Reconstruction and risk predication of a typhoon-triggered debris flow via numerical simulation: A case study of Zhejiang Province, SE China

Typhoon debris flows are recurrent phenomena with a high capacity to cause significant economic and life loss in the coastal areas. Accurately predicting the movement process and determining the potential zones and risk assessment are crucial to design mitigation strategies and to reduce societal and economic losses. In this study, the Wangzhuangwu (WZW) gully was chosen as the study object, which once broke out a debris flow induced by the Typhoon Likima on 10 August 2019. First, a detailed field investigation and interpretation of remote sensing imagery were carried out to study the trigger mechanism and quantify the characteristics of the debris flow. Second, the movement and deposition process of the 2019 WZW debris flow were reconstructed based on the Soil Conservation Service-curve number (SCS-CN) approach and a two-dimensional finite model (FLO-2D PRO model). The debris flow inundation and evolutionary trajectory were shown to be reasonably comparable with historical debris flows. Then, the potential hazard zones of debris flows with different recurrence intervals were determined based on the validated rheological parameters. Here we established a two-factors model that couples maximum flow depth with momentum to classify the hazard zones. Finally, we calculated the vulnerability distribution and economic risk of the buildings with different recurrence intervals based on a quantitative risk formula. This study provides a complete and efficient mean to determine the values of debris flow parameters and to implement a hazard and risk assessment based on numerical simulation. This proposed approach efficiently generated a debris flow risk distribution map that can be used for effective disaster prevention in the debris flow-prone areas.