Hydroacoustic Evaluation of Juvenile Salmonid Passage and Distribution at Lookout Point Dam, 2010

Abstract

This report presents the results of an evaluation of juvenile salmonid passage and distribution at Lookout Point Dam (LOP) on the Middle Fork Willamette River. The study was conducted by the Pacific Northwest National Laboratory for the U.S. Army Corps of Engineers, Portland District (USACE). The goal of the study was to provide fish passage and distribution data to support decisions on long-term measures to enhance downstream passage at LOP and others dams in USACE’s Willamette Valley Project in response to the listing of Upper Willamette River Spring Chinook salmon (Oncorhynchus tshawytscha) and Upper Willamette River steelhead (O. mykiss) as threatened under the Endangered Species Act. During the year-long study period - February 1, 2010 to January 31, 2011the objectives of the hydroacoustic evaluation of fish passage and distribution at LOP were to: 1. Estimate passage rates, run timing, horizontal distribution, and diel distribution at turbine penstock intakes for smolt-size fish. 2. Estimate passage rates, run timing and diel distribution at turbine penstock intakes for small-size fish. 3. Estimate passage rates and run timing at the regulating outlets for smolt-size fish. 4. Estimate vertical distribution of smolt-size fish in the forebay near the upstream face of the dam. The fixed-location hydroacoustic technique was used to accomplish the objectives of this study. Transducers (420 kHz) were deployed in each penstock intake, above each RO entrance, and on the dam face; a total of nine transducers (2 single-beam and 7 split-beam) were used. We summarize the findings from the hydroacoustic evaluation of juvenile salmonid passage and distribution at LOP during February 2010 through January 2011 as follows. • Fish passage rates for smolt-size fish (> ~90 mm) were highest during December-January and lowest in mid-summer through early fall. • During the entire study period, an estimated total of 142,463 fish ± 4,444 (95% confidence interval) smolt-size fish passed through turbine penstock intakes. • Diel periodicity of smolt-size fish showing crepuscular peaks was evident in fish passage into turbine penstock intakes. • Run timing for small-size fish (~65-90 mm) peaked (702 fish) on December 18. Downstream passage of small-size juvenile fish was variable, occurring on two days in the spring, eight days in the summer, and at times throughout late fall and winter. A total of 7,017 ± 690 small-size fish passed through the turbine penstock intakes during the study period. • Relatively few fish passed into the ROs when they were open in summer (2 fish/d) and winter (8 fish/d). • Fish were surface-oriented with 62-80% above 10 m deep. The highest percentage of fish (30-60%) was in the 5-10 m depth bin. We draw the following conclusions from the study. • The non-obtrusive hydroacoustic data from this study are reliable because passage estimates and patterns were similar with those observed in the direct capture data from the tailrace screw trap and were consistent with distribution patterns observed in other studies of juvenile salmonid passage at dams. • Fish passage at LOP was apparently affected but not dominated by dam operations and reservoir elevation. • The surface-oriented vertical distribution of fish we observed supports development of surface passage or collector devices. In summary, the high-resolution spatially and temporally data reported herein provide detailed estimates of vertical, horizontal, diel, daily, and seasonal passage and distributions at LOP during March 2010 through January 2011. This information is applicable to management decisions on design and development of surface passage and collections devices to help restore Chinook salmon populations in the Middle Fork Willamette River watershed above Lookout Point Dam.