汶川震区绵虒镇“8·20”登溪沟泥石流灾害调查与分析

Field Investigation and Research on Debris Flow on August 20,2019 in Mianshi Town,Epicenter of Wenchuan Earthquake

2019年8月20日汶川县绵虒镇登溪沟暴发大型泥石流灾害,导致沟口房屋、国道和高速公路损毁,交通中断长达数月,同时大量冲出物质堵塞岷江河道,使岷江河道改道左岸,水位抬升,形成链式灾害。基于登溪沟泥石流形成条件、致灾特征以及泥石流事件前后现场调查和遥感影像解译进行了分析,采用配重法和形态调查法计算获得泥石流的容重和动力特征。结果表明,登溪沟泥石流是短历时强降雨、有利的地形条件及地震作用产生的丰富物源以及沟道强烈侵蚀多种因素共同作用的结果,其成灾模式可总结为降雨快速汇流-沟道物质启动形成泥石流-泥石流沿程铲刮裹挟-岸坡坍塌堵溃-泥石流规模放大冲出沟口的运动过程,泥石流事件前后影像解译显示坡面物源和沟道物源随着时间产生了显著演化,流域内物源仍然丰富。汶川地震虽已过去十年以上,泥石流活动性仍然较高,因此针对登溪沟泥石流活动进行了详细调查分析以期加强对强震区震后中长期泥石流特征的进一步认识。

On August 20,2019,a large debris flow occurred in Dengxi valley,Miansi Town,Wenchuan County.As a result,a large number of houses,national highways and expressways were washed out at the mouth of the ditch,and traffic was interrupted for months.At the same time,a large amount of material rushed out blocked the main channel of Minjiang River,causing the channel of Minjiang River to be diverted to the left bank and the water level to rise,forming a chain disaster.Based on the formation conditions,disaster-causing characteristics of the debris flow in Dengxi valley,as well as the field investigation and remote sensing image interpretation before and after the debris flow event,the bulk density and dynamic characteristics of the debris flow,such as velocity,discharge and debris flow outflow,were calculated by using the weight method and morphological investigation method The results show that the Dengxi valley debris flow is the result of the combined action of many factors,such as short duration heavy rainfall,favorable topographic conditions,abundant provenance produced by earthquake and strong erosion of the channel.The disaster pattern is summarized as a movement process as follows:rapid confluence of rainfall-initiation-formation of debris flow by materials of the vally-erosion of materials at the bottom and both sides of the gully-collapse of bank slope and blockage and outburst-the scale of the debris flow becomes large and rushed out.The image interpretation before and after the debris flow event showed that the provenance of slope and channel evolved significantly with time,and the provenance in the basin was still rich.The activity of debris flow is still high in the Wenchuan earthquake area ten years after the earthquake.Although more than10 years have passed since the Wenchuan earthquake,the activity of debris flow is still relatively high.Therefore,the detailed investigation and analysis of the debris flow activity in Dengxi valley are carried out in order to strengthen the further understanding of the characteristics of debris flow in the medium and long term after the earthquake in the strong earthquake area.