Fig. 12

Tidal data. a The Yangtze River estuary and the location of the tidal gauge stations (red filled circles). The numbers in brackets are distance downward from Datong station (Red triangle). Datong is the maximum limit of salt-wedge intrusion, which is 650 km. From Guo et al. (2015) with additional labels by G. Shanmugam. See also other studies on the limit of tidal influence (Chen et al. 2007; Zhang et al. 2012, 2017); b Geometry and bathymetry of the Yangtze Estuary in 1997 showing river-mouth bars. Such sand bars are typical of tide-dominated estuarine systems (see Dalrymple 1992; Dalrymple et al. 1978, 1992; Shanmugam et al. 2000). From Guo et al. (2014) with additional labels by G. Shanmugam; c Discharge of the Yangtze River for 2009 and 2010 at the head of the tide at Datong; d Simultaneous water levels at Datong, Nanjing, Zhenjiang (decreased by 2 m), Jiangyin (decreased by 4 m), Xuliujing (decreased by 7 m), and Niupijiao (decreased by 11 m). The red lines indicate the daily (24 h) averaged mean water levels (MWL). Note the positive correlation between discharge and MWL in July at Datong. Both C and D from Guo et al. (2015) with additional labels by G. Shanmugam; e−f Diagram showing a river entering an ocean with three zones of interest: A normal flow area, where depth is constant along the channel, a transition zone where mean sea level influences river depth, and the offshore river plume in e cross section and f plan view. At low flow, the transitional region is a zone of backwater, where the water depth at the shoreline (hs) is greater than the normal flow depth (hn), and the water surface (blue) and bed (black) diverge downstream, resulting in deceleration (shown by length of arrows) and deposition. At high flow hn > hs, the water surface (red) is convex, resulting in spatial acceleration of flow and erosion. In both cases, the elevation of the water surface at the river mouth is relatively insensitive to discharge due to lateral spreading of the plume. Adopted from Lamb et al. (2012), after Lane (1957), U.S. Army Corps of Engineers. Caption by Hoitink and Jay (2016)