Preprints
https://doi.org/10.5194/egusphere-2024-2277
https://doi.org/10.5194/egusphere-2024-2277
16 Sep 2024
 | 16 Sep 2024
Status: this preprint is open for discussion.

Transformations in Exposure to Debris Flows in Post-Earthquake Sichuan, China

Isabelle Utley, Tristram Hales, Ekbal Hussain, and Xuanmei Fan

Abstract. Post-earthquake debris flows can exceed volumes of 1 x 106m3 and pose significant challenges to downslope recovery zones. These stochastic hazards form when intense rain remobilises coseismic landslide material. We investigate the relationship between changing exposure and hazard of post-2008 debris flows in three gullies in Sichuan province, China. These were selected based on the number of post-earthquake check dams – Cutou (2), Chediguan (2) and Xiaojia (none). Using high resolution satellite images, we developed a multitemporal building inventory from 2005 to 2019, comparing it to spatial distribution of previous debris flows and future modelled events. Post-earthquake urban development in Cutou and Chediguan increased exposure to a major debris flow in 2019 with inundation impacting 40 % and 7 % of surveyed structures respectively. We simulated future debris flow runouts using LAHARZ to investigate the role of check dams in mitigating three flow volumes – 104m3 (low), 105m3 (high) and 106m3 (extreme). Our simulations show check dams effectively mitigate exposure to low and high flow events but prove ineffective for extreme events with 59 % of buildings in Cutou, 22 % in Chediguan and 33 % in Xiaojia significantly affected. We verified our analyses through employing a statistical exposure model, adapted from a social vulnerability equation. Cutou's exposure increased by 64 % in 2019, Chediguan's by 52 % whilst only 2 % for Xiaojia in 2011, highlighting that extensive grey infrastructure correlates with higher exposure to extreme debris flows, but less so to smaller events. Our work suggests the presence of check dams increases the perception of exposure reduction downstream, however, ultimately produces a levee effect that raises exposure to large events.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Isabelle Utley, Tristram Hales, Ekbal Hussain, and Xuanmei Fan

Status: open (until 28 Oct 2024)

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Isabelle Utley, Tristram Hales, Ekbal Hussain, and Xuanmei Fan
Isabelle Utley, Tristram Hales, Ekbal Hussain, and Xuanmei Fan

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Short summary
We analysed debris flows in Sichuan, China, using satellite data and simulations to assess check dam efficacy. Our study found whilst check dams can mitigate smaller flows, they may increase exposure to extreme events, with up to 40 % of structures in some areas affected. Urban development and reliance on check dams can create a false sense of security, raising exposure during large debris flows and highlights the need for risk management and infrastructure planning in hazard-prone areas.