Analysis of Groundwater Replenishment in the Middle Reaches of Heihe River

Heihe River,as one of the greatest inland rivers in China,was confronted with water resources' shortage due to unreasonable development or utilization.To utilize optimally and effectively the limited groundwater resource,isotope technique was widely used to study groundwater cycle.Water samples were collected from wells for chemical and isotopic measurement all over the middle reaches of Heihe River.Piper diagram gives two main types of hydrochemical features.On the background of regional geology,combining isotope δ18O and Tritium with groundwater chemical analysis,different kinds of groundwater source and how to replenish groundwater were discovered.In the upper two adjoining alluvial-proluvial fans of the study area,there has no groundwater interflow;the groundwater is replenished from different sources.Groundwater near Heihe River riverside comes from river seepage flow by the highly conductive channel or from upper groundwater with the control of geography and topography.Zhangye basin and Jiuquan basin were separated by uplift bedrock of Yumu hill,so they have different groundwater replenishment systems,also different groundwater hydrochemistry and isotope characters.The groundwater's ages were approximately estimated by radioactive isotope tritium analysis,being all younger than 32 years.The research results can provide scientific bases for rationally exploiting and effectively using the groundwater resources in the middle reaches of Heihe River basin,so as to protect the fragile eco-environment.