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Understanding morphodynamic changes of a tidal river confluence through field measurements and numerical modeling
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0003-0820-617x
Division of Resources, Energy and Infrastructure, Royal Institute of Technology (KTH), Stockholm, Sweden; Vattenfall AB, Research and Development (R and D), Älvkarleby Laboratory, Älvkarleby, Sweden.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0002-1033-0244
College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing, China.
2018 (English)In: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 10, no 10, article id 1424Article in journal (Refereed) Published
Abstract [en]

A confluence is a natural component in river and channel networks. This study deals, through field and numerical studies, with alluvial behaviors of a confluence affected by both river run-offand strong tides. Field measurements were conducted along the rivers including the confluence. Field data show that the changes in flow velocity and sediment concentration are not always in phase with each other. The concentration shows a general trend of decrease from the river mouth to the confluence. For a given location, the tides affect both the sediment concentration and transport. A two-dimensional hydrodynamic model of suspended load was set up to illustrate the combined effects of run-offand tidal flows. Modeled cases included the flood and ebb tides in a wet season. Typical features examined included tidal flow fields, bed shear stress, and scour evolution in the confluence. The confluence migration pattern of scour is dependent on the interaction between the river currents and tidal flows. The flood tides are attributable to the suspended load deposition in the confluence, while the ebb tides in combination with run-offs lead to erosion. The flood tides play a dominant role in the morphodynamic changes of the confluence. 

Place, publisher, year, edition, pages
MDPI, 2018. Vol. 10, no 10, article id 1424
Keywords [en]
tidal river confluence, flow features, morphological changes, field measurements, numerical simulations
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-71350DOI: 10.3390/w10101424ISI: 000451208400139Scopus ID: 2-s2.0-85054725343OAI: oai:DiVA.org:ltu-71350DiVA, id: diva2:1258920
Note

Validerad;2018;Nivå 2;2018-10-26 (svasva)

Available from: 2018-10-26 Created: 2018-10-26 Last updated: 2019-04-04Bibliographically approved
In thesis
1. Field Measurements and Numerical Simulations of Sediment Transport in a Tidal River
Open this publication in new window or tab >>Field Measurements and Numerical Simulations of Sediment Transport in a Tidal River
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In a coastal area, an alluvial lowland river has a free connection with the open sea and its flow is bidirectional. The river basin is often highly urbanized since it hosts valuable ecosystems and natural resources. Along with the growing population, climate change and human activities (e.g., industrialization, agricultural expansion, and fishery industry) pose a significant threat to the health of the river, leading to an unbalance of the flow and the sedimentation and also a considerable degradation of water quality.

With long-term alluvial processes, the river often displays patterns such as meandering, braided, straight, wandering and anastomosing. In addition to the irregular geometry and bathymetry, a tidal river is typically influenced by the freshwater-saltwater interplay, which makes the hydrodynamic processes and sediment transport patterns extremely complicated. For many tidal river systems, cohesive sediment transported with the tides plays an important role. This is not only because of its interaction with flow but also due to its link to bed deformation.

In this thesis, field measurements and numerical simulations of flow and sedimentation in a system, including a confluence and a meandering reach are presented and discussed. The numerical simulations are performed with the Delft3D package, which allows a coupling between complex river geometry, the bathymetry, the flow and the sediment boundaries in one module. Two morpho-dynamic models, a 2D depth-averaged model for the confluence and a 3D model for the meandering reach, are set up to disclose the fluvial processes in respective area.

The objective of this thesis is, by means of extensive field measurements and numerical simulations, investigate flow features and sediment movement patterns in a tidal river. A comparatively long-term river-bed change, including a scour-hole at the confluence and asymmetric cross-sections at the bends, are also examined. Based on the perturbation theory, an improved sediment carrying capacity formula is also derived being suitable for calculations in a tidal environment. This study explores the variability of sediment transport, and reveals the relationship between the flow velocity and suspended load influenced by both the run-off and the tides. Their interactions also generate a different morphological regime as compared to a non-tidal river reach.

This research may support a decision‐making process when considering the integrated tidal river management and it also provides a reference for other similar situations. The calibrated and validated model may therefore be a powerful tool for managers or researchers.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2019
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-73423 (URN)978-91-7790-350-5 (ISBN)978-91-7790-351-2 (ISBN)
Presentation
2019-05-22, E231, Luleå university of technology, Luleå, 13:00 (English)
Opponent
Supervisors
Available from: 2019-04-04 Created: 2019-04-04 Last updated: 2019-06-05Bibliographically approved

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