FEDERAL-AID POLICY GUIDE
December 9, 1991, Transmittal 1
NS 23 CFR 650B
Guidelines For Minimizing Possible Soil Erosion From Highway Construction
Report To Congress
July 1, 1967
BUREAU OF PUBLIC ROADS IN COOPERATION WITH THE SOIL CONSERVATION SERVICE U.S. DEPARTMENT OF AGRICULTURE
June 28, 1967
Honorable Hubert H. Humphrey
President of the Senate
Washington, D.C. 20510
Dear Mr. President:
I transmit herewith the report on "Guidelines for Minimizing Possible Soil Erosion from Highway Construction," prepared in compliance with section 14 of the Federal-Aid Highway Act of 1966, approved September 13, 1966 (80 State. 766). This section directs the Secretary of Transportation to consult with the Secretary of Agriculture with respect to guidelines for minimizing possible soil erosion from highway construction and report to Congress such guidelines no later than July 1, 1967.
The report transmitted herewith sets forth the nature and scope of the problem of soil erosion due to highway construction and the guidelines for minimizing it. I am also enclosing a letter from the Secretary of Agriculture dated June 12, 1967, concurring in this report.
signed by Alan S. Boyd
Secretary of Transportation
CONTENTS Nature and Scope of Problem . . . . . . . . . . . . . . . . . . 4 Guidelines for Minimizing Erosion . . . . . . . . . . . . . . . 6 1. Planning and Location . . . . . . . . . . . . . 7 2. Design Features . . . . . . . . . . . . . . . . 7 a. Earth cut and fill slopes . . . . . . . 8 b. Waterways or channels . . . . . . . . . 9 c. Structures for erosion control . . . . 9 d. Detention or sedimentation basins . .. 10 e. Soil treatment . . . . . . . . . . . .11 3. Construction Practice . . . . . . . . . . . . .11 4. Maintenance . . . . . . . . . . . . . . . . . .13 5. Research and Development . . . . . . . . . . .14 6. Legal Requirements and Responsibilities . . . .15 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . .15
REPORT ON GUIDELINES FOR MINIMIZING POSSIBLE SOIL EROSION FROM HIGHWAY CONSTRUCTION
NATURE AND SCOPE OF PROBLEM
Recent Federal legislation and executive orders have emphasized the need to conserve our natural resources. Pollution abatement, erosion control, and beautification of highway right-of-way are major areas of concern. The control of soil and water is basic to this conservation effort; therefore, highway construction and maintenance must be continually evaluated to minimize erosion that scars the landscape and creates pollution problems.
All highway agencies recognize the detrimental effects of erosion within the highway right-of-way and give special attention in design to preventive measures where such measures are needed. The success of these measures is evidenced by the many miles of highways now serving the traveling public without serious erosion scars. Highways not properly located, designed, constructed, or maintained are at times subject to erosion and may contribute to stream pollution. Serious erosion not only results in unsightly conditions and increased maintenance costs, but sometimes cause safety hazards.
A highway built to modern standards has few erosion problems after its completion, particularly if good maintenance practices are followed. Highway builders are usually criticized because of erosion during construction, but few data exist to evaluate damages from erosion that takes place during the construction period. Good engineering demands an evaluation of the problem as a basis for imposing controls.
Problems encountered in finding feasible ways to minimize erosion are varied and complex. Several disciplines of science and engineering are required to reach an acceptable solution to most erosion problems. Adequate technical competence of both the contracting agencies and the contractors is necessary. Highway designers, project engineers, and maintenance personnel need the advice of hydrologists, hydraulic engineers, soil engineers, soil scientists, agronomists, landscape architects, and other specialists to minimize erosion problems. Emphasis must be placed on the extra cost to the contractor for correcting erosion damage resulting from poor construction practices; the economic effect of occasional pollution of streams, lakes, and watersupplies; and the lower costs of maintaining the roadsides and constructed slopes of highways built to minimize erosion.
Development and training of personnel in erosion preventive measures that should be considered in the location, design, construction, and maintenance of highway facilities must be increasingly stressed. Much research information and many practicable techniques for minimizing erosion are available in research publications and design bulletins but refresher courses and promotion of the use of these data are badly needed. Guidelines and design manuals serve an excellent purpose but they alone are not enough. Adequate technical staffs in the various highway agencies are necessary to cooperate with agencies at all governmental levels which are responsible for the prevention, abatement, and control of pollution and soil and water conservation.
