Wave overwash at low-crested beach barriers

To increase physical insight into wave overwash processes at low-crested beach barriers, wave overtopping discharge events rather than the conventional average overtopping discharge need to be quantified. Also, in order to make intelligent use of the many empirical formulations on wave overtopping discharge at breakwaters from literature, a single-valued appropriate slope for a natural beach needs to be derived. To resolve these issues, laboratory experiments of composite-slope low-crested barriers were carried out. The tests deal with overwash on a smooth non-uniform slope on shallow foreshores. The conventional average overtopping discharge concept does not represent the discontinuous character and associated strength of overtopping flow. Instead, e.g. for purposes of morphological modeling, wave overtopping should be treated as an event-based process. In this study, several new parameters such as the wave-averaged overtopping time, the relative total overtopping time, the overtopping asymmetry, the average maximum discharge and the average instantaneous discharge are defined and formulated. A new approach for defining an equivalent slope is proposed in the parameterization of the overtopping discharge that also takes into account effects of the wave period. It is experimentally shown to be an improvement over the conventional approach by Van der Meer [1998], especially eligible for low-crested sandy slopes such as barriers, dikes, dunes, etc on shallow foreshores.