Over the past three decades, field experiments have been performed primarily on beaches with relatively simple planforms (straight and parallel contours). These observations were used to verify depth-averaged wave-driven flow models. To a large extent, the local vertical flow structure in alongshore currents and undertow is understood on beaches lacking alongshore variability. However, straight and parallel bottom contours, or simple beach planforms are not a stable morphodynamic beach state, with complex morphology being the norm. This has motivated experiments on complex beaches. Rip currents, transient rip currents, and surf zone eddies co-exist with gravity waves (incident sea-swell and infragravity) in the surf zone, yet their importance and dynamic coupling have gone unrecognized owing to a lack of comprehensive field measurements and numerical model verification on complex morphologic beach systems. For this project, we will participate in a European field experiment aimed at understanding nearshore circulation associated with rip current morphology. A multi-institutional and international field experiment is planned for the spring of 2008 at Truc Vert Beach, France. This beach features an energetic wave climate, strong tidal modulation, and a typically complex beach planform composed of crescentic bars, rip channels, and an inter-tidal zone with ridge and runnel systems. The scientific objectives are to examine the nearshore mixing, mean flow patterns, sediment transport, and bathymetric coupling of low frequency rip current pulsations through observations and advance numerical modeling. Imbedded in cross- and alongshore fixed instrument arrays, new Lagrangian observations using a fleet of inexpensive surf zone drifters will provide vital spatial maps of circulation patterns. The dense Eulerian and Lagrangian observations along with the numerical modeling efforts will be used to evaluate the cross- and alongshore distribution of momentum and energy in the nearshore, the influence sedimentation patterns and transport, and the mixing of water masses in this heavily utilized segment of the ocean.
The broader impacts of the research include predicting location, persistence, and strength of rip currents for swimmer safety, understanding nearshore mixing, modeling dispersion of pollutants, and anticipating shoreline and dune erosion. This type of beach planform is more complex than any that has been previously studied in a comprehensive fashion, and thus the proposed data will be unique among available data sets obtained anywhere in the world. Among the broader imparts, this effort will provide hands-on research and thesis opportunities for up to six graduate students.
