Exchange Between the Surfzone and Inner Shelf: The Contribution of Transient Rip Currents

Suanda Sutara H, La Jolla CA

Investigators

Abstract

Rip currents - narrow jets of strong, offshore-directed flow - are a dangerous beach hazard. They account for the majority of the U.S. life guard rescue effort and potentially play a role in many coastal processes by exchanging material such as sediments, pollutants, and intertidal invertebrates across nearshore ocean systems. Because of their episodic nature, transient rip currents are particularly challenging to observe and our understanding of the processes that drive, sustain, and determine their offshore extent is limited. In this project, the fellow aims to quantify transient rip current exchange across nearshore systems. Results may provide valuable information for the safety of recreational beach goers and improve understanding on the transport of materials across and health of our coastal ecosystems. To broaden participation in marine science, the fellow will mentor a summer undergraduate intern on the use of numerical ocean models. The fellow will also work with a local high school to develop and deliver a marine science curriculum culminating with a career-oriented workshop, the Surf Science Teen Conference. The transition between the surfzone and the inner continental shelf involves a transition across dynamical regions. While wave breaking dominates the forcing of circulation within the surfzone, the inner shelf is subject to a combination of forces including wave shoaling, buoyancy, and the earth?s rotation. On alongshore-uniform beaches, transient rip currents are potentially the dominant mechanism driving the exchange of material across these regions. In this project, using a wave-resolving Boussinesq model, the fellow aims to develop a better understanding of transient rip current driven exchange. To accomplish this aim, the fellow will conduct a series of simulations over a wide parameter space including both normally and obliquely incident wave conditions and multiple beach slopes. Nearshore vortices will be tracked to analyze their dynamics and quantify the strength as well as offshore extent of transient rip currents. Predictive relationships will be determined between rip current characteristics, their bulk exchange, and the array of incident wave and beach conditions. These characteristics can then be compared to other coastal exchange processes such as wind, Stokes? drift, and internal wave-driven transports. Transient rip current exchange occurs over small scales generally unresolved by coastal circulation models. This work will also contribute towards the parameterization of transient rip current behavior in such models.