Rainbow Trout Responses to Twin Vertical Axis Turbine Hydrodynamics in an Experimental Flume

Increased energy security and access in remote communities is a target of the UN’s Sustainable Development Goals. To achieve this renewable energy sources with minimal environmental impact are the preferred solution. Hydropower dams a common renewable energy yet they have a large impact on river connectivity causing mortality in migratory fish and extensive sediment trapping upstream of dams. Vertical Axis Turbines (VAT) are a type of hydrokinetic turbine that allow energy extraction from flowing rivers without impounding water, however their environmental impact is unknown. We performed hydrodynamic analysis on three configurations of single and paired VATs in an experimental flume and then allowed groups of three rainbow trout (Oncorhynchus mykiss) to interact with the turbines and tracked their behaviour. A single VAT produced a wake characterised by high vorticity bounding either side of the wake and increased turbulence. When paired with another VAT, the interaction between turbine wakes led to a merged wake that evolved differently downstream depending on their relative rotation direction due to interaction from the wakes of both turbines. The fish responded to the turbines with general avoidance and blade strikes were extremely rare. Importantly, the turbines did not impede passage upstream of the turbines. When shoaling the fish were bolder, spent more time in the near wake and bow wake compared to single fish, and they also spent less time resting.