PIANC Smart Rivers 2022

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Abstract : *(250~1000 words)

As the intermediate connecting reach in the Changjiang River Estuary, China, for a long time, the South Channel’s evolution was often directly affected by the upper reach as the South Branch, and the lower reaches as the North and South Passages, to a certain extent. However in recent two decades, following the construction and execution of many large scale water conservancy projects as the Three Gorges Project and the South-to-North Water Diversion Project in the main stream of the Changjiang River, as well as the construction of the Deepwater Channel Regulation Project, the incoming water and sediment loads from upper river basin and lower outside sea have appeared obviously changes. These would inevitably adjust the latest evolution tendency of the South Channel, which would obviously differ from that two decades ago. 
In order to deeply reveal the evolution tendency of the South Channel in past half century, underwater topography data of the South Channel in different historical period during past 50years were adopted and digitized, then the evolution of river regimes, thalwegs, cross sections, channel volumes and river sedimentation was analyzed in detail. 
	The result showed that, after 1970s two side banks of the South Channel were basically fixed, owing to continues constructions of revetment engineering. Then the evolution of the river reach were mainly dominated by inner erosion and deposition in the river beach and channel. The river regime had undergone three stages, they were respectively as natural dynamic stability stage before 1980s, natural dynamic adjustment stage before 2000 and artificial dynamic adjustment stage till now. Correspondingly, in the first stage the main channel was in basically stable state and the annual erosion and sedimentation were basically below 1.0m; during the second stage, the channel appeared obvious erosion, the 10m isobath even extended to the lower North Passage; in the third stage, due to influences of many large scale water conservancy project, the north and south channel sustained development and their evolution presented distinctly artificial characteristics. Meanwhile, the cross section characteristics of the river reach also presented obviously alternative variation, which was represented by alternative development of the south channel and north channel. And the depth of thalwegs of the river reach also presented significant variation between 10~20m, which always changed with the variation of cross sections. Furthermore, with the impact of incoming water discharge being almost invariant and incoming sediment decreasing gradually, volume of the South Channel under the 0m depth(theoretically lowest tide level) present increasing tendency as a whole.

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