Sea dikes breaching initiated by breaking wave impacts - State of the art

Sea dikes are of crucial importance in the defence systems of low-lying coastal areas in countries such as Germany, The Netherlands or Denmark, etc. Breaches of sea dikes induced by storm surges are regarded as the main cause of coastal flood disasters. Therefore a reliable prediction of both initial conditions for the breach occurrence and the breach development is urgently needed. Depending on the structure of the sea dike and on the hydraulic and morphological boundary conditions, one may distinguish several causes for the initiation and formation of a breach. The main failure mechanisms are (TAW,1999a): \u95 wave overtopping and overflow, which may lead to the erosion of the shoreward slope and finally to breach initiation from the landward side \u95 breaking wave impact including wave run-up and run-down processes which may lead to the erosion of seaward slope (Fig. 1) and finally to breaching from the seaward side The knowledge of the processes of breach initiation and development is crucial for the prediction of the initial conditions at the defence line needed to model the flood wave propagation. For the prediction of a dike breach initiated by the wave overtopping, a PhD research was completed very recently (D'Eliso, 2007). However, as the processes associated with the dike breach initiation from the seaside as well as the breach growth itself are completely different from those related to overtopping, there is also an urgent need for a model to predict the breach growth initiated from the seaside by breaking wave impact on the outer slopeFloodsit