STUDY ON TOPOGRAPHIC CHANGE OF GRAVEL BEACH AND THE CONDITION OF OCCURRENCE OF LARGE EROSION

Abstract

 The purpose of this study is to clarify the characteristics of topographic change of gravel beach by examining the wave conditions that caused large scale erosion at Ojigahama beach in Shingu city, Wakayama. Wave data obtained off the target coast, data of nearby wave observation station, and beach section survey data before and after storms were used. In addition, a method was developed to estimate the wave condition at the time of failure of the revetment at the target coast using the data of nearby wave station. Based on the estimated results of waves at the time of failure and the results of topographic survey, the characteristics of erosion on the target coast were discussed. Erosion of gravel beach was considered to be caused not only by the offshore movement of the gravel, but also by the movement along the shoreline, because the beach erosion becames significant at the up-drift end of the coast.