River Channel Change of the Upper of Minjiang River by 5.12 Wenchuan Earthquake:A Case Study of the Section of Dujiangyan-Wenchuan

This paper discusses the river channel change of the upper of Minjiang River by geo-hazards induced by 5.12 Wenchuan Earthquake,including collapse,landslide,debris flow,geo-hazard dam lake and so on.It also studies the characteristics of geo-hazards distributed in Dujiangyan-Wenchuan Highway and establishes the mechanisms of river channel change by geo-hazards on the basis of the field observations and the remote sensing image analysis.After this earthquake,most Minjiang River channel width decreased by 5-10 m due to the deposition of collapses and landslides,somewhere by 20-30 m,and the narrowest remaining only 30-40 m.Debris flow delivered quantity of solid materials into the River and deposited on the river channel,blocked the river and generated geo-hazards dam lake,resulting in the rise of the riverbed and the increase of the river curve.Generally,in the coming 10-20 years,especially the next 5 years,the river channel of Wenchuan-Yingxiu would become narrower with more curves and higher riverbed slope.While the riverbed of Yingxiu-Zipingpu would rise rapidly because of the deposition of sediments from the upper Minjiang River.In the long term,the geo-hazards by this earthquake will accelerate the natural evolvement of the upper reaches of the Minjiang River and induce riverbed rise and extension,riverbed slope reduction and gorge expansion.