Abstract
This paper is concerned with the development of an extensive sandy beach on an initially rocky coast facing the Sea of Japan, to which a diversion channel of the Shinano River was excavated and opened in early 1920s. From its completion, a significant volume of sediment has been discharged into the sea through the mouth of the channel, forming a sandy beach of 300ha over a period of nearly 100 years. This study focuses on how the sandy beach has been developed in association with the fluvial sediment inputs. Results of GIS analysis indicated an increase of the total subaerial beach area by 230ha in a period up to 1965. Thereafter the shoreline has stayed nearly stabilized. The sedimentary architecture of the beach was identified through comprehensive geophysical/sedimentological approaches including the surface-wave prospecting, Ground Penetrating Radar exploration and sedimentary facies analysis. The sediment volume analysis for the subaqueous domain led to an estimate for the maximum possible volume of sedimentation that could accumulate from the start of operation of the diversion channel.
