Willow Creek dam kept much of Norfolk dry during the 2019 flooding. Now, the dam faces a water pressure problem.
The pressure isn’t coming from behind the dam, though, but below it.
Willow Creek dam faces high levels of water pressure coming from the aquifer below the dam, said Mike Sousek, general manager of the Lower Elkhorn Natural Resources District.
“People think that it’s the water in the dam causing this pressure. The water in the dam has no effect on the pressure, it’s the water beneath the dam in the aquifer,” Sousek said. “We could empty that dam out, it could have no water in it and we’re still going to have that pressure issue, because it’s the pressure from the bottom aquifer.”
This pressure could eventually lift the dam up, causing it to fail, Sousek said.
When the dam went into operation in the mid-1980s, there was a system in place to deal with the pressure, Sousek said.
“There’s a whole network of plumbing inside the structure itself. There’s relief wells, there’s piezometers, there’s networks of pipe that tie it all together,” he said. “Piezometers are used to measure the pressure that’s put on the dam, either from the lake itself, but more from the uplift pressure coming from the ground up.”
There were 27 relief wells on the dam that were supposed to drain water from the aquifer into the plunge pool, Sousek said. But over time, those wells stopped working.
The screens that let water into the wells became clogged with sediment and other material. The Lower Elkhorn NRD had the screens cleaned a couple of years ago, but after six months, they became clogged again, Sousek said.
The next option the district considered was putting in new relief wells, but bids for that project came in at around $1 million, Sousek said.
“At that point in time, the board said, ‘No, that’s too much money, let’s find an alternative,’ ” he said. “So for the last two years, we’ve been looking at different things we could do.”
Now, the district plans to install artisan pressure wells on either side of the plunge pool to solve the issue, Sousek said.
“Currently, we’re looking at putting in high-capacity, more or less irrigation wells, that develop these two wells near the center of the dam,” he said. “And that will for sure relieve the pressure right there. That’s the critical part where you don’t want it to bust open. That may solve the pressure issue (as a whole).”
The district will start pumping those wells if they don’t relieve the pressure, Sousek said.
“If two wells don’t do this, the plan is we’ll add two more and we’ll just keep doing this until we get to the level we need,” he said.
The new wells are being designed so the district can do maintenance work on them, and they won’t become clogged like the relief wells, Sousek said.
Sousek said the area’s geology is the reason no one is sure how many wells it will take to solve the problem. He said below the dam there’s a mix of different sediments along with the water.
Still, Sousek said he thinks the district can solve the problem without breaking the bank.
“Doing anything costs money,” he said. “I think by us working with local contractors, maybe incorporating a lot of common sense, we should be able to address the issue.”
The board of directors hasn’t approved any contracts for the project yet, but Sousek expects work to begin on the wells before the end of July, he said.
Willow Creek dam’s importance to the area goes beyond providing recreation opportunities. The 2019 flooding demonstrated this, Sousek said.
“Without that dam the whole diversion project in Norfolk would have failed. The whole eastern side of Norfolk, the part that they evacuated, would have been under water,” Sousek said. “Hadar would have got wiped out, the highways and bridges, I mean some of them did, but it would have just been to a whole other magnitude if that dam was not there. It did its job.”
The dam is nowhere close to failing yet, Sousek said. So far the pressure is the only sign there’s any problem with dam.
“We’re just wanting to make sure it continues to do its job and we don’t have a catastrophic failure,” he said.