Debris flow disaster, Churiya Hill, Lumbuni , Nepal, 1998 (Source: Sabo Dept, MLIT, Japan)
Debris flow disaster at Harihara river basin, Izumi, Japan, 1997 (Source: Sabo Dept, MLIT, Japan)
Debris flows are common in mountainous areas throughout the world. Often triggered as mudflows by torrential rains, debris flows contain varying amounts of mud, sand, gravel, boulders, and water flow down along a stream at high speed. Because of its high density and speed, it has huge destruction power. In mountain torrents, intense and localized storms may cause flash floods with important sediment transport. In steep torrents, the sediment that are the deposited on the alluvial fans, often highly populated in the case of debris flow that transport downstream huge volumes of sediment, the sediment discharge may increase so that the solid concentration often exceeds figures 40-50%. The comprehensive assessment of debris flows countermeasures both structural and non-structural requires the consideration of the various scenarios and involves the evaluation of hydrological, hydraulic, sediment size distribution and topographical parameters.