Low-Energy Rip Currents Associated With Small Bathymetric Variations

Abstract

We show for the first time that low-energy waves can induce a rip current system over subtle alongshore bathymetric variations. Comprehensive field measurements across a rip current that morphologically migrated (∼ 12 m/day) through a coherent cross- and alongshore array of co-located pressure and velocity sensors were obtained. The rip current is associated with a small bathymetric surfzone non-uniformity (1 in 300 alongshore variation). The circulation was kinematically non-uniform for ∼ 5% of the time over the course of the 20 day experiment and was present at low tides associated with increases in rip current activity. The presence of the rip current and mild-sloped rip channel induce statistically significant alongshore variations in H rms, wave direction, directional spreading, infragravity waves, and very low frequency motions. Changes in the directional spreading are correlated with the presence of very low frequency motions influenced by the presence of the rip current.