Macrotidal Beach Processes Dominated by Winter Monsoon: Byunsan, West Coast of Korea

Abstract

Macrotidal beaches are scattered in the west coast of Korea mostly in small embayments of the ria-type coastline and islands. In contrast to well-known tidal flats, these beaches have been little studied from the hydromorphologic viewpoint. Byunsan Beach was chosen to investigate beach processes affected by winter monsoon, which creates strong waves and wind-generated currents. The multiyear (2005-2008) profiling of the beach, together with the intensive sampling of surface sediments, provided the details of morphologic characteristics of the beach. Deep water winter wave characteristics were based on the measurements of an offshore buoy. A benthic tripod was deployed on the beach to observe waves, currents, and suspended sediments during a winter storm. The estimated morphodynamic parameters suggest that Byunsan Beach be classified as an ultradissipative state during winter. The tendency of grain size toward systematically fining seaward could be explained by the lateral displacements across the beach of swash and surf zones owing to a high tidal range. In addition, the tripod observations show that a storm readily generated offshore return flows capable of considerable beach erosion. The storm waves also significantly contributed to the erosion. This may reflect that the macrotidal, open beaches in the west coast of Korea are seasonally susceptible to pronounced erosion by winter monsoon. The results of this study may be useful for evaluating man-made environmental impacts caused largely by seawalls and dykes on the natural beach state intrinsic to the west coast of Korea.