Linear sandbanks are located globally in areas where there are strong currents and an abundance of sand. In recent years, these sandbanks have become a strategic interest as a potential source of marine aggregates (sand and gravel) and mineral deposits. They also commonly reach the sea surface and thus pose a threat to navigation. Headland-associated linear sandbanks are a specific type of sandbank, which are located in the lee of coastal topographic features such as headlands and islands. Interaction between tidal currents and topographic features generate complex three-dimensional circulation patterns that significantly influence the distribution of sediments in the vicinity of the feature. Field and numerical model investigations of the three-dimensional flow structure have been undertaken on the Levillain Shoal, a headland-associated linear sandbank present in the lee of Cape Levillain (Shark Bay, Western Australia). The field data indicated the presence of secondary flows near the tip of the Cape and around the bank, which were reproduced in the numerical simulations. Sediment transport paths near the Cape and the bank indicate that the sandbank is part of a sand circulation cell where the sand is circulating around the bank with exchanges between the sandbank and the headland. A morphological model (MTM) has been developed to understand processes responsible for the formation of the headland associated linear sandbanks. With an “idealized” Gaussian shaped headland, the formation of two symmetrical sandbanks on each side of the headland is observed. It is shown that sandbanks are formed in regions where there is a net accumulation of sand over a tidal cycle, due to the acceleration/⁄deceleration effects of the flow in the presence of the headland. Initially, sandbanks develop in a circular shape and grow vertically. As the sandbanks interact with the tidal flow, they evolve into elongated linear deposits (as observed in nature). The sandbank growth is dependent on the tidal regime, secondary flow, sand availability, and sediment grain size
| Identifer | oai:union.ndltd.org:ADTP/221116 |
| Date | January 2005 |
| Creators | Berthot, Alexis |
| Publisher | University of Western Australia. Centre for Water Research |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Alexis Berthot, http://www.itpo.uwa.edu.au/UWA-Computer-And-Software-Use-Regulations.html |
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