Process and characteristics of “7·5” Huangniba gully debris flow in Muli County of Sichuan Province and and prevention suggestions

On July 5, 2021, debris flow disasters broke out in the seven branch ditches of Xiangjiao gully under the condition of consecutive days of rain. Due to the efficient operation of the mass prediction and disaster prevention system, 20 households with 118 casualties and 14.21 million yuan of economic losses were avoided. Huangniba gully was one of the tributaries of debris flow outbreaks, with a drainage are of 14.47 km2. The scale of the debris flow flushed out objects was 12×104 m3, and several houses were damaged. During the "3·28" forest fire in 2020, the surface vegetation in Huangniba gully was severely burned, which led to dramatic changes in its debris flow disaster-pregnant environment. In the background of few debris flow activities in Huangniba gully, debris flow disasters broke out several times in 2020 and 2021. Through field investigation, it was concluded that the contradiction between the drastically changed disaster-pregnancy environment of the debris flow and the old layout of the villages was the key reason for the serious disaster in Xiapingzi Village. The entire disaster process is as follows: after the debris flow blocked the internal ditches of the village, the outflowing mountain torrents were not able to be discharged smoothly, causing a large area of flooding, which caused doubled the losses to the village. The primary treatment measures were to build a drainage channel connecting the ditch mouth and the main river and re-plan the layout of the village, so that the debris flow can be smoothly discharged into the main river and the village buildings were kept away from the direct range of the debris flow. Finally, the successful practice of the mass people monitoring and prevention system was analyzed, and the experience was summarized for reference.