Alongshore Variable Dune Erosion During Extreme Storms

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

Despite the importance of dunes, there are few concurrent field observations of surf and swash zone waves and currents, and beach and dune morphology during extreme storms. Thus, model simulations usually are calibrated and evaluated by comparison with observed pre- to post-storm changes in topography. The wave and current processes that drive these topographic changes, and the time and space scales of changes during periods of extreme storm activities, are not well understood. The project examines hydrodynamic processes during extreme storms that result in alongshore variable dune erosion over 100-m scales owing to wave collision. The outcomes of the project will improve coastal management, help protect coastal communities, and sustain coastal resources. The project will provide field training to undergraduates, recent graduates, and young professionals embarking on coastal careers by offering 2- to 3-week-long fieldwork-focused internships. This internship program will provide critical experience to participants enhancing the potential job placement in the field of coastal engineering. In addition, a graduate research student will be trained in the use of numerical models for the simulation of nearshore processes. Unique observations of surf and swash zone waves, and surf, beach, and dune morphology before, during, and after 3 large storms, combined with numerical model simulations, are used to determine the causes of alongshore variability of dune erosion, over 100-m scales. The hypotheses examined are: (i) alongshore variable dune erosion and recession rates depend on the initial surf zone bathymetry and associated hydrodynamics, and (2) positive feedbacks between wave runup, reflection, and offshore transport at the dune toe lead to erosional hotspots during storms. The importance during storms of surf-zone bathymetry and hydrodynamics to dune evolution, and the feedbacks between surf- and swash-zone processes and erosional hotspots are examined. The PIs will investigate how waves propagate across the surf zone and beach during extreme storms, and how parameterizations of wave processes used in numerical models may be different during more moderate conditions. Numerical simulations of dune evolution are sensitive to user-selected parameters, as well as to the offshore and surf-zone bathymetry, which often are not well known. Laboratory observations indicate that given best-fit sediment transport coefficients, models may simulate dune changes reasonably well, despite overestimating water levels and underestimating runup fluctuations. The research undertaken as part of this project will determine if the simulated hydrodynamics are accurate throughout extreme storms, and if the time history of simulated sand-level change is correct. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.