Hydroacoustic and Pressure Turbulence Analysis for the Assessment of Fish Presence and Behavior Upstream of a Vertical Trash Rack at a Run-of-River Hydropower Plant

The spatial distribution of fish upstream of a vertical trash rack was investigated at the hydropower plant Kirchbichl in the alpine River Inn (Tyrol, Austria). The objective of the research project FIDET was to establish a non-invasive methodology to study fish presence and flow characteristics at large hydro power sites. A new monitoring approach was developed combining hydroacoustic observations of fish locations with multivariate hydrodynamic data. This was accomplished by utilizing complementary observations from multiple underwater sensor technologies: First, an array of echosounders were deployed at a fixed cross-section upstream of the trash rack for long-term monitoring. Afterwards, detailed underwater surveys with acoustic cameras (DIDSON and ARIS) revealed that the spatial distributions of fish in front of the trash rack were highly heterogeneous. The spatial distribution of the flow field was assessed via the time-averaged velocity fields from acoustic Doppler current profiler (ADCP). Finally, a custom pressure-based flow turbulence probe was developed, providing spatial estimates of flow turbulence immediately upstream of the trash rack. The significant contribution of this work is to provide a multi-modal monitoring approach incorporating both fish position data and hydrodynamic information. This forms the starting point for a future objective, namely to create an automated, sonar-based detection and control systems to assist and monitor fish protection operations in near real-time.