Up And Down Summer For Dworshak Corps Will Drop Reservoir Level In Midsummer To Repair Dam
Dworshak Reservoir will be nearly full by mid-June, the Army Corps of Engineers predicts, but its stay at the top will be short-lived.
A popular recreation destination for boaters and campers, the reservoir will be full for the Fourth of July but will take a dive soon after.
Lt. Col. Donald Curtis, Corps of Engineers Walla Walla District commander, said the corps hopes to keep the reservoir full as long as a week after the holiday if conditions permit. But a drawdown will be required for a project to seal leaks in the bedrock beneath Dworshak Dam, he said.
If the flow of the Clearwater River’s North Fork drops enough, the corps will be able to keep the reservoir high, then release a lot of water quickly to pull the level down about 70 feet by Aug. 15.
The quick drawdown will be possible because the corps has received a waiver to exceed Idaho water quality standards for dissolved gas levels set by the state Division of Environmental Quality.
In the past, the state has balked at allowing the corps to release so much water from the reservoir. But the objections, based on fears that fish downstream would suffer damage from excessive dissolved gas levels, have been set aside this summer.
“We don’t see any reason to wave a red flag yet,” said Tim Cochnauer, fisheries expert for the Idaho Fish and Game Department who has monitored gas-bubble trauma in fish below Dworshak for two years.
As a result, Dworshak can stay higher longer, then be pulled down quickly.
Work on the $5.1-million grouting project is scheduled to begin July 15, said Everett Wright, the corps’ lead dam safety official for the district. By Aug. 15, the corps wants the reservoir down 70 feet so contractors can begin injecting concrete grout into cracks in the bedrock beneath the dam.
By Sept. 15, the corps plans to lower the reservoir 100 feet below full to make the work easier still.
A 1995 attempt to grout the cracks failed when an early December flood caused the reservoir to jump dramatically, forcing work to stop.
Corps officials have repeatedly said the dam is in no danger of failing. But Wright said the project needs to be completed soon to prevent a more-costly fix or a possible safety problem later.
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