Study On The Sediment Transport And Sediment Operation Of Cascade Reservoirs In The Upper Changjiang River

Sediment deposition is one of the key factors which affect the long-term utilization and efficiency of large-scale cascade reservoirs in the upper reaches of the Changjiang River. Study on the problem of reservoir sediment transport, reservoir sedimentation and sediment operation under the condition of joint operation of cascade reservoirs can provide technical support for cascade reservoirs joint optimal operation, which has important practical significance. In this paper, the sediment problem of cascade reservoirs in the upper reaches of the Changjiang River is studied. Basing on the analysis of measured data, theoretical analysis, mathematical model and other means of combination of research methods, several aspects of the research are carried out in this paper as follows:(1) Research of sediment transport characteristics of Three Gorges Reservoir (TGR) has been carried out by using the method of theoretical analysis and measured data. The research results of the sediment peak transport characteristics shows that:Main influencing factors of sediment peak propagation time in the Three Gorges Reservoir are incoming sediment peak sediment concentration and flood retention coefficient, and the sediment peak propagation time can be approximately expressed by independent variables of incoming sediment peak sediment concentration and flood retention coefficient. main influencing factor of sediment peak delivery rate in the Three Gorges Reservoir is flood retention coefficient, and the sediment peak delivery rate can be approximately expressed by single independent variable of flood retention coefficient. Based on the research, the formulas of sediment peak propagation time and sediment peak delivery rate of the Three Gorges reservoir which can be used to guide the real time scheduling are established. Based on the data of flood sediment delivery ratio after the impoundment of TGR, a formula of flood sediment delivery ratio is established by statistical regression, and a study on sediment delivery ratio of TGR in Storage period and the period of falling is carried out.(2) Based on the basic idea of the three-gradation method, A 1-D numerical model for simulating unsteady flow and sediment transport in the mainstream and its tributaries at the TGR is established in this paper under the consideration of non constancy in the process of water and sediment transport and reservoir capacity effect of more tributaries, and the numerical model is improved by sediment saturation recovery coefficient, Interval flow and reservoir storage closure. The model is verified by the measured data of 2003～2013 years after the application of the TGR, and the calculated values of water level discharge process, sediment transport volume, sedimentation and sediment delivery ratio are in good agreement with the measured values, then the improved model can be used to simulate the sediment problem in the TGR.(3) Based on the 1-D numerical model for simulating unsteady flow and sediment transport in the mainstream and its tributaries at the TGR, the mathematical model of sedimentation for joint operation of cascade reservoirs in the upper Changjiang River is established in this paper, and the length of the calculation range in the mainstream is about 1800km from Panzhihua to the Three Gorges Dam,5 large reservoirs of Wudongde, Bai Hetan, Xiluodu, Xiangjiaba and TGR are included in the calculation range. In the middle reaches of the Jinshajiang River cascade, Yalongjiang River cascade, Minjiang River cascade, Jialingjiang River cascade and Wujiang River cascade, the sediment reduction of a total of 27 reservoirs is calculated by equilibrium gradient method, the calculation results of sediment reduction of cascade reservoirs in mainstream and tributaries take part in sedimentation calculation by changing the import water sediment boundary of numerical model.(4) A 500 years long-term forecast sedimentation caoculation of cascade reservoirs in Wudongde, Bai Hetan, Xiluodu, Xiangjiaba and TGR has been carried out in this paper. The calculation results based on the water and sediment series of 1991-2000 shows that:Without considering the Longpan cascade, the preliminary balance time of reservoir sedimentation of Wudongde, Baihetan, Xiluodu, Xiangjiaba and TGR are approximately 140 years,230 years, 260 years,270 years and 340 years. Considering the Longpan cascade, the preliminary balance time of reservoir sedimentation of Wudongde, Baihetan, Xiluodu, Xiangjiaba and TGR are approximately 180 years,270 years,290 years,300 years and 370 years. The reservoir sedimentation equilibrium time of each reservoir is much longer than the original design expectations, than it provides favorable conditions for the optimal operation of cascade reservoirs.(5) Analysis on the Variation of water and sediment into and out of TGR, the Variation of water and sediment in the upper reaches of the Changjiang River, optimal operation of cascade reservoirs in the TGR and the upper reaches of the Changjiang River has been Carried out in this paper. From the point of view of water and sediment condition change and optimal operation of reservoir, the practical significance and feasibility of the flood sediment peak regulation and the dynamic use of the "Storing clear and releasing muddy" at the cascade reservoirs in the upper reaches of the Changjiang River are demonstrated.(6) Adopting the research method of data analysis and mathematical model calculation, a preliminary study on sediment regulation of cascade reservoirs in flood season is carried out in the upper reaches of Changjiang River in this paper. In the aspect of sediment regulation of TGR in flood season, this paper puts forward sediment peak scheduling scheme and sediment scheduling scheme of the dynamic use of the "Storing clear and releasing muddy" in TGR. In the aspect of sediment flushing joint scheduling of Xiluodu Reservoir, Xiangjiaba Reservoir and TGR in flood season, this paper puts forward sediment flushing joint scheduling scheme of cascade reservoirs based on sediment peak scheduling and dynamic use of the "Storing clear and releasing muddy".