古沉积盆地下切引发的泥石流侵蚀和波状流动耦合过程

Coupling Process of Debris Flow Erosion and Wavy Flow Caused by Incision on Paleosedimentary Basin

青藏高原的持续抬升导致黄河干流下切,带动支流大河坝河溯源下切,使得同德盆地由沉积区变为侵蚀区,泥石流开始群发,研究群发机理对古沉积盆地泥石流的防灾减灾意义重大.通过野外监测结合室内水槽试验,系统分析了同德盆地卵石夹砂沉积层的土力学性质,切沟发育阶段和泥石流的侵蚀、运动过程.卵石夹砂沉积层分选好,磨圆度高,无胶结,利于水流下切和物源能量的累积.大河坝河溯源下切,卵石夹砂物源能量往大河坝河上游传递,导致大河坝河不同河段的切沟发育阶段和泥石流发育趋势不同.卵石夹砂沉积层的厚度和下切深度决定了泥石流的侵蚀强度和发育趋势.水流下切、泥石流侵蚀、卵石夹砂分选和崩滑堵溃过程造成了泥石流龙头能量来源的间歇性和周期性,助推了龙头运动的波动性.

Uplift of the Qinghai-Tibet Plateau result in accelerating fluvial incision of the Yellow River.The incision of the Yellow River makes Daheba River,one of the tributaries of the Yellow River,incise quickly on the flat and broad Tongde basin covered by deep fluvial sediments and loess.Tongde basin has changed from sedimentary area to erosion area,and debris flow are developing.The study on the mechanism of debris flow groups occurrence is of great significance to the prevention and mitigation of debris flow in paleosedimentary basins.This paper analyzed the characteristics of sediments soil mechanics,water system of Daheba River and the mechanism of erosin and motion of debris flow through field investigation and physical model.Analysis showed that the Daheba River incised on thick lacustrine sediments and the sediments composed by gravel and sand,good sorting,were beneficial to the formation of debris flow.Under the condition of uplift of Qinghai-Tibet Plateau and rapid incisions of Yellow River,the headward erosion of Daheba River had made the river energy gradually extend upstream.Therefore,different distribution and development characteristics were at different river sections of Daheba River.The thickness and incision depth of pebble sand sediment layer determine the erosion intensity and development trend of debris flow.The intermittent energy source of debris flow head is caused by the process of water flow incision,debris flow erosion,pebble sand separation and collapse,which promotes the fluctuation of debris flow movement.