Optimization of fishway attraction flow based on endemic fish swimming performance and hydraulics

Attracting fish to fishway entrances is vital for ensuring successful and timely passage at dams and other in-stream barriers. This requires knowledge of both the target species' swimming ability and the hydrodynamics near the entrance. However, such knowledge is not always available during the initial design phase. The objective of this study is to propose suitable hydraulic conditions for the entrance of a fish passage facility to be built on the Jing River in China. We measured the swimming ability of three endemic cyprinid species (Phoxinus lagowskii, Triplophysa stoliczkae and Opsariich thysbidens) using three metrics: 1) induced flow velocity, 2) critical swimming speed, and 3) burst swimming speed. We then used a reduced-scale physical model of the fish passage facility and a verified 3D numerical hydrodynamic model to simulate the flow field under three fish collecting channel (FCC) operation scenarios. Connecting the fish swimming ability and the flow conditions in the river allowed to define the migration corridors present downstream of the FCC entrance under the different operation scenarios. Although the local velocity in the river near the fish passage entrance never exceeded the burst swimming speed of the target species, large backflow areas developed below the entrance in scenarios 1 and 2. The addition of a spur dike downstream of the entrance decreased the development of backflows, optimizing the width of the migration corridor by nearly 32%. This research presents a reliable and quantitative approach that combines fish swimming ability metrics and hydraulic characterization for optimizing attraction flows at fishway entrances.