Formation analysis and characteristic estimation of the debris flow disaster of Mengdong River, Malipo County on September 2nd, 2018

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Based on the on-site investigation of debris flow disasters in Mengdong River Basin of Malipo County on September 2, 2018, the characteristics of disasters and their formation and evolution process are analyzed from the aspects of source, topography and water resources. Heavy rainfall is the inducement factor of this debris flow. The complex topographic and geomorphological features in the channel provide conditions for the evolution and scale-up of the debris flow: (1) hundreds of shallow soil landslides in the region provide sufficient material resources for the debris flow, enhance the hydrodynamic conditions of the debris flow and increase the amount of erosion along the way; (2) multiple bedrock entrapments and falls in the channel enlarged the debris flow. The scale and velocity of debris flow; (3) The volume weight of debris flow increases gradually with the supply of solid materials along the way. The study shows that precipitation is the fundamental cause of debris flow. The precipitation causes the initiation and overlap of landslide, slope and channel sources in the valley. From the development trend, the debris flow in the valley is in the stage of high frequency development, and the possibility of large-scale debris flow still exists. The possibility and frequency of occurrence will be greatly increased. High frequency and small and medium-sized debris flows will be the characteristics of debris flow activities in this gully in the future. It is necessary to control ditches in time and strengthen monitoring and early warning.