SEDIMENT RUNOFF DUE TO EROSION OF DEBRIS PRODUCED BY LANDSLIDE

Abstract

Sediment runoff process in an actual small basin is discussed, based on the results of field survey and numerical analysis. In Nigorisawa river, a tributary of R. Mogami, a very active sediment runoff took place in June 1993 due to the erosion of debris produced by landslide. Numerical simulation is conducted in order to specify the sediment runoff and the characteristics of sediment movements along the river reach. The numerical results show that the flow discharge increases rapidly to a magnitude of several ten times of supplied water discharge due to the occurrence of debris flow, and the sediment transport rate and mode change from place to place according to the variation of bed slope and flow width.