1、 STD-AASHTO SRCH WMTD-ENGL 177b Ob37809 0038230 933 Guide to Wetland Mitigation Issues for Transportation Designers Prepared by the Task Force for Environmental Design of the Standing Committee on Highways, Subcommittee on Design Published by the American Association of State Highway and Transportat
2、ion Officials 444 North Capitol Street, N.W. Suite 249 Washington, D.C. 20001 September 1996 STD-AASHTO SRCH WMTD-ENGL 377b Ob37809 0038233 87T O Copyright 1996 by the American Association of State Highway and Transportation Officials. All Rights Reserved. Printed in the United States of America. Th
3、is book, or parts thereof, may not be reproduced in any form without permission of the publishers. The Hydrologic Process Model (Figure 3.3) is reprinted from “Hydrologic Processes for Models of Freshwater Wetlands” by Michael J. Duever from Developments in Environmental Modeling, No. 12: Wetland Mo
4、deling, 1 988, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington OX5 1 GB, UK. Printed on recycled paper. ISBN: 1-56051 -042-0 STD-AASHTO SRCH WNTD-ENGL L77b Ob37809 0038232 70b AMERICAN ASSOCIATION OF STATE HIGHWAY AND TRANSPORTATION OFFICIALS EXECUTIVE COMMI
5、TTEE 1995-1 996 PRESIDENT: Wm. G. Burnett, P.E., Texas VICE PRESIDENT: Darre1 Rensink. Iowa SECRETARY-TREASURER: Clyde E. Pyers, Maryland R EG I O NA L R E P R ESENTATI V ES REGION I: REGION II: REGION III: REGION IV: Carlos Pesquera, Puerto Rico Robert L. Robinson, Mississippi Robert A. Welke, Mich
6、igan Marshall Moore, North Dakota NON-VOTING MEMBERS IMMEDIATE PAST PRESIDENT: EXEC UT IV E Di RECTOR : Wayne Shackelford, Georgia Francis B. Francois, Washington, D. C. STD-AASHTO SRCH WMTD-ENGL L99b Ob37804 0038233 b42 AASHTO 1993 TASK FORCE FOR ENVIRONMENTAL DESIGN Fred Bowser - Pennsylvania (rep
7、resented by Dean Schreiber) Bruce Brumfield - New Jersey William DuBose, III - South Carolina Eb Engelmann - Oregon Randolph Epperly - West Virginia David H. Fasser - New York Larry Foote - Minnesota Charles M. Higgins - Louisiana (represented by Vince Pizzolato) Larry King - Federal Highway Adminis
8、tration Lewis Koe - California Ed Kress - California Robert P. Mickelson - Arizona Charles Raymer - Kentucky Raymond D. Richter - Delaware Charles Rountree - Idaho Harry Underwood -Wyoming William R. Yarnell, Jr. - Missouri LIST OF CONTRIBUTORS Authors Phil Quarterman, Oregon Department of Michael W
9、. Shippey, Oregon Department of Transportation* Transportation With Contributions From Eb Engelmann, Oregon Department of Vince Pizzolato, Louisiana Department of Harry Underwood, Wyoming Department of Bill Yarnell, Missouri Transportation Transportation Transportation Transportation Department Revi
