Multiobjective And Joint Optimal Operation Of The Lower Jinsha River And Three Gorges Cascade Reservoirs In Impounding Period

With the rapid development of economy and society in China,the contradiction between water supply and demand has become increasingly prominent.As a water resource regulation project,the reservoir has various functions such as flood control,water supply,power generation,navigation,and ecology protection.It has played an important role in promoting the comprehensive utilization of water resources and socioeconomic construction.Largescale reservoirs in the upper Yangtze River basin have been successively built in recent years.The proportion of the total reservoir storages to the annual average runoff has increased greatly.The impact of large-scale reservoirs impoundment may lead to the conflicts between the upstream reservoir impoundment and the downstream water demand,further reduce the downstream flow,and result the dry season early and longer,which have impact on downstream living,production,and ecological water use.As the scale of the reservoirs in the upper Yangtze River basin continues to expand,the conflicts become more severe in dry years,which is inconsistent with the requirements of the construction of ecological civilization in China.Therefore,how to further tap the potential of earlier reservoir impoundment,to find the key factors affecting reservoir impoundment,to improve the reservoir impoundment model,and to propose multi-objective impoundment plans for reservoirs have both theoretical and practical significances for many benefits.These benefits include scientific and orderly impoundment of reservoirs in the upper Yangtze River basin,improving the reservoir impoundment rate,reducing the impact on the water use in the middle and lower reaches,giving full play to the comprehensive utilization benefits of the reservoir group,practicing the concept of joint protection and development,and promoting the in-depth development of the optimal operation theory and practice of the reservoir.Supported by the national key research and development program of China and research project of the China Three Gorges Corporation,we select the impoundment operation of lower Jinsha River and Three Gorges cascade reservoirs as case study and use hydrometeorological data collection and analysis,data mining,random analysis,and mathematical model optimization as core skills.We focus on the basic researches such as the analysis of the characteristics of streamflow and rain conditions in the upper reaches of the Yangtze River,verifying the application effect of mid-to-long-term precipitation forecast SEAS5 and hydrological forecast Glo FAS Seasonal products in the reservoir impoundment period,and the quantitative analysis of the important decision-making information of the reservoir impoundment operation.Then,we carry out the application researches such as the optimization of the Three Gorges reservoir impoundment plan under the clusteringprediction-optimization operation mode,the optimal impoundment plan under different inflows and operation objects for the Xiluodu-Xiangjiaba-Three Gorges cascade reservoirs by multi-site streamflow random simulation method,and the multi-objective optimal impoundment plan considering ecological flow and downstream water level for WudongdeBaihetan-Xiluodu-Xiangjiaba-Three Gorges reservoirs.The main research works are summarized as follows:(1)Based on the measured hydrological data in the upper Yangtze River basin and the rainy season division data of Rainy And Dry Season(RADS)from Texas A&M University,this paper analyzes and reveals the characteristics of flood and rainy season time in the upper Yangtze River,demonstrates the possibility of the reservoirs impounding timing in advance.By analysis of the latest seasonal precipitation SEAS5 and runoff Glo FAS Seasonal forecast products of the European Centre for Medium-Range Weather Forecasts,Area Under Curve(AUC),Receiver Operating Characteristic Skill Score(ROCSS),and Reliability indicators are used to verify the prediction accuracy of the products in the study area.The results show that the impounding timing of some reservoirs in the upper Yangtze River basin can be appropriately advanced.The two forecast products have a good effect of judging the low water and rain conditions one month in advance,which can provide technical support for the early impounding operation of reservoirs.(2)Based on the historical actual operating data of the Three Gorges Reservoir,the hydrological information such as the early outflow,current water level,and predicted inflow of the reservoir are selected as factors to establish a random forest model that simulates the reservoir discharge decision.The important hydrological information and its ranking that affect the reservoir discharge decision are quantitatively studied.The results show that the random forest model can reasonably simulate the discharge decision of the reservoir and the early outflow is the most important information,followed by the predicted inflow,the downstream water level(Chenglingji),the current reservoir water level,and the current month.The predicted inflow is obviously more important in flood season.Combining the value of decision information and the reservoir operation guidelines,the importance of forecasts and the downstream water level in impoundment operation during the post-flood season is emphasized,which should be considered in the optimization research and operation practice of reservoir impoundment operation.(3)Aiming at the problem that the forecast of high and low inflow affects the reservoir impoundment operation,a clustering-forecasting-optimized operating model is proposed.Coupling the K-means clustering algorithm with a hydrological forecasting model and dividing historical data into three types(wet,normal,and dry)inflow series,SSA-ANN and SSA-SVM statistical forecasting model are used to predict future inflow types for the Three Gorges Reservoir.The effects of different forecast inflows on TGR impoundment operation are considered,and the Non-dominated Sorting Genetic Algorithm II(NSGA-II)algorithm is used to optimize the impoundment operation rule curve.The results show that the SSASVM-4 model can obtain the best inflow forecast in September.If the inflow forecasts are wet and normal in September,then TGR starts impoundment operation on Sept.10 th.If the predicted inflow is dry,the impoundment start time can be advanced to Sept.1st,which can significantly increase the power generation by 3.43% and the reservoir impoundment rate by3.44%.(4)Aiming at the problem that the regional combination scenarios of different inflows affect the cascade reservoir impoundment operation,a multi-station daily runoff random simulation model and multi-objective impoundment operation model of Xiluodu,Xiangjiaba,and TGR cascade reservoir are proposed,and then optimized by the NSGA-II algorithm.Under the wet,normal,and dry inflows situation,the impoundment operation rule curves with the different primary goals of risk,impoundment rate,or power generation are obtained.It is recommended to use rule curves with large power generation or full impoundment rate for wet inflow,and full impoundment rate for normal and dry inflows.After analyzing the operation process of different inflow with the lowest risk object,the Xiluodu,Xiangjiaba,and TGR reservoirs can choose the impoundment times from Aug.25 th to Sept.1st when the flood risk is relatively small.(5)Aiming at ecological flows of rivers and the problem that reservoir impoundment operation affects the downstream,a multi-objective impoundment operation model for the lower Jinsha River and TGR cascade reservoirs including building Wudongde and Baihetan reservoir is established.Then,a simulation model of the Dongting Lake outlet water level with the discharge of the TGR,the Qingjiang flow,and the Dongting Lake flow as inputs is established to consider the impact of different minimum outflow constraints of reservoirs on the water level of the Dongting Lake.The results show that the Wudongde and Baihetan reservoirs which use the current planned impoundment starting time and outflow constraints will have a greater negative impact on downstream ecology.The advance impoundment plan for cascade reservoirs considering ecological discharge constraints is proposed,which not only can increase the outflows of Xiangjiaba in September by 16.67% and TGR in October by 5.48%,but also can increase the power generation by 1.60% and raise the water level at the Chenglingji by about 0.3m from the end of September to the end of October.