1、 CHAPTER 8 HYDRAULIC ASPECTS IN RESTORATION AND UPGRADING OF HIGHWAYS 2007 by the American Association of State Highway and Transportation Officials. 2007 by the American Association of State Highway and Transportation Officials.CHAPTER 8 TABLE OF CONTENTS 8.1 INTRODUCTION. 8-1 8.2 PLANNING CONSIDER
2、ATIONS 8-1 8.2.1 Coordination and Cooperation. 8-2 8.2.1.1 Other Agencies. 8-2 8.2.1.2 Utilities. 8-3 8.2.1.3 Property Owners. 8-3 8.2.2 Permits and Approvals. 8-3 8.2.2.1 National Flood Insurance Program. 8-4 8.2.2.2 Federal Water Pollution Control Act (FWPCA)Section 404 . 8-5 8.2.2.3 National Poll
3、utant Discharge Elimination System (NPDES). 8-5 8.2.2.4 Navigation 8-6 8.2.2.5 Coastal Zone Management Act 8-7 8.2.2.6 State Permits. 8-7 8.2.3 Replace or Rehabilitate Structures. 8-7 8.2.4 Environmental Considerations. 8-8 8.3 TYPES OF RESTORATION AND UPGRADING . 8-9 8.3.1 Horizontal or Vertical Al
4、ignment Adjustments . 8-9 8.3.2 Cross Section Changes. 8-9 8.3.2.1 Widening Roadway 8-10 8.3.2.2 Flattening Foreslopes . 8-10 8.3.2.3 Adding Traffic Lanes . 8-10 8.3.3 Urban Reconstruction 8-11 8.3.4 Safety Projects . 8-11 8.3.5 Rehabilitation and Replacement of Bridges and Culverts . 8-12 8.4 DATA
5、COLLECTION . 8-12 8.4.1 Condition Survey of Existing Structures . 8-12 8.4.2 Past Hydraulic Performance. 8-13 8.4.3 Identification of Other Problems with Existing Structures 8-14 8.5 HYDROLOGIC CONSIDERATIONS. 8-15 8.5.1 Evaluation of Observed Flood Discharge 8-15 8.5.2 Changes in Hydrologic Methods
6、 8-16 8.5.3 Land Use Changes . 8-17 8.5.4 Hydrologic and Hydraulic Investigations 8-19 8.6 HYDRAULIC CONSIDERATIONS. 8-19 8.6.1 Economic Analysis of Alternatives 8-20 8.6.2 Consequences of Change in Hydraulic Performance of Existing Structures . 8-21 2007 by the American Association of State Highway
7、 and Transportation Officials.Highway Drainage Guidelines 8-iv 8.6.2.1 Adding Traffic Lanes8-21 8.6.2.1.1 With Median.8-21 8.6.2.1.2 Without Median8-22 8.6.2.2 Safety Projects 8-24 8.6.2.3 Culvert Replacement and Rehabilitation 8-25 8.6.2.3.1 Culvert Replacement 8-25 8.6.2.3.2 Culvert Rehabilitation
8、 8-25 8.6.2.4 Bridge Replacements 8-26 8.6.2.5 Changes in Type of Structure .8-27 8.6.2.6 Culvert Extensions8-28 8.6.2.7 Structures in Urban Areas.8-29 8.6.3 Influence of Adjacent Structures 8-30 8.6.3.1 Upstream Structures8-30 8.6.3.2 Downstream Structures.8-31 8.6.4 Improvements in Hydraulic Perfo
9、rmance of Existing Structures.8-31 8.6.4.1 Improved Inlets .8-32 8.6.4.2 Adding Guide Banks.8-32 8.6.4.3 Channel Modifications8-33 8.6.4.4 Bridge Modification8-35 8.6.4.5 Debris Control.8-35 8.6.5 Obsolete Structures.8-35 8.6.6 Added Structures 8-36 8.7 CONSTRUCTION-RELATED CONSIDERATIONS DURING HYD
10、RAULIC DESIGN .8-37 8.7.1 Providing for Drainage during Construction 8-38 8.7.1.1 Contractor Crossings.8-38 8.7.1.2 Detours8-39 8.7.2 Stage Construction8-40 8.7.3 Roadway Realignment8-40 8.8 EROSION AND SEDIMENTATION CONTROL.8-41 8.9 REFERENCES 8-41 2007 by the American Association of State Highway
11、and Transportation Officials.Chapter 8 Hydraulic Aspects in Restoration and Upgrading of Highways 8.1 INTRODUCTION A substantial part of highway expenditures is for improving existing highways. While many kilometers miles of these highways have been improved or upgraded, there are thousands of kilom
12、eters miles remaining that need to be improved. The type of improvements can include improvements in geometrics, level of service, safety and/or repair, and rehabilitation of various highway elements. All of these improvements may involve highway drainage. Most drainage structures on the highway sys
13、tem do not individually represent a large part of the total investment of highway funds; viewed collectively, however, drainage structures represent a very large investment. Sufficient funds may not be available at the Federal, State, and local levels to fully maintain all elements of the nationwide
14、 system of highways. When available resources are inadequate to satisfy existing needs, it becomes important to develop a means of prioritizing the work to be done and to design cost-effective highway improvements that consider construction costs and future maintenance and operating costs. Economic
15、analysis of alternative drainage designs serves as an effective means of selecting cost-effective highway improvements. A comprehensive discussion on the use of economic analysis is presented in Reference (8),1Section 7.6.3.7. The elements or constraints that are considered in determining an accepta
16、ble design are included in the discussion. Highway drainage guidelines have been oriented toward the construction of new highways on new alignment. This chapter will discuss aspects of highway drainage that are pertinent to projects that involve the improvement of existing highways and/or highway dr
17、ainage structures. The reader is encouraged to read the other chapters of the Highway Drainage Guidelines. 8.2 PLANNING CONSIDERATIONS During the planning phase of a highway improvement project, decisions are made about the type of work that needs to be done and at what future date the work is to be
