Typhoon Soudelor brought abundant rainfall in northern Taiwan on August 8, 2015. The rainfall caused a shallow landslide which was transformed instantly into a debris flow disaster in the Heliu catchment. We integrate remote sensing, rainfall analysis, micro-topography interpretation, lineament of tree fall, field investigation, a UAV survey, and RAMMS simulation to explore the failure mechanism and flow dynamics of this rainfall-induced debris flow. The high resolution shading relief map depicts the landforms of both the old deep-seated landslide and the ancient debris-flow fan. In this study, different numerical scenarios are performed by RAMMS to analyze the possible influence area via adopting the back-analysis approach. In comparison with the post-disaster landform model, the best-fit parameters for Heliu debris flow were also obtained. In addition, verification of dynamic images demonstrates that the maximum flow velocities for the event and deposition height on the debris-flow fan are about 14.3 m/s and 1-5 m, respectively.
Keywords: Typhoon Soudelor, debris flow, debris slide, lineament of trees fall, RAMMS.