| The sustainability of groundwater resources in arid and semi-arid regions is a challenging task hindered by climate changes and human activities.Exploring the evolution patterns and driving mechanisms of hydrogeological processes at different stages of social development is crucial for groundwater’s sustainable utilization and management.Reliable groundwater flow simulation frequently serves as the basis for quantitative analysis and management of groundwater resources.To reveal the evolution mechanism of hydrogeological processes in the Yinchuan Plain under environmental changes,this study proposes an integrated approach for constructing a model of hydrogeological structures using multiple data sources.The technical difficulties in hydrogeological structure modeling were solved.Based on the hydrogeological structure of thick Quaternary aquifers of the Yinchuan Plain,a 3D transient groundwater flow model was then constructed to evaluate the evolution and driving mechanisms of hydrogeological processes under changing environments.Based on the multi-scenario schemes,the evolution trends of groundwater resources were predicted.The measures were then proposed for the rational development and optimal allocation of groundwater resources.This study provides not only technical support for the hydrogeological modeling of thick sediments but also provides a scientific reference for the sustainable utilization of groundwater in large inland basins in arid and semi-arid regions.The main results are as follows:(1)An integrated approach for developing a model of thick hydrogeological structures using multiple data sources and multiple methods was proposed,revealing the impact of hydrogeological structure adjustment on the groundwater flow field.The generalized relationships between the electrical resistivity and lithology were established,achieving the characterization of the spatial distribution of deep lithologic units and the heterogeneity of hydrogeological parameters.The proposed approach avoids the multiple-solution problem of inferring hydrogeological parameters from geophysical data and improves the accuracy of the hydrogeological structure model as well as the reliability of the groundwater flow simulation.Through a comparative study of 2-D steady flow numerical simulation of the typical cross-section in both complete and shallow aquifers,the results revealed that the adjustment of hydrogeological structures affects the groundwater flow budgets as well as the patterns of the groundwater flow systems(including the types of systems,and their number,location,and extent).Changes in the K_x field only affect the local groundwater flow fields.(2)A 3D transient groundwater flow model of the thick unconsolidated basin deposits in the Yinchuan Plain was constructed,revealing the evolution laws of groundwater resources.A 3D transient groundwater flow model from 1990 to 2020 was constructed based on the developed hydrogeological structure using MODFLOW-2005 and Hydrogeologic-Unit Flow package.This approach overcomes the disadvantages of using the depth of boreholes as the lower boundary of the groundwater flow model.The results indicate that the groundwater resources continued to deplete during the simulation period,reaching a cumulative storage change of-18.9×10~8 m~3.The cones of depression in deep aquifers experienced three stages(emergence,area expansion,and area reduction in Shizuishan City;emergence,area expansion,and quantity increase in Yinchuan City).The significant seasonal variations in groundwater level in the shallow aquifers are highly consistent with the seasonal irrigation periods.The amount of groundwater discharge from the Yellow River and local lakes decreased.(3)Clarified the driving mechanisms of human activities and climate changes on the hydrogeological process in the Yinchuan Plain.Based on Regime Shift Detection and correlation analysis,the total recharge of groundwater dropped sharply in 2003,the water diversion dropped sharply in 2003 and 2016,and the groundwater abstraction increased abruptly in 2017.There is a strong correlation and a moderate correlation between the total recharge of groundwater and the water diversion as well as groundwater abstraction,respectively.The reduction in water diversion driven by policies was a decisive driving force causing a continuous reduction of groundwater resources.In this context,the reduction of irrigation return flow and canal leakage led to a significant drop in groundwater recharge;To meet the water demand,groundwater abstraction had increased,which has led to significant increases in groundwater discharge in the deep aquifers.In summary,human activities were mainly responsible for variations in regional hydrogeological processes,dominating the evolution of long-term interannual hydrogeological processes and seasonal groundwater level fluctuations.Climate changes only affected the short-term interannual fluctuations in groundwater,reflected in the differences in the recharge from precipitation between dry and wet years.(4)The evolution of groundwater resources was predicted and measures to achieve sustainable utilization of groundwater and rational allocation of water resources were proposed.Based on the current situation of groundwater development and utilization in the Yinchuan Plain,water resource management policies,and future climate changes,considering the variation trend of the main driving factors of hydrogeological processes,with the goal of restoring groundwater storage to a new balance within the simulation period,scenarios were designed and numerical models for predictions were established.A scheme for sustainable utilization of groundwater resources in the Yinchuan Plain was proposed—a plan to reduce abstraction and increase irrigation return flow.This scheme aims to achieve a new equilibrium state of groundwater by 2050.The groundwater recharge was increased by 1.32×10~8m~3/a through increasing the water supply of agricultural irrigation,and the groundwater discharge was reduced by 1.68×10~8m~3/a through reducing groundwater abstraction. |
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