LCRA provides flood hazard information for areas between Buchanan Dam and Inks Dam
New study will result in changes to some floodplain boundaries
Sept. 29, 2020
BURNET AND LLANO COUNTIES, Texas – A new floodplain study commissioned by the Lower Colorado River Authority provides updated, detailed information about flood hazards between Buchanan Dam and Inks Dam and identifies a floodway between the two dams for the first time.
Past studies by the Federal Emergency Management Agency of some areas between Buchanan Dam and Inks Lake were not based on detailed analysis and showed only approximate boundaries of floodplain areas. The new information is more accurate and will result in changes to floodplain boundaries, moving some areas into the floodplain for the first time and some areas out of it.
“We want to provide people who live between these dams with a clear and accurate understanding of their risks related to flooding,” said John Hofmann, LCRA executive vice president of Water. “For example, there are neighborhoods built in the shadow of Buchanan Dam’s floodgates, and we want to make sure property owners know the hazards they may face when we have to open those floodgates.”
Flow patterns from Buchanan Dam have historically been difficult to analyze because of the dam’s design. The dam, which is about 2 miles long, has 37 floodgates arranged in three separate sections: the seven-gate section, the 14-gate section and the 16-gate section. The dam also has an overflow spillway. Discharges from the floodgates and spillway flow over land into Inks Lake.
The new study updates flood hazards in two areas:
- The north side of Inks Lake in Burnet County, where water flows from Buchanan Dam’s 14‑gate and 16-gate sections and spillway to Inks Lake. The old information was not based on detailed analysis and shows only approximate boundaries of the flood hazard areas. The new information better identifies where water will flow and for the first time identifies how high the water will rise during 50-, 100- and 500-year floods in these areas.
- Along the length of Inks Lake in Burnet and Llano counties, from Buchanan Dam to Inks Dam. The new information identifies a floodway in this area for the first time. A floodway is the central portion of the 100-year floodplain, where flows are stronger and faster. The floodway should be kept free of new obstructions to allow a 100-year flood to pass.
The new floodplain study uses the latest digital terrain data and flood modeling methods. The model results were confirmed by observations during flooding in 2016 and 2018.
“It’s been more than 80 years since the biggest flood in Buchanan Dam’s history,” Hofmann said. “In July 1938 – less than a year after the dam was completed – a flood prompted LCRA to open 22 of the dam’s 37 floodgates at once. As operators of a series of dams in Flash Flood Alley, we are well aware we could see that kind of flooding again one day. We are sharing this information to help educate residents, emergency responders and others so they can stay prepared.”
With the approvals of Burnet and Llano counties, LCRA submitted the updated flood hazard information to FEMA for approval in the form of a Letter of Map Revision (LOMR). Upon final approval, FEMA will use the LOMR to update its Flood Insurance Rate Maps that identify a community’s flood hazard areas, including floodplains and floodways.
This month, Burnet and Llano counties are notifying affected property owners by certified mail, as required by FEMA. After the notifications are sent, FEMA will publish notices in local newspapers, and property owners and the public will have 90 days to appeal the maps on a technical basis. The revised maps will become effective 30 days after the appeal period ends and all technical appeals are resolved.
For more information and to view the floodplain maps, visit www.lcra.org/floodhazardupdate.
The Lower Colorado River Authority serves customers and communities throughout Texas by managing the lower Colorado River; generating and transmitting electric power; providing a clean, reliable water supply; and offering outdoor adventures at more than 40 parks along the Colorado River from the Texas Hill Country to the Gulf Coast. LCRA and its employees are committed to fulfilling our mission to enhance the quality of life of the Texans we serve through water stewardship, energy and community service. LCRA was created by the Texas Legislature in 1934 and receives no state appropriations. For more information, visit lcra.org.