Abstract: The ratio of the sediment carrying capacity (S*) of a river flow to its local sediment concentration (S) serves as a direct indicator of topographic change in riverbed. We have collected the field data of the upper Yangtze measured at its major hydrological stations in 2010-2020, and conducted an analysis of the ratio S*/S. The results show that with a few exceptions, the carrying capacity generally exceeded local sediment concentration, and S*/S presented a first-increase-then-decrease pattern of variation with flow discharge. This pattern is closely related to upstream dam operation and earthquakes－e.g., impoundment of the Xiluodu and Xiangjiaba reservoirs since 2013 led to an increase in S*/S at the same flow discharge, while a decrease in S*/S has been observed at the Xiaoheba and Fushun stations in recent years due to the gradually reducing effect of earthquakes. The findings in this study provide a new insight for understanding sediment transport and promoting channel regulation in mountainous rivers.

Key words: sediment carrying capacity of flow, sediment concentration, flow discharge, low water channel, upper reaches of the Yangtze River