Author(s): Reilly X. Cox; Stefan Felder
Keywords: Closed conduit flow; Fish passage; Pipe flow hydrodynamics; Silver perch; Tube fishways
Abstract: Fish travel through closed conduit systems such as hydropower turbines along river systems. Fish injuries due to turbomachinery are well known, but there is limited understanding of injuries caused by components such as intakes and connecting pipes. To identify thresholds for safe fish transport in pipes, novel experiments were conducted in a laboratory setup combining hydrodynamic measurements with live fish observations. A recirculation system that fed into a header tank with an acrylic straight pipe section of 2 m length with a bell mouth entry was used. Experiments were conducted for two pipe diameters with flow velocities of up to 5.2 m/s. Hydrodynamic measurements were conducted by sending a passive sensor package with accelerometer and pressure sensors through the experimental system. These hydrodynamic measurements were complimented with live fish experiments of juvenile silver perch, a typical Australian native fish species. Individual fish were sent through the pipe system and then closely monitored for a two-week period. No injuries were identified for any of the 46 tested fish following experiments suggesting fish could be safely transferred through closed conduit systems at tested flow conditions. Fish movement through the pipe flows were documented. Fish were observed not to behave as passive tracers, but to respond to the flows. Several fish attempted to swim upstream, while other fish were transported through the pipe in swirling or tumbling motions. These fish appeared to be entrapped within large vortical structures within the pipe flows. Fish travelling downstream travelled faster compared to the sensor package and upstream facing fish slower, confirming an active response of fish to the flow. The present research showed that safe transport of fish in closed conduits must consider fish behaviour, flow velocities compared to swimming speed and ratio of fish size to pipe diameters in addition to hydrodynamic effects. Research is currently underway to expand the present finding to further fish species and to research potential fish injuries in pipe expansions and contraction as well as bends to provide currently missing guidelines on safe fish transport through pipe systems.