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Ecology

Columbia Basin Juvenile Fish Screen Facilities

Water from the Columbia River drainage has been used for irrigation since the first homesteaders arrived in the Pacific Northwest in the mid 1850s. Screening of irrigation diversions to protect fish dates back more than 50 years. Passage of the Mitchell Act in 1938 to mitigate the impact of federal dams on anadromous fish provided the funds that initiated the current screening programs in Washington, Oregon, and Idaho.

The Northwest Power Planning Council (NPPC), through its 1984,1987, and 1994 Columbia River Fish and Wildlife Program, has listed fish protection through effective screening of diversions as an essential element in their program to restore dwindling salmon and steelhead runs.

Since the first diversion screens were built, criteria used to measure their effectiveness have become much more stringent. The allowable approach velocity at the face of screens has been reduced and sweep velocities to provide guidance to the fish bypass system have been raised. In addition, smaller mesh sizes for screens are now required to prevent small fish from passing through the screens and becoming entrained in irrigation canals. The new requirements, developed and approved by the National Marine Fisheries Service (NMFS) and fisheries agencies from Idaho, Oregon, and Washington, have resulted in the need to develop new screen designs to replace older, less effective facilities. In order to measure the effectiveness of new screens, the Bonneville Power Administration (BPA) established a monitoring and evaluation program to ensure that screening facilities meet fish protection goals.

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