18、 accomplished. 1Numbers in parentheses refer to publications in “References” (Section 8.9). 2007 by the American Association of State Highway and Transportation Officials.Highway Drainage Guidelines 8-2 It is important that any improvement project or program, no matter how small, progress through so
19、me type of planning phase before the actual design and construction work is accomplished. Many small projects (e.g., spot safety improvements, single bridge replacements, and similar work) are often planned and accomplished within several months. Large highway improvements, such as adding lanes to s
20、everal kilometers miles of highway, sometimes require as much or more time to complete as an entirely new section of highway. The hydraulic consequences of a highway improvement need to be addressed during the planning phase of the project. Failure to adequately assess the hydraulic aspects of the i
21、mprovement could result in an increase in damages to adjacent property and the highway facility. Although detailed site information may not be required, it is important that a hydraulic assessment be made in the planning phase to determine that engineering and regulatory constraints can be met. Perm
22、its, legal requirements, environmental considerations, and coordination and cooperation with individuals and agencies will be discussed in this section. 8.2.1 Coordination and Cooperation Opportunities for coordination and cooperation with utility owners, individual property owners, or with other ag
23、encies are sometimes present in highway improvement projects. The exploration of these opportunities is an important part of the planning phase of project development because, where possibilities for cooperation exist, the potential for conserving public funds is also present. Cities, other agencies
24、, or even private interests that benefit from an improvement may be receptive to making contributions towards the improvement. Cost-sharing, maintenance and other responsibilities for cooperative projects need to be addressed when planning the improvement. It is essential that appropriate coordinati
25、on with other agencies and the public be initiated early in the project and continued as necessary through subsequent stages of project development. 8.2.1.1 Other Agencies Several Federal, State, or local agencies could have an interest in the drainage aspects of a particular highway improvement pro
26、ject. The modification or replacement of a drainage structure could affect an existing or planned project or action by another agency. The proposed modification of a crossing may also render an action feasible that may not have been practicable with existing conditions. The replacement of a bridge o
27、r culvert (culvert particularly) affords some flexibility in the channel bed elevation at the crossing. This could be of particular interest to representatives of irrigation districts, drainage districts, soil conservation districts, or others who may have plans or desire to take the opportunity to
28、establish a new grade for the channel. A possible increase in size and/or conveyance characteristics of a crossing would be of interest to the above agencies and those involved in floodplain management and wetlands preservation and fisheries management. The replacement of a structure in navigable or
29、 recreational waters would be of interest to several agencies as modification or preservation of the existing vertical and horizontal clearances would be involved. Improvements within a city could present the opportunity for a cooperative storm drainage project. 2007 by the American Association of S
30、tate Highway and Transportation Officials.Hydraulic Aspects in Restoration and Upgrading of Highways 8-3Coordination could help expedite the development of another project. 8.2.1.2 Utilities Utilities include railroads, telephone lines, storm drains, sanitary sewers, gas lines, water lines, oil line
31、s, power lines, and other services both public and private. It is important that every effort be made to identify all utilities that may impact a highway improvement project because they can be a major consideration both in the design of the improvement project and in the cost of the project. For ex
32、ample, a large storm drain that is city-owned and located under an existing highway could be in need of major repair or even replacement at the time a highway improvement project is being planned. The cost of the storm drain improvement might be assessed to the highway project, to the city, or share
33、d between the two. This question should be addressed during the planning phase of the improvement project. The scheduling of the highway project could be affected by the capabilities of the city to fund the storm drain work. Detention storage may be required if the highway improvement increases runo
