1、 CHAPTER 3 EROSION AND SEDIMENT CONTROL IN HIGHWAY CONSTRUCTION 2007 by the American Association of State Highway and Transportation Officials. 2007 by the American Association of State Highway and Transportation Officials.CHAPTER 3 TABLE OF CONTENTS 3.1 INTRODUCTION. 3-1 3.2 PURPOSE AND OBJECTIVES
2、3-2 3.3 EROSION AND SEDIMENT-RELATED PLANNING AND LOCATION CONSIDERATIONS 3-4 3.3.1 Identification of Erosion Sensitive Areas 3-5 3.3.2 Identification of Sediment Sensitive Areas 3-5 3.3.3 Coordination 3-6 3.3.3.1 Coordination Within the Transportation Agency 3-6 3.3.3.2 Coordination with Other Agen
3、cies 3-6 3.4 EROSION AND SEDIMENT-RELATED GEOMETRIC CONSIDERATIONS 3-6 3.4.1 Alignment and Grade. 3-7 3.4.2 Cross Section . 3-7 3.5 PLAN DEVELOPMENT . 3-8 3.5.1 Temporary Erosion and Sediment Control Measures 3-9 3.5.1.1 Ground Cover 3-9 3.5.1.2 Channel Liners 3-10 3.5.1.3 Diversion Dikes and Ditche
4、s. 3-13 3.5.1.4 Filter Berms. 3-15 3.5.1.5 Temporary Slope Drains . 3-16 3.5.1.6 Brush Barriers . 3-18 3.5.1.7 Silt Fences. 3-19 3.5.1.8 Check Dams 3-21 3.5.1.9 Straw Bales . 3-23 3.5.1.10 Riprap. 3-23 3.5.1.11 Sediment Basins. 3-26 3.5.1.11.1 Planning and Location 3-26 3.5.1.11.2 Design . 3-29 3.5.
5、1.12 Phased Erosion and Sediment Control Plans . 3-30 3.5.2 Permanent Erosion and Sediment Control Measures. 3-30 3.5.2.1 Vegetation . 3-30 3.5.2.2 Slopes 3-31 3.5.2.3 Channels 3-32 3.5.2.3.1 Sizing and Shape. 3-33 3.5.2.3.2 Alignment and Grade 3-33 3.5.2.3.3 Linings 3-34 3.5.2.3.4 Grade Control Str
6、uctures 3-36 3.5.2.4 Shoulder Drains. 3-38 2007 by the American Association of State Highway and Transportation Officials.Highway Drainage Guidelines 3-iv 3.5.2.5 Culverts3-38 3.5.2.6 Underdrains .3-40 3.6 CONSTRUCTION 3-41 3.6.1 Scheduling Operation .3-41 3.6.2 Clearing and Grubbing .3-42 3.6.3 Con
7、struction Operations in Rivers, Streams, and Impoundments3-42 3.6.4 Excavation and Embankment Construction .3-44 3.6.5 Bridge Construction .3-45 3.6.6 Culvert Construction 3-46 3.6.7 Borrow Pits, Waste Areas, and Haul Roads .3-48 3.6.8 Maintenance of Control Features .3-48 3.6.9 Enforcement .3-52 3.
