Salmonid smolt survival relative to turbine efficiency and entrainment depth in hydroelectric power generation

The hypotheses that fish survival probabilities may be lower (1) at less th an 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 tshaw ytscha) at Lower Granite Dam, Snake River, Washington. Estimated 96 h survi val probabilities for the six test conditions ranged from 0.937 to 0.972, w ith the highest survival at turbine operating towards the lower end of its efficiency. A blanket recommendation to operate all Kaplan type turbines wi thin +/- 1 percent of their peak. efficiency appears too restrictive. Cavit ation mode survival (0.946) was comparable to that at peak operating effici ency 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 a t the same depth (0.937 to 0.954), most likely due to differential flow dis tribution. Extended-length intake fish guidance screens did not reduce surv ival. However, the sources of injury somewhat differed with depth; probable pressure and shear-related injuries were common on fish entrained at mid-d epth, and mechanically-induced injuries were common at upper depth. Operati ng conditions that reduce turbulence within the turbine environment may enh ance fish survival; however, controlled experiments that integrate turbine flow physics and geometry and the path entrained fish traverse are needed t o develop specific guidance to further enhance fish passage survival.