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Bedload sediment transport dynamics in a macrotidal embayment, and implications for export to the southern Great Barrier Reef shelf |
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| Authors: | David A Ryan Brendan P Brooke Helen C Bostock Lynda C Radke Paulus JW Siwabessy Nugzar Margvelashvili Darren Skene |
| Institution: | bDepartment of Applied Geology, Curtin University of Technology, Perth, Western Australia, 6102, Australia cCentre for Marine Science and Technology, Curtin University of Technology, GPO Box U1987, Perth, Western Australia, 6845, Australia dCSIRO Marine and Atmospheric Research, Castray Esplanade, Hobart, Tasmania, 7001, Australia eBonaparte Diamond Mines NL, PO Box 1153, West Perth, Western Australia, 6872 ePetroleum and Marine Division, Geoscience Australia, Canberra, Australian Capital Territory, 2601, Australia |
| Abstract: | Keppel Bay is a macrotidal embayment on a tectonically stable, tropical coast, which links the Fitzroy River with the Great Barrier Reef continental shelf. Estuaries and deltas act as conduits between catchments and inner shelf environments. Therefore, understanding sediment transport pathways in these complex systems is essential for the management of ecosystems such as coral-reefs that are potentially vulnerable to enhanced river sediment loads. Furthermore, the morphology and sediment dynamics of subtidal sand ridges and dunes are relatively poorly characterised in macrotidal estuaries, particularly in turbid, episodic systems such as the Fitzroy River and Keppel Bay. Our sedimentological analysis of seabed samples, shear-stress modelling and three-dimensional acoustic imaging reveals that Keppel Bay is a mixed wave- and tide-dominated estuarine system. Areas of sediment starvation and shoreward transport characterise the offshore zone, whereas a complex of both active and relict tidal sand ridges, and associated subaqueous dunes, dominate the relatively protected southern Keppel Bay. Transport within this region is highly dynamic and variable, with ebb-dominated sediment transport through tidal channels into the outer bay where there is a switch to wave-dominated shoreward transport. Ultimately, bedload sediments appear to be reworked back inshore and to the north, and are gradually infilling the bedrock-defined embayment. Our characterisation of the Keppel Bay system provides a detailed example of the physiography of the seaward portion of a tide-dominated system, and shows that sediment transport in these areas is influenced by a variable hydrodynamic regime as well as relict channels and bedrock topography. |
| Keywords: | macrotidal estuaries sediment transport Keppel Bay Fitzroy River Great Barrier Reef |
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