四川木里县项脚沟“7•5”特大型泥石流特征及发展趋势分析

Analysis of the characteristics and development trends of the“7•5”catastrophic debris flow in Xiangjiao gully,Muli County,Sichuan

2021年7月5日,凉山州木里县项脚沟暴发特大型泥石流灾害。文章通过野外调查和特征参数计算,研究了本次泥石流的形成条件、暴发过程和暴发特征。根据实地考察判断,泥石流主要在森林火灾、短时强降雨和沟道地形条件等因素共同作用下暴发,为暴雨径流冲刷引发的火后泥石流。暴雨形成的洪水冲刷坡面、侵蚀沟道,导致沟道两岸坍塌滑坡,堵溃效应明显,泥石流规模扩大。项脚沟过火面积达74.61%,高烈度火烧区面积达57.98%,泥石流临界降雨强度为77.84 mm/h,累计降雨达141.60 mm。根据泥石流特征参数计算结果,此次泥石流密度范围为1.83~1.93 g/cm^(3),属黏性泥石流,主沟下游出口流速为7.22 m/s,峰值流量759.08 m^(3)/s。结合雨洪法和形态调查法结果分析,此次泥石流重现周期为百年一遇。结合泥石流发育趋势,文章认为流域仍有可能暴发大型泥石流,提出了上游固坡、中游调控、下游排导的防治建议。

On July 5,2021,a catastrophic debris flow disaster occured in Xiangjiao gully,Muli County,Sichuan Province.This study analyzed the formation conditions,eruption process and eruption characteristics of the debris flow through field investigation and characteristic parameter calculation.Based on the results of on-site inspection,this debris flow was mainly caused by the combined effects of forest fires,short-term heavy rainfall,and channel topography.It was a post-fire debris flow caused by rainfall runoff erosion.The heavy rain caused powerful flood erosion on the slope surface,eroded the channel,led to collapse and landslides on both sides of the channel,and resulted in significant damming effects,which enlarged the scale of the debris flow.The forest fire area in Xiangjiao gully reached 74.61%,and the high-intensity burned area was 57.98%.The critical rainfall intensity for this debris flow was 77.84 mm/h,and the cumulative rainfall was 141.60 mm.According to the calculation results of characteristic parameters,the density of this debris flow was in the range of 1.83~1.93 g/cm^(3),indicating it was a viscous debris flow.The flow velocity at the downstream outlet of the main channel was 7.22 m/s,and the peak flow rate was 759.08 m^(3)/s.Combined with the results of the rainfall-runoff method and the morphology investigation method,the recurrence interval of this debris flow was estimated to be once in a hundred years.Considering the development trend of debris flow,it is believed that there is still a possibility of large-scale debris flow in the basin.Therefore,prevention and control suggestions including slope reinforcement in the upstream,regulation in the middle reach,and drainage in the downstream are proposed.