[From the U.S. Government Printing Office, www.gpo.gov]






                                                      - ANNSP12F
                          bward No
                                                                   :w"                 .4,
                          Net Loss
                          A Methodology For Identifying
                          Potential Wetland Mitigation
                          Sites Using a Geographic
                          Information System

                                                                                        A

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                                                           South Carolina Water Resources
                                                           Commission Report No. 178
                                                           USEPA Report No. EPA904-R-94-001


       TD224
       .S64T69
       1993






          Toward No
          Net Loss
          A Methodology For Identifying
          Potential Wetland Mitigation
          Sites Using a Geographic
          Information System


         SCWRC Report No. 178, November 1993
          USEPA Report No. EPA904-R-94-001          Cynthia R. Brown
                                                    Project Manager

                                                    Floyd 0. Stayner
                                                    GIS Analyst

                                                    Christopher L. Page
                                                    Field Biologist

                                                    Cynthia A. Aulbach-Smith
                                                    Consdting Botanist
















                               South Carolina Water Resources Commission
                                       1201 Main Street, Suite 1100
                                          Columbia, S.C. 29201
                                             (803) 737-0067
                         A limited number of this publication is available for distribution.
      C@J                When this supply is depleted contact the National Technical
      -i-.               Inf ormqJjpib@Wkq,"'ElS) tat @;61)A&L-465 0.
    N
    % r--q                     NoAA coastal services center Librc,---'
                               2234 south Hobson Avenue
      LLJ
      CM                       Charleston, SC 29405-2413






                                                                            State of South Carolina                                                                         CAR
                                                                 The Honorable Carroll A. Campbell, Jr., Governor
                                                  South Carolina Water Resources Commission                                                                                              2-1
                                                                                                                                                                    ME
                                                                                      Appointed Members                                                                       CEOs
                                                                            Mr. Lynn H. Youmans, Jr., Chairman
                                                                         Mr. Tom W. Dunaway, 111, Vice-Chairman

                                    Agriculture
                                                            Mr. Ben M. Gramling, III             ....................................................  Gramling
                                                            Mr. Lewis Walker           .................................................................  Sumter
                                                            Mr. Lynn H. Youmans, Jr               . ...................................................  Furman

                                    Industry
                                                            Mr. Ralph A. "Nick" Odom, Jr                 . .......................................... Rock Hill
                                                            Mr. Robert M. Rainey             . .....................................................  Anderson
                                                            Mr. Frank B.Winslow             .........................................................  Hartsville

                                    Municipalities
                                                            Mr. H.F. "Dick" Crater             ........................................................  Gaffney
                                                            Mr. Tom W. Dunaway, III               ..................................................  Anderson
                                                            Vacant


                                    Saltwater
                                                            Mr. Whitemarsh S. Smith               ................................................  Charleston

                                                                         Ex Officio Members and Designees
                                    Mr. D. Leslie Tindal, Commissioner                                          Mr. John W. Parris, Executive Director
                                    S.C. Department of Agriculture                                                    S.C. Land Resources Conservation
                                    Desig: Mr. David L. Tompkins                                                              Commission
                                                                                                                           Desig: Mr. Cary D. Chamblee
                                    Mr. Doug Br'yant, Commissioner                                                         Mr. Wayne L. Sterling, Director
                                    S.C. Department of Health                                                              S.C. Department of Commerce
                                    and Environmental Control                                                                      Desig: Mr. O'Neal Laird
                                    Desig: Mr. R. Lewis Shaw

                                    Mr. J. Hugh Ryan, State Forester                                                       Dr. Maxwell Lennon, President
                                    S.C. Forestry Commission                                                                                Clemson University
                                    Desig: Dr. Tim Adams                                                                              Desig: Dr. Earl Hayter
                                    Dr. James A. Timmerman, Jr., Executive Director Mr. Daniel P. Fanning, P.E., Executive
                                    S.C. Wildlife and Marine Resources Department                                            Director
                                    Desig: Mr. Larry D. Cartee                                                      S.C. Department of Transportation
                                                                                                                             Desig: Mr. Robert B. Ferrell

                                                                                                 Staff
                                                                            Alfred H. Vang, Executive Director
                                                                         Hank W. Stallworth, Deputy Director
                                                                            Anne Hale Miglarese, Director of
                                                                    Resource Assessment and Planning Division



          I Identifying Wetland NIfigafton SItes 11sIng 01S





            Acknowledgements
         T
            his study was prepared with funding from the United States Environmental Protection
            Agency Region IV office of Wetlands Planning under Cooperative Agreement
         #CD994081-92-1. It does not necessarily reflect the views of this agency and no official
         endorsement should be inferred.

         Several individuals and agencies contributed information and advice important to the
         development of this study. Their help is greatly appreciated. The U.S. Fish and Wildlife
         Service, the South Carolina Wildlife and Marine Resources Department, and the South
         Carolina Department of Health and Environmental Control all provided valuable input in
         the development of model criteria. Dr. James Gosselink provided extensive review of this
         project. Danny Johnson of South Carolina Water Resources Commission, Charlie Storrs
         of the National Wetlands Inventory, and Dennis De Francesco of the Soil Conservation
         Service offered considerable technical expertise. Hugh Archer of the South Carolina
         Water Resources Commission and Barbara Postles provided guidance, advice, and sup-
         port. Roy Newcome of Water Resources Commission provided technical editing of the
         final document.


































                                                                                                   M






                          Contents



                                 Introduction     ......................  ...............................................................................................I
                                          The issues       .............................................................................................................I
                                          Value of information           .............................................................................................. 2

                                 Model Development           . ........................................................................................................ 5
                                          Criteria and data evaluation            ..................................................................................... 5
                                          Model components            . ............................................................................................... 8
                                                  Physical suitability analyses       . ............................................................................... 8
                                                     Restoration sites      . ........................................................................................  8
                                                     Enhancement sites           ...................................................................................... 8
                                                     Protection sites      . .......................................................................................... 9
                                                  Opportunity analyses         ........................................................................................ 9
                                                     Wildlife habitat     . ..........................................................................................  9
                                                             Justification  . ......................................................................................... 9
                                                             Criteria . ............................................................................................. 10
                                                     Water quality and floodwater storage               . .......................................................... 11
                                                             Justification   ........................................................................................ 11
                                                             Criteria .. ............................................................................................ 12
                                                  Unique opportunities/barriers and potential threats                   ............................................. 12

                                 Model Application           ......................................................................................................... 15
                                          Study area       .......................................................................................................... 15
                                          Automating criteria         .............................................................................................. 20
                                                  Data preparation        ........................................................................................... 20
                                                  GIS analyses      ................................................................................................. 20
                                                     Initial site selection      .................................................................................... 20
                                                     Wildlife habitat opportunity analysis              ............................................................. 22
                                                     Water quality/floodwater storage analysis                 . .................................................... 28
                                                     Composite overlay           .................................................................................... 32
                                                     Unique opportunities/potential threats                 ......................................................... 32
                                                  Model complications/improvements                  ................................................................. 32
                                          Field-truthing     ....................................................................................................... 39
                                                  Verification of source data       .. ............................................................................. 39
                                                  Other observations      .. ....................................................................................... 42


                                 Conclusions      .................................................................................................................. 43


                                 References       . ................................................................................................................... 45

                                 Appendix I - Generalized NWI wetlands used in analyses                        ..................................................... 49

                                 Appendix 11 - Generalized land use data used in analyses                      ...................................................... 50

                                 Appendix III - Hydric soils list by county used in analyses                   ..................................................... 50












            V Iblenfifying Wetland Afffigallon 51tes UsIng 01S





                        Figures


                        Figure 1.      Flowchart of steps in wildlife habitat analyses                ....................................................... 11
                        Figure 2.      Flowchart of steps in water quality and floodwater storage analyses                         . ....................... 12
                        Figure 3.      Flowchart of steps for identifying optimal mitigation sites                   . ..................................... 14
                        Figure 4.      Map showing location of Four Hole Swamp sub-basin                          .......................................... 16
                        Figure 5.      Map showing counties in Four Hole Swamp sub-basin                          .......................................... 17
                        Figure 6.      Map showing land resource areas in Four Hole Swamp sub-basin                               ........................... 18
                        Figure 7.      Map of land use/land cover in Four Hole Swamp sub-basin                            ................................... 19
                        Figure 8.      Map of potential mitigation sites by mitigation class                   .............................................. 21
                        Figure 9.      Map of core habitat sites           .................................................................................. 23
                        Figure 10.       Map of core habitat sites and adjacent degraded sites                    .......................................... 24
                        Figure 11.       Map showing results of edge elimination analysis                     ............................................... 25
                        Figure 12.       Map of habitat sites 40 acres or greater                ............................................................ 26
                        Figure 13.       Map of all potential wildlife habitat sites             ............................................................ 27
                        Figure 14.       Map of potential mitigation sites and stream network                     .......................................... 29
                        Figure 15.       Map of high-order hydrology sites               .................................................................... 30
                        Figure 16.       Map of low-order hydrology sites               ..................................................................... 31
                        Figure 17.       Map of potential hydrology sites              ...................................................................... 31
                        Figure 18.       Map of all opportunity analyses sites               ................................................................ 34
                        Figure 19.       Map of final selected potential mitigation sites                .................................................... 35
                        Figure 20.       Map of unique opportunity sites              ....................................................................... 36
                        Figure 21.       Map of potential threat sites           ............................................................................ 37
                        Figure 22.       Map of hydrologic regime for potential mitigation sites                      ....................................... 38
                        Figure 23.       Map of isolated field check site            ........................................................................ 40
                        Figure 24.       Map of riverine field check site            ........................................................................ 41


                      Table


                        Table 1. Available data coverages              . ...................................................................................... 7



























                                                                                                                                                                                      V






                 Definition of terms


                   Core habitat sites - all protection NVA sites, protected areas, significant natural area, and/or intact
                      upland forest (excluding pine plantations)

                   Core habitat complex - the complex formed by core habitat sites and contiguous restoration and
                      enhancement sites

                   Enhancement sites - any NWI wetland that is modified (i.e., ditched, drained, impounded, or excavated)

                   In-kind mitigation - a project in which the replacement site has the same species composition as the
                      filled wetland site

                   Mitigation - wetland protection, enhancement, or restoration activities required to compensate for
                      wetland losses permitted under Section 404 of the Clean Water Act

                   Mitigation banking - a system in which the creation, enhancement, restoration, or preservation of
                      wetlands is recognized by a regulatory agency as generating compensation credits allowing the future
                      development of other wetland sites*

                   Mititgation class - type of mitigation (protection, enhancement, or restoration)

                   Off-site mitigation - for this study, mitigation which occurs in a different watershed or project site
                      location


                   On-site mitigation - for this study, mitigation which occurs in the same watershed or project site
                      location


                   Opportunity - the public, cultural, or natural resource benefit a mitigation site could potentially provide

                   Out-of-kind mitigation - a project in which the replacement site has a different species composition
                      than the filled wetland site


                   Physical suitability - potential for successful mitigation based on soil, hydrology, and vegetation
                      characteristics of a site

                   Protected area - public land, including state parks, national wildlife refuges, national forests, etc.

                   Protection sites - any NVA wetland that is not modified (i.e., ditched, drained, impounded, or exca-
                      vated)

                   Restoration sites - agriculture fields with hydric soils (prior converted wetlands)

                   Significant natural area - a high-quality, relatively undisturbed natural community or complex of
                      communities as identified by the Natural Areas Inventory.

                   Threat - sources of pollution that pose a potential threat to successful mitigation. These include nutrient
                      sources, sediment sources, and toxic sources. It is recognized that, in fact, a wetland might be restored
                      or enhanced to ameliorate the consequences of these potential threats.

                   Wetland order - the order assigned to a candidate mitigation site on the basis of the stream order of an
                      associated stream





                    From Environmental Law Institute



        V   IdentIfying wemano, xltlgatlon s1tes LISIng O/S






                                                                                             Thelssues
                                                                                                   Permitted land use, development pressures, and illegal
                                                                                             fill activity continue to threaten the viability of our Nation's
                                                                                             wetlands. Regulatory safeguards have been established to
                                                                                             avoid or minimize the impacts resulting from such activities,
                                                                                             but when these "sequencing" steps cannot be taken com-
                                                                                             pensatory mitigation is sometimes required to replace the
                                                                                             ecological loss resulting from wetland destruction or frag-
                                                                                             mentation. I This project proposes a methodology to system-
                                                                                             atically locate suitable mitigation sites on the South Carolina
                                                                                             Coastal Plain that could potentially contribute to the state's
                                                                                             wetland resource. It utilizes a currently available Geographic
                                 Introduction                                                Information System (GIS) and 1:24,000-scale information
                                                                                             sources to automate the mitigation site evaluation process.
                                                                                             The validity of this methodology is a function of the current-
                                                                                             ness, scale, and accuracy of available data and the selection
                                                                                             criteria used. It can be generalized or focused on the basis of
                                                                                             different scale data appropriate to the geographic coverage
                                                                                             of the investigation.

                                                                                                   When designing strategies for mitigation, it is often
                                                                                             assumed that area-for-area replacement of the same type of
                                                                                             wetland, on-site, will assure that any lost ecological function
                                                                                             is offset. However, in-kind mitigation projects are often not
                                                                                             available on-site; thus, mitigation is pursued on-site/out-of-
                                                                                             kind, off-site/in-kind and finally off-site/out-of-kind. Unfor-
                                                                                             tunately, many projects, both on-site and off-site, are frag-
                                                                                             mented or unconnected and not defensible in the long run.
                                                                                             Thus, conventional approaches to mitigation have the poten-
                                                                                             tial to counter the desired goal of "no net loss" of wetland
                                                                                             acreage. Furthermore, the ability of a replacement wetland
                                                                                             to mimic the ecological function of the filled wetland is often
                                                                                             questionable. The goal of "no net loss" of wetland function
                                                                                             can also be contradicted.


