Hydraulics of spoiler baffles for fish passage in slip-lined culverts

This study evaluates the hydraulics of spoiler baffles (SPBs) in slip-lined high-density polyethylene (HDPE) culverts. OpenFOAM Reynolds-averaged Navier–Stokes (RANS) simulations with the standard k–ε turbulence model characterized resistance, internal flow and baffle loading across SPB heights, densities and layouts. Results were validated against acoustic Doppler velocimeter (ADV) velocity measurements and piezometer headloss data. Numerical roughness coefficients matched experimental values with a mean absolute error of 5.44–6.85%, with larger deviations in denser and taller configurations. Velocity profiles showed reduced near-wall velocities upstream of baffles, strong gradients at baffle crests, and gradual downstream recovery with wake low-velocity regions. Hydrodynamic forces peaked on the upstream row and declined downstream due to wake shielding, and were dominated by pressure (form drag), with wall shear below 5%. The main contribution is the integration of bulk resistance, three-dimensional (3D) velocity and pressure fields, and row-wise hydrodynamic loading, which provide a quantitative basis for selecting geometries that enhance fish-friendly hydraulics while minimizing conveyance loss.