Assessment of Consequences of Debris Flows over Hong Kong Island under Extreme Rainfall

Debris flow is a common disaster in mountainous areas and can lead to large-scale damage to infrastructures and human lives. Rapid infiltration of rainfall, build-up of pore pressure and bed erosion are considered the main triggering factors of debris flows. Previous studies on debris flow risk assessment are limited and the risks of debris flows under extreme storms need to be studied. In order to close this gap, this paper aims to assess the risk of debris flow on entire Hong Kong Island quantitatively under large storms of 29% and 85% Probable Maximum Precipitation (PMP). Maps of debris flows and elements at risk were produced on a GIS environment. The consequences of debris flow were critically evaluated by identifying affected buildings, number of flats, floors and population at risk in the study area. The population at risk in the 85%PMP event is extremely high, showing an urgent need to cope with debris flow risks under extreme storms. The result of this work will provide a source of formulation for making risk management policy, land use planning and a guide for designing specific risk reduction measures.