中文摘要：

地下水更新时间是衡量水循环速度的重要指标，是水资源开发利用重要的水文参数。文中考虑1972年以后黄河出现的断流问题．探讨其支流地下水更新时间的估算方法。基于无定河流域10个水文站的日径流观测资料．分汛期、非汛期与全年3个不同时期研究流域的基流消退过程以及地下水的更新时间。研究结果表明：1）无定河流域汛期退水常数变化在0．72～0．89之间．非汛期退水常数变化在0．88～0．96之间，汛期基流消退速度快于非汛期；2）对于无定河流域三个不同的土地类型区而言，无论汛期、非汛期还是全系列．黄土区的基流消退最快，河源区次之，风沙区最为缓慢；3）从地下水更新时间看，11个水文站控制的水文区地下水半更新时间变化在1．8-45．5天之间．地下水全更新时间在34～105天之间．表现出明显的时空分异性。按年平均状态．无定河上游、中游和下游地下水的全更新时间分别为101天、88天和84天．表现出从上游到下游减小的趋势。

英文摘要：

In this paper, the residence time of groundwater in dry season, wet season and yearly average is estimated based on daily streamflow records of 11 hydrological stations in Wudinghe River Basin. Results show that： （1） recession constant of groundwater in the Wudinghe River Basin, ranging from 0.72 to 0.89, has a larger recession rate in wet season than in dry season. （2） Spatially, the recession rate of groundwater in hilly region is the biggest, but is the smallest in the sandy region. （3） Half-residence time of groundwater varies from 1.8 to 45.5 days while the residence time of grotmdwater is between 34 and 105days in different catchments, showing significant spatial variation. The annual average residence time of groundwater decreases from 101 days in the upper reaches to 84 days in the lower reaches.