Elk River in Kanawha and Clay Counties, West Virginia, Flood Map Files from June 2016

The mapped area boundary, flood inundation extents, and depth rasters were created to provide an estimated extent of flood inundation along the Elk River within communities in Kanawha and Clay Counties, West Virginia. These geospatial data include the following items: 1. elk_bnd; shapefile containing the polygon showing the mapped area boundary for the Elk River flood maps, 2. elk_hwm; shapefile containing high-water mark points, 3. polygon_elk_hwm; shapefile containing mapped extent of flood inundation, derived from the water-surface elevation surveyed at high-water marks, 4. depth_hwm; raster file for the flood depths derived from the water-surface elevation surveyed at high-water marks, 5. polygon_elk_dem; shapefile containing mapped extent of flood inundation, derived from the height above ground recorded at high-water marks and the digital elevation model (DEM) raster, 6. depth_dem; raster file for the flood depths derived from the height above ground recorded at high-water marks and the digital elevation model raster. The upstream and downstream mapped area extent is limited to the upstream-most and downstream-most high-water mark locations. In areas of uncertainty of flood extent, the mapped area boundary is lined up with the flood inundation polygon extent. The mapped area boundary polygon was used to extract the final flood inundation polygon and depth raster from the water-surface elevation raster file. Depth raster files were created using the "Topo to Raster" tool in ArcMap (ESRI, 2012). For this study two sets of inundation layers were generated for each reach. One raster file showing flood depths, "depth_hwm", was created by using high-water mark water-surface elevation values on the land surface and a digital elevation model. However, differences in elevation between the surveyed water-surface elevation values at HWM’s and the land-surface elevation from the digital elevation model data provided uncertainty in the inundation extent of the generated layers. Often times elevation differences of +/- 20 feet were noticed between the surveyed elevation from a HWM on the land surface and the digital elevation model land-surface elevation. Due to these elevation differences, we incorporated a second method of interpolating the water-surface layer. The recorded height above ground value from the surveyed HWM was added to the digital elevation model land-surface elevation at that point. This created a new water-surface elevation value to be used with the “Topo to Raster” interpolation method to create a second depth raster, "depth_dem". Both sets of inundation layers are provided.