An Experimental Study On Characteristics Of Overtopping Flow Against Sea Dikes In Regular Waves

With global warming causing sea levels to rise and super typhoon to appear more frequently, it will cause severe overtopping to erode the crest and the inner slope of sea dikes. In order to evaluate the safety level of sea dikes in design and operation phases, studies on the mechanism of erosion induced by the overtopping flow have been received more and more attention since the 1990s. Some advances in experimental and numerical investigation on the overtopping flows on the sea dike crest have been achieved. The motivation of present research is to understand the characteristics of the overtopping flow against sea dikes under the effect of the regular waves, particularly at considering the effects of the fence panels of sea dikes.After literature survey in the field of overtopping against sea dikes, researches on the overtopping discharge, the thickness and the velocity characteristics of overtopping flows are reviewed. By using the high-speed camera and the flow visualization approach, a physical model experiment was designed to study hydrodynamic parameters of overtopping flows on the crest, including the cases of sea dikes with and without fence panels. For the cases of sea dikes with and without fence panels, the experimental results show that the layer thickness on the crest decrease exponentially in term of the distance along the crest, which accords with the published semi-empiric formula based the approximation of the shallow water equation. However the measured velocity on the crest increases which is completely different from the velocity distribution predicted by the semi-empiric formula. For the case of the fence panels, the experimental results show that the layer thickness at the leading edge of the dike crest is consistent with the empiric formula in terms of the wave steepness and freeboard levels when the height of fence panels above the still water level is small. However, the measured value is obviously smaller than the values calculated with of the empiric formula if more fence panels are placed on the sea dikes above the still water level.Finally, conclusions are derived based on the analysis of the experimental data, and primary suggestions are offered for design of practical projects and validation of numerical models of the overtopping flow over sea dikes.