Study On Three Gorges Reservoir Optimal Operation Schedule Based On Improvement Of Ecological Environment In The Lower Yangtze River

With the operation of the Three Gorges Reservoir,the ecological environment problem from the lower Yangtze River to the estuary area has become increasingly prominent.For example,in May and June,the fecundity of the four fishes in Jianlihe River was decreased,in October the shrinkage of the wetland area in the Dongting Lake and Poyang Lake District was caused and the saltwater intrusion of estuary in Yangtze River would happened sometimes.Eco-environmental issues in the lower Yangtze River put forward new requirements for the Three Gorges Reservoir.After the completion of Xiluodu and Xiangjiaba Project,the joint operation of these three reservoirs make it possible to improve the downstream ecological environment.Based on previous research,this paper build one-dimensional hydrodynamic model of river network from Yichang to Datong and multi-objective optimization scheduling scheme evaluation model of the Three Gorges reservoir to design and choose the best scheme,which aim to improve the ecosystem in the lower Yangtze River.Then the feasibility of optimum scheme among reservoir group is analyzed.The main results are as follows:(1)Based on the literature and measured data,the status quo and changes of the ecological environment in the lower Yangtze River after the operation of Three Gorges Project were analyzed.To scientifically predict the effect on the hydrodynamic characteristics of the lower reaches of the reservoir by the changes of discharge flow rate of the Three Gorges,a one-dimensional hydrodynamic model of river network between Yichang to Datong was built in MIKE.After measurements and verifications,this model has good applicability.It will be applied to the design of the dispatching scheme and the forecast of indicators for the ecological environment downstream of the reservoir.(2)Three Gorges Reservoir multi-objective optimization scheduling program evaluation model was established.Based on the exploration and suggestions of several domestic scholars on the existing problems of the ecological environment in the middle and lower reaches of the Yangtze River,this chapter selects seven indicators from the three aspects of ecological environment objectives,flood control objectives,and power generation goals of the Three Gorges Reservoir,and constructs indicators for evaluation of multi-objective optimal operation plans for reservoirs.The evaluation model was established by the comprehensive evaluation method including analytic hierarchy process and approximation ideal point,which laid the foundation for the scientific evaluation of the dispatching plan.(3)The problems encountered by the dry-branch flow from the Yichang-Wuhan in the middle reaches of the Yangtze River were studied.The typical flat and dry years were selected for the Three Gorges Reservoir Optimal Dispatch Scheme design.Based on observed runoff data of mainstream of the Yangtze River and three tributaries from Yichang to Wuhan,normal-dry runoff coincidence and conditional probabilities were analyzed.Taking year as time scale and annual runoff as evaluation index,this paper select 2006 as typical extremely dry year and 2012 as typical normal year in the Yangtze River Basin.The mainstream and tributaries water flow processes in typical years are the basis for the improvement of the eco-environmental scheduling scheme.(4)Multi-objective optimal scheduling scheme for the Three Gorges Reservoir based on ecological environment improvement in the middle and lower reaches of Yangtze River was studied.According to the selected typical years,combined with the current Three Gorges Reservoir Dispatching Regulations and major ecological environmental goals,three schemes have been specifically designed.Through the established one-dimensional hydrodynamic mathematical model at the downstream of the reservoir,numerical simulations were performed on different design schemes.The evaluation results of different schemes were evaluated by the multi-objective optimization scheduling scheme of the Three Gorges Reservoir,and finally the scheme was optimized.The results show that:to implement the emergency dispatch to suppress the saltwater intrusion in the Yangtze River estuary a typical dry season,the discharge flow rate of the Three Gorges Reservoir should not be lower than 6450m3/s;to guarantee the ecological and environmental needs of the two lakes in typical dry year and flat year,the reservoir should maintain a flow rate of around 12500 m3/s at the end of the water storage period in late October;to promotes the spawning of the fourth domestic fish around Jianli in May and June,Three Gorges Reservoir should maintain artificial flood peak process for 5?8 day once a month,in which flow starts from 8000?10000m3/s and the total increase is about 10000?12500m3/s.When the above conditions are met,the evironmental flow in the downstream Luoshan Station and Hankou Station of the reservoir automatically reaches the standard.In addition,through the program evaluation,it is found that the reservoir's power generation benefit can be sacrificed to improve the ecological environment benefit of the downstream reservoir.(5)Based on the typical plan in flat and dry years,the feasibility of the optimal scheme in practical operation was demonstrated by the two scheduling methods of the optimized single bank scheduling of the Three Gorges Reservoir and Xiluodu-Xiangjiaba-Three-Gorges.The above research can be concluded that:single scheduling mode of the Three Gorges Reservoir is prefered in normal years,and reservoir group joint scheduling is prefered in typical dry year.