Variation tendency of runoff and sediment load in China major rivers and its causes

The variation tendency of runoff and sediment load in China major rivers is studied based on the representative hydrological stations of the rivers.The results show that there is no significant change in the mean annual runoff (1.409×10¹² m³/a)of those stations;and little change is detected in the annual sediment load before 1960.However,the sediment load decreases gradually from 26.43×10⁸ t/a in the 1950s to 5.95×10⁸ t/a in the 2000s after 1960;and the corresponding change in the average sediment concentration is from 1.74 kg/m³ to 0.46kg/m³.Regionally,the annual runoff of major southern and inner rivers in China remains almost unchanged,a significant reduction in annual runoff is however detected in many representative hydrological stations of northern rivers except for the Huaihe and Songhua rivers.Varying degrees of reduction is found in the sediment load of China major rivers except for the Tarim River,and the greater reduction occurs in northern rivers.Human activities and natural factors are mainly responsible for the detected variations in runoff and sediment load,of which natural factors include changes in precipitation amounts and land covers over the river basins,and human activities factors refer to those measures in soil and water conservation,reservoir engineering,inter-basin water transfer projects,water diversion,sand excavation,and soon.