Numerical Simulation Of Groundwater Flow In Ejina Basin

Heihe River is the second largest inland river in northwest,China,and it is also the first inland river to implement unified water resources dispatching management in China.The Ejina Basin is located in the lower reaches of the Heihe River Basin,which belongs to an extremely arid desert area.The continuous decrease of upstream water resources result in the high frequency of river cut-off.Water shortages in the Ejina Basin has seriously affected economic development in the region.By analyzing the variation law of groundwater level in Ejina Basin,predicting the amount of water resources which needed to maintain the existing ecosystem scale in the basin,and putting forward a reasonable water transfer scheme from upstream to basin,the upstream and downstream water resources can be planned scientific,and the utilization efficiency of water resources can be improved.The main work and research results are as follows:Firstly,this paper analyzed the natural geographic conditions,regional geology and hydrogeological conditions in Ejina Basin.Combined with the field geological investigation,the three-dimensional geological model and groundwater flow mathematical model of Ejina Basin are established by using the MODFLOW module of GMS software.Secondly,this paper established the numerical model of groundwater flow in the study area,which is identified and verified by the measured groundwater level data from April 2019 to March 2020.The verification results show that,among the 13 observation wells,the residual error of 12 observation wells was less than 0.5,accounting for 92%;The maximum value of linear correlation coefficient R~2of each observation hole was 0.97,and the minimum value was0.72,both greater than 0.7;The RMSE of each observation hole is only larger than 0.25m in No.6 observation hole,and less than 0.25m in other observation holes;The established model has high reliability.Finally,this paper predicted the change of the water level of phreatic aquifer in the study area in the next five years under three different upstream water delivery schemes by the verified groundwater numerical model.The results show that when the annual average runoff of Shaomaying and Langxinshan is 881.9 million m~3and 754.4 million m~3respectively,that is,the runoff of each observation station is consistent with the average data from 2004 to 2020,which can basically ensure that the water level of phreatic aquifer in Ejina Basin will not drop.This scheme can also be used as a reasonable water delivery scheme,which ensure the good development of the existing ecological environment in Ejina Basin.