The Model Of Evolution And Circulation Of Groundwater In The Tataling River Basin,Qaidam Basin

Qaidam Basin is one of the significant circular economy industrial pilot parks in our country.And the Tataling River is the largest river providing abundant water resources for Dachaidan region.At present,developing and utilizing groundwater are mainly concentrated in the alluvial plain of the Tataling River.Since surveying and evaluating the groundwater in 2003,there has been three groundwater supplies built in Dachaidan area.However,in Tataling River considered as the water supply base in this region,previous investigations and researches on the mutual conversion of surface water and groundwater and the circulation patterns are inadequate.In addition,the river in Tataling river basin flows out of the mountains and finally into different terminal lakes,which is similar to many river basins in the northwest inland basin.This drainage pattern shows the complexity of groundwater circulation evolution under the tectonic pattern of alternating basins and mountains,and also increases the difficulty of studies.Therefore,solving this difficulty has always been the basic work of the exploitation and utilization of surface and groundwater resources and the protection of ecological environment.In this paper,hydrochemistry,environmental isotopes and numerical simulation methods are used to study the cyclic evolution of water resources in the Tataling river basin under the control of special geological structure,and there is a systematic and quantitative understanding of it obtained ultimately.The followings are the researches on the evolution of groundwater circulation in the Tataling river basin.1.Starting with analyzing and researching the topography and geological structure of the watershed on the basis of data collected and field investigations,the conversion relationship between surface water and groundwater under natural conditions is clarified,and the basic pattern that geological structures control the conversion of surface water and groundwater is revealed.Namely,the Tataling River seeps to recharge groundwater on the north side of Lvliang Mountain.Influenced by structural water blocking,the underground is enriched in the north of the mountain and discharged to the Dachaidan and Xiaochaidan Lake.That includes three conversions of surface water and groundwater during discharging to the Xiaochaidan Lake and in the direction of Dachaidan Lake,groundwater is discharged to Dachaidan Lake in the form of underground runoff along the ancient river channel.Until the overflow zone,groundwater runoff is blocked,and the overflow recharges the surface water.2.The TDS of Tataling River changes along the course from high to low and then to high.In details,TDS changes from the mountain(533mg/L)pass to the Lvliang mountain(480mg/L)then to the overflow zone(690mg/L)and finally into the Xiaochaidan lake(65476mg/L)through the fine soil plain area(1878mg/L).From the mountain pass to the middle reach of Xiaochaidan Lake,Cl·HCO₃-Na·Ca·Mg type is dominant.In the limbo plain around Xiaochaidan Lake,the hydrochemical type is transformed into Cl-Na type.The shallow groundwater in alluvial-diluvial sector is of Cl·HCO₃-Na·Ca type,which gradually changed into SO₄·Cl-Na·Ca type side by side to Xiaochaidan Lake,and the hydrochemical type eventually changed into Cl-Na type.In the Dachaidan Lake area,the Tataling river supplies the Dachaidan Lake in the form of groundwater.And the river water is exposed in the overflow zone of which the hydrochemistry type is still SO₄·Cl-Na·Ca type being transformed into Cl-Na type brine around the Dachaidan Lake.Most important,the variation trend of the groundwater hydrochemistry type from the mountain pass to the Dachaidan Lake is basically consistent with the surface water.From Kuerleike Mountain to the south of Lvliang Mountain,the hydrochemical type is mainly influenced by water-rock reaction.In the fine soil plain area,the hydrochemical type is mainly influenced by evaporation and ion exchange reaction.The hydrodynamic conditions near the Dachaidan Lake are poor,and the hydrochemical composition of water is greatly affected by ion exchange recation.3.The distribution of isotopes in the plane indicates that the main supply sources of the Tataling River are the melting water of ice and snow from the Kurrek and Qaidam Mountains in the north.Moreover,the isotopic characteristics of the typical section indicate that groundwater overflows to recharge the surface water in the north side of Lvliang Mountain and the fine soil plain.In addition,the groundwater and surface water have undergone many transformations during the process.According to the analysis of ¹⁴C,the period of groundwater circulation from alluvial-diluvial fan of the Tataling River to the Dachaidan Lake area is obviously longer than it from the Xiaochaidan Lake area.As well as the groundwater renewal in the Xiaochaidan Lake area is relatively faster.4.The numerical model is established using the Modflow simulating the process of transformation of surface water and groundwater dynamics.In details,according to hydrodynamic conditions and referring to the distribution feature of hydrochemical type,the groundwater flow system is classified into local and regional circulation systems in vertical direction.The buried depth of groundwater in the local circulation system is shallow,the runoff path is short,and the runoff speed is fast.On the contrary,the regional circulation system is deeply buried,the circulation path is long,and the runoff speed is slow.5.Dachaidan and Xiaochaidan Lake are all affected by hydrogeological conditions and tectonic effects,and their cycle periods,ratios of circulation to local and regional flow systems are also different.In Xiaochaidan Lake District,the local circulation system accounted for 62.47%of the total circulation,and the circulation period was less than 2000.While the regional circulation system contributed 37.53%of the water resources,and the circulation period was greater than 2000.In the Dachaidan Lake area,the local circulation system contributes 53.31%to water resources,and the cycle period is less than 6000 years.While the regional circulation system contributes 46.69%to water resources,and the cycle period is more than 6000years.