Williamson County, Texas

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.

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:

1. 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.
2. 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) web site 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.

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 S.E. 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 (https://msc.fema.gov/portal/home) 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.

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
    * Floodplain Development Permit Application Key Elements
    * Elevation Certificate

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 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 on-line FEMA Flood Map Store at: http://msc.fema.gov/. This on-line 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, 8.5 x 14, and 11 x 17).