Robert Daigh, Williamson County senior director of infrastructure, presented the preliminary results of the Atlas 14 floodplain study to Commissioners Court on May 21.

The study shows the classification for a 100-year flood has increased by 2 inches of rainfall and updates flood plain maps throughout the county.

Long story short

In 2018, the National Oceanic and Atmospheric Administration released an analysis of storm events and rainfall data from 1994-2017. Known as Atlas 14, the study adds information from this period to previous statistics, Daigh said.

In 2020, Williamson County received a grant through the Texas Water Development Board, and partnered with them to initiate a flood risk study that outlined areas in danger of flooding and potential mitigation strategies.

Preliminary results show the county’s 100-year flood shifted from 8-10 inches of precipitation to 10-12 inches. A 100-year flood is defined as an event that has a 1% chance of happening in any given year. For Williamson County, this change means there may be an increased risk of flooding if a 100-year event occurs.

Williamson County's Atlas 14 study includes the following findings:
  • Updating flood plain information throughout the county with the most recent scientific data, including NOAA Atlas 14 rainfall
  • Modeling streams and waterways that have never been studied
  • Gathering accurate information about topography, drainage structures and bridges
  • Developing mitigation measures
What else?

The Federal Emergency Management Agency revised Williamson County’s flood plain boundaries in 2019. The revision included a flood insurance study for the county and a new flood insurance rate map. These revisions went into effect in late 2019.

The update also included a flood study conducted by the TWDB and the Upper Brushy Creek Water Control and Improvement District.

An interactive map of effective FEMA flood plains can be viewed on Williamson County’s Geographic Information Systems’ webpage.

What’s next?

Williamson County will host nine open house events to present the study’s findings to the public. All meetings are from 5-7 p.m.
  • May 29: Williamson County Georgetown Annex, 100 Wilco Way, Georgetown
  • May 30: Williamson County Jester Center, 1801 E. Old Settlers Blvd., Round Rock
  • June 3: The Retreat Activity Center in Sun City, 1220 Cattleman Drive, Georgetown
  • June 4: East Williamson County Higher Education Center, 1600 Innovation Blvd., Hutto
  • June 5: Dickey Givens Center, 1015 E. MLK Jr. Blvd., Taylor
  • June 6: Williamson County Cedar Park Annex, 350 Discovery Blvd., Cedar Park
  • June 10: Walburg Community Center, 4000 FM 972, Georgetown
  • June 11: Sonterra MUD Clubhouse, 510 Sonterra Blvd., Jarrell
  • June 17: St. Dominic Savio Catholic School, 9300 Neenah Ave., Austin