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Modelling the influence of riverine inputs on the circulation and flushing times of small shallow estuaries

Modelling the influence of riverine inputs on the circulation and flushing times of small shallow estuaries
Modelling the influence of riverine inputs on the circulation and flushing times of small shallow estuaries

Simple flushing time calculations for estuarine systems can be used as proxies for eutrophication susceptibility. However, more complex methods are required to better understand entire systems. Understanding of the hydrodynamics driving circulation and flushing times in small, eutrophic, temperate estuaries is less advanced than larger counterparts due to lack of data and difficulties in accurately modelling small-scale systems. This paper uses the microtidal Christchurch Harbour estuary in Southern UK as a case study to elucidate the physical controls on eutrophication susceptibility in small shallow basins. A depth-averaged hydrodynamic model has been configured of the estuary to investigate the physical processes driving circulation with particular emphasis on understanding the impact of riverine inputs to this system. Results indicate circulation control changes from tidally to fluvially driven as riverine inputs increase. Flushing times, calculated using a particle tracking method, indicate that the system can take as long as 132 h to flush when river flow is low, or as short as 12 h when riverine input is exceptionally high. When total river flow into the estuary is less than 30 m 3 s −1, tidal flux is the dominant hydrodynamic control, which results in high flushing times during neap tides. Conversely, when riverine input is greater than 30 m 3 s −1, the dominant hydrodynamic control is fluvial flux, and flushing times during spring tides are longer than at neaps. The methodology presented here shows that modelling at small spatial scales is possible but highlights the importance of particle tracking methods to determine flushing time variability across a system.

Estuarine dynamics, Flushing time, Microtidal, Modelling, Shallow, UK, Dorset, Christchurch Harbour, Water quality
1559-2723
1-16
Huggett, Rebecca
4c318b0e-e287-4c67-a0c6-a0cb23581df9
Purdie, Duncan
18820b32-185a-467a-8019-01f245191cd8
Haigh, Ivan
945ff20a-589c-47b7-b06f-61804367eb2d
Huggett, Rebecca
4c318b0e-e287-4c67-a0c6-a0cb23581df9
Purdie, Duncan
18820b32-185a-467a-8019-01f245191cd8
Haigh, Ivan
945ff20a-589c-47b7-b06f-61804367eb2d

Huggett, Rebecca, Purdie, Duncan and Haigh, Ivan (2020) Modelling the influence of riverine inputs on the circulation and flushing times of small shallow estuaries. Estuaries and Coasts, 44 (1), 1-16. (doi:10.1007/s12237-020-00776-3).

Record type: Article

Abstract

Simple flushing time calculations for estuarine systems can be used as proxies for eutrophication susceptibility. However, more complex methods are required to better understand entire systems. Understanding of the hydrodynamics driving circulation and flushing times in small, eutrophic, temperate estuaries is less advanced than larger counterparts due to lack of data and difficulties in accurately modelling small-scale systems. This paper uses the microtidal Christchurch Harbour estuary in Southern UK as a case study to elucidate the physical controls on eutrophication susceptibility in small shallow basins. A depth-averaged hydrodynamic model has been configured of the estuary to investigate the physical processes driving circulation with particular emphasis on understanding the impact of riverine inputs to this system. Results indicate circulation control changes from tidally to fluvially driven as riverine inputs increase. Flushing times, calculated using a particle tracking method, indicate that the system can take as long as 132 h to flush when river flow is low, or as short as 12 h when riverine input is exceptionally high. When total river flow into the estuary is less than 30 m 3 s −1, tidal flux is the dominant hydrodynamic control, which results in high flushing times during neap tides. Conversely, when riverine input is greater than 30 m 3 s −1, the dominant hydrodynamic control is fluvial flux, and flushing times during spring tides are longer than at neaps. The methodology presented here shows that modelling at small spatial scales is possible but highlights the importance of particle tracking methods to determine flushing time variability across a system.

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Huggett 2020 Article Modelling The Influence Of Riverine - Version of Record
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More information

Submitted date: 3 June 2020
Accepted/In Press date: 8 June 2020
e-pub ahead of print date: 1 July 2020
Published date: 1 July 2020
Keywords: Estuarine dynamics, Flushing time, Microtidal, Modelling, Shallow, UK, Dorset, Christchurch Harbour, Water quality

Identifiers

Local EPrints ID: 441896
URI: http://eprints.soton.ac.uk/id/eprint/441896
ISSN: 1559-2723
PURE UUID: a3db0d9e-a1ea-4404-b3cd-2b047b57989a
ORCID for Duncan Purdie: ORCID iD orcid.org/0000-0001-6672-1722

Catalogue record

Date deposited: 01 Jul 2020 16:35
Last modified: 26 Nov 2021 02:32

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