PHYSICAL ENVIRONMENT CHANGE OF LONG SANDY BEACH BY HEADLAND SYSTEM FOR EROSION CONTROL

Time variations of coastal bathymetry and sand grain size were investigated at the north Kashimanada Coast, a 40km long section of coast located between Oarai Port and Kashima Port, Japan. From the change of coastline position obtained from aerial photographs and bathymetrical surveys, it was found that the beaches located just next to Oarai Port and Kashima Port had been depositional and the areas next to those depositional beaches had been heavily eroded. Grain size distributions at the shoreline showed a tendency that grain size became coarser in the eroded areas and the areas were expanding. From analyses of the bathymetrical surveys, it was found that in almost 2/3 of the coast, offshore longshore sandbars diminished from 1984 to 2004, and it can be considered that the sediment movement caused by the headland system might be responsible for the extinction of the offshore sandbars.