Baldwin County Wetland Conservation Plan - Alabama Department ...

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Baldwin County Wetland Conservation Plan Final Summary Document 3.2.3 Remote Functional Wetland Assessment Model (RFWAM) 3.2.3.1 Conceptual Framework The ADID project developed a series of remotely sensed wetland functional assessment models to be applied using computer-based GIS analysis. The Technical Advisory Committee met several times over the course of this project, principally to provide guidance for the development of the Remote Functional Wetland Assessment Model (RFWAM). As a considerable amount of time was spent on the RFWAM during the ADID project, the Technical Advisory Committee continued to build on the existing model framework. Each model was broken down by function and then run for each 8-digit HUC watershed. The most notable difference in comparing the BCWCP to the ADID project was the lack of countywide digital soil information. To address this, the Baldwin County Commission has contracted with NRCS in Auburn to digitize the Baldwin County soil survey. As of the completion of this document, this soil data is scheduled to be released to the County in 2004. The BCWCP Technical Protocol document was developed by the Technical Advisory Committee and modified as needed at advisory committee meetings (Appendix 9.3). 3.2.3.2 Acquisition of GIS data layers for use in the BCWCP database As stated earlier, the NWI data was obtained from the USFWS. This data was broken down by watershed in the county. There are six 8-digit HUCs in Baldwin County. Only a very small portion of the Lower Tombigbee HUC is in Baldwin County and all wetlands in this HUC are riverine. Therefore, this HUC’s polygons were combined with those of the Lower Alabama HUC to help streamline the modeling process. A shapefile containing point data of known endangered species was provided by the USFWS and Alabama Natural Heritage Program. In an effort to account for wildlife movement, a 1/8 mile buffer was placed around the points to represent areas with sensitive populations. Fire locations and approximate acreages were obtained from the Alabama Forestry Commission and converted to a shapefile format. This shapefile is only an approximation of burned acreage and is not intended to reflect actual fire conditions. FEMA flood data was obtained by the County’s GIS department. This data is in shapefile format and represents areas prone to flooding during large rain events. A wellhead protection area coverage was obtained from the EPA and represents sensitive areas surrounding public drinking water wells. Land use data was broken down into four categories (urban, agriculture, forest, water) to complete the model, and four coverages were developed to represent each category. A hydrology coverage was obtained from the US Census Bureau (USCB) to represent the locations of streams, creeks, rivers, and large open water areas such as Wolf and Weeks Bay. The road centerlines file was generated by the Baldwin County Commisssion via a contract with a consultant. Due to the nature of NWI polygons, a 100 ft buffer was applied to the centerlines to more accurately identify areas where natural wetlands systems have been disrupted by roadway corridors. 19
Baldwin County Wetland Conservation Plan Final Summary Document Table 2. Summary of GIS Layers Utilized in BCWCP RFWAM. Data Layer Source NWI USFWS Endangered Species USFWS and ANHP Fire Locations AFC Flood Zones FEMA Wellhead Protection Areas EPA and GSA Land Use GSA 8 Digit HUC NRCS 11 Digit HUC NRCS Hydrology USCB TIGER CIR BCC True Color Photos BCC Centerlines BCC 3.2.3.3 Wetland Classification: HGM Classification Development Conversion of the National Wetlands Inventory (NWI) or Baldwin County Digital Wetland Layer classification to the HGM classification system was an essential task of the BCWCP, as the functional assessment models were based on the HGM system. BCWCP staff were contacted by the EPA grant manager to suggest collaboration between EPA GIS and BCWCP staff in order to accomplish this task most efficiently. BCWCP staff provided the data necessary to EPA staff in order to initiate the conversion process. After an initial review of HGM conversions provided to BCWCP staff, discrepancies were found and time became limited to correct these errors. Therefore, staff developed a protocol for the HGM classification of polygons. Riverine wetlands were identified by a geospatial relationship within the hydrology coverage. In other words, if a wetland polygon intersected the hydrology coverage, it was classified as riverine. Since many wetland polygons can exist within a riverine system, all polygons touching these riverine wetland polygons were also classified as riverine. This process was repeated until all polygons within riverine systems were identified and classified as riverine. Fringe wetlands were identified in a similar fashion using a coverage of saltwater hydrology. Polygons intersecting or touching saltwater areas were identified as fringe wetlands. Further, any polygon with the NWI classification of estuarine (E) was classified as fringe. This initial identification was then refined through spot checks conducted by local experts familiar with the coastal landscape of Baldwin County. Flat and depressional wetlands were identified using a visual interpretation of CIR photography that was taken during a very dry year in Baldwin County. Because polygons with visible standing water in such a year must have access to groundwater, they were classified as depressional, and polygons identified as wetlands but with no water present were classified as flat wetlands. Upon completion of this process, BCWCP staff evaluated the final product and found that the classifications were largely accurate. As with any remote analysis, there were some errors in classifications. After several reviews by other professionals affiliated with other government agencies involved, a final classification was reached (Figure 10). 3.2.3.4 Wetland model development 20
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