The failure probability of grass erosion due to wave overtopping: A case study of the Afsluitdijk, The Netherlands

Wave overtopping is one of main failure mechanism of flood protective structures. Experiments and numerical simulations have shown that transitions are weak spots for cover erosion. Transitions in geometry and in bed roughness affect the cover erosion significantly by local deceleration and acceleration of the flow. This paper presents a method to compute the critical average overtopping discharge for a complex dike geometry, including transition, applied to the Afsluitdijk case study. The results show that although the critical overtopping discharge decreases with increasing wave height, the sensitivity of the critical overtopping discharge for wave height decreases for higher waves. This is shown for both the COM and the VE-TM models for all locations along the dike’s cross section. Although further validation of both models is needed for a wider range of dike configurations, the results show that both models are able to probabilistically assess grass erosion based on the critical overtopping discharge for complex dike geometries, including transitions.