Inundation layers for the San Jacinto River for the August and September 2017 flood event in Texas

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 West Fork San Jacinto River and East Fork San Jacinto River within counties of Grimes and Walker, Texas. The mapped area of the San Jacinto Basin and tributaries were separated into two sections due to the availability and location of high-water marks for the West Fork San Jacinto River and East Fork San Jacinto River. The inundation map of the West Fork San Jacinto River is a 36-mi reach of the main stem of San Jacinto River near Conroe, Tex. and includes Cypress Creek (53-mi reach), Little Cypress Creek (21-mi reach), Willow Creek (6-mi reach), Spring Creek (68-mi reach), Walnut Creek (15-mi reach), Panther Branch (11-mi reach), Lake Creek (7-mi reach), and Crystal Creek (2-mi reach). The inundation map of the East Fork San Jacinto River is a 65-mi reach of the main stem of the San Jacinto River near Coldspring, Tex. and includes White Oak Creek (9-mi reach), Caney Creek (31-mi reach), Peach Creek (19-mi reach), Winters Bayou (33-mi reach), and Luce Bayou (9-mile reach). The 18-mi reach of the San Jacinto River from the confluence of the west and east forks to the Lake Houston Dam near Shelton, Tex. is also included in the inundation map. These geospatial data include the following items: 1. bnd_west and bnd_east; shapefiles containing the polygon showing the mapped area boundary for the West Fork and East Fork San Jacinto River flood maps, 2. hwm_west and hwm_east; shapefiles containing high-water mark points used for inundation maps, 3. polygon_west and polygon_east; shapefiles containing mapped extent of flood inundation for the West Fork and East Fork mapped sections of the San Jacinto River, derived from the water-surface elevation surveyed at high-water marks, and 4. depth_west and depth_east; 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). 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.

Tags: caney, caney-creek, coldspring, conroe, cypress, cypress-creek, depth, east-fork-san-jacinto-river, extent, flood, flood-inundation-mapping, harris-county, high-water-marks, hockley, huffman, humble, inland-waters, katy, lake-houston, liberty-county, luce-bayou, montgomery-county, peach-creek, porter, san-jacinto-county, san-jacinto-river, shelton, spendora, spring, spring-creek, texas, the-woodlands, tomball, usgs-5aa023ebe4b0b1c392e6881b, waller, waller-county, waverly, west-fork-san-jacinto-river, westfield
Organization: Department of the Interior