by seepage forces andmoving water, that can cause a structure to be undermined and fail.Rootwad - The ball of tree roots and dirt that is pulled from the ground when a tree is uprooted.Scour - Erosion or soil movement in a stream bed, stream bank, channel, or behind a structure, typically causedby increased water velocity or lack of protection.

Stream Barb (Jetty) - Typically low rock sills that project away from a steam bank and out into the streamchannel to redirect flow away from an eroding bank.Wing Walls - Masonry or concrete structures built onto the side of culvert inlet and outlet headwalls, designedto retain the roadway fill and direct water into and out of the drainage structure while protecting the road and fillfrom erosion.

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V. FORDS AND LOW-WATER CROSSINGS

Figure (V.1) Simple Ford

Figure (V.2) Improved, Vented Ford

Ford (Low-Water Crossing) (Drift); Simple - A rock or other hardened structure that is built across thebottom of a swale, gully, or stream channel that is usually dry, to allow improved vehicle passage during periodsof low water or no flow.Ford (Low-Water Crossing) (Drift); Improved - A masonry, concrete, gabion, or other hardened surfacestructure built across the bottom of an intermittent or live stream that improves vehicle passage during low flowperiods and minimizes channel disturbance or sediment production.Vented Ford - A structure designed to allow normal or low water flow in a stream channel or watercourse topass safely through the structure (e.g., culverts) below a hardened or reinforced roadway surface. Duringperiods of high water or flooding, the flow passes over the structure and typically prevents vehicle passage.

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VI. EROSION CONTROL

Figure (VI.1): Use of Vegetation, Woody Material and Rock for Erosion Control

Figure (VI.2): Biotechnical Erosion Control Measures-A Wall with Live Stakes

Biotechnical Erosion Control - A combination of vegetative and structural measures used to prevent erosionor stabilize slopes and stream banks. The term “biotechnical” describes several methods of establishing vegeta-tive cover by embedding a combination of live, dormant, and/or decaying plant materials into banks and shore-lines in a structure-like manner or in conjunction with riprap or physical structures such as cribs or gabions.Brush Barrier - A sediment control structure created using live brushy vegetation or slash piled at the toe of afill lope, on contour along a slope, along the road, or at the outlet of culverts, leadoff ditches, dips, or waterbars to trap sediment.

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Brush Layers - The biotechnical practice of digging shallow terraces into the surface of a slope, laying in layersof a vegetative cuttings that will resprout, and backfilling (burying) the cuttings with soil. Cuttings are placedperpendicular to the slope contour.Erosive Soils - Soils that are relatively prone to erosion and movement by rain drop impact and surface runoff.Fine granular, non-cohesive soils, such as fine sandy sand derived from decomposed granite, silts, or fine sands,are known to be very erosive.Erosion - The process by which the surface of the earth is worn away and soil moved by the actions of wind orwater in the form of raindrops, surface runoffs, and waves.Erosion Control - The act of reducing or eliminating on-going erosion caused by raindrop impact, rilling,gullying, raveling, and other surface processes.Erosion Prevention - Preventing erosion before it occurs. Erosion prevention is typically less expensive andmore effective than erosion control. Erosion prevention is intended to protect a road, including its drainagestructures, cut and fill slopes, and disturbed areas, and to protect water quality.Live Stakes - Sections of woody plants that are cut into lengths (stakes) and placed or driven into the slope.The plant material is installed during the fall or spring when the original plant (and consequently cuttings from it)is dormant. The plant materials used for stakes are usually hardy species which will root from cuttings easily andeventually grow into mature woody shrubs that reinforce the soil structure of the slope.Mulch - Material placed or spread on the surface of the ground to protect it from raindrop, rill, and gullyerosion, and to retain moisture to promote the growth of vegetation. Mulches include cut vegetation, grasses,wood chips, rock, straw, wood fiber, and variety of other natural and synthetic materials and mats.Mulching - Providing a loose covering on exposed soil areas using materials such as grass, straw, bark, orwood fibers to help control erosion and protect exposed soil.Native Species - Occurring or living naturally in an area (indigenous), such as locally grown native plants.Physical Erosion Control Measures - Non-vegetative measures used to control erosion, such as armoringthe soil with riprap, building silt fences, using woven mats, using gabions, spreading or windrowing logging slashor woody material, etc., and controlling water with settlement ponds, armored drainage ditches, etc.Scarification - The act of ripping or stripping the forest floor or a road surface and mixing it with mineral soil,typically with mechanical equipment, to loosen the soil, reduce compaction, and prepare the area for plantingwith grasses or trees.Sedimentation (Sediment) - Soil, most commonly clay, silt and sand, which is eroded from the land or poorlyconstructed roads and reaches a stream or water course, commonly reducing water quality in rivers, streamsand lakes.Sediment Catchment Basin - A constructed basin designed to slow water velocity and trap sediment as itsettles out of the water.Slash - Any treetops, limbs, bark, abandoned forest products, windfalls or other debris left on the ground aftertimber or other forest products have been cut.Silt Fence - A temporary barrier used to intercept sediment-laden runoff from slopes. It is typically made ofporous geotextile material.Vegetative Erosion Control Measures - The use of live cuttings or stakes, seed, sod, and transplants toestablish vegetation (grass, brush, trees) for erosion control and slope protection work.Vegetative Contour Hedgerow - Rows of trees and shrubs, typically planted on contour across slopes, thatform a border and can provide erosion control protection against sheet flow, as well as provide food and coverfor wildlife.

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Vetiver Grass - Any of several varieties of a non-invasive, large bunch grass widely used for erosion controland moisture conservation. When planted as a contour hedgerow, it slows runoff and filters sediment. Thecurtain-like root system helps anchor soil and competes minimally with adjacent crop roots.Wattles (Live Fascine) - Long bundles of brush or branch cuttings, bound together into sausage shapedstructures, which are buried or staked on contour along a slope, preferably to sprout, and form a sediment trapor break up sheet flow on the slope.Windrow - Logging debris and woody vegetation that has been piled in rows to trap sediment, as well asdecompose or eventually be burned; the act of building windrows.

VII. MISCELLANEOUS TERMS

Angle of Repose - The maximum slope or angle at which a granular material, such as loose rock or soil, willstand and remain stable.Best Management Practices (BMPs) - Practical guidelines that can be used to reduce the environmentalimpact of roads and forest management activities (such as the construction of roads, skid trails and log landings)and protect water quality. BMPs address the key planning, location, design, construction, and maintenanceaspects of roads or other activities that can cause adverse environmental impacts and suggest methods toprevent those impacts.Buffer Area - A designated zone along a stream or around a water body or area with sufficient width tominimize the entrance of forestry chemicals, sediment, or other pollution into the water body or protect the area.Contour - Lines drawn on a plan that connect points having the same elevation. Contour lines represent an evenvalue, with the contour interval being selected consistent with terrain, scale, and intended use of the plan.Contours are level.Environmental Impact - An action or series of actions that have an effect on the environment. An Environmen-tal Impact Assessment predicts and evaluates these effects, both positive and negative, and the conclusions areused as a tool in planning and decision-making.Gabions - Baskets (usually made of wire) filled with rocks (or broken pieces of concrete) about 10-20 cm insize, used for building erosion control structures, weirs, bank protection, or retaining structures.Geotextile (Filter Fabric) - Textile made from synthetic “plastic” fibers, usually non-biodegradable, to form ablanket-like product. Geotextiles can be woven or non-woven and have varying degrees of porosity, open area,and strength properties. They are used as moisture barriers, for separation or reinforcement of soils, filtration,and for drainage.Habitat - The natural environment that forms a home for native plants and animals. For example, riverbanks arehabitat for insects that are the primary source of food for many fish.Logging (Harvesting) - Logging is the process of harvesting timber from trees. This includes felling, skidding,loading, and transporting forest products, particularly logs.Landing (Log Deck) - Any place on or adjacent to the logging site where logs are assembled after beingyarded, awaiting subsequent handling, loading, and transport. This is typically a relatively flat area, commonlyabout 20 to 50 meters in diameter.Mitigation - The act of or a specific item used to reduce or eliminate an adverse environmental impact.Native Soil - Natural, in-place or in-situ soil that has formed on site and has not been artificially imported to thesite.

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Reclamation (Rehabilitation) - Activities that reclaim, repair, or improve part or all of an existing road,borrow pit, or disturbed area and restore it to its original or some desired final condition.Road Closure (Temporary) - Closing vehicular access to a road through the use of barricades such as gates,log barriers, earthen mounds, or other temporary structures. The end result is to restrict the use of the road forsome period of time.Road Decommissioning - Permanently closing a road through techniques that include blocking the entrance,scattering limbs and brush on the roadbed, replanting vegetation, adding waterbars, removing fills and culverts,or reestablishing natural drainage patterns. However the basic road shape, or template, is still in place. The endresult is to terminate the function of the road and mitigate the adverse environmental impacts of the road.Road Obliteration - A form of road closure that refills cut areas, removes fills and drainage structures, restoresnatural contours, revegetates the area, and ultimately attempts to restore the natural ground shape and condition.Thus, most adverse environmental impacts of the road are eliminated.Road Management Objectives - Objectives that establish the intended purpose of an individual road basedon management direction and access management objectives. Road management objectives contain designcriteria, operation criteria, and maintenance criteria.Skid Trail (Skidding) - A temporary, nonstructural pathway over forest soil used for dragging felled trees orlogs to a log landing.Streamside Management Zone (SMZ) - The land, together with the vegetation that grows there, immediatelyin contact with the stream and sufficiently close to have a major influence on the total ecological character andfunction of the stream. It is a buffer area along a stream where activities are limited or prohibited.Upgrading - The process by which the standard of an existing road is improved or altered to allow for in-creased capacity and safe use by a greater volume of traffic.

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1LOW-VOLUME ROADS BMPS:

Chapter 1

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RURAL, LOW-VOLUME, farm-to-marketaccess roads, roads connectingcommunities, and roads for logging or mining

are significant parts of any transportation system. Theyare necessary to serve the public in rural areas, toimprove the flow of goods and services, to helppromote development, public health and education, aswell as to aid in land and resource management (Photo1.1). At the same time,roads and disturbed areascan produce significantamounts of sediment(Photo 1.2). They can beone of the greatestadverse impacts on thelocal environment, onwater quality, and onaquatic life. Roads canproduce significanterosion, cause gullies, havean impact ongroundwater, wildlife, andvegetation, impact socialstructure, degrade scenicvalues, waste limitedfunds, and take useful landout of production(Photo1.3).

The basic objective of this guide is to helpengineers, planners, environmental specialists, androad managers make good decisions, protect theenvironment, and build good low-volume roads.Key issues that should be addressed when planninga road project include changes or negative impactsto the area that a road can cause which may besignificant, irreversible, or difficult to mitigate. The

“Ideas are a dime a dozen. People who put them into action are priceless.”-A. Einstein

Photo 1.1Photo 1.1Photo 1.1Photo 1.1Photo 1.1 A minimum impact rural road that is well drained, has a stabledriving surface, stable slopes, and is satisfactory for the user.

2 LOW-VOLUME ROADS BMPS:

long-term social, environmental, andfiscal cost effectiveness of a proposedroad all need to be examined.Environmental analysis is a principalway to examine all aspects of aproject, maximize its usefulness, andminimize problems. Emphasis shouldbe placed on the use of an“Interdisciplinary Team” approach.Not all adverse impacts of roads canbe avoided, but many can, and thenegative and positive impacts of aroad project should be weighed andevaluated.

Roads are necessary, but theymust be constructed andmaintained in such a way thatnegative environmental impacts arecontrolled or avoided. A wellplanned, located, designed, andconstructed road will haveminimum adverse impacts on theenvironment and will be costeffective in the long term withminimized maintenance and repair

costs. Controlling erosion andprotecting water quality areessential to the quality of life, thehealth of the forest and woodlandecosystems, and to the long-termsustainability of rural resources.Vegetated areas such as woodlandsand forests play a vital role in

Photo 1.2Photo 1.2Photo 1.2Photo 1.2Photo 1.2 A poorly drained road that has a rough driving surface for theusers, it is a source of sediment, and it is relatively expensive to maintain.

Photo 1.3Photo 1.3Photo 1.3Photo 1.3Photo 1.3 A problematic road because of roadcut failures. Instabilityproblems cause road user delays, and high maintenance or repair costs.

producing, purifying, and maintainingclean water. Roads must protectwater quality and the bioticenvironment that depends on it.

Best Management Practicesor “BMPs” are those principals andengineering design practices that willprotect water quality as well as thefunction of the road when properlyapplied. The Best ManagementPractices presented herein are acompilation of ideas and techniquesthat can be used in road managementto reduce or eliminate many of thepotential impacts from roadoperations and protect water quality.They represent good road design andconstruction practices that are costeffective in the long run by reventingfailures, eliminating repair needs, andreducing maintenance.

The purpose of this manualis to present recommended practicesfor low-volume roads. A low-volume road is commonly defined asa road that has an average daily traffic


(ADT) of less than 400 vehicles perday, and usually has design speedsless than 80 kph (50 mph). Theinformation in this manual is applicableto rural roads, and most of theinformation is applicable to all typesof roads, although high standardroads are not the emphasis of thismanual. Soil and water quality issuesrelated to temperature, nutrients,chemical pollution, debris, quantity offlow, and so on are also beyond thescope of this manual, although thereare many varied benefits from theapplication of these practices.

Each topic in this manual containsa problem statement that presentsconcerns, advantages, and potentialimpacts for that issue.R E C O M M E N D E DPRACTICES and information on theproper or most desirable way to plan,locate, design, construct, andmaintain roads are presented, alongwith drawings and tables. Finally,PRACTICES TO AVOID are listedto discourage poor and undesirablepractices.

This manual offers the BestManagement Practices associatedwith many aspects of roadsmanagement. The informationpresented in this manual shouldbecome an integral part oftransportation planning and rural roaddesign. Key to its use is the need tohire and retain good, well-trained,and experienced engineers in roadagencies to evaluate problems,consider local conditions andresources, and implement or adaptthese practices as appropriate.

“Ideas are a dime a dozen.People who put them into

action are priceless.”

The key objectives of

Best Management Practices are designed toaccomplish the following:

• Produce a safe, cost effective, environmentallyfriendly, and practical road design that issupported by and meets the needs of the users;

• Protect water quality and reduce sediment loadinginto water bodies;

• Avoid conflicts with land use;

• Protect sensitive areas and reduceecosystem impacts;

• Maintain natural channels, natural stream flow,and maintain passage for aquatic organisms;

• Minimize ground and drainage channeldisturbance;

• Control surface water on the road and stabilize theroadbed driving surface (Photo 1.4);

• Control erosion and protect exposed soil areas;

• Implement needed slope stabilization measuresand reduce mass wasting;

• Avoid problematic areas; and

• Stormproof and extend the useful life of the road.

BEST MANAGEMENTPRACTICES

4 LOW-VOLUME ROADS BMPS:

Obviously, some significantdifferences exist in roads needs anddesign details in varying geographicareas. At times, unique solutionsare needed. Mountainous regionstypically have steep slopes and coldregion conditions; deserts have littlemoisture to support vegetativeerosion control measures but havebrief, intense rainfall; jungles oftenhave poor soils and drainageproblems; high valley regions havedissected, steep terrain and difficultdrainage crossings, and so on.However, the basic planning,location, design and maintenance

concepts, and select BMPs apply toany area. Good planning and roadlocation are needed in any area.Roadway drainage must becontrolled and drainage crossingsmust be carefully selected andproperly designed. All roads needstable slopes, use of good materials,and appropriately applied erosioncontrol measures. Only some designdetails vary with specific geographicand climatic regions. Thus localexperience and knowledge are soimportant in rural roads.

PPPPPhotohotohotohotohoto 1.4 1.4 1.4 1.4 1.4 A well designed, “minimum impact” road that has an appropriate standard for its use, and astabilized cobblestone driving surface.

These BMPs are applicable toroad construction practices in mostfield situations. However, BMPsshould be selected (and maybe modified) for site-specificconditions, with guidancefrom experienced engineers,managers, or other resourceprofessionals. They must considerlocal or national regulations.Modifications should beresearched, designed, anddocumented before being used.They should be monitored, and theyshould provide for equal or greaterwater quality protection.

5 LOW-VOLUME ROADS BMPS :

Chapter 2

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EnEnEnEnEnvirvirvirvirvironmental Analyonmental Analyonmental Analyonmental Analyonmental Analysississississis

ENVIRONMENTAL ANALYSIS (the EA Process) isa systematic, interdisciplinary process usedto identify the purpose of a proposed action,

develop practical alternatives to the proposed action,and predict potential environmental effects of theaction. A few examples of proposed actions are roadconstruction, logging, tree clearing for diseasecontrol, reforestation, building a hydroelectric dam,or developing a quarry. Figure 2.1 shows some ofthe trade-offs and environmental impacts of lowversus high standard roads.

A couple of the principal environmental lawsapplied today are, the National EnvironmentalPolicy Act (NEPA), established in the United Statesin 1964, and the US Agency for InternationalDevelopment (USAID) 216 Regulations, whichdictate the environmental analysis process forUSAID funded projects worldwide. Many othercountries and agencies have environmental laws,regulations, and procedures that pattern thesefundamental documents.

Involve all parties! Communicate, communicate, communicate!

Figure 2.1 Figure 2.1 Figure 2.1 Figure 2.1 Figure 2.1 Low versus High Impact Roads: These figures show the reduced workand reduced environmental impacts from low standard roads that conform to thetopography. The low standard road reduces cut and fill slope size, reducesearth work, visual impacts, and minimizes changes to natural drainagepatterns. The high standard road can move a large volume of traffic rapidly and safely.

Low Impact RoadHigh Impact Road


An Environmental Analysis (EA)identifies problems, conflicts, orresource constraints that may affectthe natural environment orthe viability of a project. It alsoexamines how a proposedaction might affect people,their communities, and theirlivelihoods (Photo 2.1). Theanalysis should be conducted by anInterdisciplinary Team consisting ofpersonnel with a range of skills anddisciplines relevant to the project.Team members should include a teamleader and may includeengineers, geologists, biologists,archaeologists, and social workers.The EA process and findings arecommunicated to the various affectedindividuals and groups. At the sametime, the interested public helpsprovide input and comment on theproposed project (Photo 2.2). Thedocument produced as a result of theEA guides the decision maker towarda logical, rational, informed decisionabout the proposed action.

The EA process andInterdisciplinary Team studies can

reveal sound environmental, social, oreconomic reasons for improving aproject. After predicting potentialissues, the EA identifies measures tominimize problems and outlines waysto improve the project’s feasibility.Figures 2.2 a, b, & c showexamples of environmental mitigationsthat a designer can use to avoidpotential impacts on wildlife, such asuse of animal underpasses and culvert

requirements for fish passage (Photo2.3).

The EA process can providemany benefits to the road builder,local agencies, and the communitieswho will be affected by roadconstruction and maintenanceactivities. The process and resultingreports are tools that road managerscan use to guide their decisions,produce better road designs andmaintenance plans, identify and avoidproblems, and gain public support fortheir activities. An EA document canbe long and complex for major,potentially high impact projects, or itmay only be a few pages long for asimple road project. Table 2.1presents an eight-step process that isuseful for doing EnvironmentalAnalysis.

Key benefits of EA for a roadproject can include the following:

• Reducing cost and time ofproject implementation;

PPPPPhotohotohotohotohoto 2.1 2.1 2.1 2.1 2.1 A well built road that helps serve the local population in arural area, with minimum environmental damage.

Photo 2.2Photo 2.2Photo 2.2Photo 2.2Photo 2.2 A key aspect of the Environmental Analysis process iscommcommcommcommcommunicaunicaunicaunicaunicationstionstionstionstions with the public and between Interdisciplinary Teammembers.


RECOMMENDEDPRACTICES

Figure 2.2cFigure 2.2cFigure 2.2cFigure 2.2cFigure 2.2c A fish “friendly” culvert (pipe arch) with a natural streamchannel bottom that promotes fish passage and is wide enough toavoid constricting the normal or “bankfull” flow.

Figure 2.2aFigure 2.2aFigure 2.2aFigure 2.2aFigure 2.2a Example of an animal underpass used in roadconstruction to minimize the impact of roads on wildlife migration.Underpasses allow for safe animal crossings and minimize road kill.

Figure 2.2bFigure 2.2bFigure 2.2bFigure 2.2bFigure 2.2b Poorly designed or installed culverts with “fish barriers”that prevent fish passage. (Redrawn from Evans and Johnston 1980)

• Use the EnvironmentalAnalysis Process earlyduring project planning anddevelopment.

• Open project information topublic scrutiny.

• Involve all parties affectedby the project, as well askey Interdisciplinary Teammembers.

• Communicate,Communicate,Communicate!!!Communications betweenall interested parties is thekey to understanding theissues and problems and tofinding solutions!

PRACTICESTO AVOID

• Waiting until a project isfully planned or problemsdevelop before doingEnvironmental Analysis.

• Getting lost in the“process” of EA studies.

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An EIGHT Step Environmental Analysis Processand Its Associated Outputs

1. Identify the Project Identify the purpose and need of the proposed action.Develop a goal to provide a framework for EA.

2. Scoping Identify the issues, opportunities, and effects of implementingthe proposed action.

3. Collect and Interpret Data Collect data.Identify probable effects of project implementation.

4. Design of the Alternatives Consider a reasonable range of alternatives.Usually at least three alternatives are considered.Include a No-Action Alternative.Consider the mitigation of negative impacts.

5. Evaluate Effects Predict and describe the physical, biological, economic, andsocial effects of implementing each alternative.Address the three types of effects -- Direct, Indirect, and Cumulative.

6. Compare Alternatives Measure the predicted effects of each alternative againstevaluation criteria.

7. Decision Notice Select preferred alternative. and Public Review Allow for review and comment by the affected and interested public.

8. Implementation Record results.and Monitoring Implement selected alternative.

Develop a monitoring plan.Insure that EA mitigations are being followed.

PPPPPhotohotohotohotohoto 2.3 2.3 2.3 2.3 2.3 A bottomlessarch pipe culvert thatspans the active stream channeland doesn’t constrict the flow,maintains a natural streambottom, and helps promote fishpassage. (Photo provided by S.Wilson-Musser)


• Avoiding costly modificationduring construction;

• Determining the properbalance between roads needsand environmental impacts(Figure 2.1);

• Increasing project acceptanceby the public;

• Avoiding negative impacts andviolations of laws andregulations (Photo 2.4);

• Improving project design andperformance (Photo 2.5);

• Producing a healthierenvironment by avoiding ormitigating problems (Figure2.2, Photo 2.6); and

• Minimizing conflicts overnatural resource use.

Examples of typical environmen-tal mitigation measures associatedwith roads projects that have beendeveloped as a result of environmen-tal analysis are:

• Additional road surfacecross drainage structures toreduce water concentration andsubsequent erosion problems;

• Relocation of a road to avoid ameadow or sensitive area;

• Addition of extra culvert pipesto keep flows spread out acrossa meadow and prevent gullyformation from concentratedflows;

• Route location to avoidfragmentation of wildlifehabitat or avoid sensitivespecies areas;

• Addition of wildlife crossings,such as overpasses orunderpasses (Photo 2.7), orusing reduced speed zones at

PPPPPhotohotohotohotohoto 2.4 2.4 2.4 2.4 2.4 Adverse environmental impact from road surface erosioncaused by steep road grades and insufficient cross-drains. This roadis also difficult to maintain.

PPPPPhotohotohotohotohoto 2.5 2.5 2.5 2.5 2.5 A well designed, “minimum impact” road that has anappropriate standard for its use, good drainage, and stable slopes.

animal migration routes toreduce the number of animalskilled crossing highways;

• Increasing culvert pipe size,using bottomless arch culverts,or building a bridge to maintain anatural stream channel bottom,avoid channel disturbance and


Photo 2.6Photo 2.6Photo 2.6Photo 2.6Photo 2.6 Locate and manage roads to minimize degradation ofwater quality in local streams. Minimize the connectivity and amountof contact between roads and streams.

Photo 2.8Photo 2.8Photo 2.8Photo 2.8Photo 2.8 Stream bank stabilization and revegetation work can bedone in conjunction with road construction projects near a stream asan environmental mitigation measure.

Photo 2.7Photo 2.7Photo 2.7Photo 2.7Photo 2.7 A road underpass constructed to allow animals to move safelyfrom one side of the highway to the other.

impacts on aquatic organisms,and promote fish passage;

• Adding aggregate or someform of paving to the roadsurface to reduce erosion,materials loss, and dustproblems, as well as reducemaintenance frequency andimprove rider comfort;

• Developing a project quarryusing local materials, butlocated in a nonsensitivearea, and reclaiming the siteupon completion of theproject; and

• Implementing specificrevegetation and erosion controlmeasures for a project, utilizingappropriate native species ofvegetation and a local projectnursery to provide adequatetypes of plants with fastgrowth, good ground cover,and deep roots (Photo 2.8).

Remember thatEnvironmental Analysis isoften required by law, but

the process is intended to bea very useful planning tool

to help make good decisionsand improve projects.

11LOW-VOLUME ROADS BMPS :

Chapter 3

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Planning IssuesPlanning IssuesPlanning IssuesPlanning IssuesPlanning Issuesand Special Applicaand Special Applicaand Special Applicaand Special Applicaand Special Applicationstionstionstionstions

KEY ROAD ISSUES should be addressed duringthe planning phase of a road project, priorto construction or upgrading roads. These key

issues involve changes or impacts to an area that a roadcan cause that may be significant, irreversible, or difficultto mitigate. The benefits of a road project must beweighed against the long-term costs and impacts of thatproject. Once a road is built into an area, it can lead tolong-term land use changes and unplanned growth, asshown in Figure 3.1. Sediment from roads can also bea direct source of water pollution. Figure 3.2 showssome of the ways that roads directly contribute sedimentto nearby streams when they are closeby and“hydrologically connected”. Thus the social,environmental and fiscal cost-effectiveness of the roadneed to be examined.

Key issues include the following:

• Impacts on area growth, land use, deforestation,and impacts on local communities or indigenouspopulations (influences beyond the Right-of-Way of the road) (Figure 3.1);

• Optimum road location and system to serve areaneeds as well as specific project needs.;

• Long term potential use of the road versus currentuse;

• The appropriate minimum design standardto serve the road user and meet road needs(“right” sizing a road) (Photo 3.1);

• Avoiding local water quality impacts anddegradation (keep roads away from anddisconnected from water courses), as well asimproving or maintaining water qualitystandards (Figure 3.2) (Photo 3.2 and 3.9);

• Minimizing impacts on local plants and animals,both directly and indirectly;

• Ability to provide sufficient long-term roadmaintenance;

• Ability to have knowledgeable technicalpersonnel as well as good, locally experiencedindividuals involved in road projects. Hiregood people. Assure that they have the workingtools available that they need to do the job;

• Identifying and avoiding problem areas such aslandslides, wet areas, poor soils, or excessivelysteep grades.

Indicators and Watershed Assessment forProblematic Roads

How do we decide when a road is creatingor likely to cause problems? Today’s road managersare frequently faced with additional expectations

“Assess the long term impacts and benefits of a road.”


from society compared to thoseunder which many low volume roadswere originally constructed.Concerns about water quality,connectivity of roads and streams,endangered species, wildlife mortalityand impacts, land use, and watershedand ecosystem health, are allinfluencing the way roads are viewedand managed. These concerns, alongwith economic concerns anddwindling budgets for maintaining lowvolume roads, are pressing roadmanagers to better assess roadconditions and impacts. They are nowmaking reassessments about theirroad maintenance levels, designrequirements, closure options, andstorm-proofing methods.

Indicators are simple, tangiblefacts or conditions that can showprogress towards goals or impacts.They can highlight trends, a need foradditional studies, managementopportunities, or needed design andconstruction modifications. The goalsof assessment are to look forindicators and determine the impactsof roads on water, land, people, andrelated resources by reviewing roadsystems at the watershed orlandscape scale.

The following issues should beconsidered:

• Slope position and risk of slopefailure. Is there a risk of road orslope failure (and subsequentdelivery of sediments to streamsand sensitive resources) due tolocation of a road on an unstableor saturated hillslope, canyon, orvalley bottom floodplain location?

• Risk of road-stream crossingfailure. Does the road crossing

Figure 3.1Figure 3.1Figure 3.1Figure 3.1Figure 3.1 Planned and Unplanned growth along a road. Considerthe long-term impact and consequences of road development.(Adapted from Citizens for Responsible Planning)

3.1a3.1a3.1a3.1a3.1a A low-volume road can become........

3.1b3.1b3.1b3.1b3.1b ....................a small road in a town after many years.....................

3.1c3.1c3.1c3.1c3.1c ..................and eventually become an overcrowded street in a city.


structure have adequate capacityfor the site and adequatestreambank protection?

• Stream channel proximity andsediment delivery to waterbodies and riparian areas(Photo 3.9). Is the road toonear a stream and are road-related sediments beingdelivered to wetlands, lakes, andstreams?

• Groundwater and surfacewater regimes. Do roadsintercept groundwater orinterfere with direction, seasonalvariation, or the amount ofground or surface water flows?

• Wildlife, fisheries, andaquatic habitats. What are theimpacts of roads on fish andwildlife, migration routes, habitatfragmentation, and particularlysensitive species and theirhabitats, at both local and

PPPPPhotohotohotohotohoto 3.13.13.13.13.1 A low-volume, local road, with minimum adverseenvironmental impact, that serves local users by providing accessbetween communities.

FFFFFigureigureigureigureigure 3.2 3.2 3.2 3.2 3.2 The many ways roads can be “connected” to streams andcontribute sediment. Keep roads away from streams to protect waterquality as well as reduce road maintenance and damage. (Adaptedfrom M. Furniss, 1991)

landscape scales?

• Human disturbance. Is the roadnetwork responsible forpoaching, dumping, off road

vehicle use, illegal occupationand collecting, or pollution?

•Road density. Is the road systemtoo big, inefficient, or wastingvaluable land that has other, betteruses?

• Exotic species. Is the roadnetwork responsible for theintroduction and spread of exotic,non-native plants and animals?

A “yes” answer to any of thequestions above can indicate the needfor a more detailed assessment ofexisting or potential roads impacts.Additional information onassessments can be found inreferences such as the USDA’s,Forest Service Roads Analysis,1999, or the EnvironmentalProtection Agency’s NationalManagement Measures to ControlNonpoint Source Pollution, Draft2001.

Road cutfailure

Landslide debrisinto drainage

Erosion from road surface

Stream

Sedimentplumes

Naturaldrainage

Fillslumpintostream

— Roadway —


PPPPPhotohotohotohotohoto 3.33.33.33.33.3 A poorly located road, in the hazardous flood plain area ofa river, that has washed out during a major storm event.

Reducing Vulnerability of Roadsto Natural Disasters

Natural disasters such as majorstorms or earthquakes can have amajor impact on all aspects of life andon infrastructure. When transportationsystems are needed the most theymay not be functional. Roads that are

damaged or closed during naturaldisasters often compound the effectsof the disaster.

An assessment of the vulnerabilityof planned or existing roads shouldbe made, considering the factorslisted below, as well as social and

physical factors that affect theselection or priority of a project.Social factors include localcommunity support and identifiedneed of a project, the ability to dolong-term maintenance, andcontributing agencies orcommunities. Physical factorsinclude avoiding problematic areas,feasibility of repairs orreconstruction, traffic use andstandard of the road, and cost. Anassessment is useful to identify andminimize problems and ideally reducethe potential impact to roads fromdisasters before they occur!

Many planning and design factorscan be used to reduce the vulnerabilityof roads to natural disasters, or, inother words, used to “storm-proof”or limit the damage to roads duringdisasters or catastrophic events.PIARC World Roads Association’sNatural Disaster Reduction forRoads, 1999, provides excellentinformation on the topic. Some keyconsiderations applicable to low-volume roads include the following:

• Identify areas of historic orpotential vulnerability, such asgeologically unstable materials orareas, areas subject to flooding,or areas with high volcanic orseismic hazards.

• Avoid problematic areas and roadlocations in areas of high naturalhazard risk, such as landslides,rock-fall areas, steep slopes(over 60-70%), wet areas, andsaturated soils.

• Avoid or minimize construction innarrow canyon bottoms or onflood plains of rivers that willinevitably be inundated duringmajor storm events (Photo 3.3).

