汶川县古溪沟“7·10”泥石流形成特征及防治工程的影响

Giant Debris Flow Hazards in Guxi Gully,Wenchuan County of China on July 10,2013

通过对2013-07-10汶川古溪沟泥石流灾害的现场调查,从物源、地形和水源条件入手,分析了灾害成因与形成演化过程。堰塞体失稳补给、坡面泥石流入汇和沟道侵蚀是这场泥石流的三种物源形式,充沛的前期降雨和短历时强降雨是本次泥石流的诱发因素,陡峻的支沟地形促进了泥石流的加速,沿途松散物质补给,导致泥石流流量不断放大,峰值流量最大可达1 063 m3/s。主支沟泥石流呈明显的阵流特征,原因在于各支沟泥石流起动条件不同,沟道中地形条件的差异和防治工程的分布,以及各支沟汇流长度存在区别。泥石流总规模约为100×104m3,防治工程拦挡了60%的泥石流体,并拦截了泥石流中的大石块,降低了出口峰值流量和流速,同时避免了各条支沟泥石流同时到达而流量激增。沟口泥石流峰值流量约为722 m3/s,约40×104m3泥石流冲出沟口,下游泥石流破坏形式以淤埋破坏为主。本研究可为此类面积较大、修建有防治工程的流域泥石流形成和减灾提供参考。

The formation and evolvement process of debris flow on July 10,2013 was analyzed based on the field investigation on the material sources,rainfall,and topography conditions. The solid material sources supplying debris flows by failure of debris dams,which were formed by landslides and collapses induced by＂ 5 ·12 ＂Wenchuan Earthquake,slope debris flows,and bed material initiation. Plentiful antecedent precipitation and strong rainfall intensity were the inducing factors. The debris flow velocity was accelerated and peak discharge was amplified along the channel because of the steep channel gradient and solid materials supplying along the branch gullies. The peak discharges was 1 063 m3/ s. The debris flow is discontinuous-characterized for surges lasting for 6 h,because of the variation of initiation time in branch gullies,the different topography and distribution of dams,and also due to the concentration processes. The total amount is about 100 × 104m3but only 40% of them were deposit as a debris flow fan. The discharge,velocity and the impact force were decreased because of the effect of prevention engineering,therefore partly relieving the disasters. The study can contribute to formation and disaster reduction research in the comparative big basins,especially with the prevention engineering.