Shoreline erosion due to extreme storms and sea level rise

Abstract

A summary is presented of research conducted on beach erosion associated withextreme storms and sea level rise. These results were developed by the author andgraduate students under sponsorship of the University of Delaware Sea Grant Program.Various shoreline response problems of engineering interest are examined. Thebasis for the approach is a monotonic equilibrium profile of the form h = Ax2 /3 inwhich h is water depth at a distance x from the shoreline and A is a scale parameterdepending primarily on sediment characteristics and secondarily on wavecharacteristics. This form is shown to be consistent with uniform wave energydissipation per unit volume. The dependency of A on sediment size is quantifiedthrough laboratory and field data. Quasi-static beach response is examined torepresent the effect of sea level rise. Cases considered include natural and seawalledprofiles.To represent response to storms of realistic durations, a model is proposed inwhich the offshore transport is proportional to the "excess" energy dissipation perunit volume. The single rate constant in this model was evaluated based on largescale wave tank tests and confirmed with Hurricane Eloise pre- and post-stormsurveys. It is shown that most hurricanes only cause 10% to 25% of the erosionpotential associated with the peak storm tide and wave conditions. Additionalapplications include profile response employing a fairly realistic breaking model inwhich longshore bars are formed and long-term (500 years) Monte Carlo simulationincluding the contributions due to sea level rise and random storm occurrences. (PDF has 67 pages.)