PREDICTIVE MODEL OF CONTOUR LINE AND GRAIN SIZE CHANGES CONSIDERING EQUILIBRIUM SLOPE DEPENDING ON DOMINANT GRAIN SIZE POPULATION

Abstract

A model for predicting not only the three-dimensional beach changes but also the planer change in grain size distribution was developed based on the contour-line-change model. In the past model, there were some problems with respect to the stability of the calculation related to the selection method of the local beach slope in response to the grain size of the seabed materials, and in this study these problems were solved by reconsidering the fundamental characteristics of the equilibrium slope. Assuming that the equilibrium slope at a location of the beach is strongly governed by the equilibrium slope of the dominant grain size population existing at the location with forming a thick layer and the effect due to the composition change in the surface exchange layer is less important, the concept of the dominant grain size population was introduced in the model. The model was applied to the prediction of the beach changes on Kemigawa Beach and around the Shimohara fishing port in Chiba Prefecture, and the appropriateness of the model was confirmed.