Abstract: The risks of debris flow in Wenchuan County, Sichuan Province of China are assessed as a typical case study by a combination of GIS technology and hierarchy-information quantity model. According to the special geological condition after earthquake, six factors affecting the source materials of debris flow are selected (slope gradient, elevation, water system’s influence zone, earthquake intensity, fault’s influence zone, and type of rock soil mass) to analyze the susceptibility of the most important source materials. The susceptibility maps of landslide and debris flow in Wenchuan County are obtained. Furthermore, the risks of debris flows under 100-year rainfall and 50-year rainfall are analyzed respectively. Finally, the risk zoning maps are obtained in ArcGIS, and debris flow canals in need of monitoring and treatment are determined.

Key words: debris flow, rainfall frequency, hierarchy-information quantity model, GIS, risk assessment