Wave impacts on vertical and composite breakwaters

A description is given of a model to evaluate the fraction of waves which, in a sea state, break directly onto the vertical face structures, or sfightly earlier, generating severe hydrodynamic actions over the walls. The model moves from the breaking criterion proposed by Calabrese in 1998, which allows to estimate the percentage of breaking waves, as the number of waves which, according to the Rayleigh distribution, would have been larger than a threshold wave height Hb,- This portion of waves represents an upper limit for the number of impacts, including the waves which, collapsing before reaching the wall, arrive already broken at the structure. In this work a second wave height threshold Hbro is proposed, which appear effective in describing the transition from the impact to the broken mode. This permits to derive the impact waves percentage, simply removing the broken waves from the number predicted by the Calabrese's breaking criterion