The Federal Emergency Management Agency (FEMA) has recently revised floodplain boundaries for portions of Williamson County. FEMA has issued a new Flood Insurance Study (FIS) report for the entire county and incorporated areas, and has also issued new Flood Insurance Rate Map (FIRM) panels for the applicable areas included in recent studies. The revised FIS and FIRM panels became effective December 20, 2019 and replace the previous information.
This update of special flood hazard information includes a comprehensive flood study conducted by the Texas Water Development Board and the Upper Brushy Creek Water Control and Improvement District (WCID) for the Brushy Creek watershed downstream to near Coupland. The update also includes 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. These preliminary floodplains were released by FEMA on January 30, 2017 with some revisions released September 26, 2017. The FEMA 90-day public comment and appeal period for these preliminary floodplains ended on May 14, 2018.
FEMA released a second phase of floodplain revisions on March 16, 2018. These ‘San Gabriel Watershed Phase 2’ revisions are scattered throughout the remainder of the San Gabriel River watershed and encompass only existing Zone A floodplains. These Phase 2 floodplain revisions do not include all Zone A floodplains, and also do not include most floodplains recently studied with the City of Georgetown / Texas Water Development Board planning study. The FEMA 90-day public comment and appeal period for these Phase 2 revisions within the unincorporated areas of the county ended November 12, 2018.
FEMA combined both of these study phases and issued a single Letter of Final Determination on June 20, 2019, which finalizes the studies. Again, the revised flood hazard and floodplain information became effective December 20, 2019.
The floodplain revisions issued on preliminary FIRM panels are illustrated on the county’s interactive web map located here. This map simply shows the proposed increases and decreases in the 1% annual chance (100-year) storm floodplain boundaries. The 1% annual chance flood results in the commonly used phrase “100-year floodplain”, which is regulated by FEMA and the county through the National Flood Insurance Program (NFIP). The Base Flood Elevation (BFE) is the elevation of the 1% annual chance flood. FEMA studies also determine the 0.2% annual chance flood and resulting floodplain, which is commonly referred to as the “500-year floodplain”.
Additional data on the proposed revisions, including the BFE and the 0.2% annual chance floodplain, can be viewed by following the FEMA web links at the bottom of the ‘Home’ panel for our interactive web map, or by clicking this website link. For more information on this process, please refer to our Frequently Asked Questions page.