An investigation of dispersion characteristics in shallow coastal waters

Yingying Yu, Hong Zhang, David Spencer, Ryan J K Dunn, Charles Lemckert

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Hydrodynamic dispersion has a significant impact on the mass transport of sediments and contaminants within coastal waters. In this study apparent horizontal dispersion in a tidally-dominated shallow estuary was investigated using field observations and a numerical model. A cluster of four Lagrangian drifters was released in two shallow regions inside Moreton Bay, Australia: between two small islands and in an open water area. During a 16-h tracking period, the drifters generally showed similar behaviour, initially moving with the dominant current and remaining together before spreading apart at the change of tide. Two dispersion regimes were identified, a slow dispersion during the earlier stage and a rapid dispersion during the latter stage of deployment. Such change in regime typically occurred during the succeeding ebb or flow tides, which may be attributable to residual eddies breaking down during reversal of tidal direction. In addition, a power function of the squared separation distance over the apparent dispersion coefficient produced an R2 exceeding 0.7, indicating a significant relationship between them. By applying a three-dimensional hydrodynamic model, the trajectories of artificial particles spreading in the bay were simulated, which allowed the calculation of dispersion coefficients throughout the entire bay. The study results demonstrate that the tidal effects on dispersion were dependent on the effect of tidal excursion and residual current. The tide was found to be the most dominant driver of dispersion in the bay when unobstructed by land; however, bathymetric and shoreline characteristics were also significant localised drivers of dispersion between the two islands as a result of island wake.

Original languageEnglish
Pages (from-to)21-32
Number of pages12
JournalEstuarine, Coastal and Shelf Science
Volume180
DOIs
Publication statusPublished - 5 Oct 2016
Externally publishedYes

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coastal water
tides
tide
drifter
hydrodynamic dispersion
hydrodynamics
mass transfer
mass transport
trajectories
open water
estuaries
shoreline
eddy
trajectory
estuary
sediments
pollutant
sediment

Cite this

Yu, Yingying ; Zhang, Hong ; Spencer, David ; Dunn, Ryan J K ; Lemckert, Charles. / An investigation of dispersion characteristics in shallow coastal waters. In: Estuarine, Coastal and Shelf Science. 2016 ; Vol. 180. pp. 21-32.
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An investigation of dispersion characteristics in shallow coastal waters. / Yu, Yingying; Zhang, Hong; Spencer, David; Dunn, Ryan J K; Lemckert, Charles.

In: Estuarine, Coastal and Shelf Science, Vol. 180, 05.10.2016, p. 21-32.

Research output: Contribution to journalArticle

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AB - Hydrodynamic dispersion has a significant impact on the mass transport of sediments and contaminants within coastal waters. In this study apparent horizontal dispersion in a tidally-dominated shallow estuary was investigated using field observations and a numerical model. A cluster of four Lagrangian drifters was released in two shallow regions inside Moreton Bay, Australia: between two small islands and in an open water area. During a 16-h tracking period, the drifters generally showed similar behaviour, initially moving with the dominant current and remaining together before spreading apart at the change of tide. Two dispersion regimes were identified, a slow dispersion during the earlier stage and a rapid dispersion during the latter stage of deployment. Such change in regime typically occurred during the succeeding ebb or flow tides, which may be attributable to residual eddies breaking down during reversal of tidal direction. In addition, a power function of the squared separation distance over the apparent dispersion coefficient produced an R2 exceeding 0.7, indicating a significant relationship between them. By applying a three-dimensional hydrodynamic model, the trajectories of artificial particles spreading in the bay were simulated, which allowed the calculation of dispersion coefficients throughout the entire bay. The study results demonstrate that the tidal effects on dispersion were dependent on the effect of tidal excursion and residual current. The tide was found to be the most dominant driver of dispersion in the bay when unobstructed by land; however, bathymetric and shoreline characteristics were also significant localised drivers of dispersion between the two islands as a result of island wake.

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