PPPPPhotohotohotohotohoto 3.23.23.23.23.2 A poor road location where the road has become a “creek”and is hydrologically “connected” to streams around it.


PPPPPhotohotohotohotohoto 3.4 3.4 3.4 3.4 3.4 A road that has been heavily damaged during a stormbecause of an undersized, plugged culvert pipe and no overflowprotection.

• Provide good roadway surfacedrainage and rolling road gradesso that water is dispersed off theroad frequently and waterconcentration is minimized.

• Minimize changes to naturaldrainage patterns and crossingsto drainages. Drainage crossingsare expensive and potentiallyproblematic, so they must be welldesigned. Changes to naturaldrainage patterns or channelsoften result in environmentaldamage or failures.

• Out slope roads wheneverpractical and use rolling dip crossdrains for surface drainage ratherthan a system of ditches andculverts that require moremaintenance and can easily plugduring major storm events(Photo 3.4).

• Use simple fords or vented low-water crossings (vented fords) forsmall or low-flow streamcrossings instead of culvert pipesthat are more susceptible toplugging and failure. With fords,protect the entire wettedperimeter of the structure,protect the downstream edge ofthe structure against scour, andprovide for fish passage whereneeded.

• Perform scheduled maintenanceto be prepared for storms. Ensurethat culverts have their maximumcapacity, that ditches arearmored and cleaned (Photo3.5), and that channels are freeof debris and brush than can plugstructures. Keep the roadwaysurface shaped to disperse waterrapidly and avoid areas of waterconcentration.

• Keep cut and fill slopes as flat aspossible and well covered(stabilized) with vegetation tominimize slumping as well asminimize surface erosion.However, near-vertical slopesthat minimize the exposed surfacearea may best resist surfaceerosion for well-cemented buthighly erosive soils.

• Use deep-rooted vegetation forbiotechnical stabilization onslopes. Use a mixture of goodground cover plus deep-rootedvegetation, preferably with anative species, to minimize massinstability as well as offer surfaceerosion control protection.

PPPPPhotohotohotohotohoto 3.5 3.5 3.5 3.5 3.5 Maintain roads and drainage features to withstand majorstorm events with minimum erosion, such as with armored ditches thatare kept clean.


• Locate bridges and otherhydraulic structures on narrowsections of rivers and in areas ofbedrock where possible. Avoidfine, deep alluvial deposits (e.g.,fine sand and silt) that are scoursusceptible and problematic orthat otherwise require costlyfoundations. Avoid mid-channelpiers.

• Design critical bridges andculverts with armored overflowareas near the structure towithstand overtopping, or thathave a controlled “failure” pointthat is easy to repair.Alternatively, over-size thestructure and allow for extra

FFFFFigurigurigurigurigure 3.3e 3.3e 3.3e 3.3e 3.3 Streamside Managment Zone (SMZ) Activities

freeboard on bridges to maximizecapacity and minimize risk ofplugging. Also avoid constrictingthe natural channel.

• Ensure that structural designs forbridges, retaining walls, and othercritical structures includeappropriate seismic designcriteria and have goodfoundations to prevent failuresduring earthquakes.

• Place retaining structures,foundations, and slopestabilization measures intobedrock or firm, in-place materialwith good bearing capacity tominimize undermining and

foundation failure, rather thanplacing these structures onshallow colluvial soil or on loosefill material.

Streamside Management ZonesStreamside Management Zones

(SMZs), or riparian reserves, arethose areas adjacent to naturalstreams and rivers that require specialconsideration during construction orforestry operations. These SMZs areimportant zones for protecting waterquality by serving as buffer zones tofilter sedimentation that may occurfrom road construction and otherland disturbance activities such aslogging or quarry development.

Bridge crosses streamat right angle

Small Landing

Stream

SMZ

Construct skid roadswith rolling grades

and dips(15% Max Grade)

SMZ

Winch logs from the SMZ. Construct small safe, efficient landing. Minimize activities in the SMZ.Keep landings and skid roads out of the SMZ.


FFFFFigurigurigurigurigure 3.4e 3.4e 3.4e 3.4e 3.4 Streamside Managment Zone (SMZ) Widths as a Function of Slope. (See Table 3.1)

SMZ10 m

(minimum)

SMZ

30 m

(minimum)

Activities

50% Slope

Activities

10% Slope

SMZ

SMZ

Streamside Management Zone

Activities may not need to beeliminated in SMZs, but they shouldbe minimized and modified to ensurethat stream channels and streambanks are protected fromdisturbance, as seen in Figure 3.3.The width of the SMZ will vary withthe natural ground slope on each sideof the stream and with the erosionpotential of the soil (Figure 3.4).Steeper ground slopes will increasethe possibility of sediment reachingthe stream. Table 3.1 gives arecommended minimum width of the


Recommended Minimum Widths for SMZs

*Slope DistanceGround Slope Width of SMZ0 - 20 % 10 m21 - 40 % 20 m41 - 60 % 30 m60% + 40 m

*Note-The indicated slope distances should be roughly doubled in areaswith highly erosive soils, areas with bare ground or minimal groundcover, areas of intense rainfall, and near sensitive streams with fish.

Road


SMZ. The actual width of the SMZshould be determined by the local landmanager or an Interdisciplinary Team.The decision should be based uponlocal laws and regulations, as well asslope angle, soil type, vegetativecover, and sensitivity of the area(Photo 3.6).

Timber HarvestingTimber harvesting activities

should be accomplished in a mannerthat will insure the long-termprotection of water quality. Timberharvesting requires access roads andlandings in order to move forestproducts to markets. Different typesof harvest systems require differentroad standards and road spacing to

PPPPPhotohotohotohotohoto 3.6 3.6 3.6 3.6 3.6 Select the width of the Streamside Management Zone(SMZ) in accordance with the natural ground slope, amount ofvegetation, and soil type. Minimize activities and disturbances in theSMZ.

PRACTICESTO AVOID

• Getting constructiondebris in lakes and streams.

• Using mechanizedequipment within the SMZ.

• Road or landingconstruction within theSMZ.

• Contaminating forest soilswith fuel and oils.

• Cutting trees that shade thestream and cool the water.

RECOMMENDED PRACTICES

• Locate landings to avoidskidding patterns thatconcentrate water from theskid roads onto the landingor off the landing into localstreams.

• Maintain landings prior toand during periods of wetweather to avoid erosionproblems.

• During and after operationsare completed, rehabilitatelandings and access roadswith water diversion structuresand erosion control measures.

• Plan landings and accessroads as part of pre-harvestactivities.

• Limit the number of landingsand constructed access roads.

• Keep landings small,consistent with a safe andefficient operation (Photo3.7).

• Locate landings outside theSMZ (Figure 3.3).

• Construct landings withenough slope to drainproperly but not exceed 5percent.


be efficient. Generally speaking,roads and landings (not skidding andhauling operations) have the greatestpotential for impacting water quality.When care is taken, erosion andsedimentation can be minimized.

Road SpacingTotal harvesting efficiency is a

combination of logging costs androad costs. Animal logging iseffective at very short skiddingdistances and requires a densenetwork of roads and landings,whereas helicopter logging can beeffective at much greater distancesand thereby uses a much widerspacing of roads and landings.

Road StandardsThe type of harvest system used

determines the size and location offorest roads. Generally, the type ofhaul vehicle determines the roadstandards of width, surfacing,alignment, grade, and position on theslope. In some cases, a large piece

of harvesting equipment such as a cableyarder may require special roadstandard considerations. The size andlocation of landings are alsodetermined by the type of harvestsystem as well as other factors suchas volume and type of product. Highproduction systems will require larger,better stabilized, and more protected

PPPPPhotohotohotohotohoto 3.73.73.73.73.7 Locate logging roads and landings away from SMZ’s andwater courses. Keep the roads and landing areas small and efficient.

PPPPPhotohotohotohotohoto 3.83.83.83.83.8 Stabilize skid roads and trails after use with water bars andapply a ground cover or other erosion control measures.

landings than will low productionsystems. Larger landings and higherproduction systems have greaterpotential to cause water qualityimpacts.

Log LandingsLog landings should be located

so that soil movement from thelanding and skidding operations isminimized both during and afterlogging operations. Erosion controlmeasures should be planned toeffectively stabilize the landing usinggrading to control water flow, waterbars, and revegetation or otherground cover.

Skid Roads and Skid TrailsSkidding should be conducted

in such a way that soil disturbanceis minimized. Skid trails andconstructed skid roads can be amajor impact to soil and waterresources. Care and attention mustbe given to skid roads just as withtruck roads, and the same BestManagement Practices apply forthese types of roads.


RECOMMENDED PRACTICES PRACTICESTO AVOID

• Contaminating forest soils withfuel and oils.

• Locating landings and skidroads within the SMZ.

• Using stream channels asskid trails.

• Constructing skid roads onsteep slopes or with steeproad grades.

• Operating skiddingequipment within the SMZ.

• Logging and constructionoperations during wetweather.

• Design and locate main skidroads and trails beforelogging operations begin.

• Design and locate skid roads tofollow the contour of the naturalterrain.

• Winch logs from the SMZ orareas of steep slopes to avoidequipment movement in thisarea.

• Locate skid roads and trails insuch a way that water fromthe skid trail is notconcentrated into the loglanding or into creeks (Photo3.9).

• Cross natural drainages atright angles with skid roads.

• Construct skid roads withrolling grades and breaks ingrade.

• Stabilize skid roads andtrails with water bars andcover the bare ground withlogging slash afteroperations cease tominimize erosion fromexposed soils (Photo 3.8).

• Construct skid roads ongrades of 15% or lessexcept for short distances(20 meters) where 30%pitches (grades) areacceptable.

• Decommission or close skidroads after timber removaloperations.

Photo 3.9 Photo 3.9 Photo 3.9 Photo 3.9 Photo 3.9 Locate logging andother roads away from streamsand lakes. This road is too closeand thus is hydrologically “con-nected” to the stream. Sedimentfrom the road will likely reach thestream.


Chapter 4

Low-VLow-VLow-VLow-VLow-Volume Rolume Rolume Rolume Rolume Roads Engineeringoads Engineeringoads Engineeringoads Engineeringoads Engineering

ALOW VOLUME ROAD is considered a roadthat has relatively low use (an AverageDaily Traffic of less than 400 vehicles per day),

low design speeds (typically less than 80 kph), andcorresponding geometry. Most roads in rural areas arelow-volume roads. A well planned, located, designed,constructed, and maintained low-volume road systemis essential for community development, flow of goodsand services between communities, and resourcemanagement activities. However roads, and particularlyroad construction, can create more soil erosion thanmost other activities that occur in rural areas. Properplanning and design of the road system will minimizeadverse impacts to water quality. Poorly planned roadsystems can have high maintenance and repair costs,contribute to excessive erosion, and fail to meet the needsof the users.

It is very important from the outset to locateroads on stable ground, on moderate slopes, in dryareas away from drainages, and away from otherproblematic and difficult areas. Avoiding problemareas can save major design, construction, andmaintenance costs and can minimize manyundesirable impacts.

For a road project to be successful, each step ofthe road management process must be performed.

“You get what you Inspect, not what you Expect.”

Chapter 4

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The basic steps are:PlanningLocationSurveyDesign

ConstructionMaintenance

If any one of these steps is omitted, a road mayperform poorly, not meet its expectations, failprematurely, require unnecessarily high maintenance, orcause environmental impacts. Without planning andgood location, a road may not adequately serve its usersor may be in a problematic area. Survey and design areneeded to fit the road to the ground and have it functionproperly. Good construction insures that the design isimplemented and built with some degree of qualitycontrol. Maintenance is needed to keep the surfacedrivable and the drainages functioning. Finally, a badroad may need to be reconstructed or closed(decommissioned) to eliminate unacceptable problems.

Road PlanningRoad planning and analysis are key to ensuring that

a road meets the current needs of the users, that it is notoverbuilt, that it minimizes impacts to the environmentand to the people along the road, and that it considersfuture needs of an area. Road Management Objectives(RMOs) help define and document the road purpose,


standards, and how a road will beused, managed, maintained, andfunded, as well as applicable BMPsfor the road.

Some key Best Management Practices for road design and constructioninclude the following:

• Minimizing road width and area of disturbance;

• Avoiding alteration of natural drainage patterns;

• Providing adequate surface drainage;

• Avoiding steep ground with slopes over 60 percent;

• Avoiding problems such as wet and unstable areas;

• Maintaining an adequate distance or separation fromcreeks and minimizing the number of drainagecrossings;

• Minimizing the number of “connections” betweenroads and water courses, and minimizing “diversionpotential”;

• Designing creek and river crossings with adequatecapacity and bank erosion protection and allowingfor fish passage at all stages of life;

• Avoiding constriction of the active (bankfull width)stream channel;

• Having a stable, structurally sound road surface;

• Installing subsurface drainage where needed;

• Reducing erosion by providing vegetative orphysical ground cover on cuts, fills, drainage outlets,and any exposed or disturbed areas;

• Using stable cut and fill slope angles;

• Using slope stabilization measures, structures, anddrainage as needed;

• Applying special techniques when crossingmeadows, riparian areas, and when controllinggullies;

• Providing thorough, periodic road maintenance; and

• Closing or obliterating roads when not in use or whenthey are no longer needed.


Planning

• Do road transportationanalysis to determine theoptimum road system for anarea, user needs, and toevaluate future options.

• Keep minimum roadstandards consistent with userdemands, needs, RoadManagement Objectives, andpublic safety.

• Use an Interdisciplinary Teamapproach to road planning,and coordinate developmentwith local landowners.

• Use topographic maps, aerialphotos, and soils information.for planning the optimumroute.

• Consider both short-term andlong-term access needs of theroad users.

• Limit the total area disturbedby minimizing the number,width, and length of roads.

• Use existing roads only if theyserve the long-term needs ofthe area and can bereconstructed to provideadequate drainage and safety.

• Minimize the number ofstream crossings.

BEST MANAGEMENTPRACTICES


Road LocationRoad location is key to ensuring

that a road is placed in a desirablearea, that it avoids problematicfeatures or areas where constructionis very expensive, that it bestaccesses areas where the road isneeded, and that it minimizes thedriving distance betweendestinations. Flag or mark theproposed road location on theground to ensure that it meets theroad design criteria (Photo 4.1).

It is much better to havea bad road in a good locationthan it is to have a good roadin a bad location. A bad roadcan be fixed. A bad location

cannot. Most of theinvestment in the bad roadcan be recovered, but little,

if any, can be recoveredfrom a bad location!

Road Survey, Design, andConstruction

Road survey, design, andconstruction are the steps in theprocess where road user needs arecombined with geometric factors andterrain features, and the road is builton the ground. A road or site surveyis needed to identify the terrainfeatures, such as drainages,outcrops, and ground slopes, and toadd some level of geometric controlto a project. A survey may be verysimple and accomplished withcompass and cloth tape for a ruralroad, or it may be very detailed usinginstruments and a high level ofprecision in difficult terrain or for ahigh standard road.

RECOMMENDED PRACTICESLocation• Use topographic control

points and physical featuresto control or dictate theideal location of a road. Usesaddles in the terrain, followridges, and avoid rockoutcrops, steep slopes,stream crossings, etc.

• Locate roads to avoid orminimize adverse affects onwater quality and outsideof riparian areas and SMZsexcept at stream crossings.Approach stream crossingsat the least gradientpossible.

• Locate roads high on thetopography to avoid steepinner canyon slopes andprovide for more distancebetween the road andstreams.

• Locate roads on well-drained soils and slopes

where drainage will moveaway from the road.

• Locate roads to follow thenatural terrain byconforming to the ground,rolling the grade, andminimizing cuts and fills(Figure 2.1 and Figure4.1, Photo 4.2).

• Locate roads, switchbacksand landings on benchareas and relatively flatterrain.

• Avoid problematiclocations such as springs,wet areas, landslides, steepslopes, massive rockoutcrops, flood plains, andhighly erosive soils.

• Avoid very steep terrain(over 60%) and very flatterrain where drainage isdifficult to control.

Photo 4.1Photo 4.1Photo 4.1Photo 4.1Photo 4.1 Plan and locate roads using topographic control pointsand natural ground features. Verify road location and alignment onthe ground!


Elements of design includeroadway geometry, design speed,drainage, stream crossing structures,slope stabilization needs, structuralsections (materials type, use, andthickness), and road grades (Table4.1). Construction involves allaspects of implementation of thedesign and fitting the project to theground. A key link between designand construction are the use ofstandard plans and drawings thatshow how the work should look,and specifications that describehow the work is to be done.Another key part of construction isquality control and inspection toensure that the work is done in

FFFFFigurigurigurigurigure 4.1e 4.1e 4.1e 4.1e 4.1 The affects of road alignment across topography.

a. Cutting across topography causes excessive earthwork with large cuts and fills.

b. Conforming to topography minimizes earth work.

Plan view of aroad plotted on atopographic map

Perspective viewof a road seenon the ground

Photo 4.2Photo 4.2Photo 4.2Photo 4.2Photo 4.2 Locate roads to con-form to the natural terrain and rollthe road grades to dispersesurface water frequently.

accordance with the plans andspecifications. Some amount ofsampling and testing is typicallyspecified to ensure that the materialsused in construction meetspecifications.

Remember --You get what you Inspect,

not what you Expect.


RECOMMENDED PRACTICES General Design

• Use minimum RoadStandards needed forsafety and traffic use(Table 4.1).

• Use Standard Plans andSpecifications, withStandard Drawings, formost typical constructionwork. Develop SpecialProject Specifications andDrawings for unique typesof work.

• Remove merchantabletimber from the road right-of-way before excavation.Deck the material in adesignated area.

• In community and urbanareas, build footpathsalong the road for thesafety of people walkingalong the road. Useroadway surfacing andspeed bumps to controldust and traffic speed.

• Construct roads withgrades of 12% of less,using short sections of15% where necessary. Onsteep roads, drainage isdifficult to control (Photo4.3)!

• Construct the road onlywide enough to safely passthe traffic, normally 3.5 to4.5 meters wide for single-lane roads and 5 to 7meters for double-laneroads. Add turnouts asneeded. Minimize the area ofclearing.

• Locate roads with aminimum curve radius of 15meters.

Materials• Compact the road

embankments, subgradematerial, and surfacingmaterials, particularly insensitive areas (Photo 4.4),or allow new roads to“settle” for several weeksbefore using the road. In wetclimates a longer period oftime is desirable.

• Use road surfacestabilization measures, likeaggregate or pavements,where needed and as often aspossible (Photo 4.5). Utilizedurable materials that willnot degrade to finesediments under traffic.

• Dispose of unsuitable orexcess excavation material inlocations that will minimizewater quality or otheradverse resource impacts.

• Establish minimum samplingand testing requirementsand schedule for qualitycontrol of materials.

Slopes• Typically construct cut

slopes on a 3/4:1 or flatterslope. Build fill slopes on a1½:1 or flatter slope.Revegetate the slopes.

• Typically use balanced cut-and-fill construction ingentle terrain. Use full-bench

construction on slopesover 65 % and end haulthe excavated material to asuitable disposal site.

• In very steep terrain buildnarrow roads (3-4 meterswide) with turnouts, or useretaining walls as needed.End-haul most excavatedmaterial to stable disposalsites. Avoid side-casting.

Drainage• Outslope road surface 3-

5% for road grades lessthan 10% on stable soils,using rolling dips for cross-drainage structures. Inslippery soils, either inslopethe road or add aggregatesurfacing to the road.

• Construct ditches onlywhen necessary. Anoutsloped road withoutditches disturbs lessground and is lessexpensive to construct.

• Inslope road surface 3-5%with a ditch section forroad grades in excess of10% or in areas with steepnatural slopes, erodible orslippery soils, or on sharpturns. Provide crossdrainage with culvert pipesor rolling dips.

• Use a crown road sectionon a wide road with gentleslopes or flat ground toprevent water fromstanding on the roadsurface (see Figure 7.1).


Road CostsRoad construction costs are

most influenced by the standard ofroad built, particularly road widthand type of surfacing, and thesteepness of the terrain. Placing a

RECOMMENDED PRACTICES (cont.)Drainage (cont.)• Construct roads withrolling grades to minimizeconcentration of water.

• Provide filter strips orinfiltration areas to trapsediment between drainoutlets and waterways. Keeproads and streamsdisconnected!

• Use appropriate type andadequately sized drainagestructures for natural streamcrossings. Design bridgesand culverts that are largeenough to span the ordinaryhigh water width of flow(bankfull width). Usearmoring, headwalls, and trashracks as necessary toprotect the structure (Photo4.6).

• Divert water and streamflows around construction •areas as needed to keep theconstruction site dry andavoid water qualitydegradation. Restore naturalchannels as soon as possibleafter construction.

Erosion Control• Remove windrow slash,

tops, tree trunks and stumps

from the right-of-way atthe toe of the fill slopebefore excavation forerosion control (Figure 4.2).The quantity of material maybe limited for fire hazard.

• Require a final ErosionControl Plan and interimerosion control measuresduring seasonal shutdowns.Stabilize all disturbed areas,work areas, and temporaryroads. Include typicaldrawings for sediment traps,brush barriers, silt fences,biotechnical structures, and soon.

Miscellaneous• Develop dependable local

water sources for projectconstruction and maintenanceneeds where possible.Construct a well located,durable, stabilized site that willprotect water quality andaquatic life. The timing andamount of water withdrawalmay require control.

• Use constructiontechniques that are the mostappropriate and costeffective for the projectand geographic area, usingeither equipment or handlabor (Photo 4.7).

• Use best availableappropriate technologies,such as GlobalPositioning Systems (GPS),personal computerprograms, geotextiles,biotechnical erosioncontrol measures,Mechanically StabilizedEarth (MSE) retainingstructures, and soilstabilization materials whereapplicable.

• Minimize earthworkactivities when soils arevery wet or very dry orbefore oncoming storms.Time road constructionactivity and road use forthe milder, drier seasonswhere possible (Photo4.8).

• Use traffic control devicesas necessary to providesafety for constructionpersonnel and road users.

• Visit the field during boththe design and constructionphases of a project. Ensurethat you have adequateinspectors, vehicles andquality control testing tosee that the job is builtcorrectly.

road with cuts and fills on steepcross slopes greatly increases thetime of construction, the amount ofexcavation and earthwork, theareas of clearing and neededrevegetation, and adds length to

cross-drains and other drainagestructures. Figure 4.3 shows thedifference in quantities for roadconstruction on a 10 percent sideslope versus a 50 percent slope.Table 4.2 presents those typical


quantities for the major road workitems. Ideal construction is in terrainwith cross-slopes in the range of 25to 35 percent.

Road cost estimates areimportant in both the planningprocess and the overall projectbudgets to ensure that adequatefunds are available to properly buildthe road. Good design andconstruction techniques requirerelatively high initial costs but cangreatly reduce future maintenanceneeds and avoid costly failures,repairs, and adverse environmentalimpacts.

Design Element Rural Access Road Collector Road

Design Speed 25-35 kph 45-60 kphRoad Width 3.5-4.5 m 4-5.5 mRoad Grade 15% max. 12% max.Curve Radius 15 m min. 25 m min.Crown/Shape outslope/inslope in/outslope or

(5%) crown (5%)gravel, cobble-

Surfacing Type native or gravel stone orpavement


TYPICAL LOW-VOLUME ROADDESIGN STANDARDS

Photo 4.3Photo 4.3Photo 4.3Photo 4.3Photo 4.3 Avoid constructing roads with steep grades or on steepside slopes. It is difficult to control drainage with steep road grades.

Photo 4.4 Photo 4.4 Photo 4.4 Photo 4.4 Photo 4.4 Compact the roadway surface and fill material when theroad is located near streams or in areas with erosive soils.

KEY COST FACTORS• Steep side slopes

(particularly with wideroads) rapidly increase thequanities of work, includingthe area involved forclearing and revegetatation,and the amount of excavatedmaterial. Thus, steep slopesgreatly increase the cost ofconstruction (see Figure 4.3and Table 4.2)!

• High standard surfacingmaterials (aggregate,asphalt, etc.) greatly increaseroad cost -- but also greatlyimprove user comfort andreduce road surface erosion.

• Frequent or large numbersof drainage (stream)crossings greatly increaseroad costs -- but must beused as needed, particularly indissected terrain.

• Steep grades increaselong-term maintenance costsof the road.


Photo 4.5Photo 4.5Photo 4.5Photo 4.5Photo 4.5 A stable logging road with aggregatesurfacing. Use road surfacing materials as fre-quently as possible to reduce erosion and improvethe roadbed structural support and rider comfort.

Photo 4.6Photo 4.6Photo 4.6Photo 4.6Photo 4.6 A well designed and installed culvertwith head walls for efficiency and fill protection.

FFFFFigurigurigurigurigure 4.2e 4.2e 4.2e 4.2e 4.2 Windrow construction slash at the toe of the fill slope forerosion control. Place the slash before excavation begins. Do notDo notDo notDo notDo notbury the slash ininininin the fill.

Photo 4.7Photo 4.7Photo 4.7Photo 4.7Photo 4.7 Use the road construction techniques that are mostappropriate and cost-effective for the job and geographic area.Hand labor versus equipment depends on labor costs, equipmentavailability, and production rates.

Small limbs andclearing slash mashedinto the ground at thetoe of the fill

fill

cut

Road underconstruction


PRACTICES TOAVOID

General Design• Road construction on steep

side slopes.

• Side-casting material oncross-slopes steeper than50 to 60 %.

• Burying stumps, logs, slash,or organic debris in the fillmaterial or in the roadprism.

• Construction and resourceextraction activities duringperiods of wet weather(see Photo 4.8).

• Steep road grades (over12-15%). Water becomesvery difficult to control.

• Vertical cut slopes,particularly on roads withinside ditches.

• Very flat areas (wheredrainage cannot becontrolled).

• Locating roads withinflood plains, riparian areas,wetlands, or the SMZ(except at crossings).

• Wet and spring areas, land-slide areas, and large rockoutcrops.

• Construction projects withinsufficient funds forproper design, construction,inspection, and futuremaintenance. Considerbuilding fewer kilometers ofroad, and building them well.

Figure 4.3 Road quantity variation with ground slope.

TYPICAL QUANTITIES OF WORK & MATERIALS FORROAD CONSTRUCTION IN TERRAIN WITH GENTLE

AND STEEP SLOPES (FOR A 4.5 M WIDE ROAD)

Work Item 10% Side Slope 50% Side Slope

Clearing 0.62 ha/km 0.95 ha/km

Excavation 237 m3/km 2220 m3/km

Revegetation 0.10 ha/km 0.89 ha/km(cut & fill slopes)

Culvert length 8 m 22 m(natural channel)

Culvert length 6 m 11 m(ditch relief crossdrain)


Revegetation

Clearing

ExcavationRoadwayRevegetation

Culvert Length + 1m

C10%

Sideslope

L

Clearing

Reveg

etatio

n

Reve

geta

tion

Roadway

Excavation

fill

C50%

Sideslope

L

Cross-Drain Culvert Length + 1m


Road MaintenanceRural roads must be maintained

during active use, after periodicoperations have been completed,and after major storm events, toensure that the drainage structuresare functioning properly. Heavyrainstorms will cause cut slopefailures that block ditches, causewater flow on the road surface, anderode the surface and fill slopes (seeFigure 4.4). Debris moves downnatural channels during heavy rainsand blocks drainage structures,causing water to overtop the roadand erode the fill. Ruts, washboards,and potholes in the road surface willpond water, weaken the roadwaystructural section, accelerate surfacedamage, and make driving difficult,as shown in Figure 4.5. Routinemaintenance is needed on any roadto keep the road serviceable and itsdrainage system working properly.A well-maintained road will reduceroad user costs, prevent roaddamage, and minimize sedimentproduction.

How road maintenance will beaccomplished should be resolvedbefore the road is built orreconstructed. Maintenance workcan be accomplished either bystate or local agency personnel, bycontractors, or by localcommunity groups. Funding formaintenance may be allocateddirectly from agency funds, fromlocal or gas taxes, from road userfees, or from donated local labor byinterested road users.

Maintenance items that should be performed routinely include:

• Grading and shaping the roadway surface to maintain a distinctinsloped, outsloped, or crown shape to move water rapidly offthe road surface.

• Compacting the graded roadway surface to keep a hard drivingsurface and prevent the loss of fines. Replace surfacing materialwhen needed. Keep the road surface moist!

• Removing ruts through rolling dips and water bars. Reshape thestructures to function properly.

• Cleaning ditches and reshaping them when necessary to haveadequate flow capacity. Do not grade ditches that do not need it!

• Removing debris from the entrance of culverts to prevent pluggingand overtopping. Check for damage and signs of piping or scour.

• Replacing/repairing rock armor, concrete, or vegetation used forslope protection, scour protection, or energy dissipation.

• Trimming roadside vegetation (brushing) adequately, but notexcessively, for sight distance and traffic safety.

• Replacing missing or damaged road information, safety, andregulatory signs.

Key Road Maintenance Items

Photo 4.8Photo 4.8Photo 4.8Photo 4.8Photo 4.8 Avoid construction and other road activities during wetperiods when possible. Alternatively, add drainage and surfacestabilization to the roadway in weak soil areas for all-weather use.



Maintenance• Perform maintenance when

needed. DO NOT WAIT! Thelonger you wait, the moredamage will occur and repairswill be more costly.

• Keep ditches and culverts freefrom debris, but maintain anerosion resistant surfacingsuch as grass or rock in theditches. Remove debrisduring inspections (Figure4.4, Photo 4.9). Also keepoverflow channels clean.

• Regrade and shape the roadsurface periodically tomaintain proper surfacedrainage (Photo 4.10). Keepthe road surface moist duringgrading. Fill in ruts andpotholes with gravel orcompacted fill as frequently as

possible (see Figure 4.5).Keep rolling dips shaped andgraded. Ideally, compact thefinal graded road surface.

• Keep the downhill side of theroad free from a berm exceptwhere a berm is intentionallyconstructed to control water ortraffic.

• Apply a surface stabilizationmaterial, such as aggregate,cobblestone, or pavement, tothe road surface to protect theroadbed from damage andreduce the frequency ofmaintenance needed.

• Avoid disturbing soil andvegetation if not necessary.Leave as much vegetation(grasses) in ditches, on roadshoulder areas, and on cut or fill

slopes (especially grasses andlow growing brush) as possible.However, ensure sight distanceand that the drainage systems stillfunction properly.

• Remove slide material from theroadway or inside ditches wherethe material will block normalroadway surface drainage(Photo 4.11).

• Avoid widening the road or over-steepening the fill slopes formedby blading surface material offthe road.

• Close the road during very wetconditions or periods ofinactivity.

• Inspect the road at regularintervals, especially followingperiods of heavy rains.

Figure 4.4Figure 4.4Figure 4.4Figure 4.4Figure 4.4 Road maintenance is needed to maintain roadwaysurface drainage patterns and remove slides that block ditchesand culvert inlets.


Road ClosureA road may be closed because

it is no longer needed, such as if aresource is depleted, if a communityhas moved, if it will not be used forsome period of time, or if the roadis causing unacceptably highmaintenance costs or environmentaldamage. Road closure ofteninvolves input from the public andother affected road users. Basicroad closure options include thefollowing: temporary closure orblockage with gates, barricades orberms; permanent closure, ordecommissioning, where the roadsurface is stabilized and drainagestructures are removed, yet the roadtemplate is left on the terrain; or roadobliteration where the roadwayand drainage features are totallyremoved and the area is reshapedto its natural, pre-road condition.Figure 4.6 shows the range ofoptions commonly considered inroad closure.

If interim road use has beencompleted, such as after loggingor mining operations, roadsshould be temporarily closed ordecommissioned in order toprotect them from erosion duringthe period that they are not beingused. Temporarily closed roadsshould be blocked with a gate,barricade or berm to keep trafficoff the road but drainage crossingstructures should be maintained.The road surface should bereshaped for good drainage andstabilized with water bars andpossibly scarified, seeded andmulched. Permanent drainagestructures such as culverts andditches will require periodiccleaning. Use of road closuretechniques and routine

Potholes Ruts

Soft, muddy, roadway surface Rills and gullies

Implement road maintenancebefore significant surface damage occurs!

Photo 4.10Photo 4.10Photo 4.10Photo 4.10Photo 4.10 Use gradermaintenance to keepthe road surface prop-erly shaped anddrained.

