Variation Relationship among Multi-Time-Scale Runoff Series in East River Basin

East River, one of the three main river networks of Pearl River Basin, runs through Jiangxi, Guangdong province and provides drinking water to Hongkong, thus it's great important for the water supply and flood control to the above three regions. Using Hydrological Variation Diagnosis System, the article diagnosed multi-time-scale runoff series from the year 1954 to 2005 of four main stations, namely Longchuan, Heyuan, Lingxia and Boluo station on the trunk stream of East River, so as to detect the variation relationship among series at the scale of month, flood season/non-flood season and year. It found out that: 1) the runoff series at month scale of the four stations mostly varied from April to May in flood season and from November to March of the next year in non-flood season, and the change-point mostly located around the year of 1973. The majority of series at month scale in flood season took on no variations, so the minority's variation didn't affect the variation status of the whole flood season, and the series at flood season scale took on no variation. While the majority of series in non-flood season varied, and they contributed a lot to the variation of the non-flood season series. 2) At Longchuan, Heyuan and Lingxia station, the variation situation at year scale was consistent with that at non-flood season scale, and the change-point located respectively in the year of 1972 and 1973, which indicated that the variation situation at non-flood season scale contributed a great deal to that at year scale for those three stations. But at Boluo Station downstream, the variation situation at year scale didn't accord with that at non-flood season scale. Causes analysis showed that no change-point was detected in the precipitation series in East River Basin, thus it contributed little to the variation of runoff series at different scale; while the possible causes would lie in the reservoir constructions (Fengshuba reservoir e.g.), the changes of land use and cover, levee constructions, riverbed undercutting and other human activities affecting the underlying surface.