10、ewers Bill Belt, Arizona Department of Bruce Brumfield, New Jersey Department Charles Desjardins, Federal Highway William M. DuBose, III, South Carolina Pieter Dykman, Oregon Department of David Fasser, New York Department of Paul Garrett, Federal Highway Ben Hark, West Virginia Department of Robert
11、 Mickelson, Arizona Department of Raymond Richter, Delaware Department of Charles Rountree, Idaho Department of Dean Schreiber, Pennsylvania Department Transportation of Transportation Administration Department of Transportation Transportation Transportation Administration Transportation Transportat
12、ion Transportation Transportation of Transportation *Currently with W but, like the NWI maps, these are not always detailed enough for small areas. Many hydric soil areas will not be wetlands, for instance, because of historical drainage for agriculture. As with all maps, these become out of date as
13、 the landscape changes. CCI-NAME AUTHOR COMMON-NAME RSIND NAT-IND HABIT DOWNINGIA BICORNUTA DOWNINGIA ELEGANS DO WNINGIA INSIGNIS DOWNINGIA LAETA DOWNINGIA MONTANA DO WNINGIA YINA DRABA STENOLOBA DRACOCEPHALUM PARVIFLORUM DROSERA ANGLICA DROSERA LONGIFOLIA DROSERA ROTUNDIFOLIA DRYAS DRUMMONDII DRYOP
14、TERIS DILATATA DUGALDIA HOOfESll DULICHIUM ARUNDINACEUM ECHINOCHLOA COLONA ECHINOCHLOA CRUS-PA VONIS ECHINOCHLOA CRUSGALLI ECHINOCHLOA MURICATA EGERIA DENSA ELAEAGNUS ANGUSTIFOLIA ELATINE BRACHYSPERMA ELATINE CALIFORNICA ELA TINE TRIANDRA ELEOCHARIS ACICULARIS ELEOCHARIS BELLA GRAY DOWNINGIA, DOUBLE
15、-HORN (DOUGL. EX LINDL.) TORR. GREENE DOWNINGIA, PARTI-COLOR (GREENE) GREENE DOWNINGIA, GREAT BASIN GREENE DOWNINGIA, SIERRA APPLEG. DOWNINGIA, CASCADE LEDEB. WHITLOW-GRASS, ALASKA NUTT. DRAGON-HEAD, AMERICAN HUDS. SUNDEW, ENGLISH L. SUNDEW, NARROW-LEAF L. SUNDEW, ROUND-LEAF RICHARDS. MOUNTAIN-AVENS
16、, YELLOW (HOFFM.) GRAY WOODFERN. MOUNTAIN (GRAY) RYDB. ORANGE-SNEEZEWEED (L.) BRITTON SEDGE, THREE-WAY (L.) LINK JUNGLE-RICE (H.B.K.) J.A. SCHULTES COCKSPUR, GULF (L.) BEAUV. GRASS. BARNYARD (BEAUV.) FERNALD GRASS, ROUGH BARNYARD PLANCH. WATER-WEED, BRAZILIAN L. OLIVE, RUSSIAN GRAY WATER-WORT, SHORT
17、-SEED GRAY WATER-WORT, CALIFORNIA SCHKUHR WATER-WORT, THREE-STAMEN (L.) ROEM. % appropriate to the degree of impact; and s=- practicable in terms of cost, existing technology, and logistics in light of the purposes of the project. Compensation should aim for functional replacement or its equivalent.
