Atlantic salmons smolts crossing successive dams and hydropower plants: a multi year hydrodynamic analysis

Dams fragment rivers and restrict fish migration. The artificial flow conditions created by hydropower plants (HPP) in rivers disorient downstream migratory species. A detailed understanding of the hydrodynamic variables used by fish while crossing these obstacles is an essential prerequisite for more sustainable, green, and fish-friendly infrastructures. This study therefore investigates the hydrodynamic conditions used by 582 young Atlantic salmons (smolts) during the successive crossings of 6 run of the river HPP located on the Belgian Meuse River in Wallonia. The migratory patterns of smolts in the vicinity of HPP were obtained by acoustic telemetry surveys spanning from 2014 to 2023. The flow conditions encountered during the migrations were numerically modelled in 1 and 2 dimensions depending telemetric data resolution and the sites configuration. The fish trajectories and the flow variable combined unveil the major influence of the flow velocity on the migratory behaviour of smolts. An essential information for the restoration of hydrodynamic conditions favouring rapid and effective downstream migrations of fish near hydraulic structures.