Estimation of Flood Discharge Caused by Landslide Dam Overflow Erosion and the Application of Countermeasures

Abstract

Landslide dams form in river channels due to heavy rains or earthquakes. The flood discharge generated by overflow erosion, a known common cause of dam bursts [Schaster et al., 1986], must be estimated promptly to establish warning and evacuation systems downstream area residents. Previous studies [Satofuka et al., 2007a ; Satofuka et al., 2007b ; Satofuka et al., 2007c ; Mizuyama et al., 2006] have shown that the “two-layer model” proposed by Takahama et al. [2000] can be used to roughly estimate the peak discharge and hydrograph of a flood caused by overflow burst from a landslide dam at a given point in the downstream area. A landslide dam was formed in the Mimi River in Miyazaki Prefecture by local downpour due to the typhoon in September 2005, which burst later because of overflow erosion. The authors used “two-layer model” to simulate the flood discharge caused by the burst and worked out an approach to simple analysis of the risk associated with landslide dams when multiple landslide dams form simultaneously.