Photo 4.9 Photo 4.9 Photo 4.9 Photo 4.9 Photo 4.9 Perform road maintenance, etiher with equipment or byhand, to keep the roadway shaped and drainage structures function-ing. Keep ditches clean but do not remove the layer of vegetative(grass) stabilization.

FFFFFigurigurigurigurigure 4.5e 4.5e 4.5e 4.5e 4.5 Signs of need for road maintenance. (Adapted fromPIARC Road Maintenance Handbook)


maintenance after operations arecompleted will protect the roadinvestment until it is needed in thefuture.

Permanent road closure(decommissioning) involvesblocking the road, removing alldrainage crossing structures andfill material, and stabilizing theroad surface. This is commonlyaccomplished by breaking up theroad surface (scarification), thenseeding and mulching, so that theroad will naturally be revegetatedover time (Photo 4.12). The costof this work is relativelyinexpensive, most environmentaldamage from the road is eliminated,and the basic roadbed shape is stillin place in case the road is everreopened in the future.

Road closure by obliterationis where the roadbed is totallyeliminated and the ground is restored

to its natural terrain shape. Alldrainage crossing materials areremoved, the ground is reshaped,natural drainage patterns arerestored, ideally includingsubsurface groundwater flowpatterns, and the area isrevegetated. It is particularlyimportant to remove all fill

material that has been placed intodrainages, such as the culvertbackfill material. These relativelyexpensive measures are ideally usedin sensitive areas such as parks orreserves, near recreation areas, ornear streams and lakes. Thesemeasures are very effective toremove all traces of a road and

e v e n t u a l l yrestore the areato a pre-roadnatural condition.H o w e v e r ,because of highcost, simpledecommissioningis typically mostcost-effective forroad closure, andthus is the mostcommonly usedclosure option.

Photo 4.11 Photo 4.11 Photo 4.11 Photo 4.11 Photo 4.11 Remove slide material that blocks the drainage ditchesand narrows the road.

Photo 4.12 Photo 4.12 Photo 4.12 Photo 4.12 Photo 4.12 Close roads that are not needed. Stabilize the surface with waterbars, berms, and ground cover such as grass seed and mulch.


a. Gate Closure (Temporary) b. Earth Mound or Berm Closure (Temporary)

c. Decommissioning - Permanent Road Closure with Surface Scarification and Seeding forRevegetation, but Keeping Most of Road Template (Shape).

d. Road Obliteration

Old, revegetatedroadway surface

(1) Road template beforeobliteration.

(2) During obliteration, oldroad is scarified and refilled.

(3) Final obliteration, withfilling and recontouring tothe original naturaltopography, followed byrevegetation.

1

2

3

FFFFFigurigurigurigurigure 4.6 e 4.6 e 4.6 e 4.6 e 4.6 Road closure options, including temporary closure (a,b), decommissioning (c), andfull road obliteration (d).


RECOMMENDED PRACTICESRoad Closure• Involve the affected population

or road users in decisionsregarding road closure,typically using aninterdisciplinary process.

• Temporarily close roads usinggates, barricades, or largeberms.

• Install water bars (See Chapter7, Drainage) on closed roadsto divert water off the roadsurface.

• Remove berms that mayimpede surface drainage onclosed roads.

• Decommission roads withclosure structures, drainagecontrol, and erosionprotection, but withoutrecontouring the roadtemplate, if future use of theroad is likely.

• Obliterate unneeded roadswhenever possible and wherecost-effective to provide thehighest degree of road removaland land reclamation.

• Remove all drainage andstream crossing structures inpermanently closed roads.

• Close roads by reshaping theroadbed to maintain naturalsurface drainage patterns andavoid concentration of water.

• Revegetate exposed soil onclosed roads. A commontreatment includesscarification, seeding, and amulch application to promotegrass and brush growth. Treesmay be planted. On grades,waterbars should be added.

PRACTICES TOAVOID

• Leaving drainage structureson closed (decommissionedor obliterated) roads.

• Neglecting temporarilyclosed roads.


The paved road (above) and gravel road (below) are rela-tively well located and designed low-impact roads since their

surfaces are armored and they conform to the terrain, thusdispersing water effectively and avoiding heavy earthwork.


Chapter 5

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DRAINAGE STRUCTURE SIZE should be based onsome reasonable design flow, as well as sitecharacteristics and environmental

considerations such as fisheries (Photo 5.1).Determining the correct or a reasonable design flow forany engineered drainage structure is critically important,both for the structure to perform properly and to preventfailures of structures. A reasonable design flow iscommonly based upon a stormevent that will have a recurrencefrequency (return interval) of 20to 100 years, depending ontype and value of the structureand local regulations. Anyculvert has a finite flow capacitythat should not be exceeded.Bridges also have a specificcapacity for the given cross-sectional area, but typically it islarge. Low-water crossingdesign is based upon estimatesof both low flows and peakflows for that specific drainage,but are less sensitive to flowestimates.

Most flow determinationmethods require that the

drainage area be defined or estimated. This work istypically accomplished by delineating the area of thewatershed on a topographic map (Figure 5.1). Ideally,topographic maps with a scale of 1:10,000 to 1:24,000should be used for drainage project design. However,the most detailed map commonly available in manycountries is a 1:50,000 scale, so that map should beused.

“Base drainage structure size on some rationalor statistical design process.”

Photo 5.1Photo 5.1Photo 5.1Photo 5.1Photo 5.1 Determine an adequate design storm flow at any site usingavailable, appropriate hydrological methods. Install drainage crossingstructures based upon design flows and other site characteristics.

Chapter 5

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be examined statistically and usedfor hydraulic design to determineflows at different return intervals.High water marks and measure-ments of the channel geometry canbe used in conjunction withManning’s Equation (see Chapter 6)to determine flow velocity and thusflow volume (discharge, or capac-ity) through the channel for that givenhigh-water level. A variety of meth-ods may be available to the designerto determine design flows. At leastsome analytical method should beused, and ideally, several methodsshould be used and compared togain confidence in your design flowvalues. Typical analysis methods forvarying sizes of watersheds areshown in Table 5.1.

Figure 5.1Figure 5.1Figure 5.1Figure 5.1Figure 5.1 Determine the drainage area of watersheds on a topographic map to helpdetermine appropriate flows for drainage structure design.

At a minimum, the RationalMethod, a rainfall based method,should be used to determine the dis-charge from small watersheds, witha drainage area of up to around 120hectares. The Talbot Method di-rectly uses the Rational Method andcan be useful in making a prelimi-nary estimate of the pipe size neededas a function of drainage area. How-ever, the Talbot Method does notconsider varying rainfall intensity orreturn interval, so the method is notprecise. Ideally, statistical methodsbased upon regression analysis ofregional stream flow data, or actuallocal stream flow data will be avail-able and can be used.

Large watersheds may havespecific gauging station data that can

Rational MethodThe Rational Method is com-

monly used for the determination offlows from small watersheds, and itcan be applied in most geographicareas. It is particularly useful if lo-cal stream flow data do not exist,and it can be used to make a roughestimate of flow from large water-sheds if other options do not exist.Thus, the Rational Formula is pre-sented and briefly explained on thenext page. More detailed informa-tion on its use is presented in refer-ences such as the Minimum ImpactLow-Volume Roads Manual or theFHWA Manual HDS4 - Introduc-tion to Highway Hydraulics.

Scale = 1: 50,000Area = 820 Hectares (8.2 km2)


THE RATIONAL FORMULATo determine flow volume... Q= Quantity of Flow (Runoff), in Cubic

Meters per Second (m3/s).

C= Runoff Coefficient. This coefficient is selectedto reflect the watershed characteristics, such

where: as topography, soil type, vegetation, and land use.

i= Average Rainfall Intensity for the selected frequencyand for a duration equal to the Time ofConcentration, in millimeters per hour.

A = Area of the watershed, in Hectares.

Runoff Coefficient (C) values are presented in Table 5.2. These values reflect the differing watershed char-acteristics that influence runoff. The designer must develop experience and use judgment to select theappropriate value of C within the range shown. Note that the value of C may change over the design lifeof the structure due to changes in land use such as a forest converted to agricultural land or from a fire in thewatershed. Flow quantity is directly proportional to the selection of this coefficient.

Area (A) is simply the area of the watershed that contributes runoff to the drainage crossing. Its boundaries gofrom drainage divide to drainage divide and down slope to the crossing. On a roadway surface, the"drainage area" is the cut slope and road surface area between cross-drains or leadoff ditches.

Rainfall intensity (i) is the third factor, and the one often most difficult to obtain. It is expressed as theaverage rainfall intensity in millimeters per hour (mm/hr) for a selected recurrence frequency and for aduration equal to the Time of Concentration of the watershed. At the beginning of a storm, runoff fromdistant parts of the watershed have not reached the discharge point (such as a culvert). Once water hasreached the discharge point from all parts of the watershed, a steady state flow will occur. The estimatedtime when water from all parts of the watershed reaches the discharge point is the Time of Concentration(TOC). TOC depends on the overland flow rate of water in that watershed. For very small watersheds,a minimum TOC of 5 minutes is recommended for finding the intensity used in determining design flows.TOC can be estimated by dividing the length of the runoff route by the average runoff velocity (usually 0.1[flat, wooded] to 1.0 m/s [steep, barren]).

Figure 5.2 shows a typical family of rainfall intensity-duration curves for a recurrence frequency of 2 to50 years. Such curves, developed from local rainfall data, should be located or generated when work-ing in any particular area. The typical maximum intensity values for a 25 to 50-year event for desertregions are around 75 to 100 mm/hr; some coastal and jungle, or tropical regions have maximumintensities from 200 to 400 mm/hr, or more; and most areas, including semi-arid regions, mountainforests, and coastal areas typically have values of 100 to 250 mm/hr. Because of the wide range ofvalues, and the amount of local variation that can occur around islands and mountains, local data isdesirable for project design work.

Q =CiA362



DESIGN FLOW ANALYSIS METHODS FORVARIOUS WATERSHED SIZES

Watershed Size Typical Type of Analysis

Small (to 120 ha) Rational Method, Talbot Method,(300 acres) Local Experience

Medium (to 4,000 ha) Regression Analysis, High Water(10,000 acres) Marks + Manning, Local Experience

Large (over 4,000 ha) Gauging Data, High Water Marks,Statistical or Regression Analysis

Land Use or Type “C” Value

AgricultureBare Soil 0.20-0.60Cultivated Fields (sandy soil) 0.20-0.40Cultivated Fields (clay soil) 0.30-0.50

GrassTurf, Meadows 0.10-0.40Steep Grassed Areas 0.50-0.70

Woodland/ForestWooded Areas with Level Ground 0.05-0.25Forested Areas with Steep Slopes 0.15-0.40Bare Areas, Steep and Rocky 0.50-0.90

RoadsAsphalt Pavement 0.80-0.90Cobblestone or Concrete Pavement 0.60-0.85Gravel Surface 0.40-0.80Native Soil Surface 0.30-0.80

Urban AreasResidential, Flat 0.40-0.55Residential, Moderately Steep 0.50-0.65Commercial or Downtown 0.70-0.95

RATIONAL METHODVALUES OF “C”



• Use the best available hydro-logic methods to determinedesign flows.

• Where appropriate, usedrainage structures that are notsensitive to exact flow predic-tions, such as low watercrossings (fords) and drivabledips versus culvert pipes.

• Add freeboard or extracapacity to structures indrainages with uncertain flowor for debris passage inwatersheds with changing landuses, usually on the order of120% to 150%.

• To minimize risk to structures,the recommended stormfrequency (return period) fordesign of culverts is 20 to 50years, and 100 to 200 years isrecommended for bridges ordrainages with sensitiveenvironmental concerns.

• For culverts installed in areaswith limited or inadequatehydrologic data or designs,include overflow (overtopping)protection to reduce risk oftotal failure or stream diversion(see Figure 7.10).

• Involve hydrologists, fisheriesbiologists and engineers in theprocess of hydrologic andhydraulic design.

PRACTICESTO AVOID

• Installing drainage structureswithout some rational orstatistical assessment of theexpected flow.


Note: Common Maximum Intensity Values for 25-50 Year Frequency of Events:• Jungle Areas: 200-400 mm/hr• Deserts: 50-100 mm/hr• Most Areas (Semi-Arid, Mountains, Coastal Areas): 100-250 mm/hr

7

6

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00 20 40 60 80 100 120 140 160 180 200

DurationTime, in minutes

Rain

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in in

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Rain

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in m

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150

100

50

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Figure 5.2Figure 5.2Figure 5.2Figure 5.2Figure 5.2 Typical Rainfall Intensity-Duration Frequency Curves (Adapted from FHWA HydraulicDesign Series No. 4, 1997).


A drainage crossing can be a critical and vulnerablepoint in the road if the drainage structure fails. Thus,

drainage crossings must be designed to pass theappropriate storm flows plus debris or to survive overtopping.


Chapter 6

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HYDRAULIC DESIGN involves several basicconcepts that must be considered to buildsuccessful projects with a minimum risk of

failure (Photo 6.1). Use of Manning’s Formula todetermine flow capacity and velocity, use adequatelysized Riprap for stream bank and scour protection,use Filter Zones to prevent piping and scour, anduse gravels or Geotextiles to stabilize the roadstructure. Basic roaddrainage design oftenuses Manning’s Formulafor the determination offlow velocities in naturalchannels, for determiningthe quantity of that flow(as an alternative tomethods discussed inChapter 5), and fordetermining the flowcapacity of canals andditches. The use ofManning’s Formula todetermine streamvelocities and flowquantity is welldocumented in manyengineering and

“Protect against scour! Incorporate adequate riprap sizeand filters into streambank protection measures.”

hydraulics manuals. Road engineers doing basichydraulic design should become familiar with itand its applications. Complex channels withrapidly varying, unsteady, or critical flows shouldbe evaluated by an experienced HydraulicEngineer.

Photo 6.1Photo 6.1Photo 6.1Photo 6.1Photo 6.1 Scour behind a bridge abutment caused by insufficient channeland stream bank protection during a flood.


Manning’s FormulaChannel discharge quantity (Q)

is the product of the mean channelvelocity (V) and the area (A) of thechannel. To determine the dis-charge (Q) in natural drainages,canals, and non-pressure pipes, thefollowing formula is used:

Discharge = (Velocity) x (Area)or

Q = VA

where:Q = discharge, in cubic meters

per second (m3/s)V = average flow velocity, in

meters per second (m/s)A = cross sectional area, in

square meters (m2).

Manning’s Formula can be usedto compute the average flow ve-locity (V) in any channel or natu-ral stream with uniform flow asshown to the right. Manning’s For-mula can be readily solved for agiven channel when the known orassumed depth of flow is used.However, to determine the depththat a given discharge will producein a channel, a trial and error solu-tion is required. More detailed in-formation on the use of Manning’sFormula is presented in references,such as the Minimum Impact Low-Volume Roads Manual, the FHWAManual HDS4-Introduction toHighway Hydraulics, or Open-Channel Hydraulics, by V.T.Chow.

Riprap UseHigh flow velocities in channels

or along local stream banks oftenlead to bank erosion, scour, or theformation of gullies. Scour can un-dermine and cause failure of bridges

MANNING’S FORMULA

To calculate average flow velocity...

V =1

n(R 2/3 )(S 1/2 )

where:

V = average flow velocity (meters/second)

n = roughness coefficient (usually 0.04 - 0.07 for natu-ral channels); see handbooks for specific n values

S = channel slope (meter/meter)

R = hydraulic radius (meters) = A/Pwhere A and P are:A = channel cross-sectional areaP = wetted perimeter

Roughness Coefficient (n) varies considerably, depending on thecharacteristics of a channel or the smoothness of a canal, pipe,etc. Manning’s “n” values for various natural and manmadechannels are found in many hydraulics manuals and handbooks.Smooth, open stream channels with gravel bottoms have valuesaround 0.035-0.055. Very winding, vegetated, or rocky chan-nels have values around 0.055 to 0.075. Smooth earth or rockchannels have values of 0.020 to 0.035. Roughness valuestypically increase as channel vegetation and debris increase, aschannel sinuosity increases, and as the mean size of channelmaterials increases. The value decreases slightly as flow depthincreases.

Slope (S) of the canal or drainage channel is determined for thelocal reach of the channel being analyzed by dividing the rise, orchange in elevation in that reach by the distance of that reach.This slope is typically measured in the actual stream channel,upslope and downslope of the site, and ideally is also checkedon a topographic map.

Hydraulic radius (R) is determined from the channel cross-sectionalarea (A) divided by the wetted perimeter (P). The wettedperimeter is simply the distance along the channel bottom and/or sides that is under water, or within the area (A) of flow.Area should be determined from one or a couple representativecross-sections of the flow channel.


PPPPPhotohotohotohotohoto 6.26.26.26.26.2 Riprap used for stream bank slope protection to prevent scourat the entrance of a structure. Note the use of willows for additional“biotechnical” root strength.

PhotoPhotoPhotoPhotoPhoto 6.3 6.3 6.3 6.3 6.3 A root wad, log, and rock armored stream bank built forprotection against scour. Logs and vegetation can offer an attractivealternative to riprap in relatively low stream velocity areas.

and culverts. Riprap, or largestone, is commonly used to pro-tect stream banks and structuresagainst scour (Photo 6.2). Rockmay be used in conjunction withvegetation or other measures suchas root wads, gabions, or jetties toprovide bank protection (Photo6.3). Riprap rock size, as well asuse of other measures, is com-monly determined as a function ofstream velocity and local channelconditions.

Average stream channel veloc-ity (VAVE) can be determined usingManning’s Formula. Also, streamvelocities can be estimated in thefield if the surface flow can bemeasured during storm events.Stream velocity is the distance anobject, such as a log or stick, trav-els in the middle of the stream di-vided by some short period of time.The average stream velocity willbe about 0.8, or 80% of the valueof the surface velocity. Commonaverage peak velocities in streams

and rivers range from 1.5-3 m/secin flat terrain to 2-4 m/sec in steepmountain channels. Flatter channelsmay actually experience faster flowvelocities than steeper channels be-cause of their typically lower rough-ness characteristics.

Figure 6.1 presents a usefulcorrelation between water velocity(Velocity of Flow) and the size ofriprap (Diameter) needed to pro-tect the stream bank and not move.The flow along a long tangent sec-tion of stream, or the flow parallel(VP) to the stream, is assumed tobe about 2/3, or 67%, of the aver-age velocity (VAVE). The flow in acurved section of stream, with animpinging flow, has an assumedimpinging velocity (VI) equal toabout 4/3, or 133%, of the averagevelocity (VAVE). Thus, riprap in anarea with relatively fast flow, suchas a bend in the channel, will havehigher stresses and require largerrock than the size needed in astraight part of the channel.

Note that most of the rockshould be as large or larger than thesize indicated in Figure 6.1. TheIsbash Curve indicates the maxi-mum size rock that might be con-sidered in a critical application. Ifsuitably large rock is not available,


12:1

10 30 300 500 700 1500 2500

4:13:1

2:1

1 1/2:1

1:1

For Stone Weighing 2,650 Kilograms/Cu.Meter

(Gs =2.65)

(Adapted from FHWA Hydraulic Engineering Circular No. 11, 1978)

7.9

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6.7

6.1

5.5

4.8

4.2

3.6

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Equivalent Spherical Diameter of Stone (Centimeters)

Weight of Stone (Kilograms)

2 5 20 50 100 200 350 900 2000

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Side

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Note:The Riprap should be composed of a well gradedmixture of rock, but most of the stones shouldbe larger than the size indicated by the curve.Riprap should be placed over a filter blanketof geotextile or bedding of graded gravel, ina layer 1.5 times (or more) as thick as thelargest stone diameter used.

VP = 2/3 VAVE VI = 4/3 VAVE

ISBASH CURVE (F

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)

VAVE

VP

VI

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then the use of cement groutedrock, masonry, or gabions shouldbe considered.

Table 6.1 presents commongradations, sizes, and weights ofclasses of riprap. Riprap installa-tion details are shown in Figure6.2, as well as in the Note in Fig-ure 6.1. Ideally riprap should beplaced upon a stable foundationand upon a filter layer made eitherof coarse sand, gravel, or ageotextile. The riprap itself shouldbe graded to have a range of sizesthat will minimize the voids andform a dense layer. The riprapshould be placed in a layer with athickness that is at least 1.5 timesthe size (diameter) of the largestspecified stone, with the thickestzone at the base of the rock. In astream channel, the riprap layershould cover the entire wettedchannel sides, with some freeboard,and it should be placed to a depthequal or greater than the depth ofexpected scour.

FiltersA filter serves as a transitional

layer of small gravel or geotextileplaced between a structure, suchas riprap, and the underlying soil.Its purpose is to 1) prevent themovement of soil behind riprap orgabions, or into underdrains, and2) allow groundwater to drain fromthe soil without building up pres-sure. Specific filter criteria, docu-mented in other references, willestablish the particle size and gra-dation relationships needed be-tween the fine native soil, a filtermaterial, and coarse rock such asdrain rock or riprap. Also, specificgeotextile requirements informa-tion exists for filter applications, asfound in the Selected References.

Traditionally, coarse sand orwell-graded, free draining gravelhave been used for filter materials.A sand or gravel filter layer is typi-cally about 15 to 30 cm thick. Insome applications, two filter layersmay be needed between fine soil andlarge rock. Today, geotextiles arecommonly used to provide filterzones between materials of differ-ent size and gradation because theyare economical, easy to install, andperform well with a wide range ofsoils (Photo 6.4). Figure 6.2 showsthe application of a gravel orgeotextile filter between astreambank soil and the riprap rockprotection.

Use of GeotextilesGeotextiles are commonly used

to provide a filter between rock andsoil, thus preventing scour and soilmovement. They are relatively easyto install under most conditions.The fabric should be pulled tightacross the soil area to be protectedbefore the rock is placed (Photo6.5). The geotextile can be a wo-

ven monofilament or a needle-punch nonwoven geotextile, and itmust be permeable. The geotextileneeds to have an apparent openingsize of 0.25 to 0.5 mm. In the ab-sence of other information, a 200g/m2 (6.0 oz/yd2) needle-punchnonwoven geotextile is commonlyused for many soil filtration andseparation applications.

Other common geotextile orgeosynthetic material applicationson roads include subgrade rein-forcement to reduce the thicknessof needed aggregate over veryweak soils; separation of aggregatefrom soft subgrade soils; reinforce-ment of soils in structures such asretaining walls and reinforced fills;and entrapment of sediment withsilt fences (Photo 6.6), as seen inFigure 6.3. If knowledgeable en-gineers are not available, thengeotextile distributors or manufac-turers should be consulted regard-ing the function and appropriatetypes of geotextile to use in vari-ous engineering applications.

Photo 6.4Photo 6.4Photo 6.4Photo 6.4Photo 6.4 Use of geotextiles placed against fine soil to provide ad-equate filtration for an underdrain.


Percent Passing(total minus the

Category Weight Size of Rock* diameter indicated)

Kilograms(pounds) Centimeters

Class I 5 (11) 15 1002.5 (5) 12 800.5 (1) 7 50

0.1 (.2) 3 10 maximum

Class II 25 (55) 25 10015 (35) 20 80

5 (11) 15 500.5 (1) 8 10 maximum

Class III 50 (100) 30 10030 (60) 25 8010 (25) 20 50

1 (2) 10 10 maximum

Class V 100 (220) 45 10070 (150) 35 70

35 (75) 25 307 (15) 15 10 maximum

Class VII 300 (650) 60 100200 (440) 50 70100 (220) 40 30

10 (22) 20 10 maximum

Class VIII 1,000 (2,200) 90 100600 (1,320) 70 70

200 (440) 50 3030 (65) 25 10 maximum

Class X 2,000 (4,400) 120 1001,000 (2,200) 90 80

300 (660) 60 5040 (90) 30 10 maximum

Source: Adapted from USDA-Forest Service. *equivalent spherical diameter

CLASSIFICATION AND GRADATION OF RIPRAP(by Weight & Size of Rock)



FFFFFigurigurigurigurigure 6.2 Te 6.2 Te 6.2 Te 6.2 Te 6.2 Twwwwwo eo eo eo eo examples ofxamples ofxamples ofxamples ofxamples of typical ripr typical ripr typical ripr typical ripr typical ripraaaaap strp strp strp strp stream bank pream bank pream bank pream bank pream bank protection.otection.otection.otection.otection.

0.5-1.0 mFreeboard High Water Level

Plant to Grassor Shrubs inCompactedBackfill

30-90 cmThickness(Typical)

2:1 SlopePresent StabilizedStream Bottom

Geotextile “key.” Ensureintimate contact ofgeotextile and soil.

10-15 cm Gravel orGeotextile Filter Layer

30% of rock to be headersextending 2/3 thickness of riprap.If this is not possible, dump bottomportion of riprap and arrange toplayer to grade by hand.

a. Rock Toe and Blanket Detail

b. Details of Rock Riprap Layer Placed on the Stream Channel Bottom for ScourProtection

± 1 m Depthfor ScourProtection

1-2 m

Maximum Expected High Water LevelFreeboard

Riprap Layer1 ½ : 1 Slope

1 m.Minimum

2 m. Minimumor 1.5 x theDepth ofExpectedScour

Filter Layer(Geotextileor Gravel)


PPPPPhotohotohotohotohoto 6.56.56.56.56.5 A filter cloth (geotextile) backing behind a loose rock slope buttress to providea filter for drainage and to prevent movement of fine soil into the rock. (Photo by RichardVan Dyke)

Photo 6.6Photo 6.6Photo 6.6Photo 6.6Photo 6.6 Use of a geotextile as a “silt fence” to trap sediment from a constructionarea.


a. Filter Behind Riprap for Stream BankProtection.

b. Subgrade Separation and Reinforcement.

d. Filtration in an Underdrain.

c. Embankment Reinforcement over Soft SoilDeposit.

e. Reinforced Soil Retaining Structure.

f. Silt Fence to Trap Sediment.

GeotextileLayer

Riprap

GeotextileKey

Geotextile

WithoutGeotextile

WithGeotextile

Geotextile

Drain Material(Typically Sand

or Gravel)

Ditch

∆

Stake

GeotextileFence

TrappedSedimentand Water

Water

GeotextileReinforcementMaterial

WallFacingMaterial

PotentialFailureSurface

GeotextileReinforcementLayers

Fill

Soft Soil

Roadbed

FFFFFigurigurigurigurigure 6.3e 6.3e 6.3e 6.3e 6.3 Typical Geotextile Applications for Rural Roads. (Adapted with permission from AMOCOFibers Corporation)


• Determine stream channelvelocities to examine scourpotential, structure protectionneeds, and impacts on aquaticlife.

• Use well graded, hard, angular,properly sized riprap wherescour protection is needed.Needed rock size (and weight)as a function of average waterflow velocity is shown inFigure 6.1. On curves(impinging flow) increase therock size by 30 to 50 percentabove that shown in Figure 6.1for average flow velocities.

• Use clean sand, clean, wellgraded 0.5 to 1 cm gravel, or ageotextile for filters betweenfine erodable soils and coarsedrain rock or riprap (seeFigure 6.2 for typical riprapinstallation with filterbacking).

• Use scour countermeasuresto protect structures,prevent failure of structures,and avoid adverse impactsto streams. Riprap orgabions are most commonlyused in high velocity orcritical areas (Photo 6.7).Vegetation, root wads, logs,or barbs can also be used forstreambank stabilization.

• Pay attention to designdetails where rockprotection and filters areneeded.

• Use geotextiles in road andhydraulic design applicationsto provide a filter behindriprap or around anunderdrain. Usegeosynthetic materials inother applications, such asfor separation andreinforcement, wherevercost-effective and practical.

PRACTICESTO AVOID

• Installing structures withoutadequate consideration of ex-pected stream velocities andappropriately sized rock forbank protection.

• Installing subsurface drain-age measures, such asunderdrains, without filterprotection (such as use ofgeotextiles and properlysized sand or gravel filtermaterial).


Photo 6.7Photo 6.7Photo 6.7Photo 6.7Photo 6.7 Riprap with a geotextilefilter backing are being used toprotect the road from high waterflows. Note that the road is poorlylocated so close to the stream!


Chapter 7

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ROAD LOCATION and drainage of roads,construction areas, and other areas of activityare the most significant factors that can affect

water quality, erosion, and road costs. Drainageincludes controlling surface water and adequatelypassing water under roads in natural channels.Drainage issues that must be addressed in road designand construction include roadway surface drainage;control of water in ditches andat pipe inlets/outlets;crossings of natural channelsand streams; wet areacrossings; subsurfacedrainage; and selection anddesign of culverts (Chapter8), low water crossings(Chapter 9), and bridges(Chapter 10). Three of themost important aspects ofroad design are drainage,drainage, and drainage!

Adequate road drainagerequires careful attention todetail. Drainage conditionsand patterns must be studiedon the ground. Drainageshould be observed during

rainy periods to see how the water is actually moving,where it is concentrated, what damage it may cause,and what measures are needed to prevent damageand keep the drainage systems functioning properly.

ROADWAY SURFACE DRAINAGE CONTROL

The roadway surface needs to be shaped to dis-perse water and move it off the road quickly and as

“Three of the most important aspects of road design --drainage, drainage, and drainage”

Photo 7.1 Photo 7.1 Photo 7.1 Photo 7.1 Photo 7.1 Design roads that move water rapidly off the surface of theroad and minimize water concentration with the use of rolling grades andoutsloped, insloped, or crowned roads.

Chapter 7

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frequently as possible (Photo7.1). Water standing in potholes,ruts and sags will weaken thesubgrade and accelerate damage.Water concentrated in ruts or kepton the road surface for long dis-tances can accelerate erosion aswell as wash off the surface ma-terial. Steep road grades causesurface and ditch water to moverapidly, and make surface drain-age difficult to control. Steepgrades accelerate erosion unlesssurfaces are armored or water isdispersed or removed frequently.

Roadway surface watershould be controlled with positivedrainage measures usingoutsloped, insloped, or crownsections of road, as shown in Fig-ure 7.1. Outsloped roads bestdisperse water and minimize roadwidth, but may require roadwaysurface and fill slope stabilization.An outsloped road minimizesconcentration of water, minimizesneeded road width, avoids the

need for an inside ditch, and mini-mizes costs. Outsloped roadswith clay rich, slippery road sur-face materials often require rocksurface stabilization or limited useduring rainy periods to assure traf-fic safety. On road grades over 10to 12 percent and on steep hillslope areas, outsloped roads are

FFFFFigurigurigurigurigure 7.1 Te 7.1 Te 7.1 Te 7.1 Te 7.1 Typical rypical rypical rypical rypical road surfoad surfoad surfoad surfoad surface drace drace drace drace drainaainaainaainaainaggggge optionse optionse optionse optionse options.....

difficult to drain and can feel un-safe.

Insloped roads best controlthe road surface water but con-centrate water and thus require asystem of ditches, cross-drains,and extra road width for the ditch.Cross-drains, using either rollingdips (broad-based dips) or culvertpipes, must be spaced frequentlyenough to remove all the expectedroad surface water before erosionoccurs. The maximum recom-mended distances (listed in Table7.1) should be used for guidanceon spacing of cross-drains andditch relief structures. Specific lo-cations should be determined inthe field based upon actual waterflow patterns, rainfall intensity,road surface erosion characteris-tics, and available erosion resis-tant outlet areas.

Crown section roads are ap-propriate for higher standard, twolane roads on gentle grades. Theyalso require a system of inside

Crown Section

Outslope Section

Inslope with Ditch Section

Brush

ArmoredDitch

3-5%

2:12:1

2:1

2:12:1

1:1

1:1

3-5%

3-5%

3-5%

Photo 7.2Photo 7.2Photo 7.2Photo 7.2Photo 7.2 Use rolling dip (broad-based dip) cross-drains to movewater off the road surface efficiently and economically, without theuse of culvert pipes. Rolling dip cross-drains are not susceptible toplugging.


ditches and cross drains. It is dif-ficult to create and maintain acrown on a narrow road, so gen-erally insloped or outsloped roaddrainage is more effective for ru-ral roads.

Culvert cross-drains are usedto move ditch water across theroad. They are the most commontype of road surface drainage, andare most appropriate for high-standard roads where a smoothroad surface profile is desired.However the pipes are expensive,and the relatively small culvertpipes used for cross-drains aresuseptible to plugging and requirecleaning.

