Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 5599
Title: Studies to evaluate the effectiveness of extended-length screens at The Dalles Dam, 1994
Author/Editor: R. F. Absolon, Dean A. Brege, Benjamin P. Sandford, Douglas B. Dey
Publication Year: 1995
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Portland, Oregon
Contract Number: E96930030
Pages: 69
Date: 1995

Our research objectives at The Dalles Dam in 1994 were to determine fish guidance efficiency (FGE) and descaling rates of the extended-length submersible bar screen (ESBS) and extended-length submersible traveling screens (ESTS) in the higher-flow turbine units at the east end of the powerhouse.  We also evaluated horizontal distribution of migrating juvenile salmonids as they entered the turbine units across the powerhouse.

For each species, FGE was calculated as gatewell catch (guided fish) divided by the total number of fish (guided plus unguided), by species, passing through the turbine intake during the test period. We concluded the following based on tests in 1994:

  1. For yearling chinook salmon, mean FGE was similar between the ESBS (69%) and ESTS (65%).
  2. Although descaling rates were all low, the extended screens had significantly higher descaling rates (ESBS 3.2% and ESTS 3.4%) than the STS (0%) for yearling chinook salmon.
  3. For subyearling chinook salmon, mean FGE with the ESBS was 54% and was significantly higher than with the ESTS (47%) .
  4. For subyearling chinook salmon, the ESTS had a significantly higher descaling rate (3.3%) than the ESBS (1.8%) and the STS (0.7%).  There was no significant difference between the descaling rates of the extended-length submersible bar screen and the STS.
  5. Horizontal distribution measurements during spring and summer indicated that juvenile salmonid passage was considerably higher in the west turbine units of the powerhouse than in either the center or east units.