Design of a downstream migration fish pass for existing hydropower plants

This paper focuses on the research and development conducted in order to design downstream fish passages along two sites equipped with a gated dam, locks and a hydropower plant. This study has been done by combining the input of on-site biological studies, hydrodynamic modelling, scale physical modelling, as well as considerations about constructability in the narrow spaces available on these existing sites. The proposed fish passages have been designed considering the local hydrodynamics and the expected fish response at each stage (attraction, caption, still area, transfer and release). On-site fish tracking enables to define the probability of location close to the water intakes. Numerical modelling then highlighted the correlation between hydrodynamics and fish behavior. It also provided the influence area and boundary conditions for the scale physic al models representing in details the 3D flow fields around the proposed solutions, and their attractiveness. From the fish caption to the downstream release, the design of the fish passage has been realized according to the literature on biological behavior of salmo salar along such structures. Parallel, the technical constraints of existing plants have been challenged to define the best solutions. Finally, the interaction with existing or planned upstream fish ways has been analyzed to validate the design to be built on site in the coming months.