Chemical Evolution And Water Cycle Characteristics Of Groundwater In The Western Plain Of Yili River Valley,Xinjiang

The Western plain of Yili River Valley is located in the Ili Kazakh Autonomous Prefecture in northwestern Xinjiang and plays an important role in the country's implementation of the“Belt and Road”economic strategy.The economic development and the construction of ecological civilization are inseparable from the support of water resources.This paper selects the Western plain of Yili River Valley as a research area,and through field surveys,combines hydrodynamics,hydrogeochemistry,and numerical simulation to study change law of groundwater hydrodynamic field and hydrochemical field based on the 1:50,000 hydrogeological survey project.The main factor analysis method and ion ratio method were used to analyze the causes of its hydrochemical characteristics.The content of ³H and¹⁴C in groundwater was calculated to determine the age of groundwater.The groundwater numerical simulation method is used to reveal the development characteristics of groundwater flow in typical sections.The specific conclusions are as follows:?1?The unique hydrogeological conditions,especially the geomorphic conditions,are the main factors that affect the hydrochemical evolution and the characteristics of water cycle in the study area.From Piedmont to Yili River,the aquifer structure changes from single phreatic aquifer structure to multi-layer phreatic-confined water structure.Groundwater flows from the front of the mountain to the Yili River.Groundwater is discharged into Yili River.?2?The main chemical ions are HCO₃^-,SO₄^2-,Ca^2+,Mg²⁺in the study area.The TDS content of groundwater in 90%area is less than 1g/L.The TDS content of groundwater in some areas of Aeolian Loess Hills,piedmont alluvial gravel plain and river alluvial plain is more than 1g/L.The total hardness of groundwater is less than 300mg/L in most areas of the study area,which belongs to soft and hard water.The PH is less than 8.1,which is weakly alkaline.?3?It is found through research that there are certain rules for water chemical characteristics under different geomorphic units.The chemical type of groundwater in the 1-1?section shows the evolution pattern of SO₄-Ca·Mg?HCO₃-Ca·Mg?HCO₃·SO₄-Ca·Mg.The chemical type of groundwater in the 2-2?section shows the evolution pattern of SO₄-Na·Ca?HCO₃·SO₄-Ca·Mg.The chemical type of groundwater in the 3-3?section shows the evolution pattern of HCO₃·SO₄-Ca·Mg·Na?HCO₃·SO₄-Ca·Mg?HCO₃·SO₄-Na·Mg.The chemical type of groundwater in the 4-4?section shows the evolution pattern of HCO₃-Ca?HCO₃·SO₄-Ca·Na.The formation of hydrochemical types is mainly controlled by water-rock interaction,evaporation,and human activities.?4?The results of ³H isotope study show that From Piedmont to Ili River,the content of3H in phreatic water increased first and then decreased.The ³H content of phreatic water in the eolian loess hills,piedmont alluvial proluvial gravel plain is more than 4 TU,mainly modern water.The ³H content of phreatic water in aeolian desert between 0.7-4TU,which is mainly the mixture of groundwater before nuclear explosion and modern water.The variation range of ³H content in phreatic water in alluvial proluvial fine soil plain is less than 0.7TU,which is mainly the groundwater before nuclear explosion.The phreatic water in fluvial alluvial plain is closely related to river water power,with ³H content greater than 4TU,mainly modern water.The results of ¹⁴C isotope study show that the age of the deep confined water in the piedmont alluvial proluvial gravel plain is over 10000 years.The age of the river alluvial plain and part of the alluvial proluvial fine soil plain near the river is relatively young,about4000 years.The age of the deep confined water in the other alluvial proluvial fine soil plain is between 6000-8000a.?5?The development characteristics of groundwater flow system are different under different geomorphic units.According to its development characteristics,groundwater circulation system can be divided into shallow circulation system and deep circulation system.Three runoff zones are divided:strong runoff zone,medium runoff zone and weak runoff zone.Based on the research results of hydrochemistry,isotope and numerical simulation,three typical groundwater circulation laws in the western plain area of Yili River Valley are summarized:two-level drainage groundwater circulation law of double-layer structure,one-level drainage groundwater circulation law of double-layer structure and one-level drainage groundwater circulation law of single-layer structure.