Numerical investigation of the effects of roughness, a berm and oblique waves on wave overtopping processes at dikes

Abstract

The mean overtopping discharge and the overtopping flow parameters related to individual overtopping events are often used to characterize the wave overtopping processes at dikes. Roughness, berms and oblique waves have significant effects on the wave overtopping processes at dikes while these effects are still not fully understood. A 2DV OpenFOAM® model is validated using experimental data for predicting flow velocity and layer thickness at the waterside edge of the crest. The validated numerical model is then applied to investigate the effects of roughness and a berm on the flow velocity and layer thickness. The roughness is modelled by creating protrusions along the waterside slope. Numerical model outcomes indicate that existing empirical formulas underestimate wave overtopping quantities. Introducing a roughness factor to existing empirical formulas leads to better estimates of the flow characteristics. We found that the flow characteristics are more sensitive to the variation of the berm width than to the berm level. Model results demonstrate that existing formulas for predicting the flow characteristics, as derived based on smooth straight slopes, also work well for slopes with a berm. Rayleigh and Weibull distribution functions are derived to estimate the flow velocity and layer thickness with exceedance probabilities below 10%. In order to take oblique waves into account, the 2D numerical model is extended into the 3D model domain. This 3D OpenFOAM® model is validated using measured mean overtopping discharges. The influence of oblique waves on the mean overtopping discharge in combination with a berm is analysed. The numerical model computations confirm that the reductive influence factor of oblique waves is dependant on the berm width.