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Designing free-surface bypasses for fish-friendly inclined bar rack: A CFD parametric study
Guillaume Bon1, Ludovic Chatellier2, Yves Le Guer3
1Institut PPRIME, UPR3346, CNRS, Universite de Poitiers, ENSMA, Poitiers, 86073, France; France Hydro Electricite, Paris, 75008, France.
Journal of Environmental Management
|July 23, 2026
Summary
Optimizing fish bypass systems at hydropower intakes ensures ecological continuity. This study used CFD simulations to analyze flow distribution, improving fish guidance and balancing water discharge for renewable energy goals.
Area of Science:
- Environmental Engineering
- Fluid Mechanics
- Renewable Energy Systems
Background:
- Run-of-river hydropower faces challenges balancing energy needs with biodiversity preservation.
- Downstream fish migration requires effective fish-friendly bypass systems at water intakes.
- Optimal design of multi-entrance bypass systems for flow distribution is understudied.
Purpose of the Study:
- To parametrically investigate the flow distribution and hydraulic attractiveness of a two-entrance bypass system.
- To evaluate the influence of entrance geometry, orientation, and additional devices on bypass performance.
- To provide recommendations for designing effective water intake infrastructures for fish passage.
Main Methods:
- Computational Fluid Dynamics (CFD) simulations utilizing the Volume of Fluid (VOF) multiphase model.
- Modeling bar racks with narrow spacing as a porous volume for efficient meshing.
- Parametric analysis of bypass entrance width, shape, orientation, pinching systems, and downstream channel design.
Main Results:
- Optimized entrance orientation and the inclusion of a pinching device significantly improved discharge distribution balance between bypasses.
- Entrance geometry and downstream channel separation critically influence hydraulic attractiveness and flow characteristics.
- The porous volume approach for modeling bar racks proved effective for simulation feasibility.
Conclusions:
- The study provides crucial insights and recommendations for designing more effective fish bypass systems at water intakes.
- Optimizing bypass entrance design is key to ensuring equitable flow distribution and successful fish guidance.
- This research advances knowledge on hydropower infrastructure design for enhanced ecological continuity.
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