Watershed Study

The purpose of the Upper Brushy Creek Watershed Study and Flood Protection Plan was to identify existing and potential future flooding problems within the Upper Brushy Creek Watershed and to develop potential regional flood mitigation projects within the District drainage boundary. The District involved a Technical Advisory Committee comprised of floodplain administrators from each of the communities within the District: Williamson County, Leander, Cedar Park, Austin, Round Rock, and Hutto. 

Project Background
After Tropical Storm Hermine hit the area in September 2010, the District applied for and was awarded a grant from the Texas Water Development Board to perform the study.  The study area includes approximately 187 square miles in the Upper Brushy Creek Watershed and contains approximately 139 river miles of creeks with drainage areas greater than one square mile.  The District hired URS Corporation to perform the study.

Phase 1
The first phase of the study included an existing conditions analysis to develop baseline hydrologic and hydraulic models.  These models were used to evaluate future conditions based on land use development plans from each community.  The models were developed using FEMA guidelines and standards.  The Phase 1 deliverables included flood hazard area maps, flood depth grids, and velocity maps for the 10%, 2%, 1%, and 0.2% annual chance 24 hour flood events.  All of the products were provided to the city and county floodplain administrators within the District.

Phase 2
The products produced in Phase 1 of the study were used to assess flood hazards within the Upper Brushy Creek Watershed.  Approximately 25 flood mitigation projects and strategies were developed based on criteria outlined by the District and the Technical Advisory Committee.  Each project was evaluated on cost/benefit and constructability. The results of this analysis were incorporated into the final Upper Brushy Creek Flood Protection Plan.

Phase 3
The District applied for and was awarded grant funding from FEMA through the Texas Water Development Board to refine the products from the Watershed Study to be used by FEMA to create new regulatory floodplain maps for the entire Upper Brushy Creek Watershed.  The data was submitted to FEMA in April 2016.  FEMA's consultant is working on the preliminary flood hazard maps which will be provided to the communities in early 2017.