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, and depth rasters were created to provide an estimated extent of flood inundation along the San Bernard River within counties of Colorado, Wharton, Austin, Fort Bend, and Brazoria, Texas. The mapped area of the Sabine Basin was separated into three sections due to the availability and location of high-water marks; upper, middle, and lower. The upper reach includes 20-mi of the San Bernard River, extending from Interstate 10 near Sealy, Texas on the upstream end continuing downstream through the Attwater Prairie National Wildlife Refuge in Colorado County, Texas. The middle reach includes 46-mi of the San Bernard River, extending from Wallis, Texas in Austin County downstream through East Bernard, Texas in Wharton County and Kendleton, Texas in Fort Bend County. The lower reach includes 33-mi of the San Bernard River; in this reach, the San Bernard River flows past Sweeny and Brazoria, Texas in Brazoria County; the downstream extent terminates at the San Bernard National Wildlife Refuge. These geospatial data include the following items: 1. bnd_sanbernard_upper, bnd_sanbernard_middle, and bnd_sanbernard_lower; shapefiles containing the polygon showing the mapped area boundary for the upper, middle, and lower San Bernard River flood maps, 2. hwm_sanbernard_upper, hwm_sanbernard_middle, and hwm_sanbernard_lower; shapefiles containing high-water mark points used for inundation maps, 3. polygon_ sanbernard_upper, polygon_sanbernard_middle, and polygon_sanbernard_lower; shapefiles containing mapped extent of flood inundation for the upper, middle, and lower mapped sections of the San Bernard River, derived from the water-surface elevation surveyed at high-water marks, and 4. depth_sb_up, depth_sb_mid, and depth_sb_low; raster files for the flood depths derived from the water-surface elevation surveyed at 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).
These data show the area of inundation within communities along the San Bernard River, Texas. 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.
