Fish Flush Set at Dworshakby Eric Barker
Lewiston Tribune, May 18, 2010
Extra water expected to give salmon and steelhead smolts a push downstream
Flows on the lower Clearwater River will jump by 10,000 cubic feet per second Wednesday as water is flushed from Dworshak Reservoir to help juvenile salmon and steelhead migrate downstream.
A group of juvenile fish passage experts who monitor salmon and steelhead smolts as they move down the Snake and Columbia rivers requested the flow augmentation Monday.
"The purpose of the operation is to provide a fish flush - increased flow for moving juvenile fish out of the system," said Steve Hall, senior water manager for the U.S. Army Corps of Engineers at Walla Walla. "They seem to be holding up someplace in the Lower Granite pool."
In 2005, another low-water year, 10.5 million smolts were recorded passing through the juvenile fish passage facility at Lower Granite Dam. This year, only about 2 million smolts have been recorded.
So the corps will begin releasing 10,000 cfs from Dworshak Dam on Wednesday and continue the flows through Friday. Hall said the goal is to get flows at the dam in the 70,000 cfs to 100,000 cfs range.
"Data shows juvenile fish tend to take that kind of flow as a signal to move out, and we typically see more fish migrating downstream when we reach those flows."
Lower Granite Dam has been averaging between 50,000 to 60,000 cfs in recent days.
The increased flows are timed to mesh with forecasts calling for increased natural flows from the Clearwater and Salmon river basins.
"The plan is to add the Dworshak water right on top of that when the flows peak," Hall said.
But the flows will hurt the chances of Dworshak Reservoir refilling this spring. The corps previously predicted the reservoir would only come within about 10 feet of full pool this year. But Hall said a wet and cool April significantly improved the chances of refill. If current predictions come true, he said the dam would have an extra 50,000 acre feet of water without the increased flows. The three-day fish flush will use an estimated 57,000 acre feet.
Even with the flush, Hall said the reservoir still has about a 50 percent chance of reaching full pool. He said the increased flows will rob the reservoir of about 3 feet in elevation.
"I think there is still a possibility we will hit (full pool) this year," he said. "We don't know if we will or not. Based on the water supply forecast we should come very, very close."
Water from Dworshak Reservoir is used every summer to help cool the Snake River and push juvenile fall chinook toward the ocean. Starting about July 4, the reservoir is lowered 80 feet each year. The annual drawdown makes it difficult for boaters who camp on the shores of the reservoir and has been blamed for a decrease in recreation there.
The operation this week is designed to help spring chinook and steelhead. Hall said the summer drawdown will still occur but the three-day flush would be the only spring flow augmentation from Dworshak.
"The salmon managers have given us their word that this is the only request they are going to give us before we start drafting for summer releases," said.
The increased flows on the Clearwater River will change fishing conditions for anglers targeting adult spring chinook. The river is unusually low this year.
Larry Barrett, a fisheries biologist for the Idaho Department of Fish and Game at Lewiston said higher water can improve chinook fishing but the flows this week will be short-lived.
"I think people used to fishing the Clearwater in high water will welcome it but it will be a challenge because it's only three days," he said. "People will get used to fishing that and it will go back to low water."
Corps officials will conduct an information meeting from 6:30 to 7:30 p.m. at the Best Western River's Edge Hotel in Orofino tonight to answer questions about the operation.
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