Sediment transport and mixing depth on a coral reef sand apron

Vila-Concejo, Ana, Harris, Daniel L., Power, Hannah E., Shannon, Amelia M. and Webster, Jody M. (2014) Sediment transport and mixing depth on a coral reef sand apron. Geomorphology, 222 143-150. doi:10.1016/j.geomorph.2013.09.034

Author Vila-Concejo, Ana
Harris, Daniel L.
Power, Hannah E.
Shannon, Amelia M.
Webster, Jody M.
Title Sediment transport and mixing depth on a coral reef sand apron
Journal name Geomorphology   Check publisher's open access policy
ISSN 0169-555X
Publication date 2014-10-01
Year available 2013
Sub-type Article (original research)
DOI 10.1016/j.geomorph.2013.09.034
Open Access Status Not yet assessed
Volume 222
Start page 143
End page 150
Total pages 8
Place of publication Amsterdam, Netherlands
Publisher Elsevier BV
Language eng
Formatted abstract
This paper investigates the mechanics of sediment transport on a subtidal sand apron located on a coral reef environment. In this environment 100% of the sediment is carbonate bioclasts generated in situ. The sand apron is located on the back reef and only affected by waves during high tides. It is commonly accepted in the literature that sand aprons are features that prograde lagoonwards and that most of the progradation occurs during high-energy events. Measurements of water depths, waves, currents and near bed suspended sediment concentrations (all at 10 Hz) on the sand apron were undertaken over a nine day intensive field campaign over both spring and neap tides; waves and tides were also measured in the lagoon. The topography and bathymetry of the sand apron were measured and mixing depth was obtained on three transects using depth of disturbance rods. We found that sediment transport on sand aprons is not solely restricted to high-energy events but occurs on a daily basis during spring tides. The main factor controlling the sediment transport was the water depth above the bed, with depths of 2–2.3 m allowing waves to promote the most sediment transport. This corresponds to a depth over the reef crest of 1.6–1.9 m. The second most important control was waves; transport was observed when Hs on the apron was 0.1 m or greater. In contrast, current magnitude was not a controlling mechanism for sediment entrainment but did affect sediment transport. The morphology of the sand apron was shown to affect the direction of currents with the currents also expected to influence the morphology of the sand apron. The currents measured during this field campaign were aligned with a shallow channel in the sand apron. Mixing depths were small (< 2.5 cm) yet they were larger than the values predicted by empirical formulae for gentle siliciclastic ocean beaches.
Keyword Carbonate sand
Coral reef morphodynamics
Coral sand
Depth of disturbance
Sand sheet
Q-Index Code C1
Q-Index Status Provisional Code
Grant ID FT100100215
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Earth Sciences Publications
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Citation counts: TR Web of Science Citation Count  Cited 7 times in Thomson Reuters Web of Science Article | Citations
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