Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 8855
Title: Studies to determine the effectiveness of extended traveling screens and extended bar screens at McNary Dam, 1991
Author/Editor: Dean A. Brege, Stephen J. Grabowski, William D. Muir, Steven R. Hirtzel, Steven J. Mazur, Benjamin P. Sandford
Publication Year: 1992
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Walla Walla, Washington

McNary Dam, at river mile 292, is operated by the U.S. Army Corps of Engineers and is the fourth hydroelectric project from the mouth of the Columbia River.  A juvenile fish bypass system at McNary Dam is used to collect juvenile salmonids either for transport to release sites below the hydrosystem or to bypass and return them to the river below McNary Dam.  Submersible traveling screens (STSs) are used to divert juvenile salmonids away from turbines and into the bypass system.

Previous research at McNary Dam indicated that fish guidance efficiency (FGE) for coho salmon Oncorhynchus kisutch, yearling chinook salmon O. tshawytscha, and steelhead O. mykiss was greater than 70%.  However, subyearling chinook salmon, with their tendency to migrate deeper in the water column, were more difficult to guide.  Tests at McNary Dam indicated that guidance for subyearling chinook salmon ranged from only 33 to 60%, although it was generally less than 50%.

In 1991, we conducted research during the spring and summer juvenile salmonid migrations to assess the effectiveness of newly designed extended length bar screens (ESBS).  Concurrently, measurements were made of the smoltification status of the fish.  Specific findings research in 1991 are listed below.

  1.   Based upon vertical distribution measurements, extended length screens should guide a high proportion of all juvenile salmonids.
  2.   Gate position, screen angle, and/or flow through the turbine unit did not significantly change descaling rates with extended screens.  However, some baseline descaling (low levels) likely occurred because of these factors.
  3.   Varying the porosity of the perforated plate on the extended STS appeared to have the greatest positive effect on descaling rates.
  4.   For the 1991 season, mean FGE for subyearling chinook was 64% for both the extended STS and ESBS.  This was significantly higher than the mean seasonal FGEs of 33 and 42% obtained in 1986 and 1987, respectively, using standard length screens.
  5.   For the 1991 season, mean FGE for yearling chinook salmon was 81 and 78% using the extended STS and SBS, respectively.  Previous tests with a standard STS averaged 75% FGE for yearling chinook salmon.
  6.   Smoltification status of yearling or subyearling chinook salmon was not a good predictor of changes in FGE at McNary Dam in 1991.  However, the restricted spring sampling period for yearling chinook salmon and consistently high FGE may have obscured the possible relationship between smoltification status and FGE.