Relatively high-energy shallow-water wave that causes degradation of a beach by moving more material seawards than landwards, thus having a net erosional effect on the adjacent beach. It is characterized by high frequency, which implies that the swash is impeded by the backwash from the preceding wave. The backwash is more effective than the swash in moving material, and waves having this character are usually steep and associated with onshore winds. The erosional effect is also enhanced by the near-vertical plunge on breaking. It is favoured by a relatively steeply sloping offshore zone.