Debris flows produced by heavy rains on july 21, 2009 in hofu city, japan

Abstract

In this paper, we examine the debris flows which occurred in the mountain rivers in Hofu City, Japan on July 21, 2009. We estimate velocity and discharge of the debris flows in the rivers at Manao and Ishihara districts from field survey and numerical simulation. The numerical simulation indicates that the peak discharge is 181 m3/s in the river at Manao district and 258 m3/s in the river at Ishihara district. It is found that sediment yield volume by riverside erosion is larger than landslide sediment volume in the both rivers. Although the landslides triggered the debris flow initiation, they did not play the major role for the sediment out flow to the residential areas. The morphological characteristics of the river at Ishihara district increase debris flow discharge