21 Jul 2023
 | 21 Jul 2023
Status: this preprint is currently under review for the journal NHESS.

The vulnerability of buildings to a large-scale debris flow and outburst flood hazard chain that occurred on 30 August 2020 in Ganluo, Southwest China

Li Wei, Kaiheng Hu, Shuang Liu, Nan Ning, Xiaopeng Zhang, Qiyuan Zhang, and Md Abdur Rahim

Abstract. In mountainous areas, damage caused by debris flows is often aggravated by subsequent dam-burst floods within the main river confluence zone. On 30 August 2020, a catastrophic disaster chain occurred at the confluence of the Heixiluo Gully and Niri River in Ganluo County, Southwest China, that consisted of a debris flow, the formation of a barrier lake and subsequent dam breach that flooded the community. This study provides a comprehensive analysis of the damage to buildings resulting from the sequential occurrence of debris flow and dam-burst flood. The peak discharge of the debris flow in the gully mouth reached 1937 m3/s, and the change in the main river channel resulting from the dam-burst flood, which had a peak discharge of 2273 m3/s, resulted in a fourfold increase in the extent of flood inundation compared to an ordinary flood. Three hazard zones were established based on the building damage patterns: (I) primary debris flow burial; (II) secondary dam-burst flood inundation and (III) sequential debris flow burial and dam-burst inundation. Vulnerability curves were developed for Zone (II) and Zone (III) using impact pressures and inundation depths, and a vulnerability assessment chart is presented that contains the three damage categories. This research addresses a gap in the vulnerability assessments of debris flow hazard chains and can support in future disaster mitigation within confluence areas.

Li Wei et al.

Status: open (until 27 Oct 2023)

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  • RC1: 'Comment on nhess-2023-75', Anonymous Referee #1, 21 Aug 2023 reply

Li Wei et al.

Li Wei et al.


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Short summary
The damage patterns of the buildings were classified into three types: (I) buried by primary debris flow, (II) inundated by secondary dam-burst flood, and (III) buried by debris flow and inundated by dam-burst flood sequentially. The threshold of the impact pressures in Zones II and III where vulnerability is equal to 1 are 88 kPa and 106 kPa, respectively. Heavy damage occurs at an impact pressure greater than 40 kPa, while slight damage occurs below 20 kPa.