Sluiceway Operations for Adult Steelhead Downstream Passage at The Dalles Dam, Columbia River, USA

Abstract

AbstractSluiceways at hydroelectric dams are designed to enable floating ice and debris to pass through the dams and may be used as an effective, nonturbine, surface route for out‐migrating fishes to pass through dams. Each year, the sluiceway at The Dalles Dam on the Columbia River, USA, is normally operated between 1 April and 30 November and the spillway between 10 April and 31 August to enable downstream‐migrating juvenile Pacific salmonids to pass. The only route available for fishes to pass the dam between 1 December and 31 March is through the turbines. This study evaluated downstream passage of adult steelhead Oncorhynchus mykiss at The Dalles Dam during various periods between 1 November and 10 April for years 2008 through 2010. The purpose of the study was to determine the efficacy of operating the sluiceway between 1 December and 31 March to provide a relatively safe, nonturbine, surface outlet for downstream passage of adult steelhead that overwinter in the lower Columbia River (i.e., fallbacks) or for adult steelhead attempting to emigrate back to the marine environment after spawning (i.e., kelts). We applied a fixed‐location hydroacoustic technique to estimate downstream passage rates at the sluiceway and turbines. The sluiceway was used by 91–99% of the adult steelhead during all sampling periods; the remaining 1–9% passed through the turbines. This implies that adult steelhead preferred the sluiceway for downstream passage at the dam. Our results indicate that keeping the sluiceway open between 1 December and 31 March may provide an optimal, nonturbine surface route for downstream passage of overwintering or postspawned adult steelhead at The Dalles Dam. Similar operations are relevant at hydroelectric dams with surface‐flow outlets, such as sluiceways, for safe downstream passage of fish species of management concern.Received July 19, 2012; accepted March 27, 2013