Wave runup, extreme water levels and the erosion of properties backing beaches

A model has been developed to evaluate the susceptibility of coastal proper ties to wave induced erosion. The model includes analyses of the probabilit ies of extreme water levels due to tides affected by various oceanographic and atmospheric processes, and the runup elevations of storm waves on beach es. The application is to the Oregon coast where measured tides often excee d predicted astronomical tides by tens of centimeters, especially during th e occurrence of an El Nino. The measurements of wave runup on dissipative b eaches typical of the Oregon coast depend primarily on the deep-water signi ficant wave height, but when combined with other data sets show some depend ence on the wave period and beach slope. Predicted extreme water elevations due to the combined processes are compared with measured elevations of the junctions between the beach face and the toe of foredunes or sea cliffs. T he objective is to evaluate the frequency with which water can reach the pr operty, providing an evaluation of the susceptibility to potential erosion. Application is made to a number of sites along the Oregon coast, revealing differences between the various littoral cells depending on the quantity o f sand on the beach and its capacity to act as a buffer from wave attack. A more detailed application is made to the Newport Littoral Cell, demonstrat ing how this type of analysis can aid in making coastal management decision s. Although the application here is to the Oregon coast, the model can be u sed on other coastlines with evaluations of extreme tides and storm-wave ru nup specific to those locations.