Dworshak Drawdown to Start Tuesday
by Eric Barker
Lewiston Tribune, June 30, 2010
According to a tentative plan, the level of Dworshak Reservoir will start dropping Tuesday.
A group of salmon and water managers tentatively agreed Wednesday to hold the level of the lake at full pool through the Fourth of July weekend by equalizing stream and river flows into the reservoir with outflows from Dworshak Dam.
However they also agreed to hold outflows from the dam to at least 4,000 cfs even if inflows drop below that level. Starting Tuesday the dam will pass about 7,000 cfs through its power house. Infows are projected to drop to 2,000 to 3,000 cfs by July 11.
Paul Wagner of NOAA Fisheries said the flows from Dworshak should start Tuesday even though the lower Snake River has remained relatively cool this spring and early summer. Water at Lower Granite Dam has been around 60 degrees the past few days.
Wagner said there is often a four or five day delay between ramping up flows from Dworshak and temperatures droping in the lower Snake River. Because of that he said it is prudent to start the cooling flows now to make sure water managers stay ahead of rising temperatures.
But the Nez Perce tribe has asked that the dam continue to pass inflows through July 11.
Each summer Dworshak is dropped about 80 feet below full pool as water is pulled from the reservoir to cool the lower Snake to aid juvenile fall chinook and returning adult steelhead. The aim is to keep the Snake River at or near 68 degrees.
Without the flows and sometimes with them, temperatures sometimes reach into the 70s that can be lethal for salmon and steelhead.
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