                                                                                                    To adequately address the issue of functional replace-
                                                                                             ment, the potential mitigation site must first be considered as
                                                                                             an integrated component of the landscape, hydrologically
                                                                                             linked to all other land uses/land covers within the watershed
                                                                                             (Lee and Gosselink, 1988). Thus, sound mitigation strategies
                                                                                             require identifying sites that have not only a high physical
                                                                                             potential for successful mitigation (i.e., appropriate soils,
                                                                                             hydrology, and vegetation), but that also contribute to the
                                                                                             overall ecological integrity of the entire watershed. In many
                                                                                             instances, off-site/within watershed wetlands best meet these

                                                                                             1 U.S. EPA has adopted the goal of the National Wetlands Policy Forum
                                                                                             to achieve no overall net loss of the Nation's remaining wetland base,
                                                                                             as defined by acreage and function; and to restore and create wetlands,
                                                                                             where feasible, to increase the quality and quantity of the Nation's
                                                                                             wetlands resource base. Section 404 permits are evaluated under
                                                                                             guidelines that prohibit wetland loss unless all appropriate and practi-
                                                                                             cal steps have been taken to minimize and otherwise mitigate impacts
                                                                                             on the aquatic ecosystem. A February 1990 MOA between EPAand the
                                                                                             Corps of Engineers clarified that mitigation should occur according to
                                                                                             the following "sequencing" steps: 1)avoidance of impacts through
                                                                                             evaluation of practicable alternatives, 2)minimization; and 3)compen-
                                                                                             sation for unavoidable impacts through restoration or creation.


                                                                                                                                               Introduction







                 criteria. In identifying these potential mitigation sites, it is
                 necessary to recognize similar characteristics between the                     Value of Information
                 filled and replacement wetland sites.                                                 Because this methodology is especially effective in
                                                                                                identifying large complexes of mitigation sites of different
                       Our understanding of how wetland characteristics                         classes - protection, enhancement, restoration - and of
                 relate to wetland function has greatly increased in the last                   different community types, it can be a useful tool for
                 several years. Certain large-scale, physical characteristics of                identifying potential sites for mitigation banks. It is recog-
                 wetlands, including the size, shape, and position of a wetland                 nized that the potential drawbacks from mitigation banking
                 site on the landscape, generally support wetland function                      are quite significant and argued by many environmentalists
                 (Brinson, 1988, Preston and Bedford, 1988; O'Neil et al.,                      and regulatory agencies. Many who oppose mitigation
                 199 1; Whigham et al., 1988 - Kuenzler, 1989 Jaylor et al.,                    banking often refer not only to ecological concerns but also
                 1990; Harris and Gosselink, 1990). GIS is a tool that can                      to shortcomings that relate more to institutional factors.
                 be used by regulators and managers to help identify and                        Conversely, the economic and ecological advantages of
                 evaluate these landscape-scale characteristics. The GIS                        using established mitigation banks to offset the impacts of a
                 methodology proposed in this study broadly identifies com-                     particular development project, or for offering credits to
                 plexes of wetlands within a hydrologic unit that are physically                compensate for future wetland impacts, can also be strongly
                 amenable to restoration, enhancement, or protection. Sites                     argued. In spite of the complex issues surrounding mitigation
                 determined to be physically suitable for wetland mitigation                    banking, the concept appears to be gaining general accep-
                 are segregated into community type and further evaluated to                    tance as a viable alternative for mitigating the consequences
                 determine their potential to provide "opportunity", or social/                 of wetland loss and fragmentation. Indeed, recent directives
                 ecological benefits, and to assess threats that may influence                  from the Clinton administration endorse the use of mitigation
                 the utility of the site. The opportunities considered in this                  banks as a means of offsetting wetland loss:
                 study include a site's potential to contribute to 1) wildlife                     464
                 habitat on the basis of fragmentation, size, and extent of                            While a number of technical and procedural
                 interior habitat; and 2) water quality and floodwater storage                         questions regarding the establishment and
                 on the basis of hydrologic connectivity and position on the                           long term management of mitigation banks
                 landscape. Other opportunity analyses require consider-                               remain, conceptually mitigation banking,
                 ation of known locations of endangered/threatened/rare                                with appropriate environment safeguards,
                 species habitat and significant natural areas, as well as cultural                    offers numerous advantages. Banking
                 resources. Threats are identified in this study as potential                          provides for greater certainty of successful
                 toxic, nutrient, or sediment sources and include mines,                               compensatory mitigation in the permit
                 hazardous waste sites, and industrial and domestic waste                              process by requiring mitigation to be
                 landfills. The Four Hole Swamp sub-basin in South Carolina                            established before permits are issued.
                 is then used as a case study for application of this model.                           Banks are often ecologically advantageous
                                                                                                       because they consolidate fragmented
                       Wetland mitigation sites identified by this methodology                         wetland mitigation projects into one large
                 can be reported by community type, size, watershed location,                          contiguous parcel that can more effectively
                 and potential opportunity contribution. This infonnation can                          replace the lost wetland functions within the
                 help managers and regulators identify complexes of in-kind                            watershed. Mitigation banks also provide a
                 mitigation areas within the same watershed as the filled                              framework for financial resources, planning
                 wetland and, with information provided by the opportunity                             and technical expertise to be brought
                 analyses, make an initial judgment about a site's potential to                        together in a fashion often not possible with
                 replace lost wetland functions. Potential mitigation sites                            smaller mitigation projects. 99
                 indicated by this methodology might be more thoroughly
                 assessed by descriptive methods of functional evaluation such                         (White House Office of Environmental
                 as the Habitat Evaluation Procedures (HEP) or the Wetlands                            Policy, 1993)
                 Evaluation Technique (WET)2          to better determine opportu-
                 nity potential. Thus, this model can be used as an initial                            This study is not intended to be a treatise on mitigation
                 screening tool for directing mitigation decisions and can                      banking. It does, however, support the notion that ecological
                 augment the best professional judgment of natural resource                     benefits can be derived from restoring, enhancing and/or
                 managers and regulators when choosing wetland mitigation                       protecting large wetland complexes, given that mitigation is
                 sites.                                                                         opted for only after the appropriate sequencing steps have
                 2These methodologies, developed by the Fish and Wildlife Service and           taken place.
                 Corps of Engineers, respectively, are popular tools used for site-                    Presently, no national policies or regulations exist to
                 specific functional evaluations. HEP's objective isto determine habitat        insure that ecological factors are incorporated into mitigation
                 suitability (both wetlands and uplands) for a variety of species by            bank siting decisions. However, guidance clocurnents pro-
                 examining habitat features for these species. WET can be employed to           duced by various federal and state regulatory agencies do
                 evaluate the variety of functions provided by wetlands.                        exist that define, with varying degrees of specificity and

                 2       IdentIfYing weth?nd NIN98tion Sites I/Sing G/S






               prioritization, mitigation banking criteria (Environmental                    fowl Management Plans, State Comprehensive Outdoor
               Law Institute, 1993). It can be reasonably anticipated that,                  Recreation Plans, and the Wetlands Reserve Program. In
               given the recent administrative directives, these guidance                    general, these federal and state sponsored wetland protec-
               documents will eventually gain specificity or be replaced with                tion strategies are aimed at preserving the array of wetland
               regulations on mitigation banking. In general, certain com-                   functions through restoration, planning, or acquisition initia-
               mon recommendations addressing ecological considerations                      tives (World Wildlife Fund, 1992). Several existing coopera-
               emerge from the documentation that exists. These include:                     tive efforts demonstrate the benefits to be gained from the
                                                                                             integration of program objectives. The Nature Conservancy
                      ï¿½ soil type and water availability                                     offices in North Carolina and Louisiana, for example, have
                                                                                             both entered into Memoranda of Agreements with various
                      ï¿½ existing resource value, size, location                              state and federal regulatory and development agencies on
                                                                                             separate initiatives that achieve the goal of endangered or
                      ï¿½ presence of contaminants                                             threatened species protection while providing wetland banks
                                                                                             from which mitigation credits can be credited and debited
                      ï¿½ location in same watershed as impact areas                           (personal communications; Merrill Lynch, North Carolina
                                                                                             Nature Conservancy and David Pashley, Louisiana Nature
                      ï¿½ location on former wetland site                                      Conservancy).
                      ï¿½ adjacency to high-value habitat protected from                              Finally, this methodology is not meant, nor does it have
                          future development and compatibly managed                          the capability, to replace established functional assessment
                                                                                             methodologies. It is valuable for making initial identifications
                      ï¿½ habitat for rare or threatened species (Environ-                     of potential mitigation sites on the basis of broad character-
                          mental Law Institute, 1993)                                        istics indicative of function. As assessment approaches such
                                                                                             as the Hydrogeomorphic Classification SysteM3             are verified
                      In this proposed methodology, all of the above consid-                 and improved upon, it is possible that a methodology such as
               erations are incorporated to varying degrees in the identifica-               the one suggested in this study could aid in the identification
               tion of potential wetland mitigation sites. More complete,                    of functional values on the basis of hydrogeomorphic char-
               accurate, and current data can be used to provide a finer filter              acteristics - characteristics that, given sufficiently detailed
               for the GIS application proposed. The degree to which any                     data, could be modeled in a geographic information system.
               factor is included or excluded must be analyzed against
               available data sources.

                      Apart from the goal of replacing lost value resulting
               from wetland permitting activity, identifying mitigation com-
               plexes with this methodology can also contribute to strategi-                 3The Hydrogeomorphic Classification System is a recently developed
               cally broader ecological goals. For example, information                      classification too] that relies on general hydrologic and geomorphic
               obtained from these analyses can be useful in achieving the                   principles as indicators of abiotic function. A survey of these features
               protection objectives of other planning and conservation                      results in a wetland profile which is intended to provide, with expert
               efforts such as Habitat Conservation Plans, Water Quality/                    interpretation, information on the functions provided by a regionally
               Watershed Management Strategies, North American Water-                        representative wetland.



















                                                                                                                                              Introdoction 3






                                                                                  Criteria and Data Evaluation
                                                                                        In the first stage of model development, several state
                                                                                  and federal regulatory and natural resource agencies were
                                                                                  contacted and asked to list the qualities a site should possess
                                                                                  (or not possess) to qualify as a potential mitigation site. A
                                                                                  literature search was also undertaken to further identify
                                                                                  qualities that increase the likelihood of a site to accomplish
                                                                                  mitigation goals. The literature also revealed that no such GIS
                                                                                  application has been employed elsewhere to identify poten-
                             Model                                                tial mitigation sites. From the suggestions provided through
                                                                                  agency comments and from the criteria gathered through the
                                                                                  literature search, it became apparent that a wide spectrum of
                             Development                                          factors must be considered in identifying mitigation sites. In
                                                                                  general, the factors relate to one or more of the following:

                                                                                        ï¿½ The mitigation potential a site possesses on the basis
                                                                                           of physical characteristics.

                                                                                        ï¿½ The mitigation potential a site possesses (or lacks) on
                                                                                           the basis of identifiable threats.

                                                                                        ï¿½ The opportunity for public or natural resource
                                                                                           benefit that a site, if mitigated, would provide.

                                                                                        ï¿½ The political or legal logistics that mitigation of a
                                                                                           particular site would present.



                                                                                   EXAMPLE OF MITIGATION CRITERIA FROM
                                                                                   REGULATORY AND NATURAL RESOURCE AGENCIES
















                                                                                                                                           01-
                                                                                                                                             M,
                                                                                                                                  A,i









                                                                                       wv'ng'-


                                                                                                                     IyOdel '00VOPMeflt 5






                        In order to determine data availability and suitability,             data are derived frorn existing topographic maps that, in the
                and thus what criteria were realistic to consider, the data were             Edisto River Basin, range in date from 1960 to 1989. No
                inventoried. These data were developed by the South                          attempt has been made to update any of the older digital data.
                Carolina Water Resources Commission (SCWRQ as part of
                the Natural Resources Decision Support System (NRDSS)                               The significant natural areas data layer was developed
                project that began in 1988 (Hale et al., 1991). One of the                   as a result of the Natural Areas Inventory, a study sponsored
                objectives of the project was to develop a GIS to provide                    by the National Oceanic and Atmospheric Administration
                products and services to support natural resource manage-                    and conducted by the South Carolina Water Resources
                ment decisions.                                                              Commission and The Nature Conservancy (White, 1993). In
                                                                                             this study, natural areas of particular ecological significance
                        Each data layer used in this study adheres to accepted               were delineated by using NAPP photography and field
                national data classification systems and mapping standards                   verified by overflights and ground surveys. The final sites
                as established by various Federal programs. These include                    were then digitized by the SCWRC. The purpose of this
                the U.S. Geological Survey's (USGS) National Mapping                         systematic survey was to identify sites in the Edisto River basin
                Division's Digital Line Graph (DLG) program, U.S. Fish and                   with relatively undisturbed, high-quality natural communities.
                Wildlife Service's National Wetlands Inventory (NWI) pro-
                gram, and the Soil Conservation Service's (SCS) county soils                        Other data layers available for this study include domes-
                mapping program. AJI data are based on the 1:24,000 scale                    tic waste permits, industrial waste permits, hazardous waste
                USGS topographic map series. The digital data are regis-                     sites, archaeology sites, historic sites, sensitive species and
                tered to common geographic registration coordinates, insur-                  communities of concern sites, and mining and reclamation
                ing comparability of various data layers in scientific analyses.             sites. All these data were obtained from the agencies
                                                                                             responsible for the particular pennitting activities. Table 1
                        The layers of primary importance to this study are                   lists the available data coverages that were considered appro-
                wetlands, land use, soils, roads, hydrography, and significant               priate for this study.
                natural areas. The wetlands data are derived from 1:40,000
                color infrared National Aerial Photography Program (NAPP)                           After considering the suggested criteria and evaluating
                photography captured in 1989. Wetlands delineations are                      the available data, three general model components suitable
                classified according to the Cowardin classification system                   for GIS analysis were developed:
                developed by the NWI (Cowardin et al., 1979). For the
                purposes of this study, the wetland classifications are simpli-                     0 physical suitability
                fied to several categories of community types (Appendix 1).
                                                                                                    0 opportunity potential on the basis of watershed
                        The land use data are photointerpreted in conjunction                          characteristics
                with the wetlands data. Land use is mapped for all upland
                areas, or those areas not classified as wetlands. These data                        0  identified threats and unique opportunities
                are classified to Level 11 of the Anderson classification system
                (Anderson, 1976). The land use categories are also simpli-                          Logistical considerations, such as availability for acqui-
                fied to several community types for use in this study (Appen-                sition and number of landowners, were beyond the scope of
                dix 11).                                                                     this study. However, these could be considered if more
                                                                                             detailed spatial data themes covering these elements were
                        The soils data are derived from standard SCS county                  available (e.g. parcel maps, real estate data). Also beyond the
                soils maps. A hydric attribute was added to label those soils                scope of this study was consideration of those criteria
                that have hydric characteristics as defined for each county by               requiring site-specific data such as detailed soils information
                SCS. The hydric soils category used in this study was reduced                (rooting volume, fertility), site geology, and detailed elevation
                substantially (Appendix 111) to include only those with little or            differences. It should be emphasized that this proposal
                no agricultural productivity potential as determined by state                establishes a practical methodology for identifying potential
                soil scientists .                                                            mitigation sites while recognizing reasonable expectations of
                                                                                             spatial data themes and data scale availability. The findings
                        The roads and hydrography are standard USGS                          are intended to serve as a rough filter for the initial identifica-
                1:24,000-scale (DLG) products. Several attributes were                       tion of potential mitigation sites on the basis of general
                added to the DLG data by SCWRC, including drainage order,                    physical characteristics and position on the landscape. Thus,
                which is pertinent to this study. All streams in the hydrogra-               it directs mitigation efforts on the basis of landscape charac-
                phy data layer were ordered by using the Strahler method of                  teristics. It is recognized that site-specific data would be
                stream ordering (Strahler, 1952). The SCWRC employs                          required to ultimately deten-nine the potential for mitigation
                several quality control procedures on the data to correct                    success at a given site. As supported by Preston and Bedford
                various problems with the original digital data. These                       (1988), this analysis takes a qualitative, synoptic approach,
                procedures include edgematching and attribute correction                     considering "intrinsic and landscape-levelwetland attributes."
                where possible. One problem with the DLG data that could                     This approach reflects, in part, the methodology suggested
                not be corrected was the datedness of some maps. The digital                 by Leibowitz et al. (1992) in that it employs a "landscape

