Breaching of sea dikes initiated by wave overtopping. A tiered and modular modelling approach

Sea dikes are used as defence structures against flooding in lowland areas with relatively high storm surge levels. The formation of a dike breach induced by wave overtopping was one of the most frequent causes of dike failure associated with disastrous damages. Therefore, dike breaching is closely related both to the dynamics of a protected coast and flood risk assessment/management. Despite the importance of dike breaching, the underlying processes, their simulation and prediction are still not well understood. Based on an extensive literature study on the most relevant processes associated with dike breaching and models available, a tiered modular modelling strategy has been developed which consists in a preliminary and a detailed breach model that build an appropriate model system for engineering practice. The model system applies to sea dikes made of a sand core and a clay cover with grass. Results from the preliminary model provide an overview of the overall breaching process and indicate which improvements are required in the detailed model. Results from the detailed model which includes new processes and model improvements removing some assumptions of the preliminary model provide a first step toward the development of a fully process-oriented breach model. Model validation against laboratory tests and experienced dike failures, although tentative, provides very encouraging results. Model uncertainties are evaluated making use of sensitivity analysis and level III reliability analysis. The model results are associated with large uncertainties which are mainly originated by the inputs parameters, especially the material properties. The overall results illustrate a tiered modular approach for the simulation of breach formation and growth in a real sea dike initiated by wave overtopping. The model system provides a proper departure basis for a fully process-oriented description of the breaching process in sea dikes.