Morphological Evolution And Hydraulic Conditions Analysis Of Typical Braided-anabranching Channels In The Yellow River Source Region

The source area of the Yellow River is located in the hinterland of the Qinghai-Tibet Plateau and is in a state of natural evolution.It is a natural test site for studying the evolution of rivers.The Dari sections of the Yellow River source area are a special alluvial river.The single and multi-segment sections of Dari are alternately present,with frequent morphological changes and stability between the braided and Anabranching rivers.It is of great significance to study the morphological change process and stability of the braided-anabranching channel.There are four river-type changes along the Maqu River section.The large-scale river channel plane shape has remained stable for many years,and only the local river channel plane morphology has changed.For the hydraulic relationship along the river section,the variation.of the water and sediment and the adjustment method are studied.Rarely involved.The study of alluvial channels in the Yellow River source region has helped to further understand river diversity in the region.Dari river using Landsat remote sensing imagery and Google Earth in 1987-2016,typical groups of central bars and islands in six sections were selected to analyze temporal and spatial variation patterns of braiding channel count.According to the river type change,the Maqu section of the Yellow River source area is divided into five sub-river sections.By analyzing the remote sensing images from 1987 to 2016,the plane morphological changes of the local sections of the five sub-rivers are obtained,and the one-dimensional constant is obtained.The basic equation of uniform water flow is used to calculate the water depth,river width,width-depth ratio under different flow rates,and the response of hydraulic factors and flow in each river section is obtained.The river phase function relationship of different river types along the river is fitted,and the adjustment of the section geometry can be known..The main research results are as follows:(1)The spatiotemporal variation of the number of ramps in the braided-Anabranching river section is affected by different factors.The number of ramps in space is constrained by the width of the river and the nodes.The smaller the joint spacing,the fewer the number of ramps.When the joint spacing is large,the river The wider the width,the greater the number of ramps.From the time scale,the fluctuation of the number of channels in the river section is related to the vegetation coverage and the bed sand particle size.The higher the vegetation coverage or the coarser the bed sand particle size,the smaller the fluctuation of the number of channels.(2)The morphological changes of the sand-sand-sands of the braided-Anabranching river channel are severe and frequent,and the change period is less than 10 years,but the most stable sandbank can remain unchanged for 30 years.There are three types of change:the shape of the sandbar remains unchanged,the extension of the head and the tail of the continent to the upstream and downstream,and the extension of the head and the tail of the continent to the upstream and downstream or the erosion.A parameter characterizing the stability of the braided-divided river channel is proposed,which is the ratio of the sum of the area of the stable beach and the area of the river.(3)The changes of local river channel erosion and sedimentation in the network,branching and bending sections of the Maqu River section are concentrated in the mainstream road,mainly as the lateral swing of the mainstream road,and the plane pattern of the branch rivers on both sides of the mainstream road remains stable for a long time.The relationship between water depth,river width and width-to-depth ratio is good,and the relationship between the rivers is well understood.When the river is in equilibrium,the waterway changes the water geometry by increasing the water depth and increasing the flow velocity.