                6       IdentifYIng Wetl8nd Nitig8tion sites 11sing G/S






              Table 1. Available data coverages
                            COVERAGE                                     SOURCE                               SPATIAL DATA TYPE
                                                          South Carolina Land Resources                              polygon
                 Mining and reclamation                     Conservation Commission
                 Hazardous wastes treatment,              South Carolina Department of
                   storage and disposal                     Health and Environmental                                   point
                                                            Control
                 All landfills                            South Carolina Department of
                                                            Health and Environmental                                   point
                                                            Control
                                                          South Carolina Institute of                                polygon
                 Archaeology                                Archaeology and Anthropology
                                                          South Carolina Department of
                 National Register of Historic              Archives & History, U.S. De-                          polygon/point
                   Places                                   partment of the Interior
                 Protected areas (government              U.S. Geological Survey topo-                               polygon
                   parks, forests, refuges)                 graphic quadrangle maps
                 Sensitive species and                    South Carolina Wildlife and                                  point
                   communities of concern                   Marine Resources Department
                 Digital line graphs (separate            U.S. Geological Survey topo-                                  line
                   coverages for roads,                     graphic quadrangle maps
                   hydrography)

                                                          Soil Conservation Service topo-
                 Soils                                      graphic quadrangle maps                                  polygon
                                                          1989 NAPP 1:40000 photography,
                 Land use                                   10-acre resolution, South Caro-                          polygon
                                                            lina      Water         Resources
                                                            Commission
                                                          1989 NAPP 1:40000 photography,
                 Wetlands                                   1-acre resolution, National Wet-
                                                            lands Inventory, U.S. Fish and                           polygon
                                                            Wildlife Service
                                                          1989 NAPP 1:40000 photography,
                 Natural Areas Inventory                    South Carolina Water Resources                           polygon
                                                            Commission


             approach" using existing data                                         3) further assess the opportunity a site provides (or
                                                                                          potential limitations it poses) by identifying unique
                   The sequence of analytical steps used to address the                   cultural or public benefits (e.g. endangered species,
             model components is as follows:                                              historic/archaeologic sites) and assess the threats
                                                                                          (e.g. nearby mines, landfills) that may diminish a
                 1) identify wetlands (by community type and watershed)that               site's long term mitigation potential.
                      are physically amenable to mitigation; then
                                                                                      The exact procedures and rationale used to develop
                 2) evaluate the opportunity potential of these sites to        each of these model components are described in the
                      provide public benefits through either improved           following section.
                      wildlife habitat, water quality enhancement or flood-
                      water storage; and finally





                                                                                                                    mOdel OevelOmeflt 7






                                                                                          converted - are termed prior converted (PC) wetlands          in
               Model Components                                                           this study.4
               Physical Suitability Analysis -                                            DEFINING RESTORATION SITES
               defining mitigation classes                                                Segregate soils data according td hydiric.'
                     In conducting the physical suitability analysis, three                 characteristic.
               types of potential mitigation classes are identified: restora-             Determine', mitigation potential on the basis
               tion and enhancement sites, which possess potential for                      of agrid Iultural productivity of soil.
               wetland reestablishment and protection sites, which repre-                 Identify, agriculture areas in Anderson level          IIf
               sent viable, functioning wetlands important to the ecological                land use maps.
               landscape.                                                                 Overlay selected hydric soils with agriculture
                     Restoration Sites                                                      polygons.
                     The Environmental Protection Agency (EPA), in its                    Identify the hydric soils that -'correslpollidto
               1993 draft mitigation banking guidance, defined wetland                      agriculture areas.'
               restoration as the, "process of returning a significantly                  These corresponding areas represontprior
               disturbed or totally altered site to its previously existing                 converted (PC) wetlands, Qr1he                     'at
                                                                                                                                     potont*
               functional wetland condition by some action of man (e.g.,                    restora n- Sites.
               prior converted cropland or farmed wetlands reestablished as
               bottomland hardwood forested wetlands)." As mentioned                         Enhancement Sites
               previously, this model is intended to indicate potential miti-                The draft mitigation banking guidance document is-
               gation sites on the Coastal Plain of South Carolina. Here, as              sued in 1993 by EPA defined wetland enhancement as "the
               in much of the Southeast Coastal Plain, acre upon acre of                  improvement or addition of one or more functions to an
               wetlands have been drained and converted to various land                   existing wetland or other aquatic habitat (e. g., re-introduction
               uses including silviculture, agriculture, and pastureland.                 of natural meanders to a channelized stream system, instal-
               Currently, mitigation efforts in the Southeast often involve               lation of water control structures, planting of desirable
               restoration of marginal agriculture lands to wetlands (per-                species, control of exotics, creation of marsh from open
               sonal communication, Dr. Russell Lea, Hardwood Research                    water habitat)."
               Cooperative, North Carolina State University). These lands
               typically occur on the margins of flood plains where the                      In order to identify sites suitable for enhancement, the
               hydrologic regime is unpredictable. Frequent flooding makes                digital version of the 1989 NVA data are analyzed to identify
               these areas effectively unproductive for agriculture; thus,                areas that have been altered to some extent by dikes,
               farmers are often willing to allow their property to be restored           impoundments, excavations, drains, or ditches. Only those
               to an original 56ttomland hardwood community, for ex-                      areas that support hydrophytic vegetation (i.e., palustrine
               ample, and have future use restricted by perpetual conserva-               emergent, palustrine scrub shrub, palustrine forested) are
               tion easements or other transfers of development rights.                   included in this analysis. Interpretation of the alphanumeric
                                                                                          NWI code can often lend insight into community type or land
                     In this study, potential restoration sites are identified            use at the time of image capture. For example, excavated
               according to the following progression. Hydric soils, as                   areas, defined by Cowardin et al. (1979) as areas that "lie
               defined for each county by the SCS, include those soils for                within a basin or channel excavated by man, " likely represent
               which the entire mapped area is identified as hydric. These                abandoned gravel pits, large ditches, or the occasional
               areas are further analyzed to determine mitigation potential               sewage treatment pond. Impounded areas, defined as areas
               on the basis of soil productivity as derived from the SCS Land             "created or modified by a barrier or dam which purposefully
               Capability Classes. Only those soils with low reported crop                or unintentionally obstructs the outflow of water," likely
               yields are given consideration in this study. State soil                   represent wetlands associated with dams, stock ponds, or
               scientists have further reduced the list of potential soil types           some other type of impoundment. Diked areas are defined
               to those that have extremely limited or no agricultural                    by Cowardin as areas that are "created or modified by a man-
               productivity.                                                              made barrier or dike designed to obstruct the inflow of
                                                                                          water." Partly drained areas exist where "the water level has
                     Next, agricultural areas are identified in the Anderson              been artificially lowered, but the area is still classified as
               level 11 land use data layer and overlaid with the hydric soils            wetland because soil moisture is sufficient to support hydro-
               data to find corresponding areas. The agricultural areas that
               are identified as hydric are assumed, in this methodology, to              4These wetland classifications were developed by the Agriculture
               represent wetlands that have been converted to cropland. It                Department's Soil Conservation Service. Because this study is not
               is not possible with the available data to identify when these             concerned with regulatory distinctions, these classes are considered
               areas were actually converted to cropland or the degree of                 one and the same.
               flooding; thus, all such wetlands - farmed, prior converted,

               8       Identifying Wetland Nitig8tlon Slies Using 01S





               phytes. Drained areas are not considered wetlands if they can                SUMMARY OF MITIGATION CLASSES
               no longer support hydrophytes." It should be noted that
               wetland vegetation may remain for decades after drainage.
               Thus, even though hydrologically altered wetlands support
               hydrophytic vegetation, changes in hydroperiod imply changes
               in wetland function (Brinson, 1988). Although these systems
               are characterized as wetlands, restoring their hydrology could
               prevent the inevitable conversion to a system characteristic
               of drier soils. In general, it has been suggested that most
               ditched/partially drained sites likely represent silviculture
               areas or abandoned agriculture fields. In some instances, the
               surrounding flood plain of a channelized stream might also
               qualify (personal communication, Charlie Storrs, U.S. Fish
               and Wildlife Service). All modified areas are given consider-              Opportunity Analyses
               ation in this methodology if they support hydrophytic vegeta-              determining the benefits
               tion as mentioned.
                                                                                                 Opportunity analyses are performed in order to evalu-
                      It is recognized that some modified wetlands, as defined            ate the potential that an identified candidate mitigation site
               in this study, might actually qualify as restoration sites, owing          might have in providing public, natural, or cultural benefits on
               to the loss of wetland function. Determining the degree of                 the basis of watershed characteristics. The opportunities, or
               this loss would require a site investigation.                              benefits, considered for these analyses are wildlife habitat,
                                                                                          water quality, and floodwater storage.
                DEFINING ENHANCEMENT SITES                                                       Wildlife Habitat
                                                                                                The following discussion provides a rationale, as sup-
                  A#                                                                      ported by researched literature, for the choice of criteria used
                                                                                          to evaluate the potential of candidate mitigation sites to
                  _@' "'Movlo
                                                                                          provide wildlife habitat.

                                                                                                 Justification - Many native species populations
                                                                                          are in decline in South Carolina, as in other parts of the
                      Protection Sites                                                    country. While population decline is attributable to a variety
                                                                                          of causes, habitat encroachment is one of the most signifi-
                      Protection sights include all NWI wetlands that theoreti-           cant. Reduction in biological diversity and species quantity is
               cally have not been modified as described above. For                       directly related to the reduction in total area available for
               purposes of this analysis it is assumed that these wetlands are            wildlife habitat. This is especially true for far-ranging species
               fully functional jurisdictional wetlands that are crucial in               requiring extensive tracts of land. For example, data available
               providing habitat, maintaining water quality, and sustaining               for the Edisto River basin on the South Carolina Coastal
               proper hydrologic function. Ecologically, these sites are                  Plain, suggest that high-level carnivores (and omnivores)
               extremely important. While jurisdictional wetlands are pro-                including the eastern cougar, the black bear, and the red wolf
               tected through federal and state permit programs, some are                 have been extirpated from the region (Marshall, 1993).
               in fact subject to management practices that, in some cases,               Landscape fragmentation is another factor contributing to
               pose a threat to the site's ecological integrity.5 It can be               population decline. The resulting subpopulations are iso-
               assumed that preservation of these viable areas is a desirable             lated, leading to increased inbreeding and reduced fecundity.
               component of a mitigation plan. Also, the proposed                         Also, several species utilize a range of habitats during their life
               methodology requires that connected mitigation sites be                    cycle or seasonally. The elimination of any single habitat
               identified according to the status and position of currently               could have a negative impact on population size. The
               existing, functional wetlands. Thus, it is necessary to identify           conversion of much of the natural forest cover in South
               these unmodified wetlands in order to perform proximal                     Carolina to pine plantation is also likely to be responsible for
               analyses.                                                                  species decline. Studies show that a change in forest
                                                                                          structure from complex natural stands to a monoculture
                                                                                          system dramatically affects species composition. (Langley
               5For example, important exceptions to the protection authority under       and Shure, 1980; Harris et al., 1975; Noble and Hamilton,
               ï¿½404(f) include 1)normal (ongoing) farming, silviculture, and ranching     1975).
               practices; 2)maintenance and emergency reconstruction of dikes,
               dams and similar structures; 3)construction or maintenance of farm               Noss (1983) argues that habitat diversity, a measure of
               ponds and irrigation ditches, and maintenance of drainage ditches;         ecosystem integrity, can only be achieved through manage-
               4)construction of temporary sedimentation basins; and, 5)construc-         ment strategies that are comprehensive in scope, consider-
               tion or maintenance of farm, forest, mining, and othertemporary roads.     ing isolated preserves in the context of a fragmented land-

