Morphological Change at Byunsan Beach, West Coast of Korea; 14-years Monitoring During the Saemangum Reclamation Project

Abstract

Changes in beach morphology have been monitored at macro-tidal Byunsan Beach on the west coast of Korea over 14 years from 1992 to 2005. The primary purpose of the study is to find out any side-effects of Saemangum sea dike, constructed 4 km north off Byunsan Beach. Saemangum Project is a large scale tideland reclamation project involving construction of a 33 km sea dike impounding an area of over 40,000 ha. Construction began in 1991 and was completed in March, 2006. During the early phase of the dike construction from 1992 to 1997, deposition occurred rapidly on Byunsan Beach, with net accumulation rates over 4 cm/yr. Construction of the sea dike during this phase likely decreased the hydrodynamic energy level of tide and wave, hindering the offshore return of sediment materials that resulted in the cumulative accumulations. Byunsan Beach however, shifted toward the significant erosion phase from 1997 to present, with net erosion rates of about 2 cm/yr. Erosion took place along the coast at the mid- to low-tidal zone whereas net cumulative deposition continued at the zone of high-tidal level, resulting in the steeper gradient of the slope of shoreface. As the dike was constructed seaward, most of the water masses were concentrated through the narrow Gap area. Tidal flow during the ebb-period through the Gap makes counter-clockwise residual circulation, with net northward current field along Byunsan Beach. Materials eroded from the sub-tidal zone by waves and currents are thought to be transported northward and also shoreward by the residual currents.