Activity characteristics and enlightenment of the debris flow triggered by the rainstorm on 20 August 2019 in Wenchuan C
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ORIGINAL PAPER
Activity characteristics and enlightenment of the debris flow triggered by the rainstorm on 20 August 2019 in Wenchuan County, China Jiang Xiong 1 & Chuan Tang 1 & Ming Chen 1 & Xianzheng Zhang 1 & Qingyun Shi 1 & Lingfeng Gong 1 Received: 28 April 2020 / Accepted: 26 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Debris flow activity increased after the Wenchuan earthquake, and many debris flows continue to occur. Recently, a catastrophic debris flow event was triggered by strong rainfall on 20 August 2019 in Wenchuan County, China. The main purposes of this article are to analyse the activity characteristics of this disaster and further to analyse the long-term activity of debris flow in Wenchuan County based on the analysis results of this disaster. According to a field survey and remote sensing image interpretation, this strong rainfall triggered 15 debris flows that occurred simultaneously in the large watershed in northern Wenchuan County, and they were characterised by strong channel erosion and a disaster chain effect. The activity and sediment supply capacity of landslides have decreased significantly, and the landslides that provided materials for this debris flow event are mainly distributed on both banks of tributaries. The amounts of triggering rainfall and antecedent accumulated rainfall for this debris flow event were 13.7 mm and 47.1 mm, respectively. In addition, the channel runoff formed by strong short-duration rainfall eroded the channel deposits, and temporary check dams failed due to slope failures; these are the main causes for debris flows in the next period. Analyses of the debris flow volume versus watershed area and the maximum erosion modulus prove that the debris flow activity in Wenchuan County is decreasing with time, but more than 5~10 years will be required to recover to the pre-earthquake level. Keywords Wenchuan earthquake . Debris flow . Debris flow activity . Sediment supply . Strong rainfall
Introduction A catastrophic Mw 7.9 earthquake occurred on 12 May 2008 in Wenchuan County, west of Sichuan Province, China. The earthquake injured approximately 459,000 people and caused more than 87,000 casualties (Qi et al. 2010). A large number of houses and numerous infrastructures were damaged, with the total losses reaching USD 150 billion (Zhang et al. 2012). A considerable number of landslides were triggered by the Wenchuan earthquake (Dai et al. 2011). According to records, approximately 200,000 landslides were interpreted through high-resolution images (Xu et al. 2014), with 52.5 × 108 m3
* Chuan Tang [email protected] 1
State Key Laboratory of Geo-Hazard Prevention and Geo-Environment Protection, Chengdu University of Technology, Chengdu, China
of loose debris accumulating in debris flow gullies or on valley slopes (Xu et al. 2009), which provided plenty of materials for debris flows to occur. After the Wenchuan earthquake, the activity of debris flow was higher than that to the preearthquake because the critical amount of
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