Numerical Simulation Of Groundwater Flow And Resource Evaluation In Western Plain Of Yili Valley

Groundwater is a very important resource for human life and production.Due to the dual impact of climate change and human activities,groundwater resources composition has changed significantly,affecting the rational development and utilization of groundwater resources.The western plain of the Yili River Valley is located in the northwest part of Xinjiang.It is located at the important node of the"The Belt and Road Initiative"construction.It is the most front-end of our country's opening to the West.With the rapid growth of economy and population,the contradiction between supply and demand of water resources is becoming more and more prominent.Because of the stable flow of groundwater resources,the water quality is better.Therefore,it is of great practical significance to formulate a reasonable groundwater exploitation plan for this area to ensure the sustainable utilization of groundwater in this area.Based on the project fund of China Geological Survey"Survey on 1:50000 Hydrogeology of the West Plain in Yili Valley",and taking the groundwater in the western plain area of Yili Valley as the research object,the hydrogeological parameter system of the study area is constructed by combining hydrogeological survey,field in situ experiment and numerical simulation,and the hydrogeological conceptual model and three-dimensional model of the study area are established.The hydrogeological parameters are optimized by PEST inversion in groundwater flow numerical simulation model,and the sensitivity of the model parameters is analyzed.At the same time,the exploitable groundwater resources in the area are evaluated on the platform of the numerical simulation model.The main achievements are as follows:1.Source and sink items and aquifer attribute parameters in the study area were obtained by in-situ field experiments and numerical simulation.The hydrogeological parameter system in this area is constructed,and nine hydrogeological parameter zoning maps,such as Infiltration recharge coefficient of farmland irrigation,River infiltration recharge coefficient and phreatic evaporation coefficient,are compiled to provide parameter basis for groundwater resource evaluation.2.On the basis of comprehensive analysis of geological and hydrogeological conditions in the study area,the conceptual model of hydrogeology and three-dimensional numerical simulation model of groundwater flow in the study area are constructed.The model is solved by Visual MODFLOW software,and the parameters are optimized by PEST inversion.The model is identified and validated by groundwater level dynamics and flow field of observation holes in the area.The fitting errors of groundwater level are less than 0.5 m.The calculated flow field fits well with the measured flow field at the end of time.The sensitivity analysis of parameters verifies the reliability of the model.3.The groundwater flow numerical model established in the current year is used to calculate that the groundwater recharge is 21.25×10~8m~3/a,the groundwater discharge is21.94×10~8 m~3/a,and the groundwater is in a negative equilibrium state.Among groundwater recharge,the recharge of canal system leakage,farmland irrigation infiltration and rainfall infiltration is 11.2×10~8 m~3/a,accounting for 53%of the total recharge,while the recharge of lateral runoff is relatively small.Among the groundwater discharge items,the total discharge to the Yili River and lateral runoff is 10.48×10~8m~3/a,accounting for 47.8%of the total discharge,and the artificial exploitation of groundwater is 3.22×10~8m~3/a,accounting for14.7%.4.Based on the three-dimensional groundwater flow numerical simulation model,the sensitivity of permeability coefficient,water supply and permeability of riverbed sediment in the study area is calculated by Morris method.The sensitivity of parameters is in the range of0.001m~2.2m on the whole.The sensitivity of permeability coefficient is higher than that of river bed sediment.According to the contour map of sensitivity distribution,sensitive and slow areas of groundwater system are identified.The sensitivity of permeability coefficient at the southern boundary of the study area is higher than that in the eastern one.The permeability coefficient of riverbed sediments is higher in the north of the study area,up to0.55m,but lower in the south.5.On the basis of water use and ecological environment in the economic development planning of the study area,under the constraints of water level and quantity in the ecological environment,three groundwater exploitation schemes are designed.The three schemes account for 13.6%,40.9%and 45.9%of the recharge resources respectively.The third scheme can meet the needs of planned water use and predict the final groundwater under the consideration of river ecology.As the best exploitation scheme in this study,the groundwater recoverable resources in the study area are calculated to be 9.79×10~8 m~3/a.The above research results provide important technical support for the development and utilization of groundwater resources in the study area.