The wave force on vertical breakwater exerted by the standing wave with overtopping was studied experimentally in the present paper. In the experiment, vertical breakwaters with various heights under the action of a set of incident wave conditions were conducted in a two-dimensional wave channel. The relationship between height of breakwater and wave crest height in overtopping wave was firstly examined. Comparing with the situation of non-overtopping wave on the breakwater, the experimental results showed that wave forces due to wave overtopping were reducible 18% in maximum. Empirical formulas for estimating wave forces on breakwaters by wave overtopping were proposed in this study.
Wave overtopping occurs when the crest of breakwater is lowered below the maximum water surface elevation. This phenomenon is allowed for the design of maritime structures in order to reduce the wave force on the wall and to save the construction cost. Thus the estimation of the quantity of wave overtopping has been become an essential part of the design of breakwaters. Nevertheless, most previous studies paid only attention to the volume rate of wave overtopping, rather than its influence on wave forces on breakwaters. Wave overtopping is a complicated phenomenon arising from the interaction of incident waves and the structure. Studies of the feature of wave overtopping were examined by means of experiments, such as Saville and Caldwell (1953) for a vertical wall, Sibul (1955) for an inclined wall, and Iwagaki et al (1965) for effects of incident waves and mean water level on wave overtopping. The formula of wave overtopping rate given by Weggel (1976) was summarized in the Shore Protection Manual (1984) for various structure types. Endo and Miura (1983) obtained a relationship between wall height and wave crest height in wave overtopping, based on experimental results.