| This article takes the Shizuishan section of the Yellow River to reinforce and strengthen the river treatment project-the Pingluo Sipaikou ?-shaped river "cut and bend straight" project as the basis,systematic and comprehensive collection of relevant information,through a combination of theoretical analysis,prototype observation and numerical simulation,a more detailed study of the water and sediment transport and riverbed evolution of the studied river sections was conducted.adopting field research,on-site measurement,three-dimensional water and sediment transport,river bed deformation mathematical model,the calculation and verification of the flow field distribution and development of the diversion dam near the diversion spur of the Spaikou and the diversion dam behind the dam,on this basis,by adding modules of sediment transport and riverbed erosion and sedimentation,the development and migration of the river channel in this section in the future period of time are analyzed.it is hoped to provide basic data and theoretical basis for the safe and stable operation of the river regulation project(shore dams,river closure dams,diversion open channels,etc.).the main research results obtained in this paper are as follows:1)The "cut and bend" project had a great impact on the migration and evolution of the river regime in the original river section.after the river closure,the river width increased significantly.especially at the end of the Spur group and the river reach behind the dam,the degree of "collapse" and "sediment" of the bank varies from 40 to 300 m;the overall migration and swing of the river can reach 200?300 m;coastal erosion and collapse are more serious,the boundary conditions of river flow are changing drastically,and the rebuilding riverbed movement is very significant.2)Using the three-dimensional mathematical model of water and sediment transport and riverbed evolution to carry out numerical simulation research on the "cut and bend" section of the Pingluo Sipaikou of the Yellow River in Ningxia,based on the field measured terrain,hydrology,and sediment data from October 21,2018 and November 25,2018,the model was "calibrated" and "verified".The verification results show that the calculated values of water level and elevation are basically consistent with the measured values.The absolute error range is-0.035?0.038 m,and the relative error does not exceed 1.50%(absolute error/average water depth).the elevation error range of the riverbed is-0.5?1.5 m.The difference between the simulated value and the measured data is relatively large in only a few local areas.it is fully proved that the model built in this paper can simulate the evolution of erosion and deposition of actual riverbed to a certain extent.3)Under the effect of "bed-making flow" over a long period of time,the bed surface tends to be smooth and smooth,and the mainstream position continues to move to the right,which results in a slowdown of the left bank velocity and a decline in water flow and sediment capacity.as a result,a large amount of silt appeared on the left bank of the main channel near the upstream inlet and near the Spur group.the right bank was affected by the increasing flow velocity,and scoured to different degrees;however,at the end of the Spur Group and the location of the river diversion,due to the "scouring" effect of the backflow after the dam,the left riverbed and the slope are more severely washed away,leading to the main stream and the main channel of the river downstream.The left bank migrated and evolved,and a large-scale shoal was formed in the right riverbed area. |
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