Lake Limestone's dam gate replacement project kicks off
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This fall, visitors and residents of Lake Limestone will begin to see construction work take shape on the east side of the Sterling C. Robertson Dam at Lake Limestone. Crews will be creating a construction ramp off the emergency spillway that will allow the assembly and launch of a work barge to transport and support a crane and, ultimately, five newly fabricated flood gates for the 44-year-old 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 more than 40 years old. The ultimate goal is to keep the dam operating safely and at a high level for the next 40 – 50 years."
The process of replacing the gates began when periodic inspections identified a need to address the aging metal of the existing gates. The gates were simply beginning to show the wear and tear associated with decades of water exposure. "Engineering work was conducted to determine whether we should attempt to repair the existing gates or replace them with new gates. Ultimately, we decided complete replacement was the best long-term option to keep the dam operating as designed for many decades to come,” Brunett said.
"We then began detailed engineering design work for complete gate replacement several years ago," Brunett said.
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. Dam safety is our highest priority."
The design contract was negotiated with Stantec, Inc., an engineering firm that has performed numerous projects of this type, Brunett said. Once the company completed the evaluation and design, a request for bids was published earlier this year to select a contractor for the project, which will entail removal of the existing gates as well as fabrication and installation of the new gates, along with some other associated work.
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The five new flood gates will look very much like the current Tainter-style gates now in place on the dam. Named after Jeremiah Tainter of Wisconsin, who designed the style of gates now used worldwide, the metal structure uses a convex shape that is bowed toward the upstream side of the dam. When rotated upward, water passes under the gate. The long radial arms and bearings allow the gates to close with less effort than a flat surface.
As part of the project, construction will also include replacement of the hoist systems that raise and lower the gates.
The new gates will be fabricated in Houston, then transported to the reservoir for installation.
The benefits of replacing the gates (rather than simply repairing them) include fabrication and painting of the metal structures in a controlled shop environment. A new cathodic protection system will also be installed to further protect the new gates. The off-site assembly allows for the highest quality and minimal interface with existing equipment.
Another plus is that the equipment can be customized for the best installation results with minimal onsite welding and painting required.
"The metal (for the new gates) is already at the fabrication shop," said Brunett. "They're going to be building 5 of these gates, so there is a lot of prep work in terms of cutting all the metal and assembling the pieces to engineering specs. It's not a day or two of work; it's a long process."
Early stages of building the new gates are underway, and installation of the first gate is expected in the spring of 2023. The gates will be replaced one at a time, so four of the five gates will be available to release water if there are flood events over the course of the project. The last of the five gates is expected to be replaced in the summer of 2024.
For those hoping to visually follow the progress of construction, there won't be much to see since access to the dam's downstream side is not open to the public. However, much will be visible from the lakeside, but people and watercraft will still need to stay out of the restricted area marked by the buoys in front of the dam.
One of the challenges of the project is that the heavy gates will require a large crane to complete the work.
This shows the installation of a gate at the reservoir when originally constructed.
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"They'll do all the work from the dam's upstream side," said Reservoir Manager John Dickson. "You'll be able to see two barges. A crane will be put on one, and it will move down the dam as they work on each gate. There will also be a materials barge that will move the old gates off the dam and bring the new gates into place."
While under construction, crews will use a "stoplog," a hydraulic engineering control much like a temporary wall to keep the water from flowing downstream once the old gate is removed.
"The level of the lake will not be lowered for construction," said Brunett. “The project will be completed at whatever the lake elevation is over the next couple of years, given flood or drought conditions.”
Once completed, residents and visitors will notice little change in the dam structure or Lake Limestone.
"The new gates are designed for the lake to continue operating at 363 feet mean sea level," said Dickson. "So, once they're replaced, everything will look just like it always has. We are just extending the life of the dam and the lake for years to come."
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.
The project is slated for completion in 2024.