Hydraulic analysis of resting pool gradients in vertical slot fishways

Vertical slot fishways are critical for enhancing river connectivity and facilitating the upstream migration of fish. Of particular significance are resting pools – these are essential components where fish can recuperate and restore energy during their journey. Despite their importance, research regarding the impact of resting pool gradients (RPGs) on the overall performance of fishways remains limited. In this study, three-dimensional simulations were used to analyse a 96-stage vertical slot fishway and comparative analyses of flow field distributions were conducted across three different RPGs under typical operational water conditions (backwater profile, drawdown profile and uniform flow). The findings indicate that the RPG significantly influences the overall water surface profile in the fishway. A RPG of J3 = 0% minimises both overall and localised flow velocities and turbulent kinetic energy throughout the fishway. This configuration allows higher conventional pool gradients, thereby reducing the structural requirements of the fishway system.