Sediment Hydraulics

Massive sediment movements take place in steep areas when an external factor such as rainfall volcanic activity or seismic motion exceeds some critical level and can cause sediment disasters of potentially high cost. On the other hand even if a large size debris flow takes place nobody will recognize the occurrence of a disaster in the area if there are no human activities. Japan located along the tectonically active circum-Pacific island arcs is a mountainous country about seventy percent of which is steep and hilly areas with a rainy season and frequent typhoons yielding severe rainfall. In addition to such geological topographical and meteorological conditions it is densely populated. Correspondingly people have long suffered from sediment induced disasters.