Study On Optimal Operation Of Xiluodu Xiangjiaba Cascade Hydropower Stations For Spawning Demand Of Four Major Chinese Carps

With the completion and operation of large-scale hydropower base,the cascade system is becoming larger and larger,and the relationship between upstream and downstream water and power is becoming more and more complex.How to adjust the operation rules of cascade reservoirs to ensure the economic benefits of cascade reservoirs and protect the ecological environment of downstream river of cascade reservoirs has become a hot research topic.Therefore,this paper studies the joint ecological optimal operation of Xiluodu-Xiangjiaba cascade reservoirs in the lower reaches of Jinsha River,The main contents of this paper are as follows:(1)Aiming at the deficiency of NSGA-Ⅱ algorithm,the paper improves it.The original NSGA-Ⅱ algorithm still has some problems in identifying the screening efficiency of non dominated sorting,the uniformity of Pareto solution set distribution and the computational efficiency of repeated iterations.In this study,we improve the NSGA-Ⅱ algorithm in these three aspects,and get the improved NSGA-Ⅱ algorithm.In order to verify the advantages of the improved algorithm compared with the original algorithm,the improved NSGA-Ⅱ algorithm and the original NSGA-Ⅱ algorithm are used to optimize the same example,and the results are compared.The improved algorithm improves the computational efficiency,convergence and distribution of solution set.(2)This paper discusses the calculation method of the appropriate ecological discharge of the downstream river,which is the key index of the ecological objective in the joint ecological optimal operation model of cascade reservoirs.By comparing the advantages and disadvantages of different calculation methods of appropriate ecological flow,this study decided to use the physical habitat model method,which is relatively less used in China,to calculate the appropriate ecological flow of the downstream river,in order to get a more practical appropriate ecological flow of the four big fish in the spawning and breeding period in the downstream of Xiangjiaba.Through the establishment of the hydrodynamic model of the downstream channel of Xiangjiaba and the habitat model of the four big fish,the relationship curve between the weighted available area and the discharge of Xiangjiaba during the spawning and breeding period of the four big fish was obtained,and then the appropriate ecological flow range and the most suitable ecological flow during the spawning and breeding period of the four big fish were obtained.(3)Aiming at the multi-objective optimal operation problem of power generation and ecology of cascade reservoirs,a joint ecological optimal operation model of XiluoduXiangjiaba cascade reservoirs in the lower reaches of Jinsha River is constructed and solved.Firstly,the economic benefit target is the maximum total power generation in the operation period of the cascade reservoirs,and the ecological benefit target is the highest fitting degree of the appropriate ecological flow in the downstream river of Xiangjiaba Reservoir during the operation period.Then,according to the specification documents and related research,the constraints of water level,water balance,output,discharge,pulse flood and daily water level variation of each reservoir are determined.By analyzing the hydrological data of Pingshan station in the 55 year operation period from 1956 to 2010,and comparing the inflow information of Xiluodu Reservoir in recent years,the operation year of the example is determined as 2015.Finally,the improved NSGA-Ⅱ algorithm is used to solve the two-level optimal operation model of Xiluodu-Xiangjiaba cascade reservoirs in the lower reaches of Jinsha River,and the refined ecological operation scheme suitable for different needs is obtained.The research results can provide reference for the joint ecological operation scheme of cascade reservoirs.