This paper reviewed and extended the Shore Protection Manual (SPM) method and Coastal Engineering Manual (CEM) for estimating the wave overtopping rates under irregular waves. An improved formulae of applying a monochromatic wave overtopping equation to random waves is presented. When the freeboard is zero, the overtopping rate is related to not only wave height, but also wave velocity. The assumption made by the SPM method is not practical, leading to the overtopping rates are underestimated or overestimated. This paper improves the unreasonable assumptions. Furthermore, the effects of the statistical distribution of ocean wave are taken into account. The results are compared with SPM method, CEM method, Experimental data and Numerical results and other empirical method. One concludes that the improved method is analytically correct, and suggested to be a reference design principle.
When water waves reach seawalls or revetments, they usually go through the physical processes of dissipation, reflection, runup, and sometimes overtopping of the structure. The wave overtopping is a violent phenomenon which may cause the failure of coastal structures and damages to the properties and lives. Wave overtopping significantly affects the functional efficiency, safety of transit, mooring on the rear side and, to some extent, the structural safety of coastal structures. Although overtopping can be reduced or even eliminated by increasing structure heights, the better structure design in term of function, aesthetics, and cost is often one that allows overtopping under extreme conditions. On the other hand, in the design of the crest elevation of a seawall, usually a tolerable wave overtopping rate is applied (Owen,1980; Goda,1985; van der Meer,1994). In general speaking, prediction the overtopping rate of random waves is difficult, because not every wave can overtop the structure, only the fraction of waves that runup beyond the freeboard can lead to overtop.
