Effects of Including Inner Shelf Currents in Surf Zone Modeling Studies

Abstract:

When modeling surf zone circulation, it is often convenient to neglect the influence of currents generated on the inner shelf. The forces relevant to the inner shelf are generally an order of magnitude weaker than the wave induced forces in the surf zone, and their prediction may require nesting into a larger-scale model domain. However, rip currents create situations in which the surf zone and inner shelf coexist, making it potentially important to include inner shelf dynamics in a nearshore model. To investigate this, we used the Coupled Ocean Atmosphere Wave Sediment Transport (COAWST) modeling system to simulate rip currents with and without the presence of inner shelf currents. Field observations from the Field Research Facility (FRF), Duck NC, were used to validate the model, including in-situ current meter data on the inner shelf, and Argus wave-averaged movies that show the locations and trajectories of rip currents. The model results show that inner shelf currents can significantly affect rip current behavior at the field site, including determining whether rips will exit the surf zone vs. re-enter as a closed circulation cell. Thus, inclusion of inner shelf currents was essential for model skill in such cases. The different rip behavior will be further analyzed in terms of the modeled 3D momentum budget.