• turbine efficiency;
  • passage survival;
  • likelihood model;
  • salmon smolt;
  • intake screens;
  • hydroelectric generation

ABSTRACT: The hypotheses that fish survival probabilities may be lower (1) at less than peak operating turbine efficiency; (2) at deeper entrainment depth; and (3) with the deployment of extended-length intake guidance screens, are not supported by results on yearling chinook salmon smolts (Oncorhynchus tshawytscha) at Lower Granite Dam, Snake River, Washington. Estimated 96 h survival probabilities for the six test conditions ranged from 0.937 to 0.972, with the highest survival at turbine operating towards the lower end of its efficiency. A blanket recommendation to operate all Kaplan type turbines within ± 1 percent of their peak efficiency appears too restrictive. Cavitation mode survival (0.946) was comparable to that at peak operating efficiency mode (0.937), as was the survival between upper (0.947) and mid depths (0.937). Survival differed only slightly among three turbine intake bays at the same depth (0.937 to 0.954), most likely due to differential flow distribution. Extended-length intake fish guidance screens did not reduce survival. However, the sources of injury somewhat differed with depth; probable pressure and shear-related injuries were common on fish entrained at mid-depth, and mechanically-induced injuries were common at upper depth. Operating conditions that reduce turbulence within the turbine environment may enhance fish survival; however, controlled experiments that integrate turbine flow physics and geometry and the path entrained fish traverse are needed to develop specific guidance to further enhance fish passage survival.