Onion Creek is vulnerable to flooding due to the size and characteristics of the watershed. At 344 square miles, it is Austin’s largest watershed. The creek catches water from a large area, resulting in high flows and a wide floodplain.
The neighborhoods along Onion Creek were built in the 1970s, before we understood the breadth and depth of the creek’s floodplain. After the houses were built, new floodplain maps showed the potential for severe flooding.
For lower and upper Onion Creek, buyouts are the most effective way to protect the public and first responders from flood risks. There have been three studies evaluating flooding along Onion Creek. These studies have all found many drawbacks to other types of solutions, resulting in the recommendation for buyouts.
Executive Summary for the Onion Creek Floodplain Modeling and Mapping Report below, Halff Associates, Inc., 2017
Have an emergency plan. Please keep in mind that you may be safer staying at your home, on your roof, if necessary, than trying to escape a flood in your vehicle. Most fatalities during floods happen in vehicles.