Coastal Wetlands
The North Carolina Division of Coastal Management (DCM) has developed a coastal area wetlands conservation plan which relies on adequate knowledge of the location and extent of wetlands by watershed in coastal NC. After reviewing existing data, DCM determined that none of the data could be used exclusively as a wetlands inventory for the conservation plan. Therefore, DCM has developed wetland mapping methods using geographic information systems (GIS) and existing spatial data to accommodate a limited time schedule and large land area. Three primary spatial data layers provide information that are assembled into the DCM wetlands data. These layers are the National Wetlands Inventory (NWI), county soils (DSL), and classified land use/land cover from TM satellite imagery. In addition, an update was performed using a more recent version of land use/land cover data. The NWI and DSL data are 1:24,000 scale, vector data. The imagery is 30 meter resolution, filtered and unfiltered, raster data. Extracting the most relevant information from each of these layers allows DCM to produce the best information about the location and extent of Coastal Plain wetlands available today. DCM's classification scheme is based on both vegetative cover and hydrogeomorphic character. Wetland classes currently recognized by DCM are: Salt/Brackish Marsh, Estuarine Shrub-Shrub, Estuarine Forest, Maritime Swamp Forest, Freshwater Marsh, Pocosin, Bottomland Hardwood, Swamp Forest, Headwater Swamp, Hardwood Flat, Pine Flat, Managed Pineland, Human Impacted. In addition, modifiers may be applied to any of these categories indicating that they have been partially drained, cleared of vegetation, or recently cutover. An automated Arc/Info model considers the NWI classification and the imagery classification in assigning a wetland type to each polygon. Soil types are used to determine whether or not marginal areas are considered to be wetlands, including managed pine areas. Once the automation is complete, an interactive session allows the user to assign wetlands to classes specific to their position in the landscape. A hydrographic data layer is used in addition to the layers mentioned previously to more easily interpret the landscape position and hydrogeomorphology (HGM) of the wetlands. For example, a temporarily flooded, hardwood area may be classified as bottomland hardwood or hardwood flat, depending on its location: adjacent to a stream or within an interfluvial divide, respectively. Finally, each wetland is assigned to an HGM class of riverine, flat/depressional, headwater or estuarine. In addition to automated and manual processing, and a limited amount of field verification is performed.
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