1、 CHAPTER 6 HYDRAULIC ANALYSIS AND DESIGN OF OPEN CHANNELS 2007 by the American Association of State Highway and Transportation Officials. 2007 by the American Association of State Highway and Transportation Officials.CHAPTER 6 TABLE OF CONTENTS 6.1 INTRODUCTION. 6-1 6.2 CONSIDERATIONS FOR ESTABLISHI
2、NG CRITERIA. 6-2 6.3 PLANNING AND LOCATION. 6-2 6.3.1 Planning . 6-3 6.3.1.1 Coordination with Other Agencies. 6-3 6.3.1.1.1 Local Drainage Systems 6-5 6.3.1.1.2 Flood Control. 6-5 6.3.1.1.3 Floodplain Management 6-5 6.3.1.1.4 Conservation 6-6 6.3.1.1.5 Fish and Wildlife . 6-6 6.3.1.1.6 Irrigation 6
3、-7 6.3.1.1.7 Permits. 6-7 6.3.1.2 Cooperative Projects 6-7 6.3.2 Location . 6-8 6.3.2.1 Longitudinal Encroachments 6-8 6.3.2.2 Transverse Encroachments. 6-10 6.4 SURVEYS 6-11 6.4.1 Topographic Features. 6-20 6.4.2 Channel Characteristics . 6-20 6.4.3 Fish and Wildlife . 6-21 6.4.4 Highwater Informat
4、ion. 6-22 6.4.5 Hydrologic Data. 6-23 6.5 HYDROLOGY 6-23 6.6 HYDRAULICS OF OPEN CHANNELS 6-23 6.6.1 Types of Flow 6-24 6.6.2 Open Channel Equations 6-25 6.6.3 Analysis of Open-Channel Flow 6-27 6.6.3.1 Factors Affecting Open-Channel Flow 6-27 6.6.3.2 Stable Stage-Discharge Relationships 6-28 6.6.3.2
5、.1 Single-Section Analysis. 6-29 6.6.3.2.2 Water Surface Profiles. 6-29 6.6.3.2.3 Control Sections 6-30 6.6.3.3 Unstable Stage-Discharge Relationships 6-30 6.6.3.4 Flow and Velocity Distribution 6-35 2007 by the American Association of State Highway and Transportation Officials.Highway Drainage Guid
6、elines 6-iv 6.6.4 Special Analysis Techniques6-36 6.6.4.1 Two-Dimensional Analysis 6-36 6.6.4.2 Water and Sediment Routing6-36 6.6.4.3 Unsteady Flow Analysis .6-38 6.7 FLUVIAL GEOMORPHOLOGY .6-38 6.7.1 Alluvial Streams .6-39 6.7.1.1 Stream Types 6-39 6.7.1.1.1 Straight Streams .6-41 6.7.1.1.2 Braide
7、d Streams .6-41 6.7.1.1.3 Meandering Streams.6-42 6.7.1.2 Graded or Poised Streams.6-44 6.7.1.3 Stream System Response 6-44 6.7.2 Nonalluvial Channels .6-46 6.7.3 Stream Classification Methods.6-46 6.8 THE EFFECTS OF CHANNEL ALTERATIONS 6-51 6.8.1 Channel Realignment .6-52 6.8.1.1 Slope Modification
8、 .6-52 6.8.1.2 Section Modification.6-53 6.8.2 Conveyance Modification 6-54 6.9 CHANNEL STABILIZATION AND BANK PROTECTION.6-56 6.9.1 Stabilization Considerations.6-56 6.9.2 Selection of Protective Measures .6-57 6.9.3 Revetments .6-57 6.9.4 Using Vegetation for Stream Bank Stabilization .6-59 6.10 R
9、OADSIDE DRAINAGE CHANNELS 6-59 6.10.1 Safety and Aesthetics .6-60 6.10.2 Shape 6-60 6.10.3 Lining .6-60 6.10.4 Superelevation 6-63 6.10.4.1 Supercritical Flow6-64 6.10.4.2 Subcritical Flow.6-64 6.10.5 Chutes and Flumes .6-64 6.10.6 Grade Control Structures6-65 6.10.7 Transitions6-65 6.10.7.1 Supercr
10、itical Flow Transitions.6-66 6.10.7.2 Subcritical Flow Transitions6-66 6.10.8 Confluences 6-66 6.10.9 Bends and Curves.6-67 2007 by the American Association of State Highway and Transportation Officials.Hydraulic Analysis and Design of Open Channels 6-v6.11 STRUCTURAL CONSIDERATIONS 6-68 6.11.1 Subs
11、urface Investigations 6-69 6.11.2 Reinforcement for Rigid Linings . 6-69 6.11.3 Buoyancy and Heave . 6-70 6.11.4 Seepage Control Filter Blankets 6-70 6.12 CONSTRUCTION-RELATED HYDRAULIC CONSIDERATIONS. 6-71 6.13 MAINTENANCE-RELATED HYDRAULIC CONSIDERATIONS. 6-71 6.13.1 Maintenance during Contract Pe
12、riod . 6-72 6.13.2 Hydraulic-Related Maintenance Considerations . 6-72 6.14 REFERENCES 6-72 2007 by the American Association of State Highway and Transportation Officials.Chapter 6 Hydraulic Analysis and Design of Open Channels 6.1 INTRODUCTION An open channel is a conveyance in which water flows wi
13、th a free surface and may be natural or constructed. Natural streams usually consist of a normal or low-flow channel and adjacent floodplains. For purposes of this chapter, the term “open channel” will include the total conveyance facility, floodplain, and stream channel. Open channel hydraulics is
14、of particular importance to highway design because of the interrelationship of channels to all highway hydraulic structures. In the hydraulic analysis and design of bridges and culverts, open-channel hydraulic principles are utilized to evaluate the effects of proposed structures on water surface pr
15、ofiles, flow, and velocity distributions, lateral and vertical stability of the channel, stream regime, flood risk, and the potential reaction of the stream to changes in variables (e.g., structure type, shape, location, scour control measures). The hydraulic design process for open channels consist
16、s of establishing criteria, developing and evaluating alternatives, and selecting the alternative that best satisfies the established criteria. Capital investment and probable future costs, including maintenance and flood damages to properties, traffic service requirements, and the stream and floodp