The Bureau of Public Roads emphasizes erosion control on Federally financed highway construction by issuing memorandum and instructional material, by reviewing plans and specifications, by conducting schools and conferences, and by making field inspections of construction work done by State and local agencies. During the past year the Bureau of Public Roads has requested all State highway departments to review and revise, if found necessary, all sections of specifications that relate to control of erosion and pollution during or as a result of highway construction. Time will be required to inspect construction operations and evaluate the effectiveness of the States' specifications.
Direct Federal construction of highways is controlled by the Bureau of Public Roads "Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects (January 1961)." These specifications require that the contractor ". . . conduct and schedule his operations so as to avoid or minimize siltation of streams, lakes, and reservoirs . . ." (Article 8.3(g), p. 22). Article 102-3.6 (pg. 40) requires that "During the construction of the roadway, the roadbed shall be maintained in such condition that it will be well drained at all times. Side ditches or gutters emptying from cuts to embankments or otherwise shall be so constructed as to avoid damage to embankments by erosion." Other sections of the specifications give detailed requirements to accomplish these objectives.*
*Refer to appropriate sections of the latest edition of "Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects"
The policy of the Bureau of Public Roads and of the State highway agencies is well stated on page 216 of the American Association of State Highway Officials publication, "A Policy on Geometric Design of Rural Highway," 1965, as follows:
"Erosion prevention is one of the major factors in the design, construction and maintenance of highways. Erosion can be controlled to a considerable degree by geometric design, particularly that relating to the cross section. In some respects the control is directly associated with proper provision for drainage and fitting landscape development. Effect on erosion should be considered in the location and design stages."
"Erosion and maintenance are minimized largely by the use of: flat side slopes, rounded and blended with natural terrain; drainage channels designed with due regard to width, depth, slopes, alinement, and protective treatment; inlets located and spaced with erosion control in mind; prevention of erosion at culvert outlets; proper facilities for ground water interception; dikes, berms, and other protective devices; and protective ground covers and planting."
The quoted publication is used by both the Bureau of Public Roads and the State highway agencies as a design guide.
GUIDELINES FOR EROSION CONTROL
Although some standardization of methods for minimizing soil erosion in highway construction is possible, national guidelines for the control of erosion must necessarily be of a general nature because of the wide variation in climate, topography, geology, and soils encountered in different parts of the country. For example, erosion control must be given careful attention in the design of a highway traversing an area of rough topography, erodible soils, high and constant wind velocities, and heavy precipitation. A high degree of erosion control is required in a watershed that is the collecting area for a public water supply or a recreational facility.
Erosion control guidelines should encompass all phases of highway engineering to realize economical and effective control of erosion that might occur. These guidelines are stated under the headings: Planning and Location, Design Features, Construction Practice, Maintenance, Research and Development, and Legal Requirements and Responsibilities.
Planning and Location
Effective erosion control begins in the planning and location of a highway route. Control of water and knowledge of the soils to be encountered are basic in determining measures for preventing erosion and the movement of sediment. A highway location selected with due consideration of problems associated with these basic elements will greatly reduce erosion problems during and after construction.
The natural drainage pattern, soils and geology of the area, and manmade features that are associated with erosion and sediment should be examined for each route considered and should be a major factor in selecting the route to be used. Potential landslide areas, stream crossings and encroachments, and the magnitude of cut and fill sections should be evaluated relative to construction problems that will arise in reducing erosion and in preventing sediment and turbid water from entering streams, water supplies and irrigation systems. Preliminary soil surveys, geologic investigations, and hydrologic studies are necessary to define potential problem areas.
Cooperation with Federal, State, and local agencies having jurisdiction over water resources, soil conservation, and irrigation should begin in the planning and location stage. Technical information, data, standards, and guidelines available from all levels of other agencies are of considerable value in planning the extent of erosion-prevention measures deemed necessary and in defining problems likely to be encountered from erosion and from stream pollution by sediment, other minerals, and contaminants. Usually only limited sediment and turbidity data are available for natural streams, reservoirs, and lakes during floods. Therefore, special effort should be made by the highway agency to document the initial conditions in order to fix responsibility if claims and litigation arise after the construction has begun. Controls or limitations that may be imposed by other agencies on the construction contractor'soperations should be investigated early in the planning of a highway so that necessary modifications in designs and specifications can be made before the project is advertised for bids.
