Observation of Rip Current Velocity at an Accidental Event by using Video Image Analysis

Abstract

In order to investigate the magnitude of rip currents of an accident event, in which dozens of people were rescued by coast guards at Haeundae beach, the floating velocities of swimming tubes of people caught by the rip current were estimated by using an analysis of video camera images. The analysis was conducted by tracking the locations of the floating tubes in the video images, converting the image coordinate system into the conventional map coordinate system, and evaluating their Lagrangian velocities. The rip current was strongly developed southwardly from the shore at the center of the beach and its maximum velocity was about 1.12 m/s when observing waves with Hs=0.9 m, Ts=8.2 sec, and theta p =S4 degrees E. The observation results was used for a verification of the numerical simulation performed using the nonlinear Boussinesq model FUNWAVE which can resolve wave-phase interactions and simulate rapid wave-induced currents with generation, evolution, and dissipation of vortex pairs. The observation and the computation reasonably agreed with each other.