To investigate the dynamics of flows near nonuniform bathymetry, single channels (on average 30 m wide and 1.5 m deep) were dredged across the surf zone at five different times, and the subsequent evolution of currents and morphology was observed for a range of wave and tidal conditions. In addition, circulation was simulated with the numerical modeling system COAWST, initialized with the observed incident waves and channel bathymetry, and with an extended set of wave conditions and channel geometries. The simulated flows are consistent with alongshore flows and rip-current circulation patterns observed in the surf zone. Near the offshore-directed flows that develop in the channel, the dominant terms in modeled momentum balances are wave-breaking accelerations, pressure gradients, advection, and the vortex force. The balances vary spatially, and are sensitive to wave conditions and the channel geometry. The observed and modeled maximum offshore-directed flow speeds are correlated with a parameter based on the alongshore gradient in breaking-wave-driven-setup across the nonuniform bathymetry (a function of wave height and angle, water depths in the channel and on the sandbar, and a breaking threshold) and the breaking-wave-driven alongshore flow speed. The offshore-directed flow speed increases with dissipation on the bar and reaches a maximum (when the surf zone is saturated) set by the vertical scale of the bathymetric variability.

The deep ocean, continental shelf, and surf zone are defined by their unique physical processes and dynamics. The nearshore region from about 50 m water depth to the outer edge of the surf zone (SZ) is known as the inner shelf. This region is characterized by overlapping and interacting surface and bottom boundary layers. At the offshore side of the inner shelf, instabilities from wind-driven currents and fronts create cross-shelf meanders and eddies. In addition, energetic nonlinear internal waves (NLIWs) are ubiquitous on the inner shelf.

To understand and predict the exchange of water properties (heat, gases, sediment, pollutants, biota) across the inner shelf over a range of temporal and spatial scales, the Office of Naval Research Inner Shelf Dynamics Departmental Research Initiative (Inner Shelf DRI) is coordinating field observations (in situ and remote sensing) coupled to numerical modeling efforts on a 50-km section of coast off Vandenberg Air Force Base, California, located in the vicinity of Point Sal. The overall goal is to develop and improve the predictive capability of a range of numerical models to simulate the 3D circulation, density, and surface wave field across the inner shelf associated with a broad array of physical processes and complex bathymetry.