Typhoon Impact on a Pure Gravel Beach as Assessed through Gravel Movement and Topographic Change at Yeocha Beach, South Coast of Korea

This study investigated sediment movement and topographic change using radio frequency identifier (RFID) tracers and real-time kinematic (RTK)-global positioning system (GPS) data to examine the response of a gravel beach under typhoon conditions. Yeocha Beach, the study site and a pure gravel beach, was affected by strong wind and waves produced by Typhoon Goni on 24-26 August 2015. On 26 August, the main direction of the tracer movement was toward the upper part of the beach and toward the west relative to the onshore-offshore and alongshore directions. The average movement distance of the tracers differed according to the insertion points. The tracers inserted in the beach face showed a longer average movement distance of 12.07 m compared with 1.89 m for those inserted in the storm berm. In addition, the tracers inserted in the beach face showed an average movement of 0.44 m in height toward the upper part of the beach. The result of topographic change showed that sedimentation was dominant within most parts of the beach. Moreover, this study clarified sediment movement patterns according to various patterns of localized topographic changes and tracer movement. This study investigated the relationship between tracer properties and movement distance and found that significant statistical differences did not occur under the typhoon conditions; thus, the beach gravel moved collectively rather than individually under strong wave energy conditions. In addition, 3 months after the typhoon, the beach recovered back to its original topography under normal wave conditions. The beach response and recovery indicate that the pure gravel beach exhibited an outstanding natural seawall effect. However, this study investigated the beach response based on a single typhoon; future research is necessary to understand the response under various environmental conditions.