Study On Flow And Sediment Movement And Evolution Of Floodplain And Main Channel Of Compound Channel In Lower Yellow River

Basing on new requirement of floodplain and main channel harness in Lower Yellow River, using the method of data analysis and theoretical discuss, flow and sediment movement and channel evolution were researched, the main research achievements are as follows:(1) Flow and sediment movement characteristics of floodplain and main channel was analyzed. Flow movement characteristics:at the interactional region, transverse variation of vertical average velocity is biggish, far from the interactional region, transverse variation of vertical average velocity is lesser, floodplain and main channel boundary exist laigh velocity discontinuous strip. Sediment movement characteristis:transverse gradient of sediment concentration and median diameter of suspended load is biggest in floodplain and main channel boundary, toward both sides, transverse gradient became grading. Bedload diameter constitute of main channel is coarser than floodplain, upriver is coarser than downriver, deep is coarser than shallow.(2) Establishing the synthetical relationship of the separated discharge ratio of floodplain and main channel. If increasing the width、depth and area of main channel, improving the velocity of main channel, decreasing roughness of main channel, reducing width-depth ratio of main channel, the passing discharge capability of main channel should be improved, if increasing the width、depth and area of floodplain, improving the velocity of floodplain, decreasing roughness of floodplain, the passing discharge capability of floodplain should be improved. During the harnessing of the Lower Yellow River, a certain extent passing discharge capability and narrow deep configuration of main channel should be maintained; a certain extent passing discharge width of floodplain should be set aside, the influencing of human should be reduced in floodplain, keeping the straightway of passing discharge of floodplain, guaranteeing the passing discharge capability of floodplain, lightening the press of main channel, insuring the safety of control flood.(3) Putting forward four modes of floodplain and main channel evolution. Four modes of floodplain and main channel evolution in Lower Yellow River:floodplain aggradation and main channel degradation^ floodplain aggradation and main channel aggradation、 floodplain degradation and main channel degradation、atrophy of floodplain and main channel. Floodplain aggradation and main channel degradation benefit to transport flow and sediment; the configuration of floodplain aggradation and main channel aggradation can not maintain; floodplain degradation and main channel degradation happened at one time; atrophy of floodplain and main channel endangered the safety of control flood.(4) Opening out floodplain aggradation and main channel degradation mechanism of overflowing floodwater. In earlier phase, floodplain lip came into being, transporting sediment capability of main channel reduced, the floodplain aggradation and main channel degradation has not been exhibited; in metaphase, exchange of flow and sediment of floodplain and main channel was sufficient, floodplain aggradation and main channel degradation accelerated one another, main channel scoured acutely, floodplain aggraded largely, the effect of floodplain aggradation and main channel degradation was good; in anaphase, increasing amplitude of velocity reduced, riverbed become coarse, exchange of flow and sediment of floodplain and main channel decreased, the floodplain aggradation and main channel degradation slowered, further more, the influence of main channel degradation slow on exchange of flow and sediment of floodplain and main channel need time, so that floodplain aggradation slow was hysteretic.(5) Putting forward flow and sediment controlling indexes of overflowing floodwater. The advantageous flow and sediment controlling indexes of overflowing floodwater are as follows:the overflowing parameter 1.4<γ1<1.5、the flow and sediment tie-in parameter γ2<2、discharge variation parameter γ3>0.24、the flow and sediment synchronization parameter γ4<0.45; at present, the bankfull discharge of Lower Yellow River resume 4000 m3/s, in favor of figuring and maintaining logical size of channel, through the controlling of Xiaolangdi reservoir, the peak discharge of ejective of floodwater should be 5600-6000 m3/s、the incoming sediment coefficient should be less than 0.028、discharge variation parameter 73 should be bigger than 0.24、the flow and sediment synchronization parameter γ4 should be less than 0.45.