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Feedback: Surface Bypass Technology by John McKern Columbia Basin Bulletin - September 13, 2002

Your 8/23 CBB discusses the use of additional spill at The Dalles Dam for fall fish passage. The 9/6 CBB discusses BPA's budget woes and reluctance to use mass spill for fish passage.

Technology is now available to help solve the problem for the benefit of salmon and to help the region with power and funding problems. The technology is the surface bypass technology being tested by the Corps of Engineers. The Behavioral Guidance Structure (BGS) tested at Lower Granite Dam from 1998 through the present diverted over 80 percent of the juvenile salmon from the turbine intakes. The Raised Spillway Weir (RSW) tested in 2002 diverted a high percentage of fish over a better spillway configuration with over 99 percent survival.

The configuration of The Dalles Dam (powerhouse parallel to the flow and spillway perpendicular to the flow) lends itself to use of a BGS and RSW that could be even more effective than those tested at Lower Granite Dam. A BGS from the east end of the powerhouse to the north side of the spillway could deflect juvenile and adult salmon (fallbacks) safely over one or two RSWs installed in the northern spillway bays.

Adult fish exiting the south spillway/powerhouse collection system at the East Ladder exit would be above the BGS (at Lower Granite, the ladder exit is inside the BGS requiring a gap between the BGS and shore for adult fish migration). With the powerhouse and most of the spillway inside a tightly closed BGS, guidance could be well over 90 percent. With 99 percent survival over the RSWs, The Dalles Dam could go from the worst to one of the best dams for juvenile fish survival.

Installing this technology would allow reduction of spill from tens of thousands of cfs to 10 to 12 thousand cfs over say two RSWs. The RSWs could be located where recent research has found the highest juvenile survival. Juvenile fish survival past The Dalles Dam would be markedly increased. Adult fallback survival would be markedly increased. If adult injuries are being caused by fish shooting under the existing spillway gates at 60 mph and over two atmospheres of pressure change, adult survival would be increased. Adult fish passage efficiency would be increased because confusingly large amounts of spill would not longer be delaying fish approaching the dam or in finding fish way entrances.

Gas supersaturation would be decreased and, except during high flows and uncontrolled spill, would be kept within the 110 percent state standards (not the waived standard of 120 percent which may be injurious to adult and juvenile fish). Most of the water now being inefficiently spilled for fish passage could be used for power generation. Money now being used (or foregone) for mass spill could be used for other fish protective measures.

The concept that spill is the safest route for fish passage at dams is no longer true. The RSW is the safest route. It is safer because the water does not shoot out from under a spillway gate at 50 feet of depth and 60 mph accompanied by rapid decompression and injection of air with the rapid decompression. The RSW was designed to provide this safer spillway passage, and the research has shown it to be effective in doing so. The multiple benefits of the RSW make it a win-win solution; better fish passage with power (and money) savings.

It is my hope that the salmon managers and regional decision-makers will realize the potential of the surface bypass technology and use it effectively. I hope they will realize that existing spillways are not as safe as RSWs, and that the BGS is an effective way of keeping fish from entering the powerhouse turbines. Implementing this technology will save fish and help resolve power and funding problems.

Related Pages:
Early Tests of New Fish Passage Technology Positive by Barry Espenson, Columbia Basin Bulletin