Citation

Holman RA, Symonds G, Thornton EB, Ranasinghe R. Journal of Geophysical Research: Oceans 2006; 111(C1): JC002965.

Copyright

(Copyright © 2006, William Byrd Press for John Hopkins Press)

DOI

10.1029/2005JC002965

PMID

unavailable

Abstract

Four years of daily time exposure images from an embayed beach were examined to study the spacing, persistence, and location preferences of rips in a natural rip channel system. A total of 5271 rip channels was observed on 782 days. Occurrence statistics showed no evidence of the preferred location pattern associated with standing edge waves trapped in an embayed beach. The histogram of rip spacing, the primary diagnostic observable for most models, was well modeled by a lognormal distribution (mean spacing of 178 m). However, spacings were highly longshore variable (time mean of the standard deviation/longshore mean of rip spacing was 39%), so they are of questionable merit as a diagnostic variable. Storm-driven resets to the longshore uniform condition required by most models occurred only four times per year on average, making rip generation models relevant to only a small fraction of the system behavior. Rip spacings after the 15 observed reset events were uncorrelated with bar crest distance. The lifetime of the 324 individual rip channel trajectories averaged 45.6 days. Rips were equally mobile in both longshore directions, but the coefficient of variation of rip migration rates was large, even for high migration rates. The mean migration rate was well correlated to a proxy for the longshore current (R2 of 0.78). Thus there is no significant evidence that the formation, spacing, and migration of rip channels on this beach can be explained by currently existing simple models. Moreover, the alongshore uniform initial conditions assumed by these models are rare on Palm Beach, making the models generally inapplicable.

Language: en