Rolling dip cross-drains(broad-based dips) are designedto pass slow traffic, while also dis-persing surface water (Photo 7.2).Rolling dips usually cost less, re-quire less maintenance, and areless likely to plug and fail thanculvert pipes. Rolling dips areideal on low volume, low to mod-erate speed roads (20-50 kph).Spacing is a function of roadgrade and soil type, as seen inTable 7.1. Other types of roadwaysurface cross-drain structures oc-casionally used include open topwood or metal flumes, and rub-ber water deflectors.

Steep road grades are unde-sirable and problematic, but oc-casionally necessary. On grades upto 10%, cross-drains with culvertsor rolling dips are easy to use. Be-tween 10 and 15%, frequentlyspaced culvert cross-drains work,often in conjunction with armoredditches. On grades over 15%, itis difficult to slow down the wa-

Low toRoad Grade % Non-Erosive soils (1) Erosive Soils (2)

0-3 120 75

4-6 90 50

7-9 75 40

10-12 60 35

12+ 50 30


Recommended Maximum Distance Between Rolling Dip or Culvert Cross-Drains (meters)

Road/Trail Low toGrade % Non-Erosive soils (1) Erosive Soils (2)

0-5 75 40

6-10 60 30

11-15 45 20

16-20 35 15

21-30 30 12

30+ 15 10


Recommended Water Bar Spacing (meters)

Note: (1) Low Erosion Soils = Coarse Rocky Soils, Gravel, andSome Clay

(2) High Erosion Soils = Fine, Friable Soils, Silt, FineSands

Adapted from Packer and Christensen (1964)& Copstead, Johansen, and Moll (1998)



ROADWAY SURFACE

DRAINAGE CONTROL

• Design and construct roadsso that they will move waterrapidly off the road surfaceto keep the surface drainedand structurally sound.

• Avoid steep road grades inexcess of 12 to 18%. It isvery difficult and expensiveto properly control drainageon steep grades.

• Maintain positive surfacedrainage with an outsloped,insloped, or crown roadwaysection using 3 - 5 % crossslopes (up to 5% is best)(Figure 7.1).

• Roll grades or undulate theroad profile frequently todisperse water, particularlyinto and out of streamcrossings (Figure 7.2a,Photo 7.1).

• Use frequently spacedleadoff ditches (Figure 7.2band Figure 7.8) to preventaccumulation of excessivewater in the roadwayditches.

• Use roadway cross-drainstructures (either rollingdips, pipe culverts, or opentop culverts (flumes)) tomove water across the roadfrom the inside ditch to theslope below the road. Spacethe cross-drain structures

frequently enough to removeall surface water. Table 7.1gives recommended cross-drain spacing.

• Protect cross-drain outletswith rock (riprap), brush, orlogging slash to dissipateenergy and prevent erosion,or locate the outlet of crossdrains on stable, non-erosivesoils, rock, or in well veg-etated areas (Figure 7.2b).

• Construct rolling dipsrather than culvert cross-drains for typical, low-volume, low speed roadswith grades less than 12%.Construct rolling dips deepenough to provide adequatedrainage, angled 0-25degrees from perpendicularto the road, with a 3-5%outslope, and long enough(15 to 60 meters) to passvehicles and equipment (SeePhoto 7.2). In soft soils,armor the mound and dipwith gravel or rock, as wellas the outlet of the dip(Figure 7.3).

• Install culvert cross-drainswith an angle of 0-30 de-grees perpendicular to theroad, using an outslope of2% greater than the ditchgrade to prevent plugging.(Figure 7.4). (See Chapter8 for more information onculverts). Use culvert cross-drains on roads with an

inside ditch and moderatelyfast vehicle speeds.

• Construct water bars oninfrequently used roads orclosed roads to controlsurface runoff. Constructfrequently spaced waterbarsangled at 0-25 degrees withan outslope of 3-5% and adepth of 0.3 to 0.6 meters.Install water bars as shownin Figure 7.5. Spacing ofwaterbars is shown in Table7.2.

• Use catch water ditches(intercept ditches) across thenatural ground above a cutslope only in areas with highintensity rainfall and over-land flow. These ditches areuseful to capture overlandsheet flow before it poursover the cut slope anderodes or destabilizes thecut. However, be aware thatcatch water ditches are thatare not properly maintainedcan become a counter-productive pool for waterabove the slope, increasingthe probability of a slopefailure.

• Avoid the use of outsideditches, along the outsideedge of the road, except inspecific areas that must beprotected from sheet flowoff the road surface. Prefer-ably, use berms. Note that anoutside ditch or berm neces-sitates additional road width.


a.a.a.a.a. Basic road surface drainage with outsloping, rolling grades, and reinforced dips.

Cut slope

Reinforced

dip

Fill slope

Ground slope

bbbbb..... Basic road surface drainage with leadoff ditches and culvert cross-drains exiting into vegetation or astreamside buffer area. (Adapted from Montana State Univ. 1991)

PRACTICES TO AVOID

• Long sustained road gradesthat concentrate flows.

• Discharging water onto

erosive, unprotected soils.

• “Eyeballing” grades in flatterrain. Use a clinometer,

abney level, or surveyequipment to ensure thatyou have proper slopes orgrades.

FFFFFigurigurigurigurigure 7.2e 7.2e 7.2e 7.2e 7.2


ArmoredDip

Mound

Inslope or

Outslope

Riprapat DipExit

Dip Average Road Grade

Dip

2-5%Outslope

2-5%Outslope

c. Rolling Dip Profile Detail

Average Road Grade

Armor Dip and MoundSurface as Needed with5-15 cm Aggregate

For Insloped Road – Slope to Depthof Inside DitchFor Outsloped Road – 3-5 cm Deepor Match Depth of Inside Ditch atEntrance – 15-30 cm Deep at ExitReverse Slope3-6%

Road Grade2-12%

7-12m8-30m 8-30m

0-25o

b. Profile

a. Perspective View

Spacing 30 - 150 m

FFFFFigurigurigurigurigure 7.3 e 7.3 e 7.3 e 7.3 e 7.3 Rolling (broad-based) dip cross-drains.


InletStructureas Needed

Place Outlet Pipe atNatural GroundLevel or RiprapArmor the FillMaterial.

Berm

Spacing 30–150 m

0o -30o

Exit onto Stableor ArmoredGround

Berm Tied intoEmbankment Spacing 10–75 m

Road Grade

30-60 cm 30-60 cm○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○

1 - 2 m 1 - 2 m 1 - 2 m

0-25

o

a. Perspective View

FFFFFigurigurigurigurigure 7.4e 7.4e 7.4e 7.4e 7.4 Culvert cross-drains.

FFFFFigurigurigurigurigure 7.5e 7.5e 7.5e 7.5e 7.5 Water bar construction. (Adapted from Wisonsin’s Forestry Best Management Practicesfor Water Quality. 1995, Publication FR093, Wisconsin Department of Natural Resources)

b. Cross-Section


ter or remove it from the roadsurface rapidly. On such steepgrades, it is best to use frequentlyspaced cross-drain culverts, witharmored ditches. Also, the roadsurface will need armoring or sur-facing with some form of pave-ment to resist erosion. For sea-sonal or low use roads, interimdrivable waterbars could also beconstructed.

Water bars are used to con-trol drainage on closed or inac-tive roads, 4-wheel drive roads,skid roads, and skid trails. Waterbars are frequently spaced (seeTable 7.2) for maximum erosioncontrol and can be shaped to passhigh clearance vehicles or to blocktraffic.

Photo 7.3Photo 7.3Photo 7.3Photo 7.3Photo 7.3 Use masonry, concrete, or metal inlet structures tocontrol water in the ditch, direct the water into the cross-drain pipe,and prevent ditch down-cutting.

Photo 7.4 Photo 7.4 Photo 7.4 Photo 7.4 Photo 7.4 Add outlet protection and/or energy dissipators to pre-vent erosion and the formation of gullies.

CONTROL AT INLETS AND OUTLETS

OF CROSS-DRAINS AND DITCHES

Water should be controlled,directed, or have energy dissi-pated at the inlet and outlet ofculverts, rolling dips, or othercross-drainage structures. Thiscan ensure that water and debrisenters the cross-drain efficientlywithout plugging, and that it ex-its the cross-drain without dam-aging the structure or causing ero-sion at the outlet.

Culvert inlet structures (dropinlets) are usually placed in the in-side ditchline at the location of aculvert cross-drain. They are com-monly constructed of concrete,masonry (Photo 7.3), or fromround metal pipe, as seen in Fig-ure 7.6. They are typically usedwhere the ditch is eroding anddowncutting, so that the structurecontrols the ditch elevation. Inletstructures are also useful tochange the direction of waterflowing in the ditch, particularlyon steep grades, and they can helpstabilize the cut bank behind thepipe inlet.

The outlet of pipes and dipsare ideally located in a stable, non-erosive soil area or in a well-veg-etated or rocky area. The accel-erated velocity of water leaving aroadway can cause severe erosionor gullying if discharged directlyonto erosive soils (Photo 7.4).The pipe, dip, or drain outlet areacan be stabilized, and the energyof the water dissipated, by dis-charging the water onto 1-2 cu-bic meters of a graded rock riprap,as seen in Figure 7.7. Other en-ergy dissipation measures includethe use of stilling basins, rein-


forced splash aprons, or use ofdense vegetation or bedrock(Photo 7.5).

Ditches on steep road grades,

RECOMMENDED PRACTICESCONTROL AT INLETS & OUTLETS

• When ditch grade control isneeded, use drop inlet struc-tures with culvert cross-drainsto prevent ditch down-cuttingor where space is limitedagainst the cut bank (Figure7.6). Alternately, use catchbasins excavated into firmsoil.

• Discharge culverts and cross-drain dips at natural groundlevel, on firm, non-erosivesoil or in rocky or brushyareas. If discharged on the fillslopes, armor outlets withriprap or logging slash, or usedown-drain structures. (Fig-ures 7.3, 7.4, 7.7 and Figure8.1). Extend the pipe 0.5 to

1.0 meters beyond the toe ofthe fill slope to preventerosion of the fill material.

• In erosive soils, armorroadway ditches and leadoffditches with rock riprap(Photo 7.7), masonry,concrete lining or, at aminimum, grasses. Ditchdike structures can also beused to dissipate energy andcontrol ditch erosion.(Figure 7.8).

• Discharge roadway drains inan area with infiltrationcapability or into filter stripsto trap sediment before itreaches a waterway. Keepthe road and streams hydro-logically “disconnected.”

PRACTICES TOAVOID

• Discharging a cross-drainpipe or dip onto any unpro-tected fill slope or barren,erosive soil.

• Discharging cross-drainpipes mid-height on a fillslope.

• Discharging cross-drainpipes or dips onto unstablenatural slopes.

Photo 7.5Photo 7.5Photo 7.5Photo 7.5Photo 7.5 Protect the outlet of culvert pipe and rolling dip cross-drains with riprap or a masonry splash apron, or choose areas ofbedrock or dense vegetation.

in erosive soils, and with flow ve-locities over one meter per sec-ond may require armoring or theuse of small ditch dike or damstructures placed in the ditch to

slow down the velocity of water,as shown in Figure 7.8. Ditchesare commonly armored with grass,erosion control matting, rock, ormasonry /concrete paving (Photo7.6). Grasses can resist flow ve-locities to 1-2 meters per second.A durable armoring such as gradedrock riprap or concrete is recom-mended on grades over 5 percentin erosive soils or for velocitiesover a few meters per second.

Ditch dikes will prevent ditcherosion, and dikes can serve tocatch sediment, but they requiremaintenanceneed in that they needto be periodically cleaned out.Common ditch dike constructionmaterials include loose rock, ma-sonry, concrete, bamboo, andwooden posts. Each dike structureshould be keyed into the banks ofthe ditch and a notch is neededover each structure to keep theflow in the middle of the ditch.


Slope

Culvert Pipe (30-60 cm diameter)

Sand trap

0.6-1.2 m

Roadbed Surface

Drop inletstructure

Bottom of ditch

Roadbed surface EnergyDissipationwith Riprap,ConcreteApron orSplash poolwith water

Use drop inlet structure to control the level of water,turn water into the pipe, and prevent downcutting and erosion of the ditch.

Design and Installation Detail

"1 m

General Information

MetalMasonry

Window

45 cm

45 cm

30 cm

90 cm

30 cm

Slope

Grass forErosionControl

FFFFFigurigurigurigurigure 7.6 e 7.6 e 7.6 e 7.6 e 7.6 Typical drop inlet structure types (with culvert cross-drains).

Photo 7.6Photo 7.6Photo 7.6Photo 7.6Photo 7.6 Armor ditches with vegetation, rock, masonry, or concrete toresist ditch erosion and carry the water to a stable exit point.


Fill Slope

0.5 mminimum

15-30 cmminimumdepth

Ground Line1-2 m

Rocks:15-50 kg5% greater than 25 kg

FFFFFigurigurigurigurigure 7.7 e 7.7 e 7.7 e 7.7 e 7.7 Culvert outlet protection.

Photo 7.7Photo 7.7Photo 7.7Photo 7.7Photo 7.7 A rock armored ditch and metal drop inlet to control thewater and prevent down-cutting of the ditch.


a. Ditch Layout and Leadoff (Adapted from Wisconsin’s Forestry Best Management Practices for WaterQuality, 1995)

Excavate ditch into firm soil.Armor ditch in erosive soil areas.

Exit ditch instable, vegetatedarea

Insloped Roadbed Armor the ditch withrock, masonry or grass

1 m

30 cm min.

Cut slo

pe

b. Typical Ditch Armoring and Shape

Cut slope

Ditch dikes made of rock orwood to reduce flow velocity

c. Use of Ditch Dikes

Weir shape to keepflow mid-ditch

Roadway

Flow

Roadway

FFFFFigurigurigurigurigure 7.8e 7.8e 7.8e 7.8e 7.8 Ditches and ditch armoring.


NATURAL STREAM CROSSINGS

Road crossings of naturaldrainage channels and streams re-quire hydrologic and hydraulic de-sign expertise to determine theproper size and type of structure,as discussed in Chapters 5 and 6.Structures for small drainages canbe sized using Table 8.1. Thechoice of structure includes cul-vert pipes, arch or box culverts,low water fords, or bridges, asshown in Figure 7.9.

Because drainage crossingsare at areas of running water, theycan be costly to construct and canhave major negative impacts onwater quality. Impacts from im-proper design or installation ofstructures can include degradedwater quality, bank erosion, chan-

a. Bridge b. Low-Water Crossing

c. Arch Pipe d. Culvert with Single or Multiple Pipes

FFFFFigurigurigurigurigure 7.9 e 7.9 e 7.9 e 7.9 e 7.9 Structural options for crossing natural streams. (Adapted from Ontario Ministry of NaturalResources, 1988)

nel scour, traffic delays, and costlyrepairs if a structure fails. Also,structures can greatly impact fish,as well as other aquatic species,at all stages of life. Stream cross-ings should be as short as possibleand cross perpendicular to thechannel (Photo 7.8). The road andditches should be armored, ditchesshould divert surface water beforeit reaches the stream channel, andconstruction should minimize thearea of disturbance, as shown inFigure 7.10. Large drainagecrossings should receive site-spe-cific analysis and design input, ide-ally by an experienced hydraulicengineer and other specialists.

In drainages with uncertainflow values, large quantities of de-bris in the channel, or on sites with

existing undersized pipes, there isa high risk of a culvert pipe plug-ging and the site washing out orfailing. In such areas, or in par-ticularly sensitive watersheds,overflow protection is desirable.A low point in the fill and an ar-mored overflow “spillway,” asshown in Figures 7.11a & b, willprotect the fill and keep the flowin the same drainage, thus reduc-ing diversion potential and usuallypreventing a failure. A pluggedpipe that diverts the stream waterdown the road can cause a greatdeal of off-site damage or gully-ing or cause landslides, as seen inFigures 7.11c & d. Overflowstructures should not be used as asubstitute for good hydraulic de-sign, but they can offer “cheapinsurance” against failure at cul-vert crossings.


PRACTICES TO AVOID• Working with equipment in

an unprotected naturalstreambed.

• Locating stream crossingsin sinuous or unstablechannels.

RECOMMENDED PRACTICESNATURAL STREAM CROSSINGS

• Use drainage structures thatbest conform to the naturalchannel and that are as wideas the active stream channel(bankfull width). Minimizenatural channel changes andthe amount of excavation orfill in the channel.

• Limit construction activity toperiods of low flow in livestreams. Minimize use ofequipment in the stream.Stay out of the stream!

• Design structures and useconstruction practices thatminimize impacts on fish andother aquatic species or thatcan enhance fish passage.

• Cross drainage channels asinfrequently as possible.When necessary, crossstreams at right anglesexcept where prevented byterrain features (Figure7.10).

• Keep approaches to streamcrossings to as gentle a

grade as practical. Rollgrades into and out of thecrossing to disperse water.

• Stabilize disturbed soilaround crossings soon afterconstruction. Remove orprotect fill material placed inthe channel and floodplain.

• Use bridges, low-water fordsor improved fords, and largearch pipes with naturalstream bottoms whereverpossible to maximize flowcapacity, minimize thepossibility of a plugged pipe,and minimize impacts onaquatic species.

• Locate crossings where thestream channel is straight,stable, and not changingshape. Bedrock locations aredesirable for concretestructures.

• For overflow protection,construct fills over culvertswith an armored low pointnear the pipe in low fills oradd an armored rolling dipon native ground just be-

yond a large fill to returnwater to the drainage andprevent off-site damage(Figure 7.11).

• Stabilize roadway ap-proaches to bridges, fords,or culvert crossings withgravel, rock, or othersuitable material to reduceroad surface sedimentfrom entering the stream(Figure 7.12). Installcross-drains on both sidesof a crossing to preventroad and ditch runoff fromentering the drainagechannel.

• Construct bridges andculvert fills higher than theroad approach to preventroad surface runoff fromdraining directly into thestream -- but ONLY iflikelihood of culvertfailure is VERY small.(Figure 7.13). Typically,the crossing should bedesigned to minimize theamount of fill.

• Adversely impacting fisherieswith a stream crossingstructure.

• Allowing runoff from road-side ditches to flow directlyinto streams.


Poor Stream Crossing Better Stream Crossing

Drainage crossings perpendicular to the creekminimize the area of disturbance. Armor thestream crossing and roadway surface.

Cross-drain

Cutslopes

Road

Road

FFFFFigurigurigurigurigure 7.10e 7.10e 7.10e 7.10e 7.10 Natural drainage crossings. Minimize the area of disturbance with a perpendicularstream crossing alignment, and armor the roadway surface.

Crossings near parallel to the drainage cause alarge disturbed area in the channel, streambank,and approach cuts.

Largecutslopearea

Road

Road

Photo 7.8Photo 7.8Photo 7.8Photo 7.8Photo 7.8 Avoid natural drainage crossings that are broad and that arenot perpendicular to the drainage. Stay out of the stream! This broadchannel is a good site for a vented ford.


B

C

Culvert Installed with Protection using an ArmoredOverflow Dip to Prevent Washout and Fill Failure

D

A

Road Profile Across the Drainage and Dip

DCB

Pipe

Armored dip

Fill

(A) Roadway Cross Drain (Dip)(B) Culvert(C) Overflow Protection Dip(D) High point in the road profile

A

FFFFFigurigurigurigurigure 7.11e 7.11e 7.11e 7.11e 7.11

a.a.a.a.a. Overflow dip protection at a fill stream crossing. (Adapted from Weaver and Hagans, 1994)


FFFFFigurigurigurigurigure 7.11 (contine 7.11 (contine 7.11 (contine 7.11 (contine 7.11 (continued)ued)ued)ued)ued)

bbbbb..... Armored dip over a low fill to prevent stream diversion.

ccccc..... Sketch of a stream diverted down the road, forming a new channel.

d.d.d.d.d. Consequence of stream diversion out of its natural channel. (Adapted from M. Furniss, 1997)

Good Installation

Poor Installation

AbandonedChannel

Slumping

New Channelin a Gully

Plugged Culvert


FFFFFigurigurigurigurigure 7.12e 7.12e 7.12e 7.12e 7.12 Protection measures at stream crossings.

Armor or stabilize the actual stream crossing (ford), add surfacing to the roadbed, anddrain water off the road surface before reaching the crossing. Set stream channelarmoring at the elevation of the natural stream bottom.

15-30 m stoneor gravelapproach

Hardened

streambottom

Ditch

Riprap (rock)

Gravelor stonesurfacing

Debris

Rolling dipor

cross-drain

If a plugging failure is unlikely to occur, place fill directly over a culvert higher thanthe road approach to prevent surface road runoff from draining toward the crossingstructure and into the stream.

Road

FFFFFigurigurigurigurigure 7.13 e 7.13 e 7.13 e 7.13 e 7.13 High point over the crossing. (Adapted from Wisconsin’s Forestry Best ManagementPractices for Water Quality, 1995)


WET AREAS AND MEADOW

CROSSINGS, USE OF UNDERDRAINS

Road crossings in wet areas,including damp meadows,swamps, high groundwater areas,and spring sources are problem-atic and undesirable. Wet areas areecologically valuable and difficultfor road building, logging, or otheroperations. Soils in these areas areoften weak and require consider-able subgrade reinforcement.Drainage measures are expensiveand may have limited effective-ness. Wet areas should beavoided!

If wet areas must be crossedand cannot be avoided, specialdrainage or construction methodsshould be used to reduce impactsfrom the crossing. They includemultiple drainage pipes (Photo7.9) or coarse permeable rock fillto keep the flow dispersed,subgrade reinforcement withcoarse permeable rock, grade con-trol, and the use of filter layers andgeotextiles, as shown in Figure7.14. The objective is to maintainthe natural groundwater level andflow patterns dispersed across themeadow and, at the same time,provide for a stable, dry roadwaysurface.

Local wet areas can be tem-porarily crossed, or “bridged”over, using logs, landing mats,tires, aggregate, and so on. (seeFigure 7.15). Ideally, the tempo-rary structure will be separatedfrom the wet area with a layer ofgeotextile. The geotextile helps fa-cilitate removal of the temporarymaterial and minimizes damage tothe site. Also, a layer of geotextile

can provide some reinforcementstrength as well as provide sepa-ration to keep aggregate or othermaterials from punching into theweak subgrade.

Subsurface drainage, throughuse of underdrains or aggregatefilter blankets, is commonly usedalong a road in localized wet orspring areas, such as a wet cutbank with seepage, to specificallyremove the groundwater andkeep the roadway subgrade dry.A typical underdrain design usesan interceptor trench 1-2 metersdeep and backfilled with drainrock, as shown in Figure 7.16.Subsurface drainage is typicallyneeded in local wet areas and ismuch more cost-effective thanadding a thick structural sectionto the road or making frequentroad repairs. Design and filtrationrequirements for underdrains arediscussed in Chapter 6 and otherreferences.

In extensive swamp or wet ar-

eas, subsurface drainage will of-ten not be effective. Here, eitherthe roadway platform needs to beraised well above the water table,such as with a turnpike roadwaysection, or the surfacing thicknessdesign may be based upon wet,weak subgrade conditions thatwill require a relatively thickstructural section. A thick aggre-gate layer is commonly used, withthe thickness based upon thestrength of the soil and anticipatedtraffic loads.

Photo 7.9Photo 7.9Photo 7.9Photo 7.9Photo 7.9 Avoid crossing wet meadow areas. When necessary tocross, use multiple drainage pipes to keep water flow dispersedacross the meadow.

PRACTICESTO AVOID

• Crossing wet areas unnec-essarily.

• Concentrating water flowin meadows or changingthe natural surface andsubsurface flow patterns.

• Placing culverts below themeadow surface elevation.


ROCK FILL WITHOUT CULVERTS(for minimal overland flow)

PERMEABLE FILL WITH CULVERTS(for periodic high flows on flood plains and meadows)

CulvertsBerm

Berm

Flow

Mea

dow

Flow

Road

way

Meadowsurface

Geotextile

Flow

Roadway

10-15 cm minus rock

Roadway

FlowFlow

15 cm ThickAggregateBase Course

15 cm Minus RockCourse Placed Approx.30 cm Thick

FFFFFigurigurigurigurigure 7.14 e 7.14 e 7.14 e 7.14 e 7.14 Wet meadow road crossing options. (From Managing Roads for Wet Meadow EcostreamRecovery by Wm. Zeedyk, 1996)

c.

b.

a.

Geotextile


FFFFFigurigurigurigurigure 7.15e 7.15e 7.15e 7.15e 7.15 Pole or plastic pipe fords for wet area and bog crossings. Pole fords must be removedimmediately after use or before the upstream end becomes clogged with debris and impedes streamflow. (Adapted from Vermont Department of Forests, Parks and Recreation, 1987)

RECOMMENDED PRACTICESWET AREAS AND MEADOW

CROSSINGS, UNDERDRAINS

• For permanent road cross-ings of meadows and wet-lands, maintain the naturalgroundwater flow patternsby the use of multiple pipesset at meadow level tospread out any overlandflow (See Photo 7.9).Alternatively, a coarse,permeable rock fill can beused where overland (sur-face) flow is minimal (seeFigure 7.14).

• In areas with local wet spotsand limited road use, rein-force the roadway with atleast 10-30 cm of coarsegraded rock or a very coarsegranular soil. Ideally, sepa-rate the coarse rock and wet

soil with a filter layer ofgeotextile or gravel.

• For temporary crossing ofsmall, wet drainages orswamps, “corduroy” theroad with layers of logsplaced perpendicular to theroad and capped with a soilor gravel driving surface.PVC pipe, landing mats,wood planks, tire mats andother materials have alsobeen used (see Figure 7.15).Place a layer of geotextilebetween the saturated soiland logs or other materialfor additional support and toseparate the materials.Remove logs from anynatural drainage channelbefore the rainy season (seePhoto 8.8). A layer of chain-

link fencing or wire underthe logs can help facilitateremoval of the logs.

• In spring areas, use drainagemeasures such asunderdrains or filter blanketsto remove local groundwa-ter and keep the roadsubgrade dry (Figure 7.16,Photo 7.10).

• Use underdrains behindretaining structures toprevent saturation of thebackfill. Use underdrains orfilter blankets behind fills(embankments) placed oversprings or wet areas toisolate the fill material andprevent saturation andpossible subsequent fillfailure.


FFFFFigurigurigurigurigure 7.16e 7.16e 7.16e 7.16e 7.16 Typical road underdrain used to remove subsurface water.

Photo 7.10 Photo 7.10 Photo 7.10 Photo 7.10 Photo 7.10 Use subdrains or filter blankets when necessary to remove groundwa-ter from the roadway subgrade in local wet or spring areas. Note that this designneeds a second layer of geotextile between the soft subgrade soil and the coarsefilter rock to keep the rock clean.

VariableDepth(Typically+/- 1.5 mDeep)

5-10 cm60 cmmin.

Pipe, Perforated15 cm dia. (min)

Filter Material, Permeable SandyGravel, Well GradedNOTE: With Geotextile, use clean,coarse gravel.Without Geotextile, use fine, cleansand.

Ground Water

Geotextile Enveloping theFilter Material

Ditch15 cm Cap ofImpermeable Soil

Roadbed

Cut


Chapter 8

CulvCulvCulvCulvCulvererererert Uset Uset Uset Uset Use, Installa, Installa, Installa, Installa, Installation,tion,tion,tion,tion,and Sizingand Sizingand Sizingand Sizingand Sizing

CULVERTS ARE commonly used both as cross-drains for ditch relief and to pass water undera road at natural drainage and stream

crossings. In either case, they need to be properlysized and installed, and protected from erosion andscour (Photo 8.1). Natural drainages need to havepipes large enough to pass the expected flow plusextra capacity to pass debris without plugging (Photo8.2). Fish passage may also bea design consideration.Discharge (design flow) willdepend on the watersheddrainage area, runoffcharacteristics, design rainfallintensity, and return period(frequency) of the designstorm. Culvert designtypically uses a minimumstorm event of 20 years, andmay design for as much as a100-year event (Photo 8.3),depending on localregulations and the sensitivityof the site (such as withendangered species).

For small watersheds (upto 120 hectares) pipe size can

“Ensure that culverts are adequately sized or have overflow protection.”

Chapter 8

Cu

lvC

ulv

Cu

lvC

ulv

Cu

lver

er er

er

ert U

set U

set U

set U

set U

se, Insta

lla, In

stalla

, Insta

lla, In

stalla

, Insta

llatio

n, a

nd

Sizin

gtio

n, a

nd

Sizin

gtio

n, a

nd

Sizin

gtio

n, a

nd

Sizin

gtio

n, a

nd

Sizin

g

be estimated using Table 8.1 (if better local data isnot available). For larger drainages, specific sitehydrologic and hydraulic analyses should be done.These analyses must consider the watershed andchannel characteristics, high water levels, localrainfall data, and other available flow information(see Chapter 5, Chapter 6, and Chapter 7- NaturalStream Crossings).

Photo 8.1 Photo 8.1 Photo 8.1 Photo 8.1 Photo 8.1 Protect the outlet of culverts against erosion. Graded riprap iscommony used for this purpose.


Photo 8.2Photo 8.2Photo 8.2Photo 8.2Photo 8.2 A culvert failure caused by insufficient flow capacity orinadequate pipe size to pass the debris (boulders) moving through thedrainage.

Photo 8.3Photo 8.3Photo 8.3Photo 8.3Photo 8.3 Install masonry/concrete box or metal culverts with a largeenough size (capacity) to safely pass the anticipated design flow(typically a 20- to 50-year recurrence event), based upon hydrologicalanalysis. Use headwalls and wingwalls whenever possible.

Culverts are made of concreteor metal (corrugated steel oraluminum), and plastic pipe isoccasionally used, as well as woodand masonry. The type of materialused depends on cost andavailability of the materials.However, corrugated metal pipe(CMP) and concrete pipe aregenerally more durable thanplastic pipe. The shape of theculvert, such as a round pipe, pipearch, structural arch, or box,depends on the site, the neededspan, and the allowable height ofsoil cover. The key factors inculvert selection are that theculvert has adequate flowcapacity, fits the site, and that theinstallation is cost-effective.

Cross-drain culvertinstallation options and details forditch relief are seen in Figure 8.1,as well as Figures 7.6 and 7.7.The cross-drain pipe shouldideally be placed at the bottom ofthe fill, the inlet should beprotected with a drop inlet

structure or catch basin, and theoutlet area should be protectedagainst scour.

Culvert installation andalignment factors for drainagecrossings are shown in Figures8.2, 8.3, 8.4, and 8.5. Importantinstallation details include:

minimizing channel modifications;avoiding constriction of thebankfull flow channel width;maintaining the natural grade andalignment; using quality, wellcompacted bedding and backfillmaterial; and using inlet, outlet,and streambank protectionmeasures (Photo 8.4). Trash racks(Figure 8.6) are often desirable inchannels with significant amountsof debris to prevent pipe plugging(Photo 8.5).

Bedding and backfill materialfor culverts is commonly specifiedas “select granular material” or“select mineral soil”. Actually,most soils are satisfactory if theyare free of excessive moisture,muck, lumps of frozen soil, roots,highly plastic clay, or rock largerthan 7.5 cm. Bedding materialbeneath the pipe should not haverocks larger than 3.8 cm. Clay soilcan be used if it is carefullycompacted at a uniform, near-optimum moisture content. Ideal


backfill material is a moist, well-graded granular or sandygravel soil with up to 10 percentfines and free of rocks. Thematerial should be wellcompacted, at least as dense as theadjacent ground, and preferably ata density of 90-95% of theAASHTO T-99 maximum density.It should be placed in 15cm thicklayers (lifts). A dense, uniformbackfill is important to structurallysupport the lateral pressure fromthe pipe, particularly with plasticpipes.

Uniform fine sand and silt soilscan be problematic when used forculvert bedding or backfillmaterial. These fine, non-cohesivesoils are very susceptible to scourand piping from moving water(Photo 8.6). Thus their use is

discouraged. If used, they shouldbe very well compacted againstthe pipe. Ideally, a clay plug oranti-seepage collar, made ofmetal, concrete, or evengeotextile, should be placedaround the culvert pipe to forceany water channel to flow in alonger path through the soil.Concrete headwalls also deterpiping.

Because of changing climaticconditions, debris and bedload inchannels, changing land usepatterns, and uncertainties inhydrologic estimates, culvert sizeand capacity should beconservative, and should beoversized rather than undersized.Ideally, a culvert will be of a sizeas wide as the natural channel toavoid channel constriction.

