Abstract
Debris flow is an abrupt phenomenon of earth surface movement and typical disaster in mountainous areas with steep terrace, quantity of loose soil and abundant surface runoff. Intense rainfall and rainstorm easily triggered debris flows and generated huge losses. The disastrous debris flows, on July 4, 2013 at the gullies of Hou, Heilinzi and Xiongjia in Shimian County, Sichuan Province, resulted in 18 casualties and endangering Shimian city with a population of 50,000. These debris flows were characterized by low viscosity with only 0.9% - 1.4% clay soil of less than 0.05mm, density of 1.77 - 1.84 t/m3, velocity of 4.4 - 13.5m/s and discharge of 827 - 1248 m3/s, respectively, and also delivered sediment of 16.8 × 104m3, 12.7 - 13.5 × 104 m3, 20.5 × 104m3 out of the outlet, respectively. These three events all generated a hazard chain, which involved in flash flood, channelized debris flow, dammed lake and outburst flood. The threshold conditions of debris flow blocking Nanya River and forming this hazard chain are that the unit width peak discharge and the deposition volume in river channel are more than 37.0 m3/s and 4500 m3, respectively. These debris flows were initiated by intense rainfall with the antecedent rainfall of over 52 mm and triggering rainstorm of over 36 mm/h. And, the property losses and casualties mainly originated from impacting and scouring, burying and blocking, highway destructing and river channel rising. The irrational location of constructions and the destruction of under-standard prevention constructions were responsible for loss worsening. It was strongly recommended for mitigating that hazards reassessment, integrated control, emergency plan and integrated risk management were made at mountainous urban areas, especially in high-hazard areas.
Highlights
Debris flow, an abrupt earth surface phenomena and process, is extensively distributed and frequently occurs at mountainous areas in Western China
Risk Management Considering the hazards of debris flows on Shimian County, the following works must be carried out, including risk assessment, risk monitoring, exploitation supervising and mining wastes processing, which are necessary to provide a valuable solution to hazard identification, hazard evaluation, risk assessment and risk control for mountainous urban areas
The three disastrous debris flows on July 4 2013, triggered by intense rainstorm with the rainfall of over 36 mm per hour, were characterized by low viscosity, density of 1.77 - 1.84 t/m3, velocity of from 4.4 - 13.5 m/s and discharge of 827 - 1248 m3/s, and delivered sediment of 16.8 × 104 m3, 12.7 - 13.5 × 104 m3 and 20.5 × 104 m3 out of the outlet, respectively
Summary
An abrupt earth surface phenomena and process, is extensively distributed and frequently occurs at mountainous areas in Western China They generally form and occur in where are featured with steep geomorphology, quantity of loose sediment accumulating, and abundant surface runoff [1]-[3]. A group of disastrous debris flows occurred and threatened the city of Shimian, Sichuan province They occurred at the gullies of Hou, Heilinzi and Xiongjia on July 4, 2013, and blocked the Nanya River as well as formed 3 lakes, endangering the city with a population of over 50,000 persons. This work aimed to analyze characteristics, hazards and causes of these debris flows and provide suggestions and solutions for mitigation, contributing to debris flow hazards mitigating at urban areas of mountain
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