Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 5600
Title: Studies to evaluate the effectiveness of extended-length screens at The Dalles Dam, 1995
Author/Editor: Dean A. Brege, R. F. Absolon, Benjamin P. Sandford, Douglas B. Dey
Publication Year: 1997
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Portland, Oregon
Contract Number: E96930030
Pages: 24 p. plus appendices
Date: 1997
Abstract:

As part of the continuing evaluation of extended-length screens at The Dalles Dam, orifice passage efficiency (OPE) tests were conducted during spring and summer 1995 in Turbine Units 5, 12, and 17, which are located at the west, middle, and east end of the powerhouse, respectively.

For these evaluations, we conducted mark/recpature studies with release groups of yearling and subyearling chinook salmon Oncorhynchus tshawytscha.  Orifice passage efficiency tests were conducted in the west and east orifices of each test slot, with the number of replicates per orifice ranging from 8 to 10 in spring and 8 to 9 in summer. 

For yearling chinook salmon in spring 1994, mean OPEs were 77.5, 80.3, and 82.8% for west orifices and 65.4, 56.9, and 80.8% for east orifices in slots 5B, 12B, and 17B, respectively.  These mean OPEs were significantly higher for west orifice slots 5B and 12B, but there was no significant difference between east and west orifices in slot 17B.

For subyearling chinook salmon in summer 1994, mean OPEs were 78.8, 90.5, and 87.6% for west orifices and 42.6, 57.9, 87.0%f or east orifices in slots 5B, 12B, and 17B, respectively.  As in spring, mean OPEs were significantly higher for the west orifice slots 5B and 12B, but there was no significant difference between east and west orifices in Slot 17B.

In addition, descaling and horizontal passage distribution were monitored in these units, and dip-basket efficiency and gatewell mortality tests were conducted.  Descaling was low for both yearling chinook salmon in spring (<3%) and subyearling chinook salmon in summer (< 1%).

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