Sources of Drag in Estuarine Meanders: Momentum Redistribution, Bottom Stress Enhancement, and Bend-Scale Form Drag
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phoc-JPO-D-22-0211.1.pdf
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Author(s)
Bo, Tong
Ralston, David
Geyer, And
Date Issued
July 3, 2023
Journal
Journal of Physical Oceanography
Publisher
American Meteorological Society
Citation
Bo, T., D. K. Ralston, and W. R. Geyer, 2023: Sources of Drag in Estuarine Meanders: Momentum Redistribution, Bottom Stress Enhancement, and Bend-Scale Form Drag. J. Phys. Oceanogr., 53, 1629–1650.
Version
Final published version
Abstract
Curvature can create secondary circulation and flow separation in tidal channels, and both have important consequences for the along-channel momentum budget. The North River is a sinuous estuary where drag is observed to be higher than expected, and a numerical model is used to investigate the influence of curvature-induced processes on the momentum distribution and drag. The hydrodynamic drag is greatly increased in channel bends compared to that for straight channel flows. Drag coefficients are calculated using several approaches to identify the different factors contributing to the drag increase. Flow separation creates low-pressure recirculation zones on the lee side of the bends and results in form drag. Form drag is the dominant source of the increase in total drag during flood tides and is less of a factor during ebb tides. During both floods and ebbs, curvature-induced secondary circulation transports higher-momentum fluid to the lower water column through vertical and lateral advection. Consequently, the streamwise velocity profile deviates from the classic log profile and vertical shear becomes more concentrated near the bed. This redistribution by the lateral circulation causes an overall increase in bottom friction and contributes to the increased drag. Additionally, spatial variations in the depth-averaged velocity field due to the curvature-induced flow are nonlinearly correlated with the bathymetric structure, leading to increased bottom friction. In addition to affecting the tidal flow, the redistributed momentum and altered bottom shear stress have clear implications for channel morphodynamics.
Subjects
Estuaries
Channel flows
Secondary circulation
Boundary layer
Tides
Numerical analysis/modeling
Terms of Use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
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DOI of Published Version
https://doi.org/10.1175/JPO-D-22-0211.1
