ネパール中央部で1993年7月に発生した土石流災害について

抄録

Unprecedented heavy rainfall between 19 and 21 July 1993 caused destructive disasters in Nepal damaging major infrastructures and taking about 1, 500 lives. Debris flows were the major cause of catastrophe in the mountain areas especially in the central region. Authors executed a preliminary study on the physical characteristics of debris flow such as geology of the catchment, boulder size and its shape of deposited materials, sediment volume, bed gradient and rainfall through field survey as well as aerial photo interpretation in seven rivers. The survey result shows that the types of debris flow can be divided into three mainly based on the geology of the catchment. The first type is in the granite area of which boulder size (diameter) of deposited materials is a few meters with round shape. The second type belongs to the schist and quartzite area of the Bhimphedi Group of which boulder size is several 10s cm with rectangular shape. The last one is in the Upper Siwaliks (conglomerate) of which boulder size is about 10cm with round shape.