PNNL

Abstract

Mechanical injury is among the most significant and least understood injury mechanisms for fish that pass through hydroelectric turbines. Mechanical injuries to fish are caused by their collision with hydraulic structures, such as fixed guides, stay vanes, wicket gates, flow-straightening walls in the draft tube, and moving turbine runner blades. Information on mechanical strike is necessary for establishing biological criteria for operation and design of turbine and non-turbine structures. Hatchery-reared juvenile fall Chinook salmon (Oncorhynchus tshawytscha) that were 110–140 mm long were introduced through a submerged, 6.35 cm diameter water jet at velocities ranging from 9.1 to 18.3 m/s and encountered a fixed hydraulic structure. The structures included a baffle block, a deflector, and a model of the leading edge of a turbine blade. All the exposures were captured by two high-speed cameras. Three-dimensional trajectories were obtained by performing motion analysis on the videos. Velocity and acceleration were then computed by numerical differentiation of the trajectories. For all three configurations, fish exited the nozzle and impacted the structures at roughly the same velocities. Velocities tested were 9.1, 12.2, 15.2, and 18.3 m/s for the baffle block and 9.1, 12.2, and 15.2 m/s for the deflector and blade. Injury levels for each group increased with increasing nozzle velocity. Minor injury first occurred at 9.1 m/s for both the blade profile and baffle block tests. Major injuries were near 40% for both the baffle block and blade profile test at velocities of 15.2 m/s. Direct and delayed mortality were near 50% for all speeds using the blade profile and direct mortality increased from 10 to 50% with the baffle block. Injuries were far less common when using the deflector, with major injuries of ~5% at a velocity of 15.2 m/s. The findings of this study can reveal ways these structures can impair juvenile salmonids’ ability to safely pass hydroelectric facilities.