FEMA Floodplain Maps
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.
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. 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 email Floodplain Management, 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.
A floodplain is a geographic area subject to flooding and/or land adjacent to a waterway necessary to contain a flood. Floodplains can be associated with rivers, lakes, streams, channels, or even small creeks that are normally dry most of the year. There are two types of floodplains we generally deal with:
- 100-year floodplain: an area subject to flooding as a result of the occurrence of a 100-year storm event - a storm that has a 1% chance of occurring in any given year. The 100-year floodplain, also called the 1% annual chance floodplain, is regulated by FEMA and Williamson County. This floodplain is also called Zone A or Zone AE.
- 500-year floodplain: an area subject to flooding as a result of the occurrence of a 500-year storm event - a storm that has a 0.2% chance of occurring in any given year. The 500-year floodplain, also called the 0.2% annual chance floodplain, is currently not regulated by FEMA or Williamson County. This floodplain is also called Zone X shaded.
See also the Federal Emergency Management Agency (FEMA) website for more information on floodplains and floodplain management.
Floodplain regulations are enforced to protect public safety and health. In addition, they encourage sound engineering practices and efficient floodplain management techniques. All construction in Williamson County must adhere to federal floodplain regulations. Regulations are established by the Federal Government and implemented by the Federal Emergency Management Agency (FEMA). The County Engineer's Office is responsible for examining construction for compliance with local and federal floodplain regulations.
Evaluating and Permitting Floodplains
County Engineer's Office is the designated floodplain administrator for Williamson County. Official floodplain maps for the County are available for viewing in our office at 3151 SE. Inner Loop, Georgetown, TX, 78626. Floodplain permitting within various cities in Williamson County is handled by those cities directly.
Currently, residents may come to the County Engineer's Office for consultation to determine whether any specific location is within the floodplain. Alternatively, FEMA maintains a website where you can view the same maps. Per county ordinance, a Certificate of Compliance is required for all structures or other developments outside of a floodplain in unincorporated areas of the county. The Certificate of Compliance verifies that no 100-year floodplain exists in the area of proposed development. Certificate of Compliance applications can be submitted online at MyGovernment Online website.
For a helpful video regarding the Certificate of Compliance process, please visit the Williamson County Youtube page.
If your property is within or adjacent to a 100-year floodplain, you will need to elevate proposed structures at least one foot higher than the base flood elevation. A Floodplain Development Permit must be issued by this office prior to construction.
- Floodplain Development Permit Application (PDF)
- Floodplain Development Permit Application Key Elements (PDF)
- Elevation Certificate (PDF)
To complete this permit process, you must hire a licensed land surveyor to certify the elevation of the structure and complete the FEMA Elevation Certificate. Completion of the process qualifies the home for the National Flood Insurance Program (NFIP). Development within the flood way portion of the 100-year floodplain is prohibited except with extensive engineering analysis. The Williamson County Flood Damage Prevention Order (PDF) contains the full text of regulations.
Effective FEMA floodplains within Williamson County are provided on this interactive map (located on our GIS Department page). The County also regulates construction/development within local floodplains (not FEMA-mapped) that are documented on official public records such as plats. Floodplain boundaries will change over time based on the latest engineering studies. Please note that the most recent final floodplain boundaries will supersede floodplains shown on older documents.
If you have questions, please contact the County Engineer's Office at 512-943-3330.
Digital versions and images of flood maps are now available for viewing and printing from the online FEMA Flood Map Store page. This online store provides paper, scanned images on CD-ROM, and downloads of maps. The Flood Map Store allows users to create a FIRMette at no cost. A FIRMette is a section of the flood hazard map at 100% scale that can be printed on standard paper sizes (8.5 x 11 inch, 8.5 x 14 inch, and 11 x 17 inch).