Corps Not Convinced Turbine Tweaks
by Bill Rudolph
Fish and dam managers spent more time last week discussing ways to reduce descaling of juvenile sockeye at Bonneville Dam, after most of the fish folks drafted an official request for turbine operations designed to reduce water velocity in the bypass system.
Corps of Engineers' spokesman Doug Baus told Technical Management Team members May 29 that most of the request was already being implemented, but his agency wasn't convinced that smolt monitoring of descaled sockeye was correlating with any particular factor, including operating turbines to within 50 percent of 1-percent peak efficiency. Baus said part of the fish managers' request had policy implications and so it was kicked to the next level for discussion.
Mandated modifications to the gatewells a few years ago, pushed by NOAA Fisheries, seems to have led to the increased water speeds that have caused problems for some juveniles, notably sockeye, who are the most prone to descaling, compared to other migrating salmon. NOAA was the only fish agency that did not sign the request.
Baus said the descaling might have something to do with debris at the dams, but reduced descaling of fish was not observed after screens that guided fish were cleaned, which happens twice a week. "We'd like to see more of a trend, and we're not," said Baus. He said 4 to 15 percent of the monitored sockeye showed signs of descaling in recent days at the Powerhouse 2 bypass.
The question of how many fish were actually being affected came up during the May 29 TMT meeting. Some argued that only 4 percent of the juvenile sockeye passing Bonneville Dam used the Powerhouse 2 bypass system, so the actual numbers being descaled were very low compared to the run at large, which was dropping fast. The May 29 sockeye smolt index at Bonneville was less than 10 percent of the number from the previous week.
By May 29, only 4 percent of the young sockeye in the Bonneville bypass showed some descaling. However, upstream, 8-percent descaling was seen at the John Day Dam bypass and 18 percent was seen in the McNary bypass, where debris problems related to tumbleweeds in the dam's tailrace had been seen earlier in the month.
A May 30 email from the Corps confirmed that more debris was rolling into the McNary tailrace, causing increased descaling of all species. Turbines were slated to be operated to roll the debris toward the dam's spillway to get it past the project.
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