                                                                                                                                 Model Development 9





              scape. As Harris (1985) points out, a collection of parts is           Areas as identified by the Natural Areas Inventory. The
              very different from a functional system. He contends that              Natural Areas Inventory was a study sponsored by the
              isolated habitat islands, such as the isolated wetlands found          National Oceanic and Atmospheric Administration and
              on the Coastal Plain, could be transfon-ned into an "inte-             conducted by the South Carolina Water Resources Commis-
              grated island archipelago system" if a passageway between              sion and The Nature Conservancy. The purpose of this
              patches was secured. It is feasible that these scattered isolated      systematic survey was to identify sites in the Edisto River basin
              wetlands might be connected by the large stretches of                  - the larger drainage system of which Four Hole Swamp is
              contiguous strearnside habitat, or riparian corridors, that            a component - with relatively undisturbed, high-quality
              exist in many areas of the Coastal Plain. Streamside buffers           natural communities. Thus, Natural Areas Inventory data
              provide permanent habitat for a myriad of plant and less far-          exist for the study area selected for model application. Such
              ranging animal species. Many mast-producing plant species              data do not exist for other basins in the South Carolina
              occur in the riparian zone, thus providing a consistent food           Coastal Plain.
              source in many streamside habitats. Also, because of
              adequate soil moisture and the aerobic conditions existing in               Contiguous enhancement and restoration sites that, if
              many riparian ecosystems, decomposition is rapid in riparian           mitigated, would extend the acreage of these core habitat
              zones and nutrients are readily available to both the terrestrial      sites are then identified. This association of core habitat sites
              and aquatic food chains. As Forman and Godron (1981)                   and contiguous mitigation sites is termed "habitat complex. "
              noted, however, many species cannot survive the seasonal               Identified habitat complexes as well as contiguous mitigation
              flooding or wet soils characteristic of lowlands and must have         sites (without associated core habitat sites) are further ana-
              an associated well-drained upland area on which to seek                lyzed to determine optimal wildlife habitat on the basis of
              refuge.                                                                ffiree criteria: fragmentation, extent of interior habitat, and
                                                                                     size.
                     Oftentimes, the species that are better able to adjust to
              barriers posed by fragmentation and isolation are in less need              All habitat complexes and potential mitigation sites are
              of protection. As previously stated, populations of large, far-        evaluated for fragmentation by considering the existence of
              ranging species are declining in the region. Interestingly,            paved roads. Large multilane or divided highways pose
              there seems to be a healthy abundance of species more                  significant barriers to wildlife movement. These highways
              characteristic of edge/field habitat, such as deer (Marshall,          are overlaid on the selected habitat sites to further divide the
              1993). As supported by Diamond (1976), Noss (1983),                    sites and determine true habitat boundaries.
              Forman and Godron (1981), and Saunders et al. (1991),
              mitigation strategies should consider habitat needs for those                The existence of edge habitat is ubiquitous across the
              species less adaptable to human-induced perturbations on               landscape; it can therefore be argued that habitat needs for
              the landscape and thus should place priority on large intact           edge species are already met by the existing landscape
              sites with a large proportion of interior habitat and areas            conditions. Thus, the habitat complexes meeting the above
              providing habitat connectivity.                                        criteria are further analyzed to determine conditions support-
                                                                                     ing good interior habitat. In this analysis, the complex
                     Criteria - Many of the criteria used to identify                boundaries are reduced by 328 feet (100 meters) to deter-
              mitigation sites in this analysis are based on properties              mine interior habitat (Temple, 1986; from O'Neil et al.,
              espoused by Harris (1984) as important for wildlife habitat            1990). It is theorized that this distance effectively represents
              and include total habitat area, interior habitat extent, and the       edge habitat. If any of the complex remains after reduction,
              distribution of habitat patches in relation to one another and         it can be assumed that the complex provides some interior
              drainage patterns in the watershed.                                    habitat function. The habitat sites remaining after reduction
                                                                                     are expanded back to their original boundaries.
                     Mitigation sites that are optimal for wildlife habitat are
              identified by first defining core habitat sites and then identi-             Finally, only habitat complexes of at least 40 acres in
              fying contiguous enhancement and restoration sites. Core               size are considered for the rest of the habitat analysis
              habitat sites are defined in this study as all unmodified wetland      (Adamus, 1987). Also considered are all enhancement and
              sites (protection sites), as well as a intact upland forests           restoration sites that are not part of a habitat complex but that
              (excluding pine plantations), protected areas (i.e. wildlife           are at least 40 acres in size.
              refuges, state parks, national forests), and Significant Natural









               10 Identifying Wetland Afifigstion Sites Using GIS










                            orest,
                            g pine
                            ns


                            nt                               Determine                     Reestablish
                             reas                            fragmentation of              extent of rem
                                            Core             habitat complex by            complexes b
                                           habitat           overlaying multi-lane         buffering 32
                                            sites            and divided roads             (100 meters)
                            cted
                   areas                                                                                                                       Optimal
                                                                                                                ,7V                            Wildlife
                                                Identify contiguous modified        Buffer inward 328                Eliminate all             Habitat
                   Protection                   NWI and PC wetland sites            feet (100 meters)                habitat                   sites
                   mitigation sites             and define habitat complex          to determine                     complexes less
                   (unmodified NWI                                                  extent of interior               than 40 acres
                   wetlands)                                                        habitat


               Figure 1. Steps in wildlife habitat analyses

                      Water Quality and Floodwater Storage                              among the three. In general, basin or depressional wetlands
                     The following discussion provides a rationale, as sup-             receive runoff from a relatively small area since they are most
              ported by researched literature, for the choice of criteria used          often located in headwater areas. Soils in these areas are
              to evaluate the potential of candidate mitigation sites to                generally well suited to assimilate nutrients; however, be-
              provide water quality and floodwater storage function.                    cause of their location it is often the case that little water
                                                                                        actually flows through them, and opportunity for nutrient
                     Justification - Because wetland systems are ex-                    transformation is low compared to the other wetland types.
              tremely variable in structural characteristics, it is difficult to        Consequently, they might be considered more valuable as
              identify unifying concepts that would allow a convenient                  wildlife habitat than as nutrient assimilation zones. Riverine
              breakdown of wetland types on the basis of water quality or               wetlands, because of their extensive association with upland
              hydrologic function. Hydrology, for example, is influenced                systems and the nature of their soils, have both high capacity
              by such site-specific characteristics as 1) site geometry, which          and opportunity to positively impact water quality and store
              determines storage capacity; 2) microtopographic relief or                floodflow. Because of this, and because of their abundance
              "roughness," which determines flow velocity and duration; 3)              in the South Carolina Coastal Plain, these wetland sites are
              vegetation, which influences evaporation/transpiration and,               given sole consideration in the water quality and floodwater
              therefore, flood duration; and 4) soil properties, such as                storage analyses. Fringe wetlands, or those occurring
              permeability, which influence water routing (Gosselink et al.,            adjacent to large bodies of water or at the base of a drainage
              1990). There are also site-specific characteristics, many of              system (e.g., tidal marsh), are small compared to the large
              which are closely tied or identical to those above, that largely          bodies of water that flush them. Fringe wetlands do not
              influence a site's ability to serve a water quality enhancement           compose a major portion of the selected sub-basin and were
              function. Stich characteristics include slope, sinuosity, water           not given independent treatment in this study. While the
              velocity on tract, stem density, soil clay and organic matter             above described relationships generally hold across geo-
              content, and loading rates (Scott et al., 1990). As mentioned             graphic regions, it is recognized that some exceptions may
              previously, it is not the intent of this model to definitively            apply to a particular region. Thus, for application in other
              characterize the effectiveness of a site in performing a water            areas, the presence and function of isolated or fringe wet-
              quality or hydrologic function according to such site-specific            lands may demand a more thorough consideration of their
              characteristics. Rather, it is recognized that there also exist           contribution to water quality and floodflow storage.
              watershed level characteristics that influence a site's potential
              to serve these functions. The primary characteristics consid-                   Not only is watershed position an important deterrninant
              ered in this analysis are hydrologic and watershed position,              of a wetland's opportunity to contribute to water quality, but it
              as discussed below.                                                       can also be argued that its position along a drainage network
                                                                                        dictates its opportunity to contribute to water quality (Kuenzier,
                    Wetland location within a watershed is an important                 1989; Brinson, 1988, Whigharn et al., 1988). Potential flood
              determinant of its contribution to water quality. Brinson                 storage capabilites are also linked to fl-tis charactenstic. Brinson
                                                                                                                              e al
                                                                                                                              ,   11
                                                                                                                              'es less
                                                                                                                              acres
















































              (1988) contended that the geornorphological setting of three              (1988) distinguishes between two transport vectors forwater and
              wefland categories - basin, fringe and riverine - is the                  nutrients - riparian transport and overbank transport - with
              driving factor contributing to water quality impact because of            one mode of transport dominating over the other depending on
              differences in hydroperiod, hydrologic energy, and nutrients              stream order. Riparian transport, or overland water rurioff, from


                                                                                                                            MOM DeV01OPMON 11






                   agriculture, urban and silviculture areas first encounters wetlands               wetlands represent those that might have the greatest opportu-
                   associated with small order streams. It is here that a majority of                nity to store floodflow while effectively removing pollutants from
                   the nutrients and sediments resulting from these land uses settle                 floodwaters.
                   out and are recycled. Also, runoff is attenuated in these wetlands,
                   helping to alleviate dowristream flooding. Those wetlands                                 Hydrologic connectivityof allother riverine mitigation sites
                   immediately adjacent to a stream have an even greater opportu-                    is then determined by identifying sites that are adjacent to the sites
                   nityto remove pollutants beforethey are introduced intothewater                   adjacent to a stream (as defined in above paragraph). AD
                   column. Research supports the notion that, with some excep-                       comectedsitesaredassifiedaccordingtotheirassociatedwefland
                   tions, the percentage of overland runoff that contacts wetland                    and termed secondary wetlands. The steps involved in the water
                   environments decreases as stream order increases. Thus, with                      quality/hydrology opportunity analyses are summarized in
                   some exceptions, low-order wetlands have a greater opportunity                    Figure 2.
                   toenhancewaterquaWthandohgherorderweflands"gham
                   et al., 1988; KuenzIer, 1989). These riparian areas are                           Unique Opportunities/Barriers and Poten-
                   particularly important in an agricultural landscape such as the                   tial Threats - locating endangered
                   Four Hole Swamp sub-basin (from Wf-Agham et al., 1988;
                   Peterjohn and Correll, 1984).                                                     species, cultural resources, and potential
                        Iri higher order wetlands the dominant transport vector is                   contaminant sources
                   overbank flow. In general, these downstream wetland systems,                              Endangered species habitat and cultural resource sites
                   especially if immediately adjacent to a stream, have greater                      (archaeologic/historic sites) represent important public re-
                   opportunity to store excess strearnflow during peak events                        sources and benefit from some protection provided by state
                   (I'aylor et al., 1990; Harris and Gosselink, 1990). It is also                    and federal programs. Sites containing these resources may
                   recognized that a pollutant removal fuinction will subsequently                   or may not be optimal for mitigation. The impact, either
                   result from water storage.                                                        negative or positive, of a mitigation project on these re-
                                                                                                     sources should be determined on a site-specific basis. These
                         Criteria - In this analysis, a riverine wetland mitigation                  sites are identified and overlaid on the final composite,
                   sites immediately adjacent to a stream, as delineated on the DLGs,                created by overlaying the results of the habitat and water
                   are identified. To detem-une wetland adjacency, streams are                       quality/floodwater storage analyses.
                   buffered 98.4 feet (30 meters) on both sides, and sites falling                           In many instances, cultural and endangered species
                   within the resulting polygon are identified. These areas, because                 inventories have primarily been done in areas where devel-
                   of their adjacency, are considered primary sites for hydrology and                opment has occured. While occurrence information exists
                   waterquality function. Each is assigned awetland orderaccording                   for those sites, geographically extensive spatial data cover-
                   the order of its associated stream. Lower order wetlands                          ages that are "complete" for these themes do not exist. It
                   represent those that, theoretically, have the greatest potential                  should be noted that this methodology will, in most cases,
                   impact on water quality while attenuating ninoff . Higher order                   direct initial selections for priority mitigation sites to areas that

                   1_0

                                                                                                                                                   y high-order wetlands
                                                                                                        order wetlands       g
                                                                                                                             g
                                                                                                                                                   A for floodwater
                                                                                                        im order 4,5,6)      72
                                                                                                                             Q                       defined by mitigation
                                                                                                                                                   [nd community t    1)
                                                                                                                                                                        e.
                       Mh


                     Identify all rive                                                             entify all contig                               Jary high-order
                     mitigation sites                                                                                                      wetlands defined by mitigation
                                                            Determine wetland                                tes
                     (protection or                                                                                                        class and community type
                                                            order based on
                     enchancement                                                                                                                                               kw@
                                                                                                                                                                                 g_-,
                                                            stream order of
                     restoration) wh
                                                            adjacent stream.
                                      s
                                                                                                                                           Primary low-order wetlands            p@
                                                                                                                                                   I for water quality
                                                                                                   ow-order wetla ds
                                                                                                                                                   ement) defined by
                                                                                                   stream order 1,2,3)                             ion class and
                                                                                                                                                   nity type


                                                                                                                                           Secondary low-oraer
                                                                                                                     uous
                                                                                                 Identify all contig                       wetlands defined by mitigation
                                                                                                 wetland sites
                                                                                                                                           class and community type              11C
                                                                                                                                                          '1757;JM
                   Figure 2. Steps in water quality and floodwater storage analyses


                   12 Identifying Weiland NIfigatiofl Sites Using GIS







              are fairly remote and are least likely to have thorough                         Finally, it is recognized that surrounding land uses and
              preestablished rare/endangered species habitat and cultural               management practices may pose a threat to the continued
              inventories. Thus, synoptic assessment of these impacts are               viability of a mitigation site. Conversely, the negative impacts of
              deemed appropriate for this methodology only with subse-                  these activities could be ameliorated by a restored or enhanced
              quent site-specific inventory work.                                       wetland. In this study, potential sources of threat are defined as
                                                                                        nutrient, sediment, and toxicant sources and include domestic
                    As previously mentioned, a Natural Areas Inventory of               and industrial landfills, mines, and hazardous-waste sites. The
              the Edisto River basin was performed in 1992 in order to                  proximity of these potential sources to niitigation sites is graphi-
              identify natural areas of significance. The results of that               cally represented on the final composite. Determining whether
              inventory indicate that natural habitat acreage - especially              these sources would threaten the success of a mitigation project
              upland habitat - has dramatically decreased in the basin. In              or, in fact, be mitigated by a restored wetland, would obviously
              fact, for the most part, river corridors serve as the last refuge         have to be done on a site-by-site basis. The overlay does provide
              for natural plant communities. Thus, these identified com-                an infori-nation tool that can assist in the indicated field work but
              munities as well as any upland significant natural areas are              it cannot provide a substitute for the site-specific analysis. A
              overlaid on the composite to graphically display priority                 summary schematic of the GIS analyses as discussed in the above
              wetland mitigation sites in relation to these features.                   section is presented in Figure 3.












































