Study On Optimal Allocation Of Ecological Water Resources In Ejina Oasis Based On Multi-objective Model

Ejina Oasis is located in the lower reaches of the Heihe River.Its ecology is very fragile and its strategic position is very important.It is not only a natural barrier to prevent wind and sand invasion and protect the ecology of northwest and North China,but also an important support for the survival and reproduction of the local Turhut Mongolian people and the construction of national defense scientific research.At the end of last century,a serious ecological crisis broke out in this area.In order to contain the further deterioration of the ecological environment,the Heihe River ecological water regulation was implemented in 2000.In the past 20 years,the ecology of Ejina Oasis has been improved obviously,but the allocation of ecological water resources in this area is extensive,and the related research on water allocation is less,which leads to the low utilization efficiency of water resources.At present,the water resources entering Ejina are mainly concentrated in the core area of the oasis,and the ecological water demand can be satisfied.Even some of the core areas are salinized by excessive water,which seriously affects the growth of vegetation.However,the water distribution in the marginal area and the ecologically fragile area of the oasis is very little,and the vegetation is still in a degenerated state.Valuable water resources have not been effectively utilized,which seriously restricts the ecological benign succession of Ejina Oasis.Based on the multi-objective model,the Ejina Oasis Belt is divided into 13 sub-regions,and the annual water allocation period is divided into five periods.The relationship between the allocatable water amount and the actual water demand of the oasis ecology in 13 sub-regions is established in five periods.The objective function is set as the difference between the allocated water amount and the actual water demand,and the ecological water demand of the water area,the ecological water demand of the oasis vegetation and the suitable ecological groundwater are taken as the basis.Taking the ecological water demand as the goal and the minimum water demand difference as the ultimate goal,the allocation water quantity of 13 sub-districts under the "multi-objective allocation scheme" is calculated by model coupling and using Matlab toolbox function f min con,with the restriction of Dongjuyanhai recharge amount,total control index,underground ecological water level index and vegetation restoration area index as the input.Configuration results are compared with the current scheme,and the multi-objective optimal configuration scheme is determined to be the best one.At the same time,the current situation of water resources,the law of oasis and ecological water demand in Ejina Oasis are analyzed,and the relationship between ecological water demand and groundwater in Ejina Oasis is clarified.A multi-objective optimal allocation scheme with a guaranteed rate of 50%is proposed.The allocation ratio of the East and West rivers determined by the scheme varies with the amount of water coming from the Langxinshan section.The more abundant the water coming,the lower the allocation ratio of the East and West rivers.That is to say,when the water coming is dry,the allocation of the East River is mainly directed towards the East River,while that of the West River is less;when the water coming is abundant,the allocation of the East River remains unchanged and the allocation of the West River The volume gradually increased.The advantage of this scheme is that the water distribution ratio of the East and West rivers can be adjusted in real time according to the water inflow of the Langxinshan section,instead of being maintained at 7:3 according to the current situation,which can lay a good theoretical foundation for the fine water resources allocation in Ejina after the Heihe River water inflow has been controlled in the future;in view of the current dispatching practice,this scheme can guide Ejina.The region formulates the ecological water distribution plan more rationally,while guaranteeing the basic water consumption in the core area,increases the allocation of water in the ecologically fragile area and the oasis fringe area as much as possible,and gives full play to the maximum ecological benefits of limited water resources.