Alternate erosion and deposition in the Yangtze Estuary and its future change

Zhu Boyuan, Yitian Li, Yao Yue, Yunping Yang, Liang Enhang, Alistair Borthwick, Chuncai Zhang

Research output: Contribution to journalArticlepeer-review

Abstract

The morphological changing trend of the Yangtze Estuary, the largest estuary in Asia, has become a focus of research in recent years. Based on a long series of topographic data from 1950 to 2015, this paper studied the erosion-deposition pattern of the entire Yangtze Estuary. Alternating erosion and deposition has occurred during the past 65 years, corresponding to changes between flood and dry periods identified by multi-year average duration days of high-level water flow (defined as discharge ≥ 60,000 m3/s, namely, D≥60,000) from the Yangtze River Basin. A quantitative relationship was proposed between the erosional/depositional rate of the Yangtze Estuary and the interpreting variables of yearly water discharge, D≥60,000 and yearly river sediment load, with contributing proportions of 1%, 59% and 40%, respectively. The mechanism behind the alternate erosion and deposition pattern was analyzed by examining the residual water surface slope and the corresponding sediment transport capacity in flood and dry periods. In flood periods, a larger discharge results in a steeper-sloped residual water level, which permits a greater sediment transport capacity. Therefore, more bed material can be washed to the sea, leading to erosion of the estuary. In contrast, a flatter slope in residual water level occurs in dry periods, and deposition dominates the estuarine area due to the decreased sediment transport capacity and the increased backwater effect of the flood-tide. Coastal dynamics and estuarine engineering projects impacted on local morphological changes, but slightly affected the total erosional/depositional rate of the whole estuarine region. Heavy sedimentation within the Yangtze Estuary after the impoundment of the Three Gorges Dam was attributed to the reduced occurrence frequency of flood years due to water regulation by the dam, and largely (at least 36-52%) sourced from the sea. Deposition could still occur in the Yangtze Estuary in the future, because the multi-year average D≥60,000 is unlikely to exceed the critical value of 14 days/yr corresponding to the future equilibrium state of the Yangtze Estuary, under the water regulation of large cascade dams in the upper Yangtze. Nevertheless, the mean depositional rate is highly unlikely to surpass the peak value of the past years, because of the decreasing trend in total sediment load entering the Yangtze Estuary.
Original languageEnglish
Pages (from-to)145-163
JournalJournal of Geographical Sciences
Volume30
Issue number1
Early online date6 Jan 2020
DOIs
Publication statusE-pub ahead of print - 6 Jan 2020

Keywords

  • Yangtze Estuary
  • erosion and depsition
  • alternation
  • total sediment load
  • evolutional trend

Fingerprint

Dive into the research topics of 'Alternate erosion and deposition in the Yangtze Estuary and its future change'. Together they form a unique fingerprint.

Cite this