Experimental modeling of a rip current system

Results from an experimental investigation of a rip current system in a laboratory wave basin are presented. The modeled system includes a planar beach with a superimposed longshore bar containing two rip channels. Dense measurements of water surface elevation, cross-shore and longshore currents are presented. The experimental results indicate that, in addition to the steady mean water level gradients which drive the steady nearshore circulation, time varying pressure gradients are generated in the rip current system and these gradients are directly related to measured current oscillations in the rips. Oscillations in the rip currents are shown to have multiple scales. A simple calculation shows that classical jet instability theory can predict the order of magnitude of the measured short time scale rip current oscillations.