Many problems involving erosion during and after construction can be avoided by proper design. Careful selection of alinement and grade of a highway is as important as the general location. Special effort should be made to minimize disturbance of the soil. Slopes of the roadway cross sections should be based on soil stability, climatic exposure, geology, proposed landscape treatment, and maintenance procedures to be followed. The cross section should be varied, if necessary, on a particular project to minimize erosion and to facilitate safety and drainage. Generally, good landscaping and drainage design are compatible with both erosion control and safety to vehicles.
Erosion is usually caused by concentrated runoff or by the impact of rain falling on unprotected soil or unstable rock. In some areas, erosion is caused by wind or runoff from snow melt. The erosion potential should be estimated and measures to prevent erosion selected on the basis of both the effectiveness of the control measures and the consequences of the erosion. In most instances the designer has a wide range of choice in type of erosion-control measures; but intensity of rainfall, the season of the year, severity of erosion, and cost must all be considered in the design selected. Design for erosion control is complex and should be done by trained specialists.
Some features of a highway are more vulnerable to erosion than others and therefore, require special consideration at the design stage. Guidelines for the treatment of erosion in several of these critical areas and for the design of erosion and sediment control structures follow:
a. Earth cut and fill slopes -- Severe erosion of earth slopes is usually caused by a concentration of storm water flowing from the roadway section or from the area at the top of cut slopes down unprotected embankments or other slopes. Preventing concentration of water in these critical areas is essential. Channels, ditches, berms, or shoulder dikes for diverting water tosatisfactory outfalls should be constructed at appropriate locations early in the construction of the project. Rainfall on cut and fill slopes will cause erosion to varying degrees, depending on the intensity of rainfall, the type of soil, the degree of slope, the length of the exposed surface, the climatic exposure, and the effectiveness of the vegetative or other protective cover. Benches or terraces, enclosed drainage systems, or the mulching or covering of the soil with various materials may be required to reduce slope erosion. The need for and the type of protection should be determined in the design stage. Protective treatment of cut and fill slopes, whether temporary or permanent, should be a part of the grading contract and should be applied insofar as practicable as the grading operations progress.
b. Waterways or channels -- Surface channels, natural or manmade, are usually the most economical means of collecting and disposing of runoff in highway construction. Such channels, however, if not designed properly, can create serious erosion problems.
Care in the location and the design of roadway channels is necessary both for efficient drainage and for traffic safety. A primary design principle is to provide channels with flat side slopes and wide bottoms, protected adequately to avoid soil erosion. If designs, such as rectangular concrete channels, are needed to accommodate flood flows, the channel should be placed at a safe distance from the traveled way or a barrier erected to protect traffic. Sometimes drainage easements are necessary to provide a well designed and safe channel.
Protective linings for channels and streams can be very expensive and a considerable percentage of the highway dollar is spent on this item of work. Special effort must be made to develop the lowest-cost type of erosion protection for the particular location. Channel design and protectivetreatments are discussed in Hydraulic Design Series No. 4, "Design of Roadside Drainage Channels," published by the Bureau of Public Roads and available from the Government Printing Office. Field manuals and publications of the Soil Conservation Service also contain valuable channel design information. Several research projects are in progress to develop more economical and satisfactory channel linings.
c. Structures for erosion control -- Special structures other than open channels are used in highway construction to convey water and to control erosion. Grade-control structures, energy dissipators, special culverts, and various types of pipelines have been used for this purpose. These structures are usually costly and are recommended for use only after it has been determined that vegetation, rock or other types of treatment will not control the anticipated erosion. As a general rule, designers should avoid large accumulations of flowing water and use a type of erosion protection that keeps velocities to a minimum. Such a guideline will minimize erosion and avoid the need for costly erosion-control structures. Where such structures are required, designs should receive careful attention since these structures are vulnerable to failure or are ineffective if not properly designed and installed. Erosion caused by high velocity flows at the outlet of highway structures deserves particular attention.
