Risk assessment of debris flow hazards based on GIS-A case study in Dongchuan district, Yunnan Province, China

Risk assessment of debris flow involves five steps: field survey, background condition analysis, risk modeling, hazard appraisal and hazard mitigation. In order to evaluate the risk level fora certain unit efficiently, ten factors, representing physical changes in energy, mass quantity and trigging conditions of debris flows, are taken into account with two different models: a weight model and a square root model. The two models are used to examine physical risks of debris flow in the Dongchuan district of Yunnan Province, China. We found that the weight model is better than the square root model in terms of agreement between observation and modeling. Four socioeconomic indicators are introduced into investigating economical conditions. Physical risk and economic factors are considered as a whole for the comprehensive risk assessment. Modeling results Concluded that the integrated risk of debris flow within the study area can be divided into four risk-scale levels: "most severe risk areas", with a total area of about 133 km(2), encompassing about 79% of the total debris flow gullies identified; "severe risk areas", about 579 km(2) encompassing 19.8% of the debris flow gullies; "moderate risk areas", about 723 km(2) encompassing 1.2% of the debris flow gullies; and "no risk", about 118 km(2), without debris flow gullies. This result fits the field survey well, which indicates that the method used is reliable. Suggestions on the mitigation of debris flow hazards are also discussed.