Study On The Variation Of Scouring And Deposition Of Riverbed And The Impact Analysis Of Flood And Ice Flood In The Ningxia Reach Of Yellow River

The influence factors of scouring and deposition in riverbed evolution is very complex,that mainly depends on the incoming runoff and sediment and river boundary conditions.The sources of water and sediment are different in the Yellow River,which results in that the characteristic of water and sediment in the downstream of Yellow River is closely related to its source area.The flood with different combination of water and sediment has different effects on the erosion and deposition in the downstream of Yellow River.The successive operation of large hydraulic projects,for instance Liujiaxia,Qingtongxia and Longyangxia reservoirs,have changed the incoming water and sediment conditions in the upstream of Yellow River.As a result,the scouring and deposition of the main stream in the Ningxia reach of Yellow River have brought out new changes.Especially in recent decades,the deposition of the main stream is serious,the erosion and deposition of the beach and trough is frequent,the mainstream swings randomly and the increasing water level makes flood disasters happen every year,such as water flow backward and levee engineering slump.On the whole,the situation of flood control and ice flood prevention is extremely serious.In this paper,the research object is the plain river from Xiaheyan to Shizuishan in the Ningxia reach of Yellow River.Changes of scouring and deposition in the main stream and the confluence in recent decades are studied from different stages and different reaches quantitatively.The influence factors of activities on the swing and the change of river facies relationship characteristics are analyzed firstly.Then,different methods are adopted to predict sediment thickness.Ultimately,the effect of deposition and erosion of the riverbed on flood and ice dam flood is analyzed in a one-dimensional hydrodynamic model.This paper has seven chapters.The main work and results obtained from these researches are summarized as follows:(1)The research status and present schemes about scouring and sedimentation in the riverbed evolution have been systematically expounded,and the main research contents and technical route have been put forward in this paper.The calculation principle,parameter setting,model modification and so on about the hydrodynamic model have also been described.(2)The sediment discharge and cross-section methods are used to quantitatively calculate the river sedimentation in the main stream and the confluence respectively in the Ningxia reach of Yellow River.The relationship between different water-sediment combinations from the main stream and the confluence and changes of erosion and deposition of the river are analysed deeply.(3)Based on the measured cross-section data and image data for many years,influence factors of the mainstream swing and changes of river facies relationship characteristics are studied through VBA language and macro programming.The correlation between main channel migration and the height difference of beach and trough has been established through regression analysis.The influence of scouring and sedimentation of the riverbed to the river regime stability and the mainstream swing has been discussed.(4)According to the measured data of runoff and sediment in the Xiaheyan and Shizuishan hydrometric station,the erosion and sedimentation amounts are calculated through different predicting methods,such as mathematical model,empirical formula and cross-section methods.And then,the sediment thickness are predicted by different methods.(5)The one-dimensional hydrodynamic model is established based on measured cross-section data in different periods to simulate the typical flood,design flood and ice dam flood systematically.The influence of riverbed evolution to flood control and ice dam prevention are analysed though comprehensive analysis of calculation results.