Dam Safety Program

Since 1957, the Upper Brushy Creek Water Control and Improvement District (the District) and its predecessor district have effectively managed the 23 dams in its jurisdiction. All of the District’s 23 dams were constructed between 1959 and 1967. Beginning in the 1980s, federal and state laws were enacted that required significantly more stringent design standards for dams to protect public safety and property. Several sites were inspected by the U.S. Army Corps of Engineers and declared “unsafe” if overtopping occurred during the probable maximum flood event. The purpose of the District’s Dam Safety Program is to upgrade the existing dams to these newer, more stringent design and safety regulations.

History


The state’s dam safety rules, updated in 2009, allowed for a variance to the Probable Maximum Flood (PMF) design criterion if dam owners can prove that economic and physical limitations prevents them from complying and that they are capable of protecting the public's safety.

In 2000, the District completed an assessment of its dams and began developing a dam safety program to satisfy state dam safety rules. The 2000 study estimated it would take nearly 30 years to structurally upgrade all of its dams to safely pass the PMF at a cost of $65-98 million.

Faced with limited economic resources and a sense of urgency in addressing public safety, the District adopted the following project approach:
  • Implement the Dam Safety Program using a variance of the existing dam safety rules requiring all high-hazard dams to safely pass 100% of the PMF. In May 2003, the Texas Commission on Environmental Quality (TCEQ) granted the District the first-ever variance allowing District dams to pass 50% PMF, with conditions.
  • Upgrade the high hazard dams to safely pass the 50% PMF and install a flood monitoring system at each dam per the approved variance.
  • Complement structural upgrades by developing emergency action plans, formal operation and maintenance programs, formal instrumentation and monitoring programs, flood monitoring systems, dam inspection programs, and public education.
  • Establish a 10-year program to modernize all of the Districts' dams.

Updated Program


In January 2007, TCEQ published new “Hydrologic and Hydraulic Guidelines for the Design of Dams in Texas.” The Guidelines present standards and acceptable procedures for the hydrologic and hydraulic analysis of existing dams. One of the most significant chapters is related to the determination of the design flood precipitation and, more specifically, to the temporal distribution of the rainfall. Basically, this guidance document provided new assumptions for how fast the Probable Maximum Precipitation (PMP) falls during the storm and can change the magnitude of the probable maximum flooding events.

The District reevaluated all of its dams using the new hydrologic design criteria to determine the potential impact to the Dam Safety Program, including the five dams it upgraded to 50% PMF since the Fall 2003. New models indicated that the new temporal distribution reduced the PMF in the District’s dams. In fact, the reduction was significant enough that the District modified the program approach to provide 100% PMF protection to all dams as long as the construction costs and funding will allow the program to be completed within the original 10-year window. Further, even though the dams will meet all of the state design criteria and not utilize the variance from the dam safety rules, the District will continue to maintain and operate the flood monitoring systems at each dam for the benefit of the local jurisdictions and general public.

Program Status


The program is currently on track with the original, projected 10-year schedule. As of 2007, flood monitoring systems have been installed and commissioned at all 21 high hazard dam sites and a public Website has been established to provide current rainfall and reservoir level data. As of January 2012, 19 of the 21 high hazard dams have been upgraded to safely pass the 100% PMF and design is underway for the next 2 modernization projects.