APPLICATION OF MULTIPLE GRAIN SIZE MODEL FOR EVOLUTION PROCESS OF LEVEE BREACH AND FLOOD INUNDATION

Abstract

 This study focused on grain size distribution of materials of riverbed, levee and substructure since river channel dynamics are characterized by nonuniform sediment transport of mixtures of gravels, sands and silts during floods. A multiple grain size model, which has not been applied very much for levee breach due to overtopping flow, was examined to discuss availability of the numerical model for hydro-morphodynamic process of river flood, levee failure and inundation. Numerical modeling with three sediment size classes corresponding to levee materials was carried out for overtopping breach test using a large-scale experimental flume located in Tokachi River (Chiyoda waterway). The numerical results of the levee breaching showed that the model could reproduce main features of breaching processes and morphological changes on riverbed and floodplain. The model with bedload transport formula by Ashida and Michiue in combination with hiding-exposure formula by Parker et al. estimated the time variation of breaching rate and discharges of river flow and inundation flow with good accuracy.