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Snowpack Has Upper Basin Dam Managers Looking For Ways To Avoid Flooding During Peak Runoff
Posted on Friday, April 29, 2011 (PST)

The U.S. Army Corps of Engineers will ramp up releases from Libby Dam, possibly in an unusual way, to ensure that flows can be curtailed during the peak runoff to avoid flooding on the Kootenai River.

 

Operations at dams across the Northwest have adjusted operations to account for unusually high snowpack and precipitation.

 

Libby Dam already has been operated to draft Lake Koocanusa 100 feet below full pool, but releases from the dam will be increased to keep up with expected inflows from a high-elevation snowpack that is 128 percent of average and a low-elevation snowpack that is 153 percent of average.

 

“Forecasts suggest we could see significant rapid rises in reservoir elevation, up to eight feet per day, by mid-May through July,” said Joel Fenolio, Upper Columbia senior water manager for the Corps. “The Kootenai River may be at or near flood stage for a period of time starting mid-May. Downstream tributaries to the Kootenai which are not controlled by Libby Dam, such as the Yaak, Moyie and Fisher rivers, are expected to be at or above flood stage as well.”

 

Those rivers and other Kootenai River tributaries fed by low-elevation snowpack complicate the flood control picture greatly, said Mick Shea, project superintendent at Libby Dam.

 

“That low-elevation snowpack ... that’s the 500-pound gorilla in the whole mix,” Shea said. “In the historical record in the Kootenai Bbasin below Libby Dam, we haven’t had this much snowpack this late ever, or at least on record.”

 

Flows at Libby Dam will have to be held back substantially when it gets warmer and runoff picks up in those drainages. Planning for that period is all focused on protecting Bonner’s Ferry, Idaho, by preventing the Kootenai River from exceeding the flood-stage surface level elevation of 1,764 feet.

 

Dam operations have been complicated this year because one of the turbine generating units has been broken down for about five weeks. The remaining four turbines have not been able to operate at full capacity because the reservoir is so low.

 

 

Releases through the powerhouse have been at capacity at about 17,000 cubic feet per second for the last few days. The dam’s normal powerhouse capacity is 25,000 cfs. Now the Corps is considering an unusual alternative for releasing more water — using the dam’s sluice gates.

 

Shea said that if the Corps needs “to use those sluice gates, we will. And we will probably make that decision over the weekend and could see them go into operation by Monday.”

 

The problem with using the sluice gates is the water will be cooler than normal releases and it will tend to “gas the river” below the dam with potential harmful effects on fish. Past releases of water over the dam’s spillway have shown to start having effects on fish after about a week.

 

Because of this year’s abundant water supply, Shea said the dam may not go into its annual boosted releases to improve spawning conditions for Kootenai River white sturgeon.

 

“We could very well see the normal spring sturgeon operation being totally overtaken by a flood control operation,” he said. But the result would be the same, because there would still be high flows in the primary spawning stretches near Bonners Ferry.

 

Meanwhile, Hungry Horse Dam releases have been unusually high, around 10,000 cfs, since the first week of April.

 

Dennis Philmon, the dam’s facility manager, said because there is confidence that Hungry Horse Reservoir has adequate storage capacity, flows will be reduced to 8,000 cfs by next week. Releases will be further curtailed as the runoff picks up on the other forks of the Flathead River system.

 

Hungry Horse Reservoir is currently at 3,477 feet, about 83 feet shy of its full pool elevation of 3,560.

 

The Bureau of Reclamation normally tries to get the reservoir near full pool by the end of June, but this year refill is not expected until mid-July, Philmon said.

 

At the lower end of the Flathead River system, Kerr Dam has been releasing beyond powerhouse capacity since April 12.

 

“Right now, we are releasing the maximum that we can at the level we are at,” said Deb Mullowney, resource coordinator for PPL Montana. “We’ve been spilling since April 12. We are past the turbine capacity of the plant so we are releasing beyond what we are able generate.”

 

Even more water can be spilled, but not before inflows pick up into Flathead Lake, because of channel restrictions in the river flowing to the dam from the foot of the lake.

 

“Once the lake is higher we can release more, but we are releasing everything we can right now,” Mullowney said.

 

Flathead Lake is at 2,886 feet, about seven feet shy of its full pool elevation of 2,893.

 

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