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Dworshak Dam Turbine gets Temporary
Repair Allowing Cool Water for Fish

by Staff
Columbia Basin Bulletin, June 19, 2009

Dworshak Dam's unit 3 stirred to life Wednesday afternoon, providing hydro operators and hydro managers assurance that the turbine can generate power and deliver cool water downstream for fish during the fast approaching hot season.

The turbine is the largest at the west-central Idaho dam operated by the U.S. Army Corps of Engineers. It controls more than half of the powerhouse flows -- 5,500 cubic feet per second of the 10.5 kcfs total when Unit 3 and two smaller turbines are operating at capacity.

Unit 3 was idled nearly four weeks ago when Corps personnel discovered a leak in the turbine pit. At the time Corps said they couldn't be certain whether or not the problem posed the risk of some sort of catastrophic failure. They said stemming the leak could be a relatively quick fix or it could require a year or more depending on what the problem was.

Luckily the diagnosis indicated the leak could be patched with a concerted effort in the short term. A continued outage would have limited the amount of power that could be generated and the amount of water that could be released to augment flows downstream in the tepid Snake River.

Dworshak is on the North Fork of the Clearwater, which ultimately feeds into the Snake. The deep reservoir's cool waters are used in late summer to cool flows for migrating salmon and steelhead.

Dworshak crews have been "working weekends and nights doing everything they can to get that unit working," the Corps' Steve Hall told the Technical Management Team Wednesday. The TMT's federal, state and tribal members help guide operations, such as the Dworshak flow augmentation, that are intended to benefit salmon and steelhead stocks that are listed under the Endangered Species Act.

After getting the proper equipment in place to dewater the unit and conduct an inspection, the Corps found the unit was "leaking through the head cover seal in about the same area that had been repaired several times before" dating back to the 1980s, Hall said.

The temporary repairs consisted of drilling into the seam between the head cover and stay ring and then pressure-injecting an adhesive/sealant into that seam to reduce the leakage.

"We are hopeful that the temporary repairs will last until that time (mid-September), but cannot make that guarantee," said David Tucker, Dworshak's acting operations project manager.

A more permanent fix would likely happen whenever the powerhouse is scheduled for a major overhaul.

Unit 3 resumed its operation at about 3:30 p.m. Wednesday.

With all units running the dam's outflowcan be lifted to as much about 14 kcfs before "total dissolved gas" levels approach legal legal limits. That maximum flow includes full powerhouse generation with additional water released through spill gates and/or the dam's "regulating outlets." The powerhouse flows create little gas, but the spilled water and RO releases stir up TDG quickly in the dam's tailwater. Elevated gas levels can be harmful to fish and other aquatic organisms.

Without unit 3 operating, outflows would likely be limited to about 7-8 kcfs before reaching the TDG cap.

The flow augmentations typically begin following the July 4 weekend and stretch into September.

Dworshak Dam Turbine gets Temporary Repair Allowing Cool Water for Fish
Columbia Basin Bulletin, June 19, 2009

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