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River Managers Spill to Deal with Brief Rise in Fish Mortality by CBB Staff Columbia Basin Bulletin - May 7, 2004

Juvenile salmon and steelhead mortality rose briefly at McNary and Lower Granite dams and at the Snake River dam the mortality ultimately resulted in spilling water this week, something operating agencies had stopped April 23 due to low water flows in the river.

U.S. Army Corps of Engineers biologists found dead fish in the gatewells at Lower Granite Dam early this week, the victims of overcrowding as a huge slug of chinook and steelhead juveniles waited for their places on a barge.

Some of the mortalities also were caused by an apparent increase in flows that brought debris into an orifice leading into one of the dam's turbines, trapping fish in the process. Fish mortality at the dam rose Tuesday morning to about 2 percent of juveniles being collected at the dam for transportation in barges downstream. The majority were steelhead juveniles, according to the Corps.

With over 800,000 juveniles showing up at the dam Wednesday and only room for 700,000 on the barge, the dam operating agencies were left to wonder what to do with the excess juveniles, according to the Corps' Rudd Turner. The Fish Passage Plan, which guides operations at dams, calls for bypassing the excess juveniles. However, when an even larger number of fish showed up Wednesday, operating agencies decided instead to route the fish through the dam's removable spillway weir and to spill 3,800 cubic feet per second of water during the night.

Initially, the action agencies opposed spilling the water because, after considerable discussion during April, a decision had already been made to stop spring spill in the lower Snake River (except for Ice Harbor, which lacks fish collection facilities). But the agencies recanted and provided the spill as long as it was revenue neutral, Turner said. To make up for spilling all night at Lower Granite Dam, spill was reduced at Bonneville Dam during the same period by 25 kcfs, a 20 percent reduction.

"This is not spill for fish passage," Turner told the Implementation Team this week. "This is short term spill due to unique conditions."

He added that biologists counted 823,000 juveniles at the dam again Thursday morning and noted that the count would have exceeded 1 million fish if some had not been spilled the night before.

"The operation should have been fish neutral," commented Ron Boyce of the Oregon Department of Fish and Wildlife. "It was part of the recommendation from salmon managers to reduce spill at Bonneville."

"Things were happening quickly and we needed to do a trade off for spill in order to get everyone on board," Turner said.

Mortality, along with descaling, also occurred last week at McNary Dam as a result of tests by the U.S. Army Corps of Engineers. They had been operating several generating units at maximum discharge to test the biological effects of running the turbines outside the 1 percent efficiency range. The 2000 NOAA Fisheries biological opinion for the Federal Columbia River Power System calls for the Corps to operate turbines within the 1 percent range to protect juvenile salmon while they migrate.

Corps biologist Mark Smith said at this week's Technical Management Team meeting that fish descaling at McNary Dam had risen to 14 percent Thursday, April 29 and gatewell mortality at the project had risen to 2.5 percent, which caused the Corps to shut down the testing until this coming weekend.

"Yesterday the mortality was still at about two and a half percent, but the descaling had dropped significantly," Smith told TMT Wednesday.

He also said that Washington Department of Fish and Wildlife biologists, who are overseeing the tests at McNary Dam, confirmed the descaling at 14 percent and also noticed that fish were being pinched by the traveling vertical barrier screen (test screen) in slot A of unit 4 at the dam. That may need to be corrected, he said. Also running above the 1 percent efficiency range were units 2, 3 and 5.

"The MCN Modernization study for gatewell fish condition has been temporarily postponed while we investigate descaling conditions at the facility," Smith wrote in a memo presented to TMT. "Testing was stopped as a first measure (as coordinated in the study plan) while other possible causes are investigated."

The BiOp set the operating limits as a result of studies in the 1980s that determined turbine efficiency and fish survival are directly related. However, after re-evaluating the studies, BPA concluded that operating outside the 1 percent efficiency limit at McNary may not result in survival that is different than operating within the 1 percent limit. The Corps has been testing that conclusion.

Turner said the Corps will resume the tests Saturday, May 8, on two turbines, and reconsider resuming the test at all turbines Monday, May 10.

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