The effect of onshore wind on wave overtopping of a vertical sea wall

Abstract

Strong winds can produce overtopping rates that are considerably higher than predicted by the EurOtop formulae, which do not make provision for wind. However, no detailed industry guidance exists about the quantification of those wind effects. Physical modelling tests (scale 1:21) investigated how the mean rate of overtopping changed with wave frequency under the influence of various wind speeds. The nature and quantity of overtopping was found to be strongly related to the frequency of the incident wave. The wind had a significant effect on the mean overtopping rate, with the most pronounced effect occurring when the overtopping was at its most impulsive. Analysis showed that the wind had more influence than had been seen in other experiments, perhaps due to shallow water at the toe of the wall. Whilst the test results’ specific values may not represent reality, it is suggested that their trends do. The findings suggest that design decisions that do not fully consider the wind’s effect on overtopping might result in vertical sea walls that are too low to limit overtopping to acceptable rates when strong onshore winds influence it. These concerns are heightened if it is accepted that wind scaled according to Froude’s law should be increased to make it compatible with real-life conditions.