Fish Injury and Mortality from Fluid Forces of Conventional Hydroelectric Turbines – Implications for New River and Tidal Hydrokinetic Projects

Developers of several hydrokinetic pilot projects (tidal, river) are seeking permits to field-test the turbine designs selected for installation.  The permitting agencies for these projects are struggling with the uncertainties associated with potential impacts on fish and other aquatic organisms, including listed salmon species.  Uncertainties include how fish will perceive and behave near moving turbine blades, given the types of turbines and their siting, current speeds, and fish swimming ability and detection capabilities.  Because hydrokinetic projects involve new technologies and energy development schemes, information on their performance and environmental effects is limited. Many permitting agencies are taking a conservative approach and assuming that fish may suffer considerable injury or mortality by blade strike or some other mechanism. To help address these uncertainties and provide reliable information for assessing potential impacts, we reviewed existing information on injury and mortality mechanisms experienced by fish passing through conventional hydro turbines.  Our analyses indicate that fish passage through hydrokinetic turbines is not directly comparable to that of conventional hydro units, mainly because fish can avoid passage through hydrokinetic turbines and mechanisms and conditions that can lead to fish injury are much less severe or do not occur. For example, pressure changes and shear stresses associated with hydrokinetic turbines are well below thresholds known to cause injury to fish passing through conventional turbines.  Also fish are able to detect and avoid/use structure based on visual cues and other sensory perception systems.  Using their lateral line system, fish can perceive relatively small changes in pressure and velocity, including changes associated with stationary and moving obstacles.  Further, their inner ear can detect changes in fluid acceleration.  Fluid dynamics computations are available for some hydrokinetic turbine designs and demonstrate hydraulic conditions that are detectable by, but non-injurious to fish.  Such modeling predicts a region of relatively elevated pressure and decreased velocity upstream of the turbine that would allow fish to detect and avoid the turbine.  In addition to avoidance, field observations at turbine installations indicate that fish use the downstream side of a tidal turbine as a velocity refuge, which is a common fish behavior to minimize energy use.