Predictive simulation of concurrent debris flows: How slope failure locations affect predicted damage

Predictive simulation of concurrent debris flows using only pre-disaster information has been difficult, partly because of problems faced in predicting debris-flow initiation locations (i.e., slope failure). However, because catchment topography has convergent characteristics with all channels in it joining each other as they flow downstream, damage to downstream areas could be predicted using relatively inaccurate initiation points. Based on this hypothesis, this study uses debris-flow initiation points generated randomly with statistical slope failure prediction and performs a many-case simulation across numerous initiation points to quantify the effect of slope-failure locations in terms of deviations in the predicted water level and topographic change. This paper presents the results of 2D simulations based on a conventional debris-flow model that was run on a supercomputer to realise simulations of many cases. The obtained relative standard deviation was found to decrease as the debris flow and sediment-laden flood approached the downstream area, indicating that the predictability of the inundation and topographic change can be decided from the terrain characteristics.