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Hydrodynamics of Meander Bends in Intertidal Mudflats: a Field Study From the Macrotidal Yangkou Coast, China
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  • Chao Gao,
  • Alvise Finotello,
  • Andrea D'Alpaos,
  • Massimiliano Ghinassi,
  • Luca Carniello,
  • Yupeng Pan,
  • Dezhi Chen,
  • Ya Ping Wang
Chao Gao
Ministry of Education Key Laboratory for Coast and Island Development, Ministry of Education Key Laboratory for Coast and Island Development, Ministry of Education Key Laboratory for Coast and Island Development
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Alvise Finotello
Dept. of Geosciences, University of Padova, Dept. of Geosciences, University of Padova, Dept. of Geosciences, University of Padova
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Andrea D'Alpaos
University of Padova, University of Padova, University of Padova
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Massimiliano Ghinassi
Università di Padova, Università di Padova, Università di Padova
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Luca Carniello
Department of Civil, Environmental, and Architectural Engineering, University of Padova, Department of Civil, Environmental, and Architectural Engineering, University of Padova, Department of Civil, Environmental, and Architectural Engineering, University of Padova
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Yupeng Pan
Nanjing University, Nanjing University, Nanjing University
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Dezhi Chen
Nanjing University, Nanjing University, Nanjing University
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Ya Ping Wang
Nanjing University, Nanjing University, Nanjing University

Corresponding Author:[email protected]

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Abstract

Meandering channels are ubiquitous features in intertidal mudflats and play a key role in the eco-morphosedimentary evolution of such landscapes. However, the hydrodynamics and morphodynamic evolution of these channels are poorly known, and direct flow measurements are virtually nonexistent to date. Here, we present new hydroacoustic data collected synchronously at different sites along a mudflat meander located in the macrotidal Yangkou tidal flat (Jiangsu, China) over an 8-day period. The studied bend exhibits an overall dominance of flood flows, with velocity surges of about 0.8 m/s occurring immediately below the bankfull stage during both ebb and flood tides. Unlike salt-marsh channels, velocities attain nearly-constant, sustained values as long as tidal flows remain confined within the channel, and reduce significantly during overbank stages. In contrast, curvature-induced cross-sectional flows are more pronounced during overbank stages. Thus, a phase lag exists between streamwise and cross-stream velocity maxima, which limits the transfer of secondary flows and likely hinders the formation of curvature-induced helical flows along the entire meander length. Our results support earlier suggestions that the morphodynamics of intertidal mudflat meanders does not strongly depend on curvature-induced helical flows, and is most likely driven by high velocities and sustains seepage flows at late-ebb stages, as well as by other non-tidal processes such as waves and intense rainfall events. By unraveling complex flow structures and intertwined morphodynamic processes, our results provide the first step toward a better understanding of intertidal mudflat meanders, with relevant implications for their planform characteristics and dynamic evolution.
Dec 2022Published in Water Resources Research volume 58 issue 12. 10.1029/2022WR033234