Exchange of Groundwater and River Water in a Basin of the Middle Heihe River by Using δ~(18)O

In arid regions of western China, water resources come from mountain watersheds and disappear in the desert plains. The exchange of surface water and groundwater takes place two or three times in a basin. It is essential to analyze the interaction between groundwater and surface water, so as to use water resources effectively and predict the change in the water environment. The conventional method of analysis, however, measures only the flow of a stream and cannot determine groundwater seepage accurately. Because of the distinct difference of {δ~(18)O} between groundwater and surface water, the method of using {{}~(18)O} was examined as an indicator for analyzing the interaction. With the addition of the mass balance equation, the composite proportion of different mixing components can be calculated. A conclusion was drawn from the computed result that, in the oases of the middle Heihe River, flood irrigation on vast farmlands has made a great impact on the transform between groundwater and surface water. The irrational irrigation has caused some problems, such as environmental deterioration and land subsidence.