Hazard Assessment of Debris Flow Based on Cluster Analysis in Three Parallel Rivers Area

The Three Parallel Rivers area is not only the concentrated area inhabited by minority people and a famous tourist hotspots, but also an ecological fragile area and disaster-prone (landslide and debris flow) area in our country. Especially debris flow disaster is threatening the social and economic development in the Three Parallel Rivers area. Therefore, hazard assessment of debris flow disaster has the important meaning in revealing the ecological environment problems, establishing regional environment construction policy and development strategy in the Three Parallel Rivers area. Cluster analysis and maximum likelihood classification (MLC) are exploited to map the hazard assessment of debris flow in the Three Parallel Rivers area. The methodology is applicable even if there is short of training data. Debris flow hazard can be viewed as a kind of spatial probability of hazard occurrence at a certain terrain unit and usually calculated as a function of effective factors or predictor variables such as lithology, fault, slope gradient, land-use type etc. The hazard assessment factors of debris flow can be divided into three types: topography conditions, the sources of loose solid material and dynamic conditions. Based on the field investigation and indoor analysis, eight effective factors are chosen for mapping the hazard assessment, including slope gradient, aspect, vegetation, lithology, fault zone density, river cutting density, rainfall and road network density. Because each measurement unit of effective factors is different, and its value is also belonging to different extents, therefore, we must deal with the above eight factors in unified handling. Four clusters are grouped from sampling grid cells by k-means clustering approach using above eight effective factors. MLC classifies all the cells in the study area into the four clusters according to their statistical characteristics. Four hazard classes (extreme low, low, moderate, and high) are assigned to these clusters applying expert experience and hazard density. The final map gives a reasonable assessment of debris flow hazard in the Three Parallel Rivers area. The result using cluster and MLC classification has a better agreement with the dot density value of debris flows in the Three Parallel Rivers area. The hazard assessment map of the Three Parallel Rivers area can be used to identify safety spots within the high danger area, which are suitable for habitations and facilities. It is also found that more debris flows are densely concentrated at the boundary between high and moderate regions, and between high and extreme low regions.