PNNL

Abstract

We analyzed five years of route-specific fish-passage data acquired by fixed-aspect hydroacoustic sampling of juvenile salmonids passing downstream through Bonneville Dam. High passage effectiveness of surface-flow outlets relative to the spillway and turbines suggests that juvenile salmonids are preferentially selecting surface outlets over adjacent turbines. Seasonal estimates showed that median combined effectiveness of surface-flow outlets (7.8) was 7.1 times higher than that of the spillway (1.1) and 9.8 times higher than that of turbines (0.8). Islands prevent the spillway from attracting fish from either powerhouse, something that may occur at other projects. Regressions indicated that percent flow passing a specific route explained from 50 to 97% of fish-passage variation, and relations were useful for evaluating fish-passage alternatives. Fitted curves for surface-passage routes, including the sluiceway at Powerhouse 1 (B1) and Powerhouse 2 (B2) were much steeper at low percent low (2-15%) than were curves for the spillway or turbines. Regressions indicate that increasing surface-flow percentages of B1 flow from 1% to 10% could increase B1 sluiceway-passage efficiency from 40% to 83%. Increasing B2 flow to the B2 sluiceway from 4% to 15% could increase fish passage from 31% to 62%. Without spill, about 50% of fish passed by non-turbine routes.