Knowledge of estuarine morphodynamics and associated sediment source-to-sink systems is very significant to understand the physical, chemical and biological processes on the Earth’s surface. Based on long-term records of water discharge, sediment, riverbed morphology and estuarine hydrology along the mega-Changjiang estuary are holistically presented. The estuary bifurcates at four islands, Chongming, Hengsha, Changxing and Jiuduan Shoal, forming a 3-tiered branching delta that has 4 distributary mouths debouching in the East China Sea (North Branch, North Channel, North Passage, and South Passage).

(1)     The results indicate that morphodynamic process of the Changjiang estuary has experienced greatly changes in recent 50 years. The North Branch (NB), a tidally-dominated distributary of the Changjiang estuary, has displayed distinct morphological patterns. Two basic morphological patterns have characterized the evolution of the NB in the last 50 years. The dominant pattern is a reduction of the entire channel volume, accompanied with erosion at the estuary mouth, and aggradation of the tidal bars. The second pattern represents variations in channel volume below -5 m. The 70% reduction of the Changjiang sediment load seems not having an impact on the NB morphology, while reclamation of the intertidal area along the NB is directly responsible for the reduction of the NB tidal prism. Enhanced flood-tidal currents have possibly carried sediments into the NB between 1958 and 2013 reducing the channel volume below 0 m. Enhanced tidal asymmetry due to lower water depths has likely favored tidal pumping, one of the main processes responsible for silting.

(2)     North Channel (NC), the largest bifurcated estuary of the Changjiang River, Channel capacity of the entire NC has been decreasing during the period 1880-2013. Although the upper reach (inner side of the mouth bar) has exhibited significant erosion in channel volume below −5 m during 1970-2013, this is overruled by the dramatic deposition in the lower reach (mouth bar area and its outer side). Bathymetric variations of the NC are dominated by both the upstream sediment availability and the relative strength between the river discharge and local tidal force. While the recent period, erosion in the upper reach is attributed to riverine sediment declining, particularly since 2003 when the TGD was established. In contrast, deposition along the lower reach since 2003 can be explained by landward sediment transport due to the flood-tide force increasing under the combined effects of a decrease in TGD-induced river discharge and land reclamation induced lower reach narrowing.

 (3)     The North Passage (NP), where the main shipping channel of the Changjiang waterway is located, has been continually dredged from the average depth less than 7 m to the present day 12.5 m using trailing-suction hopper dredgers. Our findings show that there are two modes of bathymetric changes. The first mode represents 85% of the variability, which includes the deposition in the peripheral groin fields along the shipping channel and deepening of the shipping channel, which is primarily due to the channel maintenance. The second mode represents 6% of the variability of the river-mouth shoal (seaward migration and size reduction), attributable to the declining sediment discharge of the Changjiang due to the Three Gorges Dam, and the enhancement of the ebb flow as the result of dredging.

 (4)     Morphological evolution of the South Passage (SP) could be divided into two stages: between 1987 and 1997, the SP had a single stable channel with closure of a cross-channel. Between 1997 and 2012, SP displayed southeastward elongation of a spit into the main channel, and westward shoal incision by a cross channel. The opening of the SP developed a two-channel morphology, which stabilized and showed infilling during 2003-2012. The average deposition rate was 10 cm/yr. In the past 30 years, the most dominant morphological changes of SP included the deposition around the upstream opening of the channel. The second most important pattern of morphological change was related to the downstream elongation, retreat, and lateral migration of the spit of the Jiangyanan Shoal, which resulted in the two channel configuration of the SP. Additionally, these morphological changes were not triggered by the decline of the distal sediment source from the upstream, but due to the input of proximal sources of the shoal at the upstream opening of the SP and spill-over sediment from the North Passage via a short-cut channel.

We conclude that rising sea levels and frequent storms may terminate landward sediment transport, aggravating estuary erosion and inducing seaward sediment transport. It can be expected that erosion could occur in the near future in the Changjiang estuary delta.