Review and analysis of “7·20” flash flood and debris flow disaster in Hanyuan, Sichuan

Abstract

[Objective] On July 20^th, 2024, a severe flash flood and debris flow disaster occurred in Xinhua Village, Malie Township, Hanyuan County, Ya'an City, Sichuan Province, affecting over 1 500 people and causing severe damage to infrastructure. A disaster review and analysis is conducted to investigate the formation mechanism of this compound flash flood and debris flow disaster, analyze the scope and degree of its impact, and propose targeted disaster prevention and mitigation measures, providing references for the prevention and control efforts of similar flash flood and debris flow disasters in the future. [Methods] Remote sensing measurement, field investigation, numerical simulation, and comparison with design indicators were employed. In the simulation analysis, the inferential formula method, area analogy method, and distributed hydrological simulation method were employed for multi-method comparative analysis to comprehensively determine the return period of this flood. [Results] Using the inferential formula method, the peak discharge of a 30-year return period design flood at the confluence of Dagotou and Malie Gully was calculated to be 286.00 m³/s. Based on surveyed flood marks, the peak discharge of this disaster was estimated to be approximately 263.00 m³/s using the area analogy method. By applying the distributed hydrological simulation method, the peak discharge of this disaster was calculated to be 249.70 m³/s. A comprehensive analysis indicated that the return period of this flood was approximately 30 years. [Conclusion] The analysis confirms that the intense rainfall is the primary triggering factor of this compound disaster. The unfavorable topographic, geomorphic, and geological conditions in the watershed exacerbate the severity of the disaster, while the blockage of bridges and culverts further expands the impact of the disaster. Moreover, deficiencies in early warning systems, emergency response mechanisms, and risk management during disaster response are key factors leading to the severe loss.

Keywords

flash flood and debris flow / compound disasters / disaster review / disaster mechanism / Hanyuan,Sichuan / risk assessment / flood / numerical simulation