The District was created to construct and maintain a series of disseminated dams along tributaries of local creeks that address regional flooding. These dams hold rainwater back during storms and release it slowly when it rises, reducing flooding and protecting lives and property.
The original Brushy Creek Water Control and Improvement District (WCID) No.1 of Williamson and Milam Counties was established in 1956 as the local sponsor of 46 planned floodwater retarding structures.
The earthen dams were constructed between 1957 and and 1967 by the Soil Conservation Service (SCS) [now known as the Natural Resources Conservation Services (NRCS)] in Williamson and Milam counties. At that time, the area was mostly rural. Farming and agriculture made up a large part of the local economy.
During the 1980’s, Legislation was passed that required high hazard dams to safely pass the 100% of the Probable Maximum Flood (PMF). The rural economy had largely given way to rapid urbanization as Central Texas grew. As a result, all of the western half of the District’s dams were reclassified as high hazard.
Reclassified to High Hazard-1999
By 1999, most of the District’s dams were classified as high-hazard structures by the state dam safety regulatory agency, the Texas Commission on Environmental Quality (TCEQ). A hydraulic study on the dams performed in 2000 determined that the dams were hydraulically inadequate and passed between 31 and 67 percent of the probable maximum flood (PMF). The study also found that more than 1,100 homes were at risk due to potential dam breaches. Initially, the State required the dams to safely pass 100% of the PMF. (That standard was eventually revised to approximately the 75% PMF.)
Dam Modernization Program-2002
The District had limited resources and no income at the time; it could not afford to repair all of the dams. In 2002, the District sought to implement its taxing authority, and a property tax was approved by taxpayers for 2 cents per $100 of valuation beginning in 2003.
The District developed a risk-based prioritization program to modernize the dams to implement as funds became available. The dam improvements were prioritized based on hydraulic capacity and downstream risk. This approach was acceptable to the state regulatory agency with the addition a flood monitoring system. The modernization program began in 2003 and involved primarily raising the dams to pass the required flood flows. The risk-based prioritization was updated throughout the program to account for continued downstream development.
Flood Monitoring System-2005
To mitigate risk in the interim of the program, each dam was equipped with an early warning flood monitoring system, which was integrated into the District’s website for public access. The first phase was installed in 2005 with the final phase installed by 2011. In 2014, the District upgraded the system to USGS gauges at all 23 dams and added four stream gauges on Brushy Creek and two on Lake Creek. The District’s website has an interactive map that provides real-time reservoir elevations, stream stage and precipitation.
TCEQ adopted new hydrologic and hydraulic guidelines that reduced conservatism in the design storm and made it more economically feasible for the District to modernize all the dams.
Tropical Storm Hermine-2010
In September 2010, Tropical Storm Hermine dropped 11 inches of rain in 24 hours in parts of the Upper Brushy Creek watershed, which then equated to the 0.2% ACE (Annual Chance Event) (aka 500-year storm event). Auxiliary spillways engaged on four of the District’s dams. As a result, the District initiated a watershed-wide study to identify regional opportunities for additional flood mitigation. The District was awarded a grant from the Texas Water Development Board to perform the study.
The District performed a watershed-wide hydraulic study to assess the impacts of the dams on the watershed. The study confirmed the flood control benefit of the dams and identified additional flood control projects to increase protection to the public, including multiple new flood control structures. For this study, the District assembled a technical advisory committee consisting of the cities in the watershed. Even though the study is complete, the committee continues to discuss and collaborate on regional issues. The study also led to revised FEMA floodplain maps; the District received a grant from FEMA to upgrade the data and prepare preliminary maps. The maps became effective in December 2019. Click here for more information about flood maps.
Final design for the modernization of the District’s largest and most visible dam began in 2013. The dam is a popular recreational destination due to an adjacent city park as well as a hike-and-bike trail that crosses the dam. An innovative design was required to modernize Dam 7 due to the development around the dam and constrained easement area as well as needing to accommodate the trail system. A labyrinth weir was selected as a practical solution due to its ability to maximize discharge within a limited footprint. (Construction occurred in 2016-2018.)
Risk Based Assessments-2017
The District initiated a risk-based comprehensive assessment of the dams to identify deficiencies and prioritize rehabilitation, maintenance efforts and funding for the next 10 years. Prioritization will be based on evaluations of risk associated with updated hydraulic loading, potential dam failure modes and resulting consequences. (The study was finalized in early 2020.)
Going Forward-2020 and beyond
As of 2020, all the dams except one have completed modernization efforts. The final dam requiring modernization to meet the TCEQ Dam Safety regulations will start construction in 2020.
The two new flood control structures identified in the watershed-wide flood study reached the 30% design milestone. Dam 101 is currently under final design which was funded by the City of Round Rock. (Construction funding has not been identified.)
In addition, the District continues to perform regular maintenance and technical inspections of all its dams.