RANDOM WAVE OVERTOPPING OF SIMPLE SEA WALLS - A NEW REGRESSION-MODEL

Sea walls are expensive, and fixing a seawall freeboard at too large a value has a financial penalty and is unnecessarily damaging to the na tural environment owing to the increased impact of the structure on it s surroundings. On the other hand, if the crest of a sea wall is set t oo low then there are potential problems with structural safety and fl ooding from wave overtopping. Hence, it is important to strike the cor rect balance between satisfying the structural and functional requirem ents of the project, avoiding unnecessary expense, and having undesira ble impacts on the surrounding environment. The prediction of wave ove rtopping rates is usually based on empirical equations fitted to labor atory data. These equations do not have any theoretical basis. However , a new model has now been developed which, unlike existing expression s, accounts for the fact that no overtopping (apart from wind-blown sp ray) occurs if the sea-wall freeboard exceeds the maximum wave run-up on the face of the structure. This fact is of practical importance bec ause allowable overtopping discharges to ensure the safety of people a nd property are quite small. This paper starts with a brief review of existing overtopping equations, then presents the new model, and concl udes by giving an example of its practical implications. It is shown t hat, for some conditions, the new model predicts sea-wall freeboards w hich are several metres less than those predicted by the well-known ex pression given by Owen.