Analysis of dotation discharge impact at a fishway entrance via numerical 3D CFD simulation

The success of a fishway depends on two criteria: (1) fish passage capability, and (2) fish-way detectability. Only if both criteria are fulfilled a fishway can be considered as successful. To design a passable fishway structure defined geometric value limits due to hydraulics and fish physiology must be considered. Additionally, the entrance of the fishway must be passable as well as detectable. The present paper deals with a planned fishway in northern Germany. Due to tidal influenced flow parameters, the fishway outlet was designed to be orthogonal to the downstream river system. Hence, negative influences concerning fish entering the structure as well as ship movement can be assumed. Besides passable flow velocities and a minimum of turbulence at the entrance area, the appearance of a continuous leading flow with velocities larger than 0.2 m/s are important parameters to guarantee a successful structure. These parameters were taken into account to design a fish friendly entrance. Furthermore, public authorities gave limitations of maximum mean inlet velocities because the downstream water body is a small federal waterway with ship traffic where obstruction has to be avoided. The entrance of the fishway as well as 100 m of the downstream water body is analyzed via numerical 3D CFD simulations. The main aim is to verify the hydraulic flow situation at the inlet zone of the fishway. Investigations include three different inlet structures and results lead to an optimized design of the fishway's entrance.