Wave overtopping: impact of water jets on grassed inner slope transitions

The project SBW ('Sterkte & Belastingen Waterkeringen' with respect to grassed inner slopes focuses on the improvement of reliable overtopping criteria for the present dike structures. Experiments are carried out using a wave overtopping simulator. This device is developed to create full scale overtopping conditions on a inner slope. Experiments show initiation of erosion of the grass layer downstream of the transition of the slope and a horizontal part. The focus of the present research is modelling of the erosion process at a transition. The erosion process is described by two different models. The Transition Model (TM) is derived to describe the development of the scour hole due to the impinging forces of the overtopping wave tongue, known as surface erosion; The SSEA (Sites Spillway Erosion Analysis) model is taken to describe the headcut erosion process which occurs after the scour hole has reached a certain depth. The TM is based on a oblique impinging jet and a depth variable strength profile, in where near the surface the root system dominates, whereas with increasing depths cohesion and internal friction of the clay dominates.