                                                                                                                              190010/ DevOlOPIn"t 13








                         Define protection sites                      Define enhancement                      Define restoration
                         (intact NWI wetlands) by                     sites (all modified                     sites (PC wetlands)
                         community type                               NWI wetlands) by
                                                                      community type                                Physical Suitability
                                                                                                                   Analyses


                 Natural Areas
                 Inventory sites

                 Upland forests             Core wildlif
                 (excluding pine            habitat sites
                 plantations)
                                                                                                                    Analyset,
                 Protected sites
                 (State Parks
                 National For@sts)
                                            Identify core/mitigation                  Identify all riverine
                                            complexes based on:                       potential mitigation sites
                                            1) fragmentation                          based on:
                                            2) interior habitat                       1) stream order
                                            3) size                                   2) hydrologic connectivity




                          Optimal Wildlife Habitat              Optimal Water Quality                 Optimal Flood Storage
                          Mitigation Sites                      Mitigation Sites                      Mitigation Sites
                          (large unfragmented                   (primary and secondary                (primary and secondary
                          complexes with adequate               low-order wetland sites)              high-order wetland sites)
                          interior habitat)


                                                                                        OR

                                        Determine endangered                           Determine sources of
                                        species, significant                          potential threat
                                        natural areas, cultural
                                        resource site occurrence






                                                                 Optimal Potential Mitigation
                                                                 Sites Based On:
                                                                 0 Physical suitability
                                                                 0 Wildlife habitat benefit
                                                                 I Water quality/floodflow
                                                                   storage contribution
                                                                 I Consideration of
                                                                   endangered species, natural
                                                                   areas, cultural resources
                                                                   site occurrence
                                                                 0 Consideration of potential
                                                                                                              S















                                                  w
                                                 a@t@





                                                                   sources of threat



              Figure 3. Summary of steps for identifying optimal sites


              14 Identifying Wetland ffifigition Sites Using GIS





                                                                                     Study Area
                                                                                            The Four Hole Swamp sub-basin is one of four sub-
                                                                                     basins in the Edisto River basin (Figure 4) in South Carolina
                                                                                     and is the study area for this model application. In 1992, the
                                                                                     South Carolina Water Resources Commission performed an
                                                                                     ecological characterization of the Edisto River Basin. The
                                                                                     purpose of the ecological characterization was to describe
                                                                                     overall ecosystem health on the basis of land use/land cover
                                                                                     trends, water quality trends, changes in hydrology, and
                                                        Model                        biological indicators (Marshall, 1993). The following infor-
                                                                                     mation about Four Hole Swamp sub-basin and the vicinity
                                  Application                                        resulted from or was compiled during the characterization.
                                                                                            The Four Hole Swamp headwaters originate in the
                                                                                     Coastal Plain in Calhoun and Orangeburg Counties and
                                                                                     drain about 650 square miles from four counties-
                                                                                     Orangeburg, Calhoun, Dorchester, and Berkeley (Figure 5).
                                                                                     The Four Hole Swamp system spans approximately 50 miles
                                                                                     before it discharges into the mainstern of the Edisto River.

                                                                                            The SCS has divided the state of South Carolina into
                                                                                     six Land Resource Areas on the basis of soil conditions,
                                                                                     climate, and land use (U.S. Department of Agriculture,
                                                                                     1978). These Land Resource Areas are defined primarily by
                                                                                     soil characteristics that provide a basis for describing potential
                                                                                     vegetation and land uses. The Four Hole Swamp sub-basin
                                                                                     encompasses two of the six Land Resource Areas: the
                                                                                     Atlantic Coast Flatwoods and the Southern Coastal Plain
                                                                                     (Figure 6).

                                                                                            The Atlantic Coast Flatwoods, which composes the
                                                                                     vast majority of the study area, is nearly level and is dissected
                                                                                     by many broad, shallow valleys with meandering stream
                                                                                     channels. Elevations range from about 25 to 125 feet with
                                                                                     local relief of a few feet to about 20 feet. The soils are
                                                                                     predominantly somewhat poorly to very poorly drained and
                                                                                     fonned in sandy to clayey Coastal Plain sediment. The
                                                                                     Southern Coastal Plain is an area of gentle slopes. Local relief
                                                                                     is in tens of feet. The soils are predominantly well or
                                                                                     moderately well drained and formed in loamy or clayey
                                                                                     Coastal Plain sediments.


                                                                                            There are distinct patterns of land use and land cover
                      IN "I'llow
                                                                                     in the Four Hole Swamp sub-basin that correspond to the
                                                                                     natural characteristics of the landscape (Figure 7). The fertile
                    I% ï¿½            I  'F
                                                                                     loamy and clayey soils of the Southern Coastal Plain area
                                                                                     support some of the most productive agricultural land in
                                                                                     South Carolina. The sandy and clayey soils of the Atlantic
                      400                                                                                                        ry large agricultural
                           . ......                                                  Coast Flatwoods also support some ve

                       -
                        `.TWN11.1, 01,
                        ,6N@o                                                        areas. As the watershed narrows at its base, however, the
                                                                                     Flatwoods become dominated by forestland, primarily pine
                                                                                     plantations. The riverine bottomlands or flood plains remain
                                                                                     mostly forested, and they form a dendritic or branching
                                                                                     pattern of forested wetland corridors throughout the sub-
                                                                                     basin. Many of these wetlands are in a modified condition
                                                                                     and have been ditched, drained, diked, or impounded. In
                                                                                     many areas these wetlands have been totally altered, with the
                                                                                     native vegetation converted to agriculture, pine plantations,

                                                                                                                           Model APPlication 15










                         FOUR HOLE SWAMP SUB-BASIN




















                    Eg FOUR HOLE SWAMP LOCATION

                        EDISTO RIVER BASIN

                    ...... EDISTO RIVER SUB-BASINS













                                                                     45         75














            Figure 4. Location of Four Hole Swamp sub-basin


            16    IdenfifYing Wetl8nd Afifigatlon Sites Using O/S













                  FOUR HOLE SWAMP SUB-BASIN WITH COUNTIES

























                   F__1 FOUR HOLE SWAMP LOCATION

                       COUNTY BOUNDARIES















                                                                          15











           Figure 5. Counties in Four Hole Swamp sub-basin


                                                                                            MOM APPlic-7tiOn 17










                          SCS LAND RESOURCE AREAS

                                                          Four Hole Swamp Sub-basin




                                                                                 Four Hole Sub-basin






























                      LAND RESOURCE AREAS
                      SOUTHERN COASTAL PLAIN
                      ATLANTIC COAST FLATWOODS















                                                                      lo        1W











           -Figure 6. Land Resource Areas in Four Hole Swamp sub-basin

            18 Identifying Wetland Mitigation Sites UsIng GIS










                           1989 LAND USE/LAND COVER TYPES

                                                                                       Four Hole Swamp Sub-basin




                                                                                                                          Four Hole Sub-basin























                                                                                                                                                    it,





                                 LAND USE/LAND COVER TYPE ACRES PERCENT
                                 NON-FORESTED WETLANDS                     8,856      2.20%
                                 FORESTED WETLANDS                         78,069     19.40%
                                 UPLAND FORESTED/MIXED                     60,370     15.00%
                            F-1  UPLAND FORESTED/PLANTATION                72,511     18.02%
                                 OPEN WATER                                1,902      .47%
                                                                                                                     1W
                                 -AGRICULTURE                              167,109    41.53%
                                                                                                                            A@
                                 URBAN                                     13,607     3.38%


                                 FRANCIS BEIDLER FOREST
                                                                                                                              Pik


                                                                               2      4                  lo .1-
                       V









               Figure 7. Land use/land cover in Four Hole Swamp sub-basin


                                                                                                                                     Model ApplIcation 19






                and, adjacent to Orangeburg, urban land uses. The city of                         The complexity issue required that the model be
                Orangeburg is the only large urban area within the sub-basin.              implemented by using the GRID module in ARC/INFO. As
                                                                                           a consequence, all data layers were converted to a grid cell
                       The only protected natural area in the Four Hole                    fon-nat using the POLYGRID command. It was decided that
                Swamp sub-basin is the Francis Beidler Forest, an 11,000-                  a 16.4-foot (5-meter) cell size should be used to insure that
                acre bottomland hardwood swamp. It contains the largest                    even very small candidate mitigation sites were not general-
                old-growth stand of tupelo and cypress in the country, as well             ized. This did not eliminate the map complexities - data
                as a large variety of birds, mammals, reptiles and amphibians,             layers are 12,726 rows by 11,431 columns of grid cells -
                and many rare plants. The habitats of many plant and animal                but permitted the data to be analyzed. The polygon identi-
                species in the sub-basin are threatened by hydrologic alter-               fication numbers from ARC ('AU' value) are used for the cell
                ations and other manmade impacts. Several animal species                   values. The use of these values serves two purposes:
                that occur in the sub-basin, including the red-cockaded                    preserving the original polygon boundaries and providing a
                woodpecker, the bald eagle, and the wood stork, all of which               tie to associated INFO attributes. The preservation of
                have specific habitat needs, are listed as federally endangered            polygon boundaries was necessary for later analyses where
                or threatened. Numerous plants and animals listed as state                 wetland polygons were used as surrogates for elevation data.
                threatened or endangered are also found in Four Hole                       No digital elevation model or hypsography data were avail-
                Swamp.                                                                     able for the study area. Additionally, the polygon identifica-
                                                                                           tion number pen-nitted all original INFO data attributes to be
                                                                                           used in subsequent GRID analyses. Attributes were added to
                Automating Criteria                                                        grid cell data by using the JOINITEM command.
                Data Preparation                                                           GIS Analyses
                       The SCWRC has been building a natural resources GIs                        Initial Site Selection
                for the last five years. The Commission's efforts have been
                funded primarily through the support of NOAA and the state                        The initial phase of applying this model to the Four
                of South Carolina. Additional support has been received                    Hole Swamp sub-basin required defining mitigation classes.
                ffom USGS, USFWS, SCS, and the National Park Service.                      The three mitigation classes - restoration, enhancement,
                ARC/INFO GIs is used to implement this model             .6 This GIs       and protection - and the rationale for their selection criteria
                provides a full complement of various GIs functions, includ-               are discussed in the previous section. Restoration sites were
                ing raster-based processing.                                               selected by overlaying the hydric soils data layer with the
                                                                                           uplands data layer, t1sing the CON function. The CON
                       The hardware used was an IBM RISC/6000 technol-                     function provides data evaluation capabilities by using condi-
                ogy and includes a model 970 server and model 360                          tional statements that test the presence or absence of
                workstation. The server is equipped with 12 gigabytes(GB)                  specified data values in individual grid cells. Each cell was
                of disc storage and 128 megabytes(MB) of memory (RAM).                     evaluated and only those areas containing both a hydric soil
                The workstation has 1 G13 of disc storage and 64 MB of                     and an agricultural land use were defined as potential
                RAM. These systems are connected by Ethernet.                              restoration sites.
                       The original intent of implementing this model was to                      The protection and enhancement sites were selected
                use the ARC module with data in a traditional vector format.               from the NWI data on the basis of their classification codes.
                It became apparent early on that this would not be possible                Cells having a NVA code lacking a modifier (i.e. ditched or
                because of the complexity of the data. The Four Hole                       drained (d), diked or impounded (h), or excavated (x)) were
                Swamp sub-basin consists of portions of 17 quadrangles                     identified as protection sites. Conversely, those cells possess-
                containing over 402,000 acres. These individual quad-                      ing one of these codes were identified as enhancement sites.
                rangles were merged by dissolving their associated bound-                  Also, only those areas that apparently support hydrophytic
                aries, and then clipped to the hydro-unit boundary, creating               vegetation, as indicated by the codes PEM, PSS, or PFO,
                large individual datafiles; for each data layer required by the            were selected.
                study. This procedure created polygons that exceeded the                          All restoration, enhancement, and protection sites
                maximum number of arcs per polygon (i.e. 10,000 arcs per                   were combined to create a data file representing all potential
                polygon) permitted in ARC. The proximal analyses required                  mitigation sites in the Four Hole Swamp sub-basin. The
                by the model prevented the analyses being conducted on an
                individual quadrangle basis because it would introduce arbi-               COMBINE function was used because all sites are indepen-
                trary polygon boundaries at the quadrangle boundaries.                     dent and mutually exclusive. Finally, any potential mitigation
                                                                                           site contained within a protected area was eliminated since,
                                                                                           theoretically, these areas are already protected and not a
                6ARC/INFO is a proprietary software package developed and marketed         viable mitigation alternative (Figure 8). The CON function is
                by the Environmental Systems Resource Institute, Redlands, California.     used to test for the existence of a protected area. In this study
                                                                                           case, the only protected area in the Four Hole Swamp is the


                20 Idefitifying Wetland Mitigation Sites tlslflg GIS










                          POTENTIAL MITIGATION SITES

                                                                 Four Hole Swamp Sub-Basin




                                                                                            Four Hole Sub-Basin


                                  -44 &









                                                                                          M; I Z_




                                                                                            4W





                        MITIGATION SITE TYPE     ACRES
                                                  74,441
                        PROTECTION                                                                k

                        ENHANCEMENT               9,166
                        RESTORATION               39181


                     0 FRANCIS BEIDLER FOREST


















           Figure 8. Potential mitigation sites by mitigation class


                                                                                                     Model Applicatioft 21







               Francis Beidler Forest, which is a private preserve managed                     In order to examine adjacency, the fragmented core
               by the National Audubon Society. Figure 8 shows that the                 habitat sites and the degraded mitigation sites are combined.
               overwhelming majority of potential mitigation sites within the           The REGIONGROUP function in GRID, using the CROSS
               study area are protection sites. Four Hole Swamp has                     option, evaluates the connection of each cell in relation to its
               undergone much landscape alteration but still contains large             surrounding or neighbor cell. All connected cells are given a
               areas of these quality wetlands. Several large enhancement               unique identifier. In this particular case the command syntax
               sites, many of which appear as remnants of former Carolina               appears as follows:
               Bays, exist and may provide significant mitigation opportu-
               nities. Few restoration sites exist in the study area. This
               scarcity does not seem problematic of the source data since
               these sites follow streams and are adjacent to "wetter" areas,
               as would be expected. Instead, the scarcity appears to be a
               function of the very restricted list of hydric soils used for the
               selection criteria. This will be discussed later.

