Characterization and formation mechanism of the catastrophic flash flood-debris flow hazard triggered by the July 2023 extreme rainstorm in Hantai Gully of Beijing, China

• Published in: Landslides Vol. 22; no. 3; pp. 877 - 893
• Main Authors: Ma, Junxue, Gao, Huiran, Xu, Chong, Qi, Shuwen
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Nature B.V 01.03.2025
• Subjects: Aerial surveys; Catastrophic events; Data acquisition; Debris flow; Detritus; Disasters; Entrances; Extreme weather; Flash flooding; Flash floods; Flood flow; Floods; Geological data; Geological mapping; Geological maps; Geological surveys; Gullies; Heavy rainfall; Hurricanes; Image acquisition; Mountain regions; Mountainous areas; Precipitation; Prevention; Rain; Rainfall; Rainstorms; Regional analysis; Remote sensing; Surface runoff; Topographic mapping; Topographic maps; Topography; Typhoons; Unmanned aerial vehicles; Beijing China; China
• ISSN: 1612-510X; 1612-5118
• DOI: 10.1007/s10346-024-02433-3

Recent extreme rainfall events have led to frequent flash flood-debris flow hazards in the mountainous regions of western and northern Beijing, China, resulting in significant loss of life and property. To decipher the formation mechanism and hazard characteristics of these local disasters, the July 2023 flash flood-debris flow in Hantai Village (HTV) and Hantai Gully (HTG) of Changping District, Beijing, was selected as the focus of this study. This study acquired topographic and geological data of the study area through regional disaster investigation, field surveys in severely affected regions, and indoor assessments and analyses, utilizing 1: 1000 topographic maps and 1: 20,000 geological maps sourced from unmanned aerial vehicle (UAV) remote sensing images. Then, the characteristics of rainfall and the associated hazard processes (flash flood and debris flow) were systematically investigated and analyzed. By further exploring the formation mechanism of these events, relevant hazard prevention and mitigation suggestions were proposed. The results indicate that the total flood volume in the upstream channel of HTG is approximately 6870 m3 within 1 h, demonstrating significant destructive power. The leading edge of the flash flood/debris flow exits the gully (the southern entrance of HTV) at an instantaneous speed of 74.47 km/h and maintained a speed of 16.42 km/h by the time it reached the northern exit of HTV (outlet of the HTG), with a movement time of 1.83 min. This brief event duration presents significant challenges for timely evacuation. This catastrophic flash flood-debris flow event is identified as a compound hazard triggered by extreme rainfall from the remnant circulation of Typhoon Doksuri, with the sudden increase in surface runoff amount due to short-term heavy rainfall being the primary cause. It is hypothesized that the debris flow occurred later than the flash flood or during the weakening period of the flash flood and was subsequently eroded by weak flood flows, demonstrating clear characteristics of a mutual transformation between flash flood and debris flow. This study provides fundamental support and reference for hazard prevention and response improvement in other small watersheds.