HORIZONTAL TWO DIMENSIONAL ANALYSIS OF MUD FLOW OCCURRED IN IZUOSHIMA ISLAND ON OCTOBER 2013

Abstract

Mud flows were occurred in the west part of the Izuoshima Island on 16 October 2013. The Izuoshima Island is a volcanic island and the land surface is covered by the volcanic ash sediment in about 1m depth. The laminar layer is formed in the debris flow from the bed to the fluid surface. On the other hand, the laminar flow is restricted near the bed in the mud flow and the turbulence flow is formed on the laminar flow layer. As a result, the equilibrium slope of the mud flow becomes smaller comparing to the debris flow. In this study, the horizontal two dimensional mud flow model considering the both the laminar and the turbulence flows is developed. Subsequently, the model is applied to the mud flow occurred in the Izuoshima Island and discussed the applicability of the model. The differences of the horizontal flow areas between the simulated results and the field data are discussed and it was found that the outline of the horizontal shape of the flow areas is reproduced well. Furthermore, the horizontal distribution of the erosion and deposition area is reproduced by the numerical analysis well except for the residential area.