CHANGING CHARACTERISTICS OF SEDIMENT YIELD AND DISCHARGE DURING PAST 40 YEARS IN CATCHMENT OF THE YANGTZE RIVER

Trend of the sediment load and streamflow of Pingshan,Yichang,Hankou and Datong station along the mainstem Yangtze River and the Beipei station in the Jialingjiang River,the Huangzhuang station in the Hanjiang River was analyzed with the help of Mann-Kendall trend analysis.The results indicate that:①The sediment yield of the upper catchment of the Yangtze River is in significant upward trend and is in downward trend in the middle and lower cachment of the Yangtze River;②Various influencing factors combined to result in the complicated changing patterns of the sediment yield and streamflow in different parts of the Yangtze River catchment.Natural factors(e.g.precipitation changes)exerted more influences on streamflow changes in the upper catchment of the Yangtze River.In the middle and lower cachment of the Yangtze River,climatic changes and human activities(human use of water resources)combine to have impacts on streamflow variability;③Jump time of sediment yield is in good agreement of the time when the construction and function of water reservoir starts;④Water reservoirs exert more influences on the sediment yield changes and these influences are more obvious in the river catchment of smaller drainage area than in river cachment of larger drainage area;⑤Smaller riverbed slope leads to tremendous deposition of sediment yield in the middle cachment of the Yangtze River,which together with construction of Three Gorges Dam will further reduce the downstream discharge of the sediment yield in the middle and lower catchment of the Yangtze River.