A method that can take into account the transmitted wave heights and the allowable overtopping discharges together has been presented in order to determine the crest freeboards of breakwaters. Thus, the relationships of the incident waves, mean overtopping discharges and the transmitted wave heights have been quantitatively analyzed by various empirical equations which have separately been used according to the types of breakwaters up to recently. The present results have been satisfactorily

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... ibrated through the comparison with the previous results of EurOtop (2018) for the same condition. The relationships of dimensionless mean overtopping discharges and wave transmission coefficients for any incident waves have also been presented and compared them with the types of breakwaters. In addition, the allowable overtopping discharges can be evaluated from the combinations of the transmitted wave heights and the mean overtopping discharges with respect to the various periods and heights of incident waves. Finally, the method for determining the relative crest freeboards of breakwaters with the allowable overtopping discharges has been applied to both the rubble-mound breakwaters and the composite breakwaters. It has been found that the relative crest freeboards of breakwaters tend to be decreased sharply as the allowable overtopping discharges are increasing. In particular, the relative crest freeboards of composite breakwaters should be larger than those of the rubble-mound breakwaters under the condition of the same overtopping discharges in the small ranges, whereas the opposite trends can be shown for the allowable overtopping discharges in the large range over some amounts of level. This may be due to the effects of that the relatively larger transmitted wave heights can be induced by the direct impacts of the overtopping discharges to the harbors inside the composite breakwaters, while, in the rubble-mound breakwaters, the overtopping discharges are mildly transferred along the inside slopes of breakwaters. However, these effects seem to be neglected when the overtopping discharges become very large, the penetration effects may even be considered in the rubble-mound breakwaters instead.