8、7 REFINEMENT OF METHODS 3-53 3.7.1 Research and Development 3-53 3.7.2 Feedback.3-53 3.8 REFERENCES 3-54 2007 by the American Association of State Highway and Transportation Officials.Chapter 3 Erosion and Sediment Control in Highway Construction 3.1 INTRODUCTION Soil erosion is a natural process wh
9、ereby soil particles are dislodged by rainfall and carried away by runoff. The removal rate of the soil particles is proportional to the intensity and duration of the rainfall, the volume and characteristics of the water flow, and the terrain characteristics and soil properties. This erosion process
10、 is accelerated where the land has been disturbed by removing the vegetative or other natural protective cover of the soil. Sedimentation is the natural process of deposition of the eroded soil. This eroded soil in the form of sediment may contaminate lakes, streams and reservoirs, restrict drainage
11、 ways, plug culverts, damage adjacent properties, and affect the ecosystems of streams. Because modern highway construction may involve the disturbance of large land areas, control of erosion and sedimentation is a major concern. A commitment to erosion and sedimentation prevention during all phases
12、 of highway design construction and maintenance is stated in the AASHTO publication A Policy on Geometric Design of Highways and Streets, 2004 (1).1While much of the effort for control of erosion and sedimentation is expended during the construction phase of a highway development, a successful progr
13、am must address erosion and sedimentation control during the planning, location, design, and future maintenance phases as well. This erosion and sediment control program should be a plan of action and provision of contract documents to achieve an acceptable level of control within established criter
14、ia and control limits. This plan of action is analogous to an agencys highway development process, which results in contract plans and documents to provide and maintain transportation facilities based on certain criteria and controls. This chapter will address the establishment of criteria and contr
15、ols for erosion and sedimentation and the consideration, process and measures that must be taken to achieve the desired result. The primary thrust will be directed at water-related erosion and sedimentation although some of the practices are also applicable in controlling wind erosion. 1Numbers in p
16、arentheses refer to publications in “References” (Section 3.8). 2007 by the American Association of State Highway and Transportation Officials.3-2 Highway Drainage Guidelines Figure 3-1. Highway Construction Can Disturb Large Areas of Land Figure 3-2. Bare Soil Exposed to Erosion 3.2 PURPOSE AND OBJ
17、ECTIVES The purpose of an erosion and sediment control program is to allow the development of a highway facility while also accomplishing the three general erosion and sediment control objectives of (1) limiting off-site effects to acceptable levels, (2) facilitating project construction and minimiz
18、ing overall costs, and (3) complying with Federal, State, and local regulations. 2007 by the American Association of State Highway and Transportation Officials.Erosion and Sediment Control in Highway Construction 3-3 The first objective is to limit off-site effects to acceptable levels. One problem
19、with this approach is that, not only are many of the effects uncertain, there is no universal agreement as to what constitutes an undesirable effect. However, many off-site conditions are readily definable relative to the levels of sediment that may cause damage. Examples include clear water streams
20、, impoundments, and developed areas. The designer of the erosion and sediment control measures should attempt to make some determination of the type and magnitude of off-site effects to be expected, to determine whether the effects will be detrimental, beneficial, or neutral, and temper the design a
21、ccordingly. This determination may require some prediction or estimates of the quantity of eroded material that would be expected from the construction site. This information will allow an evaluation of what, if any, control measures are required and their size and extent of application. Several acc
22、eptable procedures for predicting soil loss quantities are presented in References (6), (19), and (27). The second objective deals with integration of the erosion control measures into the construction processes to facilitate construction and afford an overall cost effective program. Control measure
23、s should be simple to construct, afford as little interruption to normal construction procedures as practicable, and be effective in their operation. Much is lost when a shotgun approach is taken, where the designer attempts to achieve total control of both erosion and sediment by calling for rigoro
24、us or inflexible design plan measures of questionable effectiveness. Central to the preparation of an erosion and sediment control plan is an evaluation of each site for possible actions and their consequences. It is necessary to analyze the probable effects to be expected from both the implementati
25、on of the control measures and their omission, the location of the effects, whether or not the potential damage is acceptable, and the cost-effectiveness of the chosen action. This analysis will establish if, and to what extent, a plan for erosion and sediment control is needed. Figure 3-3. Roadway
26、Slope Protected with Shoulder Dike, Temporary Slope Drains, and Vegetation The third objective is complying with Federal, State, and local regulations. As a result of the National Environmental Policy Act of 1969, much attention has been directed to the control of erosion and sedimentation. Promulga
27、ted by this concern are numerous State and Federal regulations and controls governing land disturbing activities. At the Federal level, several Executive Orders (E.O.) and regulations address erosion and sediment control requirements on Federally supported highway activities. There are also Federal
28、control requirements exerted by numerous agencies (USACE, U.S. 2007 by the American Association of State Highway and Transportation Officials.3-4 Highway Drainage Guidelines EPA, U.S. FWS) through their administration of various permitting requirements (Section 404, Section 402 of the Federal Water
