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Field Studies and 3D Modelling of Morphodynamicsin a Meandering River Reach Dominated by Tides and Suspended Load
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0003-0820-617x
Vattenfall AB, Älvkarleby; Royal Institute of Technology, Stockholm, Sweden.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0002-1033-0244
2019 (English)In: Fluids, ISSN 2311-5521, Vol. 4, no 1, article id 15Article in journal (Refereed) Published
Abstract [en]

Meandering is a common feature in natural alluvial streams. This study deals with alluvial behaviors of a meander reach subjected to both fresh-water flow and strong tides from the coast. Field measurements are carried out to obtain flow and sediment data. Approximately 95% of the sediment in the river is suspended load of silt and clay. The results indicate that, due to the tidal currents, the flow velocity and sediment concentration are always out of phase with each other. The cross-sectional asymmetry and bi-directional flow result in higher sediment concentration along inner banks than along outer banks of the main stream. For a given location, the near-bed concentration is 2−5 times the surface value. Based on Froude number, a sediment carrying capacity formula is derived for the flood and ebb tides. The tidal flow stirs the sediment and modifies its concentration and transport. A 3D hydrodynamic model of flow and suspended sediment transport is established to compute the flow patterns and morphology changes. Cross-sectional currents, bed shear stress and erosion-deposition patterns are discussed. The flow in cross-section exhibits significant stratification and even an opposite flow direction during the tidal rise and fall; the vertical velocity profile deviates from the logarithmic distribution. During the flow reversal between flood and ebb tides, sediment deposits, which is affected by slack-water durations. The bed deformation is dependent on the meander asymmetry and the interaction between the fresh water flow and tides. The flood tides are attributable to the deposition, while the ebb tides, together with run-offs, lead to slight erosion. The flood tides play a key role in the morphodynamic changes of the meander reach.

Place, publisher, year, edition, pages
MDPI, 2019. Vol. 4, no 1, article id 15
Keywords [en]
tidal meandering river, field measurements, 3D numerical model, flow features, sediment transport, erosion-deposition patterns
National Category
Water Engineering Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-72664DOI: 10.3390/fluids4010015OAI: oai:DiVA.org:ltu-72664DiVA, id: diva2:1282135
Note

Validerad;2019;Nivå 2;2019-01-31 (svasva)

Available from: 2019-01-24 Created: 2019-01-24 Last updated: 2019-01-31Bibliographically approved

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Xie, QianchengLundström, Staffan

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4142434445464744 of 66
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