Corps Reduces Dworshak
by Eric Barker
Move designed to lower gas levels in water ahead of fingerling release
At the behest of fish managers, the U.S. Army Corps of Engineers reduced flows exiting Dworshak Dam on Monday and will leave them at lower levels for a week.
The operation is designed to reduce dissolved gas levels in the North Fork of the Clearwater River beneath the dam and at Dworshak National Fish Hatchery. Managers there and at the nearby Clearwater Hatchery plan to release juvenile salmon and steelhead during the weeklong spill reprieve.
Springtime releases from the reservoir that are implemented to eliminate downstream flooding have caused headaches for both fish and water managers over the past two years. The corps operates the dam and reservoir and typically releases high-volume flows this time of year to make room to capture spring runoff. Much of the water is released through hydroelectric turbines at the dam and the rest of it is spilled.
However, its been a different scenario of late. The largest turbine at the dam - unit 3 - was taken offline last year for repair. The work is ongoing and won't be completed until this summer. That means the turbine, which has a capacity of about 5,600 cubic feet per second, hasn't been available. The remaining two turbines - units 1 and 2 - have a combined capacity of 4,800 cfs.
Because unit 3 is unavailable, more water has to be released from the dam's spillway. As that water plunges hundreds of feet into the North Fork of the Clearwater River, it creates high dissolved-gas levels that can be harmful to fish in the river and at Dworshak Hatchery, which draws most of its water from the river. Special equipment is used to reduce gas levels at the hatchery, but during high-spill operations the levels are still high enough to affect the juvenile fish there.
"Although the total dissolved gas levels we are experiencing in the hatchery are not lethal, they are higher than desired and do cause some fish health issues," said Adam Izbicki, assistant manager at Dworshak Hatchery.
Clearwater Hatchery gets its water directly from the reservoir, so fish there are not effected by the high gas levels. But the fish must deal with the higher gas levels when they are released to begin their migration to the ocean.
Izbicki said both spring chinook and steelhead will be released from Dworshak Hatchery during the lower flows this week. For chinook, the timing is normal, but for steelhead it's a little early.
"We are seeing signs of gas bubble trauma in the fish so we are going to get them off-station. It's about two weeks earlier than normal."
The hatchery sits on a triangle of land between the North Fork and the main Clearwater River. To help shield fish from high gas levels, Izbicki said they will be released into the Clearwater River instead of its North Fork.
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