ABSTRACT
The non-uniform sediment input has played a significant role in the bed evolution in the middle and lower Yangtze River, which indirectly influences the amount of the sediment transported into the East China Sea every year. However, it has been dramatically changed by the climate change, especially the human activities in the upper Yangtze River, not only the amount, but also the grading. The average annual sediment load has reached to 402.6 million tons since 1960 ‘, while showing a decreasing and refining trend mostly influenced by the human activities, such as soil and water conservation, and large hydropower projects. The most direct consequence of these changes was to cause severe erosion in the middle and lower Yangtze River, further to bring about fluvial regime adjustment. In this article, a series of daily and annual averaged sediment transport data since 1960 ‘ were collected and analyzed to find the impacts of the significant human activities on the non-sediment input of the middle Yangtze River, and then its variation tendency was predicted, affected by the existed large hydropower projects and to be build ones in the upper Yangtze River. The result shows that the non-uniform sediment input of the middle Yangtze River was slightly reduced by the operation of Gezhouba Project and the up and middle Yangtze River water and soil conservation prevention and control projects, and further less after the impoundment of Three Gorges Reservoir, meanwhile its grading has been getting finer and finer. In future, along with the normal operation of the Three Gorges Reservoir and the built of the cascade reservoirs in the upper main stream and tributaries of the Yangtze River, it will be continuously reduced and refined.
