1、 CHAPTER 12 STORMWATER MANAGEMENT 2007 by the American Association of State Highway and Transportation Officials. 2007 by the American Association of State Highway and Transportation Officials.CHAPTER 12 TABLE OF CONTENTS 12.1 INTRODUCTION. 12-1 12.1.1 History 12-1 12.1.2 Potential Impacts. 12-2 12.
2、2 REGULATIONS. 12-4 12.2.1 Federal Regulations 12-4 12.2.2 State and Local Regulations 12-6 12.3 IMPLEMENTATION OF STORMWATER MANAGEMENT DESIGN 12-7 12.3.1 Best Management Practices 12-9 12.3.2 Facility Types 12-10 12.3.2.1 Enhanced Ponds: Wet Detention/Extended Detention 12-10 12.3.2.1.1 Wet Detent
3、ion Ponds . 12-10 12.3.2.1.2 Extended Detention Ponds. 12-11 12.3.2.2 Stormwater Wetland Basins 12-11 12.3.2.3 Infiltration Facilities 12-12 12.3.2.4 Filtering Devices . 12-13 12.3.2.5 Water Quality Inlets 12-13 12.3.2.5.1 Vegetative Systems 12-14 12.3.3 Design Aspects 12-15 12.3.3.1 Ponds . 12-15 1
4、2.3.3.2 Infiltration Facilities 12-17 12.3.3.3 Filtering Devices . 12-18 12.3.4 Documentation 12-19 12.4 CONSTRUCTION 12-20 12.4.1 Pre-Bid/Preconstruction Conference. 12-21 12.4.2 Construction of Best Management Practices 12-21 12.4.2.1 Ponds/Basins . 12-22 12.4.2.2 Infiltration Facilities/Filtering
5、 Devices . 12-23 12.4.2.3 Vegetative Systems . 12-23 12.4.3 Grading . 12-24 12.4.4 Inspection/Quality Control 12-25 12.4.5 Certification and Documentation 12-25 12.4.6 Training and Communication . 12-26 12.5 MAINTENANCE 12-26 12.5.1 Maintenance/Inspection Programs 12-27 12.5.2 Documentation 12-28 12
6、.5.3 Maintainability 12-29 12.5.4 Budgetary Requirements. 12-30 2007 by the American Association of State Highway and Transportation Officials.Highway Drainage Guidelines 12-iv 12.5.5 Training .12-30 12.6 FUTURE ISSUES.12-31 12.7 CITED REFERENCES12-32 12.8 BIBLIOGRAPHY.12-32 APPENDIX 12A COMMON HIGH
7、WAY RUNOFF CONSTITUENTS AND THEIR PRIMARY SOURCES 12-35 APPENDIX 12B DAM INSPECTION CHECKLIST.12-36 APPENDIX 12C A COMPARATIVE ASSESSMENT OF THE EFFECTIVENESS OF CURRENT URBAN BEST MANAGEMENT PRACTICES.12-41 2007 by the American Association of State Highway and Transportation Officials.Chapter 12 St
8、ormwater Management 12.1 INTRODUCTION Storm drainage, which now includes stormwater management facilities, is an integral and expensive aspect of highway design, highway construction and, all too often forgotten, highway maintenance. This chapter provides an overview of the concepts and practices of
9、 this challenging aspect of highway drainage. The purpose of this chapter is to acquaint the hydraulics engineer with the principles and practices of stormwater management as they relate to transportation facilities. This Chapter provides a brief review of the current and ever-changing maze of regul
10、ations and a discussion of the potential impacts of unmanaged runoff on downstream properties and ecosystems. A large section of the chapter is allotted to the development and implementation of an effective stormwater management program including the application, design, construction and maintenance
11、 of Best Management Practices (BMPs). This chapter also offers some insight into the future of stormwater management and provides a list of reference materials. A stormwater management program should involve a comprehensive approach to both water quantity and quality. Practices, which are adopted in
12、 the areas of operations and maintenance, such as salt containment and reduced pesticide/herbicide usage, can have significant benefits to the environment. Construction practices, which stage grading operations and reduce sediment loads, are also important to the overall management program. This cha
13、pter, however, will focus on the use of permanent structural controls to reduce surface water flood hazards and environmental impacts resulting from highway facilities. Information on temporary controls suited to manage runoff during construction can be found in Chapter 3. 12.1.1 History The methods
14、 with which highway engineers deal with stormwater runoff have evolved and will continue to change as our knowledge grows. To early designers, storm drainage was somewhat incidental to the geometric design of a roadway. As the magnitude, complexity and cost of highway construction grew, along with c
15、oncern for the safety of the traveling public, engineers were required to focus increasing attention on highway drainage. One objective of highway design and construction has always been to protect the highway and its users within the highway right-of-way. Although narrow in scope, the emphasis from
16、 a drainage perspective was on fast and efficient collection, conveyance and discharge of runoff. In response to growing concerns over urban flooding in the 2007 by the American Association of State Highway and Transportation Officials.Highway Drainage Guidelines 12-2 1960s and subsequent environmen
17、tal concerns in the 1970s of water pollution and stream erosion due to increased development, drainage engineers began to consider the impacts of stormwater runoff beyond the highway right-of-way line. They developed methods to quantify the flood hazards and impacts and devised means to minimize and