                      One apparent problem resulting from a delineation                        The above command specifies that each cell will be
               error was the misclassification of what is clearly a road                evaluated in relation to its eight neighbors but will not be
               crossing the bottomland area. Although it should have been               connected to any neighbor cell with a value of 0. Surrounding
               coded as transportation/utilities, this area was classified as           cells with values other than 0 will be connected. Connecting
               agriculture in the Uplands data layer and thus was identified            these degraded and core habitat sites results in regions with
               as a restoration site. It was not changed because doing so               unique cell values. These grouped regions, or habitat
               would invalidate the field verification of source data.                  complexes, further define all potential wildlife habitat areas
                                                                                        within the study area.
                       Wildlife Habitat Opportunity Analysis
                      The wildlife habitat opportunity analysis evaluated the                  Subsequently, each complex boundary is buffered
               potential mitigation sites with regard to their ability to serve         inward by a distance of 3 28 feet (100 meters or 2 0 cells) using
               a wildlife habitat function. The first step in this analysis was         the REDUCE function to eliminate all "edge" habitat (Figure
               the assembling of core habitat sites. These core habitat sites           11). The REDUCE function simply eliminates successive
               comprised all the protection sites selected above, all upland            rows until the distance specified is met or the feature is
               forests (excluding pine plantation sites) from the uplands data          eliminated. Thus, the reduction along the boundary elimi-
               layer, all protected areas (Francis Beidler Forest), and all             nated all habitat complexes 656 feet (200 meters) or less in
               significant natural areas (Figure 9). On the basis of the model          width- A comparison of Figure 10 and Figure 11 demon-
               definition, these sites represent prime wildlife habitat areas in        stratesthis. By definition, areas within 328 feet (100 meters)
               the sub-basin.                                                           of a region boundary are "edge" habitat areas and not viewed
                                                                                        as significant, since the fragmented nature of the study area
                      The model defines multilane roads as significant barri-           provides an abundance of this particular habitat. The habitat
               ers to wildlife movement. These multilane roads were                     complexes remaining represent areas containing adequate
               selected from the DLG roads data layer (codes 203 and 307).              interior habitat for wildlife. The rei iaining regions were
               Since these codes represent only divided highways, South                 buffered outward to a distance of 3D feet (100 meters) -
               Carolina county highway maps were used to update other                   the original boundaries - using the EXPAND function.
               multi-lane roads. The selected roads were buffered to a
               distance of 131 feet (40 meters or 8 cells) to represent the                    The remaining habitat complexes were evaluated for
               highway right-of-ways, using the EXPAND function. This                   size characteristics. The model defines only habitat com-
               function adds successive rows of cells to a feature until                plexes of 40 acres or greater as containing adequate space
               reaching the specified distance. All added cells are given               for wildlife habitat. Given this criteria, each habitat complex
               values identical to the parent feature. No attempt was made              was evaluated and only those containing a minimum of 40
               to add new roads or to make a distinction between roads                  acres were selected using the CON function. The areas
               according to the number of lanes they might have. There-                 remaining after this procedure represent the optimal wildlife
               fore, all multilane roads were buffered the same distance.               habitat complexes contained within the study area (Figure
               The buffered roads were overlaid with the original core                  12). Finally, the original potential wetland mitigation sites,
               habitat sites, using the CON function. All cells containing a            defined by mitigation class, were overlaid with the optimal
               core habitat site and a road were eliminated.                            habitat complexes, using the CON function. Only those cells
                                                                                        containing both an optimal habitat complex and a potential
                      Adjacent restoration and enhancement sites (termed here-          mitigation site were selected. These represent the potential
               after as "degraded sites") are added to the fragmented core habitat      mitigation sites meeting the wildlife opportunity analysis
               map to detern-Ane the amount of habitat each would add, upon             criteria.
               mitigation, to the core habitat sites. The added sites were bisected
               with the same buffered roads used above (Figure 10).


               22 IdentifYing Netl8nd AVIA98tion Sites Using GIS










                                         ALL CORE HABITAT SITES


                                                                                 Four Hole Swamp Sub-basin




                                                                                                                  Four Hole Sub-basin



















                                                                                                     Ar


                                                                                                                 M.

                                                                                                 r





                               CORE HABITAT SITES































              Figure 9. Core habitat sites


                                                                                                                            90d0l APPlic8tiOfl 23










                    ALL CORE HABITAT AND DEGRADED SITES

                                                            Four Hole Swamp Sub-basin




                                                                                     Four Hole Sub-basin

















                                                                                    U.
                                                   W                                   _#d'
                                                                                                      ?






                                                                                fk





                       CORE HABITAT SITES

                       ENHANCEMENT SITES

                       RESTORATION SITES


                       MULTI-LANE ROADS











                                                   o I                   lo
















           Figure 10. Core habitat sites and adjacent degraded sites


           24   IdenfifYing Wetland mlfivflon Sites UsIng 01S









                                HABITAT EDGE ANALYSIS

                                                               Four Hole Swamp Sub-basin




                                                                                        Fo        in






















                                                                                                   f




                        ALL HABITAT SITES WITH EDGE ELIMINATED                        Ak -.1

                                                                                           4(

                                                                                                         -Ara













                                                        2











          Figure 11. Results of edge elimination analysis


                                                                                               Model Applicati0fl 25









                                                          HABITAT SIZE ANALYSIS

                                                                 v                                        Four Hole Swamp Sub-basin
                                                          L



                                                                                                                                                     Fou@ Hole Sub-basin






                                                                                              L%
                                                                                           -, --

                                                                                             UP              P

                                                             a

                                                                                                 L

                                                                                                own                                                            op 6
                                                                                                                                                             db
                                                                                                                                                                     dr tj

                                                                                                                              AV



                                         HABITAT SITES 40 ACRES OR GREATER
                                                                                                                                                             T
                                                                                                                                               vd* Wf                        Ad


                                                                                                                                                            Win






                                                                                                                                1. MILES

















                    Figure 12. All habitat sites 40 acres or greater in size


                   26 IdentifYing Wetland Mitig,flon s1tes Using ON










                              POTENTIAL WILDLIFE SITES

                                                                  Four Hole Swamp Sub-basin




                                                                                             Four Hole Sub-basin
















                                                                                                    A. A



                                                                                                bt


                                                                           P4@V




                        MITIGATION SITE TYPE      ACRES
                        PROTECTION                50,286
                        ENHANCEMENT                4,081                                               N

                        RESTORATION                776



                        FRANCIS BEIDLER FOREST










                                                                 4    1         'd MILES
















           Figure 13. All potential wildlife habitat sites


                                                                                                     Noolel Applicoftfl 27






                       Figure 13 depicts the potential mitigation sites that              by polygonal boundaries, to be retrieved for each potential
                theoretically provide the greatest wildlife habitat benefit. Not          mitigation site.
                surprisingly, a larger number of protection sites satisfy the
                wildlife opportunity criteria than do restoration or enhance-                   Initially, execution of the EUCDISTANCE function in
                ment sites. While several large enhancement sites were                    GRID was attempted to retrieve these IDs; however, this required
                identified as serving a wildlife habitat function, few of the             massive amounts of temporary storage. The fi-inction exhausted
                restoration sites were considered optimal for wildlife habitat,           800 MB of free space on the disk and required more to complete
                owing to the restrictive size criteria.                                   the task. As a result, an alternative method was devised. The
                                                                                          buffered streams were overlaid with the potential mitigation sites.
                       Water Quality and Floodwater Storage                               AD selected cells were given the original polygon ID value. The
                       Analyses                                                           FREQUENCYcom-nandinARCwasusedtoehnmateduphcate
                       These analyses considered the potential flood storage              polygon IDs. An arbitrary value was assigned to each D and
                capacity a potential mitigation site might possess and the                joined to the existing VAT data files using the JOINITEM
                ability of a site to contribute to stream water quality. Streams          corrimand in ARC. The arbitrary value peraiitted the retrieval of
                and their associated drainage order were obtained from the                all cells that defined the polygonal area of each adjacent potential
                DLG hydrography data layer. High-order streams were                       mitigation site.
                defined as all 4th-, 5th-, and 6th-order streams, while low-                    Figure 15 illustrates one problem with the definition of
                order streams were defined as 1st-, 2nd-, and 3rd-order                   primary high-order sites. While many adjacent sites were
                streams. All streams were selected and recoded to single                  accurately classified as primary high-order by this methodology,
                values reflecting either a high or low order. Figure 14                   the mairistern of Four Hole contains numerous areas or islands
                represents all potential mitigation sites, and their stream               wholly contained wifl-tin these primary high-order bottornland
                network, plotted by their respective order. Because of the                wetlands. These wetlands were not identified as primary high-
                braided nature of portions of the Four Hole drainage system,              order because they did not satisfy the distance criteria. Upon
                some portions of the high-order stream network had to be                  examination, most of these areas were found to be potential
                added. In these areas on the mainstem, the stream network                 mitigation sitesanddefinedasweflands; however, GRIDdoesnot
                disappears from the digital data. A single stream was digitized           afford any easy means of selecting and recoding these areas in an
                to complete the drainage pattern.                                         automated fashion.
                       Potential flood storage sites (high-order sites) were                    AD other unselected potential mitigation sites were evalu
                defined as any potential mitigation site adjacent to a high-              ated to determine if they were adjacent to a primary high-order
                order stream. Additionally, each site was defined as a                    site or to other secondary 1-ugh-order sites that were adjacent to
                primary and secondary site depending on its position on the               primary high-order sites. The adjacency of sites was evaluated by
                landscape. In this study, wetland sites were used as a                    the REGIONGROUP function and according to the same
                surrogate for elevation data. If elevation data had been                  method used in the wildlife opporwnity analysis as described
                available, the landscape topography could have been defined               above. Additionally, the CON function was used to differentiate
                and used to assess hydrologic flow. No elevation data exist               between primary and secondary sites.
                in a digital format for the study area; thus, this model assumes
                that any adjacent site receives overbank flow from its related                  Figure 15 shows all identified primary and secondary high-
                stream or an adjacent wetland site. By definition, primary                order sites. 'Me methodology was very successful in selecting
                sites are those potential sites immediately adjacent to a high-           high-order sites - the bottorriland areas were identified as
                order stream and assumed to be most effective in stoning                  providing important flood control functions. However, the
                overbank flow. Secondary sites are adjacent to any primary                inclusion of numerous secondary siteswithiri the bottorriland area
                site or adjacent to any secondary site that is adjacent to a              was adeparture from the expected outcome of fl-lis methodology.
                primary site and assumed to be less important in floodflow                A judgment was made to treat all high-order potential sites
                storage.                                                                  identically regardless of their ranking (Le. primary or secondary).
                       All high-order streams were buffered to a distance of                    Water quality sites, termed low-order sites, were defined as
                32.8 feet (10 meters or 2 cells) using the EXPAND function.               any potential mitigation sites adjacent to low-order streams. All
                This width was an arbitrary value selected to represent the               selected sites were segregated into primary and secondary sites,
                stream surface, since the hydrography data layer is repre-                using methods and selection criteria described above. Figure 16
                sented by a single line in the data base. The assumption was              shows all primary and secondary low-order sites identified by this
                that any potential mitigation site within 32.8 feet (10 meters)           method.
                of a stream would receive overbank flow from the identified
                adjacent stream. This assumption requires each potential                        The model did not function well in the identification
                mitigation site within 32.8 feet (10 meters) of the stream to             of low-order sites. Again, for purposes of this study, low-
                be retrieved with its associated polygon identification number            order sites were defined as Ist-, 2nd- and 3rd-order sites and
                ("-ID") used to code the cell value in the original grid                  were assumed to represent headwater wetlands. As can be
                conversion of the data. The ED r-w-m-fits the entire area, as defined


                28 IdenfifYing Wetland MV198fion SItes Using GIS











                 POTENTIAL MITIGATION SITES AND STREAM NETWORK


                                                           Four Hole Swamp Sub-basin




                                                                                  Four Hole Sub-basin















                                                                                 'A          C4













                      MITIGATION SITE TYPE

                      PROTECTION

                      ENHANCEMENT

                      RESTORATION


                      LOW ORDER STREAMS

                      HIGH ORDER STREAMS


                      FRANCIS BEIDLER FOREST







                                                     2        a       lo  ILES
















          Figure 14. Potential mitigation sites and stream network


                                                                                          Model Applicati0fl 29









                           HIGH ORDER HYDROLOGIC SITES

                                                                    Four Hole Swamp Sub-basin




                                                                                               Four Hole Sub-basin





























                           HYDROLOGIC ORDER TYPES         ACRES
                           PRIMARY HIGH ORDER             30,470
                           SECONDARY HIGH ORDER           22,346





                                                                                                .0@` It-











             Figure 15. High-order potential wetland mitigation sites


             30    IdentIfYing Wetland lyffig8fion Sites Using O/S









                     LOW ORDER HYDROLOGIC SITES


                                                           Four Hole Swamp Sub-basin




                                                                                   Four Hole Sub-basin







                                age








                                                                          A
                                                                                  V




                                                            IV
                                                                              ir






                      HYDROLOGIC ORDER TYPES      ACRES
                      PRIMARY LOW ORDER           52,754
                      SECONDARY LOW ORDER         24,876














