Sluiceway Operations to Pass Juvenile Salmonids at The Dalles Dam, Columbia River, USA

Abstract

AbstractExisting ice and trash sluiceways are commonly used as benign, nonturbine routes for downstream passage of juvenile salmonids at hydropower dams. At The Dalles Dam on the Columbia River, we studied various operational configurations of sluiceway weirs to maximize sluiceway passage of juvenile Pacific salmon Oncorhynchus spp. and steelhead O. mykiss. We applied hydroacoustic methods to compare fish passage rates and sluiceway efficiencies for two weir configurations in each year: three weirs (SL 1; i.e., collectively referring to the three weirs above main turbine unit [MU] 1) versus six weirs (SL 1+18) during 2004; and middle (SL 2+5) versus east (SL 2+19) powerhouse weir locations during 2005. Horizontal distributions at the sluiceway and turbines and the effects of operating turbines beneath open sluiceway gates were also analyzed. Sluiceway passage efficiency relative to the powerhouse (SLYphs) varied between study years, between spring and summer, and between day and night. In 2004, sluiceway passage rates were significantly higher (P = 0.0003) for SL 1+18 than for SL 1 during summer–night but were not significantly different between the two configurations during the other three season–day/night periods. The SLYphs was significantly higher for SL 1+18 than for SL 1. The location comparison during 2005 revealed no significant differences between the SL 2+5 and SL 2+19 configurations, except for summer–day. The experimental findings led to recommendations for long‐term operations of The Dalles Dam sluiceway: open six rather than three sluiceway weirs to take advantage of the maximum hydraulic capacity of the sluiceway; open the three weirs above the westernmost operating MU and the three weirs at SL 8, where turbine passage rates are relatively high; operate the MUs below open sluiceway weirs as a standard procedure; operate the sluiceway 24 h/d year‐round to maximize its benefits to juvenile salmonids; and use the same weir configuration year‐round. These operational concepts are transferable to dams where sluiceway surface flow outlets are used to protect downstream‐migrating fishes.Received July 19, 2012; accepted June 26, 2013