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Wetland Mapping Using Spatial Analyst and Soil Attributes

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2012 Dallas, Texas, July 29 - August 1, 2012  121338076.(doi:10.13031/2013.41867)
Authors:   Richard A Weber, Waylon D Daniels
Keywords:   Wetlands, floodplains, Geographic Information Systems, SSURGO, Web Soil Survey, hydrogeomorphic, HGM

Wetlands and floodplains are unique landscape positions where the presence and actions of water creates unique landforms and soil properties. Land managers have a critical need for accurate maps of these landscapes for purposes such as land use planning, and restoration planning and design. In addition, there is a growing need for the development of wetland assessment models for wetland mitigation where hydrologic and biogeochemical functions are evaluated. Finally, the Natural Resources Conservation Service (NRCS) has embarked on a comprehensive effort to define ecological sites for the Ecological Site Description (ESD) project. Geographic Information Systems (GIS) are powerful tools for use in correlating multiple data sources to create boundaries that separate floodplains and wetlands from adjacent landscape positions. However, the challenge is to define wetlands and floodplains according to a robust system that uses the attributes available for GIS analysis. The use of the Hydrogeomoprhic (HGM) wetland classification system is presented as a superior classification system for wetland and floodplain mapping. The HGM system incorporates all wetlands and floodplains into a comprehensive system under 7 broad classes: Riverine, Depression, Mineral Flats, Organic Flats, Slope, Lacustrine Fringe, and Estuarine Fringe. These classes are defined by 3 parameters: Landscape Position, Dominant Water Source, and Hydrodynamics. This system is especially well suited for use with GIS tools because the 3 parameters can be correlated with attributes in soil, elevation, and land use and cover layers. In addition, HGM incorporates the extent of floodplains into the Riverine HGM wetland class, so there is no separation between the definition of wetland and floodplain. The following GIS mapping examples using soil attributes are presented: The use of Soil Survey Geogrpahic (SSURGO) database attributes including geomorphic description, taxonomy, water features, and physical properties. In addition, examples are presented illustrating the use of elevation data to extract: watershed boundary, and Strahler Stream Order. The use of soils data alone is limited to efforts where individual soil map units can be used to delineate wetland boundaries. However, spatial analyst tools can be used to delineate wetland boundaries within soil map units. Taken together, these processes can be combined to create reasonably accurate delineations of wetland landscape positions ready for ground truthing. Successful map projects are defined as those where mapped wetland HGM class boundaries match neatly with adjacent non-wetlands, and class boundaries match neatly with adjacent transitional wetland classes. Wetlands are mapped as landscapes including the non-wetland areas which are an integral part of the system . As such, the boundaries do not define jurisdictional wetlands. For instance, the Riverine class includes non-hydric soils found on natural levees and other depositional features. Depression wetlands are mapped in a complex which include the critical upland areas between individual depressions. Slope HGM classes nearly always transition into adjacent HGM classes.

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