In central Washington state, teams of engineers are scrambling to figure out what’s gone wrong with part of the Wanapum Dam’s spillway structure.
The problem with the dam is on a structure called the ogee, a big piece of concrete that is anchored to the bottom of the river. It has a big curve on the top where the water flows over it.
It’s like a river speed bump. When the spillway gate is lifted, the water flows through from the upriver side of the dam to the downriver side over this ogee. This is how dam operators let extra water through the dam that’s not needed for power production.
Searching for answers
But the ogee is cracked all the way across its upstream face, underwater. The dam operators and engineers aren’t sure how deep the crack goes back into the massive concrete hump, but that’s what they are trying to figure out.
“Right now the main focus is that particular area," says Chuck Berrie, who helps manage the dam for the Grant County Public Utility District. "But we are going to do a complete and thorough evaluation of the structure before we’re through.”
Berrie says there are three teams of engineers working on the dam -- county engineers, a federal team and an independent panel of experts from across the U.S. They don’t have any answers yet and Berrie wouldn’t speculate on what they could be.
Still, what’s troubling to experts on dams and concrete structures is that the ogee is not only cracked, it has slipped a little.
Rob Shogren is the technical director at a French-owned concrete company called Lafarge International. If it’s big and it’s concrete in the west, there’s a good chance Shogren has worked on it or knows about it.
He says cracks in concrete dams aren’t unusual but he adds, “A two-inch thick crack can be significant. It just depends on where it is in the structure, how deep it goes and what caused it.”
And what’s caused the mighty crack in the Wanapum Dam is the big question.
A "sunny day scenario"
John Osteraas, a reknowned disaster expert who has worked on the aftermath of Hurricane Katrina and the Oklahoma City bombing, doesn’t like the sound of what’s happening at Wanapum.
“We’ve certainly over history seen some fairly spectacular failures of dams," he says. "There is an enormous amount of energy stored in the water behind the dam.”
What troubles Osteraas, is that the dam failed with no clear cause. It's what disaster experts call a sunny day scenario.
“When things just fail in the normal course of events, under loads and forces that we thought were in the safe region," explains Osteraas. "Then we have to be much more aggressive, much more thorough in our inspection to make sure we understand the total picture.”
Osteraas says a good move right now would be to reduce the water between Wanapum Dam and the next dam downriver, Priest Rapids. That would create a space between the two dams for the extra water if Wanapum was to fail.
Grant County’s Chuck Berrie would not say if that was happening. But argues that even if part of the dam was to fail it would not create a tidal wave downstream. "That is not a situation that would happen at all.”
Berrie believes if the ogee topples, the rest of the dam should remain in place. When asked about the contingency plan for what happens if the dam does bust, county officials say they have drills and plans, but they aren’t sharing a lot of specifics.
Looming snowmelt
They are certainly not sharing them with Steve Allen, a major employer in the area who lives about three miles downstream from the dam. His farmhouse overlooks the Columbia River and his 100 acre apple and cherry orchard rolls out below. His eyes betray his worry about the dam.
“If it broke, if it actually came apart, my orchard would be severely affected," says Allen. "It’s only 10 or 15 feet above the water level. It would wipe out my orchard probably.”
Back at ground zero, the Wanapum Dam looks like it has on any normal day. There are a few orange traffic cones and signs. But that’s it.
Confidential sources within the federal government say the last government review of the dam’s overall safety found no significant findings. But the coming months could get complicated for dam engineers’ Band-Aid efforts.
Right now, the mighty Columbia River is at its low winter levels. But soon spring snowmelt will swell the downstream river flows and sensitive salmon runs will be making their way up stream.