Most highway departments have standard designs for various types of erosion-control structures. Considerable use is made of Soil Conservation Service and Bureau of Reclamation publications containing designs for this purpose. If unusual and expensive designs are contemplated, model testing is often desirable to study performance. Models frequently show needed modifications or refinements in design that improve performance and effect considerable saving in the construction costs.
d. Detention or sedimentation basins -- Small dams can be placed in a waterway to form reservoirs or basins for detaining flood water and trapping sediment caused by erosion. Such dams can be of the temporary or permanent type, depending on the need. A highway embankment can serve as a dam for this purpose at some locations. The Soil Conservation Service and several highway departments have developed special culvert designs that control degrading of stream channels and detain sediment and flood water.
Dams for trapping sediment must be properly located and designed because failure during a major flood could have consequences far greater than most sediment problems created by highway construction. Health and safety hazards, methods of disposing of the trapped sediment and the future flood potential must also be evaluated.
e. Soil treatment -- The use of grasses or other plants for landscaping and erosion control which are not ecologically adapted to a particular area usually results in poor erosion control and increases maintenance. Every effort should be made to use ecologically adapted vegetation that will survive in a particular area with minimum maintenance. Proven soil conservation practices, including the use of mulches and temporary protective measures, are all important in developing permanent vegetative covers. Irrigation is often required to establish ground cover or maintain a satisfactory stand in semi-arid areas. With further development, dust palliatives may be effective in erosion control, particularly in arid areas where wind erosion is a problem. Agronomists who have a technical knowledge of soils and plants of the area can be very helpful in suggesting methods and kinds of treatments. Cooperation with local offices of the Soil Conservation Service in developing new methods and hardy strains of grass or other plants to resist erosion has been found beneficial by the State highway departments.
The plans, specifications, and special provisions of a highway contract should be explicit in showing the location, scope, and manner of performing erosion-control measures. If deficiencies in the design or performance of these measures are discovered during construction, the engineer should take immediate steps for correction. Measures left to the discretion of the engineer should be as few as practicable and the method of measurement and payment for such work should be stated in the contract.
Proper planning and scheduling of construction operations are major factors in controlling erosion. A construction schedule that meets the highway agency's requirements for erosion control should be made a part of the construction project proposal or a schedule should be submitted by the contractor for approval by the engineer. Sufficient erosion-control measures should be included as a part of the initial grading contract. On subsequent paving or other contracts, the project engineer should not allow construction operations which contribute to soil erosion.
Permanent soil protection and drainage facilities should be completed as early as practicable, particularly intercepting channels and similar controls that will divert runoff from work areas and unprotected soil. Sections of bare earth and the length of their exposure to erosion should be minimized by proper scheduling and limiting the work areas with consideration of the program of the contractor and climatic conditions. Temporary protection such as fiber mats,plastic, straw, dust palliatives, and fast-growing grasses may be required in some areas to prevent erosion from water or wind on newly completed slopes. Partially completed drainage structures should be inspected carefully during construction to prevent unnecessary erosion and to avoid damage to these structures.
Special precautions should be taken in the use of construction equipment to prevent operations which promote erosion. Wheel tracks from heavy equipment are especially vulnerable to erosion from the concentration of water. Fording of streams with equipment should be kept to a minimum, and in locations where frequent crossings of streams are contemplated, temporary bridges or culverts should be constructed if the sediment created is detrimental to fish and wildlife, water supplies, or irrigation systems. Plans by a contractor for work roads showing the method of construction, erosion-control measures, and restoration should be approved by the engineer.
Although disturbance by highway construction of streams, lakes, or reservoirs should be avoided, drainage structures, channel changes, and embankment encroachments are sometime necessary in building a highway. Specifications or special provisions should include controls for the contractor's operation in performing work in these areas, particularly in conforming with regulations of water resources and fish and wildlife agencies. Some types of construction and stream conditions may necessitate the construction for diversion dikes or other protective measures to avoid sediment problems. Embankment slopes that encroach on stream channels should be adequately protected against erosion. Where practicable, a protective area of vegetative cover should be left or established between the highway embankment and adjacent stream channels. At some locations, temporary or permanent training works placed in the channel can reduce bed or bank scour.
Areas for borrow pits and waste disposal should be selected with full consideration of erosion control during borrow operations and the final treatment or restoration of the area. When it becomes necessary to locate such areas near or in stream channels, special precautions should be taken to minimize erosion and accompanying sediment problems. Regardless of the responsibility for the selection of borrow areas, whether it be the contractor or the contracting agency, plans of operation and restoration, or cleanup and shaping should be approved by the engineer.
