Long-term Changes in Beach Profiles at Ogata Coast

Abstract

To investigate the characteristics of beach profile changes, continuous observations of nearshore topography have been carried out at Ogata coast along an observation pier since 1973. Systematically analized are the data of beach profiles collected for more than eight years, to find out the role of beach changes. An outline of the characteristics of the coast is described, and characteristics of beach profiles in the time-space coordinates are elucidated. A relationship between beach slopes and shoreline changes was found, and an explanation of beach changes is also made by the method of empirical eigenfunction by Winant et al., from which how to select each period of the data to be analyzed is considered from the seasonal wave conditions. Continuous beach erosion at the coast is recognized from the annual changes in sediment volume in averaged beach profiles for the period of observation, in which two remarkable beach changes are included in the periods from 1973 to 1974 and from 1978 to 1980, respectively.