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Turbines Tweaked for Juvenile Sockeye at Bonneville by Bill Rudolph NW Fishletter, June 8, 2012

Hydro managers have been adjusting turbine operations at Bonneville Dam for weeks now to improve the passage of juvenile sockeye. The change began on May 15 after sockeye smolts showed excess descaling from passing through the bypass system at Powerhouse 2 along the Washington shore.

The operation was similar to what they did to accommodate millions of young newly released hatchery fall chinook, released from Spring Creek Hatchery a few weeks earlier.

More than 20 percent of the sockeye smolts sampled in the bypass system May 12 showed descaling, after large numbers of smolts showed up at the dam. Numbers spiked May 16, when the smolt index at Bonneville climbed to over 90,000, and began tapering off rapidly.

At the May 16 meeting of the Technical Management Team, biologists said that the young sockeye traveled close together and would be past the dam in just a few days. Most originated from British Columbia's Lake Osoyos, traveling down the Okanogan River before entering the Columbia on their way to the ocean.

Beginning last Wednesday, managers began running turbines in Powerhouse 2 in the lower 50-percent range of 1-percent efficiency to reduce adverse effects from gatewell screens on the young fish. The operation was slated to be "power-neutral," according to Doug Baus of the Corps of Engineers' Reservoir Control Center, who said more flow would be diverted to Powerhouse 1.

The operation was slated to run at least through May 20, when hydro and fish managers would see monitoring results from weekend passage.

Flows at Bonneville remained above 300 kcfs towards the end of that week, but spill was down considerably, to around 100 kcfs.

That made passage for adult spring chinook adults easier than the previous week, and counts remained above 4,000 a day by May 17, when the run topped 130,000, nearly catching up to the 10-year average after an extremely late start.

Fish managers announced May 17 they thought more than 50 percent of the upriver spring chinook run was past Bonneville, and updated its size to 216,500 (to Columbia River mouth) from 202,000.

The good news allowed harvest managers to tack on two days of sport fishing for chinook above the dam. Below the dam, sport fishing for chinook was closed.

Flows Back Up

Hydro managers tuned turbines during the week of May 21 in hope of reducing descaling of young sockeye from the Snake River. Flows were up to 380 kcfs by May 24 and spill had increased to 148 kcfs, with about half the spring runoff yet to show.

But the relatively mellow spring flows kept wind integration issues at a minimum. BPA cancelled its weekly meeting on the topic, and NOAA forecasters expected overall flows at The Dalles to trend downwards in the near future.

Fish managers said they figured Snake River juvenile sockeye would show up at Bonneville by May 26, and called for the turbine changes after more than 20 percent of monitored sockeye smolts showed signs of descaling at the dam. The fish seem to travel in a group and three days with the change in turbine efficiency should be enough, managers said.

The Corps said it would slightly shift flows over to Powerhouse 1 by the afternoon of May 23, but would not increase spill, out of concern for adult fish passage. Adult numbers were down in the 1,000-fish daily range by the middle of last week, but managers weren't sure if the run was just tapering off or was held back because of the river conditions.

At the May 23 Technical Management Team meeting, managers also discussed the upcoming operation at Libby Dam to spill in excess of powerhouse capacity that is designed to help ESA-listed sturgeon in the Kootenai River. About 1.1 MAF will be released to aid white sturgeon spawning after adequate river temperatures and other conditions are met.

The operation was mandated in the 2008 sturgeon BiOp after other operations in 2008 and 2009 did not help the fish to spawn. Flows were slated to be ramped up for several days to 15 kcfs, then will stay at 20 kcfs for several days before ramping down to full powerhouse capacity plus spill of up to 10 kcfs for up to seven days.

Last year's large volumes of water didn't get the fish to spawn either, but some managers are hopeful after some "teenage" radio-tagged hatchery-bred sturgeon began showing upriver around old spawning grounds. Even though they are already 17 years old, the fish are not expected to be ready to spawn until they are 30. But managers say the fact that the fish are already upriver could mean they might mature faster than wild fish.

The ESA-listed wild sturgeon haven't spawned since the late 1970s in the Kootenai River near Bonners Ferry, Idaho, when flows were permanently curtailed by the Libby project.

Flows Drop, Fish Numbers Stay Steady

Dam operators took some heat from fish managers last week by only partially fulfilling their request to adjust operations at Bonneville Dam to reduce descaling of juvenile sockeye through the dam's bypass system. The fish managers said more Snake River sockeye were on the way.

Turbines at Powerhouse 2 were operated below the 50-percent mark of 1 percent efficiency, and the extra flow was used to boost generation slightly in Powerhouse 1, similar to operations earlier in the month. But fish managers had wanted to spill that bit of water freed up by the operation.

At the May 30 TMT meeting in Portland, Corps managers said that flows and spill were both down compared to recent weeks, but they were concerned about dissolved gas levels below the dam. The TDG meter in question was out of service, so they could only estimate what gas levels really were--but they figured it was above 120 percent--the legal limit for spring operations. The Corps also said adult fish passage would likely be hindered by more spill.

Fish monitoring showed that descaling had declined significantly before the operations even started, from more than 14 percent on May 29 to less than 6 percent on May 30 (two fish out of 36 sampled). Overall flows had declined about 100 kcfs since early May, to about 300 kcfs, with spill around 100 kcfs by the morning of May 31.

The upriver spring chinook run was still running, to the tune of more than 1,000 fish a day, and totaled about 156,000 by May 30, about 6,000 fish above the 10-year average. As for the juvenile sockeye heading the other direction, their numbers continued to dwindle after the fish managers' request. The smolt index dropped from more than 5,000 on May 27 to less than 1,500 on May 30, but climbed above 5,000 by June 2, when more than 13 percent of the sampled sockeye showed some descaling. The following day, descaling was down to 4 percent, but back up to 9 percent the following day.

At the June 6 TMT meeting, fish managers said about 25 percent of the Snake sockeye run had yet to appear and stumped for the turbine operations to remain in place with more spill, as flows were projected to increase over the next few days. Hydro managers said dissolved gas levels below the dam were still a concern, and were likely to rise in a few days, when most projects would be passing involuntary spill from the added volume created by the recent precipitation event. They also pointed out that sockeye were descaling at similar levels at John Day Dam and raised questions over whether the descaling seen at Bonneville may have occurred earlier, or may have been caused by previous injury.

But they agreed to move the project up to the third spot in the spill priority list, which governs the order in which the extra spill is handled. They also agreed to continue operating the two powerhouses as they did the previous week until the evening of June 11.

Related Pages:
Bonneville Dam Flows Configured to Limit Descaling of Idaho's ESA-Listed Sockeye by Staff, Columbia Basin Bulletin, 5/25/12