Anatomy of a Texas Flood: Causes, Challenges, and Conclusions of the October 2018 Llano and Colorado River Flooding

The Texas Hill Country has a notorious reputation for rapid onset flood events. Aided by sharp changes in terrain, narrow river channels, and limited soil permeability, heavy rainfall events can turn into a torrent of water that quickly overwhelms communities. A series of heavy rainfall events in October 2018 produced flash flooding along the Llano and Colorado Rivers that were no exception, resulting in five fatalities, the evacuation of over 150 people, the decimation of an RV park and numerous roads and bridges, and an unprecedented Flash Flood Warning for Lake Travis. When the initial flash floods ended, the disaster translated downstream into the City of Austin with a subsequent multi-day water shortage crisis.

Effective messaging in the Texas Hill Country of rapid onset flood events and their cascading effects requires not just a knowledge of local hydrology, but accurate diagnosis of antecedent and meteorological conditions during extreme rainfall events. This information is used to anticipate event trends for warning decisions and public safety response as well as coordinate media communication. In order to capture how this information was utilized and messaged during the October 2018 floods, an Integrated Warning Team (IWT) workshop was held in Austin, TX in Fall 2019. Not only will this presentation explore the causes behind the floods and their associated messaging challenges, but it will bridge that science and its effective communication by presenting the results from the Austin IWT workshop. Conclusions from this workshop will also be used to discuss how meteorological analysis and IWT messaging can be applied in future events for regions with similar terrain-induced hydrologic events.