Big Disaster from Small Watershed:Insights into the Failure and Disaster‑Causing Mechanism of a Debris Flow on 25 September 2021 in Tianquan,China

作     者：Runing Hou Mingyang Wu Zhi Li Ningsheng Chen Xiaohu Chen Taixin Peng Na Huang Runing Hou;Mingyang Wu;Zhi Li;Ningsheng Chen;Xiaohu Chen;Taixin Peng;Na Huang

作者机构：Key Laboratory of Mountain Hazards and Surface ProcessesInstitute of Mountain Hazards and EnvironmentChinese Academy of SciencesChengdu 610041China School of GeosciencesYangtze UniversityWuhan 430100China Academy of Plateau Science and SustainabilityXining 810016China University of Chinese Academy of SciencesBeijing 100049China 

出 版 物：《International Journal of Disaster Risk Science》 (国际灾害风险科学学报（英文版）)

年 卷 期：2024年第15卷第4期

页      面：622-639页

核心收录：

学科分类：08[工学] 0837[工学-安全科学与工程] 

基　　金：supported by the National Key Research and Development Program of China(Grant No.2023YFC3008301) the Postdoctoral Fellowship Program of CPSF(Grant No.GZC20232571,2024M753153) the Special Research Assistant Program of CAS(Grant No.2024IMHE01) the National Natural Science Foundation of China(Grant No.42361144880) the Basic Research Program of Qinghai Province(2024-ZJ-904) the International Cooperation Overseas Platform Project,CAS(Grant No.131C11KYSB20200033) 

主　　题：China Colluvial soil Low-frequency debris fows Risk reduction Topographic hollows 

摘      要：The occurrence of debris flow events in small-scale watersheds with dense vegetation in mountainous areas that result in significant loss of life and missing individuals challenges our understanding and expertise in investigating and preventing these disasters. This has raised concerns about the occurrence of large debris flow disasters from small watersheds. This study focused on a catastrophic debris flow that took place in Longtou Gully(0.45 km^(2)) in Tianquan County, Ya an City on 25 September 2021, which resulted in 14 deaths and missing individuals. Through comprehensive field investigations, highprecision remote sensing data analyses, and numerical simulations, we analyzed the triggering mechanisms and dynamic processes of this event. Our results indicate that the convergence hollow at the channel head exhibited higher hydraulic conditions during rainfall compared to gentle slopes and convex terrains, leading to the instability of colluvial soil due to the expansion of the saturated zone near the soil–bedrock interface. The entrainment of material eroded from the channel resulted in an approximately 4.7 times increase in volume, and the channel scarp with a height of about 200 m amplified the destructive power of the debris flow. We emphasize the need to take seriously the possibility of catastrophic debris flows in small-scale watersheds, with colluvial deposits in hollows at the channel head under vegetation cover that serve as precursor material sources, and the presence of channel scarps formed by changes in the incision rate of the main river, which is common in the small watershed on both sides. This study provides insights for risk assessment of debris flows in small-scale catchments with dense vegetation cover in mountainous areas, highlighting the importance of vigilance in addressing disasters in small-scale catchments, particularly in regions with increasing human–environment conflicts.