18、 In most cases this will mean at least equal area replacement of an in-kind wetland type. The agencies tend to prefer in-kind replacement (meaning similar wetland type as was impacted) to out-of-kind in most cases. On-site replace- ment (meaning adjacent to or contiguous with the impact) is usually
19、preferred to off-site (Corps/EPA MOA). However, see discussion of “Mitigation Banking” and “Site Selection” in the following chapters. It is important to recognize the scientific uncertainty about the success of created wetlands in replacing actual lost functions and values. In a significant policy
20、shift, restoration of former wetlands is now preferred to creation from uplands due to the greater likelihood of success (Corps/EPA MOA). STD*AASHTO SRCH WMTD-ENGL L77b m Ob37809 0038251 bb8 m CHAPTER 2 MITIGATION 2.1 Introduction Federal regulations (Council on Environmental Quality, 1978) define m
21、itigation as a step-wise sequence of actions, in which agencies must: (1) avoid impacts, (2) minimize impacts, and (3) compensate for unavoidable impacts. This chapter will explore specific measures that can be taken to fulfill these requirements. Mitigation requirements apply both to temporary cons
22、truction impacts and to permanent impacts. Both temporary and per- manent impacts should be avoided or minimized and, where unavoidable, must be repaired, restored, or compensated. Restoration of construction or other temporary impacts is sometimes regarded as a distinct category of mitigation actio
23、ns, in addition to the three-part mitigation sequence. 2.2 Avoidance and 2.2.1 Permanent Impacts Minimization of Wetland Impacts Avoidance and minimization are dealt with together because the same measures are often used to achieve both. In prac- tice, where complete avoidance is not possible, it ma
24、y still be possible to minimize impacts substantially. Section 404(b)(l) guidelines require the selection of the least damaging practi- cable alternative. At each stage of project development, there are several alter- native measures that can avoid or minimize permanent wet- land impacts. STDmAASHTO
25、 SRCH WMTD-ENGL 1996 Ob39804 0038252 5Tg I GUIDE TO WETLAND MITIGATION ISSUES FOR TRANSPORTATION DESIGNERS 14 $1 1 k Photo Courtesy of South Carolina Department of Transportation Figure 2.1. Impact Minimization by “Top Down Construction.” Isle of Palms Connector, South Carolina. STD-AASHTO SRCH WMTD
26、-ENGL L99b Ob39804 0038253 410 W , GUIDE TO WETLAND MITIGATION ISSUES FOR TRANSPORTATION DESIGNERS 15 These measures fall under the categories of needs assess- ment, choice of corridor or alignment, modification of the project design, or construction practices. Needs Assessment: * Consider whether t
27、he project is truly needed in this location, when weighed against the impacts. + Consider whether the project scope or purpose can be modified, while still meeting worthwhile objectives. + Consider whether to build on a new alignment versus improving the existing highway. Choice of Corridor/Aiignmen
28、t: + Evaluate alternative corridors or general alignments that avoid or minimize temporary and permanent wet- land impacts (such as detours and staging areas). + Consider whether the project needs can be met in a dif- ferent location on an existing route (such as passing lanes). Modification of Proj
29、ect Design Components: + Adjust the project termini, by shortening or shifting the project longitudinally. * Shift part of the alignment to avoid or minimize impacts. Use a split alignment to leave a wetland within a broad median. This may still reduce the value of the remaining isolated wetland. %
30、Steepen the slopes of cut or fill sections to the maxi- mum allowed under the standards. This may require use of guardrails. Reduce the width of the typical section to the minimum allowed under applicable standards in conformance with the project purpose. * Consider the use of retaining walls or sim
31、ilar structures to avoid the impacts of sideslopes. + Consider a bridge where wetlands are especially sensi- tive, or lengthen it where one is already planned over a waterway, or when it would be more economical than fill. STD-AASHTO SRCH WMTD-ENGL L77b Ob37809 0038254 377 I GUIDE TO WETLAND MITIGAT
32、ION ISSUES FOR TRANSPORTATION DESIGNERS 76 $i) I * As a last resort, consider requesting an exception to federal or other standards for pavementshoulder width or sideslopes where a slight reduction will make a sig- nificant difference. Construction Practices: Site staging areas and spoil disposal ar
33、eas away from wetlands. * Take care that temporary construction impacts listed in Section 2.2.2 are not so severe that the impacts become permanent. Before minimization measures are implemented in the project, an analysis should be carried out to determine the feasibility of avoiding the wetlands. A
