Processes Governing Rip Spacing, Persistence, and Strength in a Swell Dominated, Microtidal Environment

Two years of daily time exposure video images were analysed to examine the effect of incident wave conditions on the spacing and persistence of rip channels along a swell dominated, microtidal beach (Palm Beach, Sydney, Australia). The results indicated that rip channels do not have any preferred locations along the beach. Rip spacing did not increase or decrease with likewise variations in wave height. Once formed, rip channels migrated longshore under obliquely incident waves, while they were fixed in location under normal wave incidence. Gradients in longshore sediment transport caused by longshore currents due to obliquely incident waves appear to govern longshore migration of rip channels. A two-dimensional depth averaged hydrodynamic model (2DBEACH) was applied to idealised bathymetry to examine processes governing rip strength. The model results indicated that both rip velocity and transport increased with increasing wave height. Rip velocity also increased with falling tide levels, while rip transport initially increased and then decreased with falling tide levels.