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Install Removable Spillway Weirs at All Corps Dams by John McKern Columbia Basin Bulletin - October 29, 2004

I continue to be puzzled by the reluctance of the fishery agencies to implement removable spillway weir (RSW) technology at all the Corps dams. Anyone who has taken the time to analyze how water is spilled through conventional spill bays should realize that conditions for fish are not good. Water typically shoots out from under the spill gate with 40 to 50-feet of head and a pressure loss that would quickly kill a human diver.

I was a member of the Corps team that came up with the RSW concept precisely to eliminate the harmful conditions described above. With free flow over the weir, the acceleration and pressure change (not to mention air entrainment) are reduced to more natural levels. Research has shown that not only do the fish survive as well or better than through the normal spillway bay, fish are attracted to the overflow spill at seven times the rate they are attracted to undershot spill. This seems natural because they are attracted to the central (overflow) spill over the natural rapids they have encountered before reaching the dams.

I am also puzzled why the fishery agencies have not grasped the idea that by implementing RSW technology, the hydropower system would generate more funding that could be used for other fish habitat and facility improvements. It seems logical to me that the region should install RSWs with all possible haste and reap the benefits of increased fish survival and increased power revenues.

John McKern, fishery biologist (retired)
Fish Passage Solutions
1444 Lowell Drive
Walla Walla, WA 99362
509-525-6283

bluefish.org notes that juvenile survival through spillway passage at Little Goose is estimated to be 100%. Very little further spillway survival benefit is possible at Little Goose. Ice Harbor, however, has substantial spillway mortality.

Related Pages:
Weirs: Which Dams Should Get Them First? by Barry Espenson, Columbia Basin Bulletin,10/29/4