DWORSHAK OUTFLOWS REDUCED TO SAVE FOR LOW-FLOW SUMMER
Posted on Friday, June 01, 2007 (PST)

Flows from central Idaho's Dworshak Dam were ratcheted down slightly Thursday and will be nearly halved this evening at the request of fish managers, who want a secured cache of reservoir water to cool Snake River reaches downstream later this summer.

The U.S. Army Corp of Engineers on Thursday throttled back the flow through the dam's three power generating units from 5,300 cubic feet per second Wednesday to 4.2 kcfs Thursday and plan to run only a single unit, about 2.6 kcfs beginning this evening, according to Cindy Henriksen, chief of the Corps' Reservoir Control Center.

She predicted that the reservoir could be within two feet of full toward the end of next week, well ahead of the previously planned refill schedule, unless some unforeseen weather event occurs.

The cool water deep in the reservoir on the North Fork Clearwater River is depended upon each summer to augment flows in the Snake River for migrating juvenile and adult salmon and steelhead. The Clearwater flows into the Snake at the Idaho-Washington border at Lewiston.

Temperatures in the Snake often rise to levels that are unhealthy for the coldwater salmonids, which include salmon and steelhead stocks that are listed under the Endangered Species Act.

The upper Snake's water supply this year is predicted to be miserly, the most likely scenario being only 16.1 million acre feet or 67 percent of the 30-year average as measured at Lower Granite Dam from April through September, according to the Northwest River Forecast Center's May 31 runoff forecast. Lower Granite is the first federal hydro project below the Snake-Clearwater confluence.

Flows past Lower Granite apparently peaked in May.

"That particular flow is receding," Henriksen said. Lower Granite reservoir inflows reached as high as 100 kcfs on May 10 but have since steadily declined. The last day of May had inflows at 58.6 kcfs.

"It's going to be a low flow summer and the Snake River is heating up," NOAA Fisheries' Paul Wagner said Wednesday in urging a quicker fill-up of Dworshak reservoir. "It's going to be a struggle this year."

Henriksen, during a Wednesday meeting of the Technical Management Team, said that the Corps' plan to hold outflows at 4.6 would still bring the reservoir up to full pool by the end of June, and reserve space in the event of a rain "event" or events that might spike inflows.

The Corps' most probable streamflow scenario, calculated May 1, says the May through July Dworshak inflows will be about 66 percent of average. Inflows have dropped from a peak of 16.7 kcfs on May 13to 8.9 kcfs Thursday.

"There's no space, no options" for avoiding spill at the dam if the reservoir is full and Mother Nature chooses to increase reservoir inflows, Henriksen said. If the inflows are higher than the powerhouse capacity to pass water, water must be spilled to ward off flooding.

The Nez Perce Tribe's Dave Statler urged Henriksen to boost the reservoir as high as possible, and as quickly as possible. He noted that the reservoir was well below its flood control target of no higher than 1,595 feet at the end of May. The reservoir rose from 1,591.4 to 1,591.9 from Wednesday to Thursday. Maximum pool is 1,604,7; full pool is 1,600 feet.

Russ Kiefer of the Idaho Department of Fish and Game noted that the NOAA Climate Prediction Center's latest forecast calls for below average precipitation in the region over the next month.

"I believe it's going to be tough in the later part of June" to top off the reservoir, he said. "I think the risk of us having to fill and spill is going to be pretty darn low."

The Corps agreed to the early fill up plan, Henriksen said, though opted to maintain a two-foot buffer against spill risk – the equivalent of about 40,000 acre feet of water.