Channel protection, riprap,overflow dips, headwalls, andtrash racks can all help mitigateculvert problems, but none are asgood as an adequately sized andwell placed pipe. An oversizedculvert, designed to avoid piperepairs or failure as well asprevent environmental damage,can be very cost-effective in thelong run. Also, the addition ofconcrete or masonry headwallshelps reduce the likelihood of pipeplugging and failure.

Pipe size, as a function ofanticipated design flow (capacity)and headwater depth, can easilybe determined using theNomograms presented in Figures8.7a, 8.7b, and 8.7c. These figuresapply to commonly used culvertsof round corrugated metal pipe,

DRAINAGE STRUCTURE SIZING

Drainage Area Size of Drainage Structure(Hectares) Inches and Area (m2)

Steep Slopes Gentle SlopesLogged, Light Vegetation Unlogged, Heavy Vegetation

C= 0.7 C=0.2Round Pipe (in) Area (m2) Round Pipe (in) Area (m2)

0-4 30” 0.46 18" 0.174-8 42" 0.89 24" 0.298-15 48" 1.17 30" 0.4615-30 72" 2.61 42" 0.8930-50 84" 3.58 48" 1.1750-80 96" 4.67 60" 1.8280-120 72" 2.61120-180 84" 3.58

Notes: If pipe size is not available, use the next larger pipe size for the given drainage area. For interme-diate terrain, interpolate between pipe sizes.

-Pipe size is based upon the Rational Formula and Culvert Capacity curves. Assumes a rainfall intensity of75 mm/hr. (3"/hr) to 100 mm/hr (4”/hr). Values of “C” are the Runoff Coefficients for the terrain.

-For tropical regions with frequent high intensity rainfall (over 250 mm/hr or 10”/hr), these drainage areasfor each pipe size should be reduced at least in half.



The outlet of the pipe should extend beyond the toe of the fill and shouldnever be discharged on the fill slope without erosion protection.

YesCulvertcross-drain

Outlet protectionwith rock riprap

No

Erosion or scourunless slopeprotection isadded.

Inletstructure

Compacted fill

Anchor the downdrainpipe to the fill slopewith stakes, cable,anchor blocks, etc.

Optional

Optional use of a downdrain pipe, especially in large fills with poor soils and highrainfall areas, where fill settlement may require culvert repairs.

Roadbed

Pipe

Natural Ground

FFFFFigurigurigurigurigure 8.1e 8.1e 8.1e 8.1e 8.1 Culvert cross-drain installation options in a fill.

Photo 8.4Photo 8.4Photo 8.4Photo 8.4Photo 8.4 A structural plate arch pipe culvert with stream bankprotection using large rock riprap placed upon a geotextile filterlayer.

round concrete pipe, and concreteboxes. Each of these figuresapplies to pipes with inlet control,where there is no constraint on thedownstream elevation of thewater exiting the structure.Ideally, the inlet water elevation(headwater depth) should notgreatly exceed the height ordiameter of the structure in orderto prevent saturation of the fill andminimize the likelihood of the pipeplugging from floating debris.More detailed information isfound in FHWA Manual HDS-5,Hydraulic Design of HighwayCulverts, 1998)


a.a.a.a.a. Culvert alignment options.

bbbbb..... Culvert installation in a broad channel.

Poor – Single pipe concentrates flow in thebroad channel or floodplain.

Better – Multiple pipes disperse the flowacross the channel. Middle pipe may beslightly lower to pass the normal low flowand to promote fish passage.

Poor – Requires a stream channelmodification.

Adequate – No channel modifications butrequires a curve in the road.

Best – No channel modification, and the road is perpendicularto the culvert without a curve in the road alignment.

FFFFFigurigurigurigurigure 8.2 e 8.2 e 8.2 e 8.2 e 8.2 Culvert alignment and installation detail (continued on next page).


Slope 1

Do not change stream bottom elevation!

ccccc..... Install culverts at natural stream grade.

YESRoadbed

Seed and mulch or protectwith riprap

2

NO – TOO DEEP NO – TOO HIGH

30 cm min.

FFFFFigurigurigurigurigure 8.2 e 8.2 e 8.2 e 8.2 e 8.2 (continued)

FFFFFigurigurigurigurigure 8.3 e 8.3 e 8.3 e 8.3 e 8.3 Culvert backfill and compaction. (Adapted from Montana Department of State Lands, 1992)

Roadbed

At least 30 cm of coverfor CMP or one-third ofdiameter for largeculverts. Use 60 cmcover for concrete pipe.

gravel or soilculvert bed

(no rock larger than 8 cm)

Tamp backfill material atregular intervals (lifts) of

15 to 20 cm.

Existing ground

Culvert Level ofnaturalstreambed

Base and sidewall fillmaterial should becompacted. Compact thefill a minimum of oneculvert diameter on eachside of the culvert.


Geotextile or gravel filter (or both)

FFFFFigurigurigurigurigure 8.4e 8.4e 8.4e 8.4e 8.4 Culvert inlet and outlet protection.

a. Normal metal culvert installation using riprap around the inlet and outlet of culverts. Also usegeotextile (filter fabric) or gravel filter beneath the riprap for most installations. (Adapted fromWisconsin’s Forestry Best Management Practice for Water Quality, 1995)

b. Concrete box culvert with concrete wingwalls for inlet/outlet protection and fill retention.


Typical culvert installation with headwalls and splashapron or plunge pool with riprap for energy dissipa-tion and scour control.

or

Roadbed width

Compactedfill

Fill30 cm min.Entrance

elevation

Naturalground

Headwall with orwithoutwingwalls

Total length of pipe

Slope of channel

Distance between headwalls

Slope 1½ : 1 Slope 1½ : 1 or flatter

Outlet elevationat ground level

Splash apronwith Key

Detail of outlet with riprapand plunge pool.

Detail of splash apronwith scour cutoff key.

Pool todissipate energy

Water level

Riprap liningKey 0.3-1.0 m deep

FFFFFigurigurigurigurigure 8.5e 8.5e 8.5e 8.5e 8.5 Culvert installation and outlet protection details with splash apron or rirap lined plungepool.

1-2 m widewith roughened orrocky surface


FFFFFigurigurigurigurigure 8.6e 8.6e 8.6e 8.6e 8.6 Trash rack options for culverts to prevent plugging from debris. Note that some trash racksare located at the pipe and others are located upstream of the pipe, depending on site conditions andaccess for cleaning and maintenance. Location at the pipe is typically best.

Photo 8.5 Photo 8.5 Photo 8.5 Photo 8.5 Photo 8.5 Use trash racks onculverts where a lot of debris isfound in the channel. Remem-ber that trash racks requirecleaning and maintenance.

Photo 8.6Photo 8.6 Photo 8.6Photo 8.6 Photo 8.6 Piping can occurunder poorly installed culvertsand lead to failure. Avoid theuse of fine sand and silt bed-ding and backfill soil, andensure that the material is wellcompacted. Use clay plugs oranti-seepage collars as needed.


FFFFFigurigurigurigurigure 8.7ae 8.7ae 8.7ae 8.7ae 8.7a Headwater depth and capacity for corcorcorcorcorrrrrrugugugugugaaaaated metal pipe culvted metal pipe culvted metal pipe culvted metal pipe culvted metal pipe culvererererertststststs with inletcontrol (metric system). (Adapted from FHWA, HDS 5, 1998)

Example

Cor

ruga

ted

Met

alSt

ruct

ural

Pla

teD

iam

eter

of

Cul

vert

-(D

) (i

n M

eter

s)

Dis

char

ge -

(Q

) (i

n m

3 /sec

)

Stan

dard

Cor

ruga

ted

Met

al P

ipe

Hea

dwat

er D

epth

in D

iam

eter

s -(

He/

D)

ScaleHe/D Entrance Type

(1) Headwall (withwingwalls)

(2) Mitered (to conformto theslope)

(3) Projecting

To use Scale (2) or (3) projecthorizontally to scale (1), thenuse a straight inclined linethrough Scales D and Q, orreverse as illustrated in theexample above.

○○○○○○○○○○○○○○○

○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○

○

○

○

○

He

D

He/D SCALES

EXAMPLE

D = 0.9 mQ = 1.8 m3/sec

Entrance He/D He Type (meters)

(1) 1.8 1.67(2) 2.1 1.89(3) 2.2 1.98

Mitered (Type 2)

∆∆∆∆∆

Headwall and Wingwalls (Type 1)Projecting beyond the Embankment

(Type 3)


Dis

char

ge -

(Q)

(in

m3 /s

ec)

Dia

met

er o

f th

e C

ulve

rt -

(D)

(in

Met

ers)

Hea

dwat

er D

epth

in D

iam

eter

s -

He/

D

EXAMPLE

D = 0.8 mQ = 1.7 m3/seg

Inlet He/D He(meters)

(1) 2.5 2.00(2) 2.1 1.68(3) 2.15 1.72

Example

He/DScale Entrance Type

(1) Square Edge withConcrete Headwalls

(2) Groove end withConcrete Headwall

(3) Groove end withProjecting Pipe

T o use Scales (2) or (3) projecthorizontally to Scale (1), and thenuse a straight inclined line throughD and Q, or reverse as illustratedabove.

SCALES

FFFFFigurigurigurigurigure 8.7be 8.7be 8.7be 8.7be 8.7b Headwater depth and capacity for concrconcrconcrconcrconcrete pipe culvete pipe culvete pipe culvete pipe culvete pipe culvererererertststststs with inlet control.(Adapated from FHWA, HDS 5, 1998)


Rat

io o

f D

isch

arge

to W

idth

- (

Q/B

) (i

n m

3 /sec

/m)

Hei

ght o

f B

ox-

( D

) (i

n M

eter

s)

Hea

dwat

er D

epth

in T

erm

s of

Hei

ght -

( H

e/D

)

He/D WingwallScale Flare

(1) 30° to 75°(2) 90° and 15°(3) 0° (extensions

of the sides)

To use Scales (2) or (3),project horizotally to Scale(1), then use straightinclined line through the Dand Q/B Scales, or reverseas illustrated above.

Angle ofWingwallFlare

EXAMPLE

D x B = 0.60 x 0.80 mQ = 1.08 m3/sec

Q/B = 1.35 m3/sec/m

Inlet He/D He(Meters)

(1) 1.75 1.05(2) 1.90 1.14(3) 2.05 1.23

Example

SCALES

FFFFFigurigurigurigurigure 8.7c e 8.7c e 8.7c e 8.7c e 8.7c Headwater depth and capacity for concrconcrconcrconcrconcrete boete boete boete boete box culvx culvx culvx culvx culvererererertststststs with inlet control.(Adapted from FHWA, HDS5, 1998)



Ditch Relief Cross-DrainCulverts

• Ditch relief cross-drainpipes should typically havea diameter of 45 cm (mini-mum diameter of 30 cm).In areas with debris,unstable cut slopes, andraveling problems, use 60cm or larger pipes.

• Ditch relief cross-drainpipe grade should be atleast 2% more (steeper)than the ditch grade andskewed 0 to 30 degreesperpendicular to the road(see Figure 7.4). Thisadditional grade helps keepthe pipe from pluggingwith sediment.

• Ditch relief cross-drainsshould exit at the toe of thefill near natural groundlevel, at least 0.5 metersbeyond the toe of the fillslope. Armor the pipeoutlet (see Figures 7.6,7.7, and Figure 8.1).Don’t discharge the pipeon unprotected fill mate-rial, unstable slopes, ordirectly into streams (seePhoto 8.1 vs. Photo 8.9).

• In large fills, culvert down-drains may be needed tomove the water to the toeof the fill (Figure 8.1).Anchor downdrains to theslope with metal stakes,concrete anchor blocks, orcable. Pipes, flumes, orarmored ditches may beused.

Drainage Crossing Culverts• Install permanent culverts

with a size large enough topass design flood flows plusanticipated debris. Designfor 20- to 50-year stormevents. Sensitive streamsmay require designs to passa 100-year flood. Pipe sizecan be determined usinggeneral design criteria, suchas in Table 8.1, but is ideallybased upon site-specifichydrologic analysis.

• Consider impacts of anystructure on fish passage andthe aquatic environment.Select a structure such as abridge or bottomless archculvert that is as wide as theordinary high water width(bankfull width), that mini-mizes channel disturbance,and that maintains thenatural channel bottommaterial (Photo 8.7).

• Make road crossings ofnatural drainages perpen-dicular to the drainage tominimize pipe length andarea of disturbance (Figure8.2a).

• Use single large pipes or aconcrete box versusmultiple smaller diameterpipes to minimize pluggingpotential in most channels(unless roadway elevationis critical). In very broadchannels, multiple pipesare desirable to maintainthe natural flow spread

across the channel (Figure8.2b).

• For sites with limitedheight, use “squash pipe”or arch pipes and boxculverts that maximizecapacity while minimizingheight.

• Use concrete or masonryheadwalls on culvert pipesas often as possible. Theadvantages of headwallsinclude: preventing largepipes from floating out ofthe ground when theyplug; reducing the lengthof the pipe; increasing pipecapacity; helping to funneldebris through the pipe;retaining the backfillmaterial; and reducing thechances of culvert failure ifit is overtopped (Photo8.8).

• Install culverts longenough so that both endsof the culvert extendbeyond the toe of theroadway fill (Figure 8.2c,Photo 8.9). Alternatively,use retaining walls(headwalls) to hold backthe fill slope (Figure 8.5).

• Align culverts in thebottom and middle of thenatural channel so thatinstallation causes nochange in the streamchannel alignment orstream bottom elevation.Culverts should not cause


damming or pooling orincrease stream velocitiessignificantly (Figure 8.2).

• Firmly compact well-gradedfill material around culverts,particularly around thebottom half, using placementin layers to achieve a uniformdensity (Figure 8.3). Useslightly plastic sandy gravelwith fines. Avoid the use offine sand and silt rich soilsfor bedding material becauseof their susceptibility topiping. Pay particular atten-tion to culvert bedding andcompaction around thehaunches of the pipe. Do notallow the compaction tomove or raise the pipe. Inlarge fills, allow for settle-ment by installing the pipewith camber.

• Cover the top of metal andplastic culvert pipes with fillto a depth of at least 30 cmto prevent pipe crushing byheavy trucks. Use a minimumcover of 60 cm of fill overconcrete pipe (Figure 8.3).For maximum allowable fillheight, follow the manufac-turer’s recommendations.

• Use riprap, flared metal endsections or masonry/concreteheadwalls around the inlet

and outlet of culverts toprevent water from erodingthe fill or undercutting thepipe, as well as to improvepipe efficiency. With riprap,use graded small rock,gravel or a geotextile filterunder the coarse riprapslope protection (Figure8.4).

• At culvert outlets where pipevelocities are accelerated,protect the channel witheither a plunge pool (ongentle slopes), rockarmoring (riprap) or with asplash apron with a rough orrock inset surface and cutoffkey (Figure 8.5).

• On existing pipes withplugging potential, add atrash rack upstream of thepipe or at the pipe entrance(inlet) to trap debris beforeplugging the pipe (Figure8.6, Photo 8.5). Trash racksmay be constructed withlogs, pipe, rebar, angle iron,railroad rail, H-Piles, and soon. However, trash rackstypically require additionalmaintenance and cleaning.They are undesirable if otheralternatives, such as install-ing a larger pipe, are avail-able.

• Examine stream channels forthe amount of debris, logs,and brushy vegetation. Inchannels with large amountsof debris, consider using alow-water ford, oversizedpipes, or placing a trash rackupstream of the pipe en-trance.

• Install overflow dips off theside of the culvert in drain-age channels with a large fillthat could be overtopped.Also use overflow dips onlong sustained road gradeswhere a plugged culvertcould divert water down theroad, plugging subsequentculverts and causing exten-sive off-site damage (seeChapter 7, Figure 7.11).

• Temporary log culverts(“Humboldt” culverts)usually have very little flowcapacity. When used, ensurethat the structure and all fillmaterial are removed fromthe channel before the rainyseason or expected largerunoff events (Photo 8.10).

• Do periodic maintenance andchannel cleaning to keepculverts protected and clearof debris that could plug thepipe.

RECOMMENDED PRACTICES (cont.)


PRACTICES TO AVOID

• Discharging cross-drainpipes on a fill slope unlessthe slope is protected or adown drain is used.

• Using pipes undersized forthe expected flow andamount of debris.

• Using non-cohesive finesands and silt beddingmaterials that are verysusceptible to piping.

• Installing pipes too short tofit the site.

• Placing pipes improperly (i.e.buried or aligned with thenatural stream channelbottom).

• Leaving low-capacity tem-porary drainage crossingstructures in place over therainy season.

Photo 8.7Photo 8.7Photo 8.7Photo 8.7Photo 8.7 Use structures withnatural stream bottoms, such asarch pipes, bottomless arches,or concrete box culverts, topromote fish passage andminimize impacts to the stream.

Photo 8.8 Photo 8.8 Photo 8.8 Photo 8.8 Photo 8.8 Install culverts withadequate capacity. Useheadwalls to improve culvertcapacity, protect the roadwayfill, resist overtopping damage,and prevent bank scour, par-ticularly at a bend in the chan-nel.


Photo 8.10Photo 8.10Photo 8.10Photo 8.10Photo 8.10 Most log culverts have very little flow capacity. Removetemporary log (Humboldt) culverts before major rainstorms or beforethe rainy season.

Photo 8.9Photo 8.9Photo 8.9Photo 8.9Photo 8.9 Avoid culvert outlets in the middle of a fill slope. Use cul-verts long enough to extend to the toe of the slope, or use headwallstructures to retain the fill material and minimize the pipe length.


Chapter 9

FFFFFororororords and Low-Wds and Low-Wds and Low-Wds and Low-Wds and Low-Waaaaater Crter Crter Crter Crter Crossingsossingsossingsossingsossings

LOW WATER CROSSINGS, fords, or drifts, as theyare commonly called, can offer a desirablealternative to culverts and bridges for stream

crossings on low-volume roads where road use andstream flow conditions are appropriate. Like otherhydraulic structures for stream crossings, they requirespecific site considerations and specific hydrologic,hydraulic, and biotic analyses.Ideally, they should beconstructed at a relativelynarrow, shallow streamlocation and should be in anarea of bedrock or coarse soilfor good foundationconditions. A ford can benarrow or broad, but shouldnot be used in deeply inciseddrainages that require a highfill or excessively steep roadapproaches.

Low-water crossings mayhave a simple rock reinforced(armored) driving surface oran improved surface such asgabions or a concrete slab, asseen in Figure 9.1a and Photo9.1. Vented fords combine the

“Keep the ford profile low, armor the driving surface,and protect against scour.”

Photo 9.1Photo 9.1Photo 9.1Photo 9.1Photo 9.1 Use armored low-water crossings, fords, or drifts as often aspossible to cross low flows in broad, shallow natural drainages, thusavoiding the use of pipes. Note that part of this reinforced driving sur-face needs repair.

Chapter 9

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use of culvert pipes or box culverts to pass low flowsand a reinforced driving surface over the culverts tosupport traffic and keep traffic out of the water mostof the time, as seen in Figures 9.1b and c. The rein-forced driving surface over the pipes also resists ero-sion during overtopping at high water flows (Photo9.2). The entire wetted perimeter of the structure

LOW-VOLUME ROADS BMPS:92

Photo 9.2Photo 9.2Photo 9.2Photo 9.2Photo 9.2 A vented ford, using multiple culvert pipes to handle lowflows through the pipes, yet allow major flows and debris to overtopthe entire structure.

should be protected to a levelabove the anticipated high waterelevation.

Key factors to consider for thedesign and location of a ford in-clude the following: low and highwater levels; foundation condi-tions; scour potential; allowabletraffic delays; channel cross-sec-tion shape and confinement; pro-tection of the downstream edgeof the structure against localscour; stream channel and bankstability; locally available con-struction materials; and gradecontrol for fish passage.

commodate larger flows.

• Vented fords can be used topass low flows and keepvehicles out of the water,avoiding water qualitydegradation.

• The structure can bedesigned as a broad-crested weir that can passa large flow volume overthe top of the ford. It is

not very sensitive tospecific flow volumessince a small increase inflow depth greatly in-creases capacity. They canbe more “forgiving” andaccommodate moreuncertainties in the designflow and thus are ideal fordrainages with unknownor variable flow character-istics.

• The major advantage is thata ford is usually not suscep-tible to plugging by debris orvegetation the way a culvertpipe may plug.

• Fords are typically lessexpensive structures thanlarge culverts or bridges.They may be initially moreexpensive than culverts, butthey require less fill in thechannel, and they can ac-

ADVANTAGES OF LOW-WATER CROSSINGS

DISADVANTAGES OF LOW-WATER CROSSINGS

• Ford-type structures implysome periodic or occasionaltraffic delays during periodsof high flow.

• The shape is not easilysuitable to deeply inciseddrainages that would requirehigh fills.

• Since the shape of the struc-ture involves a dip andperiodic delays, they aretypically not desirable forhigh use or high-speed roads.

• Vented fords may back up thebedload in a stream channel,causing culvert plugging,requiring maintenance, and

causing other channeladjustments.

• Fish passage may bedifficult to incorporate intothe design.

• Crossing the structure canbe dangerous duringperiods of high flow(Figure 9.2).


a. Simple Low-Water Crossing with Reinforced Roadbed of Rock or Concrete

b. Improved (Vented) Ford with Culvert Pipes in a Broad Channel

c. Vented Ford with Pipes or Box Culverts in an Incised Channel

Maximum ExpectedHigh Water Level


Reinforced Roadbedwith Rock orConcrete Slab

Original Ground Reinforced Road

Surface

Normal Water Level

FFFFFigurigurigurigurigure 9.1e 9.1e 9.1e 9.1e 9.1 Basic low-water crossing (fords or drifts) options. Note: Armor the road surface (withrock, concrete reinforcement, etc.) to an elevation aaaaabobobobobovvvvveeeee the high water level!

For fish or aquatic speciespassage, a natural or rough streamchannel bottom should be main-tained through the ford, and wa-ter velocities should not be accel-erated. Ideal structures are either

vented fords with box culverts anda natural stream bottom (seePhoto 9.5) or simple on-gradefords with a reinforced, roughdriving surface (Figure 9.1a).


Reinforced Roadbed withRock or Concrete Slab

Freeboard0.3-0.5m


b. Low-water crossing at high water – WAIT!

c. Crossing during high water can be dangerous!

a. Low-water crossing at low water.

FFFFFigurigurigurigurigure 9.2e 9.2e 9.2e 9.2e 9.2 Danger of crossing a ford at high water. Fords require occasional traffic delays duringperiods of high water. (Adapted from Martin Ochoa, 2000 and PIARC Road Maintenance Handbook,1994)



• Use an adequately long slabor structure to protect the“wetted perimeter” of thenatural flow channel. Addprotection above the ex-pected level of the high flow(Photo 9.3). Allow for somefreeboard, typically 0.3 to0.5 meters in elevation,between the top of thereinforced driving surface(slab) and the expected highwater level (see Figure 9.1).The flow capacity of a ford,and thus the high waterlevel, can be estimated usinga “Broad-Crested Weir”formula.

• Protect the entire structurewith cutoff walls, riprap,gabions, concrete slabs, orother scour protection. Thedownstream edge of a fordis a particularly criticallocation for scour and needsenergy dissipators or riprapprotection because of thetypical drop in water level

off the structure and theaccelerated flows across theslab.

• For simple rock fords, uselarge graded rock in theroadbed through the creek,large enough to resist theflow of water. Use criteria asshown in Figure 6.1. Fill thevoids with clean, small rockor gravel to provide asmooth driving surface. Thissmall rock will have to beperiodically maintained andreplaced.

• Use fords for crossingseasonally dry streambedsor streams with low flowsduring most periods ofroad use. Use improved(vented) fords with pipesor concrete box culverts topass low water flows(Photo 9.4). Accommo-date fish passage whereneeded using box culvertswith a natural stream

channel bottom (Figure9.1c and Photo 9.5).

• Locate fords where streambanks are low and wherethe channel is well con-fined. For moderatelyincised drainages, useimproved fords with pipeor box culverts (Figure9.1c).

• Place foundations intoscour resistant material(bedrock or coarse rock)or below the expecteddepth of scour. Preventfoundation or channelscour with the use oflocally placed heavyriprap, gabion baskets,concrete reinforcement ordense vegetation.

• Use well placed, sturdydepth markers at fords toadvise traffic of dangerouswater depths (Figure 9.2).

PRACTICES TO AVOID

• Constructing sharp verticalcurves on fords that can traplong trucks or trailers.

• Placing approach fill materialin the drainage channel.

• Crossing fords during highwater flows.

• Placing low-water cross-ings on scour susceptible,fine grained soil deposits,or using designs withoutscour protection.

• Constructing fords thatblock upstream and down-stream passage of fish.


Photo 9.3Photo 9.3Photo 9.3Photo 9.3Photo 9.3 With low-watercrossings, the downstreamedge of the structure typicallymust be protected againstscour and the entire wettedperimeter (to a level above thehigh water level) should bereinforced.

Photo 9.4Photo 9.4Photo 9.4Photo 9.4Photo 9.4 Use vented fordswith pipes or openings to keeptraffic out of the water most ofthe time, minimize trafficdelays, and allow for fishpassage. Note the downstreamscour protection with gabionsand rock.

Photo 9.5 Photo 9.5 Photo 9.5 Photo 9.5 Photo 9.5 Some fords can bedesigned as “low-water bridge”structures. They must bedesigned to be occasionallyovertopped and have an erosionresistance deck and ap-proaches. This structure is idealfor fish passage.


Chapter 10

BridgBridgBridgBridgBridgeseseseses

BRIDGES ARE relatively expensive but often arethe most desirable stream crossing structurebecause they can be constructed outside of

the stream channel and thus minimize channelchanges, excavation, or placement of fill in the naturalchannel. They minimize disturbance of the naturalstream bottom and they do notrequire traffic delays onceconstructed. They are ideal for fishpassage. They do require detailedsite considerations and specifichydraulic analyses and structuraldesign.

The bridge location and sizeshould ideally be determined by anengineer, hydrologist, and fisheriesbiologist who are working togetheras a team. When possible, a bridgeshould be constructed at a narrowchannel location and should be inan area of bedrock or coarse soiland rock for a bridge site with goodfoundation conditions. Manybridge failures occur due tofoundations placed upon finematerials that are susceptible toscour.

“Bridges -- usually the best, but most expensive drainagecrossing structure. Protect bridges against scour.”

Chapter 10

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Bridges should be designed to ensure that theyhave adequate structural capacity to support theheaviest anticipated vehicle or posted for load lim-its. Simple span bridges may be made of logs, tim-bers, glue-laminated wood beams, steel girders, rail-road car beds, cast-in-place concrete slabs, pre-

Photo 10.1Photo 10.1Photo 10.1Photo 10.1Photo 10.1 Culverts, fords, or bridges may be used for streamcrossings. Use bridges to cross large permanent streams, mini-mize channel disturbance, and to minimize traffic delays. Use anopening wide enough to avoid constricting the natural channel.Locate the bridge foundation on bedrock or at an elevation belowthe anticipated depth of scour.

LOW-VOLUME ROADS BMPS: 98

Brow Log

Native Log(typ.)

Shot RockFill Liner

Brow Log

19mm Ø Cable

Native Log Stringer Bridge

Curb

Untreated Timber Running Surface

Curb

Steel Beam

Treated Timber Decking

W Shape(typ.)

Stationary DiaphragmMovable Diaphragm

Stationary Diaphragm

Hamilton EZ Bridge (Modular)

Curb Curb

Metal Diaphragm(typ.)

Untreated Timber Running SurfaceTreated Timber Decking

Glulam Beam(typ.)

Treated Timber Glue Laminated Bridge

Curb Curb

PrestressedConcreteDouble-T(typ.)

Prestressed Concrete Single or Double-T Bridge

FFFFFigurigurigurigurigure 10.1e 10.1e 10.1e 10.1e 10.1 Cross-sections of typical types of bridges used on low-volume roads.


fabricated concrete voided slabs or“T” beams, or using modular bridgessuch as Hamilton EZ or BaileyBridges (see Figure 10.1). Manytypes of structures and materials areappropriate, so long as they are struc-turally designed (Photo 10.1).

“Standard designs” can be foundfor many simple bridges as a functionof bridge span and loading conditions.Complex structures should be spe-cifically designed by a structural en-gineer. Bridge designs often requirethe approval of local agencies or gov-ernments. Concrete structures aredesirable because they can be rela-tively simple and inexpensive, requireminimal maintenance, and have arelatively long design life (100+ years)in most environments. Log bridgesare commonly used because of theavailability of local materials, particu-larly in remote areas. However, keepin mind that they have relatively shortspans and they have a relatively short

Photo 10.2Photo 10.2Photo 10.2Photo 10.2Photo 10.2 A bridge structure typically offers the best channelprotection by staying out of the creek. Use local material for bridgesas available, considering design life, cost, and maintenance. Inspectbridges regularly, and replace them when they are no longer structur-ally adequate.

design life (20-50 years) (Photo10.2).

Foundations for bridges may in-clude simple log sills, gabions, ma-sonry retaining walls, or concrete

Photo 10.3Photo 10.3Photo 10.3Photo 10.3Photo 10.3 Scour is one of the most common causes of bridgefailure. Use an opening wide enough to minimize constriction of thenatural channel. Locate the bridge foundation on bedrock whenpossible, or below the depth of scour, and use stream bank protectionmeasures such as riprap.

stem walls with footings. Some simplebridge foundation details are shownin Figure 10.2. Deep foundationsoften use drilled piers or driven piles.Most bridge failures occur either be-cause of inadequate hydraulic capac-ity (too small) or because of scourand undermining of a foundationplaced upon fine soils (Photo 10.3).Thus, foundation considerationsare critical. Since bridge structuresare typically expensive, and sites maybe complicated, most bridge designsshould be done with input from ex-perienced structural, hydraulic, andgeotechnical engineers.

Periodic bridge inspection (every2-4 years) and maintenance is neededto ensure that the structure is safe topass the anticipated vehicles, that thestream channel is clear, and to maxi-mize the design life of the structure.Typical bridge maintenance items in-clude cleaning the deck and “seats”of the girders, clearing vegetation anddebris from the stream channel, re-


placing object markers and signs, re-pairing stream bank protection mea-sures, treating dry and checkingwood, replacing missing nuts andbolts, and repainting the structure.

RECOMMENDED PRACTICES• Use an adequately long

bridge span to avoid constrict-ing the natural active (bankfull)flow channel. Minimize con-striction of any overflowchannel.

• Protect the upstream anddownstream approaches tostructures with wing walls,riprap, gabions, vegetation, orother slope protection wherenecessary (Photo 10.4).

• Place foundations onto non-scour susceptible material(ideally bedrock (Photo 10.5)or coarse rock) or below theexpected maximum depth ofscour. Prevent foundation orchannel scour with the use oflocally placed heavy riprap,gabion baskets, or concretereinforcement. Use scourprotection as needed.

• Locate bridges where thestream channel is narrow,straight, and uniform. Avoidplacing abutments in the activestream channel. Where neces-sary, place in-channel abut-ments in a direction parallel tothe stream flow.

• Consider natural channeladjustments and possiblechannel location changes overthe design life of the structure.Channels that are sinuous, havemeanders, or have broad floodplains may change locationwithin that area of historic flowafter a major storm event.

• For bridge abutments orfootings placed on naturalslopes, set the structure intofirm natural ground (not fillmaterial or loose soil) at least0.5 to 2.0 meters deep. Useretaining structures as needed insteep, deep drainages to retainthe approach fills, or use arelatively long bridge span(Figure 10.2).

• Design bridges for a 100- to200-year storm flow. Expensivestructures and structures withhigh impacts from failure, suchas bridges, justify conservativedesigns.

• Allow for some freeboard,typically at least 0.5 to 1.0meter, between the bottom ofbridge girders and expectedhigh water level and floatingdebris. Structures in a jungleenvironment with very highintensity rainfall may needadditional freeboard. Alterna-tively, a bridge may be designedfor overtopping, somewhat likea low water ford, and eliminatethe need for freeboard, butincrease the need for a erosionresistant deck and approachslabs (Photo 10.6).

• Perform bridge inspectionsevery 2 to 4 years. Do bridgemaintenance as needed toprotect the life and function ofthe structure.

