Kim, I.; Lee, J.L.; Hwang, J.S.; Lee, S., and Lee, J., 2014. Vertical structure of rip current observed at Haeundae Beach.

On 4 and 7 August, 2012, more than 200–300 people were swept away by the fast moving seaward current at Haeundae Beach, which is located on the southeastern corner of the Korean Peninsula, and they then had to be rescued Beach patrons were carried away 50 to 100 meters away from the shore by rip currents, to an area where swimming is restricted due to safety reasons. Rip currents are narrow currents that begin close to the shoreline and strongly flow seaward through the surf zone and beyond. Although rip currents can cause tragic accidents and are of considerable interest to scientists and to the general public, our current understanding of the spatial and temporal behavior of rip currents is limited. As a result, the Korean Meteorological Administration installed monitoring equipment that can assess weather conditions and issue rip current warnings on Haeundae beach starting from 2010. Rip current kinematics and beach morphodynamics were measured for 50 days at Haeunadae beach using several instruments, including velocity and pressure sensors, such as an Aquadopp profiler for shallow water, and the morphology consisted of a low-tide terrace with incised quasi-periodic rip channels, which are representative of transverse bars. The spatial distribution of the sediment is reflected in the background rip current flow field with mean velocity magnitudes within the rip channel that increase offshore both with a decrease in the tidal elevations and with an increase in the sea-swell energy. The vertical velocity profile on the bar indicated that the flow was predominantly shoreward. The Aquadopp profiler is a high-resolution current profiler that operates at sub-cm scales and collects data at up to 8 Hz. The instrument is generally used in boundary layer studies at the bottom 1–2 meters of the ocean and in low energy environments. In addition, the HR profiler excels at providing flow details that are not attainable with any other instrument. In this study, the data from the Aquadopp profiles was used to investigate the detailed vertical structure of dangerous rip currents at Haeundae beach, and we were able to quantitatively understand the mechanism of a rip current.