Study On The Coupling Relationship Between The Siltation Of The Three Gorges Reservoir And The Water Level In Front Of The Dam Under The Condition Of New Water And Sediment

The construction of the Three Gorges reservoir is the key project of the Yangtze River Management and development,and plays an important role in China's social and economic development.Since it was initially built and put into trial operation in 2003,the Three Gorges reservoir has gradually achieved the three design goals of flood control,power generation and shipping.However,with the rise of the water level of the Three Gorges reservoir,the movement characteristics of water and sediment in the reservoir area have changed greatly,and the sediment in the reservoir area is gradually silted up.In the long run,the flood control capacity will be occupied,and the sediment deposition will reduce the regulation capacity of the reservoir,affect the power generation,and even cause navigation obstruction.Therefore,the problem of sediment deposition is one of the most important issues in the study of the Three Gorges.The process of water level in front of dam is closely related to the development of reservoir sedimentation,and the reservoir sedimentation can be controlled to a certain extent by changing the water level in front of dam.However,the condition of water and sediment coming from upstream is the dynamic source of the change of sediment deposition.The process of sediment deposition is complex,and the law of sediment deposition under the influence of all factors needs to be explored.In recent years,the change of water and sediment from the Three Gorges reservoir makes the sedimentation law of the Three Gorges different from before.Therefore,under the condition of new water and sediment,it is necessary to study the comprehensive influence of incoming water and sediment and the water level in front of the dam on the sedimentation of the Three Gorges reservoir,which can provide a reference for slowing down the sedimentation of the Three Gorges Reservoir and making a reasonable operation mode.Based on the measured data of the Three Gorges reservoir from 2003 to 2017,this paper studies the coupling relationship between the sedimentation of the Three Gorges Reservoir and the water level in front of the dam under the condition of new water and sediment by the method of theoretical research and statistical analysis.And the paper puts forward the statistical relationship of sediment deposition including water level before dam,inflow discharge and inflow sediment concentration,and its main work contents and achievements are as follows:(1)Collecting the measured data of water,sediment and topography of the Three Gorges Reservoir after impoundment and operation,analyzing the regulation process of the water level in front of the dam of the Three Gorges Reservoir and the change of the incoming water and sediment conditions,so as to lay a foundation for the study of the sedimentation characteristics of the Three Gorges Reservoir and the relationship between the sedimentation amount and the influencing factors.(2)According to the measured topography and water and sediment data,the sediment deposition characteristics of the Three Gorges reservoir are analyzed and compared from the total amount of sedimentation,the variation along the way,the change of longitudinal section and cross section.The analysis shows that the deposition of the Three Gorges reservoir is gradually decreasing,and the cumulative growth trend of sediment deposition is slowing down.The annual average sedimentation amount increases first and then decreases in the cofferdam impoundment period,initial impoundment period and 175 m experimental water storage period.The deposition is mainly concentrated in the flood season,and the deposition situation is not the same within the year,most of which occurs in the perennial backwater area.With the rise of the water level in front of the dam in different operation stages,the deposition distribution in the reservoir area presents an upward trend.The sedimentation in the reservoir area is discontinuous and mainly distributed in wide valleys,bends and bifurcations,and the longitudinal profile of the thalweg is still serrated.(3)From different angles,the relationship between the sedimentation volume of the Three Gorges Reservoir and the inflow sediment concentration,inflow discharge,inflow sediment volume and water level in front of the dam is analyzed.The main factors affecting the sedimentation amount are different in different periods,and the obvious factors will have a great influence on the sedimentation amount in this period.The influence of water level in front of dam on the sedimentation amount is best combined with the comprehensive analysis of the water and sediment conditions of the Three Gorges reservoir.(4)The combined factors including water level in front of the dam,inflow discharge and sediment concentration are selected to conduct multi factor coupling analysis on the sedimentation volume of the Three Gorges reservoir.It is found that when the sediment concentration of the reservoir is included in the analysis of the influence of the sediment concentration on the sedimentation in the three Gorges Reservoir area,the sedimentation amount is positively correlated with the sediment concentration in the reservoir under different time scales,and the influence of the sediment concentration into the reservoir area is greater than that of the flood detention Between the impact of.The influence of flood detention time on the deposition of the Three Gorges reservoir is different under different reservoir operation periods and time scales,and the calculation method of the sedimentation amount of the Three Gorges reservoir is proposed.