The current floodplain maps for Onion Creek are based on data from the 1980s. The floodplain study updates the data for more accurate floodplain maps.
Onion Creek is Austin’s largest watershed. In fact, most of the watershed is outside of Austin in Hays County. The floodplain study focuses on the part of Onion Creek within Austin and Travis County. It also looks at three of the creeks that feed Onion Creek: Bear, Little Bear and Rinard.