                                                 o    2













           Figure 16. Low-order potential wetland mitigation sites


                                                                                            Model ApplicatiOn 31






               seen, however, it was often the case that many bottomland             Model Complications/improvements
               sites were assigned a low-order as a result of this methodol-              The wildlife habitat analysis was quite successful in
               ogy. Figure 14 reveals that this occurred because a large             identifying potential mitigation sites that might serve as
               number of low-order streams flow directly into the mainstern          optimal habitat according to model definitions. The water
               areas of the study area.                                              quality/floodwater storage analyses were not as successful in
                     Finally, all high- and low-order potential mitigation sites     distinguishing between primary and secondary sites or in
               were combined to illustrate the relationship between the              further identifying low- and high-order sites.
               high-order sites and low-order sites. Figure 17 depicts the                 Because elevation data were not available for the study
               combined sites and illustrates those areas that serve single or       area, it was decided that wetlands data would be used as a
               dual hydrologic functions as defined by the model. The low-           surrogate for characterizing the flood plain. An initial look at
               order stream assignment, described above, causes the major-           the wetlands data revealed that, especially on the mainstem,
               ity of the wetlands in the study area to be identified as dual        the only modifier that distinguished adjacent polygons was
               hydrologic function sites.                                            the modifier relating to hydrologic regime. In large part,
                                                                                     wetland "system," "class," and "subclass" were coded iden-
                     Composite Overlay                                               tically for adjacent polygons. Thus, it was originally theorized
                     Figure 18 is a composite overlay of the opportunity             that the hydrologic modifier incorporated into the NWI
               analyses depicting all selected wildlife, and high- and low-          alphanumeric code (A,B,C,F,G, or H) might adequately
               order potential mitigation sites that meet any or all of the          describe hydrologic properties within the riparian system.
               defined opportunity analyses criteria. Figure 18 illustrates          For example, permanently flooded areas ("H") would have
               the importance of the mainstern area in the Four Hole                 greater connection to a water body than intermittently
               Swamp sub-basin. The area serves multiple opportunity                 exposed areas ("G") and so on. If this theory held true, sites
               functions in the sub-basin.                                           adjacent to a stream as defined in the DLGs (i.e. primary sites)
                                                                                     would be distinguished from areas farther from the stream
                     Figure 19 shows the same identified opportunity sites           (i.e. secondary sites) as denoted by different hydrologic
               shown in Figure 18 broken out by mitigation class. A                  modifiers (e.g., F vs. C) in the data base. Upon testing this
               comparison of Figures 8 and 19 shows that the sites                   theory in the procedures described above, it became appar-
               eliminated by this methodology are those very small isolated          ent that, due to the complexity of the hydrologic system in
               candidate sites that exist in the study area.                         Four Hole Swamp, these relationships do not necessarily
                                                                                     hold true. Figure 22 shows the highly complex hydrologic
                     Unique OpportunitylPotential Threats                            nature of the wetland system especially as it occurs on the
                     Analysis                                                        mainstem. The braided stream network pattern, which in
                     The potential mitigation sites identified in the overlay        some parts of the data base was digitized as a single line,
               composite were evaluated with respect to the unique oppor-            further prevents a clear characterization of the riparian
               tunities existing in the sub-basin. Unique opportunities were         system according to this methodology.
               defined as the occurrence of sensitive species or communities
               of concern, archaeology sites, significant natural areas, or                The second problem encountered in this methodology
               historic sites. These sites, in combination with the identified       was the identification of wetlands on the basis of stream order
               sites, present unique opportunities for mutual protection of          of the adjacent stream. As mentioned, many of the wetland
               important sub-basin resources. The identified unique sites            areas associated with the mainstern of Four Hole Swamp
               are overlaid with the potential mitigation sites to determine         were actually identified as having low-order wetland proper-
               the number and type of unique opportunities failing within            ties. While many of these wetlands serve the dual hydrology
               each site (Figure 20). Each site is labelled with its related         function identified in this study, it can be argued that,
               unique opportunities for future reference.                            according to the assumptions and definitions provided by this
                                                                                     model, these areas are critical for floodflow storage. A
                     Lastly, identified mitigation sites are evaluated with          reevaluation of stream order definition could possibly contrib-
               respect to the potential threats existing in the sub-basin.           ute to a clearer distinction between the two wetland types.
               Potential sources of threats were defined as hazardous- waste         For example, had low-order streams been defined as only 1 st-
               sites (including generating, disposal, treatment, or storage          and 2nd-order, perhaps fewer low-order wetlands would
               sites), mining sites, and industrial and domestic waste sites.        have been identified on the mainstem.
               Figure 21 shows the potential threats in the sub-basin in
               relation to the identified sites.








               32 Identifying Netland Nitigation Sites Using GIS









                        POTENTIAL HYDROLOGIC SITES

                                                             Four Hole Swamp Sub-basin




                                                                                     Four Hole Sub-basin







                                               %fir,


                                                                                    Old











                       HYDROLOGIC ORDER       ACRES
                       LOW ORDER              24,908
                       HIGH ORDER              93
                       LOW AND HIGH ORDER     49,410


                       FRANCIS BEIDLER FOREST










                                                                        1. MILES













          Figure 17. All potential wetland mitigation sites identified by water quality/floodwater storage analyses


                                                                                            ff0d01 AAPlicatiOn 33









                 ALL OPPORTUNITY ANALYSES SITES

                                                           Four Hole Swamp Sub-basin




                                                                                    Four Hole Sub-basin



                               ik



                                        4
















                                                                 dk








                       OPPORTUNITY ANALYSES CATEGORIES             ACRES
                       LOW ORDER                                   13,286

                       HIGH ORDER                                   45
                       LOW AND HIGH ORDER                          9,632                  rr.
                       POTENTIAL HABITAT                           3,695
                       POTENTIAL HABITAT AND LOW ORDER             11,621
                       POTENTIAL HABITAT AND HIGH ORDER             48
                       POTENTIAL HABITAT AND LOW AND HIGH ORDER    39,778


                       FRANCIS BEIDLER FOREST


                                                  o   I    I










            Figure 18. Composite overlay of potential wetiand mitigation sites identified by all opportunity analyses

           34 IdenfifYing Wetland NIV98fidn s1tes t/s/flg O/S










                  FINAL SELECTED MITIGATION SITES


                                                                   Four Hole Swamp Sub-basin




                                                                                               Fow Hole Sub-basin



                                   1k






                                   is





                                                           (k.                            t      jA






                         MITIGATION SITE TYPE      ACRES
                         PROTECTION                67,733
                         ENHANCEMENT                7,427
                         RESTORATION                2,946



                         FRANCIS BEIDLER FOREST



                                                                                                             W..;5







                                                        G    1    4               lo "LES
















            Figure 19. Final selected potential mitigation sites identified by mitigation class


                                                                                                         Model ApplicatlOn 35








                           UNIQUE OPPORTUNITY SITES

                                                            Four Hole Swamp Sub-Basin




                                                                                     Fou@ Hole Sub-Basin



                                fA


                             'A










                                                                                   W
                                                                                     -Owl-


                       UNIQUE OPPORTUNITY SITES

                       SENSITIVE SPECIES SITE
                       ARCHEOLOGICAL SITE

                       HISTORIC SITE
                       SIGNIFICANT NATURAL AREA


                       MITIGATION SITE TYPE

                       PROTECTION

                       ENHANCEMENT

                       RESTORATION



                       FRANCIS BEIDLER FOREST



                                                   o                 8    1@
















            Figure 20. Unique opportunity occurrence

            36    Identlfylflg Wetland 91figstlon Sltes Using GIS









                                POTENTIAL THREAT SITES

                                                                Four Hole Swamp Sub-basin




                                                                                           Four Hole Sub-basin












                                                              Y44"








                         POTENTIAL THREAT SITES                                      A          .0

                         MINING SITE

                         HAZARDOUS WASTE SITE
                                                                                                It
                         LANDFILL SITE


                         MITIGATION SITE TYPE

                         PROTECTION

                         ENHANCEMENT

                         RESTORATION



                         FRANCIS BEIDLER FOREST





                                                                               lo MILES
















            Figure 21. Potential threat occurrence


                                                                                                    Model Application 37










                       NWI FLOOD REGIME CATEGORIES

                                                                 Four Hole Swamp Sub-Basin


                                                         A-
                                                                                           Four Hole Sub-Basin






                                                                      41




                                                   1101







                         NWI FLOOD REGIME CATEGORIES
                         A -TEMPORARILY FLOODED

                         B-SATURATED

                         C - SEASONALLY FLOODED

                         D - SEASONALLY FLOODED/WELL DRAINED
                         E - SEASONALLY FLOODED/SATURATED

                         F - SEMIPERMANENTLY FLOODED

                         G
                          - INTERMITTENTLY EXPOSED

                         H - PERMANENTLY FLOODED

















            Figure 22. Hydrologic regime of potential mitigation sites in Four Hole Swamp

           38 10"entIfY1179 Wetland 91fig,7tion 51tes Using O/S





              Field-Truthing                                                           Verification of Source Data
                                                                                             The results of the field work done as part of this study
                    After identifying potential mitigation sites through the           indicated that the thematic data used in applying this meth-
              GIS analyses, a sample set was extracted for field sampling.             odology are accurate with some exceptions. Acreages
              The objective of the field visits was to generally validate the          derived from the NWI data appeared to be, for the most part,
              assumptions made for identifying the three mitigation classes            accurate, although precise boundaries were not delineated in
              as described earlier in this study. This was accomplished by             the field. Acreage figures derived during field verification
              1) verifying the accuracy of the GIS-generated and source                were estimates.
              data regarding community type or land use, approximate
              size, presence of alteration (if indicated by the NWI modifiers);              General community types, with few exceptions, were
              and 2) generally assessing the logic used in defining mitiga-            also accurate; however, in several instances, especially in the
              tion classes. It should be noted that because of resource                headwater bottoms, large tracts have been recently clearcut.
              constraints the rigorous sampling of species type, species               Thus, these areas obviously do not presently support the
              composition, and soil types was not performed. Rather,                   community types indicated in the NWI data derived from
              qualitative assessments of these factors were made. In                   1989 photography. The implication for mitigation in these
              addition, a qualitative assessment of the site's wetland status          instances is not clear. It could be argued that, depending on
              was made. Such characteristics as wetland plant species and              the hydric status of species pioneering the clearcut sites, these
              various soil properties indicative of "driving" hydrology were           areas could potentially serve as enhancement sites, with the
              generally assessed to confirm that the site would likely qualify         planting of bottomland species being indicated (personal
              as jurisdictional or could be brought into jurisdictional status         communication, Kent Campbell, United Consulting Group,
              upon mitigation. Precise delineations, which would ulti-                 Ltd.).
              mately determine the status of selected polygons, were not
              within the purview of this study. It should be noted that the                  Some exceptions to the NWI-based classification of
              assumptions made to define the opportunity criteria outlined             palustrine emergent areas were noted. Many of these areas
              in this study were not verified in the field - i.e. site-specific        are actually young pine plantations and, in some cases,
              field evaluations were not made to determine the ability of a            agricultural fields. It is thought that environmental conditions
              wetland site to serve a wildlife habitat, water quality, or              at the time of image capture might have contributed to the
              hydrology function. Rather, the rationale used to develop the            misinterpretation of these communities. South Carolina
              criteria used for these analyses is supported by the literature,         experienced above-average precipitation in 1989, the year
              as described earlier in this study.                                      during which the photography was taken. Also, the image
                                                                                       was captured in early spring, a wet time of year. Thus, some
                    In sampling the sites for field verification, several factors      areas interpreted as emergent wetlands were probably ponded
              were considered. It was desired that statistical rigor be used           agricultural fields or pine plantations. Finally, the immature
              in site selection - that is, that a proportionate number of              status of the pine species at the time of image capture and the
              potential mitigation sites be randomly selected for each                 short stature of agriculture crops contributed to the
              mitigation class (enhancement, restoration, and protection).             misclassification. of an emergent, persistent community type
              However, because of limited resources and time, it was                   for these polygons.
              necessary that sites be relatively accessible. While it is
              recognized that the identification of sites on the basis of their              For the most part, it was possible to locate restoration
              accessibility, rather than a random sample, would result in a            sites, or PC wetlands, on the ground; however, this mitiga-
              biased sampling of sites, the reality of resource constraints            tion class was more difficult to assess (i.e. to verify on the basis
              dictated that those sites most accessible be identified and field-       of the two factors defining this class - agricultural land use and
              truthed.                                                                 a specific soil type) since detailed soil surveys were not made
                                                                                       in the indicated areas.
                    The final composite overlay of potential mitigation sites
              (defined by the three mitigation classes) was visually analyzed                Without exception, it was found that NWI polygons
              to identify clusters of sites, representative of the three               coded with a modifier indicative of ditching, impoundment,
              mitigation classes, that might serve as potential field-truthing         or excavation had, in fact, been modified accordingly.
              sites. Roads providing access to these field sites were                  Unfortunately, the converse was not always true. It was
              identified by overlaying the primary and secondary road data             sometimes the case that a site, although listed as a protection
              layer. Quad maps were then cross referenced to identify                  site because of the lack of a modifier in the NWI data base,
              roads, other than primary and secondary roads, that might                had experienced some degree of ditching or was otherwise
              yield access to the field sites. An attempt was made to locate           modified. This condition was especially apparent in the case
              both isolated (Figure 23) and riverine (Figure 24) clusters              of side ditching and, in some instances, where the main
              throughout the length of the basin.                                      channel had been straightened or excavated to enhance




