Quantifying transient rip current-driven exchange between the surfzone and inner shelf

Abstract:

On beaches with along-shore uniform bathymetry narrow, episodic, offshore-directed jets (transient rip currents) can induce cross-shelf exchange of tracers such as nutrients, pollutants, or larval invertebrates. The relationship between the time and space scales of transient rip currents and fundamental surfzone parameters such as beach slope, wave height, wave period, and wave directional spread is poorly understood.

Numerical simulations using the Boussinesq, wave-resolving model, funwaveC, are conducted across a broad range of fundamental surfzone and wave forcing scales. These model results are used to determine the relationship between the magnitude, width, spacing, and duration of transient rip currents to a variety of idealized beach and wave conditions. We also quantify the efficiency of cross-shelf exchange by a surfzone flushing time and compare two wave-driven mechanisms; the Eulerian return flow balancing the onshore Stokes’ drift and transient rip currents. Preliminary results suggest that transient rip currents increase the efficiency and offshore extent of wave-driven exchange up to 2.5 times the width of the surfzone. This work is supported by the National Science Foundation.