34、lthough avoidance must be the high- est priority, other considerations, such as safety, costs, and conflicts with other environmental or social resources, may make impacts to wetlands unavoidable. Some of the minimiza- tion measures, such as bridging, are very costly, while others, like modified ali
35、gnment or steeper sideslopes, may be highly cost-effective. Federal regulators, in weighing the public inter- est in wetland protection against other social or economic val- ues, may take cost into consideration. Avoidance and minimization actions also have the long-term benefit of reduced monitorin
36、g and maintenance requirements. The costs of long-term management of mitigation areas are responsibilities that also may best be minimized. 2.2.2 Temporary Construction Impacts Care must be taken during construction to prevent temporary impacts to wetlands. These impacts are also regulated. Impacts
37、can affect both the immediate project site and down- stream areas. Actions to avoid and minimize temporary impacts include: s- Confine construction activities within wetlands to the smallest area possible. This includes staging, stockpil- ing, and equipment access. Designate areas to be pro- tected
38、as ?no-work areas.? Confine clearing and grubbing to the minimum area beyond toe of slope needed for equipment operation. * Protect wetland soil from permanent compaction by the use of geotextile fabrics placed prior to impacts by con- struction equipment and rock. I I STD-AASHTO SRCH WMTD-ENGL L99b
39、 Ob3980Y 0038255 203 GUIDE TO WETLAND MITIGATION ISSUES FOR TRANSPORTATION DESIGNERS di& 17 * Protect exposed soil and slopes from erosion by the use of geotextile mats or other effective erosion control measures. This also protects downstream/downslope areas from sedimentation. + Construct temporar
40、y sedimentation containment ponds to protect downstream water quality. Prevent hydrologic disruption. Sufficient hydrology to support the remaining wetlands must be maintained during and after the construction phase. * Develop specifications calling for staged construction or a certain order of work
41、 to avoid working in sensitive areas. Wetland mitigation plans should include measures to avoid and minimize temporary construction impacts. Wetland permit conditions should also be included in the plans. It will be nec- essary to precisely translate general language into clear direc- tions in the p
42、lans and specifications. It is important to control construction impacts carefully because they are difficult to quantify and often, in practice, exceed initial estimates. This may constitute a permit violation, resulting in possible fines and project delay. Photo Courtesy of Pennsylvania Department
43、 of Transportation Figure 2.2. Restoration of Temporary Impacts by Planting. Northumberland County, Pennsylvania. STD*AASHTO SRCH WMTD-ENGL L99b W Ob37809 003825b L4T W 18 A GUIDE TO WETLAND MITIGATION ISSUES FOR TRANSPORTATION DESIGNERS Construction impacts to adjacent (or sometimes downstream) wet
44、lands are unavoidable to some extent. It will be necessary to restore the affected wetland environment to at least the same conditions as existed before construction. Therefore, it is important to document (including photographs) the existing conditions for both wet and dry seasons. What kinds of we
45、tland impacts need to be repaired? Most incidental construction impacts occur in the narrow zone between the toe of slope and the right-of-way boundary. Typical construction impacts that need to be repaired may include: * Incidental deposits in adjacent wetlands of soil or rock, displaced by constru
46、ction, raveling from slopes, or deposited by erosion or blasting. * Blockages of culverts, which cause water to pond or impede fish and small animal passage under the road- way. * Destruction of vegetation by heavy equipment or by trench excavation for utilities. Many impacts can be anticipated in t
47、he mitigation plan and should be provided for in the plans and specifications. During construction, impacts often occur that cannot easily be fore- seen, such as the need for heavy equipment access. Disturbance of the wetland soil surface by equipment may be regulated under Section 404. The specific
48、ations need to include some language on restoration to handle these contin- gencies. Construction activities may be only temporary but can have long-term effects. Impacts are not always confined to the right- of-way adjacent to the toe of slope. For instance, at stream crossings, sedimentation effec
49、ts may occur some distance downstream. How should wetland impacts be repaired? Soil, sediment, or rock that inadvertently impact wetlands dur- ing construction should be removed. It will often be possible to remove the material with a backhoe working from the top of the embankment, or without otherwise causing more impacts. STD*AASHTO SRCH WMTD-ENGL 197b Ob39804 0038257 OBb D , GUIDE TO WETLAND MITIGATION ISSUES FOR TRANSPORTATION DESIGNERS Sometimes heavy equipment access is needed in the wetland to remove material. In such situations, a
