Breaching of sea dikes initiated from the seaside by breaking wave impacts

Abstract

Sea dikes are of crucial importance for the protection against flooding in low-lying coastal areas in Germany as well as in the Netherlands and Denmark. Since the breaching of sea dikes induced by storm surges is regarded as one of the main causes of coastal flood disasters, the detailed knowledge on the processes of breach initiation and development is crucial for the reliable prediction of the warning time and the initial conditions at the defence line which are needed to properly model the flood wave propagation. In order to fulfill those needs, the focus of this research was on the development of a computational model for the simulation of erosion and breaching of sea dikes. The entire model system consists of two parts: preliminary and detailed model. The preliminary model provides a fast, but rough estimation of dike breaching and it needs only basic input data, since only simple empirical equations are used. The detailed model is more demanding in terms of computational effort and input data, but it represents a step towards a completely process-oriented simulation of dike breaching. Based on the results of laboratory experiments a completely new model for the estimation of grass roots effect on the soil erosion resistance was developed on the basis of new laboratory experiments. The results of the performed laboratory experiments formed the basis for the detailed erosion model of the grass reinforced clay cover, while the small-scale tests performed in a wave flume provided general information on the breach growth, from the breach initiation till the full breach. Compared to the preliminary model, the developed detailed model requires more input data, but it includes detailed simulation of grass and clay erosion.