Variations in Basin Sediment Yield and Channel Sediment Transport in the Upper Yangtze River and Influencing Factors

To study the impact of human activity on river basin sediment erosion and sediment transport in the upper Yangtze River, variations in the sediment delivery modulus and the incoming sediment coefficient during the period from 1956 to 2015 were investigated with a cumulative curve method and the Mann-Kendall test. Then, the contribution of human activity on sediment load reductions was calculated quantitatively with a hydrologic method. The results showed that the values of the sediment delivery modulus and the incoming sediment coefficient decreased with time, which indicated a decrease in basin sediment yield and an increase in sediment deficit in recent decades. Moreover, human activities such as reservoir construction, soil conservation, and sand excavation were the main reasons for sediment load reductions, whereas there were no significant trend changes in rainfall, which had a minimal effect on the sediment yield changes in the upper Yangtze River. Of the total reductions in sediment load, sediment trapped by reservoirs contributed close to 88%, whereas soil conservation and other factors only contributed 12%.