The Research On Groundwater Circulation In Aksu River Basin Based On Isotope Technology

Aksu River Basin,located at the southern foot of the Tianshan Mountains and the northwestern margin of the Tarim Basin,is a small minority settlement.The development of Aksu Region plays an important role in the rapid economic development and national unity of the whole southern Xinjiang.However,since the implementation of the Western Development Strategy,the increasing population and the expanding area of the Aksu Region have led to the increasingly prominent contradiction between the supply and demand of water resources in the Aksu River Basin,which has become an important problem restricting the economic development in the Aksu Region.Therefore,deep understanding of the groundwater circulation in Aksu River Basin,scientific management and distribution of groundwater resources should be attached great importance to.This article use the isotope,hydrogeochemistry and the numerical simulation methods,combining previous research results,comprehensive analysis of aksu river basin groundwater circulation rule,summarizes the groundwater circulation patterns.The main achievements are as follows:(1)Results of the numerical simulation show that there are local,shallow and deep groundwater flow systems in the Aksu River basin.The local groundwater flow system is mainly distributed on the alluvial and diluvial fan group in the upper reaches of rivers.The circulation depth of groundwater is about 170m,the runoff speed is>0.3m/d,and the runoff conditions are good.The shallow system is mainly developed in the south area of alluvial and diluvial inclined plain.The groundwater circulation depth is about 120m,the runoff speed is 0.05-0.3m/d,and the runoff conditions are general.The deep groundwater flow system is developed in the whole basin.The circulation depth of groundwater is large,the circulation depth of upstream is greater than 250m,and the circulation depth of downstream is also greater than 150m.The runoff velocity of groundwater is about 0.05m/d,and the runoff condition is poor.(2)The hydrochemical characteristics in the Aksu River Basin change with the change of geomorphic units.As a whole,the groundwater salinity gradually increases with the change of geomorphic units from north to south.The hydrochemical type changed from HCO₃·SO₄-Ca·Mg to and Cl-Na.The hydrochemical reactions occurred gradually changed from filtration to cation adsorption and concentration.(3)Using the method of environmental isotopes,it is found that both surface water and ground water in Aksu Basin are affected by evaporation to a certain extent,and the recharge of ground water is mainly from two aspects:one is the recharge of meteoric precipitation,the other is the recharge of runoff infiltration of ice and snow melt water in mountain areas.According to the results of tritium and ¹⁴C isotopes,the age and regeneration rate of the groundwater have obvious certain zoning characteristics.According to the results of D and O isotope,the main recharge sources of surface water and groundwater in the basin are precipitation and melt water from ice and snow in mountainous areas,and the surface water and some phreatic water in the study area are subjected to strong evaporation.(4)Hydrogeochemistry and environmental isotope methods were used to study the relationship between surface water and groundwater transformation in typical sections of Aksu River Basin.The results show that there are three times of groundwater transformation from upstream to downstream in Aksu River Basin,which can be divided into four transformation stages.In the first section,from the exit of the mountain pass to the north side of Wenshu,surface water is infiltrated to replenish groundwater.In the second section,from the north side of Wenshu to the south side of Aksu City,groundwater overflowed to replenish surface water.In the third section,from the south of Aksu City to the town of Karatale,the surface water and groundwater interlayer mixed under the influence of artificial activities.In the fourth section,from Karatale to the southern boundary of the study area,the groundwater spills out to replenish the surface water.(5)According to the results of hydrochemistry and tritium isotope studies,the groundwater above 150m is regarded as a positive circulating zone and below 150m as a weak circulating zone.The groundwater circulation model is summarized respectively from four aspects:aquifer medium,hydrodynamic condition,hydrochemistry and isotope.The positive circulation zone is divided into the groundwater circulation model under the influence of river action,geological conditions,human activities and natural conditions.Among them,the circulation mode under the influence of river action:the circulation transformation of groundwater is greatly affected by the flow of the original river;in upstream of the river,the groundwater is out of touch with the river;the river replenish the groundwater;the groundwater runoff speed is high and the runoff conditions are good.The groundwater in the middle and lower reaches of the river is not out of touch with the river,and the recharge relationship between the river and the groundwater depends on the groundwater level.The speed of groundwater runoff is relatively small,and the runoff conditions are general.Groundwater circulation mode under the influence of geological conditions:it is distributed in the vicinity of Wenshu.Due to the influence of uplift structure,the groundwater runoff from the upstream is blocked and overflows and mixes with surface water near Wenshu.The speed of groundwater runoff is relatively slow and the runoff conditions are ordinary.The circulation pattern of groundwater under the influence of human activities:it is mainly distributed in densely populated agricultural areas.The man-made excavation of water channels and mechanical and civilian Wells lead to serious damage to the regional inner layer structure,the interaction and mixing of groundwater and surface water,the slow speed of groundwater runoff and poor runoff conditions.The circulation mode under the influence of natural conditions:it is mainly distributed in remote deserts and desert.Groundwater belongs to the drainage area of groundwater.The upstream groundwater runoff here collects into lakes or flows into reservoirs and is finally discharged through evaporation.In the weak circulation zone,there are mostly deep phreatic water in upstream of the basin,and confined aquifers in downstream of the basin.The groundwater runoff is slow in upstream,sluggish in the middle and lower reaches,and the groundwater overflows the surface in some areas of downstream.