Breaking-wave crest lengths and associated vorticity input under varying directional spread

Under directionally spread wave conditions, waves with finite crest lengths lead to alongshore gradients in wave-breaking force, resulting in the injection of small-scale eddies at wave-crest ends. These eddies are hypothesized to interact and develop into offshore-directed flows known as transient rip currents. These currents are important to nearshore hydrodynamics, as well as geomorphology and ecosystem dynamics through cross-shore transport of nutrients, larvae, sediment, and other particulate matter. To investigate the injection of vorticity and resulting cross-shore exchange under varying wave conditions, we use observations from laboratory experiments at the O.H. Hinsdale Wave Research Laboratory's Direction Wave Basin and numerical simulations using a phase-resolved nonlinear Boussinesq model (FUNWAVE-TVD). For the laboratory's alongshore-uniform barred beach, the modeled spatial patterns of phase-resolved quantities (short-crested breaking and orbital velocities) and phase-averaged quantities (bulk wave statistics and mean circulation) were compared with in-situ and remotely-sensed measurements for a range of significant wave heights (0.15 to 0.3 m) and directional spreads (0 to 40 degrees). Simulated model fields will be used to investigate breaking wave-crests statistics, wave-breaking force (computed from simulated breaking induced eddy viscosity), and cross-shore exchange under varying directional spreads. Preliminary analysis has shown that simulated mean crest lengths were similar to laboratory observation derived estimates and decrease with increasing directional spread. Analysis of the processes linking forcing mechanisms to transient rip current activity provide essential insight into the dynamics leading material transport within the nearshore.