Coastal-erosion processes and assessments of setback distances
Komar, P.D.; Marra, J.J.; Allan, J.C.
Solutions to Coastal Disasters '02: 808-822
Methodologies have been developed to establish setback distances for use on the coast of the Pacific Northwest where the principal hazards are wave runup and surge during major storms, and El Ninos that produce unusually high tides and the northward movement of beach sand within littoral cells, creating "hot spot" erosion sites. Of concern is the discovery that the severity of storms and their generated waves have been increasing for at least the past 25 to 50 years, with the underlying cause and possible connection to global-climate change not being fully understood. Important are extreme water levels that result from combinations of high predicted astronomical tides, processes related to El Ninos that elevate tides still further, and the occurrence of a major storm that produces high levels of wave runup on beaches. Having made such an assessment, a geometric model is employed to evaluate the potentially maximum horizontal retreat of foredunes, thereby serving as a guide for the placement of setbacks in dune areas. In areas where the beach is backed by sea cliffs, the analysis yields a determination of the average number of hours per year the cliff is impacted by the high waters of tides plus wave runup, providing an assessment of the susceptibility of the property to wave attack, one component in the evaluation of an appropriate setback distance.