Abstract
After analysing the catastrophic debris flows on August 18, 2012, and on July 9, 2013, in Jushui River basin, An County, the Wenchuan Earthquake seriously striken areas, it was found that they were characterized by the clay soil content of 0.1~1.2%, the density of 1.68~2.03 t/m3, the discharges of 62.2 m3/s to 552.5 m3/s, and the sediment delivery modulus of 1.0~9.4 × 104 m3/km2. Due to intense rainstorm, many large debris flows produced hazard chain, involved in flash flood, debris flow, dammed lake, and outburst flood, and rose Jushui River channel about 1~4 m as well as amplified flood. The hazards and losses mainly originated from the burying and scouring of debris flows, flood inundating, and river channel rise. The prevention of debris flows is facing the intractable problems including potential hazard identification, overstandard debris flow control, control constructions destructing, and river channel rapid rise. Therefore, the prevention measures for the basin, including hazard identification and risk assessment, inhabitants relocating, monitoring and alarming network establishing, emergency plans founding, and river channel renovating, and the integrated control mode for watershed based on regulating the process of debris flow discharge, were recommended for mitigation.
Highlights
Debris flow, an abrupt earth surface phenomenon, extensively and frequently occurs at mountain areas with steep terrain, quantity of unconsolidated soil, and abundant surface runoff
Because the Yingxiu-Beichuan faults, the triggering faults of the Wenchuan Earthquake, pass through this basin, rock falls and landslides extensively formed at the hardrock areas and at the soft-rock areas, respectively, with the density of 15 sites/km2 [8], and unstable slopes densely distributed in the steep mountains after the earthquake
In the formula (3), QC is the peak discharge of debris flow and QB is the peak discharge of flash flood, which is calculated by the parameters of the watershed using the methodology that was represented by the calculation handbook for rainstorm-flood at watersheds of Sichuan Province [14]. φ indicates the correctional coefficient of debris flow, which is calculated by formula (4). q is the amplification coefficient of debris flow, which is confirmed according to the situation of channel blocks [10]. γD is the density of debris flow, which was obtained by formula (1), and γH = 2.65 t/m3 is the density of solid in debris flow
Summary
An abrupt earth surface phenomenon, extensively and frequently occurs at mountain areas with steep terrain, quantity of unconsolidated soil, and abundant surface runoff. It is often exasperated by extreme rainstorms, intensive exploitation activities, and intensive earthquakes. The debris flows following Wenchuan Earthquake are characterized by lower triggering rainfall threshold, high density, higher velocity, larger discharge, bigger magnitude, and intensive impact and impose the heaviest-dangerous hazards on local living and reconstructions at the seriously stricken areas [1, 2]. This work aims to discuss the problems of debris flow control and explore rational solutions for this basin, which contribute to the mitigation of debris flows in the whole seriously stricken areas
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