18、 control stormwater. Thus, the concept of stormwater management was first applied. Early attempts (practiced by only a few State and local governments) to control runoff by stormwater management were limited to peak discharge attenuation (quantity management) for flood control or reduction in draina
19、ge system cost. The concept has expanded to include removal of certain pollutants (quality management) regulated by various State, local and regional jurisdictions. Now, under the Clean Water Act as administered through the National Pollutant Discharge Elimination System (NPDES) permit program and t
20、he Coastal Zone Reauthorization Act, stormwater quality management is in effect nationwide. A detailed outline of the program requirements is included in Section 12.2.1. 12.1.2 Potential Impacts Large-scale, land-disturbing activities characterized by highway construction and other development may c
21、ause increases in runoff volumes and peak runoff rates. These increases are attributable to a higher percentage of impervious cover, removal of vegetation, more efficient conveyances, and a loss of soil permeability caused by compaction during development. The decreased time of concentration contrib
22、utes to higher peak rates of runoff, while the loss of infiltration and interception create greater runoff volumes. These effects are most noticeable on frequent storms (return periods of less than 10 years). The resultant increases in peak runoff rates and runoff volumes create additional stress on
23、 the stream channels and can increase the potential for channel erosion/degradation. The extent of impacts resulting from highway construction alone will vary depending on the watershed size, state of present development, additional pavement proposed, topography and drainage patterns. The hydraulics
24、 engineer must be aware of these possible consequences and evaluate each project according to the potential risk to the watershed. The potential impacts to receiving waters, which result directly and indirectly from highway construction and other development, as a whole, include: flooding, bank eros
25、ion, stream degradation, sedimentation/aggradation, groundwater depletion, increased pollutant loadings, thermal effects, and habitat loss. An increase in the frequency and magnitude of flooding (Figure 12-1) is the most obvious impact of construction and, as a result, receives the most attention an
26、d regulatory action. Increases in flooding due to urbanization take place gradually, coincident with the pace of development. Highway construction may, in some instances, collect and concentrate sheet flow through cross drain culverts. Highway embankments may create a potential upstream impact by te
27、mporarily impounding stormwater runoff. However, this temporary storage may mitigate the potential impacts previously mentioned in this Section. This is especially true in the case of rural highways and interchanges. 2007 by the American Association of State Highway and Transportation Officials.Stor
28、mwater Management 12-3Figure 12-1. Localized Flooding Increased stream velocities, concentration of flow and higher frequencies and duration of bankfull flows can result in undercutting of stream banks. Bank erosion can threaten structures (Figure 12-2) and can result in the loss of aquatic habitat.
29、 The increase in frequency of bankfull floods and the extended duration of flood hydrographs increases a streams ability to move bed material. This often results in the lowering of the streambed and headcutting between fixed points (e.g., culverts). The resulting drop at culvert outlets can be a bar
30、rier to fish passage. Figure 12-2. Stream Erosion Increases with Highwater Peaks and/or Longer Duration Bankfull Flows The material eroded from stream banks and channel bottoms in the upper reaches of the watershed deposits in flatter stream reaches. This deposition can decrease culvert capacity, re
31、nder flood control or irrigation facilities inoperative and smother aquatic plants and animals. Streams subjected to heavy aggradation will lose channel definition and can become braided. Increases in impervious areas and the compaction of adjacent soils by construction equipment reduce the potentia
32、l for groundwater recharge. Additionally, cut slopes may expose and drain perched water tables via surface ditches. 2007 by the American Association of State Highway and Transportation Officials.Highway Drainage Guidelines 12-4 Highway runoff has the potential to increase the number and concentratio
33、n of pollutants in our streams. In particular, closed section highways with fast, efficient stormwater collection systems may eliminate the natural filtering capabilities of the soil/vegetative cover complex. A list of common highway runoff constituents and their sources is included in Appendix 12A.
