Formation mechanism and hazard assessment of debris flow in Yizhong River, Deqin County, Yunnan Province

Deqin County in Yunnan Province is among the most severely affected regions in China by debris flow disasters. The Yizhong River in Deqin County has witnessed numerous large-scale debris flow disasters, causing significant damage and substantial economic losses to residential areas and the G214 national road. To elucidate the range of hazard zones and initiation mechanisms of debris flow disaster triggered by potential sources in the upstream Yizhong River under conditions of heavy rainfall and earthquakes, this study conducted field investigations and causal analyses. High-precision Digital Elevation Model (DEM) data derived from close-range UAV aerial photography were utilized as topographic data. The RAMMS software simulated a debris flow of 16.05×104 m3 under heavy rain and earthquake conditions. Two hazardous zones within the Yizhong River Basin were delineated, and the disaster initiation mode of debris flow in Yizhong River was expounded. The results show that the debris flow in Yizhong River belongs to the gully-type viscous debris flow typical of plateau mountainous regions, characterized by large scale, high frequency, and severe impact. Its disaster mechanism is summarized as a gully and valley disaster chain involving high-altitude landslide, debris flow, dammed lake, and flood breach. Risk zone I is located in the area from G214 national road to Dewei Road, while risk zone II is in the gully mouth area prone to accumulation and blockage, presenting high risk. During debris flow movement, the maximum flow velocity reached 23.93 m/s, maximum impact force was 1000 kPa, maximum accumulation depth was 9.33 m, and the maximum single outburst volume of debris flow was approximately 80000 m3, with a danger area of about 0.31 km2. The research results provide a scientific basis for debris flow control projects in Yizhong River and are of practical significance for improving the comprehensive prevention and control of geological hazards in Deqin County.