Citation

Bruneau N, Castelle B, Bonneton P, Pedreros R. J. Coast. Res. 2009; (SI 56): 1731-1735.

Copyright

(Copyright © 2009, The Coastal Education and Research Foundation)

DOI

10.2307/25738086

PMID

unavailable

Abstract

Biscarrosse beach, located on the French Aquitanian Coast, is a high-energy meso-macrotidal double-barred beach. The outer and the inner bars exhibit most of the time crescentic patterns and transverse bar and rip morphology, respectively. Breaking waves over these three-dimensional features induce strong rip currents that are responsible of several drowning accidents each year. To improve our knowledge on this kind of complex environment, an intensive 5-day field experiment was carried out in June 2007 at Biscarrosse Beach. The present study is focused on Very Low Frequency motions (VLF) of a rip current system over a well-developed bar-rip morphology. Using both a drifter experiment and virtual drifter modeling, the study aims at analyzing the rip current pulsations and the drifter retention in the surf zone. The main results show the oscillating behavior of the rip currents, in particular within the rip neck where the VLF pulsations are intense (reaching 1m/s on time scales of 10 to 30 minutes). In addition, most of the drifters are retained within the surf zone (about 80%), with the other 20% exiting the surf zone. These results are reproduced by our numerical model, which shows that shear instabilities of the rip current can be the cause of such retention/expulsion proportions. In addition, here we present the spatial variability of the VLF motion over the entire rip current system.