The Federal Emergency Management Agency (FEMA) revised floodplain boundaries for portions of Williamson County in 2019. FEMA issued a revised Flood Insurance Study (FIS) report for the county and incorporated areas, and issued new Flood Insurance Rate Map (FIRM) panels for only the applicable areas included in recent studies. The revised FIS and FIRM panels became effective December 20, 2019 and replace the previous information from 2008.
This 2019 update of special flood hazard information included a comprehensive flood study conducted by the Texas Water Development Board (TWDB) and the Upper Brushy Creek Water Control and Improvement District (WCID) for the Brushy Creek watershed downstream to near Coupland. The update also included floodplains immediately north and east of this watershed boundary because the existing floodplains are within a FIRM panel already being revised with the watershed study.
The 2019 FEMA update also included the ‘San Gabriel Watershed Phase 2’ revisions, which updated some of the Zone A floodplains scattered throughout the remainder of the San Gabriel River watershed. Note that these Phase 2 floodplain revisions did not include all floodplains within the watershed. FEMA combined both studies and issued a single Letter of Final Determination on June 20, 2019, with the revised flood hazard information becoming effective December 20, 2019.Not all floodplains within the county have been revised with these two studies. There are still many effective Zone AE floodplains that were last studied about 30 years ago, and many effective Zone A floodplains that have never received a detailed engineering study. We are currently addressing this issue.
The effective FEMA floodplains may be viewed on our interactive web map, FEMA Flood Zones, located in the map section of our GIS Department webpage (here).
With recent updates to the National Weather Service rainfall data (Atlas 14), the recent 2017 Lidar topographic data, and the changing land use in this rapidly developing county, various flood studies are ongoing. Our GIS Department webpage also includes a separate interactive map illustrating proposed changes resulting from recent studies or proposed development activities. To view pending floodplain updates that may extend across a larger area, open the ‘Proposed FEMA Floodplain Changes’ map application on this same GIS webpage (here). Currently there is only one proposed update reflected on this map regarding the WCID proposed Dam 101 in the Lake Creek watershed.
For questions or concerns regarding floodplains or floodplain management in the unincorporated areas of Williamson County, feel free to contact us at firstname.lastname@example.org, or at 512-943-3330. Please be aware that within the corporate boundaries of a city, that city has floodplain jurisdiction (not the county) and the city should be contacted for floodplain inquiries.