LONG-TERM SHORELINE CHANGES ON MARGINAL COAST OF TIDAL FLAT IN TOKYO BAY AND RAPID DEFORMATION OF SAND BARS OWING TO TSUNAMI

Abstract

Long-term shoreline changes on the marginal coast of the Banzu tidal flat in Tokyo Bay were investigated using aerial photographs. In the area immediately north of the Obitsu River mouth, the beach was eroded owing to the decrease in sand supply from the river, resulting in the exposure of a layer composed of cohesive material in the previous tidal flat, and sand was transported northward to form a sand spit at the mouth of the north tributary. In 2011, the giant tsunami generated by the Great East Japan Earthquake propagated deep into Tokyo Bay, and sand bars were pushed landward by 7 m parallel to the shoreline owing to the tsunami overflow.