34、 Generally, deposition of heavy metals (e.g., lead, zinc, copper, iron) result from engine and tire wear. The presence of these pollutants increases proportional to traffic volumes (5).1Thermal impacts of urbanization are often overlooked because they are not readily detectable. Slight increases in
35、stream temperatures over long periods of time or large, single-event temperature spikes can be hazardous to intolerant fish and invertebrate species. Runoff from asphalt surfaces (e.g., parking lots, roads); discharges from shallow, unshaded ponds; and deforestation can have detrimental effects on a
36、 stressed watershed. Primary impacts to aquatic habitat, such as placement of stormwater ponds within wetlands or stream channels, construction of culverts and deforestation, and the secondary impacts noted above, combine to adversely influence the general health of a stream system. All of the impac
37、ts identified above are potential impacts that could and have resulted from highway development. However, they do not necessarily occur for each and every highway project or at every stream crossing on a particular project. The size of a stream, the extent of the highway development, the type of fac
38、ility, type of traffic and volume and many other factors determine whether an adverse impact will or will not occur. The identification of the expected levels of impact, and what management measures are justified and appropriate, are very important aspects of a comprehensive stormwater management pr
39、ogram. 12.2 REGULATIONS Until expansion of the National Pollutant Discharge Elimination System (NPDES) in 1990, management for stormwater pollutant control was limited to a few State, regional, and/or local regulations. As a result of having those early programs in place, some States, municipalities
40、 and transportation departments have not been seriously impacted by the NPDES permit program; others have been required to implement new programs to reach compliance. For further discussion of regulations and legal aspects of highway drainage, the reader is directed to Chapter 5. However, due to the
41、 ever-changing nature of laws, regulations and standards, hydraulics engineers must be constantly aware of the latest Federal, State, and local requirements for the jurisdiction in which they work. 12.2.1 Federal Regulations The enabling legislation for all Federal stormwater management regulations
42、stems from the 1972 Water Pollution Control Act as amended by the 1977 Clean Water Act (CWA) and the 1987 Water Quality Act (WQA). The goals of these laws are to control the discharge of pollutants into “waters of the United States.” U.S. EPA defines “waters of the United States” in part as all lake
43、s, rivers, streams and their tributaries (including intermittent streams) that degradation or destruction of would or could 1Numbers in parentheses refer to publications in “References” (Section 12.7). 2007 by the American Association of State Highway and Transportation Officials.Stormwater Manageme
44、nt 12-5affect interstate or foreign commerce. A complete definition may be found in 40 CFR Section 232.2(q). The implementation of these laws lies mainly with the State governments in States with delegated authority and with U.S. EPA in the remaining States. The CWA provided that the States develop,
45、 implement and enforce a Water Quality Certification Program. The WQA provided for the application of the CWA as it related to stormwater discharges through implementation of the NPDES program. These requirements include: source identification; characterization of pollutants; sampling of pollutants
46、in discharges; prohibition of non-stormwater discharges; storm flow monitoring of selected outfalls; a water quality management program; legal authority for implementation; and fiscal analysis of capital, operational, and maintenance expenses. In November of 1990, U.S. EPA published regulations to e
47、xpand permit requirements under the CWA for the discharge of industrial stormwater and to bring municipal stormwater discharges under the authority of the Act. These regulations are administered by either U.S. EPA or State environmental agencies that have requested and obtained delegated authority.
48、Generally, permits will be in effect for five years, at which time reapplication will be necessary. State transportation departments may have to apply for permits in three areas: construction activities, industrial stormwater discharges, and municipal storm sewer discharges. Construction activities
49、that disturb areas in excess of the minimum area established by U.S. EPA or the State regulatory agency will require an industrial stormwater discharge permit. A stormwater pollution prevention plan to control erosion and sedimentation on a project-by-project basis must be developed prior to the start of construction. Within those States operating under the nationwide general permit process (issued by U.S. EPA), a Notice of Intent (NOI) to comply with that plan must be subm
