Understanding of Rip Current Generation Mechanism at Haeundae Beach of Korea: Honeycomb Waves

Abstract

Many studies have proposed the generation mechanism of rip currents observed at Haeundae beach. Most of them suspect the rip channels as a rip current generating mechanism at this beach. This study focuses on the understanding of rip current generation mechanism in a different point of view based on the CCTV images and the numerical simulations. The CCTV images captured when the rip currents occurred show that the rip currents are accompanied by the waves of honeycomb pattern. The rip currents are developed along the nodal lines of honeycomb waves. To confirm the new mechanism of rip current generation at Haeundae Beach a series of numerical experiments are conducted using a phase resolving numerical model based on the nonlinear Boussinesq equations. The numerical results with the simplified beach topography and the incident honeycomb waves similar to real ones show that the rip currents can be generated without the rip channels. The rip currents generated by the honeycomb waves can grow much faster and the intensity of the rip currents is much stronger than those generated by the unidirectional waves over the rip channels. The magnitude of rip currents agrees reasonably well with that observed using CCTV image analyses. The role of rip channels developed by the rip currents is also discussed.