Narrow Results

The majority of prediction methods for overtopping of seawalls are based on physical model tests under simple 2-dimensional conditions. There is some evidence (not unambiguous) that overtopping may increase at small degrees of obliquity, and that corners (in plan) may give local concentrations of overtopping. This paper, produced as part of the VOWS project on impulsive (violent) overtopping of vertical seawalls, describes experiments to measure mean and wave-by-wave overtopping discharge under conditions of oblique wave attack and at 3-d corners. Results analysed in the first phase of this 3-d study suggest that mean overtopping discharges reduce significantly with increasing angle of wave attack and that the occurrence of impulsive overtopping diminishes rapidly with obliquity of wave attack > 30°. It is also observed that overtopping may not increase in corners with an approach beach or berm.

Current empirical methods often predict inadequately the overtopping discharges of waves on shallow sloping seawalls. As part of the DEFRA/EA funded research project FD2410, Coastal Flooding Hazard by Wave Overtopping, physical model studies have been undertaken for structure configurations of 1:2,1:10 and 1:15. For 1:10 and 1:15 sloping structures, no data or method is currently available for predicting accurately the overtopping discharge. Although discharge quantities are widely used for analysing the hazard of overtopping, this may not be the best way of defining a violent overtopping event. Discharge velocities may also be of key importance and it is these velocities that are reviewed here for overtopping of waves on sloping structures. Two numerical non-linear shallow water models have also been used for comparison against the physical results to see whether they can be implemented as a valid prediction tool.