Analysis on the mechanism of debris flow in Meilong valley in Danba County on June 17，2020
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摘要:
2020年6月17日丹巴县梅龙沟爆发了一次大规模泥石流，一次性冲出固体物质42.7×104 m3，形成泥石流-堰塞坝-溃决洪水-滑坡灾害链，造成5100余户2.12万余人被迫转移，直接经济损失达8亿元。根据现场调查、无人机航拍以及遥感解译，分析梅龙沟泥石流的成因及致灾机理，阐述了“物源成因”、“降雨激发”和“地形促进”对泥石流形成产生的影响。结果表明：（1）梅龙沟泥石流是在前期累计降雨和短时强降雨共同作用下形成；（2）梅龙沟泥石流源头为大石堡沟，起动模式为“沟岸垮塌-泥石流”；（3）泥石流沟内持续的物源补给以及东风棚子、梅龙村、大邑村三处大型滑坡产生的级联堵溃效应，致使泥石流流量不断放大，最终导致大量固体物质冲出沟口；（4）沟口形成的堰塞坝-溃决洪水-阿娘寨滑坡灾害链进一步增强了泥石流的致灾能力；（5）现阶段梅龙沟内物源丰富，临界启动降雨阈值降低，极易在雨季发生大规模泥石流，建议及时采取综合防治措施。
Abstract:A destructive debris flow broke out in Meilong gully, Danba County, on June 17, 2020, discharging almost 427000 cubic meters of solid material, triggering a disaster chain consisting of debris flow, debris-flow dam, outburst flood, and landslide, forcing more than 5100 households and 21200 people to transfer and causing direct economic losses of 800 million yuan. The authors analyzed the causes and mechanism of the Meilong gully debris flow based on on-site investigation, aerial photography, and remote sensing interpretation, and elucidated the influence of material source, rainfall and terrain on the formation of debris flow. The results are shown as follows: (1) The Meilong gully debris flow was formed by the interaction of accumulated rainfall and short-term heavy rainfall. (2) The source of the debris flow in Meilonggou is in Dashibao ditch, which was caused by the collapse of the ditch bank. (3) The cascade blocking effect caused by the recharge of material and the three massive landslides named Dongfeng Shed, Meilong village, and Dayi village further amplifies the quantity of the debris flow. A large amount of solid material rushed out of the ditch mouth as a result. (4) The disaster chain consisted of debris-flow dam, outburst flood, and landslide at the mouth of the ditch, which further enhanced the risk of the debris flow. (5) The abundance of material in the Meilong ditch and lower rain threshold will tend to trigger destructive debris flow in the rain season. It is recommended to take comprehensive prevention and control measures in time.
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Key words:
- debris flow /
- mechanism of disaster /
- burst-blocking effect /
- disaster chain /
- development trend
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