17、lain environment must be considered in the design process. The detail in which risks are considered should be commensurate with the flood hazard at the site, economics, and current engineering practices. Highway encroachments on streams and floodplains should be avoided where practicable; however, e
18、ncroachments are necessary in some locations. The short- and long-term effects of changes to natural streams should be evaluated during both the planning and design phase of project development. Highway-related channel work is generally local in nature and should not be associated with extensive mod
19、ifications generally referred to as channelization projects. In this chapter, the hydraulic engineering aspects of open channels are discussed, proceeding from hydraulic considerations in planning and location through studies necessary for design and construction to hydraulic considerations as relat
20、ed to maintenance. Channels along, across, approaching, and leaving the highway are included. 2007 by the American Association of State Highway and Transportation Officials.6-2 Highway Drainage Guidelines The chapter is not all inclusive, but salient considerations are discussed, suggested procedure
21、s are presented and references to sources of more detailed information are cited. 6.2 CONSIDERATIONS FOR ESTABLISHING CRITERIA Criteria are the standards by which a project feature is judged for acceptability. Criteria for open channels are the hydraulic, environmental, and legal considerations that
22、 reflect the unique and individual requirements of each location. Design criteria should include consideration of the existing stream characteristics over a range of flood magnitudes, the class, and type of highway facility involved, the level of service to be maintained and environmental considerat
23、ions (e.g., fish and wildlife habitat). These considerations must necessarily be weighed against the risks incurred and related economics. Based on these considerations, design criteria should include a range of flood magnitudes and frequencies, velocity and flow distributions, scour and erosion pot
24、entials, maintenance access, budget constraints, and maintenance or restoration of the stream environment. Studies necessary to determine whether a proposed design satisfies the established criteria may reveal bounds within which modifications may be accomplished without disrupting the natural balan
25、ce or trends of the system. Thresholds that should not be crossed may be discovered by orderly and thorough investigations of existing conditions for the following types of proposed projects: existing streams where encroachments on the floodplain are proposed, existing channels that will be modified
26、 by the project, and locations where some type of new channel will be constructed. Consideration of the potential response of streams to encroachments and channel modifications may influence the selection of design criteria. These potential responses are discussed in Section 6.7. 6.3 PLANNING AND LO
27、CATION The planning and location phase for a highway section usually involves consideration of a number of alternative highway locations and schemes of development. A preliminary hydraulic study of the various alternatives should be conducted during the planning stage because the type and cost of dr
28、ainage facilities required could be the determining factor in location selection. The hydraulic aspects of each alternative should be given sufficient study to ensure that the environmental effects, risks, and costs of required drainage facilities can be considered in the final selection of an alter
29、native. As project development proceeds, locations selected without adequate consideration of the hydraulic requirements of floodplain encroachments or extensive channel modifications can be found to be unacceptable for environmental reasons or because of costs and risks. 2007 by the American Associ
30、ation of State Highway and Transportation Officials.Hydraulic Analysis and Design of Open Channels 6-3 Delays in plan development while acquiring survey data necessary for the hydraulic study may be avoided if locations where additional data will be required are identified during the planning and lo
31、cation study phase of development. 6.3.1 Planning Many highway locations require construction across or along streams and floodplains. An evaluation, commensurate with the complexity of the system, should be made during the planning phase of the effects location alternatives would have on stream sys
32、tems. Analysis of alternative alignments may reveal possibilities for reducing construction costs, flood damage potential, maintenance problems, and adverse environmental impacts. Detailed information and survey data are seldom available for an in-depth hydraulic study during the planning phase; how
33、ever, it is possible to ascertain basic requirements and consequences of a particular location or alignment and the relative merits of alternatives. Topographic maps, aerial photography, stream gage data, floodplain delineation maps, and a general knowledge of the area will often provide the basis f
