Groundwater Circulation Patterns Of Yuqia-Mahai Basin In The Middle And Lower Reaches Of Yuqia River

The contradictions of water supply and water demand is very prominent in theNorthwest inland Region of China due to the arid climate and relatively poor waterresources.Supplied by precipitation and snowmelt，the water resources of Northwestinland arid basin is mainly formed in the mountains and consumed in theintermountain basin.Because the water resources mainly originates from highmountains, experiencing a long runoff and finally transformed into groundwater in theplain area of the basin, the groundwater circulation in arid basin is intricate,includingthe origin and genesis of groundwater and the interaction relationship of surface waterand groundwater, temporal changes of groundwater recharging amount, groundwaterrenewability evaluation process and other issues which are the difficulties during thecurrent water resources evaluation in arid regions. Therefore, researches ongroundwater circulation patterns within typical river valley in arid areas can lead to ascientific understanding of the formation mechanism of regional water resource, so asto develop a reasonable development and utilization of regional water resources.This paper is based on the project―The study of interaction relationship betweensurface water and groundwater and renewability of groundwater in Yuqia valley‖, onespecial topic of the project of Chinese Geological Survey Bureau named―Hydrogeology survey of key areas of circular economy pilot area in Qaidam Basin‖of. This analyses focus on Yuqia-Mahai basin,the middle and lower reaches of Yuqiavalley,. We performed a systemic research on groundwater origin, the transformationof surface water and groundwater, and the circulation of groundwater, thus, to providethe basis for project of utilization of Yuqia valley and surrounding areas.The TDS concentration and δ18O value of river and the surrounding groundwaterare used，respectively，to reveal the interaction relationship betweenYuqia River andgroundwater. In the upper mountain area of Yuqia River,the interaction relationship ismainly that the groundwater transformed into the river water；in the the middlereaches, Yuqia Basin,the river water infiltration recharges the groundwater and then the groundwater overflows to the river again；In the Lvliangshan Gorge, the hydraulicconnection of surface water and groundwater is not close, and groundwater overflowsonly in part of the gorge.In the piedmont Gob zone,the river water infiltrationrecharges the groundwater；Within Mahai River，the tail section of Yuqia river, thegroundwater overflow recharges the river.Based on the analyses of spacial and temporal characteristic of hydrochemicaland environmental isotope distribution of the natural water in Yuqia valley, the sourceof groundwater and the basic characteristics of water circulation of this area areillustrated preliminary.Studies have shown that the groundwater recharging of Yuqia valley comes fromhigh mountain areas.Affected by the surface water runoff and transformation ofsurface and ground water, the middle and lower reaches of Yuqia valley, theYuqia-Mahai basin gets steady and abundant water recharging. The groundwater ofYuqia Basin, the phreatic water of gobi zone and most confined water of fine soil zoneof Mahai Basin basically keeps the hydrogeochemical characteristics of Yuqia riverwater. In the fine soil plain of Mahai basin,the farther away from the river,the greaterthe TDS content of phreatic water effected by evaporation and leach and the slowlygreater the TDS content of confined water effected by leach.Also the14C activity and3H concentration of groundwater was gradually reduced，indicating that the age ofgroundwater grow old gradually, and the update and replacement of groundwater isgradually slow.The δ18O and δ2H value of groundwater are below the river watergradually, show a characteristics of ancient atmospheric precipitation recharge.Mahaibasin is the final discharge area of Yuqia valley，and in the fine soil plain of.Mahaibasin，buried depth of groundwater becomes shallow，then groundwater discharge inthe form of evaporation and springs.Based on systemic analysis of the distribution characteristics of hydrochemic,hydrogen and oxygen stable isotope, temperature and the age of spring cluster in northof Mahai Basin. the origin of spring cluster is inferred as follows: most rechargingsource of the spring in north Mahai Basin comes from infiltration of Yuqia River and its tributary，Aolao River，in the Mahai basin. Then the groundwater which is formedby river water infiltration flow to the west until the NE fault lead it to NW block waterfault,so it exposed in the form of spring.The age of Spring is between1837~5228a,its update and replacement is slow.