Abstract:

The study area is located in the arid area in the Northwestern China and two levels of water storage basins exist. The firstlevel basin receives the lateral recharge from the southern mountain area. Spring discharge from the firstlevel basin flows into and recharges the next basin, at the same time groundwater in each levels of basin receives recharge from direct precipitation and indirect infiltration of flood flow. Based on hydrogen and oxygen isotope mixture formula, the precipitation amount accounts for 60% of the total recharges, of which, direct recharge from precipitation is estimated 21%, and recharge from flood flow is estimated 79%. Lateral recharge from the mountain area is about 40%. The secondlevel basin receives 38% recharge from precipitation, and the upstream spring discharge accounts for 62%. The quantity of tritium indicates that the se
condlevel basin is not affected by present precipitation. Using the piston model and the complete mixing model, the age of shallow groundwater in the firstlevel basin is estimated to range from 32 to 60 a.

Key words: stable hydrogen and oxygen isotopes, tritium isotope; , arid area, Northwestern China