Preliminary analysis of the deadly debris flow on August 11th, 2023, at Xi’an of China: characteristics, mechanism, and hazard assessment
摘要
On 11th August 2023, a catastrophic debris flow, so-called Haogou debris flow, occurred in Luan Township, Changan District, Xi’an City, located in the Qinling Mountains of China. It resulted in 25 deaths and two people unaccounted for, thus gaining public attention. By using the detailed field survey, optical remote sensing data, a physically based model, and FLO-2D simulation, a preliminary analysis was provided regarding the development, characteristics, causative factors, and hazard assessment of the event. It was found that the steep source areas, open gully channel, strongly weathered rocks, and sufficient deposits provided necessary foundations. The calculations using the FSLAM (Fast Shallow Landslide Assessment Model) revealed that a short-term heavy rainstorm caused a peak water discharge of 20.4 m3/s, resulting in rapid movements of water-saturated debris along the channel. The big rocks and continuous instabilities along the channel amplified the disaster effect. Despite an evident turning during the flowing path, the accumulative runout distance of the debris flow reached 1.2 km with a decrease of elevation of 950 m. The FLO-2D simulation revealed the highest velocity of 6 m/s before reaching the fan-shaped deposition zones of the channel terminus and the peak accumulation depth of 3.7 m at the damaged houses. The event highlights the importance of increasing public perception of the risks associated with such events and of improving monitoring and early warning abilities in similar settings.