Effects Of Control And Guide Engineering On Flow Movement And Riverbed Deformation In Typical Reach Of Yellow River In Ningxia

This paper takes the Sipaikou reach of the Yellow River in Ningxia as the research object,and studies the flow movement laws and river bed deformation conditions of the reach after the implementation of the control and guidance project,and uses on-site measurement methods and numerical simulations to combine the flow movement of the reach.The laws and riverbed deformation conditions are systematically summarized and summarized.According to the characteristics that the horizontal scale of the Sipaikou reach is much larger than the vertical scale,and the water pressure is close to the static pressure distribution,a two-dimensional hydrodynamic mathematical model of the Sipaikou reach is established,and the calculation area of the Sipaikou reach is established using MIKE21 software.The grid was divided and the terrain of the complex moving boundary in the area was processed,and the mathematical model was verified by the field measurement data;four typical working conditions were set to carry out a numerical simulation study on the Sipaikou reach,Analyzed the simulation calculation results under four typical working conditions,and predicted and analyzed the river bed deformation of this reach.The main research results are as follows:(1)Through the analysis of the changes in the measured river bank line,after the implementation of the control and guidance project in the Sipaikou reach,the water movement and river regime migration of the reach have a huge impact.After the project has been in operation for two years,The width of the river course is obvious.On the left bank of the entrance of the diversion section at the end of the spur dike,the river bank retreats and collapses for tens of meters,and some areas even retreat and collapse for hundreds of meters,and the bed-making movement is very significant.(2)Analyzed the measured longitudinal velocity at the typical cross section of the measured data on October 27,2020.The flow velocity of the 13 typical cross section of the river changes with the change of the river bed,and the characteristic shown is the flow velocity at the main channel of the river.Both are slightly larger than the main trough,and the maximum flow velocity in the bend is constantly changing on the concave and convex banks of the river.The equilibrium position of the flow velocity changes is roughly a parabolic distribution,that is,the flow velocity at the center of the river is relatively large,while the flow velocity on both banks is relatively small.(3)By comparing and analyzing the measured topography of typical cross-sections in different years,the riverbed erosion and siltation conditions of the four-row river section in the past two years have been studied.Since the measurement time is in the dry season,the flow of the river section is smaller and the water level is lower.The comparison of the two actual measurement results showed that the river bed has little change in the CS3-CS6 section.The river channel at the CS7 section has changed from narrow and deep to wide and shallow,and the adjustment effect of the upstream spur on the flow has also been significantly weakened,and the mainstream of the river has returned to the left bank.This has caused the phenomenon of erosion on the left bank of the river and siltation on the right bank.After two years of scouring,the river diversion section has no form of man-made excavation,and the main channel of the river channel is obviously offset to the left bank,making the left bank of the river section obvious scouring and the right bank seriously silting.(4)The mathematical model established by the measured data in October and November of 2018 was used to verify the water level and flow rate.Through the comparison and analysis of the simulated calculated value and the measured value,the absolute error of the water level was-0.024?0.052m,the relative error is controlled within 1.63%,within the allowable error of the numerical simulation of water movement,through the analysis of 13 typical cross-sections CS3,CS7,CS10 three sections of the vertical average flow velocity simulation value and measured value,its The simulated value and the measured value are generally close to the requirements of calculation accuracy as a whole,which proves that the mathematical model established is reliable and reasonable.(5)Through the analysis of the simulation calculation results under four typical working conditions,it is concluded that under the conditions of the dry season,most areas of the left bank at the entrance of the river reach have more silt land and beach land.Due to the small flow,the water level is low,and the water flows to the spur dam.The scouring effect of the spur dike and the side bank is almost non-existent,and the water flow moves along the original river course;under the condition of normal water period,the water flow has a scouring effect on the spur dam and some areas behind the dam,but the scouring effect is very weak,and the flow rate is small on the right bank of the inlet section.A large amount of silt land;under the conditions of high water period,the stability of the spur dike is threatened.At the end of the spur dike group and the main flood discharge channel behind the dam,there is a tendency to further deepen and migrate to the left bank,although two years after the implementation of the control and guidance project,The width of the river is obvious,and the cross-flow section can carry a certain amount of flood,but most of the area on the left bank behind the dam will still be scoured,and the collapse and retreat of the river bank will continue.