Comprehensive investigation of the debris flow triggered by heavy rainfall in Xi’an, Shaanxi, on August 11, 2023

Abstract

Amidst the ongoing global climate change, short-term heavy rainfall in local areas is occurring more frequently, exacerbating the risk of chain disasters caused by geohazards such as landslides and debris flows. On August 11, 2023, around 16:00, a large debris flow named Jiwozi occurred in the Haogou small watershed in the middle section of the Qinling Mountains, causing 27 deaths and a direct economic loss of about 15.6 million. To identify the triggering factors and the evolution process of the debris flow, this study carried out a comprehensive investigation using a variety of technical methods, including optical satellite remote sensing, spaceborne interferometric synthetic aperture radar (InSAR), UAV, LiDAR, and field surveys. The study found that: 1) The Jiwozi debris flow is approximately 2.5 km in length, with a catchment area of about 1.2 km². Jiwozi hydrological station recorded short-term heavy rainfall between 15:00 and 17:00 on 11 August, with a cumulative rainfall of 53 mm. Heavy rainfall provides sufficient hydrodynamic conditions to trigger the debris flow. 2) The loose deposits and fragmented rock mass in the Haogou gully provided the material source conditions for the Jiwozi debris flow. Preliminary calculations reveal that the slope erosion volume is 1.46×10⁴ m³, and the total erosion volume of the debris flow is 15.3×10⁴ m³; the ratio of slope erosion material transformed into debris flow is 3%. The flow velocity of the debris flow is approximately 3.5 m/s, and the corresponding downstream debris flow discharge can reach 103.3 m³/s. 3) A preliminary analysis indicates that the destabilization and evolutionary mechanism of the Jiwozi debris flow follows a pattern of ‘shallow sliding – shovelling – damming – breaching – shovelling – debris flow’. Studying the triggering mechanisms and dynamic processes of the Jiwozi debris flow contributes valuable insights for hazard assessment and early warning systems in mountainous gully areas, especially during the rainy season when there is continuous heavy rainfall.