PRACTICES TOAVOID

• Placing piers or footing in theactive stream channel or mid-channel.

• Placing approach fill materialin the drainage channel.

• Placing structural foundationson scour susceptible soildeposits such as silts and finesands.

• Constricting or narrowing thewidth of the natural streamchannel.


Typical Log Bridge InstallationEnsure that the bridge has adequate flow capacity beneath the structure. Keep fill mate-rial and the abutments or footings out of the stream channel. Set footings into thestreambank above the high water level or below the depth of scour if they are near thechannel. Add protection against scour, such as riprap, gabions, or vegetation.

Set the stringers or deck slab at least 0.5 to 2.0 meters above the expected high waterlevel to pass storm flow plus debris.

Bridge Abutment DetailSet bridge foundation (gabion abutment, footings, or logs) into rock or firm, stable soil.Set footings 0.5-2.0 meters into firm material.

Timbersill

Install bottom of stringersat least .5 m above high water

LogAbutmentGabion

Abutment

0.3-1.0 m widebench into firmsoil (not fill) infront of abutments.

1 m x 1 mGabionsor masonryabutment

Slab or Girder

Bridge Deck Roadbed

Set into firmsoil 0.5 to 2.0 m

1-2 m

Install bottom of stringers atleast 0.5 m above high water

Logs

FFFFFigurigurigurigurigure 10.2e 10.2e 10.2e 10.2e 10.2 Bridge installation with simple foundation details.


Photo 10.4Photo 10.4Photo 10.4Photo 10.4Photo 10.4 Concrete struc-tures have a long design life andare typically very cost-effectivefor long bridge spans. Medium-length structures often combinea concrete deck placed uponsteel girders. Use bank protec-tion, such as riprap, to protectthe entrance and outlet of struc-tures.

Photo 10.5 Photo 10.5 Photo 10.5 Photo 10.5 Photo 10.5 Locate the bridgefoundation on bedrock or on non-scour susceptible material whenpossible. When it is necessary tolocate the bridge foundation onmaterials susceptible to scour,use a deep foundation or designthe bridge with scour protection.

Photo 10.6 Photo 10.6 Photo 10.6 Photo 10.6 Photo 10.6 Here is a well builttreated timber bridge with goodstreambank protection andadequate span to minimizestream channel impacts. Thefreeboard is marginally ad-equate.


Chapter 11

Slope StaSlope StaSlope StaSlope StaSlope Stabilizabilizabilizabilizabilization andtion andtion andtion andtion andStaStaStaStaStability ofbility ofbility ofbility ofbility of Cuts and F Cuts and F Cuts and F Cuts and F Cuts and Fillsillsillsillsills

THE OBJECTIVES OF ROUTINE ROAD CUTS AND FILLS

are 1) to create space for the road templateand driving surface; 2) to balance material between

the cut and fill; 3) to remain stable over time; 4) to not bea source of sediment; and 5) to minimize long-term costs.Landslides and failed road cuts and fills can be a majorsource of sediment, they can close the road or requiremajor repairs, and they can greatly increase roadmaintenance costs (Photo 11.1). Vertical cut slopesshould not be used unless the cutis in rock or very well cementedsoil. Long-term stable cut slopesin most soils and geographicareas are typically made withabout a 1:1 or ¾:1 (horizontal:vertical) slope (Photo 11.2).Ideally, both cut and fill slopesshould be constructed so thatthey can be vegetated (Photo11.3), but cut slopes in dense,sterile soils or rocky material areoften difficult to vegetate.

Fill slopes should be con-structed with a 1 1/2:1 or flatterslope. Over-steep fill slopes(steeper than a 1 1/2 :1 slope),commonly formed by side-cast-ing loose fill material, may con-tinue to ravel with time, are diffi-

“Construct cut and fill slopes that are flat enough to bestable over time and that can be revegetated.”

Photo 11.1Photo 11.1Photo 11.1Photo 11.1Photo 11.1 Over-steep slopes, wet ares, or existing slide areas cancause instability problems for a road and increase repair andmaintanance costs, as well as sediment production.

Chapter 11

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cult to stabilize, and are subject to sliver fill fail-ures (Photo 11.4). A rock fill can be stable with a1 1/3:1 slope. Ideally, fills should be constructedwith a 2:1 or flatter slope to promote growth ofvegetation and slope stability (Photo 11.5). Ter-races or benches are desirable on large fill slopesto break up the flow of surface water.


Photo 11.2Photo 11.2Photo 11.2Photo 11.2Photo 11.2 Construct cutslopes at a 3/4:1 or flatter slopein most soils for long-termstability. In well-cemented soilsand rock, a 1/4:1 cut clope willusually be stable.

Photo 11.3Photo 11.3Photo 11.3Photo 11.3Photo 11.3 A well-stabilized cutslope, with about a 1:1 slope, thatis well covered with vegetation.

Photo 11.4Photo 11.4Photo 11.4Photo 11.4Photo 11.4 Avoid loose, over-steep fill slopes (steeper than 1 1/5:1), particularly along streamsand at drainage crossings.


Photo 11.5Photo 11.5Photo 11.5Photo 11.5Photo 11.5 Construct fill slopes with a 1 1/2:1 or flatter slope (topromote vegetation growth) and stabilize the fill slope surface. Usebenches (terraces) on large fill slopes to intercept any flow of surfacewater.

Table11.1 presents a range ofcommonly used cut and fill slope ra-tios appropriate for the soil and rocktypes described. Also Figure 11.1and Figure 11.2 show typical cutslope and fill slope design options, re-spectively, for varying slope and siteconditions. Note, however, that lo-cal conditions can vary greatly, sodetermination of stable slopes shouldbe based upon local experience andjudgment. Groundwater is the majorcause of slope failures.

Slope failures, or landslides, typi-cally occur where a slope is over-steep, where fill material is not com-pacted, or where cuts in natural soilsencounter groundwater or zones ofweak material. Good road locationcan often avoid landslide areas andreduce slope failures. When failuresdo occur, the slide area should be sta-bilized by removing the slide mate-rial, flattening the slope, adding drain-age, or using structures, as discussedbelow. Figure 11.3 shows some ofthe common causes of slope failuresalong with common solutions. De-signs are typically site specific andmay require input from geotechnicalengineers and engineering geologists.Failures that occur typically impactroad operations and can be costly torepair. Failures near streams andchannel crossings have an added riskof impact to water quality.

A wide range of slope stabiliza-tion measures is available to the en-gineer to solve slope stability prob-lems and cross an unstable area. Inmost excavation and embankmentwork, relatively flat slopes, goodcompaction, and adding neededdrainage will typically eliminate rou-tine instability problems (Photo11.6). Once a failure has occurred,

COMMON STABLE SLOPE RATIOSFOR VARYING SOIL/ROCK CONDITIONS

Soil/Rock Condition Slope Ratio (Hor:Vert)

Most rock ¼:1 to ½:1

Very well cemented soils ¼:1 to ½:1

Most in-place soils ¾:1 to 1:1

Very fractured rock 1:1 to 1 ½:1

Loose coarse granular soils 1 ½:1

Heavy clay soils 2:1 to 3:1

Soft clay rich zones or 2:1 to 3:1wet seepage areas

Fills of most soils 1 ½:1 to 2:1

Fills of hard, angular rock 1 1/3:1

Low cuts and fills (<2-3 m. high) 2:1 or flatter(for revegetation)



FFFFFigurigurigurigurigure 11.1 e 11.1 e 11.1 e 11.1 e 11.1 Cut slope design options.

Use Full Bench Cuts When theGround Slopes Exceed +/- 60%

High CutTypically SteeperWhere Stable

Typical RockCut Slopes¼:1 to ½:1

Typical Cut Slopes inMost Soils ¾:1 to 1:1

Natural Ground

0-60% Ground slopes

60% +

¾:1 1:1 ½

:1

¼:1

Road

Road

Road Cut

Fill

¾:1 to

1:1

0 - 60%

Low CutCan be Steep

or Flatter

2:1

Use a Balanced Cut and FillSection for Most Constructionon Hill Slopes.

2:1 Typical

a. Balanced Cut and Fill

b. Full Bench Cut

c. Through Cut


FFFFFigurigurigurigurigure 11.2e 11.2e 11.2e 11.2e 11.2 Fill slope design options

a. Typical Fill Natural ground

0-40%Ground slope

40-60%

Typically60% +

Geogrid or geotextilereinforcement layers

Drain

Road

On ground where slopes exceed 40 - 45%, constructbenches +/- 3 m wide or wide enoughfor excavation and compaction equipment.

Scarify and removeorganic material

Road

Road

Typically place fill on

a 2:1 or flatter slo

pe.

Long fill

slope

1:1

1 1/2:1 Typical

Road

0-40%

3:1

Slash

Slash

Fill material placed in layers . Uselifts 15-30 cm thick. Compact tospecified density or wheel rolleach layer.

Note: When possible, use a 2:1or flatter fill slope to promoterevegetation.

2:1

Short fillslope

Note: Side-cast fill materialonly on gentle slopes, awayfrom streams.

Reinforced fills are used onsteep ground as analternative to retainingstructures. The 1:1 (Over-steep) face usually requiresstabilization.

d. Through Fill

c. Reinforced Fill

b. Benched Slope Fill with Layer Placement


The Problem

Solutions

Oversteep (nearvertical) cutslope Cut failure

Uncontrolledwater Fill failure in

oversteep oruncompactedfill material

Loosesidecast fillon a steepslope

FFFFFigurigurigurigurigure 11.3e 11.3e 11.3e 11.3e 11.3 Slope problems and solutions with stabilization measures.

Cut slope laid backto a stable angle

Cut slopefailure

Rock buttresswith underdrain

Originalover-steepenedslope

Fill compacted in15-30 cm thick layers

Retaining structureNote: This drawing shows avariety of slope stabilizationmeasures which can be used tostabilize cuts and fills.

Vegetation on fillslope surface,preferably 2:1 orflatter

Subdrainage

Potential fillfailure surface

1:1

2:1


the most appropriate stabilizationmeasure will depend on site-specificconditions such as the size of the slide,soil type, road use, alignment con-straints, and the cause of the failure.Here are a range of common slopestabilization options appropriate forlow-volume roads, presented roughlyfrom simplest and least expensive, tothe most complex and expensive:

• Simply remove the slide mate-rial.

• Ramp over or align the roadaround the slide.

• Revegetate the slope and addspot stabilization (See Photo13.10).

• Flatten or reconstruct the slope.

• Raise or lower the road level tobuttress the cut or removeweight from the slide, respec-tively.

• Relocate the road to a newstable location.

• Install slope drainage such asdeep cutoff trenches or dewaterwith horizontal drains.

• Design and construct buttresses(Photo 11.7), retaining struc-tures, or rock anchors.

Retaining structures are relativelyexpensive but necessary in steep ar-

eas to gain roadway space or to sup-port the roadbed on a steep slope,rather than make a large cut into thehillside. They can also be used forslope stabilization. Figure 11.4 (aand b) presents information on com-mon types of retaining walls andsimple design criteria for rock walls,where the base width is commonly0.7 times the wall height (Photo11.8). Figure 11.4c presents com-mon gabion gravity wall designs andbasket configurations for varying wallheights. Gabion structures are verycommonly used for walls up to 6meters high, particularly because theyuse locally available rock and are la-bor intensive (Photo 11.9).

For low to high walls in manygeographic areas today, MechanicallyStabilized Earth (MSE), or “Rein-forced Soil” structures are the leastexpensive type of wall available. Theyare simple to build, and often they canuse on-site granular backfill material.They are commonly constructed us-ing layers of geotextile or welded wireplaced in lifts 15 to 45 cm apart inthe soil, thus adding tensile reinforce-

Photo 11.6Photo 11.6Photo 11.6Photo 11.6Photo 11.6 Simple hand compaction behind a low rock wall. Compac-tion is important behind any retaining structure or fill. It can beachieved by hand or, preferably, using equipment such as a wacker orsmall compactor.

Photo 11.7Photo 11.7Photo 11.7Photo 11.7Photo 11.7 A drained rock buttress can be used to stabilize a cutslope failure area.


Concrete

a.a.a.a.a. Common Types of Retaining Structures.

HeadersStretcher

Crib Wall

Gabion Wall

Reinforced Soil Wall

FacingReinforced Soil

Brick or Masonry Rock

Reinforced Concrete

“H" Piles

Road

Piles

Concrete with Counterforts

Counterfort

Keys

High Rock WallConfiguration

Low Rock Wall Configuration

bbbbb..... Typical Rock Wall Construction.

½ : 1 toVertical

Width(W)

ForH = 0.5 m, W = 0.2 mH = 1.0 m, W = 0.4 mH = 1.5 m, W = 0.7 mH = 2.0 m, W = 1.0 m

Rock

AggregateFill

Rock Height(H)± 70 cm

Hm

ax =

5 m

eter

s

1

2

0.7 H

0.3-0.5 m

Gravity Walls

Figure 11.4 Construction of various types of retaining structures. (Adapted from Gray & Leiser, 1982)


bbbbb..... Standard design for Gabion Retaining Structures up to 20 feet in height (6 meters) withflat or sloping backfill.

No. oflevels

No. ofgabions

(perwidth)BH

1 3' 3" 3' 3" 1

2 6' 6" 4' 11" 11/2

3 9' 9" 6' 6" 2

4 13' 1" 8' 2" 21/2

5 16' 4" 9' 9" 3

6 19' 7" 11' 5" 31/2

Fill at 1 1/2:1 (face with steps)

6

B

1

H

4

2

1

5

6

3

1.5

H

20"

1

1

2

3

4

5

6

B

Flat Backfill (smooth face)

No oflevels

No. ofgabions

(perwidth)BH

1 3' 3" 3' 3" 1

2 6' 6" 4' 3" 11/2

3 9' 9" 5' 3" 2

4 13' 1" 6' 6" 2

5 16' 4" 8' 2" 21/2

6 19' 7" 9' 9" 3

β = 34°

Note: Loading conditions are for silty sand to sand and gravel back fill. For finer or clay rich soils,earth pressure on the wall will increase and the wall base width (B) will have to increase for eachheight. Backfill weight = 110 pcf. (1.8 Tons/m3) (1,762 kg/m3)- Safe against overturning for soils with a minimum bearing capacity of 2 Tons/foot2 (19,500 kg/m2)- For flat or sloping backfills, either a flat or stepped face may be used.

Figure 11.4 Continued. (Adapted from Gray & Leiser, 1982)


ment to the soil (see Figure 6.3e).Driven “H” piles or sheet piles, withor without tiebacks, are relativelyexpensive but are often the most en-vironmentally acceptable type of wall.They cause less site disturbance thangravity or MSE structures that requirea large foundation excavation. Most

types of retaining structures and de-signs provided by manufacturers areinternally stable for the specified use,site conditions, and height. Most wallfailures occur due to foundation fail-ure. Thus structures must be placedon a good foundation, such as bed-rock or firm, in-place soil.

Photo 11.8Photo 11.8Photo 11.8Photo 11.8Photo 11.8 Use physical slope stabilization methods, such as retain-ing walls, reinforced fills, or rock buttresses where necessary in areasof space limitation on steep slopes.

Photo 11.9Photo 11.9Photo 11.9Photo 11.9Photo 11.9 Gabions are a commonly used type of low gravity retain-ing structure because they use locally available rock and are relativelyinexpensive.

PRACTICES TOAVOID

• Constructing vertical cutslopes (except in very wellcemented soils and rock).

• Road locations and construc-tion practices where the toe ofthe fill ends up in the creek. Donot use side-cast fill placementmethods on steep slopes nextto streams.

• Placing fills or “side-casting”materials on natural groundslopes steeper than 60%.

• Road locations in areas ofknown instability.

• Leaving cut slopes and, par-ticularly, fill slopes barren andexposed to erosion.


• Use balanced cut and fillconstruction in most terrain tominimize earthwork (Figure11.1a).

• On steep ground (>60%slope) use full bench con-struction. Consider construct-ing a narrow, single lane roadwith inter-visible turnouts tominimize excavation (Figure11.1b).

• Construct cut slopes in mostsoils using a cut slope ratio of3/4:1 to 1:1 (horizontal:vertical) (Figure 11.1). Useflatter cut slopes in coarsegranular and unconsolidatedsoils, in wet areas, and in softor clay-rich soils. Use rela-tively flat cut slopes (2:1 orflatter) for low (<2-3 metershigh) cuts to promote growthof vegetation.

• Construct cut slopes in rockusing a cut slope ratio of 1/4:1 to 1/2:1 (Figure 11.1).

• Use vertical cuts (1/4:1 orsteeper) only in stable rock orin very well cemented soils,such as cemented volcanicash or in-place decomposedgranite soil, where the risk ofsurface erosion or continuedravel from a relatively flat cutslope is great and the risk oflocal failures in the steep cutis low.

• Where long-term examplesare available, use localexperience, as well as ideallymaterials testing and analysis,to determine the stable cut

slope angle in a particular soiltype.

• Direct concentrated surfacewater (runoff) away from cutand fill slopes.

• Place construction slash androcks along the toe of fillslopes (See Road Design,Figure 4.2) (Do not bury theslash in the fill!).

• Dispose of unsuitable orexcess excavation material inlocations that will not causewater quality degradation orother resource damage.

• Construct fills with a fillslope ratio of 1 1/2:1 orflatter. In most soils, a 2:1 orflatter fill slope ratio willpromote vegetative growth(Figure11.2a). For clay-richtropical soils in high rainfallareas, a 3:1 fill slope isdesirable.

• Compact fill slopes insensitive areas or when thefill is constructed witherosive or weak soils. Usespecific compaction proce-dures, such as wheel rolling,layer placement of the fill(with 15 to 30 cm lifts), oruse specific compactionequipment when available(Figure 11.2b).

• Remove organic surfacematerial, construct a toebench, and bench the naturalground surface on slopes of40-60% before the fill isplaced over the native soil(Figure 11.2b) to prevent a

“sliver fill” failure at thecontact of the native soil andfill. Once a fill failure occurson a steep slope, a retainingstructure or reinforced fill istypically needed for repairs(Photo 11.10).

• Consider the use of reinforcedfills where a 1:1 fill slope willfit (catch) on natural, stableground (see Figure 11.2c).Use reinforced fills as a costsaving alternative to retainingstructures.

• Use physical and bio-techni-cal slope stabilization mea-sures such as retainingstructures, buttresses, brushlayering, and drainage, asneeded to achieve stableslopes (see Figure 11.3 andFigure 13.4). Retainingstructures may be loose rock,gabions, reinforced concrete,piles, crib walls, soil nails, ormechanically stabilized soilwalls with a variety of facingssuch as geotextile, weldedwire, timber, concrete blocks,or tires (Photo 11.11). Wallbackfill is typically compactedto 95% of the AASHTO T-99 maximum density.

• Use retaining structures togain roadway width in steepterrain.

• Place retaining structures onlyupon good foundationmaterials, such as bedrock orfirm, in-place soils (Photo11.12).



Photo 11.10Photo 11.10Photo 11.10Photo 11.10Photo 11.10 A road fill failure insteep terrain which now needseither a retaining structure or alarge road cut around the failure.

Photo 11.11Photo 11.11Photo 11.11Photo 11.11Photo 11.11 A tire-faced,mechanically stabilized earth(MSE) retaining wall, with layersof geotextile reinforcement,being used to gain road width in afill failure area. MSE (reinforcedsoil) structures are often theleast expensive retainingstructure available. Welded wireMSE walls are also commonlyused.

Photo 11.12Photo 11.12Photo 11.12Photo 11.12Photo 11.12 A gabion retainingstructure which will fail soon dueto lack of a suitable foundation.All retaining structures, eithermechanically stabilized earth(MSE) walls or gravity walls,require a good foundationgood foundationgood foundationgood foundationgood foundation.


Chapter 12

RRRRRoadwoadwoadwoadwoadwaaaaay May May May May Materialsterialsterialsterialsterialsand Maand Maand Maand Maand Material Sourterial Sourterial Sourterial Sourterial Sourcescescescesces

LOW-VOLUME ROAD surfaces and structuralsections are typically built from nativematerials that must support light vehicles and

may have to support heavy commercial truck traffic.In addition, low-volume roads should have a surfacethat, when wet, will not rut and will provide adequatetraction for vehicles. The surface of native soil roadsis also an exposed area that can produce significantamounts of sediment, especially if rutted (Photo12.1).

Roadway MaterialsIt is usually desirable and,

in many cases, necessary toadd subgrade structural sup-port or to improve the road-bed native soil surface withmaterials such as gravel,coarse rocky soil, crushedaggregate, cobblestone, con-crete block, or some type ofbituminous seal coat or as-phalt pavement, as shown inFigure 12.1. Surfacing im-proves the structural supportand reduces road surface ero-sion. The selection of surfac-ing type depends upon thetraffic volume, local soils,

“Select quality roadway materials that are durable,well-graded, and perform well on the road.

Maintain quality control.”

Chapter 12

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available materials, ease of maintenance, and, ulti-mately, cost.

A range of options exists for improving the struc-tural capacity of the roadway in areas of soft soils orpoor subgrades. These commonly include:

• Adding material of higher strength and qualityover the soft soil, such as a layer of gravel or

Photo 12.1 Photo 12.1 Photo 12.1 Photo 12.1 Photo 12.1 A rutting road caused either by soft subgrade soil or inad-equate road drainage (or both).


a. Native Soil

b. Aggregate

c. Aggregate and Base

d. Cobblestone

e. Concrete Block

f. Asphalt Surfacing

g. Typical Aggregate Surfaced Road Template

— Native (In-Place) Soil

— Crushed Surface Aggregate or Gravel— Native Soil

— Native Soil

— Crushed Surface Aggregate or Gravel

— Aggregate Base

— Concrete Blocks

— Native Soil

— Sand

— Native Soil

— Sand

— Cobblestones

— Aggregate Base

— Asphalt Pavement

— Aggregate Sub-Base (Optional)

— Native Soil

Fill Slope Road Surface Ditch

FFFFFigurigurigurigurigure 12.1e 12.1e 12.1e 12.1e 12.1 Commonly used low-volume road surfacing types and structural sections.


crushed aggregate;

• Improving the soft soil inplace (in-situ) by mixing itwith stabilization additivessuch as lime, cement, as-phalt, or chemicals;

• Bridging over the soft soilwith materials such asgeotextiles or wood pieces(corduroy);

• Removing the soft or poorsoil and replacing it with ahigh quality soil or rockymaterial;

• Limiting the use of the roadduring periods of wetweather when clay soils aresoft;

• Compacting the native soilto increase its density andstrength; and

• Keeping moisture out of thesoil with effective roadwaydrainage or encapsulatingthe soil to keep water out.

Various soil stabilization ma-terials such as oils, lime, cements,resins, lignin, chlorides, enzymes,and chemicals may be used to im-prove the material properties ofthe in-place soil. They may be verycost-effective in areas where ag-gregate or other materials are dif-ficult to locate or are expensive.The best soil stabilization mate-rial to use depends on cost, soiltype, performance and local ex-perience. Test sections are oftenneeded to determine the most de-sirable and cost-effective product.However, many soil stabilizers still

need some type of wearing sur-face. A stabilized road surface im-proves traction and offers erosionprotection as well as structuralsupport.

Gravel, pit run rock, selectmaterial, or crushed aggregate arethe most common improved sur-facing materials used on low-vol-ume roads (Photo 12.2). Aggre-gate is sometimes used only as“fill” material in ruts. However, itis more desirable to place it as afull structural section, as shownin Figure 12.2. The roadway sur-facing aggregate must performtwo basic functions. It must havehigh enough quality and be thickenough to provide structural sup-port to the traffic and prevent rut-ting, and it must be well gradedand mixed with sufficient fines,preferably with some plasticity, toprevent raveling andwashboarding.

Necessary aggregate thick-ness typically ranges from 10 to

30 cm, depending on soil strength,traffic, and climate. Specific ag-gregate thickness design proce-dures are found in the SelectedReferences. Over very weak soils(CBR less than 3), aggregatethickness can be reduced with theuse of geotextile or geogridsubgrade reinforcement. Also,geotextile layers are useful oversoft soils to separate the aggre-gate from the soil, keep it uncon-taminated, and extend the usefullife of the aggregate.

Figure 12.3 presents some ofthe physical properties andtradeoffs of various soil-aggregatemixtures, first with no fines (nomaterial passing the #200 sieve,or .074 mm size), second with anideal percentage of fines (6-15%),and finally with excessive fines(over 15 to 30%). Figure 12.4shows the typical gradation rangesof aggregates used in road con-struction, how the materials, rang-ing from coarse to fine, best per-form for a road, and the approxi-

Photo 12.2Photo 12.2Photo 12.2Photo 12.2Photo 12.2 Stabilize the roadway surface with crushed rock (orother surfacing) on steep grades, in areas of soft soil, or in erosivesoils.


For surfacing aggregate usecrushed rock, gravel or 3 cmminus rock with fines.

If crushed rock or gravel isnot available, use coarse soil,wood chips or soil stabilizers.

0-30 cm min.

10-30 cm

(5-10 cm size or smaller)

POOR

MEDIOCRE– ADEQUATE

BEST

a. Minimal aggregatefilled into ruts whenthey develop.

b. Ruts filled plusaddition of 10-15 cm-thick layer of aggregate.

c. Full structural sectionplaced upon a reshapedcompacted subgrade.

Aggregate Surface orAsphalt Surfacing

Aggregate Base Course or CleanFractured Rock

FFFFFigurigurigurigurigure 12.2e 12.2e 12.2e 12.2e 12.2 Aggregate options to prevent rutting.


FFFFFigurigurigurigurigure 12.3e 12.3e 12.3e 12.3e 12.3 Physical states of soil-aggregate mixtures. (Adapted from Yoder andWitczak, 1975)

Aggregate withno Fines

• Grain-to-grain contact

• Variable density

• High Permeability

• Non-Frost Susceptible

• High stability whenconfined, low if uncon-fined

• Not affected by water

• Difficult to compact

• Ravels easily

Aggregate withSufficient Fines forMaximum Density

• Grain-to-grain contactwith increased resistanceagainst deformation

• Increased to maximumdensity

• Low permeability

• Frost susceptible

• Relatively high stabilityin confined or uncon-fined conditions

• Not greatly affected byadverse water conditions

• Moderately easy tocompact

• Good road performance

Aggregate with HighAmount of Fines

(>30 percent)

• Grain-to-grain contactdestroyed, aggregate is"floating" in soil

• Decreased density

• Low permeability

• Frost susceptible

• Low stability and lowstrength

• Greatly affected by water

• Easy to compact

• Dusts easily


PRACTICES TO AVOID

NOTE: Gradation Ranges Shown Are Approximate.

The best roadbed surfacing materials have some plasticity and are well graded. They havegradations parallel to the curves shown above, and are closest to the “Ideal” dashed curve in themiddle of the gradation ranges shown.

• Construction operations orheavy traffic during wet orrainy periods on roads withclay rich or fine-grained soilsurfaces that form ruts.

• Allowing ruts and potholes toform over 5 to 10 cm deep in

the roadway surface.

• Road surface stabilizationusing coarse rock larger thanabout 7.5 cm. Coarse rock isdifficult to drive upon or keepstabilized on the road surface,and it damages tires.

• Using surfacing materialsthat are fine grain soils,soft rock that will degradeto fine sediment, or clean,poorly graded coarse rockthat will erode, ravel, orwashboard.

FFFFFigurigurigurigurigure 12.4 e 12.4 e 12.4 e 12.4 e 12.4 Gradation ranges of roadway surfacing materials and their performance characteristics.(Adapted from R. Charles, 1997 and the Association of Asphalt Paving Technologists)

PER

CEN

T FI

NER

BY

WEI

GH

T (P

ERC

ENT

PASS

ING

- %

)

PERC

ENT C

OA

RSER

BY W

EIGH

T


mate limitations to the desirablegradation ranges. Note that thedesirable percentage of fines in anaggregate can be sensitive to theclimate or road environment. Insemi arid to desert regions, a rela-tively high percentage of fines,such as 15 to 20%, with moder-


ate plasticity, is desirable. In a highrainfall “wet” environment, suchas tropical, coastal mountain, orjungle areas, a low percentage,such as 5 to 10% fines, is desir-able to prevent rutting and main-tain a stable road surface.

Ideally, aggregate surfacingmaterial is (1) hard, durable, andcrushed or screened to a minus 5cm size; (2) well graded toachieve maximum density; (3)contains 5-15% clayey binder toprevent raveling; and (4) has aPlasticity Index of 2 to 10. The

• Stabilize the roadwaysurface on roads that formruts or ravel excessively.Common surface stabiliza-tion techniques includeusing 10-15 cm of crushedaggregate; local pit run orgrid roll rocky material(Photo 12.4); cobblestonesurfacing; wood chips orfine logging slash; or soilsmixed and stabilized withcement, asphalt, lime,lignin, chlorides, chemi-cals, or enzymes.

• For heavy traffic on softsubgrade soils, use asingle, thick structuralsection consisting of atleast 20-30 cm of surfac-ing aggregate. Alterna-tively, use a structuralsection consisting of a 10-30 cm thick layer of baseaggregate or coarsefractured rock, cappedwith a 10-15 cm thicklayer of surfacing aggre-gate (Figure 12.2-BEST).Note that soft clay-richtropical soils and heavytire loads may require athicker structural section.The structural depthneeded is a function of thetraffic volume, loads andsoil type, and should

ideally be determinedthrough local experienceor testing, such as usingthe CBR (CaliforniaBearing Ratio) test.

• Maintain a 3-5% roadcross-slope with insloping,outsloping, or a crown torapidly move water off theroad surface (see Figure7.1).

• Grade or maintain theroadway surface beforesignificant potholes,washboarding, or rutsform (see Figure 4.5).

• Compact the embankmentmaterial, road surfacematerial or aggregateduring construction andmaintenance to achieve adense, smooth road sur-face and thus reduce theamount of water that cansoak into the road (Photo12.5).

• “Spot” stabilize local wetareas and soft areas with10-15 cm of coarse rockymaterial. Add more rockas needed (Figure 12.2).

• Stabilize the road surfacein sensitive areas nearstreams and at drainage

crossings to minimize roadsurface erosion.

• Control excessive roaddust with water, oils,wood chips, or use ofother dust palliatives.

• Blend coarse aggregateand fine clay-rich soil(when available) to pro-duce a desirable compositeroadway material that iscoarse yet well-gradedwith 5-15 % fines forbinder (see Figures 12.3and 12.4).

• Use project constructionquality control, throughvisual observation andmaterials sampling andtesting, to achieve speci-fied densities and quality,well-graded road materials(Photo 12.6).

• On higher standard, hightraffic volume roads(collectors, principals, orarterials) use appropriate,cost effective surfacingmaterials such as oils,cobblestone, paving blocks(Photo 12.7), bituminoussurface treatments (chipseals) (Photo 12.8), andasphalt concrete pave-ments.


Photo 12.3Photo 12.3Photo 12.3Photo 12.3Photo 12.3 A road in need ofmaintenance and surfacing.Add roadway surface stabiliza-tion or do maintenance withgrading and shaping of thesurface to remove ruts andpotholes before significant roaddamage occurs, to achievegood road surface drainage,and to define the roadbed.

Photo 12.4Photo 12.4Photo 12.4Photo 12.4Photo 12.4 A grid roller can beused to produce a desirablesurfacing material when thecoarse rock is relatively soft.Level and compact the roadwaysurface aggregate to achieve adense, smooth, well-drainedriding surface.

Photo 12.5Photo 12.5Photo 12.5Photo 12.5Photo 12.5 Compaction of soiland aggregate is typically theleast expensive way to improvethe strength and performanceof the material. Compaction isuseful and cost-effective bothfor the stability of fill embank-ments and for the road surface.


Photo 12.6Photo 12.6Photo 12.6Photo 12.6Photo 12.6 Here, a “nucleargauge” is being used to checkthe density of aggregate. Useproject construction qualitycontrol, gradation and densitytesting, etc., as needed toachieve the desirable materialsproperties for the project.

Photo 12.7Photo 12.7Photo 12.7Photo 12.7Photo 12.7 Concrete blocks(Adoquin) or cobblestone offeran intermediate alternative toaggregate and pavement roadsurfacing. These materials arelabor intensive to construct andmaintain, but are very cost-effective in many areas.

