The Xiaogangjian Gully is typical for debris flow in the earthquake zone. Located in the left of Mianyuan river,it has a drainage area of 1. 36 km and an average longitudinal slope of 412‰. After Wenchuan earthquake, many debris flow occurred in this gully, causing great disasters to the reconstruction of Qingping town, The debris flow formation process is as follows: torrents→ torrent scourage → small-scale debris flow → debris flow in mainstream channel, with powerful energy and strong capacity of scouring →, incision of streambed sediment and old deposit platform → large-scale debris flow, at the outlet There were 10 debris flows in the following 4 years after the earthquake,which cut the gully up to the depth of 35 m,and brought 50×104 m3 of solid mass out of the gully. Debris flows buried the Hanwang - Qingping road, blocked the river and formed a dam lake, carried a huge volume of sediment to the downstream, uplifting the water level and silting the highway. At present, the gully still has 334. 3 ×104 m3 of solid material,of which about 156. 8×104 m is prone to debris flow in the future when it encounters great rainstorms. The development trends of the debris flow in Xiaogangjian gully are as follows: 1) its strength of activity will keep reducing with the decrease of loose granular materials and total amounts of debris flow; 2 ) the debris-flows activity is transport-limited system right after the earthquake,followed by the transitional type between transport-limited system and weathering-limited system and ultimately is weathering-limited system.%小岗剑沟是汶川地震区内一条典型的泥石流沟,位于绵远河的左测,流域面积1.36 km2,沟床平均纵比降412‰.该沟在2008年“5.12”汶川地震后多次暴发泥石流,掩埋从沟口通过的汉(旺)清(平)公路,给四川省绵竹市清平乡的地震灾后重建造成重大危害.通过初步分析,小岗剑沟泥石流的形成过程为:暴雨作用下沟因上游良好的汇流条件而产生山洪→山洪冲刷堆积在沟道内的松散固体物质形成小规模泥石流→泥石流沿大比降沟道向下运动,因具有强大动能而具有强大冲刷下切侵蚀能力,下切侵蚀下游沟床质以及沟口的老台地→在沟口形成大规模泥石流.地震后4 a内共暴发泥石流10次,将沟口老堆积体下切侵蚀深度达35 m,泥石流冲出固体物质50×104 m3.目前,沟内仍有固体物质量334.3×104m3,可能参与泥石流活动的动储量为156.8×104m3.如此大量的松散固体物源,使小岗剑沟可能还暴发大规模泥石流.通过泥石流形成因素分析,该沟泥石流活动总体呈强度下降趋势,泥石流活动类型:震后一段时间内为输移控制型、然后为输移控制型向松散固体物质控制型过渡,最后发展成为松散固体物质控制型.通过这些分析,为泥石流治理提供科学支撑.
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