Analysis on variation of runoff and sediment load in main stream of upper Yangtze River in recent period

The variation process,characteristics and trend of runoff and sediment load in the main stream of upper Yangtze River are analyzed based on more than 50 years′ hydrological data.The results show that there is no obvious variation trend in annual runoff of the main stream of upper Yangtze River,however,annual sediment load decreases on the whole;the transported sediment load in middle and lower reaches of the Yangtze River has decreased obviously since 2003 due to the sediment retaining of TGP reservoir and sediment load reduction from the upper Yangtze River.The annual flow and sediment distribution are characterized by concentrating in flood season from May to October,especially for sediment.For recent 50 years,the annual runoff of the upper reaches of Yangtze River varies in a main cycle of 12-years,and based on correlation analysis results,the annual runoff is positively correlated with annual sediment on the whole.The trend analysis shows that the runoff of upper reaches of the Yangtze River is relatively low at present,and after a few years the Yangtze River will turn into a wet period;with the construction of soil-water conservation works and the appearance of sediment retaining function of reservoirs in the upper reaches of Yangtze River,the sediment load in the middle and lower river reaches will remain in a low level during the reservoirs′ equilibrium period.