Author(s): Serhat Kucukali; Reinhard Hassinger

Linked Author(s): Serhat Kucukali

Keywords: Diagonal brush fish pass; Energy dissipation; Turbulence; Flow field; Fish trajectory

Abstract: 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 Darcy-Weisbach friction factor was derived from dimensional analysis and experimental measurements. The findings reveal the dependence of the friction factor to the relative submergence and the bed slope for the proposed fish pass structure for the tested flow conditions. Also, we found a strong relationship between the energy dissipation per unit mass ε and the Reynolds number Re. In most of the international standards, it is recommended that energy dissipation per unit volume ΔP 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 measured maximum velocity of 1.5 m/s both in the full-scale physical model and in the prototype validates that the brush fish pass meets the requirements of allowable maximum velocity value of 2 m/s defined for fish passage structures. Immediately behind the brush block, the time-averaged flow velocity is reduced by 70%, but the flow has not separated and no recirculation zone forms. The vertical velocity profile behind the brush blocks is not logarithmic related with the flow–bristle interaction. The correlations between those hydrodynamic parameters and the measured fish trajectories were examined. It has been shown that the reduced velocity and turbulence regions behind the brush blocks constitute important resting sites for fish and the macro-scale vortices with vertical axis formed in the stream environment can help fish in their upstream migrations. Underwater video recordings, conducted in the laboratory and in the field, show that fish occupied positions with energetically hydrodynamic conditions that are likely to minimise swimming costs. It is suggested that S-shape flow structure and horizontal turbulent momentum exchange that matches the body undulation of the swimming fish can be beneficial for fish passage.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022665

Year: 2022