Author(s): Antoine Ecorce; Dominique Courret; Ludovic Chatellier; Laurent David

Linked Author(s): Laurent David

Keywords: Fish migration; Water drops; Impact pressure; OpenFOAM; URANS; VOF

Abstract: During their downstream migration, fish encounter obstacles such as waterfalls, spillways and downstream migration devices, and are forced to pass through them. However, the current criterion for ensuring the safe reception of fish is not entirely satisfactory as it overlooks jet characteristics. This study investigated the waterfall at the outlet of the Pébernat hydro-power plant's downstream migration device (Ariège River, France), where fish are forced to pass through a 3 m drop. The aim was to characterize the jet's hydrodynamics in the air and in the receiving pool, before and after the deepening work on the pool. The study combines in situ measurements of the pressure exerted by the jet on the pool's bottom with URANS-VOF 3D modelling. The model captures the order of magnitude of the high dynamic pressure values recorded on site. As the risk of damage to fish is likely to be related to the highest dynamic pressures, this modelling approach appears to be a promising tool for characterizing the jet's hydrodynamics in detail, both in the air and in the receiving pool. This is all the more interesting given that in situ measurements are difficult to carry out. A comparison of the situation before and after the deepening work, based on measurements and modelling results, reveals a significant improvement in fish reception conditions. The sharp decrease in maximum dynamic pressure at the bottom (from ~280 mbar to ~150 mbar) is consistent with the observed reduction in fish injury rates. These findings highlight the reliability of 3D modelling as a tool for refining criteria to ensure safe fish reception and for designing solutions.

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.259

Year: 2026