Velocity and flow depth variations during wave overtopping

Nowadays the protection of our country for high sea levels and heavy storms is daily news. The ComCoast project (COMbined functions in the COASTal defence zones) is originated by ten organisations out of five European countries bordering the North Sea coasts in order to develop innovative solutions for flood protection in coastal areas. Instead of automatically raising the coastal defence zone on places where more protection is needed, ComCoast creates multifunctional flood management schemes with a more gradual transition from sea to land. Part of the new solutions is the wave overtopping resistant dike. This so called "overtopping durable dike", should withstand wave overtopping during a storm in much better than the current ones. More knowledge about the loads on the dike by wave overtopping is therefore needed. Recently formulae have been derived for maximum flow depths and velocities on the crest and inner slope. These formulae are based on the difference between fictive wave run-up and the crest freeboard. This is a good measure to determine the flow depths and velocities on the dike. These formulae have been calibrated by two independent physical model test programs in different wave flumes by Schüttrumpf in Germany and by Van Gent in the Netherlands. If these two studies are compared there appears to be a large difference in the empirical coefficient of the flow depth equation of a factor 2.2. They collectively wrote a paper and found the test set-up as primary cause for the discrepancy in the flow depth coefficient. The differences between the test set-up and analysis have been studied in the present thesis. The overtopping time and the variation of velocity and flow depth in time have been investigated as well. These quantities are also necessary to be able to give a full description of the loads on the dike during wave overtopping. The present study shows that the outer slope is of great importance in the flow depths and velocities on the crest. This is new knowledge. Schüttrumpf performed his tests on a dike model with an outer slope of 1:6 and Van Gent used a dike model with an outer slope of 1:4. The empirical coefficients appeared to be dependent on the outer slope steepness. Subsequently a formula for the overtopping time is created, based on the difference between fictive wave run-up and crest freeboard. The overtopping time appeared not to be a function of the outer slope. The variation of flow depth and velocity in time can be approached with a linear function. The new equations for wave overtopping are compared to the results obtained by tests with the wave overtopping simulator. The wave overtopping simulator is a machine which is able to simulate wave overtopping on a dike on full scale. Despite the difficulties in measuring velocities and flow depths during these tests, one can conclude that the wave overtopping simulator works very well. Storms with high overtopping discharges can be simulated accurately for testing strength and stability of a dike.Civil Engineering and Geoscience