Rip Currents Generation by Geomorphological Change in Gyeongpo Beach, South Korea

Abstract

Most beaches in Gangwon-do, South Korea have topographic characteristics that are mainly influenced by waves and seabed conditions. Gyeongpo Beach is one of the most famous beaches as a tourist attraction in the east coast of South Korea, and many people have visited and enjoyed sea-bathing in this area during the summer holiday season. However, rip currents are often source of danger for the swimmers because rip currents drag the swimmers away from the beach and put them to death by drowning. As Gyeongpo Beach has a straight shoreline, it is directly exposed to high waves that induce a significant change of bottom topography. Sandbars are usually formed in the processes of topographical changes from the swash zone to the surf zone and increase the possibility of rip current occurrence. Therefore, the monitoring of the topographic changes in this region is important to understand the mechanism of rip current generation. In this study, field observations were performed to measure foreshore slopes, water depths, and cross-sectional changes of bottom topography from the swash zone to the surf zone from December, 2013 through February, 2014. In order to trace nearshore currents, a GPS mounted on buoy-type equipment was designed, considering the minimization of wind effect. A single beam echo sounder equipped with RTK GPS (Real Time Kinematic GPS) was also used to observe the formation and movement of sandbar. The field observation results were used to understand the correlation between the sandbar movement and the rip current generation. According to the analysis results of two different field observation events in Gyeongpo Beach, a kind of salient beach is formed between O-ri Rock and the beach. Also, the results show that both arc sandbars and straight sandbars are mixed in the entire area. Finally, the field investigation results in this study show that the mechanism of rip current generation is closely related to the shape and location of sandbars.