Sources of drag in estuarine meanders: momentum eedistribution, bottom atress wnhancement, and bend-scale form drag
Sources of drag in estuarine meanders: momentum eedistribution, bottom atress wnhancement, and bend-scale form drag
Date
2023-07-01
Authors
Bo, Tong
Ralston, David K.
Geyer, W. Rockwell
Ralston, David K.
Geyer, W. Rockwell
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DOI
10.1175/jpo-d-22-0211.1
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Keywords
Estuaries
Channel flows
Secondary circulation
Boundary layer
Tides
Numerical analysis/modeling
Channel flows
Secondary circulation
Boundary layer
Tides
Numerical analysis/modeling
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.
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Author Posting. © American Meteorological Society, 2023. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 53(7), (2023): 1629–1650, https://doi.org/10.1175/jpo-d-22-0211.1.
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Citation
Bo, T., Ralston, D., & Geyer, W. (2023). Sources of drag in estuarine meanders: momentum redistribution, bottom stress enhancement, and bend-scale form drag. Journal of Physical Oceanography, 53(7), 1629–1650.