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Juvenile Fish Screen Facilities

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 and Conservation Council, through its 1984 and 1987 Columbia River Fish and Wildlife Programs, 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. Maximum allowable approach velocities at the face of screens have been decreased, while required sweep velocities that provide guidance to the fish bypass system have been increased. Also, screen opening sizes have been decreased to prevent early life stages of salmonids 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.

PNNL staff perform a variety of juvenile fish screen evaluations for BPA to determine if fish screens are being designed, operated and maintained to meet NMFS criteria over a wide range of conditions. Specifically, evaluations are performed to determine if:

  • Flows in front of screens promote fish bypass without chance of delay or impingement
  • Screens are adequately sealed to prevent fish injury or entrainment
  • Screen submergence levels preclude fish roll-over or entrainment, yet promote debris removal
  • Bypass outfall conditions promote safe fish access to the river
  • Conditions in front of screens deter predation of juvenile salmonids.

Past investigations have also determined movement and injury rates to chinook salmon at fish screen facilities, compared the effectiveness of submerged orifices and overflow weirs for fish bypass and compared salmon passage rates for two different approach angles to rotary drum screens.

The development of the modular fish screening facility has made it possible to conduct some of these evaluations under controlled laboratory conditions at the PNNL's Flow Biology Laboratory. To ensure high-quality results, both laboratory and field studies are conducted using underwater video equipment, acoustic velocimeters and other state-of-the-art equipment.

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