Monitoring of crescentic sandbar migration processes associated with seasonal wave climate

This study conducted eight nearshore bathymetry surveys using a single-beam echosounder, a IMU sensor and a real-time kinematic (RTK) GPS system at the Hujeong Beach, South Korea from June 2011 to May 2012 in order to examine nearshore-sandbar migration processes in a wave-dominant coastal environment. Directional wave data collected from a waverider buoy moored offshore at 30-m water depth were used to examine the relationship between the sandbar migration and seasonal wave-climate pattern. Results of the bathymetric surveys showed that six crescentic sandbars well developed along the shore. The crescentic sandbars appeared to be about 370 m in average length, while maximum distance between the bar crest and shore was about 230 m. The crescentic sandbars of June 2011 were symmetric rhythmic-bar and beach (RBB). The sandbars in September 2011 were changed to northwesterly oblique transverse bar and rip (TBR)/RBB. In March 2012, sandbars became TBR with easterly oblique rip channel. During the winter waves of higher than 3 m in wave height (Hs) occurred more frequently than during the summer. Incidence directions of the winter waves were NE or NNE whereas E or SE during the summer. Based on bathymetric survey results, the sandbars were northwesterly migrated by a maximum of 202 m between June 2011 to September 2011 and were then migrated southeasterly by a maximum of 252 m between September 2011 to March 2012. This result indicates that seasonal pattern of wave climate might influence strongly on the deformation and migration of crescentic sandbars in the study site.