STATISTICAL EVALUATION OF TURBINE BYPASS EFFICIENCY AT WELLS DAM ON THE COLUMBIA RIVER, WASHINGTON

The statistical and logistical aspects of conducting a rigorous hydroa coustic assessment of fish passage at a hydroelectric project are pres ented. A 3-year evaluation was conducted at Wells Dam (river km 830.1 Columbia River) to estimate bypass efficiency. Wells Dam has a unique hydrocombine structure where the spillway is located directly above th e turbine intakes. Baffles placed in the spill intakes create attracta nt flow for bypassing downstream migrant salmon smelts Fixed-location hydroacoustic techniques coupled with finite sampling methods were use d to estimate bypass efficiency at the project using 25-29 transducers located in turbine and spill intakes. Spring bypass efficiency estima tes ranged from 84.3 to 95.0% with a 3-year average of 89.4% (SE 3.1%) . Bypass efficiency for summer migrants varied from 76.5 to 97.0% betw een years with a 3-year average of 89.0% (SE 6.3%).