Hydroacoustic Evaluation of Juvenile Salmonid Passage at Detroit Dam, 2011

We evaluated downstream passage and distribution of juvenile salmonids at Detroit Dam on the North Santiam River, Oregon during 2011.  The study was conducted by the Pacific Northwest National Laboratory for the U.S. Army Corps of Engineers.  The study goal was to provide information on fish passage rates and distribution at the dam to support decisions on long-term measures and operations to enhance dam passage conditions for downstream-migrating juvenile salmonids.  The study period is from February 1, 2011 to January 31, 2012.  The objectives were to estimate total number, and seasonal, daily, and diel distribution of juvenile salmon passage through the dam.  We obtained passage data using fixed-location hydroacoustics.   Transducers are deployed to sample fish in four main areas of the dam: 1) inside the penstock intakes; 2) forebay vertical face of the dam; 3) Spillway; and 4) the operational regulating outlet (RO).  Data are being collected 24hr/d, 7d/wk.  The study is still in data collection and analysis phase; however, preliminary fish passage data were analyzed for February 1 – December, 2011 for the penstock intakes, spillway, regulating outlet, and forebay vertical distribution. 

Preliminary estimates of passage rates show a total of 162, 966 ± 3,875 (95% CI) juvenile size fish passed through the penstock intakes between February and December, 2011.  Run timing peaked on March 26.  For periods when both turbine units were operating concurrently, results indicate more fish passed at penstock intake 2 than intake 1.  Diel distribution was highly variable.  For the spillway, preliminary estimates show a total of 11,591 ± 726 (95% CI) juvenile size targets passed over the bays between June and September.  For periods when both spill bays were operating concurrently, results illustrate reasonable uniform horizontal distribution.  Diel distribution indicates passage was highest during the day and was lowest during nighttime.  Estimates of passage through the RO show a total of 10, 556 ± 442 (95% CI) juvenile size fish passed between October and December.  Passage peaked in mid-November.  Diel distribution was highly variable. 

Vertical distribution data at the forebay face of the dam show a bi-modal distribution of juvenile fish in the water column throughout most of the year; one group was in the top 10m (during spring) and 40m (in summer) and another group was deeper, between 20m – 40m (spring) and 60m – 80m (summer).  All fish were in the top 60m in fall and winter.