Flow and Turbulence Structure of Diagonal Brush Fish Pass: Full-Scale Physical Model and Prototype Measurements

The flow and turbulence structure of the diagonal brush fish pass was investigated in the laboratory and in the field. The turbulence structure was revealed by measuring the three-dimensional instantaneous velocity fields using Micro acoustic Doppler velocimeter in the fish pass for various discharges. The maximum measured velocity about 1.5 m/s both in the physical model and prototype is well below that set for fish passages maximum velocity of 2.0 m/s. In most of the international standards, it is recommended that energy dissipation per unit volume should not exceed 200 W/m³. But, full-scale physical model and prototype measurements reveal that this threshold value is not a relevant criterion for brush fish pass. Because a significant proportion of energy dissipation takes place in brush blocks with the vibration and bending of bristles which gives rise to energy transfer from the main flow to the bristles rather than by the viscosity of the water in an energy cascade process. This energy transfer is depended on the drag force and bristle displacement is streamwise direction. Hence, in this case energy dissipation cannot be an indicator of turbulence in the same manner of conventional technical fishways. Moreover, with compared to the natural type and vertical slot fish passes, spatially-averaged turbulent kinetic energy in the basin reduced considerably for the same dissipated power, respectively. The prototype and experimental results from this study would be useful to both fish-pass designers and fish biologists.