The John C. Stennis Lock and Dam is still struggling with damage from a collision with a barge several years ago, U.S. Army Corps of Engineers Navigation Manager Roger Wilson told the Columbus Rotary Club on Tuesday.
A barge broke away from its moorings in high water in June 2021 and struck the spillway.
Damage to the spillway gate was “pretty bad,” Wilson said.
“Several years before that we had the same type of incident, but we were lucky enough not to have quite as much damage,” he said. “This incident caused quite a bit of damage, and we have quite a bit of work to do.”
About half the concrete on one of the apron upstream of the spillway was damaged by the runaway barge, he said.
“It was about 300 feet long by 60 feet wide, and 18 inches thick of concrete,” he said. “About 50 percent of that was damaged, and we had to have salvage companies come in and clean out all that concrete.”
Repairs are ongoing, he said.
“We placed about 4,000 pounds of stone in layers,” Wilson said. “And then we grouted it. We’re about 90 percent complete.”
The Corps still needs to install a one-foot-thick cap of grout over the existing work, he said.
“You may ask what the purpose of that is,” Wilson said. “… There was a big area scoured out. The issue with that is that you have flows coming into the spillway, and it created a path where there could potentially be seepage under the dam. If we experience that seepage, you’re talking about imminent failure.”
The grout is “really, really strong concrete,” he said.
“We basically created a blanket where water can’t penetrate and undermine the spillway,” Wilson said. “Then we went in with the rock, which is designed not to move during high-flow situations. Of course when you put rock in you have voids … and then we went in and locked everything in place.”
The dam is in “really good shape,” but large amounts of rain are preventing that final piece of work from being done.
Wilson estimated work will be done in June or July, when flow through the spillway slows down.
“We’ve got a few days of dry weather, but all the creeks are full and one little rain can kick up the headwater pretty quick,” he said. “We really need about a three or four day window of dry weather before we can go in and finalize that last pour.”
The spillway gate was also damaged, he said.
“It was damaged pretty well, and engineering came up with a temporary patch for us to kick the can down the road,” Wilson said.
“Probably about two years from now this gate is going to be removed and another gate placed in service.”
The work is expected to take about 18 months, he said.
Brian Jones is the local government reporter for Columbus and Lowndes County.
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