New Fish Studies Suggest
by Bill Rudolph
A paper published in the North American Journal of Fisheries Management (22:1193-1200, 2002) has raised questions about whether turbines at mainstem dams on the Snake and Columbia rivers are being operated to ensure maximum fish survival. The paper suggests that discharging more water through some turbines could boost juvenile fish survival by several percent, even though it would mean operating the machines at less than peak power production efficiency. Such a survival increase is similar to the improvement expected for expensive fixes at dams that cost millions of dollars.
The NMFS BiOp that governs operations calls for turbines to run within one percent of peak efficiency because federal fish folks believe this assures the highest survival rates for juvenile salmon and steelhead that pass through turbines. Peak efficiency occurs when turbines produce the most electricity for the amount of "head" behind the dam and generally occurs when flows are smoothest through the turbines.
But the paper, by U.W. professor John Skalski and consultants Dilip Mathur and Paul Heisen of Normandeau Associates, says there is some evidence that higher flows than those that make Kaplan turbines most efficient may offer improved fish survival.
The authors reexamined older evidence that serves as the foundation for NMFS' belief in peak efficiency and compared it to research conducted by Normandeau from 1994 to 2000 that has used the latest balloon-tag technology for measuring smolt survival at several Northwest dams. They say earlier unpublished studies conducted in the mid-1960s by Milo Bell of the Corps of Engineers do not support his conclusion that "the data offers some support...to the hypothesis that the best points of machine efficiency should give the best points of fish passage survival."
The paper looks at recent studies the authors conducted at Lower Granite, Wanapum, Rocky Reach and Bonneville dams, in which they manipulated operations to examine the possible relationship between fish survival and turbine efficiency. Other than at Bonneville Dam, maximum survival was not observed at peak efficiency. At Bonneville, survival of fish released at the middle and tips of turbine blades was highest when turbines were running at peak efficiency, but those fish released at turbine hubs, which showed generally higher survivals anyway, did not have their highest survivals when the turbines were run at peak efficiency. The study reports about 100 percent survival when turbine discharge levels were both lower and higher than during peak efficiency, when survival was about 97 percent.
The paper also reported on a meta-analysis that examined results from 11 different hydro projects and found no relationship between turbine passage survival and operating efficiency.
A few percent difference in survival does not sound like much until the huge cost of modifying dams for such small survival gains is factored into the policy picture. The authors say the difference in survival, such as the 3.2 percent boost at Wanapum Dam that was observed when turbines were operated outside of peak efficiency, "is as great as the benefits of some other mitigation efforts under consideration at hydro projects in the Snake and Columbia River basins (e.g., surface bypass collectors, diversion screens). The survival benefit in this case, however, can be more rapidly achieved, and without major new capital investment, by simply fine-tuning the turbine operations and modifying the plus or minus 1 percent efficiency rule."
As new equipment is developed to replace older turbines, the authors say the premise of the efficiency rule will have to be "carefully reexamined so that optimal operating conditions for the fisheries resource can be better defined."
Similar research the consultants conducted at McNary Dam in 2002 was discussed at the recent Corps of Engineers' research review. The highest fish survivals were reported outside of the peak operating efficiency of the turbine under study, with about a 3 to 5 percent improvement, up to 98.3 percent, when the turbine was operated at a higher level of discharge than at peak (14,000 cfs v. 11,200 cfs).
But the issue was confounded by a related NMFS study underway at the same time, which was also discussed at the research review. The NMFS study, using only radio-tagged fish passing through the same turbine at McNary Dam, tracked them to 4 km. below the tailrace and found about 84 percent and 85 percent survival (48 hr) of juvenile chinook at operational levels of both peak efficiency (11,200 cfs) and a discharge of 16,400 cfs, suggesting the possibility of a predation effect below the dam. NMFS researcher John Ferguson said there weren't enough test fish available to partition the study area below the dam and test for such a condition.
The Normandeau folks had also found that operating the turbine at these two discharge levels resulted in nearly identical survivals, though about 10 percent higher than in the NMFS study because the test fish were retrieved just a few minutes after they passed through the turbine. Whether the fish are more susceptible to predation after passing through a turbine than over a spillway is still a matter of conjecture, with little data to support any conclusion, scientists say.
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