Research On Coupling Mechanism Of Water And Sediment Movement And Riverbed Evolution In Bending Braided River

After operation of Three Gorges reservoir,the conditions of water and sediment has changed dramatically in the the middle and lower Yangtze river,and sediment discharge also decreased significantly,The evolution process of the bend braided river downstream of the reservoir will also respond,it may have an impact on flood control,shipping,the use of shoreline and other aspects.Therefore,it is of important theoretical and practical significance to study the coupling mechanism between flow and sediment movement and river bed evolution in curved branching channels.On the basis of summing up the domestic and foreign research results,through the combination of prototype observation data analysis,generalized model test and theoretical explanation,this paper conducts a comprehensive research on the characteristics of water and sediment movement and regularity of riverbed evolution,and coupling mechanism between the two,to predict the evolution trend of the bend braided river channel.The main work and achievements obtained in this paper are as follows:(1)Through the analysis of the prototype observation data and the generalized model test,the law of water flow in curved branch channel under the different flow conditions is revealed in this paper,including the water surface gradient in the distributary,inlet and confluence areas,the change of the mean velocity in section along the channel,the cross section velocity distribution,the hydrodynamic axis,the turbulent intensity and the turbulent kinetic energy of the flow.(2)On the basis of analysing and selecting suspended sediment carrying capacity formula and the bedload sediment transport rate formula,which is tested by measured data,combining the river terrain,water and sediment data,which were observed in different years in Jianli reach,and the generalized model experimental velocity data,it illustrates the movement law of suspended sediment and bedload sediment of bending braided river under the different flow conditions,and the phenomenon that anomalous distribution of suspended sediment concentration and the main distribution is dicussed in this paper.(3)Through analysing prototype observation data and model test,the change law of scour and silting and the evolution law of the distributary,inlet and confluence under different water and sediment of the bend braided river are revealed.In addition,the evolution pattern of main and branch branches shift is also explored in this paper.(4)By conducting the relationship between water and sediment movement and riverbed evolution of the bending braided channel,the coupling mechanism between the two is revealed.Taking Jianli River as an example,the evolution trend of this river under the condition of sand decrease is well predicted.