Exploration of Decadal Tidal Evolution in Response to Morphological and Sedimentary Changes in the Yangtze Estuary. Issue 9 (7th September 2021)

• Record Type: Journal Article
• Authors: Zhu, Chunyan; Guo, Leicheng; van Maren, D. S.; Wang, Zheng Bing; He, Qing
• Is Part Of: Journal of geophysical research. Volume 126:Issue 9(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-09-07
• Subjects: tidal damping -- morphological change -- roughness -- human activities -- Yangtze Estuary; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2020JC017019
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Estuarine tidal dynamics are influenced by changes in morphology and friction. In this work, we quantified changes in tidal damping in the Yangtze Estuary and explored the impact of morphology and friction using a numerical model. In‐depth analyses of tidal data reveal a strong reduction in tidal damping from 1990 to 2010, followed by a slightly enhanced damping from 2010 to 2020 in the South Branch. The reduced tidal damping in the South Branch from 1990 to 2010 is controlled by sediment decline which induces an increase in water depth (erosion), thereby strongly amplifying tides. However, the effective bottom roughness (Manning coefficient) is increased by 60%, which is probably related to the ∼ 80% decrease in the suspended sediment concentration (SSC). Such an effect may enhance tidal damping, which counteracts the contribution of water depth increase on amplifying tides by ∼ 75%. From 2010 to 2020, the tides in the South Branch became more damped, suggesting a dominance of the decrease in SSC over the morphological changes. In the mouth zone, tidal dissipation is enhanced from 1997 to 2010, which is mainly caused by an overall increase in effective bottom roughness. Local structures dominate the increase in effective bottom roughness; however, fluid mud formation may contribute to a decrease after 2010. Overall, we argue that estuarine morphological and sedimentary changes in response to riverine sediment decline and local engineering works control the tidal evolution in the Yangtze Estuary, which is important for evaluation of human activities and estuarine management. Plain Language Summary: In many estuaries, human interventions have strongly influenced bed levels and sedimentary features (e.g., sediment concentration, sediment grain size), which led to consequent changes in tidal dynamics. In this study, we investigated decadal changes in the tidal propagation in the Yangtze Estuary from field data and explored the mechanisms responsible for these changes using a numerical model. This study suggests that tidal damping is weakened in the South Branch and enhanced in the mouth zone of the Yangtze Estuary. Local structures enhance tidal damping, whereas a reduction in riverine sediment supply has a more complex response by influencing bed roughness and bed levels. These findings are important for understanding and management of morphodynamic changes in strongly engineered estuaries. Key Points: Tidal damping was stronger in the mouth zone of the Yangtze Estuary since 1997, mainly due to an increase in the effective bottom roughness This increase in the effective bottom roughness in the mouth zone is mainly the result of local engineering works Reduced sediment supply amplified tides in the South Branch via its effects on morphology but weakened tides through its effect on friction