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Dworshak Water Releases to Cool Down Snake River Begin by Mike O'Bryant Columbia Basin Bulletin - July 11, 2003

A shot of cold water from Dworshak Dam on the North Fork Clearwater River was released this week to help cool water in the lower Snake River.

Flows from the dam's reservoir, which is nearly full, increased from minimum flows to 14,000 cubic feet per second on Wednesday (July 9).

River temperatures at the Lower Granite Dam tailwater on the Snake River, the first dam downstream of Dworshak Dam, hit 67 degrees Fahrenheit Wednesday morning and the annual summer release of water from the dam is used to ensure the water stays below the water quality limit of 68 degrees (about 20 degrees Centigrade).

That operation, which is in keeping with NOAA Fisheries 2000 biological opinion, could continue through August 24 based on modeling by the U.S. Army Corps of Engineers. However, the Nez Perce Tribe and Idaho Fish and Game are asking that cool water releases extend into September in order to provide good conditions for returning adult salmon and steelhead.

Although the two proposed operations are identical in their early stages, they diverge in less than two weeks, when the Nez Perce proposal would drop flows slightly in order to save water for late summer.

The Technical Management Team, which makes in season decisions on how to use available water in the Columbia and Snake river systems to aid fish listed as threatened or endangered, will debate the differences between the two plans at its meeting next week and make at least a preliminary decision on which operation will work best this year given available water.

"We are attempting to extend the flow augmentation (from the Dworshak Reservoir) to late summer," said Steve Pettit of Idaho Fish and Game. "We realize that the peak of the (juvenile) run is now and that is why we front load the operation in July, but we believe the tail end of the migration is important, too, and deserves protection. We think this is a more equitable way to use the 1.4 maf (million acre feet) of Dworshak water."

Many of the wild sub-yearling chinook juveniles have already passed Lower Granite Dam, according to Paul Wagner of NOAA Fisheries. Some 4,500 wild sub-yearlings were tagged and 900, or about 26 percent, have been detected at the dam. However, because some fish pass through spill at the dam, it is likely that 60-80 percent of the run has already passed, he said.

The Corps filled Dworshak Reservoir to an elevation of 1,600 feet as required by the BiOp on June 30 and has been drafting since Monday when it increased flows to 9.4 kcfs. It increased flows again Tuesday morning to 13 kcfs, including some spill, and, after ensuring that total dissolved gas was not exceeding 110 percent, increased flows from the dam Wednesday morning to 14 kcfs.

The difference between the BiOp operation and the Idaho/Nez Perce proposal begins July 21st when the latter proposal calls for a reduction in flows to 12 kcfs. However, the BiOp operation this year sets and maintains the 14 kcfs flow as long as possible, projected to be Aug. 24 this year, and stepping down to 5.7 kcfs the last week of August. At that point, the Dworshak Reservoir is projected to have reached an elevation of 1,520 feet.

The Idaho/Nez Perce proposal would draft the reservoir to 1,535 feet by the end of August, leaving 200,000 acre feet of augmentation water to be used in September. The proposal would drop flows to 11 kcfs Aug. 4, to 10 kcfs Aug. 11, and 8 kcfs Aug. 25, and then it would increase flows slightly to 8.4 kcfs from Sept. 1 to Sept. 15. At that time, flows would drop to 1.4 kcfs as the reservoir reaches an elevation of 1,520 feet.

Both proposals call on the Corps to release cold water -- 45 degrees to 48 degrees -- during the flow augmentation period. Water colder than 45 degrees would impact a hatchery located downstream of the dam. However, the Corps said repairs at the dam's selector gates, which allows cold water releases from the reservoir's depths, will make maintaining steady cold water releases more difficult. The Corps' Rudd Turner said the gates will have to be set to release a certain temperature of water before the repairs begin July 14 and that adjustments will not be possible until repairs are complete about 10 days later.

"We need to set those gates to release water between 45 and 48 degrees on July 13," Turner said. "There might be some drift (in water temperature), but once they are set, they can't be moved."

A study by Laura Hamilton of the Corps found that the potential for drift could be as much as 3 degrees over the 10 day period. Part of the problem is that the reservoir will drop close to 1 foot per day with the 14 kcfs discharge, or 10 feet over the repair period, bringing the warm surface water closer to the selector gates.

"If we get the collector gate close to warm water, then we could suck that water into the outflow," she said. It won't just draw the water horizontally, she added, it could draw water down like in a funnel. Turner said the Corps would set the gates this week so that 45 degree water is released and make sure that is working before setting it July 13.

In other announcements made at this week's TMT meeting, Turner told members that a planned repair of transformers at Lower Granite Dam on July 15 will require special operations that will drop flows at the dam to 11.5 kcfs for 12 hours. The flow Tuesday was 36.5 kcfs. Bonneville Power Administration transmission employees who will do the repair asked to de-energize transmission lines going into the dam as a safety precaution. That will provide the safety from outside electricity sources the workers need, but the shut down also means that the dam can produce only enough energy to provide station service (electricity needed for dam operations). Consequently, the Corps will operate just one generator, which passes about 5 kcfs, and spill water to bring total flow to 11.5 kcfs. Spill will pass some juveniles at a time when the Corps is collecting all fish at the dam to be transported downstream by barge.

Related Sites:
Technical Management Team: www.nwd-wc.usace.army.mil/TMT/index.html