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Seminar: Modifying the Seafloor to Study Surf-Zone Dynamics: Breaking Waves, Rip Currents, and Shifting Sandbars
6 May 2019 @ 1:00 pm - 2:00 pm
Dr. Melissa Moulton
Applied Physics Laboratory
University of Washington, Seattle
The surf zone is the boundary between land and the open ocean. In the surf zone, ocean waves refract, steepen, and break, driving strong currents and transporting sand, biota, and pollutants along the coast and between land and sea. Improving our knowledge of these processes is important for making better predictions of flooding, erosion, swimmer hazards, and storm impacts on infrastructure and ecosystems. Previous work has used numerical and laboratory models, which may lack important physics, and passive observations in the field, where it is difficult to isolate individual processes. Here, we adopt a novel approach to studying complex coastal systems by artificially perturbing the seafloor to create large hydrodynamic and morphodynamic signals.
In a series of experiments conducted on an energetic ocean beach at the US Army Corps of Engineers Field Research Facility in Duck, NC, we dredged large holes and channels in the seafloor and observed the subsequent hydrodynamic and morphologic evolution. We used in situ and remote sensing observations of the system response, paired with numerical model simulations, to study the feedbacks between waves, currents, and bathymetry. Excavated holes smoothed and filled in at varying rates as a result of gravity-driven sediment transport controlled by wave-current bed shear stresses. Rip currents that formed in dredged channels grew faster with increasing wave breaking and were suppressed by the inertia of alongshore currents. Results from these experiments are being used to improve forecasts of coastal morphologic change and swimmer hazards.