| The operation of the Three Gorges Reservoir changed the conditions of water and sediment out of the reservoir,and the relative balance between sediment transport and erosion and sedimentation in the curved river downstream was broken.Under the action of severely subsaturated sandy currents,the main channel and Shenhong moved to the convex bank side.The high beach on the convex bank side of the lower section of the curved river channel continued to collapse.In this paper,through the collection of measured data,analysis of prototype observation data,numerical simulation,etc.,the characteristics of the river course evolution and the characteristics of water and sediment movement in the study section are analyzed,and the response mechanism of the river bed evolution to the changes of water and sediment in the study section is studied.The main research contents and results are summarized as follows:1.Analysis of the channel evolution characteristics of the Jiaolaipu curved section of the middle reaches of the Yangtze RiverThe flow and sediment characteristics of the river section before and after the operation of the Three Gorges Reservoir were collected,the variation characteristics of the runoff process and the sediment transport process after the operation of the Three Gorges Reservoir were analyzed,and the changes along the course of the water flow force axis and the distribution of sediment content were analyzed according to the measured data As for the mass transport characteristics,it is believed that the increase in the duration of reclaimed water leads to an increase in the time for the main stream to flow through the convex bank,and a significant decrease in the sediment content of the upstream flow is the cause of the convex bank erosion.2.The establishment of the mathematical model for the evolution of the curving channel at the Jiajiao LaijiapuOn the basis of data collection,a two-dimensional mathematical model of water and sediment in the Laijiapu curved channel in Diaoguan was established,and hydrodynamic verification was carried out.The calculated velocity distribution and water level are in good agreement with the measured data.It can better simulate the erosion and siltation trend of this section.3.Research on the characteristics of water and sediment movement and the response mechanism of riverbed evolution to water and sediment changesThe hydrodynamic numerical simulations were used to compare the swing amplitude of the water flow force axis of each section under different flow rates.It is considered that the change of water flow conditions is the main factor that causes the water flow force axis to swing.The magnitude of the channel curvature affects the response of the water flow force axis swing to the change of flow rate.The numerical simulation of water and sediment shows that the phenomenon of convex scour and siltation in the curved channel after the Three Gorges operation is the result of the combined effect of water and sediment.Different water and sediment factors are used to calculate the relative contribution rate to the evolution of the channel,and the sediment of the Three Gorges Reservoir is greatly reduced.It is the key factor leading to convex flushing and silting.4.Prediction of the evolution trend of the riverbed of the Guanlaijiapu curved channel under changing water and sediment conditionsThe numerical simulation of the evolution of erosion and siltation in the next ten years has shown that the river section will generally maintain the scouring trend in the next ten years.Considering the effect of the Three Gorges Reservoir,the reduction in incoming sediment will continue for a long time in the future Affected by the changes in the conditions of incoming water and sediment,the convex bank beach at the entrance of the Diaojiuan bend and the convex bank beach near the Laijiapu bend will continue to be washed away for a long period of time. |
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