SEASONAL VARIATIONS OF TOPOGRAPHY AND SURFACE SEDIMENTS DURING 2014 TO 2016 ON OPEN-COAST INTERTIDAL FLAT OF THE GOCHANG, SOUTHWESTERN COAST OF KOREA

The Gochang open-coast, intertidal flat is located in the southwestern coast of Korea (the eastern part of the Yellow Sea), characterized by macro-tide in tidal range, an open-coast in its type, and sand substrates. This study has investigated seasonal variations in surface topography and sedimentary facies of surface sediments in the Gochang intertidal flat. During the twelve seasons of winter (Feb.), spring (May), summer (Aug.), and fall (Nov.) in 2014 to 2016, the topographic elevation of total 756 sites was measured along three survey lines. It consists of 21 sites at 30 m intervals in each transverse line perpendicular to the shoreline, respectively. During the twelve seasons of the year 2014 to 2016 such as winter (February), spring (May), summer (August), and fall (November), surface sediments of total 756 sites were sampled and analyzed along the three survey lines. The surface sediments of the Gochang intertidal flat in 2014 to 2016 consisted mainly of fine-grained sand sediments showing a trend in grain size to be coarser in winter and finer in summer. Based seasonal wave and tidal level data recorded near the study area, it was interpreted that seasonal effects of wave were stronger than those of tide as a factor controlling surface sedimentation. High waves in winter may result in the coarsening trend of grain size in surface sediments, whereas, in summer, the sediments may get finer by relatively low waves. Spatial sedimentary facies of the Gochang intertidal flat in 2014 to 2016 represented that seasonal deviation of the upper tidal zone was larger than that of the lower tidal zone, hence sediments getting coarser in grain size and poorly sorted in the upper tidal zone. From upper to lower tidal zone, grain size became finer and sediments were better-sorted, showing smaller seasonal deviations.

Acknowledgements: This study was supported by the research grant from the Korean Ministry of Oceans and Fisheries (PJT200538). This presentation is an interim result of the coastal research program in the study area.