Study On Multi-reservoir Ecological Operation In The Longxi River Basin

With the progress of society and more and more reservoirs are put into use,the multiobjective joint operation of reservoirs will become an important way to develop and utilize water resources in river basins.The Longxi River basin is located in the north of Chongqing City.There are many reservoirs in the region,which play an important part in sustainable economic development.At present,there are three problems of multireservoir in the basin.Firstly,each reservoir is scheduled according to its own state,which directly or indirectly leads to the inadequate utilization of water resources in the basin.Secondly,reservoirs built on trunk or tributaries impede the continuity of rivers,which has detrimental impacts on the natural flow regime.Thirdly,the ecological water demand of the lower reaches is not considered in reservoir operation,which leads to serious ecological water shortage in the river system,and even casues zero flow channels.Therefore,this paper explores the Longxi River Basin reservoir group from three aspects: multi-objective joint optimal operation of reservoir group,the impact of reservoir group on natural flow regime,and the design flow considering river ecological water demand and river water environmental capacity.The main research contents and conclusions are summarized as follows:(1)Taking the maximum urban water supply,agricultural water supply and power generation as objective functions,the multi-objective joint dispatching mathematical model of reservoir group in Longxi River Basin is established.The multi-objective Pareto solution set is obtained by using the NSGA-II algorithm,and the optimal decision is selected by using the comprehensive index method.There is great competition among the objectives,and the overall benefit of the reservoir group after optimization is significantly improved.(2)Based on the measured runoff of Liujiantan Reservoir,the SWAT model in Longxi River Basin under natural condition is established.The process of runoff in the reservoir is compared and analyzed between the SWAT model and the basic scheme dispatching model.Then the uncertainty of the model is described by Bayesian probability prediction model.Compared with the natural state,the influence of reservoir groups on the runoff process in the basin is mainly manifested in the reduction of peak flow in flood season,and the difference of runoff outflow in normal and dry years in the downstream main stream is not obvious.(3)Tennant method is used to determine different ecological water demand schemes of rivers.The objective function of minimizing ecological water shortage is added to the original reservoir group joint dispatching model.The optimal decision-making of reservoir group under different ecological water demand schemes is used to guide the joint dispatching of reservoir group.When the ecological water supply of rivers increases,the satisfaction degree of urban water supply and agricultural water supply decreases.Meanwhile,the total power generation,the total diversion water supply and the corresponding guarantee rate have a slight fluctuation,with a slow increasing trend.(4)Based on three ecological discharge schemes,the optimal decision-making and joint operation of reservoirs are obtained by considering the designed discharge of sewage intake in some sections of the river.Increasing the designed discharge of sewage will reduce the water supply benefit of urban and agricultural targets,and increase the target benefit of power generation.What's more,the discharge of reservoirs in the designed discharge reach will be affected.Based on the results of this study,if the ecological water demand in the river basin is considered as the main priority,the second ecological discharge scheme is the most suitable two,and the fifth is recommended if the design discharge of sewage collection in the river reaches is also considered.Finally,the content of this paper is summarized systematically,and the prospect of further research is given.