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BOISE — Idaho Power Co., under direction from the U.S. Army Corps of Engineers, is lowering Brownlee Reservoir to make room for spring runoff.

At 58 miles long, the reservoir extends from Brownlee Dam in Hells Canyon upstream to Farewell Bend, Ore. Water stored there is critical to Idaho Power’s hydroelectric system, which is the company’s largest source of electricity.

Beginning in January each year, Idaho Power lowers the reservoir as part of the Columbia Basin regional flood-control plan directed by the USACE. How far and how fast the reservoir is drafted depends largely on mountain snowpack that feeds the Snake and other rivers in the Columbia Basin.

The preliminary draw-down requirement is 2,045 feet by the end of February, which is 20 to 25 feet below the current elevation and 32 feet below full pool. The official end-of-February draw-down level will be set earlier in the month. March and April elevation targets will be set later as the snow-pack develops. Snow-pack is now below-normal upstream of Brownlee Reservoir, which could mean a less dramatic draw-down than was seen last year.

The draw-down comes at a time when stream-flows in the mid-Snake River are higher than normal for this time of year, as upstream reservoirs with above-average carryover release water to meet winter storage targets and make room for spring runoff. The result is higher-than-normal flows below Hells Canyon Dam where daily average flows are expected to range between 18,000 and 25,000 cubic feet per second through January.

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