Temporal and spatial charactristics of base flow in Wei River basin and its affection factors

Using Series of daily runoff recorded at 4 hydrological stations which are Linjiacun, Weijiabu, Xianyan, Huaxian in the Wei River basin, based on BFI-Base Flow Separation method, this paper analyzed the base flow changes in Wei River from 1955 to 2000. The results showed:(1) The base flow was an important component of runoff in Wei Ri ver, accounting for about 47%. (2) The proportion of base flow in three segments which are above Weijiabu station, Weijiabu - Xian yang, Xian yang - Huaxian were 33%, 20%, 47%. (3) Wei River Base Flow was downward in the past 50 years. 1970 was a dividing line, before which the average base flow reached 42 Billion cubic meters and after which was 27 Billion cubic meters.(4) The base flow index in Weijiabu - Xian yang section is 60%, Linjiacun - Weijiabu section of that is 43%, Xian yang - Huaxian section is 40%. (5) By Correlation analysis between the base flow and rainfall, obtained the last century 60´ s and 70´s the base flow correlated well with the rainfall, after 70´s it was mainly influenced by human activities that included building Hydraulic engineering, exploiting groundwater, etc.