Analysis of Measured Surface Nearshore Currents Using Multiple Drifters on Anmok Beach, South Korea

Abstract

To understand the mechanism of sediment transport and beach erosion processes in the surf zone near the coast of the Korean Peninsula, the development of coastal erosion control technology, an R&D project supported by the Korean government, has been conducted since 2013. Anmok Beach, located on the eastern coast of the Korean Peninsula, has been studied by measuring currents and sediment transport using bottom-mounted acoustic sensors and offshore long-term wave observation since February 2015. Moreover, for measurement of surface currents, multiple Lagrangian drifters were developed and successfully deployed nine times near the surf zone and submerged breakwaters close to Kangneung northern breakwaters. The variation of the measured bottom currents was induced directly by seasonal wave height and direction, depending on the incoming waves from the NNE in winter, ENE in summer, and NE, normal to the shoreline, in the case of high waves. However, the measured surface currents were affected not only by the incoming waves in the presence of high-energy waves, but also by wind speed and direction in the presence of low-energy waves. In this study, the observed surface nearshore currents measured by small Lagrangian GPS drifters near the surf zone and submerged breakwaters at Anmok were analyzed to investigate the variability of the wave-induced currents and nearshore surface currents generated by different wave and wind environments. The drifter experiments showed that offshore surface currents in the surf zone were predominantly developed, especially by strong seaward winds that opposed the direction of the weak waves. However, onshore surface currents were developed by wave-induced currents generated by the interaction of waves from offshore accompanied by sea winds. This measurement is now used to calibrate and validate the coastal sediment modeling system for the eastern coast of the Korean Peninsula.