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 

机构地区：[1]Key Laboratory of Mountain Hazards and Surface Processes,Institute of Mountain Hazards and Environment,Chinese Academy of Sciences,Chengdu 610041,China [2]School of Geosciences,Yangtze University,Wuhan 430100,China [3]Academy of Plateau Science and Sustainability,Xining 810016,China [4]University of Chinese Academy of Sciences,Beijing 100049,China

出　　处：《International Journal of Disaster Risk Science》2024年第4期622-639,共18页国际灾害风险科学学报（英文版）

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).

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.

关 键 词：China Colluvial soil Low-frequency debris fows Risk reduction Topographic hollows 

分 类 号：P642.23[天文地球—工程地质学]