2014年8月20日広島市安佐南区八木地区で発生した土石流災害にっいて

摘要

On August 20, 2014, a record heavy rain attacked the northern part of Hiroshima City. This heavy rain caused many debris flows in Asakita-ku and Asaminami-ku of Hiroshima city. This disaster killed 74 people. It is the worst debris flow disaster for several decades in Japan. The purpose of this study is to examine the characteristics of the debris flow. The Ueyama River in Asaminami-ku was selected as the study area. First, we surveyed and collected the material of the debris flow disaster. Second, we simulated the debris flow in the Ueyama River by the numerical calculation of the basic equations of debris flow. Five basic equations were used in this simulation; they are the momentum equation, the continuity equations of liquid phase and solia phase, and the equations of erosion rate of river bed and side. There are five unknown quantities, such as flow discharge, flow depth, sediment concentration, riverbed elevation, and river width. The initial inflow condition at the upstream end of the river was given as sediment volume of 4,000m~3 by the slope failure. The results obtained in this study are as follows:(1)Total outflow of sediments and woody debris was about 30,000m~3 and 620m~3, respectively. (2) The debris flow reached the outlet of the valley in 90 seconds after the slope failure. (3) At the outlet of valley, the peak discharge was 950m~3/sec, the flow depth was 5m and flow width was 21m.