UW Prof Debunksby Mike O'Bryant
A longstanding assumption that the more efficient a hydroelectric turbine is run, the higher the survival for juvenile salmon that pass through the churning action of the turbine was challenged this week by Dr. John Skalski of the School of Aquatic and Fishery Sciences at the University of Washington.
The assumption that there is a direct relationship between high turbine efficiency and the survival of juvenile salmon and steelhead that travel through those turbines is found in several iterations of NOAA Fisheries' biological opinions and in the Northwest Power and Conservation Council's 1994 Columbia River Fish and Wildlife Program. That notion began with a 1981 study (M.C. Bell), but Skalski challenged that assumption at this week's Council meeting.
He said that only one of Bell's two studies actually found the direct relationship between turbine efficiency and smolt survival to be true, but that the hydro system is being operated as if the correlation is absolute. On the other hand, his analysis of more recent studies shows that the correlation can be found in only two of ten studies and he suggests operating the hydro system to peak survival efficiency rather than peak turbine efficiency.
"In only one out of two studies, Bell found this relationship (the assumption that the best efficiency for the turbine is the best for smolt survival), but he concluded it was significant," Skalski said. That conclusion, which Skalski said was not entirely true, was then codified in BiOp's and other documents governing the operations of dams in the Columbia River Basin.
Simply stated, turbine efficiency is the ratio of energy into the turbines in the form of water flow and head (distance the water drops), measured in foot/pounds. of energy (horsepower), to the amount of energy produced by a turbine. The peak efficiency is never 100 percent, he said, and is more likely to be 85 percent to 90 percent.
Skalski, who recently published his work in the "North American Journal of Fisheries Management," arrived at his conclusion when looking at site specific studies at Lower Granite, Wanapum, Rocky Reach, Bonneville and McNary dams on the Columbia and Snake Rivers that were completed between 1995 to 2002. Unlike Bell's studies, the studies were all completed at dams located in the Columbia River Basin and they all used Kaplan turbines.
What he found in most cases is that peak survival generally is within the plus or minus 1 percent window for turbine efficiency, but that it rarely coincides directly with the peak turbine efficiency and that survival can fluctuate dramatically within that band. For example, of three tests at Lower Granite Dam on the Snake River, peak survival fell outside the plus or minus 1 percent band on one test and within the band on the other two tests, but peak survival and peak turbine efficiency never coincided.
He found similar results from a Wanapum Dam study (operated by Grant County PUD on the mid-Columbia River), but also found that peak survival can be a function of where fish enter the turbine. Peak survival was better when smolts entered the turbine at a 30-foot depth than when smolts entered the turbine at 10 feet.
In a Rocky Reach Dam study (also located on the mid-Columbia River), peak survival for three discharge levels were within the 1 percent band, but none fell on the point of peak efficiency. Of the four studies at Bonneville Dam, all fell within the 1 percent band and in one study survival and efficiency coincided. Again, at McNary four of five tests were not coincident. An additional analysis that included 51 tests at 17 turbines and 13 projects across the United States also did not find a correlation between peak turbine efficiency and peak survival.
Skalski said he is 95 percent confident that no relationship exists between peak survival of smolts that travel through turbines and the peak efficiency of the turbines, so turbines can no longer be operated to peak efficiency under the "guise to benefit fish."
"The good thing about this, though, is that the 1 percent window is wide enough in most cases that it generally captures peak survival," he said. "One possibility to gain survival is by operating to peak survival, not to peak efficiency. It requires no further investment (at the projects). We just have to play with our toys differently."
He also said this is only one factor in survival. Others include size of fish and the depth at which the fish enter a turbine and those factors require continued study.
"This is an intriguing study that raises other questions," said Tom Karier of Washington, who is co-chair of the Council. "It does appear to be important where the fish enter the turbine." In some cases, extended length screens could force juveniles into the lower reaches of the turbine to get better survival. It also shows that very specific discharge and efficiency rates are important for survival, he added.
"Yes. If we can operate to the plus or minus 1 percent efficiency rule, it seems like we could also operate to plus or minus 1 percent peak survival and allow the turbine efficiency to be what it is," Skalski said.
He added that because 10 of 13 tests of the Minimum Gap Runner turbines, also known as "fish friendly turbines," at Bonneville Dam that are touted to be more efficient showed no coincidence, the results may call into question the need for the new turbines.
Northwest Power and Conservation Council: www.nwppc.org
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