Hydrodynamic Implications of Levee Breach Width Variation on Turbulence Structures and Discharge Efficiency

Abstract

This study investigates the effects of levee breach width on flow and turbulence structures, as well as on the discharge coefficient, under river-type flow conditions using the open-source computational fluid dynamics (CFD) software OpenFOAM. A three-dimensional (3D) Reynolds-averaged Navier–Stokes (RANS) model coupled with the volume of fluid (VOF) method was employed to capture the complex free-surface flow dynamics in the vicinity of the breach. The numerical model was validated against experimental data, showing good agreement in terms of discharge coefficients, water surface profiles, and velocity distributions. Under the fixed upstream discharge, approach Froude number ( F r ), channel width, and downstream boundary condition considered in this study, the simulation results revealed that increasing the breach width causes the flow to become more asymmetric, with high-velocity regions shifting toward the downstream side of the inundated area. This transition enhances velocity gradients and flow deflection, as indicated by the increasing flow deflection angle. Furthermore, as the breach width increases, the vertical vorticity, Reynolds shear stress, and turbulent kinetic energy (TKE), along with its production and dissipation, are intensified, indicating stronger turbulence and greater energy conversion from mean flow to turbulent energy. These combined effects result in increased hydraulic resistance and a gradual decline in discharge efficiency as breach width increases. The findings suggest that breach width is a critical parameter influencing overflow into inundated areas during levee failure under flood conditions and should be carefully considered in flood risk assessments and hydraulic design.