Variations and influence factors of runoff and sediment in the Lower and Middle Yangtze River

Human activities in the basin severely affected flow and sediment in the Lower and Middle Yangtze River. In order to study the relationship between variations in flow and sediment and human activities,runoff and sediment during the period from 1950 to 2011 in the trunk stream,main tributaries and two lakes( the Dongting Lake and the Poyang Lake) of the Middle and Lower Yangtze River were investigated with the cumulative curve analysis method and the Mann-Kendall test method. Changes in human activities were also analyzed in this paper. Data analysis shows that there is no obvious changing trend for annual runoff in the Hankou station and the Datong station in the trunk steam,main tributaries and the Poyang Lake in the Middle and Lower Yangtze River. There is an obvious reducing trend in the Yichang station at the trunk and the Chenglingji station in the Dongting Lake. Annual sediment load reduced significantly in the main tributaries,the Dongting Lake and the trunk stations except for the Poyang Lake without obvious changing trends. The impacts of human activities such as sediment trapping by reservoirs,soil and water conservation,water and sediment changes in the both lakes and sand mining in river on water and sediment changes of the river are analyzed according to the characteristics of water and sediment variations in the Middle and Lower Yangtze River. The different human activity plays a different role in the changes of river runoff and sediment. The influence of the trapping sediment by reservoirs is more obvious than other factors,and the Three Gorges Reservoir takes a great role in the water and sediment variations in the trunk of the Middle and Lower Yangtze River.