Optimal Operation Of The Three Gorges Reservoir Subject To The Ecological Water Level Of Dongting Lake During The Dry Season

Dongting Lake is the first great river-connected lake in the Yangtze River after the Three Gorges.It plays an important role in flood regulation,biodiversity conservation,fish migration,water resources utilization and so on.In recent years,due to less rainfall in the basin,unequal distribution of precipitation time,extreme climate and reclaiming farmland from lakes,etc.Drought disasters frequently occur in Dongting Lake,which has a great impact on the domestic water,industrial and agricultural production,navigation and fisheries,threatening the health of the lake wetland ecosystem.It can become a powerful measure to improve the lake ecological environment in the near future through the Three Gorges reservoir optimization scheduling.However,because of the reservoir water inflow is less and random in dry season.The optimization scheduling may affect generation capacity and power generation guarantee rate of the Three Gorges hydropower station,so that the Three Gorges power generation can't meet the design power generation plan and lose the benefit of the power generation.Therefore,how to make the reservoir discharge as close as possible to the appropriate ecological water level of the Dongting Lake,and ensure the minimum loss of the power generation of the Three Gorges hydropower station are still problems to be solved at present.In order to realize the huge ecological benefits of the Three Gorges Reservoir effectively and meet the requirements for the ecological water requirement of the Dongting Lake,this paper do research on the typical river-connected lake--Dongting Lake,taking historical data statistical analysis method?comprehensive technical means combined qualitative and quantitative evaluation,building a optimal operation model of reservoir based on the maximum power generation of the Three Gorges hydropower station and the minimum change of suitable ecological water level of Dongting Lake.Study on optimal operation of Three Gorges Reservoir in dry season under different typical years.It reveals the mutual feedback relationship between the change of suitable water level of the Dongting Lake and the benefits of power generation,and initially puts forward the optimal operation plan for maintaining the ecological health of Dongting Lake.The main contents and conclusions are as follows:?1?Taking Chenglingji station as the representative site of Dongting Lake,and taking the long time water level sequence data of Chenglingji hydrological station in1978²015 as the analysis object.Based on the hydrological variation method and the frequency drainage method,the appropriate ecological water level of Chenglingji is quantified.The results show that the suitable ecological water level from early January to late April are 20.52 m,20.68 m,20.83 m,20.59 m,21.00 m,19.32 m,22.22 m,22.04m,22.79 m,22.91 m,23.96 m,23.13 m.The corresponding Lake area is 436⁵70 km².From the aspect of maintaining the area of the natural reserve,the lake area provided by ecological water level can meet the requirement of protecting the core area and the calculation results are reasonable.?2?Analysis of the influence factors of the water level change in Chenglingji station,and analyzing the correlation between the factors and the water level of Chenglingji respectively.The results show that the impact of the discharge of the Three Gorges Reservoir on the water level of Chenglingji station is the most significant,however,the flow of"four water"into the lake and the discharge of the Qingjiang discharge can't be ignored.In order to find out the quantitative relationship between the discharge of the Three Gorges Reservoir and the water level of the Chenglingji in Dongting Lake,the water level prediction model based on support vector regression is established.The water discharge of the Three Gorges Reservoir in the year of 2006-2008,Qingjiang flow and the flow of"four water"into the lake are used as the input variables to train the water level sequence of Chenglingji.The accuracy of the model after training is tested by the measured water level data of Chenglingji in 2009.The mean square error MSE is 1.477×10^-3,and the fitting degree is 0.9807.It shows that the model after training can simulate the dynamic relationship between the discharge of the Three Gorges Reservoir and the water level of the Chenglingji station at the Dongting Lake exit.?3?The non-dominated sorting genetic algorithm and the improved fast non-dominated sorting genetic algorithm?NSGA-II?based on the elite strategy are introduced,and the specific steps and calculation process of the NSGA-II algorithm applied to the two-objective optimization scheduling are studied.According to the calculation flow of the algorithm,the scheduling target is considered.The key scheduling period is selected,the calculation period is divided,and the necessary constraints are selected.The optimal scheduling model of Three Gorges reservoir in dry season is built based on the maximum power generation of the Three Gorges hydropower station and the minimum change of suitable ecological water level in Dongting Lake.?4?The NSGA-II algorithm is used to find a series of Pareto optimal solutions under the typical year conditions by selecting the wet year,the normal flow year and the dry year.After the optimal scheduling of wet year,the change of the ecological water level can be reduced by 8.211%and the power generation increase by 0.989%,or the change of the ecological water level is reduced by 19.36%at the cost of the loss of 2.544%of the power generation as compared with the conventional scheduling;After the optimal scheduling of normal year,the change of the ecological water level can be reduced by 10.845%and the generating capacity is increased by 2.911%,or the change of the ecological water level is reduced by 20.563%at the cost of 0.234%of the loss of electricity as compared with the conventional scheduling;After the optimal scheduling of dry year,the change of the ecological water level can be reduced by 3.390%and the generating capacity is increased by 0.865%,or the change of the ecological water level is reduced by 20.339%at the cost of4.166%of the loss of electricity as compared with the conventional scheduling;Which indicate the scheme to increase the power generation or reduce the change of the suitable ecological water level by the reservoir optimization scheduling is feasible.