Considerable efforts have been underway to develop hydrokinetic energy resources in tidal and riverine environments throughout North America. Potential for fish to be injured or killed if they encounter hydrokinetic turbines is an issue of significant interest to resource and regulatory agencies. To address this issue, flume studies were conducted that exposed fish to two hydrokinetic turbine designs to determine injury and survival rates and to assess behavioral reactions and avoidance. Also, a theoretical model developed for predicting strike probability and mortality of fish passing through conventional hydro turbines was adapted for use with hydrokinetic turbines and applied to the two designs evaluated during flume studies. The flume tests were conducted with the Lucid spherical turbine (LST), a Darrieus-type (cross flow) turbine, and the Welka UPG, an axial flow propeller turbine. Survival and injury for selected species and size groups were estimated for each turbine operating at two approach velocities by releasing treatment fish directly upstream and control fish downstream of the operating units. Behavioral observations were recorded with underwater video cameras during survival tests and during separate trials where fish were released farther upstream to allow them greater opportunity to avoid passage through the blade sweep of each turbine. Survival rates for rainbow trout tested with the LST were greater than 98% for both size groups and approach velocities evaluated.
Turbine passage survival rates for rainbow trout and largemouth bass tested with the Welka UPG were greater than 99% for both size groups and velocities evaluated. Injury rates of turbine-exposed fish were low for tests with both turbines and generally comparable to control fish. When adjusted for control data, descaling rates were also low (0.0 to 4.5%). Video observations of the LST demonstrated active avoidance of turbine passage by a large proportion fish despite being released about 25 cm upstream of the turbine blade sweep. Video observations from behavior trials indicated few if any fish pass through the turbines when released farther upstream. The theoretical predictions for the LST indicated that strike mortality would begin to occur at an ambient current velocity of about 1.7 m/s for fish with lengths greater than the thickness of the leading edge of the blades. As current velocities increase above 1.7 m/s, survival was predicted to decrease for fish passing through the LST, but generally remained high (greater than 90%) for fish less than 200 mm in length.
Strike mortality was not predicted to occur during passage through a Welka UPG turbine at ambient current velocities less than about 2.5 m/s. This research effort has resulted in a better understanding of the interactions between fish and hydrokinetic turbines for two general design types (vertical cross-flow and ducted axial flow). However, because the results generally are applicable to the presence of a single turbine, more analysis is needed to assess the potential for multiple units to lead to greater mortality rates or impacts on fish movements and migrations. Additionally, future research should focus on expanding the existing data by developing better estimates of encounter and avoidance probabilities.