Abstract
Characterized by large scale, high frequency, and strong destructiveness, debris flow has become the most noticeable geohazards throughout the world, especially in the mountainous areas of southwestern China. On August 20, 2019, large-scale heavy rainfall pummeled Wenchuan County, Sichuan Province, Southwestern China, which resulted in a cluster of debris flows (the “8·20” clustered debris flows event), and caused considerable economic losses (approximately 3.4 billion RMB were lost) and heavy casualties (48,862 people were displaced, 16 people died and 22 people went missing). Based on field investigation, image data interpretation, mechanism analysis, and other methods, this study reveals the formation mechanism, dynamic evolutionary process, and impacts of human activities on the “8·20” clustered debris flows event. Results from a comprehensive analysis indicate that the occurrence of short-term, high-intensity rainfall and the excessive supply of solid material were the main factors that triggered this catastrophic event. With the debris flow flowing into the main river, this event presented an extremely apparent disaster chain effect. It is also found that improper site selection and inadequate design of human activities played a crucial role in the movement process of the debris flow that directly aggravated the losses. Finally, to improve debris flow prediction and prevention, some early warning and mitigation measures are discussed.
Highlights
Debris flow occurs when masses of poorly sorted sediment, agitated and saturated with water, surge down slopes in response to gravitational attraction (Iverson, 1997)
Previous studies have shown that the rainfall thresholds for the subsequent generation of debris flow within the affected area were remarkably lower after the Wenchuan earthquake
With the reduction of effective material sources that can be transformed into debris flow, the rainfall thresholds will gradually recover over time, but how long it takes to achieve recovery requires further in-depth study
Summary
Debris flow occurs when masses of poorly sorted sediment, agitated and saturated with water, surge down slopes in response to gravitational attraction (Iverson, 1997). On August 20, 2019, Wenchuan County suffered large-scale heavy rainfall that caused a cluster of debris flow disasters (Figure 2B). The terrain of Wenchuan County is complex with high mountains, steep slopes, and deep valleys This topography is extremely conducive to the accumulation of loose solid material and the collection of surface runoff; it provides favorable topographic conditions for the rapid formation of debris flow. Another noteworthy problem is that the long-term accumulation of loose solid material under the bridge has not been cleaned up in time or effectively, which is one of the reasons for the lack of cross-section when the debris flow event occurred. Severe damage to transportation facilities is much more likely to delay emergency rescue work, such as searching and rescuing missing people and transferring disaster victims
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