                                                                                                                            NOdOl APPlic8tiOn 39













                                                   FIELD CHECK MAP
                                     WADBOO SWAMP QUADRANGLE



                                                    'HECK P- -A




                         MITIGATION - COMMUNITY TYPES


                         PROTECTION -EMERGENT

                         PROTECTION - WET FLATWOOD/SAVANNAH

                         PROTECTION - BAY FOREST/SHRUB BOG

                         PROTECTION - BOTTOMLAND/SWAMP


                         ENHANCEMENT-EMERGENT

                         ENHANCEMENT - WET FLATWOOD/SAVANNAH

                         ENHANCEMENT - BAY FORESTSHRUB BOG

                         ENHANCEMENT - BOTFOMLAND/SWAMP


                         RESTORATION


                         SENSITIVE SPECIES SITE

                         ARCHAEOLOGICAL SITE
                     El  HISTORICAL SITE

                         MINING SITE

                         HAZARDOUS WASTE SITE


                         LANDFILL SITE


                         PRIMARY OR SECONDARY ROAD
                                                 VPES


















































              Figure 23. Isolated field check site


             40 IdeftfifyIng Wetland ffifigotlon Sites Using GIS














                                                                             FIELD CHECK MAP
                                                                   HARLEYVILLE QUADRANGLE






                                                                                                      -CK Pi,,, r --






                          MITIGATION - COMMUNITY TYPES

                          PROTECTION - EMERGENT

                          PROTECTION - WET FLATWOOD/SAVANNAH

                          PROTECTION - BAY FOREST/SHRUB BOG

                          PROTECTION - BOTTOMLAND/SWAMP

                          ENHANCEMENT-EMERGENT

                          ENHANCEMENT - WET FLATWOOD/SAVANNAH

                          ENHANCEMENT - BAY FOREST/SHRUB BOG

                          ENHANCEMENT - BOTTOMLAND/SWAMP

                          RESTORATION


                          SENSITIVE SPECIES SITE

                          ARCHAEOLOGICAL SITE

                          HISTORICAL SITE

                          MINING SITE

                          HAZARDOUS WASTE SITE

                          LANDFILL SITE

                          PRIMARY OR SECONDARY ROAD




















            Figure 24. Riverine field check site


                                                                                                                  Model ApplicatiOly 41






              drainage of the surrounding landscape. On the basis of the           farmed, while others were fallow or planted in wildlife food
              noted exceptions between data and field checks, it can be            plots. Again, this mitigation class was the most difficult to
              reasonably inferred that the number of potential enhance-            assess because detailed soil surveys were not made. It was
              ment sites in the Four Hole sub-basin is greater than the            noted, however, that in many cases these areas provided
              number found through application of this methodology.                contiguity for fragmented riverine systems, especially in
                                                                                   headwater areas. It was also observed that abandoned
              Other Observations                                                   agricultural fields, not identified by this methodology, were a
                     An effort was also made to generally assess the wetland       common feature of the landscape, occurring both in associa-
              status of the selected mitigation field sites. Ailthough identi-     tion with wetland systems and in upland areas. It became
              fied NWI polygons, both modified (enhancement sites) and             apparent that the criteria used in this methodology to locate
              unmodified (protection sites), generally supported a wetland         potential wetland restoration sites were not adequate for
              community and were delineated as such during image                   identifying all prior converted wetlands or farmed wetlands
              interpretation, it was sometimes the case where "driving"            that have since been abandoned. As mentioned previously,
              hydrology did not appear to be present "on the ground" as            the soils used to define hydric agriculture fields were those
              indicated by non-hydric soil conditions or the invasion of           identified by soil scientists as the least productive because of
              plant species requiring more xeric habitat conditions. This          their extreme hydric condition. However, complex eco-
              "drying out" of certain areas, especially those areas indicated      nomic factors and environmental factors other than soil
              in the NWI data as temporarily flooded, could be attributed          productivity are also responsible for the abandonment of
              to one or a combination of several factors, as follows:              farming operations. Thus, additional data and/or an amended
                                                                                   methodology would be required for a thorough identification
                    ï¿½ The ditching and subsequent drainage of many                 of all PC wetlands in this watershed.
                        modified wetland areas to the point where                         Finally, the alphanumeric NWI code provides some
                        water tables are significantly lowered.                    subtle clues about specific land use activity that, if properly
                    ï¿½ The possibility that South Carolina is at the end            interpreted, might allow for the identification of polygons
                        of a 15-year drought cycle.                                having a greater desirability for mitigation. For example,
                                                                                   while many palustrine, unconsolidated bottom areas (coded
                    ï¿½ Increased water withdrawals over the past                    as "PUB" in the NWI data base) were actually reservoirs
                        decades.                                                   lacking mitigation potential, sites exist that qualify as prime
                                                                                   areas for mitigation, depending on the degree of soil distur-
                    If, in fact, ditching is responsible for the drying out of     bance and other physical factors. It has been suggested that
              some wetland areas, it becomes obvious that hydrologic               some palustrine, unconsolidated bottom areas that have
              restoration might reverse the observed trend. While there            been excavated actually represent gravel pits, abandoned or
              has been some fear expressed by the farming community that           otherwise, and possess potential for vegetation reestablish-
              such activity might reverse draining so that productive              ment (personal communication, Charlie Storrs, U.S. Fish
              farmlands again become flooded, successful agricultural              and Wildlife Service). These areas were not identified by this
              water table management has occurred in the Coastal Plain of          methodology, since only sites currently supporting vegeta-
              North Carolina. In these circumstances, it has been possible         tion were selected. Other mitigation sites identified through
              for fanners to regulate water table levels to optimize water         this methodology, but that might be given more detailed
              availability for crop growth. At the same time, the contrib-         attention during the physical suitability analyses, were veg-
              uting watershed receives the ecological benefit of restored          etated areas that have been excavated. In many cases, these
              hydrology and, subsequently, wetland maintenance (per-               areas have been manipulated and then abandoned, as
              sonal communication, Bud Badr, SCWRQ.                                indicated by the establishment of vegetation. Again, depend-
                                                                                   ing on the composition of species pioneering these sites, they
                    It was also observed in the field that PC wetlands, as         may or may not be desirable for mitigation.
              defined and identified in this study, varied in their ability to
              support agricultural crops. Some appeared to be actively













              42 IdentIfYing Wetland lIfffigatlon SItes Using G/S







                                                                                             The methodology described in this report identifies
                                                                                      potential wetland mitigation sites on the basis of physical
                                                                                      factors (soils, hydrology, vegetation) and according to the
                                                                                      following characteristics indicative of ecological function:

                                                                                         ï¿½ Fragmentation.

                                                                                         ï¿½ Contiguity with other wetland areas and, thus, inclusion
                                                                                                in large complexes.

                                                                                         0 Existence of interior habitat for wildlife.

                                                                                         ï¿½ Juxtaposition to water bodies and thus the opportunity
                                                                                                to provide floodflow storage and water quality
                                Conclusions                                                     improvement.
                                                                                         ï¿½ The existence of potential threats to the ecological
                                                                                                integrity of a site.

                                                                                         ï¿½ Opportunities to provide habitat for rare, threatened,
                                                                                                or endangered species and communities.

                                                                                             The value of considering these ecological factors in
                                                                                      mitigation site selection, for banking or otherwise, cannot be
                                                                                      overstated. Indeed, fragmentation continues to persist as a
                                                                                      result of wetland fill activity. Thus, large complexes of
                                                                                      wetland sites - areas vital to the ecological integrity of
                                                                                      watersheds - are dwindling. Strategic reconstruction of
                                                                                      indicated mitigation sites could restore or improve the
                                                                                      ecological health of many watersheds across the country.

                                                                                             The physical suitability analyses were successful in
                                                                                      thoroughly inventorying the landscape for potential protec-
                                                                                      tion and enhancement sites according to their respective
                                                                                      definitions, although wetlands other that those delineated by
                                                                                      NWI were not identified. It was noted in the field, however,
                                                                                      that abandoned farmed wetlands and prior converted wet-
                                                                                      lands were common throughout the study area although not
                                                                                      always selected by this methodology as potential restoration
                                                                                      sites. It is felt that this is partially attributable to the rather
                                                                                      conservative selection of hydric soils in the overlay operation.
                                                                                      If the entire list of hydric soils had been used for each county
                                                                                      rather than the few identified in this study as extremely hydric,
                                                                                      it is probable that this methodology would have identified a
                                                                                      greater number of the abandoned farmed wetland and prior
                                                                                      converted sites existing in Four Hole Swamp sub-basin.
                                         TY                                           However, the factors contributing to the wholesale abandon-
                                                                                      ment of farming operations in the Coastal Plain and in other
                                                                                      places are largely a function of complex economic conditions
                                                                                      and only partially related to the physical characteristics of the
                                                                                      soil. Data on farmland abandonment are available in hard
                                                                                      copy from SCS. It is feasible that these data, in digital forrn
                                                                                      or otherwise, could be used to supplement the results
                                                                                      obtained from these GIS analyses in identifying PC wetlands.

                                                                                             Results from this study also indicate that although the
                                                                                      model was successful in identifying enhancement sites -



                                                                                                                                   C017clusiOns 43






              many of which appear to have true mitigation potential as             clear delineation of primary and secondary sites was not
              they are currently being effectively drained - there are              always possible. This component of the methodology could
              actually a greater number of potential enhancement sites in           not consider the complex hydrology existing in the Four Hole
              the field than determined by this methodology. This is due            Swamp drainage system. Elevation data would be required
              to the fact that a large number of sites identified as protection     to better characterize hydrologic conditions in the riparian
              sites have actually been modified in some way. While the data         system.
              used for application of this methodology were fairly current,
              it is recognized that cross-referencing the final sites selected            As would be expected, the results of the opportunity
              through this methodology with NAPP or other aerial photog-            analyses indicate that the mainstern of Four Hole Swamp is
              raphy, prior to field verification, would expedite the site           an area that contributes greatly to the ecological integrity of
              selection process. Interpretation of current aerial photogra-         the sub-basin. The mitigation and annexation of degraded
              phy can detect recent changes in land use or land cover as well       wetland sites to intact and protected portions of this riparian
              as verify the alphanumeric code provided by the National              system, could ensure the long-term ecological viability of Four
              Wetlands Inventory data.                                              Hole Swamp.

                    Execution of the wildlife habitat component resulted in               While the information resulting from this methodology
              successful identification of potential mitigation sites that          can better direct mitigation decisions made by those in the
              might serve as optimal habitat according to model definitions.        regulatory arena, there is of course no substitute for the
              Many of the restoration sites fell out of the model; however,         expertise contributed by knowledgeable specialists. This
              large complexes of the three mitigation classes, all which            methodology is intended to be a decision support tool, not
              possess adequate interior habitat, were found. Execution of           a decision system. It considers landscape level indicators of
              the water quality/floodwater storage analyses was not com-            function and places priority on contiguous complexes of
              pletely successful in identifying distinct low- and high-order        potential mitigation sites. By explicitly stating ecological
              wetland sites. While high-order wetlands were consistently            assumptions that should be considered when selecting sites
              identified along the mainstern, low-order wetlands were               for wetland mitigation, it can help streamline the decision-
              identified in the headwaters as well as on the mainstern. A           making process through an initial identification of potential
              different characterization of wetland orders, would likely            mitigation sites requiring further site-specific evaluation by
              contribute to better definition of these areas. In addition, a        wetland specialists.

































              44 Ident1frIng wetland Ofig8fion SlIes I/Sing GIS








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                                                                                                             ReferencOs 47




         Appendices                                     Appendix I

                                                           Generalized NWI Wetlands Used in
                                                                         Amalyses*

                                                        Emergent (Savannahs, Wet Meadows,
                                                        Freshwater Marsh)

                                                           PEM1A          PEMY           PEM1N
                                                           PEM1B          PEM1H          PEM1R
                                                           PEM1C          PEM1K          PEM1T
                                                           PEMA           PEMlMh         PEMFx
                                                           PEMC           PEM1P          PEM/SS1T
                                                                                         U/PEM1T



                                                        Wet Flatwoods and Pine Savannah


                                                           PF04A          PF04/SS3A -    PSS4C
                                                           PF04C          PF04/SS3C      PFOSS4A
                                                           PF04R          PF07A          PSS3A-
                                                           PF04S          PF07S
                                                           PF04/1A        PSS4A



                                                        Bottomland Hardwoods, Wooded Swamps, Decidu-
                                                        ous Shrub Swamps
                                                           PFOIA          PF01B          PSS1C
                                                           PF01S          PFOIC_         PSS1F_
                                                           PF01/2A        PFOIF-         PSS1N
                                                           PF01/3A        PF01G-         PSS1R
                                                           PF01/4A_       PF01P          PSS1T
                                                           PF01/4S        PF01R-         PSS2KH
                                                           PFOl/SS3A-     PF01T          PSS6C
                                                           PFOI/SS4A-     PF01/2-        PSS6F -
                                                           PF01/4C        PF01/3C        PSS6K -
                                                           PF01/4R        PFOI/3R        PSS6M
                                                           PFOl/SS4R      PFO1/SS3C      PSS6N
                                                           PF04/1C        PFO1/SS3F      PSS6R-
                                                           PF04/1R        PFO1/SS3R      PSS1/2F-
                                                           PFO/SSIC       PF02           PSS1/2T
                                                           PSS1A          PF05           PSS1/3C
                                                           Pssis          PF06C -        PSS1/3F -
                                                           PSS1/3A-       PF06F -        PSS1/3H
                                                           PSS1/3S        PF06G-         PSS1/3R
                                                           PSS1/4A        PF06N          PSS1/3T
                                                           PSS1/4C        PF06/AB4Hh     PSS1/4T
                                                           PSS3/1A        PFO/EMIC       PSS1/7R
                                                           PSS6Ad         PFO/EM1F       PSSC
                                                           PSS6S          PFO/SS6Fh      PSS6/EMIF
                                                           PFO/SS6T       PSS/EMlC




                                                         John Hefner, Fish and Wildlife Service, National Wetlands Inventory

                                                                                      AppefldiCOS49





          Bay Forests, Evergreen Shrub Bogs                Appendix N
                 PF01/3B                    PSS1B -
                 PF01/413                   PSS3A             Hychic Soils List by County Used
                 PF01/SSB,                  PSS3B-                        for Analyses*
                 PF03/SS1B                  PSS3C-
                 PF04B                      PSS3R-
                 PF04/IB                    PSS3S               Berkeley
                 PF04/3C                    PSS7A-              Meggett loam
                 PF04/2C                    PSS7B               Pamlico mucl@
                 PF04/SS1B                  PSS7C               Pickney loamy fine sand
                 PF04/SS3B                  PSS7F
                 PF07B                      PSS7R
                 PF07C                      PSS1/3B             Calhoun
                 PF07Kh                     PSSIAB              Swamp
                 PF07R -                    PSS3/1A
                 PFO/SS3B                   PSS3/1B             Dorchester
                 PSS3/1C                                        Elloree loamy fine sand
                                                                Grifton fine sandy loam
                                                                Mouzon fine sandy loam
                                                                Osier loamy fine sand
           Appendix                                             Rutlege loamy fine sand
           Generaked Land Use Data Used in                      Orangeburg
                           Analyses                             Bibb sandy loam
                                                                Elloree loamy sand
               Urban                                            Johnston sandy loam
               U11                                              Mouzon fine sandy loam
               U12
               U13
               U14
               U15                                          -@'Dennis De Francesco, Soil Conservation Service
               U16
               U17

               Agricultural Cropland/Pastureland
               U21


               Mixed Forest
               U41
               U42
               U43


               Pine Plantation
               U42P


               Other Upland
               U22
               U31
               U32
               U75
               U76






           50 IdentifYing WetlOflar NItig-1ti" Sit" Ils'ng G/S



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