Early Tests of New Fish Passage Technology Positiveby Barry Espenson
Columbia Basin Bulletin - September 20, 2002
Preliminary testing of a "removable spillway weir" (RSW) at the Snake River's Lower Granite Dam indicates that the fish passage device has great drawing power -- flooding more juvenile salmon and steelhead downstream per volume of water than is accomplished with traditional spill.
The surfaced-oriented bypass method is also believed to be more benign than spill, which has long been considered the safest means of passage for the migrants.
The passage method has been touted as having the potential to move fish more quickly and safely past dams with a lesser amount of water being diverted from power generating turbines. The testing and analysis done at Lower Granite could be used to determine if the RSWs should be installed permanently there and elsewhere in the federal Columbia-Snake river hydrosystem.
The overriding objectives of surface bypass collection and passage concepts is to increase the number of fish passed through the dams by non-turbine routes and to reduce fish stress, injury and migration delays. The surface bypass is also expected to reduce high-spill levels that are associated with dissolved gas problems, and allow that water to be used for power generation.
Preliminary analysis of biological data collected this past spring shows promise for the Lower Granite prototype, though Corps of Engineers officials urge caution. The analysis of many variables involved in the spill vs. RSW passage is not yet complete.
The researchers used a variety of tools to track the test fish through the hydro project. One method was hydroacoustics or sonar -- what Corps' biologist Tim Wik calls "scientific grade fish finders." The research also employed three-dimensional acoustic tags to track fish movements at the RSW.
A key portion of the study involved following the course of some 1,600 radio-tagged fish (800 chinook and 800 steelhead smolts) through the dam under three basic operational scenarios. The fish were released three miles above the dam and monitored via radio telemetry.
Under the one scenario, the dam was operated with spill levels prescribed in the National Marine Fisheries Service's 2000 biological opinion -- passing the maximum amount of water through seven dam spillways that is allowed within a 120 percent total dissolved gas limit. Generally the more water that is spilled, the more gas is created in the tailwater below the spillways. High gas levels can be harmful to fish and other aquatic organisms.
The BiOp spills, generally about 40,000 to 45,000 cubic feet per second during the test period, are carried out during 12 nighttime hours. The average river flows during the mid-April to early June testing period were about 85 kcfs so roughly half the river was spilled during the BiOp spill portion of the test.
The other two operations or treatments involved passing about 6,500 to 7,000 cfs through the RSW (located in the spillway nearest the power house and its turbines) with two levels of "training" spill. The training spill -- regulated at 8,000 and 16,000 cfs from nearby spillways in two separate treatments-- is intended to help draw the young fish toward the RSW. The RSW operations were 24 hours per day.
The preliminary analysis indicates that as many or more radio-tagged fish passed through the RSW during those operations as passed through the other seven spillways during the BiOp spill.
Wik said that 60 to 70 percent of the radio tagged fish released up stream found their way to the RSW during its operations. The BiOp spill passed a similar, though slightly lower, percentage of the tagged migrants.
The RSW was operated in conjunction with the existing behavioral guidance structure that is intended to steer fish away from turbine intakes, the Corps said. The balance of the fish passed by other means, in the training spill, into the existing juvenile bypass system or under the screens and through the turbines.
Both the National Marine Fisheries Service's 2000 biological opinion and the Corps' Lower Snake River Juvenile Salmon Migration Feasibility Study prescribe the development of surface bypass technology.
"They do look favorable and we hope they hold up," NMFS' Jim Ruff said of the preliminary data. The agency's federal hydrosystem branch chief said NMFS will withhold judgment on the Lower Granite RSW testing until the more rigorous analysis of the data is completed and a final report written.
"We think that it is a promising technology. We are hoping to apply this technology at other projects," Ruff said, if biological benefits can be derived.
Initially it looks like a "very cost effective and good passage measure," he said. The concept is also consistent with the Independent Scientific Advisory Board's comments that migrating fish be provided more normative passage routes, Ruff said.
The Bonneville Power Administration is watching the RSW testing closely. The federal power marketing agencies spends hundreds of millions annually on fish and wildlife mitigation and recovery efforts, shouldering responsibility under both the Northwest Power Act and the Endangered Species Act. The agency repays the federal treasury for the majority of the capital projects at hydro projects that are intended to improve passage. It also foregoes revenue opportunities when water is spilled for fish instead channeled through turbines to generate saleable electricity.
"We haven't concluded that application of the RSW elsewhere is justified," said fish biologist Bill Maslen. The lack of data precludes that sort of decision making, for now anyway. But the preliminary results do whet the appetite for more information, he said.
"Everything that I'm hearing is not only favorable, but make it sound like we have something we may be able to capitalize on," Maslen said.
He said that, regardless of the test results, the technology can not be considered a "silver bullet" for salmon recovery.
"We're concerned what may work at one site may not work at another site," Maslen said. "We don't want to build up expectations."
On the other hand, if the technology does allow passage with less water and without biological risk, BPA would look to see it move forward at the appropriate sites. BPA has pressing deadlines. NMFS' BiOp sets out performance standards for improving salmon survival through the hydrosystem and elsewhere. And a dire financial situation has Bonneville looking for efficiencies any where it can find them, including in hydrosystem fish operations. If the RSW technology performs as expected, it could help BPA on both fronts.
The ideal would be to get "higher levels of survival at less cost," Maslen said.
The RSW prototype was built in Vancouver, Wash., and shipped upriver to the southeast Washington dam early last summer. The RSW was installed at Lower Granite Lock and Dam last winter. The cost to build and install the structure is estimated at $11.8 million.
The structure is designed to be "removable" by controlled descent to the bottom of the dam forebay. This allows the capability to return the spillway to original flow capacity during major flood events, then raised to operating position after the flood event. The RSW weighs over 2 million pounds, and is 115 feet tall, 83 feet wide, and 61 feet deep in the upstream to downstream dimension.
At Corps dams on the lower Snake River, juvenile fish can pass three ways -- through existing juvenile fish bypass systems, through the spillway or through the turbines. Spill is generally regarded as the most benign form of passage for outmigrating juvenile salmon and steelhead.
The Corps in November used balloon tagged fish in initial biological testing to ensure the RSW passage did not cause some "unforeseen harm," Wik said. The survival rate for fish passed near the midpoint was 99 percent and was 97 percent for fish passed at what appeared to be the most turbulent point at one side of the structure. The 98 percent average is about par with traditional spill survival, though survival via conventional spill done as a comparison during the November testing produced 100 percent survival, Wik said.
A tailwater egress study was also carried out early in the spring testing period to determine how long it too the fish to exit the area immediately below the spill where predators often congregate. In both RSW operations the fish continued downstream "in a matter of minutes," Wik said.
Because juvenile fish tend to be surface oriented and surface flow is thought to be a more effective method to pass fish than spill gates, the RSW is expected to improve passage conditions for fish by reducing injury and passage delays at the dams.
The Corps plans to meet with state, federal and tribal representatives this fall to discuss final results from this year's testing and consider options for the next round of testing in the spring of 2003.
learn more on topics covered in the film
see the video
read the script
learn the songs