Abstract:

The principle and methods of base flow index (BFI) and line separation have been employed to calculate the baseflow in 13 hydrologic sections on the main stream and 31 hydrologic sections on 20 major tributaries of the Yellow River basin. Based on the baseflow separation results, a comprehensive analysis was made on the forming mechanism of baseflow,the contribution of groundwater to the Yellow River,baseflow changes,the composition and the total amount of groundwater resources in the basin,which has provided a sound and reliable foundation to evaluate the groundwater renewal capability and  set up a rational water resources management strategy in the Yellow River basin.The research result shows that the baseflow of the Huayuankou section accounts for 44% runoff for many years average. The extremely close relationship existed between groundwater and the Yellow River and the groundwater had great contribution to the river. The runoff and baseflow of the Yellow River are mainly from the source area above Lanzhou.The annual runoff and baseflow of the Lanzhou section account for 59% and 60% of the Huayuankou runoff section. However, the groundwater contribution to the Yellow River water was very small in the vast area of upper and middle reaches of the Yellow River between Lanzhou and Huayuankou. Around 1990s, the baseflow in the main stream and tributaries of the Yellow River had been changed greatly. The main stream above Lanzhou had a sharp baseflow reduction (decrease rate of 0.08-0.20) except the source above Maduo (decrease rate of 0.38).However,in the major hydrological sections downstream the Yellow River in Lanzhou, baseflow had large reduction rate(0.22-0.31). The dramatic reduction of baseflow mainly results from the reduction of groundwater resources quantity affected by the nature and human activities such as groundwater exploitation. From the viewpoint of hydrologic cycle on the basin scale,the regional groundwater resource of the Yellow River basin was constituted of three following parts: groundwater resource that participates in the Yellow River water cycle, groundwater not involved in the Yellow River water cycle and the groundwater exploitation in the basin. The natural groundwater quantity from June 1990 to June 2000 is estimated to be 35.39 billion m³/a, which is 15% less than that of groundwater resource of many years average.

Key words: Yellow River basin, baseflow separation, baseflow amount, base flow index (BFI), groundwater