Identification of the groundwater flow system in the middle reaches of Heihe River Basin (northwestern China) based on stratified groundwater exploration technology

Heihe River is the second largest inland river in China, but groundwater is the main source of water in the middle reaches of the Heihe River Basin (HRB). The middle reaches of HRB consists of Zhangye and Jiuquan basins. In view of deficiencies in the groundwater exploration techniques, methods, and accuracy associated with previous studies in the HRB, this study used stratified groundwater exploration (monitoring and sampling) techniques to identify the groundwater flow systems. Three fields were considered—groundwater flow dynamics, temperature, and chemical. The results show that stratified groundwater-level monitoring technology can be used to quickly identify groundwater recharge and discharge areas. The main groundwater recharge area in the HRB’s middle reaches is in the piedmont plain, and most of the rest of this middle basin comprises groundwater runoff areas and discharge areas. Shallow groundwater temperatures (average and variation) reflect the characteristics of groundwater recharge, runoff, and discharge. The shallow groundwater temperature gradually increased from the recharge area to the discharge area, and the temperature annual variation tended to be greatest in the central area. Along the direction of groundwater flow, the δD content of shallow groundwater in the HRB’s middle reaches initially increased and then decreased, and the δD content of groundwater in the vertical direction decreased gradually from shallow to deep. The surface-water/groundwater exchange in the central Zhangye Basin mainly occurred in the shallow areas, within 200 m depth. Thus, stratified groundwater exploration technology is helpful for identifying groundwater flow systems in inland arid basins.