Balancing Fisheries Management and Water Uses for Impounded River Systems

<em>Abstract</em>.—We analyzed 5 years of route-specific fish passage data acquired by fixed-aspect hydroacoustic sampling of juvenile salmonids passing downstream through Bonneville Dam. High fish-passage effectiveness of surface-flow outlets (SFOs) relative to the spillway and turbines suggested that juvenile salmonids preferentially selected surface outlets over adjacent turbines. Seasonal estimates showed that median combined effectiveness of SFOs (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 prevented the spillway from attracting fish from either powerhouse forebay, something that does not occur at most hydropower projects. Regression analyses 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 flow (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 B2 sluiceway passage efficiency from 31% to 62%. Without spill, about 50% of fish passed by nonturbine routes. We recommend increasing percent flow to the B1-and B2-sluiceways because those surface-flow outlets are highly effective, adjacent to turbines, and capable of attracting smolts away from turbines.