Numerical simulations of debris flows and its application in hazard assessments

As over seventy percent of the land of Hong Kong is mountainous, rainfall-induced debris flows are not uncommon in Hong Kong. The objective of this study is to incorporate numerical simulations of debris flows with GIS to identify potential debris flow hazard areas. To illustrate this approach, the proposed methodology is applied to Tsing Shan and Leung King Estate in Tuen Mun, Hong Kong. A three-dimensional Digital Elevation Model (DEM) of the terrain and the potential debris-flow sources were generated by using GIS to provide the required terrain and flow source data for the numerical simulations. A theoretical model by Takahashi et al. [9] improved by incorporating a new erosion initiation criterion was used for simulating the runout distances of debris flows. The well-documented 1990 Tsing Shan debris flow, was used to calibrate most of the flow parameters needed for computer simulations. Based on the simulation results, a potential hazard zone was identified and presented by using GIS. Our proposed hazard map was thus determined by flow dynamics and a deposition mechanism through computer simulations without using any so-called expert opinions.