Photo 12.8Photo 12.8Photo 12.8Photo 12.8Photo 12.8 A chip seal roadsurface being compacted. Avariety of surfacing materialscan be used, depending onavailability, cost, and perfor-mance.


surfacing applied to the road mustbe maintainable in order to pre-vent rutting and erosion. Signifi-cant deterioration of the road canoccur if ruts, raveling,washboarding, or surface erosionare not controlled (Photo 12.3).Road damage can be greatly re-duced by restricting road use dur-ing wet conditions if road man-agement allows for this option.

Compaction is usually themost cost-effective method to im-prove the quality, includingstrength and water resistance, ofsubgrade soils and to improve theperformance of aggregate surfac-ing. It increases the density andreduces the void spaces in thematerial, making it less susceptibleto moisture. Thus, compaction isuseful to protect the investmentin road aggregate, maximize itsstrength, minimize loss of fines,and prevent raveling. Road per-formance has been excellent insome semi-arid regions with theuse of blended local materials,very high compaction standards,and a waterproof membrane suchas a bituminous seal coat.

Compaction can best beachieved with a minimum of ef-fort if the soil or aggregate is wellgraded and if it is moist. Ideally,it should be close to the “optimummoisture content” as determinedby tests such as the “Proctor”Moisture-Density Tests. Expan-sive soils should be compacted onthe wet side of optimum. Handtamping can be effective, but onlywhen done in thin lifts (2-8 cm)and ideally at a moisture contenta few percent above optimum.

The best compaction equip-ment for granular soils and aggre-gate is a vibratory roller. A tamp-ing, or sheepsfoot roller is mosteffective on clay soils. A smoothdrum, steel wheel roller is ideal forcompaction of the roadway sur-face. Vibratory plates or rammers,such as “wackers”, are ideal inconfined spaces. No one piece ofequipment is ideal for all soils, butthe best all-purpose equipment forearthwork in most mixed soils isa pneumatic tire roller that pro-duces good compaction in a widerange of soil types, from aggre-gates to cohesive silty soils.

Materials SourcesThe use of local materials

sources, such as borrow pits andquarries, can produce major costsavings for a project compared tothe cost of hauling materials fromdistant, often commercial,sources. However, the quarry orborrow pit material quality mustbe adequate. Sources may benearby rock outcrops or granulardeposits adjacent to the road orwithin the roadway. Road widen-ing or lowering road grade in frac-tured, rocky areas may producegood construction materials in anarea already impacted by con-struction. Rock excavation andproduction may be by hand (Photo12.9), or with the use of varioustypes of equipment, such asscreens and crushers. Relativelylow-cost, on-site materials can re-sult in the application of consid-erably more roadway surfacingand more slope protection withrock since the materials are readilyavailable and inexpensive. How-ever, poor quality materials willrequire more road maintenance

and may have poor performance.

Borrow pits and quarries canhave major adverse impacts, in-cluding sediment from a large de-nuded area, a change in land use,impacts on wildlife, safety prob-lems, and visual impacts. Thusquarry site planning, location, anddevelopment should usually bedone in conjunction with Environ-mental Analysis to determine thesuitability of the site and con-straints. A Pit Development Planshould be required for any quarryor pit development to define andcontrol the use of the site and thematerials being extracted. A pitdevelopment plan typically definesthe location of the materials de-posit, the working equipment,stockpile and extraction areas(Photo 12.10), access roads,property boundaries, watersources, and final shape of the pitand back slopes. Materials sourceextraction can cause long-termland use changes, so good siteanalysis is needed.

In-channel gravel deposits orstream terrace deposits are oftenused as materials sources. Ideally,deposits in or near streams or riv-ers should not be used. Gravel ex-traction in active stream channelscan cause significant damage tothe stream, both on-site anddownstream (or upstream) of thesite. However, it may be reason-able to remove some materialsfrom the channel with adequatestudy of the fluvial system andcare in the operation. Some gravelbar or terrace deposits may beappropriate for a materials source,particularly if taken from abovethe active river channel. Equip-


Photo 12.9 Photo 12.9 Photo 12.9 Photo 12.9 Photo 12.9 Develop quarriesand borrow sites (materialssources) close to the projectarea whenever possible. Eitherhand labor or equipment may beappropriate, depending on thesite conditions and productionrates.

Photo 12.10 Photo 12.10 Photo 12.10 Photo 12.10 Photo 12.10 Quarries andborrow sites (materialssources) can provide an excel-lent, relatively inexpensivesource of project materials. Asite may require simple excava-tion, screening, or crushing toproduce the desired materials.Control use of the area with aPit Development Plan.

ment should not work in the wa-ter.

Site reclamation is typicallyneeded after materials extraction,and reclamation should be an in-tegral part of site developmentand included in the materials cost.Reclamation work should be de-fined in a Pit Reclamation Plan.Reclamation can include conserv-ing and reapplying topsoil, reshap-ing the pit, revegetation, drainage,erosion control, and safety mea-sures. Often, interim site use, clo-

sure, and future reuse must alsobe addressed. A site may be usedfor many years but be closed be-tween projects, so interim recla-mation may be needed. Roadsideborrow areas are commonly usedas close, inexpensive sources ofmaterial (Photo 12.11). These ar-eas ideally should be located outof sight of the road, and they tooneed reclamation work after use.

The quality of the local mate-rial may be variable or marginal,and the use of local material of-

ten requires extra processing orquality control. Low quality ma-terial may be produced at a costmuch lower than commerciallyavailable material, but may notperform well. Zones of good andbad material may have to be sepa-rated. The use of local materials,however, can be very desirableand cost-effective when availableand suitable.


RECOMMENDED PRACTICES• Develop local borrow pits,

quarries and pit-runmaterial sources whereverpractical in a project area.Ensure that EnvironmentalAnalysis has been done forthe establishment of newmaterials sources.

• Use a Pit DevelopmentPlan to define and controlthe use of local materials.A Pit Development Planshould include the locationof the site, extent ofdevelopment, excavation,stockpiling and workingareas, shape of the pit,volume of useable mate-rial, site limitations, a planview, cross-sections of thearea, and so on. A planshould also address interimor temporary closures andfuture operations.

• Develop a Pit Reclama-tion Plan in conjunctionwith pit planning to return

PRACTICES TO AVOID

• In-stream channel gravelextraction operations andworking with equipment inthe stream.

• Developing materialssources without planning

and implementing reclama-tion measures.

• Using low quality, ques-tionable, or unprovenmaterials without adequateinvestigation and testing.

the area to other long-termproductive uses. A PitReclamation Plan shouldinclude information suchas topsoil conservationand reapplication, finalslopes and shaping, drain-age needs, safety mea-sures, revegetation, anderosion control measures(Photo 12.12).

• Reshape, revegetate andcontrol erosion in roadsideborrow areas to minimizetheir visual and environ-mental impacts (Figure12.5). Locate materialssources either within theroadway or out of view ofthe road.

• Maintain project qualitycontrol with materialstesting to guarantee theproduction of suitablequality material fromquarry and borrow pitsources.


Good Practices for Quarry Development

Poor Practices for Quarry Development

• Screen pit area from road• Leave gentle slopes• Reshape and smooth the area• Leave pockets of vegetation• Seed and mulch the area• Use drainage control measures• Replace Topsoil

DO!

Ideal Location and Sequence of Excavation

41

2

3

DO NOT!• Expose large, open area• Leave area barren• Leave steep or vertical slopes

Road

Locate borrow areas out of sight of the road.(NOTE: Safe backslope excavation height depends on soil type.Keep backslopes low, sloped or terraced for safety purposes.)

FFFFFigurigurigurigurigure 12.5 e 12.5 e 12.5 e 12.5 e 12.5 Good and bad roadside quarry development practices. (Adapted from Visual QualityBest Management Practices for Forest Management in Minnesota, 1996)


Photo 12.12 Photo 12.12 Photo 12.12 Photo 12.12 Photo 12.12 A reclaimed and revegetated borrow site. Reshape, drain,plant vegetation, and rehabilitate borrow pits and quarries once theusable materials are removed and use of the area is completed.

Photo 12.11 Photo 12.11 Photo 12.11 Photo 12.11 Photo 12.11 This roadside borrow area lacks drainage and erosioncontrol. Roadside quarry development can be inexpensive and useful, butthe areas should be hidden if possible, and the areas should be reclaimedonce the project is completed.


Chapter 13

ErErErErErosion Controsion Controsion Controsion Controsion Contrololololol

EROSION CONTROL on roads is fundamental forthe protection of water quality (Photo 13.1).Soil stabilization and erosion control practices

are needed and should be used in areas where soil isexposed and natural vegetation is inadequate. Bareground should be covered, typically with grass seedand some form of matting or mulch. This will helpprevent erosion and subsequent movement ofsediment into streams, lakesand wetlands. This movementof sediment can occur duringand after road construction,after road maintenance, duringlogging or mining activities, asthe road is being used, if a roadis closed but not stabilized, orfrom poor land managementpractices near the road (Photo13.2). Roughly half of theerosion from a loggingoperation, for instance, comesfrom the associated roads.Also, most erosion occursduring the first rainy seasonafter construction.

Erosion control measuresneed to be implemented im-mediately following construc-

“Erosion control -- one of the best, most inexpensive waysto protect the road and the environment. Just do it!”

Photo 13.1Photo 13.1Photo 13.1Photo 13.1Photo 13.1 Do not leave disturbed or barren areas exposed to rain-drops and runoff. Use erosion control measures to protect the area andprotect water quality.

Chapter 13

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tion and every time an area is disturbed. Soil erosionprediction models such as the Water Erosion Pre-diction Project (WEPP) or Unified Soil Loss Equa-tion (USLE) can be used to quantify erosion andcompare the effectiveness of various erosion con-trol measures. Concentrated water flow can beginas minor sheet flow, produce rills, and eventually re-sult in major gully formation (See Chapter 14).


Photo 13.2Photo 13.2Photo 13.2Photo 13.2Photo 13.2 Erosion on a slope adjacent to a highway due to lack ofvegetation or poor land use practices. Note that vegetation ispreventing erosion next to the highway.

Erosion control practices in-clude surface armoring andground cover with netting (Photo13.3), vegetative material or slash(Photo 13.4), rock, and so on; in-stalling water and sediment con-trol structures; and mulching,seeding, and various forms ofrevegetation, as seen in Figures13.1 through Figure 13.4. Effec-tive erosion control requires at-tention to detail, and installationwork requires inspection andquality control.

Physical methods includesuch measures as armored ditches(Photo 13.5), berms, wood chips,ground cover mats, and silt orsediment fences (Photo 13.6).These control or direct the flowof water, protect the ground sur-face against erosion, or modify thesoil surface to make it more resis-tant to erosion (Photo 13.7).

Vegetative methods, usinggrasses, brush, and trees, offer

ground cover, root strength, andsoil protection with inexpensiveand aesthetic “natural” vegetation,as well as help control water andpromote infiltration (Photo 13.8).Ideally, vegetation should be se-lected for good growth proper-ties, hardiness, dense groundcover, and deep roots for slope

stabilization. Local native specieshaving the above mentioned prop-erties should be used. Howeversome grasses, such as Vetiver,have been used extensively world-wide because of their strong, deeproots, adaptability, and non-inva-sive properties (Photo 13.9).

Biotechnical methods suchas brush layering, live stakes, andcontour hedgerows (Figure 13.4)offer a combination of structureswith vegetation for physical pro-tection as well as additional long-term root support and aesthetics(Photo 13.10).

An Erosion Control Plan anduse of erosion control measuresshould be an integral part of anyroad construction or resource ex-traction project. Most disturbedareas, including landings, con-struction storage areas, skidroads, road fills, some road cuts,drainage ditches, borrow pits, theroad surface and shoulders, andother working areas should re-

Photo 13.3Photo 13.3Photo 13.3Photo 13.3Photo 13.3 Cover fill slopes, work areas, and other exposed soilareas with straw, netting, rock, or other material to protect theground and promote vegetative growth.


A. Description of Project1. Project Objectives2. Project Location3. Description of Local Environment

B. Planning1. Site Analysis

a.Climate and Microclimateb.Vegetation Optionsc.Soils and Fertility

2. Developing the Revegetation Plana.Suitable Plant Speciesb.Soil and Site Preparationc.Aesthetics vs. Erosion Control Needsd.Use of Local “Native” Species

C. Implementation1. Planting Methods—Cuttings and Transplants

a.Tools and Materialsb.Planting Holes and Methods

2. Planting Methods—Seeding and Mulchinga.Hand Broadcasting or Hydroseedingb.Range Drillsc.Type / Quantity of Seedd.Type / Quantity of Mulch and Fertilizere. Holding Mulch with Tackifiers or Netting

3. Plant Protectiona.Wire Caging around Plantsb.Fencing Around the Entire Site

4. Maintenance and Care After Plantinga.Irrigationb.Weed Controlc.Fertilization

5. Biotechnical Planting Methodsa.Wattlingb.Brush Layering or Brush Mattingc.Live Stakes

D. Obtaining Plants and Handling of Plant Materials1. Timing and Planning

a.Fall versus Spring Plantingb.Summer Plantings

2. Types of Plant Materialsa.Cuttingsb.Tublingsc.Other Container Plants

3. Hardening-off and Holding Plants (Acclimatizing)4. Handling Live Plants and Cuttings


Key Elements of an Erosion Control andRevegetation Plan for Road Projects

ceive erosion control treatment. Itis more cost effective and efficientto prevent erosion than to repairthe damage or remove sedimentfrom streams, lakes, or ground-water.

Elements of an Erosion Con-trol and Revegetation Plan includeproject location and climate, soiltypes, type of erosion controlmeasures, timing of implementa-tion of the vegetative erosion con-trol measures, source of seeds andplants, and planting methods.Table 13.1 presents the many as-pects of planning, implementation,and care involved in an ErosionControl Plan for roads projects.

PRACTICES TOAVOID

• Disturbing unnecessarilylarge areas.

• Leaving native soil un-protected against ero-sion after new construc-tion or ground distur-bance.

• Earthwork and road con-struction during periodsof rain or the winter.


Grass seedand mulch

Aggregatesurfacedroadbed

Old landing orconstructionwork area

Sedimentcatchmentbasin

Logging slashor woodymaterial spreadover the area

Various erosion control ground coversinclude seeding and straw mulch,grasses and other mulch, vegetation,rock, slash, chips, and leaves.

Deep rootedvegetation forslope stabilization

Woody slash

Grasses

Aggregate roadsurfacing orscarification, seedand mulch forclosed roads

Vegetative ground cover

Grasses or othervegetation

Cross-section

Perspective View

Vegetative contourhedgerow or wattles

FFFFFigurigurigurigurigure 13.1e 13.1e 13.1e 13.1e 13.1 Use of vegetation, woody material and rock for erosion control and ground cover.(Adapted from Wisconsin’s Forestry BMP for Water Quality, 1995)


Photo 13.4 Photo 13.4 Photo 13.4 Photo 13.4 Photo 13.4 A disturbed workarea covered with woodymaterial such as brush fromclearing or logging slash forerosion control . Ensure thatthe material is well mashedonto the ground.

Photo 13.5 Photo 13.5 Photo 13.5 Photo 13.5 Photo 13.5 A roadside ditcharmored with graded rock(riprap) for erosion control.

Photo 13.6 Photo 13.6 Photo 13.6 Photo 13.6 Photo 13.6 Sediment controlfences (silt fences), live vegeta-tive barriers, or brush fencescan all be used to controlsediment movement on slopes(also see Photo 6.6).


Photo 13.7 Photo 13.7 Photo 13.7 Photo 13.7 Photo 13.7 Rock armoring,placed on a very erosive soil fillslope adjacent to a creek, usedfor durable, permanent erosioncontrol.

Photo 13.8 Photo 13.8 Photo 13.8 Photo 13.8 Photo 13.8 Seed and mulch(cover for seed protection andmoisture retention) applied tothe ground surface to promotegrass growth on barren areas,closed roads, and on erosivesoils.

Photo 13.9 Photo 13.9 Photo 13.9 Photo 13.9 Photo 13.9 Use of Vetivergrass for slope stabilization anderosion control. Choose vegeta-tion that is adapted to the site,has strong roots, and providesgood ground cover. Ideally, usenative species.


a. Hay Bales (or bundles of grass)

b. Silt Fences

Leave no gapsbetween bales.

Staked and entrenchedstraw bale. (Use twostakes per bale.)

Bales keyed(buried )10 cm deepinto soil.

Overland

Flow(runoff)

Tampedsoil

Runoff

Filter fabricsilt fence

Compactedbackfill intrench

10cm

Runoff

FFFFFigurigurigurigurigure 13.2ae 13.2ae 13.2ae 13.2ae 13.2a Sediment control structures using hay bales or silt fences. Note that hay bales mustbe installed correctly and keyed into the ground! (Adapted from Wisconsin’s Forestry BMP forWater Quality)

10 cm

Filter fabricsilt fence

Stake

Note: Problems can develop from water running between and underhay bales. Install them carefully. Long-term structures must be periodi-cally cleaned and maintained.


c. Brush Barrier

Brush Fence (buried 10 cm deep into soil).

Outlet for Cross-Drain

or Outsloped road

Barrier constructed of smallbrush and limbs pushed tothe ground at the toe of thefill slope

OverlandFlow

FFFFFigurigurigurigurigure 13.2be 13.2be 13.2be 13.2be 13.2b Sediment control structures using brush barriers and brush fences.


Ground protected withgrasses

Ditch armoredwith rock,concrete,masonry or grass

Berm protected withgrasses and brush

30-50 cmDeep

30 cmWide

a. Water Control with Ditches and/or Berms

FFFFFigurigurigurigurigure 13.3e 13.3e 13.3e 13.3e 13.3 Water control structures.

NO YESMasonry orrock walls

Broken byrunoff

Vetiver grasscontour hedgesand rockwalls

b. Water Control with Vegetative Barriers(and Terracing) (Adapted from Vetiver, 1990)

Road

Road

Fieldcrops

Fieldcrops

Fieldcrops

Masonrywall

Field crops orroad

Vetiver grass hedge

(Detail)

Deep roots forstabilization


Photo 13.10 Photo 13.10 Photo 13.10 Photo 13.10 Photo 13.10 Use of grasses,planted on contour, to providesurface slope stabilization anderosion control on a steep roadcut.

Photo 13.11 Photo 13.11 Photo 13.11 Photo 13.11 Photo 13.11 Live vegetativebarriers (contour hedgerows),using Vetiver, other grasses, orvegetation, located on contourto prevent down-slope erosionfrom barren or disturbed areas.

Photo 13.12 Photo 13.12 Photo 13.12 Photo 13.12 Photo 13.12 A local nursery,developed in conjunction with aconstruction project, to providea source of plants and growappropriate (preferably native)vegetation for the erosioncontrol work.


• Develop a project ErosionControl Plan to addressinterim and final erosioncontrol needs, specificmeasures, and how toimplement or install thosemeasures. Develop typicaldrawings for sediment traps,sediment fences, brushbarriers, ground cover,check dams, armoredditches, and biotechnicalmeasures.

• Disturb as little ground areaas possible, stabilize thatarea as quickly as possible,control drainage through thearea, and trap sediment on-site.

• Conserve topsoil with its leaflitter and organic matter, andreapply this material to localdisturbed areas to promotethe growth of local nativevegetation.

• Apply local, native grassseed and mulch to barrenerosive soil areas or closedroad surfaces. Mulchmaterial may be straw, woodchips, bark, brush, leavesand limbs, shredded paper,or gravel. (Figure13.1).

• Apply erosion controlmeasures before the rainyseason begins and after each

season of construction,preferably immediatelyfollowing construction.Install erosion controlmeasures as each roadsection is completed.

• Cover disturbed or erodingareas with limbs, tree topsand woody debris such aslogging slash placed oncontour and mashed down toachieve good contact withthe soil (Figure 13.1).

• Install sediment controlstructures where needed toslow or redirect runoff andtrap sediment until vegeta-tion is established. Sedi-ment control structuresinclude windrows of loggingslash, rock berms, sedimentcatchment basins, strawbales, brush fences, and siltfencing (see Figures 13.1,13.2a and 13.2b).

• Control water flow throughconstruction sites or dis-turbed areas with ditches,berms, check structures, livegrass barriers, and rock(Figure 13.3).

• Place windrows of loggingor clearing slash along thetoe of roadway fill slopes(See Low-Volume RoadsEngineering, Figure 4.2).

• Stabilize cut and fill slopes,sliver fills, upland barrenareas, or gullies with brushlayers, rock structureswith live stakes, vegetativecontour hedgerows (Photo13.11), wattling, or otherbiotechnical measures(Figure 13.4).

• Maintain and reapplyerosion control measuresuntil vegetation is success-fully established. Do soilchemistry tests if necessaryto determine available soilnutrients.

• Use fertilizers in areas ofpoor, nutrient deficientsoils to promote fastergrowth and better erosioncontrol. Fertilizer shouldbe used only if needed.Add water or irrigationonly if necessary to ini-tially establish vegetation.

• Develop local plantsources and nurseries forvegetative erosion controlmaterials. Use local nativespecies whenever possible(Photo 13.12). Selectspecies appropriate for theuse, the site, and thebioregion.



Vetiver grasscontour hedges

a. Contour HedgesFor Erosion Control andSlope Stabilization (Adaptedfrom Vetiver, 1990)

b. Brush Layering(for Stabilization of Gullies and Slides)

Live stakes1.5-5.0 cmdiameter placedin layers

Compacted fill15-20 cm thicklayers

Road

Sprouts with roots

Fill

Rock wall and face1.5-3.0 m high

Live stakes 1-3 cmin diameterRoad bed

0.3-0.5 m

c. Live Retaining WallsConstructed with Rock orGabions and Vegetation

Base of a gullyor slump area

FFFFFigurigurigurigurigure 13.4e 13.4e 13.4e 13.4e 13.4 Biotechnical slope stabilization measures.


Chapter 14

StaStaStaStaStabilizabilizabilizabilizabilization oftion oftion oftion oftion of Gullies Gullies Gullies Gullies Gullies

GULLIES ARE A SPECIFIC FORM OF SEVERE EROSION

typically caused by concentrated water flowon erosive soils. Figure 14.1 shows a typical

gully on a hillside and how it can impact a road andland use. Concentrated water flow may begin asminor sheet flow, produce rills, and eventually resultin major gully formation. Gullies can have majorimpacts on an area by taking land out of productionand by lowering the groundwater table, as well asbeing a major source of sediment (Photo 14.1). They

“A gram of erosion control and gully stabilization canprevent a kilogram of sediment loss.”

FFFFFigurigurigurigurigure 14.1e 14.1e 14.1e 14.1e 14.1 A gully caused by or impacting a road.

Chapter 14

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can be caused by concentrated water flowing offroads, or they can impact roads by necessitating extradrainage crossings and more frequent maintenance.

Once formed, gullies typically grow with timeand will continue down-cutting until resistant mate-rial is reached. They also expand laterally as theydeepen. Gullies often form at the outlet of culvertsor cross-drains due to the concentrated flows andrelatively fast water velocities. Also, gullies can form

A

Gully

Road

LB

RockStructure

HeadcutStructure


Photo 14.1Photo 14.1Photo 14.1Photo 14.1Photo 14.1 A typical gully caused by concentrated water on erosivesoils and/or poor land use practices.

Slope of the GullyChannel

180

150

120

90

60

30

0.3 0.6 0.9 1.2 1.5 1.8

4%

6%

8%

20%

10%12%14%16%18%

25%

Effective Height - H (meters)a.

2:1Height (H)

2:1

b.

Note: Use aslope of 2:1 or flatterfor rock dams structures.

L = Sufficient distancebetween points A andB so that the two damshave the same elevation(toe to top).

Slope of the channel

2%

FFFFFigurigurigurigurigure 14.2e 14.2e 14.2e 14.2e 14.2 Spacing details of gully control structures. (Adapted from D. Gray andA. Leiser, 1982)

upslope of culvert pipes, espe-cially in meadows, if the pipe isset below the meadow elevation.This causes a drop in the meadowor channel elevation and subse-quent headward migration of thegully. Gullies formed throughmeadows often lower the localwater table and may dry up themeadow.

Stabilization of gullies typi-cally requires removing or re-ducing the source of waterflowing through the gully and re-filling the gully with dikes, orsmall dams, built at specific inter-

Spac

ing

Bet

wee

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e St

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- L

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vals along the gully. Reshapingand stabilizing over-steep banksmay also be needed. Typical gullystabilization structures are con-structed of rock, gabions, logs(Photo 14.2), wood stakes withwire or brush, bamboo, or veg-etative barriers. Biotechnicalmethods offer a combination ofphysical structure along with veg-etative measures for physical pro-tection as well as additional long-term root support and aesthetics.A headcut structure also typicallyis needed to stabilize the upslope,or top-most portion of the gully,and prevent additional headwardmovement (see Figure 14.1).

The recommended spacing forstructures depends on the slope ofthe terrain or gully channel and theheight of each structure, as pre-sented in Figure 14.2. Figure14.2a shows the ideal spacingneeded between structures forvarying channel slope and struc-ture height. Figure 14.2b showsthe physical relationship betweenstructure height and spacing in asloped channel so that water andmaterial stored behind the lowerstructure is level with the toe ofthe upper structure. Thus, waterwill spill over the crest of the up-per structure into the pool behindthe lower structure.

In gully prevention, a “gram”of erosion control measures canprevent a “kilogram” of sedi-ment loss and damge caused byerosion. Take action to preventthe formation of gullies and to sta-bilize existing gullies before theygrow larger! Once large, gully sta-bilization measures can be verydifficult and expensive.

Design details important for successful gully stabilization struc-tures begin with removing the source of water and, as shown onFigures 14.2 and 14.3, include:

• Having a weir, notched, or “U” shaped top on the structures tokeep the water flow concentrated in the middle of the channel;

• Keying the structures into the adjacent banks tightly and far enoughto prevent erosion around the ends of the structures (Photo 14.3);

• Burying the structures deep enough in the channel to prevent flowunder the structure;

• Spilling the water over the structures onto a splash apron, protec-tive layer of rock, or into a pool of water to prevent scour andundermining of the structure; and

• Spacing the structures close enough so that the flow over thestructure spills into backwater caused by the next structure down-stream (Figure 14.2).

Note: Rock commonly used in loose rock check dams should behard, durable, well-graded with fines, and large enough to resistmovement. A commonly used gradation is shown below.

Size (cm) Percent Passing60cm 10030cm 5015cm 206 cm 10

SUCCESSFUL GULLY STABILIZATION

Photo 14.2Photo 14.2Photo 14.2Photo 14.2Photo 14.2 Logs being used to build gully stabilization structures ina fire damaged area. Physical or vegetative dams (dikes or debrisretention structures) may be used to control sedmient and stabilizegullies. Prevent water concentration befbefbefbefbeforororororeeeee gullies form.



• Remove the source ofwater. Control water flowas needed with ditches,berms, outsloping, and soon. to divert water awayfrom the top of gullies.

• Use gully control checkdam structures constructedof materials such as stakes,logs, gabions, or looserock, live vegetativebarriers or brush layeringplanted on contour indisturbed areas to controlgully erosion (see Figure13.4b and Figure 14.3).

• Install gully control struc-tures as soon as possibleafter the initial formationof a gully. Gullies only getbigger with time!

• Ensure that gully controlstructures are installedwith needed design details.Such structures should beproperly spaced, wellkeyed into the banks andchannel bottom, notchedto keep flows over themiddle of the structure,and protected from downslope scour (Photo 14.4).

• Install headcut structuresat the top of the gully toprevent up-channel migra-tion of gullies in meadows.

• Develop local plantsources and nurseries fornative vegetation that canbe used in gully controlmeasures.

PRACTICES TO AVOID

• Leaving gullies unpro-tected against continuederosion.

• Installing check damstructures with a straight,flat top, without scourprotection, and withoutbeing well keyed into thebanks.

Photo 14.3Photo 14.3Photo 14.3Photo 14.3Photo 14.3 An expensive but failed gabion gully control structurethat was not properly keyed into the banks of the gully. Further, theflow was not kept over the protected middle of the structure.

Photo 14.4Photo 14.4Photo 14.4Photo 14.4Photo 14.4 Construct debris retention and gully control structureswith a notched wier to keep flow over the middle of the structure,add scour protection at the outlet of each structure, and key thestructures into the firm soil banks.


FFFFFigurigurigurigurigure 14.3e 14.3e 14.3e 14.3e 14.3 Stabilization of gullies and severe erosion areas with check structures.

Erosion Gully Vetiver Hedge Structures

a. Rock Check Structures

b. Vegetative Check Structures (Adapted from Vetiver Grass. “The Hedge Against Ero-sion,” World Bank, 1993.)

Side View

Front View

30-50 cm

Scour protection

Key check structure into thenative soil at the base of thegully. Add scour protectionbelow each structure.

Key into native soil banks.Maintain a “U” or “V” shape overthe top of the check structure.


Depicted above is a loose rock gully control structure being used tostop headcutting up into the meadow. Note that the rock structure

is well keyed into the banks and channel bottom.


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Arranged by Topic:Best Management Practices - General 147Environmental Analysis 148Planning Issues and Special Applications 148Basic Engineering Considerations for Low-Volume Roads 151Hydrology for Drainage Crossing Design 152Tools for Hydraulic Design: Manning’s Formula, Riprap, Filters, & Geosynthetics 152Drainage of Low-Volume Roads 153Culvert Use, Installation, and Sizing 153Fords and Low-Water Crossings 154Bridges 155Slope Stability and Stabilization of Cuts and Fills 155Roadway Materials and Materials Sources 156Erosion Control: Physical, Vegetative, and Biotechnical Methods 157Stabilization of Gullies 158

BEST MANAGEMENT PRACTICES- GENERALEnvironmental Protection Agency. Draft 2001. National Management Measures to ControlNon-point Source Pollution from Forestry. EPA Contract No. 68-C7-0014, Work Assignment#2-20. Prepared for Office of Water, U.S. Environmental Protection Agency by Tetra Tech,Fairfax, Virginia. A comprehensive guide to measures for reducing water pollution from roadsand logging activities.

Michigan Department of Natural Resources. 1994. Water Quality Management Practices onForest Lands.

Minnesota Department of Natural Resources, Division of Forestry. 1994. Visual QualityBest Management Practices for Forest Management in Minnesota.

Montana State University. 1991. Montana Forestry Best Management Practices. MontanaState University Extension Service. July BMPs also produced by Montana Department of StateLands in 1992.

Ontario Ministry of Natural Resources. 1988. Environmental Guidelines for Access Roads andWater Crossings. Queen’s Printer for Ontario, Canada.

U.S. Department of Agriculture, Forest Service. 2000. Water Quality Management forNationalForest System Lands in California-Best Management Practices. Vallejo, CA: PacificSouthwest Region, U.S. Department of Agriculture, Forest Service. 186 pp.


U.S. Department of Agriculture, Forest Service. Draft 2001. Best Management Practices for ForestRoads: A performance-based framework. Washington, DC: A cooperative effort between the U.S. Depart-ment of Agriculture, Forest Service, and U.S. Environmental Protection Agency. 24 pp.

Vermont Department of Forests, Parks and Recreation. 1987. Acceptable Management Practices forMaintaining Water Quality on Logging Jobs in Vermont.

Wisconsin Department of Natural Resources. 1995. Wisconsin’s Forestry Best Management Practicesfor Water Quality-Field Manual for Loggers, Landowners and Land Managers. Publication No. FR093.March. Madison, WI. 76 pp.

ENVIRONMENTAL ANALYSISBingham, Cc; Knausenberger, Wc; Fisher, W. 1999. Environmental Documentation Manual forP.L.480, Title II Cooperating Sponsors Implementing Food-aided Development Programs, February.Food Aid Management, U.S. Agency for International Development, Washington, DC.

Burpee, G.; Harrigan, P.; Remington, T. Second Edition 2000. A Cooperatoring Sponsor’s Field Guideto USAID Environmental Compliance Process- Based on Regulation 216 to the USAID EnvironmentalDocumentation Manual for PL 480 Title II Food for Development Programs. Published jointly by Catho-lic Relief Services and Food Aid Management. Baltimore, MD. 69 pp.

Forman, R.T.; Sperling, D.; et al. 2003. Road Ecology: Science and Solutions. Washington, DC: IslandPress. 482 pp. (ISBN 1-55963-933-4) A comprehensive and thoughtful book addressing the manyecological impacts of roads, their principles, and approaches to solving transportation problems.

