Impact on the Yangtze (Changjiang) Estuary from its drainage basin: Sediment load and discharge

This paper focuses on the sediment transport and freshwater discharging from tipper Yangtze drainage basin downstream, primarily on the basis of multiyear hydrological data collected from three major hydrological gauge stations (Yichang, Hankoa and Datong). Data indicate highest sediment load in Yichang (5.6 X 10(8) t/a), lowest in Hankou (5.1 X 10(8) t) and second highest in Datong (5.4 X 10(8) t). This fluctuations are identical with what has been observed from the annual flood season. About one thirds of the sediment load are trapped in the middle Yangtze River course, where meandering river pattern prevails; rest of them are directly transported to the river mouth area via lower Yamgtze River channel, where the river is typically confined by the exposed base rock and almost none is being trapped, instead, minor being drained to the mainstream from the local tributaries. To recognize this sediment delivery and river flow media is vital, because it can highlight morphologic/topographic correlation between the upper drainage basin and the estuary and the erosion and siltation in the river mouth area, where extensive coast has been exclaimed and or being exclaimed, and new navigation channel and port is being constructed. It is particularly crucial for monitoring the impact on estuarine change after 3-Gorges dam being closed in 2009. Data also indicate an increase in freshwater discharging downstream (>7.7 X 11(11) m(3)/a), of which similar to50% derived from the upstream and another half concentrated from the local tributaries. The result shows that this numerous freshwater has constantly flowed into the rivers mouth area to support the estuarine aquaculture and ecosystem, where it is confronted with huge amount of tidal prism (>10 times more than that of the annual runoff) transforming from offshore. Thus, a great concern for salt-water intrusion especially during the dry season is aroused, largely due to the intense upstream agriculture irrigation and large water transfer project, such as the well-planned South-North Water Transfer project.