29、Pollution Control Act (FWPCA) and Sections 9 and 10 of the River and Harbor Act). The National Pollutant Discharge Elimination System (NPDES) authorized under 40 CFR 122.26(b)(14)(x) addresses stormwater discharge from construction sites. In 1990, the Phase I regulations were applied to construction
30、 activities which disturb greater than five acres (two hectares). A subsequent signing of the Phase II Final Rule addresses disturbed areas between one acre and five acres (0.4 hectare to two hectares). Most States have enacted some form of an erosion and sediment control program through specific le
31、gislated sediment control acts or as a part of their Section 208 (PL 92-500) planning. In most instances, highway agencies are required to meet their State regulations. Some basic principles hold true when developing an erosion and sediment control program for a project. These include the following:
32、 erosion prevention is generally more effective than sediment control; sediment control is generally more effective than the repair of damage caused by uncontrolled sediment; and an erosion and sediment control plan carefully prepared for the specific conditions to be expected for a particular proje
33、ct will be more effective than a generalized nonspecific approach. Figure 3-4. Silt Fence Protecting Adjacent Property 3.3 EROSION AND SEDIMENT-RELATED PLANNING AND LOCATION CONSIDERATIONS Effective erosion control begins in the planning and location of a highway route. All highway route alternative
34、s have a base erosion potential that varies from route to route. These alternative routes can also present a range of potential sedimentation problems and controls. These sediment and erosion sensitive areas should be identified and considered in selection of the final route location and the establi
35、shment of criteria on which the control measures and procedures will be established. Unless damage from erosion and sediment is considered in selecting a route location, the cost of solving problems that may have been avoided sometimes becomes great. The total cost of erosion 2007 by the American As
36、sociation of State Highway and Transportation Officials.Erosion and Sediment Control in Highway Construction 3-5 control measures on each of the alternatives under study must be considered as a part of the economic analysis. 3.3.1 Identification of Erosion Sensitive Areas All highway route alternati
37、ves have a base erosion potential that is dependent on soil types, terrain features, and climate. Some soil types are known to be more erosive than others and their identification is a valuable aid in route selection. Information on soil erodibility can often be obtained from (1) soil and geological
38、 maps and reports, (2) local agricultural offices, or (3) local highway personnel familiar with previous work in particular soil types. Areas with unstable or troublesome soils (e.g., landslide areas, loess soils, alluvial fans, some glacial deposits) are potential problem areas when disturbed by hi
39、ghway construction. Soil reports and investigations by knowledgeable engineers and engineering geologists can be made during the route location stage to identify these areas. The natural drainage pattern, including subsurface flow, should be examined for the alternative routes considered. A dense pa
40、ttern of steep gradient natural channels presents a greater erosive potential than would a flatter gradient and more dispersed natural system. Subsurface flow can present problems with slope stability in areas requiring extensive cut sections. A knowledge of the geology of the area allows the highwa
41、y engineer to detect problem areas and anticipate subsidence, landslides, and erosion problems. Such areas and problems can sometimes be avoided in route selection. Terrain features are the result of past geologic and climatic processes. Erosion and deposition by running water are major geologic pro
42、cesses in shaping the terrain. A study of the terrain and the natural erosion can aid in judging the complexity of erosion and what control measures, if any, are required. Seasonal variations of climatic conditions (e.g., rainfall and snowmelt amounts, wind intensity and direction, temperature extre
43、mes) can be identified for the expected construction phases and exposed soil periods. This will allow evaluation of their effects on the potential erodibility of the route. 3.3.2 Identification of Sediment Sensitive Areas During the planning and location stages of project development, areas of poten
44、tial damage from excessive sedimentation should be identified. These would include such things as water supply sources, impoundments, irrigation systems, recreational waters, croplands, homes, wetlands, developed areas, and streams with particularly sensitive ecological systems. This identification
45、should include threshold limits for the accelerated introduction of sediment into the system as a result of the proposed project construction. This information will first assist in evaluating if the project can be located in a particular area without potential damaging results and, secondly, it will
46、 provide the criteria on which to base cost-effective erosion and sediment control measures. These threshold limits are addressed in more detail in Reference (5). 2007 by the American Association of State Highway and Transportation Officials.3-6 Highway Drainage Guidelines 3.3.3 Coordination The hig
47、hway planning process requires contact and coordination with the private and public sectors of society that may either have an interest in, or control of, the effects of proposed development. This process provides a means to obtain input identifying erosion and sediment sensitive areas and regulator
48、y controls. Coordination within the highway agency is also imperative. 3.3.3.1 Coordination within the Transportation Agency The development of an erosion and sediment control plan spans the entire planning, design, and construction stages of a highway project development. To be successful, it is im
49、perative that communication be established and maintained throughout each stage of development to ensure a coordinated effort. The designer must be aware of the erosion and sediment sensitive areas identified during project planning and any accepted criteria from others that would affect the control provisions included in the plans. This information, along with a clear purpose for the control provisions, must be passed on to those responsible for project construction and maintenance. Conversely, designers and planners must be aware of what is practicable, reasonable, a