Before borrow or disposal operations are begun, plans for the control of drainage water must include measures to keep sediment from entering streams. Diversion channels, dikes, and sediment traps may be used for this purpose. Good topsoil from the borrow pit area should be saved for use inrestoring the excavated area. Final restoration of borrow or waste disposal areas should include grading, establishment of vegetative cover, or other necessary treatments that will blend the area into the surrounding landscape. The restored area should be well drained unless approval is given to convert the pit area into lakes for fish and wildlife, recreation, stock water, or irrigation.
Specifications should include adequate control for the prevention of grass and brush fires since burned-over areas are usually highly vulnerable to erosion. In areas where a severe fire hazard exists, fire equipment should be available for ready use. The contract should provide for suspending fire-hazardous operations at the direction of the engineer or local fire control agency and compliance with local fire regulations should be required.
Preventive maintenance built into the highway in the location, design, and construction phases will save many dollars in maintenance costs. Experts in soil conservation, agronomy, and drainage should be available to assist in maintenance inspections and to recommend appropriate erosion-control measures.
Inspections of drainage and erosion-control measures should be made shortly after completion of construction to locate and correct deficiencies before they develop into major problems. Deficiencies in design or in construction procedures should be discussed with the engineering staff so that similar deficiencies can be prevented on future projects. Coordination of responsibilities for erosion-control measures among design, construction, and maintenance departments needs to be emphasized.
Because of the rapid turnover of maintenance personnel, frequent training schools should be conducted in maintenance techniques, including methods of making inspections, care or management of vegetative covers and plants, and measures to prevent and correct erosion.
Maintenance records should give sufficient detail to permit analysis of maintenance problems, particularly those related to erosion control. With the advent of the computer, coding of maintenance costs for the various elements of the highway could serve in tabulating and analyzing data for use in making changes in design and construction that will reduce erosion problems and lower maintenance costs.
Research and Development
Although several State highway departments in cooperation with the Bureau of Public Roads, the Department of Agriculture, and other agencies have developed economical and practicable measures to control erosion, additional research is needed to improve present methods and provide even more economical and effective means for preventing erosion both during and subsequent to construction.
Methods and sequence of construction require further study in many areas of the country. Weather conditions, soil characteristics, and types of effective erosion-control measures vary, thus requiring a different approach to the erosion problem. Investigations are needed to develop protective covers and treatment of soils to avoid expensive sodding practices and to reduce the cost of channel linings. Further development in the use of dust palliatives could prove beneficial in areas subject to wind erosion.
Data on the amount of sediment transported to streams due to erosion during the construction of highway are very limited. The increase of sediment in a stream due to highway construction and its estimated damage over that produced under natural conditions are not well defined. Such information is necessary to evaluate properly the extent of controls needed for the control of sediment during the construction of a highway.
The Department of Agriculture, through its Agricultural Research Service and Soil Conservation Service, has developed methods to prevent soil erosion that are effective in specific areas of the country. Many of their designs and procedures are now being used in highway construction. An additional cooperative effort between the State highway departments and the Department of Agriculture, especially in developing vegetation and in improving soil conservation methods, should be actively promoted. This cooperation will provide assurance that the best methods for preventing erosion are being used.
Legal Requirements and Responsibilities
Legal requirements and governmental responsibilities in matters related to water vary throughout the States. The responsibility for damage to upstream and downstream property must be considered in highway design, particularly with respect to flooding, erosion, and sediment. Statutes in some States establish rigid controls in matters related to fish and wildlife, pollution of streams and water supplies, irrigation, and diversions of natural stream courses. It is the policy of the Bureau of Public Roads to participate with Federal highway funds in construction of highway projects that meet the requirements of otherFederal, State, and local agencies, if such requirements are in accordance with good design practice and are determined to be the responsibility of the highway agency.
The following measures should be taken to minimize soil erosion from highway construction:
These guidelines are intended to aid in the preparation of appropriate construction specifications and design procedures. They are not meant to be directives that apply in all areas and under all conditions. Effort to prevent erosion during highway construction and on the completed highway is rewarding both in the enhanced beauty of the highway and in the contribution of highway agencies to conservation of our land and water and to the reduction of pollution in our waterways.