The influence of a berm and roughness on the wave overtopping at dikes

A reliable estimation of average wave overtopping discharge is important for dike design and safety assessment. Berms and roughness elements are widely applied to reduce the overtopping discharge over dikes. In this study, the effects of a berm and roughness on the wave overtopping discharge are investigated by means of physical model tests. New empirical formulae are derived from the analysis of the experimental data in order to provide more accurate estimations of reductive influence of berms and roughness on the wave overtopping discharge. Additionally, a new formula is developed to estimate the reductive influence of varying roughness along the waterside slopes with a berm. The new equations show a significantly better performance within the tested range when compared with existing formulae for the average overtopping discharge. •Physical model tests showed that the permeability of berms affects the berm influence factor.•New formulae are derived for the roughness influence factors and berm influence factors.•A new formula is derived for the roughness influence factor of combined multiple roughness elements along the bermed slope.•The new formulae outperform the existing formulae.