This paper examined the impacts of the regional developments and dwellers behavior on the Seacoast. Seacoast features a variety of landforms which are created by the action of waves and tidal flows. The coastal landforms are found mainly in the interface between land and sea. Although erosional landforms constitute prominent landscape features as sea stack, sea arch, and rock cliff do, it is nonetheless the depositional features such as beaches, tidal flats, offshore bars, deltas, sanddunes, and coastal plains that have various ramifications for human communities. Among these, beaches and coastal sanddunes are special in that their formation is attributable to the combined action of waves, tidal flows, and winds. The main line of discussion in this dissertation is concerned with the transformation of group of beaches sanddunes along the coastline of Chungcheong-Namdo Province. To some extent, the erosion of coastal dunes has been a global phenomenon. The degradation process occurs most actively when the spring tides attack beaches, berms, and foredunes. Also involved in the transformation of coastal dunes are factors of human agency. The extent, speed, and pattern of their morphological changes are a function of land-use pattern. The reclamation of swale and the exploitation of sands as construction material and silica sand, for example, ruin the feature of coastal dunes.