Wave Overtopping at Smooth Impermeable Steep Slopes with Low Crest Freeboards

Abstract

Extensive knowledge is available on the overtopping behavior of traditional smooth impermeable sea defense structures, such as mildly sloping dikes and vertical walls, both typically featuring a high crest freeboard to reduce wave overtopping. A particular design application emerges in the development of wave energy converters of the overtopping type, where maximization of wave overtopping is required, i.e., smooth impermeable steep sloping structures with low crest freeboards subjected to nonbreaking waves. To date, relatively limited knowledge is available on the overtopping behavior of those structures. In this study, the average overtopping rate obtained from new experiments has been analyzed and compared with existing prediction methods. This study contributes to a better knowledge on the overtopping behavior of the steep low-crested structures, which is positioned in between that of mildly sloping dikes and vertical walls and that of structures with zero crest freeboards and relatively large crest freeboards. The existing prediction methods seem unable to predict the significant effects of the slope angle and small relative crest freeboards on the average overtopping rate accurately. Therefore, a new set of prediction formulas is proposed based on the new experiments combined with existing data from literature. These formulas include wave overtopping at vertical walls subjected to nonimpacting waves and at structures with zero crest freeboard.