Study on Volume Variation and Stability of Riverbed in the Yangtze Estuary

In recent years, regional floods and typhoons have occurred in the Yangtze Estuary. Changing dynamic conditions and dramatic reduction of sediment discharge in the basin are affecting the dynamic equilibrium pattern of the Yangtze Estuary. Based on the field measurement data and theoretical derivation, this paper analyzed the changing process of runoff-sediment discharge into the sea after the operation of the Three Gorges Project (TGP), and the tidal dynamics and sediment variation characteristics of the Yangtze Estuary. The erosion of South Branch mainly occurs in the channel below −10 m contour, and the riverbed volume below contours 0 m and −10 m has a good correlation with the sediment discharge of Datong Station in the previous year. On this basis, the ratio of the horizontal distance from the starting point to the section centroid below the average water level ( B c ) and the water depth at the section centroid ( H c ) was proposed to describe the change of the section shape. The relationships between the water-diverting ratio, the sediment-diverting ratio and the water-diverting angle, the conditions of runoff and sediment discharge from the upper reach and the characteristics of the riverway section were established, and the theoretical calculation equations of the water-diverting ratio, the sediment-diverting ratio and the diverting angle of each bifurcation were also established.