· · · Repository Hydraulic Engineering Reports

Wave overtopping is one of the most important processes for the design of seadikes which was responsible for many severe dike failures in the past. Wave overtopping can not be avoided due to the random nature of the waves and the uncertainties associated with the determination of the design water level. The present design on wave overtopping is based on average overtopping rates. Nevertheless, average overtopping rates are not sufficient for the design of seadikes, because overtopping velocities and overtopping layer thicknesses are required to assess the infiltration and erosion on the landward side of seadikes by overtopping water. The objective of the present thesis is the determination of the velocities and layer thicknesses on the seaward slope, the dike crest and the landward slope as a function of the relevant wave and dike parameters by means of theoretical and experimental investigations. Small scale model tests have been carried out in a wave flume with typical dike profiles by using regular waves and wave spectra. Small scale model tests are influenced by scale effects and the transfer of the results to nature might be affected. Therefore, theoretical investigations on the influence of viscosity and surface tension on the model results are performed. It can be concluded that the results of the present study are not significantly influenced by scale effects and can be transfered to prototype scale. Wave overtopping is dependent on the processes associated to wave breaking and wave run-up on the seaward slope. Therefore, these processes are investigated first. Breaker type, breaking water depth, wave run-up height, wave run-down and the impact point of the breaking wave on the seaward slope are determined and described by means of empirical equations. The main part of this thesis is the determination of layer thicknesses and velocities on the seaward slope, the dike crest and the landward slope. Layer thickness and wave run-up velocities on the seaward slope are closely connected to the wave run-up height. Empirical formulae for layer thicknesses and a theoretical approach for overtopping velocities are derived for the dike crest. Overtopping velocities and layer thicknesses on the landward slope are derived on the basis of the two-dimensional momentum equation and the continuity equation. All derived formulae are calibrated by model tests with regular waves and verified by model tests with wave spectra.

Cost comparision of an Elastocoast revetment in comparison with a classical revetment in coastal protection.