Decadal link between longitudinal morphological changes in branching channels of Yangtze estuary and movement of the offshore depo‐center. Issue 11 (26th June 2020)

• Record Type: Journal Article
• Authors: Zhu, Boyuan; Yue, Yao; Borthwick, Alistair G.L.; Yu, Wenjun; Liang, Enhang; Tang, Jinwu; Chai, Yuanfang; Li, Yitian
• Is Part Of: Earth surface processes and landforms. Volume 45:Issue 11(2020)
• Page Start: 2689
• Page End: 2705
• Publication Date: 2020-06-26
• Subjects: Yangtze estuary -- longitudinal evolution -- depo‐center movement -- ebb partition ratio -- runoff discharge -- human interference; Geomorphology -- Periodicals; 551.4
• DOI: 10.1002/esp.4923
• Languages: English
• ISSNs: 0197-9337

Abstract

Abstract: In estuaries, the morphology of inland and offshore areas usually evolves synergistically. This study examines the decadal link between longitudinal changes in morphology of branching channels and movement of the offshore depo‐center (where sediment deposition rate is maximum) of the Yangtze River estuary, under intense human interference. Integrated data analysis is provided on morphology, runoff discharge, and ebb partition ratio from 1950 to 2017. Channel‐volume reductions and change rates between isobaths in branching channels reflect the impact of estuarine engineering projects. Ebb partition ratio and duration of discharge ≥ 60 000 m 3 s ‐1 act as proxies for the water excavating force in branching channels and runoff intensity. It is found that deposition occurs in the lower/upper sub‐reaches (or further downstream/upstream channels) of the inland north/south branching channels, and the offshore depo‐center moves southward or southeastward, as runoff intensity grows; the reverse occurs as runoff intensity declines. This is because the horizontal circumfluence in the Yangtze estuary rotates clockwise as ebb partition ratios of the north/south branching channels increase/decrease for increasing runoff, and conversely rotates anticlockwise for decreasing runoff. Land reclamation activities, the Deepwater Channel Project, and the Qingcaosha Reservoir have impacted greatly on longitudinal changes of morphology in the North Branch and the South Passage and on ebb partition ratio variations in the North/South Channel and the North/South Passage. Dam‐induced runoff flattening has enhanced deposition in the upper/lower sub‐reaches of the north/south branching channels and caused northward movement of the offshore depo‐center, except in areas affected by estuarine engineering projects. Dam‐induced longitudinal evolution of branching channel morphology and offshore depo‐center movement will likely persist in the future, given the ongoing construction of large cascade dams in the upper Yangtze and the completion of major projects in the Yangtze estuary. © 2020 John Wiley & Sons, Ltd. Abstract : As runoff rises/falls, deposition within inland north/south branching channels usually occurred in lower/upper and upper/lower sub‐reaches, with the offshore depo‐center moving southward (southeastward)/northward. Major estuarine engineering projects disturbed longitudinal morphological changes and caused variations in ebb partition ratios for certain inland branching channels. Under dam‐induced runoff flattening, major depositional areas within inland north/south branching channels and the offshore depo‐center have generally experienced historical trends of upstream, downstream, and northward movement, which are likely to be maintained in the future.