Groundwater Formation And Evolution In The Western Plain Of Yili Valley

Western Plain of Yili Valley located in the northwest of Yili Kazak Autonomous Prefecture plays an important role in the national economic strategy namely "The Belt and Road".With the increasing demand for water resources as economic development and the construction of ecological civilization,It is quite urgent to explore the groundwater for another round.For the demand of the plan of groundwater resource development and utilization,the degree of the hydrogeological investigation in the study area is low,research on the formation and evolution of groundwater are not enough.Therefore,the laws of groundwater formation evolution need to be studied continuously on the basis of previous work,so as to deepen the understanding of groundwater cycle in study area,and provide theoretical support for groundwater resources assessment and reasonable development and utilization.Based on the theories of regional groundwater system and hydrogeological conditions in the studied area,groundwater dynamics,hydrology geochemistry and environmental isotope literary theories and methods are comprehensively used to analyze spatial evolution law of groundwater dynamic field,chemical field and isotopic field,and reveal groundwater formation evolution process and law of water cycle in the Yili river valley of western plains.The main results achieved and understanding are as follows:1?There is mainly Quaternary pore water in loose rock mass in study area,where the topography is the East West high low,the northern mountain area is the main forming region of water resources,in the piedmont groundwater accepts the vertical infiltration recharge,subsurface flow recharge and bedrock fissure water lateral recharge.The plain and the desert are the mainly runoff areas of groundwater,groundwater is dominated by horizontal runoff.The Yili River located in the southern boundary of the study area is the final discharge area of groundwater.There are two interconversion processes of groundwater and the rivers flowing from the north to the south.2?The hydrodynamic condition of groundwater from Piedmont to the alluvial plain of the Yili River gradually becomes worse.In the piedmont groundwater recharge area,the shallow groundwater head is higher than the deep groundwater head,the runoff velocity is greater than 0.15m/d.In the runoff area,the shallow groundwater head is lower than the deep groundwater head,the runoff velocity of shallow water is greater than 0.02m/d,while the runoff velocity of deep groundwater is less than 0.008m/d.Near the Yili River valley,groundwater leakage discharge in the Yili river,groundwater head in deep area is higher than that in shallow area.Based on the result of groundwater flow system,the system can be divided into shallow groundwater flow system and deep groundwater flow system.3?The chemical characteristics of the groundwater has spatial differences and evolutionary law along the runoff path.Groundwater quality is generally better,only water quality in some areas is slightly bad.Water quality of confined water is better than unconfined water.Influenced by surface meteorological and hydrological factors,the TDS and hardness of unconfined water increase gradually,hydrochemistry type of phreatic water become complex gradually along the runoff pathway,the hydrochemistry indexes of confined water are relatively stable.4?the relationships of isotopic content between D and 18 O in different water body are as follows: precipitation in plain area > surface water > phreatic water > confined water.Groundwater mainly accepts vertical infiltration from surface water and lateral supplies from river valley and bedrock fissure water in the piedmont sloping gravel plain,discharges to surface water in the fine soil plain,the surface water in desert area has a certain amount of supply of phreatic water.The confined water in plain mainly comes from precipitation and snow-ice melting water,for supplying elevation the west is higher than the middle-east.Isotopic dating shows,age of phreatic water in plain is generally less than 60 years,and increases from north piedmont to south.In fine soil plain below 150 m,the 14 C age of the deep confined water is 1824-5091 years.5?The underground water cycle mode can be classified into shallow circulation model and deep circulation model.Among them,the shallow water cycle model has features of short water circulation way,fast cycling speed,good water quality and strong renewal ability,the cycle depth is generally less than 80 m,the influence range is about 20 km,TDS increase gradually and hydrochemical type changes from simple to complex along the circulation path,groundwater age are less than 60 years and increase gradually.the deep water cycle model has features of long water circulation way,low cycling speed,better water quality and weak renewal ability,the cycle depth is generally more than 80 m,the influence range is more than 50 km,the change of TDS,hydrochemical type and stable isotope content are slight along the circulation path,groundwater age are more than 60 years and positively associated with circulation depth,local groundwater age are greater than 5000 years.