Numerical Prediction Of The Deposition And Scouring Process In Flucuating Backwater Area For The Three Gorges Reservoir Under The New Water-sediment Discharge Condition

Since the impoundment of the Three Gorges Reservoir,the law of sediment transport in the fluctuating backwater area and the regulation of the channel have been one of the key technical issues of the project.With the changes of the Three Gorges Reservoir’s operation mode and upstream inflow and sediment conditions,the characteristics of bed load movement at the end of the reservoir have changed to a certain extent,which has brought uncertain effects to the improvement and enhancement of channel conditions in the fluctuating backwater area.At present,with the construction of the Yangtze River Economic Belt and the construction of the national three-dimensional transportation network,it is necessary to upgrade the level of the channel at the end of the reservoir.To ensure the effectiveness of the channel upgrade project in the variable backwater area,it is necessary to control the sediment in the river section of the variable backwater area.Carry out quantitative research on the characteristics and trends of erosion and deposition.In this paper,combining the analysis of measured data at the end of the Three Gorges Reservoir and two-dimensional numerical simulation,the evolution characteristics of the key reaches of the end of the Three Gorges Reservoir are analyzed.Based on the existing two-dimensional mathematical model of water and sediment in the end of the Three Gorges Reservoir,The scouring and silting changes of the channel from Chaotianmen to Fuling in Chongqing were simulated for a series of years(2009-2016),and the distribution of sediment scouring and silting in the key reaches of the Three Gorges Reservoir tail and its impact on the channel were predicted in 30 years.The main research results are as follows:Combined with the measured data,the changes in the water and sediment conditions of the Three Gorges Reservoir after the 175 m test impoundment and the erosion and deposition characteristics of key beach sections under the new water and sand conditions are summarized and analyzed.Excluding sand mining in the river channel,the Luoqi and Qingyanzi reach are mainly characterized by siltation,while the overall change in the Guangyangba,Dajiantan and Changshou reachs is not large.Based on the characteristics of the bed load movement,a two-dimensional mathematical model of water and sediment in the tail channel of the Three Gorges Reservoir was established,and the water level,velocity distribution,and erosion and deposition positions of the river section were simulated,and compared with the measured data for verification.The water level verification error control of the water flow module Within 0.1 m,the flow velocity error is controlled within 15%;for the sediment module,the calculation error of bed load transport is controlled within 12%,and the calculation error of sediment erosion and sedimentation is controlled within25%.The research results show that the model can reflect the characteristics of sediment movement in the Chaotianmen-Fuling section at the end of the Three Gorges Reservoir.This model can be used as a quantitative method to study the erosion and deposition process of the channel from Chaotianmen to Fuling in Chongqing.Based on the selected series of water and sand years(2008-2017),the distribution and total amount of sedimentation and sedimentation in the 30 years from Chaotianmen to Fuling section under new water and sediment conditions are predicted,and the sediment erosion and sedimentation changes and bed load of key beach sections are analyzed.Distribution of sand transport.The results show that the maximum sedimentation thickness of the sediment in the Guangyangba,Dajiantan,Luoqi,Changshou and Qingyanzitan sections is 0.36-1.12 m,and the impact on the channel is concentrated in the range of 10-100 m from the channel boundary.