34、ff to the extent of overloading existing storm drains or if State requirements for stormwater management apply. It may also provide an alternative solution where existing drainage structures are undersized. In many cases, commitments regarding use or disposition of the utilities need to be reached i
35、n the project-planning phase. 8.2.1.3 Property Owners The drainage elements of an existing highway and their operation, satisfactory or otherwise, should be familiar to residents along the route, and input from these local residents can be of benefit to an improvement project. The kinds of informati
36、on that would be of interest include the location of new or existing drains, the frequency and degree of roadway overtopping, and channel changes planned by the property owner that could affect the location of a culvert or bridge replacement structure. This input should be obtained during the planni
37、ng phase of the improvement and considered in the planning and design of the project. 8.2.2 Permits and Approvals Highway improvement projects are subject to the same permit requirements as highways on new alignments. Applications for permits and approvals required by State and Federal agencies shou
38、ld be made as soon as practicable in the process of project development (when the drainage design details have been agreed upon) to provide adequate time for processing of the permits. Permits and other legal requirements are discussed in several other chapters as follows: Chapter 1 Hydraulic Consid
39、erations in Highway Planning and Location (2). Chapter 5 The Legal Aspects of Highway Drainage (6). Chapter 6 Hydraulic Analysis and Design of Open Channels (7). Chapter 7 Hydraulic Analysis for the Location and Design of Bridges (8). Chapter 10 Evaluating Highway Effects on Surface Water Environmen
40、ts (9). 2007 by the American Association of State Highway and Transportation Officials.Highway Drainage Guidelines 8-4 In addition, the facets of the permit requirements that are unique to an improvement project are discussed in the following sections. 8.2.2.1 National Flood Insurance Program Under
41、the National Flood Insurance Program, flood profiles that are published as part of a flood insurance study should include the effects of existing highway facilities that are located in the study area. Improvements to highways within the limits of flood insurance studies can usually be accomplished w
42、ithout objection so long as they do not have the effect of increasing the elevation of the base floodwater surface elevations computed for the regulatory floodway. Formal approval of such projects from the agency administering the flood insurance program may, however, still be required. One example
43、of an improvement project that would not raise the flood profile would be a bridge replacement where the new bridge has the same or larger waterway opening than the existing bridge and no flow over the roadway is involved. Another example would be widening a highway without raising the gradeline whe
44、re flow over the roadway is a consideration. Usually, information concerning two water surface profiles for the 100-year flood is published in the flood insurance study. One of these 100-year flood profiles is for the natural floodplain and the other is for the floodway. A floodway, normally designe
45、d as a part of the insurance study, will convey the 100-year flood without increasing the water surface by more than a designated rise, which can be no more than 0.3048 m (1 foot) and is frequently less than this amount (Figure 8-1). When a flood insurance study is adopted, the floodway becomes regu
46、latory. Encroachments into the floodway are not permitted unless the changes in the water surface caused by the encroachment remain within established limits, and the floodplain management agency and FEMA approves. Figure 8-1. Floodway Schematic Where the existing cross section that is available to
47、carry flood flows is greater than the designated floodway, it may be possible to accommodate minor encroachments in the floodway through the 2007 by the American Association of State Highway and Transportation Officials.Hydraulic Aspects in Restoration and Upgrading of Highways 8-5purchase of easeme
48、nts, altering of flood boundaries or through accomplishing other mitigations that would provide for greater conveyance than the floodway published in the flood insurance study. This type of mitigation may allow the highway project to be consistent with the flood insurance study, because the increase
49、d conveyance of the revised floodway may compensate for the additional backwater caused by the highway. For some highway improvement projects, easements may be a cost-effective design approach (for example, a project in which the approach grade to a bridge overflows and it is desired to raise the grades without changing the bridge). The Flood Insurance Program is discussed in Section 5.5.2 of Chapter 5, “The Legal Aspects of Highway Drainage” (6). Additional information can be obtaine