Knausenberger, W.; et al. 1996. Environmental Guidelines for Small-scale activities in Africa. SD Pub.Series, Technical Paper 18, Section 3.8, Rural Roads. June. Bureau for Africa, Office of SustainableDevelopment, U.S. Agency for International Development, Washington, DC. [Online] http://www.afr-sd.org/SDPublications.htm.

Public Law 91-190. [S. 1075]. National Environmental Policy Act of 1969. Act of January 1, 1970. [Anact to establish a national policy for the environment, to provide for the establishment of a Council ofEnvironmental Quality, and for other purposes.] In: United States statutes at large, 1969. 42 U.S.C. sec.4231, et seq. (1970). Washington, DC: U.S. Government Printing Office; 1970: 852-856. Vol. 83.

World Bank, The. 1997. Roads and the Environment: A Handbook. Report TWU 13, and update WBTechnical Paper No. 376. Washington, DC: The World Bank Environmentally Sustainable DevelopmentVice-Presidency and Transportation, Water & Urban Development Department Transport Division.[Online] http://www.worldbank.org/transport/publicat/reh/toc.htm.

PLANNING ISSUES AND SPECIAL APPLICATIONSDykstra, D.; Heinrich, R. 1996. FAO Model Code of Forest Harvesting Practice. Rome, Italy: Food andAgriculture Organization of the United Nations. 85 pp. (ISBN 92-5-103690-X). [Online] http://www.fao.org.


Evans, W.; Johnston, B. 1972. Fish Migration and Fish Passage:A Practical Guide to Solving FishPassage Problems. EM-7100-12. Washington, DC: U.S. Department of Agriculture, Forest Service. 63pp.

Keller, G.; Sherar, J. 2000. Practicas Mejoradas de Caminos Forestales (Manual of Best ManagementPractices for Forest Roads). Manual written in Spanish for US Agency for International Development(Forestry Development Project) and ESNACIFOR (Honduras National School for Forestry Sciences),Tegucigalpa, Honduras. 95 pp.

Oregon Department of Forestry. 2000. Forest Roads Manual. Forest Engineering Coordinator, StateForests Program, Oregon Dept. of Forestry, Salem, OR. (503-945-7371). This manual provides basiclogging road design, construction, and maintenance information.

PIARC World Roads Association. 1999. Natural Disaster Reduction for Roads, Final Report 72.02B,Paris, FR: PIARC Working Group G2. 275 pp. (ISBN 2-84060-109-5) [Online] http://www.piarc.org.Also see Comprehensive Report 72.01B, 1995.

Rajvanshi, A.; Mathur, V.; Teleki, G.; Mukherjee, S. 2001.Roads, Sensitive Habitats and Wildlife:Environmental Guidelines for India and South Asia. Wildlife Institute of India, Dehradun, India, incollaboration with Canadian Environmental Collaborative Ltd. Toronto, Canada. [Phone # 1-416-488-3313] 215 pp. (ISBN 81-85496-10-2) A comprehensive book on the issues of wildlife, their habitats,and roads, discussing problems,mitigations, and case histories.

U.S. Department of Agriculture, Forest Service. 2000. Water/road Interaction Toolkit- FishXing: CDsoftware and Interactive Learning for Fish Passage through Culverts. Water/Road Interaction TechnologySeries-SDTDC. November. Washington, DC: U.S. Department of Agriculture, Forest Service. San DimasTechnology & Development Program. [Online] http://www.stream.fs.fed.us/fishxing. A CD coveringvarious aspects of fish passage.

U.S. Department of Transportation, Federal Highway Administration. 1996. Transportation andWildlife: Reducing Wildlife Mortality and Improving Wildlife Passageways Across Transportation Corri-dors. Report No. FHWA-PD-96-041. Proceedings of the Florida Department of Transportation/FederalHighway Administration-Related Wildlife Mortality Seminar. Washington, DC. [Online] http://www.itre.ncsu.edu/cte/cte.html Case histories and information on wildlife mortality and animal move-ments across roads. Also see www.wildlifecrossings.info for extensive information and links on thesubject.

U.S. Department of Transportation, Federal Highway Administration. 1990. Fish Passage throughCulverts. FHWA-FL-90-006. San Dimas, CA: U.S. Department of Agriculture, Forest Service. SanDimas Technology and Development Center. A good handbook on fish passage, with a literature review.

Walbridge, T.A. 1997. The Location of Forest Roads. Virginia Polytechnical Institute and State Univer-sity, Blacksburg, VA: Industrial Forestry Operations. 91 pp. A primer on basic road planning, reconnais-sance, location and drainage in mountainous terrain. Also available in Spanish.


BASIC ENGINEERING CONSIDERATIONS FOR LOW-VOLUME ROADSAmerican Association of State Highway and Transportation Officials. 2001. Guidelines for geomet-ric design of very low-volume local roads (ADT<400). Washington, DC. (ISBN 1-56051-166-4).[Online] http://www.transportation.org. Covers the geometric design standards for very low-volume,local roads.

Australian Road Research Board Limited. 2000. Unsealed roads manual- Guidelines to good practice.(Revised Edition) Vermont South Victoria, Australia: Australian Roads Research Board, TransportResearch Ltd. [Online] http://www.arrb.org.au A useful manual for gravel road design and maintenance,particularly in semi-arid regions.

Casaday, E.; Merrill, B. 2001. Field techniques for forest and range road removal. Eureka, California:California State Parks, North Coast Redwoods District. 63 pp. A useful Field Guide to Road Closureand Obliteration, with great photos and figures.

Charles, R. 1997. Design of low-volume low cost roads. UWI Public Information Series/Roads, Volume1. Dept of Civil Engineering, University or West Indes, West Indes. 132 pp. A practical design manualthat covers all aspects of rural road design, particularly considering tropical climates.

Department of Transport, South African Roads Board. 1993. Guidelines for upgrading of low volumeroads. RR 92/466/2, Division of Roads and Transport, South African Roads Board, Pretoria. (ISBN 1-874844-90-9) A manual that provides information, considerations, and needs for upgrading rural gravelroads.

Geunther, K. 1999. Low maintenance roads for ranch, fire and utility access. Wildland Solutions FieldGuide Series, Clyde, CA: Wildland Solutions. 48 pp. [Online] www.wildlandsolutions.com.

Keller, G.; Bauer, G..; Aldana, M. 1995. Caminos rurales con impactos minimos (minimum impact ruralroads). Training Manual written in Spanish for U.S.D.A., Forest Service, International Programs,USAID, and Programa de Caminos Rurales. Guatemala City, Guatemala. 800 pp. Manual is currentlybeing rewritten into English.

Moll, J.E. 1996. A guide for road closure and obliteration in the Forest Service. San Dimas Technologyand Development Program. Pub. No. 7700. Washington, DC: U.S. Department of Agriculture, ForestService. 49 pp.

National Research Council, Transportation Research Board. 1978. Geometric design standards forlow-volume roads. Transportation Technology Support for Developing Countries Compendium 1. Wash-ington, DC: National Academy of Sciences. 297 pp. Compendium contains ten selected texts intended toprovide useful documentation to those in developing countries concerned with the geometric design oflow-volume roads.

Nichols, R; Irwin, L. 1993. The basics of a good road. CLRP Report No. 93-3, Ithaca, NY:CornellUniversity Local Roads Program, Revised by Paul Clooney as CLRP Report 96-5. 40 pp.

Ochoa, M. 2000. Technical guidelines for rural road design, construction, and improvement incorporat-ing environmental considerations. Jicaro Galan, Honduras. Proceedings of International Environmental


Workshop on Design, Construction, and Rehabilitation of Rural Roads, sponsored by CARE Honduras,USAID, and US Forest Service.

PIARC World Roads Association. 1994. International Road Maintenance Handbook-Practical guide-lines for rural road maintenance. A Four Volume set published by Transport Research Laboratory,Crowthorne, Berkshire RG116AU, United Kingdom. (ISBN 0-9521860-12) A comprehensive guide onall aspects of maintenance for rural paved and unpaved roads, drainage, structures, and traffic controldevices. Available in English, Spanish, Portuguese, and French.

Strombom, R. 1987. Maintenance of aggregate and earth roads. See reference under Roadway Materi-als.

U.S. Department of Agriculture, Forest Service. 1999. Road analysis: Informing decisions aboutmanaging the national forest transportation system. Misc. Report FS-643. Washington, DC: U.S.Deptartment of Agriculture, Forest Service. 222 pp. [Online] http://www.fs.fed.us/news/roads Coverscosts to maintain and mitigate in relationship to values at risk – uses and benefits as opposed to environ-mental damage.

Weaver, W.; Hagans. D. 1994. Handbook for forest and ranch roads: A guide for planning, designing,constructing, reconstructing, maintaining, and closing wildland roads. Ukiah, CA: Pacific WatershedAssociates for the Mendocino County Resource Conservation District, in cooperation with CDF and theNRCS. 161 pp.

Weist, R. 1998. A landowner’s guide to building forest access roads. Report NA-TP-06-98. Radnor, PA:U.S. Department of Agriculture, Forest Service, Northeastern Area. Published in cooperation with Stateand Private Forestry. 45 pp.

HYDROLOGY FOR DRAINAGE CROSSING DESIGNAmerican Association of State Highway and Transportation Officials. 1999, Highway DrainageGuidelines (Metric Edition). Washington, DC. (ISBN I-56051-126-5). 630 pp. [Online] http://www.transportation.org. A comprehensive guide on all aspects of highway drainage design.

Jennings, M.E.; Thomas, W.O.; Riggs, H.C. 1994. Nationwide summary of U.S. Geological Surveyregional regression equations for estimating magnitude and frequency of floods for ungaged sites, 1993.Water Resources Investigation Report 94-4002. Reston, VA: U.S. Geologic Survey. 38 p. Prepared incooperation with FHWA and FEMA. [Online] http://www.ntis.gov. Available through NTIS, Springfield,Va. Phone (703) 605-6000.

Linsley, R.; Kohler, M.; Paulhus, J. 1958. Hydrology for engineers. New York, NY: McGraw-HillBook Company, 340 p. A classic text on hydrology.

McCuen, R.; Johnson, P.; Ragan, R. 1996. Highway hydrology. Hydraulic Design Series No. 2. Pub.No. FHWA-SA-96-067. September. Washington, DC: U.S. Department of Transportation, Federal High-way Administration. 326 pp. [Online] http://www.fhwa.dot.gov/bridge. Covers hydrologic techniques andmethods suitable to small drainage areas.


Rosgen, D. 1996. Applied river morphology. Pagosa Springs, CO:Wildland Hydrology. (ISBN 0-9653289-0-2)

TOOLS FOR HYDRAULIC DESIGN: MANNING’S FORMULA, RIPRAP, FILTERS, AND

GEOSYNTHETICSBarnes, H. Jr. 1967. Roughness characteristics of natural channels. U.S. Geological Survey WaterSupply Pap. 1849. Washington , DC: U.S.Government Printing Office. Available through U.S. GeologicalSurvey, Arlington, VA. 213 pp. [Online] http://www.engr.utk.edu/hydraulics/openchannels/cover.htm.Presents many color photos comparing stream types and their Mannings Roughness Coefficient “n”.

Brown, S.; Clyde, E. 1989. Design of riprap revetment. Hydraulic Engineering Circular No. 11, March.Washington, DC: U.S. Department of Transportation, Federal Highway Administration. 156 pp. [Online]http://www.fhwa.dot.gov/bridge. Covers detailed design guidance for sizing and placing riprap. Up-dated from 1978 version.

Chow, V.T. 1959. Open channel hydraulics. New York, NY: McGraw-Hill Book Company. 680 pp.(ISBN 07-010776-9) A classic, basic textbook on hydraulics and flow in open channels.

Copeland, R.; McComas, D.N.; Thorne,C.R.; Soar, P.J.; Jonas, M.M.; Fripp, J.B. 2001. HydraulicDesign of Stream Restoration Projects. ERDC/CHL TR-01-28, U. S. Army Engineeering Research andDevelopment Center, U. S. Army Corps of Engineers. 175 pp. [Online] http://libweb.wes.army.mil/uhtbin/hyperion/CHL-TR-01-28.pdf Covers a systematic hydraulic design methodology to aid in the design ofstream restoration projects.

Holtz, R.D.; Christopher, B.R.; Berg, R.R. 1998. Geosynthetic design and construction guidelines.Participant Notebook, NHI Course No. 13213 (Revised April 1998). Rep. No. FHWA-HI-95-038.Washington DC: U.S. Department of Transportation, Federal Highway Administration. 484 pp. [Online]http://www.fhwa.dot.gov/bridge. A comprehensive guide on the use and design of geotextiles, geogrids,and geocomposites in highway applications.

Koerner, R. 1998. Designing with geosynthetics. 4th ed. Englewood Cliffs, NJ: Prentice Hall. 761 pp.(ISBN 0-13-726175-6) This updated edition covers the latest materials and design techniques usinggeosynthetics.

Racin, J.; Hoover, T.; Avila, C. 1996. California bank and shore rock slope protection design. FHWA-CA-TL-95-10 Sacramento, CA: California Department of Transportation and Federal Highway Administration,139 pp. A useful reference on riprap sizing and placement.

Schall, J.D.; Richardson, E.V. 1997. Introduction to highway hydraulics. Hydraulic Design Series No.4. Pub. No. FHWA-HI-97-028. June. Washington, DC: U.S. Department of Transportation, FederalHighway Administration. 192 pp. http://www.fhwa.dot.gov/bridge. Covers hydaulic techniques appliedto roadway surface drainage and for drainage crossings.

Steward, J.; Williamson, R.; Mohney, J. 1977. Guidelines for use of fabrics in construction and mainte-nance of low-volume roads. Interim Rept. June. Portland, OR: U.S. Department of Agriculture, ForestService, Region 6. 174 pp. Covers basic porous woven and non-woven fabrics use in road constructionin the U.S. Forest Service.


U.S. Department of Agriculture, Natural Resources Conservation Service. 1994. Gradation design ofsand and gravel filters. Chapter 26. In: Part 633, National Engineering Handbook. Washington, DC. 40pp.

U.S. Department of Agriculture, Natural Resource Conservation Service. 1996. Streambank andshoreline protection. In: Engineering Field Handbook, Chapter 16. Rep. No. NEH-650-16. December.Washington, DC. 130 pp. Covers bank protection from scour and erosion by using vegetative plantings,soil bioengineering, and structural systems.

DRAINAGE OF LOW-VOLUME ROADSBlinn, C.R.; Dahlman, R.; Hislop, L.; Thompson, M. 1998. Temporary stream and wetland crossingoptions for forest management. Forest Service Gen. Tech. Rep. NC-202. St. Paul, MN: U.S. Departmentof Agriculture, Forest Service, North Central Forest Experiment Station. 136 pp. Discusses temporaryoptions for crossing streams and wetland soil areas with forest harvesting equipment and logging trucks.

Cedergren, H. 1977. Seepage, drainage, and flow nets. 3rd ed. New York: John Wiley and Sons. 496 pp.(ISBN 0-471-14179-8)

Copstead, R.; Johansen, K.; Moll, J. 1998. Water/road interaction: Introduction to surface crossdrains. Water/Road Interaction Technology Series. Res. Rep. 9877 1806 – SDTDC. September. Wash-ington, DC: U.S. Department of Agriculture, Forest Service. San Dimas Technology & DevelopmentProgram. 16 pp. A water-roads interaction toolkit is also available on a CD.

Elliot, W.; Graves, S.; Hall, D.; Moll, J. 1998. The X-DRAIN cross drain spacing and sediment yieldmodel. In: Water/Road Interaction Technology Series. Res. Rep. 9877 1801 – SDTDC. June. Washing-ton, DC: U.S. Department of Agriculture, Forest Service. San Dimas Technology & Development Pro-gram. 23 pp. [Online] http://www.stream.fs.fed.us/water-road/index.htm.

Furniss, M.; Love, M.; Flanagan, S. 1997. Diversion potential at road-stream crossings. In: Water/Road Interaction Technology Series. Res. Rep. 9777 1814 – SDTDC. December. Washington, DC: U.S.Department of Agriculture, Forest Service. San Dimas Technology & Development Program. 12 pp.[Online] http://www.stream.fs.fed.us/water-road/index.htm.

Furniss, M.; Roelofs, T.; Yee, C. 1991. Road construction and maintenance. In:Meehan, W.R.,ed.Influences of forest and rangeland management on salmonid fishes and their habitat, Chapter 8. SpecialPub. 19. Bethesda, MD: American Fisheries Society. pp. 297-324.

Orr, D. 1998. Roadway and roadside drainage. CLRP Publication No. 98-5. Ithaca, NY: Cornell LocalRoads Program. 88 pp.

Packer, P.; Christensen, G.. 1964. Guide for controlling sediment from secondary logging roads. [pam-phlet] Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and RangeExperiment Station. 42 pp. (Government Printing Office 1980-682-866/222)

Washington Department of Fish and Wildlife. 2002. Integrated Streambank Protection Guidelines.Aquatic Habitat Guidelines: An Integrated Approach to Marine, Freshwater, and Riparian Habitat Protec-tion and Restoration, June. In cooperation with Washington Department of Transportation and Washing-


ton Department of Ecology. 329 pp. [Online] http://www.wa.gov/wdfw/hab/ahg/ispgdoc.htm. Presentsand describes a broad range of streambank protection techniques.

Zeedyk, W.D. 1996. Managing roads for wet meadow ecosystem recovery. November. Tech. Rep.FHWA-FLP-96-016. Albuquerque, NM: U.S. Department of Agriculture, Forest Service, SouthwesternRegion. 76 pp. Includes a riparian restoration guide for wet meadows.

CULVERT USE, INSTALLATION, AND SIZINGAmerican Iron and Steel Institute. 1994, Fifth Edition. Handbook of steel drainage and highway con-struction products. Washington, DC: American Iron and Steel Institute. 518 pp.

Johansen, K.; Copstead, R.; Moll, J. 1997. Relief culverts. Water/Road Interaction Technology Series.Res. Rep 9777 1812-SDTDC. October. Washington, DC: U.S. Department of Agriculture, Forest Ser-vice, San Dimas Technology & Development Program. 7 pp. [Online] http://www.stream.fs.fed.us/water-road/index.htm. Covers surface drainage and ditch relief culvert spacing and design.

Normann, J.M.; Houghtalen, R.J.; Johnston, W.J. 1985 (Reprinted 1998). Hydraulic design of high-way culverts. Hydraulic Design Series No. 5. Tech. Rep. No. FHWA-IP-86-15 HDS 5. September.McLean, VA: Department of Transportation, Federal Highway Administration, Office of Implementation.265 pp. [Online] http://www.fhwa.dot.gov/bridge/hydpub.htm. Includes a comprehensive design for bothconventional culverts and culverts with inlet improvements.

FORDS AND LOW-WATER CROSSINGSBerger, L.; Greenstein, J.; Arrieta, J. 1987. Guidelines for the design of low-cost water crossings. Trans-portation Res. Record 1106. Washington, DC: National Researach Council, Transportation Research Board.pp. 318-327.

Coghlan, G.; Davis, N. 1979. Low-water crossings. Transportation Res. Record 702, Washington, DC:National Research Council, Transportation Research Board. pp. 98-103.

Eriksson, M. 1983. Cost-effective low-volume-road stream crossings. Transportation Res. Record 898.Washington, DC: National Research Council, Transportation Research Board. pp. 227-232.

Lohnes, R.A.; Gu, R.R.; McDonald, T.; Jha, M.K. 2001. Low-Water Stream Crossings: Design andConstruction Recommendations. Final Report CTRE Project 01-78, IOWA DOT Project TR-453, Centerfor Transportation Research and Education, Iowa State University. 50 pp. [Online] www.ctre.iastate.eduA useful publication on specific design information for low-water crossings.

Motayed, A.K.; Chang, F.M.; Mukherjee, D.K. 1982. Design and construction of low-water streamcrossings. Report No. FHWA/RD-82/163. June. Washington, DC: U.S. Department of Transportation,Federal Highway Administration. 119 pp. A thorough review on low-water stream crossing structuredesign criteria, site selection, and structure types. This publication is currently being revised and up-dated by Robert Gu at Iowa State University.


Moll, J. 1997. Site and selection of low water crossings. In: Ecosystem Road Management. Compiled bySan Dimas Technology and Development Center. San Dimas, CA:U.S. Department of Agriculture, ForestService.

Ring, S.L. 1987. The design of low-water stream crossings. Transportation Res. Record 1106. Washing-ton, DC: National Research Council, Transportation Research Board. pp. 309-318.

U.S. Department of Transportation, Transportation Research Board. 1979. Low-cost water crossings.Compendium 4, Transportation Technology Support for Developing Countries. Prepared for U.S. Agencyfor International Development. Washington, DC. 203 pp. Provides useful information for those in deveopingcountries who have direct responsibility for low-cost water crossings.

Wahrhol, T.; Pyles, M. 1989. Low water fords: An alternative to culverts on forest roads. August 27-30;Coeur d’Alene, ID: Proc. 12th Annual Council on Forest Engineering Meeting.

BRIDGESAmerican Association of State Highway and Transportation Officals, Inc. 1996. Standard specifica-tions for highway bridges, 16th Edition (and Interim Revisions 1997, 1998, 1999, and 2000) Washington,DC. [Online] http://www.aashto.org and http://www.transportation.org. Covers all aspects of design forwood, steel, and concrete bridges, substructures, foundations, retaining walls, as well as structural platestructures and culverts.

Nagy, M.; Trebett, J.; Wellburn, G. 1980. Log bridge construction handbook. FERIC Handbook #3,Vancouver, B.C., Canada: Forest Engineering Research Institute of Canada. (ISSN 0701-8355) 421 pp.

Neill, C. 1973. Guide to bridge hydraulics (plus Metric Revision Supplement). Toronto, ON: Project Com-mittee on Bridge Hydraulics, Roads and Transportation Association of Canada, University of Toronto Press.191 pp. (ISBN 0-8020-1961-7)

Richardson, E.V.; Davis, S.R. 1995. Evaluating scour at bridges. Hydraulic Engineering Circular No.18. Pub. No. FHWA-HI-96-031. November. Washington, DC: U.S. Department of Transportation,Federal Highway Administration. 204 pp. [Online] http://www.fhwa.dot.gov/bridge. Covers all aspects ofscour evaluation and determination of scour depth.

SLOPE STABILIZATION AND STABILITY OF CUTS AND FILLSBarrett, R.K. 1985. Geotextiles in earth reinforcement. Geotechnical Fabrics Report, March/April:15-19.

Elias, V.; Christopher, B.R. 1997. Mechanically stabilized earth walls and reinforced soil slopes - designand construction guidelines. August. Tech. Rep. No. FHWA-SA 96-071, reprinted September 1998.FHWA Demonstration Project 82.Washington, DC: Department of Transport., Federal Highway Admin-istration. 396 pp. [Online] http://www.fhwa.dot.gov/bridge. Covers the design of mechanically stabilizedearth walls and reinforced soil slopes.

Gray, D.; Leiser, A. 1982. Biotechnical slope protection and erosion control. Melbourne, FL: KriegerPublishing Co. 288 pp. (ISBN 0-442-21222-4) Covers various biotechnical slope stabilization anderosion control techniques.


Hoek, E.; Bray, J. 1974. Rock slope engineering. London: Institute of Mining and Metallurgy. 358 pp.(ISBN 0-900488-573)

Keller, G.; Cummins, O. 1990. Tire retaining structures. Engineering Field Notes. 22:15-24, March/April.Washington, DC: U.S. Department of Agriculture, Forest Service.

Mohney, J. 1994. Retaining wall design guide. 2d ed. Tech. Rep. No. EM-7170-14. Washington, DC:U.S. Department of Agriculture, Forest Service, Engineering Staff. Also Pub. No. FHWA-FLP-94-006.September. Washington, DC: Department of Transportation, Federal Highway Administration, FederalLands Highway Program. 537 pp. [Online] http://www.ntis.gov. Covers the analysis and design of a widevariety of low-cost retaining structures.

Turner, A.K.; Schuster, R.L. 1996. Landslides — investigation and mitigation. Tech. Rep. No. TRB-SR-247. Washington, DC: National Research Council, Transportation Research Board. National AcademyPress. 680 pp. (ISBN 0-309-06208-X) A comprehensive publication on all aspects of landslide hazards,investigation, their analysis, the design of unstable soil and rock slope stabilization measures, andspecial applications.

U.S. Department of Agriculture, Forest Service. 1994. Slope stability reference guide for NationalForests in the United States. EM-7170-13. Engineering Staff, Washington, DC: U.S. Department ofAgriculture, Forest Service. Available from the Government Printing Office, Phone (202) 512-1800,http://www.bookstore.gpo.gov A comprehensive 3-volume set of information on all aspects of slopestability, identification, planning and risk, analysis methods, and stabilization techniques, written byfield practitioners. A practical guide for geologists and engineers dealing with slope stability problems.

ROADWAY MATERIALS AND MATERIALS SOURCESAustralian Roads Research Board. 1996. Road dust control techniques – Evaluation of chemical dustsuppressants’ performance. Spec. Rep. 54. Victoria, Australia: Australian Roads Research Board, Trans-port Research Ltd. [Online] http://www.arrb.org.au. Covers the products available, how they work,selecting the product, and the product’s environmental impacts.

Bolander, P.; Yamada, A. 1999. Dust palliative selection and application guide. Technology & Develop-ment Program No. 9977 1207—SDTDC. November. Washington, DC: U.S. Department of Agriculture,Forest Service. San Dimas Technology and Development Program. 19 pp.

Dunne, T.; Collins, B. 1990. Fluvial geomorphology and river gravel mining: A guide for planners, casestudies included. Special Publication SP 098. Sacramento, CA: California Department of Conservation,Division of Mines and Geology. 29 pp.

Rodriguez, A.; del Castillo, H.; Sowers, G. F. 1988. Soil mechanics in highway engineering. FederalRepublic of Germany: TransTech Publications. 843 pp. (ISBN 0-87849-072-8)

Scholen, D.E. 1992. Non-standard stabilizers. Pub. No. FHWA FLD-92-011. July. Washington, DC: U.S.Department of Transportation, Federal Highway Administration, Office of Direct Federal Programs.Covers the Forest Service use of various non-standard road surface stabilization products.


South Dakota Local Transportation Assistance Program. 2000. Gravel roads: maintenance and designmanual. November. Published in cooperation with U.S. Department of Transportation, Federal HighwayAdministration. 63 pp. [Online] http://www.epa.gov/owow/nps/gravelroads/. A useful manual on designand maintenance of gravel roads, with great photos and figures.

Sowers, G. F. 1979. Introductory soil mechanics and foundations: Geotechnical Engineering. 4th ed.New York: Macmillan. 621 pp. (ISBN 0-02-413870-3) A basic textbook on soil mechanics.

Strombom, R. 1987. Maintenance of aggregate and earth roads. WA-RD 144.1. June. Olympia, WA:Washington State Dept. of Transportation. Reprinted as Federal Highway Administration Publication No.FHWA-TS-90-035. 71 pp. A state-of-the-art manual on maintenance and management of aggregate andnative earth roads.

U.S. Department of Agriculture, Forest Service. 1996. Earth and aggregate surfacing design guide forlow-volume roads. Pub. No. EM-7170-16. September. Washington, D.C. 302 pp. Covers the designmethodology for Surface Thickness Program, as well as an aid in selecting the type of surfacing mate-rial, and surface maintenance.

U.S. Department of Transportation, Federal Highway Administration. 1998. Problems associatedwith gravel roads. Publication No. FHWA-SA-98-045. May. Washington, DC: Produced through LocalTechnical Assistance Program.

Yamada, A. 1999. Asphalt seal coat treatments. Technology & Development Program No. 9977 1201—SDTDC. April. Washington, DC: U.S. Department of Agriculture, Forest Service, San Dimas Technology& Development Program. 24 pp.

Yoder, E.J.; Witczak, M.M. 1975. Principles of pavement design. 2d ed. New York: John Wiley & Sons.711pp. (ISBN 0-471-97780-2) A classic text on fundamentals of pavement design.

EROSION CONTROL: PHYSICAL, VEGETATIVE AND BIOTECHNICAL METHODSAssociation of Bay Area Governments. 1995. Manual of standards for erosion & sediment controlmeasures, 2d ed.. May. San Fransisco, CA. 500 pp. A comprehensive field guide for controlling soilerosion in California.

Burroughs, E.; King, J. 1989. Reduction of soil erosion on forest roads. Tech. Rep. No. FSGTR-INT-264, July. Moscow, ID: U.S. Department of Agriculture, Forest Service, Intermountain Research Station.26 pp. Covers expected reduction in surface erosion from selected treatments applied to forest roadtraveled ways, cutslopes, fillslopes, and ditches.

Clackamas County Water Environment Services. 2000. Erosion prevention and sediment control:planning and design manual. Oregon: Developed in cooperation with City of West Lynn and the UnifiedSewerage Agency of Washington County. Ph 503-353-4567. Presents many erosion and sediment controlBest Management Practices, with nice photos and illustrations.

Gray, D.; Leiser, A. 1982. Biotechnical slope protection and erosion control. Melbourne, FL: KriegerPublishing Co. 288 pp. (ISBN 0-442-21222-4) A good textbook covering various biotechnical erosioncontrol techniques, their design and construction.


Gray, D.; Sotir, R. 1996. Biotechnical and soil bioengineering slope stabilization-A practical guide forerosion control. New York, NY: A Wiley-Interscience Publication, John Wiley and Sons, Inc. 378 pp.(ISBN 0-471-04978-6) Covers various biotechnical erosion control techniques and their application.

Grimshaw, R.G.; Helfer, L. (eds.). 1995. Vetiver grass for soil and water conservation, land rehabilita-tion, and embankment stabilization: a collection of papers and newsletters compiled by the vetiver net-work. World Bank Technical Pap. No. 273. Washington, DC: The World Bank. 288 pp. A collection ofpapers and newsletters suporting the use of vetiver grass conservation as a low-cost biological system oferosion control and water conservation.

Lewis, L. 2000. Soil Bioengineering -- An Alternative for Roadside Management, A Practical Guide.Technology & Development Program No. 0077-1801-SDTDC, September. Washington, DC: U.S. De-partment of Agriculture, Forest Service, San Dimas Technology & Development Center, San Dimas, CA.43 pp.

Morfin, S.; Elliot, W.; Foltz, R.; Miller, S. 1996. Predicting effects of climate, soil, and topography onroad erosion with the WEPP model. In: Proceedings of the 1996 American Society of Agricultural Engi-neers, Annual International Meeting; 1996 July 16; Phoenix, AZ. ASAE Paper No. 965016. St. Joseph,MI: ASAE. 11 pp. Use of the Water Erosion Prediction Project (WEPP) soil erosion model.

U.S. Department of Agriculture, Soil Conservation Service. 1978. Estimating sheet-rill erosion andsediment yield on rural and forest highways. WTSCTN Woodland 12. US Department of Agriculture, SoilConservation Service, 33 pp. Basic information on use of the Universal Soil Loss Equation (USLE) topredict erosion loss on roads.

U.S. Department of Agriculture, Soil Conservation Service. 1992. Soil bioengineering for uplandslope protection and erosion reduction. In: Engineering Field Handbook, Chapter 18. October. Rep. No.EFH-650-18.Washington, DC. 62 pp. Covers biotechnical erosion control techniques and their use, withgreat photos and drawings.

World Bank, The. 1993. Vetiver grass: The hedge against erosion. Washington, DC. 78 pp. (ISBN 0-8213-1405) [Online] http://www.vetiver.org. A basic, useful pamphlet on the applications of VetiverGrass. Spanish version first published in 1990.

STABILIZATION OF GULLIESGray, D.; Leiser, A. 1982. Biotechnical slope protection and erosion control. Melbourne, FL: KriegerPublishing Co. 288 pp. (ISBN 0-442-21222-4) Covers various erosion control techniques and gullystabilization measures.

Heede, B. 1976. Gully development and control: The status of our knowledge. Research Paper RM-169.Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and RangeExperiment Station. 42 pp. A basic primer on gully formation, gully stabilization techniques, and typesof control structures.

low-volume roads engineeringpdf.usaid.gov/pdf_docs/pnadb595.pdf · virginia tech transportation...

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