Effects of Natural Sea States on Wave Overtopping of Seadikes

The influence of natural sea states on wave overtopping constitutes one of the investigated aspects within the German research project "Loading of the Inner Slope of Seadikes by Wave Overtopping" (BMBF KIS 009). In fact, the incident wave spectrum is influenced by the very complex morphology in shallow coastal zones like wadden seas and shallow forelands. Therefore, the wave spectra in these areas are quite different from the commonly used theoretical single peak wave spectra. Wave run-up and wave overtopping are influenced by the shape of these wave spectra and can not be simply described on the basis of theoretical single peak wave spectra like PM, JONSWAP or TMA wave spectra. The objective of this paper is to study experimentally the influence of different wave spectra on wave overtopping for seadikes by means of small and large scale model tests. For this purpose, model tests were run for the following boundary conditions: (i) Regular waves, (ii) TMA-spectra (single peak), (iii) JONSWAP-spectra (single peak and double peak spectra composed of two superposed JONSWAP-spectra) and (iv) Measured single, double and multi peak spectra from different locations at the German and Dutch coast. The investigated wave spectra were provided by Dipl.-Ing. H.D. Niemeyer (Coastal Research Station, Norderney) and Dipl.-Ing. J. Grüne (Coastal Research Centre, Hannover) for several locations at the German North sea coast, by Dipl.-Ing. H. Bergmann (LWI) for Probstei / Baltic Sea, by Dipl.-Ing. T. Trampenau (LWI) for Warnemünde / Baltic Sea, by ir. John G. de Ronde (Rijkswaterstaat) for several locations in the Netherlands. Their contributions are gratefully acknowledged. The support of the german ministery of education and research (BMBF) within the project BMBF-KIS 009 is also gratefully acknowledged.