The lower Colorado River basin has a higher risk of flooding than most regions of the United States. Over the decades, LCRA has developed an intricate system of dams, lakes, information gathering and experience that strengthens its ability to forecast floods and manage them.
LCRA also is working with cities, counties and state and federal agencies to reduce the likelihood of flood damages.
The dam, lake and river system
Since their completion in 1941, Mansfield Dam and Lake Travis have protected downstream residents by reducing the force of floods by holding water that would otherwise inundate downstream regions. The dam and the lake are the only facilities in the lower Colorado River basin specially designed for flood control. This means Lake Travis includes a significant flood pool -- from 681 feet above mean sea level, the level when the lake is considered "full" to the top of Mansfield Dam and higher. The lake's flood pool can hold more than 240 billion gallons of floodwaters below the spillway, which is at 714 feet msl, and more than 640 billion gallons of floodwaters below the top of the dam, which is at 750 feet msl.
The Highland Lakes and dams viewed from the side look like stair steps or cascading waterfalls. Each lake backs up to the one upstream. During normal operations, this is just an interesting characteristic. During floods, however, each dam's operations may have an immediate impact on the next lake and the people living there. Each pair of dams — Buchanan and Inks, Wirtz and Starcke, and Mansfield and Tom Miller — operate in tandem.
LCRA manages floods from two centers:
- The River Operations Center (ROC) in Austin determines what reservoir releases must be made every day to meet water supply and environmental flow needs. During a flood the ROC also forecasts lake levels and determines what flood releases will be made to manage the flood in accordance with federal rules and LCRA procedures.
- The Hydro Operations Control Center (HOCC) at Buchanan Dam controls the hydroelectric generators and is LCRA's 24-hour eyes and ears for conditions on the river and lakes. In lesser floods, the HOCC releases water through the hydroelectric generators to supplement the Central Texas power grid. When conditions call for opening floodgates, the HOCC dispatches crews to open them manually. The 24 floodgates at Mansfield Dam each are 8 1/2 feet in diameter. It takes about 8 minutes to open or close each one.
Other ways to minimize risk
But dams and other flood management facilities do not eliminate flood damage. They are only part of the solution. Another part is wise floodplain management. Texas ranks second in the nation (behind Louisiana) for the number of flood-prone structures that flood repeatedly, according to the Federal Emergency Management Agency. To keep property and lives out of danger, it is the responsibility of local county and city governments to provide information people who live and work on the Colorado River and to regulate development.
To help reduce the damage from floods, LCRA is:
Information and expertise
Since the devastating floods of the 1990s, LCRA also has developed an elaborate system of data gathering and dissemination that takes advantage of technology and human experience. Bob Rose, the staff meteorologist, is the first line of information, providing weather forecasts that alert river operators to prepare for the possibility of flood operations. LCRA staff stay on 24-hour duty when weather threatens.
As rain begins to fall, the Hydromet, a system of more than 250 automated weather and river gauges spread throughout the basin, transmits data through a network of 900-MHz radio towers to a central computer system. In addition to supplying information in near real-time to LCRA's Web site, the Hydromet data feeds a computer model. The ROC uses the model to forecast what will happen on tributaries, such as Sandy Creek and the Llano and Pedernales rivers, which feed into the Highland Lakes and how this will affect lake levels and flood operations at the dam.
This stream of data allows LCRA, the National Weather Service (NWS), local emergency management officials and others to closely monitor rapidly changing conditions and frequently update forecasts and response plans. LCRA helps the NWS share information with the public through recorded messages, news releases, phone banks, and weather radio broadcasts.
Based on this data and information from NWS, the ROC issues orders for floodgate operations according to standard operating procedures established by the U.S. Army Corps of Engineers.