Hurricane Harvey made landfall near Rockport, Texas on August 25 as a category 4 hurricane with wind gusts exceeding 150 miles per hour. As Harvey moved inland the forward motion of the storm slowed down and produced tremendous rainfall amounts to southeastern Texas and southwestern Louisiana. Historic flooding occurred in Texas and Louisiana as a result of the widespread, heavy rainfall over an 8-day period in Louisiana in August and September 2017. Following the storm event, U.S. Geological Survey (USGS) hydrographers recovered and documented 2,123 high-water marks in Texas, noting location and height of the water above land surface. Many of these high-water marks were used to create flood-inundation maps for selected communities of Texas that experienced flooding in August and September, 2017.
The mapped area boundary, flood inundation extents, depth rasters, and coastal surge layer were created to provide an estimated extent of flood inundation in Coastal basins including East and West Matagorda Bay Subbasins, East and West San Antonio Bay Subbasins, and Aransas Bay Subbasin, Texas. The mapped area of the Coastal basins were separated into three sections based on the availability and location of high-water marks. The maps of the eastern part of the East Matagorda Bay Subbasin include a 17-mi reach of Peyton Creek and a 16-mi reach of Big Boggy Creek, and flood-inundation map for 6-mi reach of Little Boggy Creek in Matagorda County. The maps of the western part of East Matagorda Bay Subbasin include a 13.5-mi reach of West Carancahua Creek, 14.5-mi reach of East Carancahua Creek, and 9.6-mi reach of Keller Creek within Matagorda, Jackson, and Calhoun Counties. The maps of the middle part of the East Matagorda Bay Subbasin are for a 21-mi reach of the Tres Palacios River within Matagorda County. These geospatial data include the following items: 1. bnd_emb1, bnd_emb2, and bnd_tres_palacios; shapefiles containing the polygon showing the mapped area boundary for the Coastal basins flood maps, 2. hwm_emb_1, hwm_emb2, and hwm_tres_palacios; shapefiles containing high-water mark points used for inundation maps, 3. polygon_emb1, polygon_emb_2, and polygon_tres_palacios; shapefiles containing mapped extent of flood inundation for the Coastal basins, derived from the water-surface elevation surveyed at high-water marks, 4. depth_emb1, depth_emb2, and depth_tres; raster files for the flood depths derived from the water-surface elevation surveyed at high-water marks, and 5. coastal_surge.lyr; a layer file generated from the depth raster depicting water height above ground recorded at the high-water marks. 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).
The HWM elevation data from the USGS Short-tern Network (STN) was used to create the flood water-surface raster file (U.S. Geological Survey [USGS], 2018, Short-Term Network Data Portal: USGS flood information web page, accessed February 13, 2018, at https://water.usgs.gov/floods/FEV.). The water-surface raster was the basis for the creation of the final flood inundation polygon and depth layer to support the development of flood inundation map for the Federal Emergency Management Agency's (FEMA) response and recovery operations.
