From 1990 to now, the Highland Lakes chain has experienced 17 flood events requiring the Lower Colorado River Authority to open floodgates at one or more of its dams, LCRA said in a report.
Click the image to see the Highland Lakes chain and dams:
Since the mid-1990s through LCRA’s fiscal year 2017, LCRA has invested more than $134 million in dam improvements and plans to spend another $39.3 million from FY 2018 through FY 2022 on dam rehabilitation projects, the report said.
The role of the LCRA
The Texas Legislature created the LCRA in 1935 to address flooding on the Colorado River, provide a source of reliable water and generate electricity through a series of dams.
“Before the LCRA, Central Texas did not have electricity,” said Bill Lauderback, LCRA’s vice president for public affairs. “In the establishment of the dams along the river, two supply reservoirs were created—Lake Travis and Lake Buchanan.”
A water supply reservoir is a body of water designated for supply, meaning it is going to fluctuate in elevation, Lauderback said. The rest of the Highland Lakes are considered pass-through reservoirs and have more consistent elevation.
“[Supply reservoirs] are designed because we live in Central Texas where there are two phenomena—we are either in periods of drought, or we are in periods of a lot of rain,” he said. “When it is raining, we must have the ability to capture that water and hold it so it is available to us when it is dry.”
Operating past 100 percent
Lake Travis is well into its flood pool as of Thursday and is projected to rise to between 705 to 710 feet above mean sea level by this Friday, according to a press release from LCRA.
Water would flow over the spillway of Mansfield Dam should Lake Travis rise above 714 feet above mean sea level (feet msl).
During floods, LCRA operates Lake Travis and Mansfield Dam under U.S. Army Corps of Engineers regulations and protocols. Depending on how much is in the Lake Travis flood pool as well as downstream conditions, these protocols determine how much water LCRA may release, according to information on its website.
LCRA makes controlled releases of floodwater through Mansfield Dam using any combination of three hydroelectric generating units and 24 floodgates, the information said.
Releases from Lake Travis will cause higher levels in Lake Austin, Lady Bird Lake and the Colorado River downstream of Austin. Water released from Mansfield Dam will travel down the Colorado River to Matagorda Bay.
Under typical conditions, water released from Mansfield Dam would take about one day to get to Bastrop, two days to Columbus, four days to get to Wharton and five-plus days to reach Matagorda, the LCRA press release said, but travel times will be faster because the area is in a flood.