Floodgate replacement planned for Lake Limestone’s Sterling C. Robertson Dam

After a decade-long gate replacement program at Possum Kingdom Lake’s Morris Sheppard Dam, the Brazos River Authority will begin work to replace the five floodgates at Lake Limestone’s Sterling C. Robertson Dam. The project is part of the BRA’s ongoing efforts to maintain and update the aging infrastructure that creates the system’s water supply reservoirs.

“It’s important for everyone to know that the dam is safe and the gates are currently working correctly,” said Brad Brunett, Central and Lower Basin Regional Manager for the Brazos River Authority. “But it’s time to replace the gates, which are now 40 years old, so we can continue to operate the reservoir efficiently far into the future.”

All five gates will be replaced with the installation being done one at a time, Brunett said.

“That will allow us to continue to pass water through the floodgates as needed for the duration of the project,” he said.

The floodgates are often referred to as Tainter gates, named after Jeremiah Tainter of Wisconsin, who designed the style of gates now in use worldwide.

The need for the Lake Limestone project was first identified during a comprehensive corrosion study of the Sterling C. Robertson Dam. The study recommended repair of not only metal corrosion in the gates, but also recommended replacement of the floodgate rollers that help maintain the seal between the gate and the dam structure.

In addition to improving the long-term protection of the gates and enhancing the quality of the Sterling C. Robertson Dam, the project may also improve access to the floodgates to help with future routine maintenance work. The approved cost of the engineering and design phase of the project is just over $4.2 million.

According to Brunett, the biggest challenge to the project is working with the size of the massive gates -- each of which is about 40 feet wide and 29 feet high.

“The sheer size and weight of the gates makes for an interesting replacement process,” he said. “This is a high priority for us because although the dam is safe now, we want to make sure that continues well into the future. After 40 years, it’s time for replacement. Dam safety is our highest priority.”

There are no plans to lower the lake elevation as part of the Tainter gate replacement project. BRA will use bulkheads to isolate each gate from the lake while it is being replaced, so lake levels will not be impacted.

The Brazos River Authority Board of Directors approved a contract with Stantec Consulting Services, Inc. at its April 30, 2018 meeting for the engineering and design work to replace the floodgates and evaluate rehabilitation of the gate hoist systems. Stantec was selected to perform the work based on their experience and expertise with such projects. The company has completed 25 similar projects in the past 17 years, including 14 Tainter gate projects.

“Their overall experience in doing this type of work and their recent experience in replacing Tainter gates led to Stantec being selected to complete the work,” Brunett said.

The Sterling C. Robertson Dam was built on the Navasota River (a tributary of the Brazos River) to form Lake Limestone in the 1970s. Replacement of the gates and other rehabilitation work will help ensure the structure’s longevity.

Benefits of replacing the gates (rather than simply repairing them) include fabrication and painting of the structures in a controlled shop environment to allow for the highest quality, and minimal interface with existing equipment that will lower the risk of fit-up problems. Another plus is that the equipment can be customized for the best installation results with minimal onsite welding and painting required. One of the challenges is that the heavy skin plate and girder assembly will require a large crane to complete the work, and favorable weather conditions will be required.

From start to finish, the project is expected to take about three years.