34、or preliminary evaluations of alternatives. Water quality standards and stream characteristics (e.g., movable beds, heavy debris discharge during floods, highly erodible banks, fish and wildlife resources) are also factors to be assessed during the planning phase. These assessments may require the c
35、ooperative efforts of office and field engineers and others with experience on similar projects or specialized expertise in the particular area. During the planning phase, contacts should be made with Federal, State, and local agencies regarding plans or uses that could affect the highway drainage d
36、esign. Examples of such plans or uses are dams and reservoirs, irrigation, flood-control levees or channel modifications, navigation, floodplain management, recreational use and fish or wildlife management. Agencies having regulatory authority over navigation and construction activities in waters of
37、 the United States and agencies with special expertise, such as in the limits and classification of wetlands, should also be consulted for preliminary information that may affect location decisions. Additional discussion of the role of hydraulics in planning is given in Chapter 1, “Guidelines for Hy
38、draulic Considerations in Highway Planning and Location” (5).16.3.1.1 Coordination with Other Agencies There are numerous Federal, State, local, quasi-governmental, and private agencies engaged in water-related planning, construction, and regulation that could affect highway location and design. The
39、se agencies have interests in drainage, flood control, floodplain management, navigation, hydroelectric power generation, conservation, water supply, irrigation, fish and wildlife, and recreation. Early coordination with these agencies will help to avoid delays in the orderly advancement of project
40、planning, design, and construction. Several agencies have responsibilities for issuing permits for construction activities, and their comments and recommendations should be considered in the planning stage of project development. Coordination in the planning phase may also reveal 1Numbers in parenth
41、eses refer to publications in “References” (Section 6.14). 2007 by the American Association of State Highway and Transportation Officials.6-4 Highway Drainage Guidelines opportunities for cooperative projects that will be of benefit to both the highway agency and the water resources agency. Followin
42、g is a partial listing of agencies commonly involved in activities that could affect highway planning and location: Bureau of Reclamation; Bureau of Land Management; Bureau of Indian Affairs; drainage districts; Environmental Protection Agency; Federal Emergency Management Agency; Fish and Wildlife
43、Service; flood-control districts; Forest Service; International Boundary and Water Commission; irrigation districts; Indian councils; municipal governments; National Marine Fisheries Service; National Oceanic and Atmospheric Administration; Natural Resources Conservation Service; planning districts;
44、 private citizens; private industry; river basin compacts, commissions, committees and authorities; State environmental protection agencies; State coastal zone management agencies; State and regional 208 planning agencies; State fish and game agencies; State floodplain management agencies; State wat
45、er resource agencies; Tennessee Valley Authority; U.S. Army Corps of Engineers (USACE); U.S. Coast Guard (USCG); U.S. Geological Survey (USGS); and watershed districts. The advantages of early coordination with these agencies are discussed in the following sections. 2007 by the American Association
46、of State Highway and Transportation Officials.Hydraulic Analysis and Design of Open Channels 6-5 6.3.1.1.1 Local Drainage Systems Drainage is generally defined as the removal of surface or groundwater from a given area, either by gravity or pumping. Highways and highway drainage systems should be de
47、signed with consideration of existing and planned local drainage systems. Coordination with local agencies will help to preclude adverse effects on local systems. 6.3.1.1.2 Flood Control Flood control involves protecting land areas from overflow by the use of levees, increased channel capacity, wall
48、s, stream diversion, cutoffs, channelization, or reservoirs. There are certain stream reactions and hydrologic changes that result from flood-control features that should be considered by the highway agency. The construction of channel cutoffs and channelization projects may cause degradation of the
49、 channel, change flow distribution and stage-discharge relationships, and increase flood-peak discharges, thus, endangering highway embankments and structures. Levees will affect flow distribution, peak flows, and stage-discharge relationships to the possible detriment or benefit of existing or proposed highway features. Highways located upstream of flood control reservoirs could be subjec
