Effects of Turbine Operating Efficiency on Smolt Passage Survival

Abstract

We conducted a retrospective analysis of data on the relationship between operating efficiency of Kaplan turbines and direct passage survival of salmonid smolts. A review of a key report instrumental in establishing ±1% turbine efficiency rule for operating Snake and Columbia river hydroelectric stations found a weak association (r ² = 0.112) but also found misspecification of the turbine efficiency data. At four Snake and Columbia river dams, manipulative studies were performed to investigate the relationship between turbine performance and smolt passage survival, as estimated with balloon-tag releases and recoveries. At all sites, peak passage survival did not coincide with the observed turbine operating efficiency peak. The difference between maximum survival and survival at peak turbine efficiency was as much as 3.2%. However, at three sites, maximum survival was within the ±1% peak efficiency operating rule. A meta-analysis that used balloon-tag survival results from 11 different hydroprojects also found no association between relative turbine efficiency at a site and smolt passage survival (r ² = 0.0311, P = 0.2640). For the benefit of smolt survival during passage, we recommend managing turbine operations to achieve maximum passage survival rather than focusing solely on peak operating efficiency of Kaplan turbines.