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Abstract: Headland-associated linear sandbanks are a specific type of sandbanks 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. A morphological model, using a three-dimensional hydrodynamic model, has been developed in order to determine the mechanisms responsible for the formation of the sandbanks. The model has been applied to an idealised gaussian shaped headland and long-term simulation have been undertaken. Sandbanks are created on each side of the headland but are not located in the centre of the tidal residual eddy as suggested previously. The sandbanks modify the tidal current residual as they grow. Their growth is controlled by the tidal regime, the availability of sand, the sediment grain size and the presence of secondary flows. Sandbanks are formed due to the asymmetry in the sediment transport on each side of the bank, due to the reversing tidal flow. They initially develop as a circular shape and then evolve into a more elongated shape. [Copyright &y& Elsevier]

Abstract: The complex three-dimensional tidal flow measured in the vicinity of a headland-associated linear sandbank near Cape Levillain and the Levillain Shoal (Shark Bay, Western Australia) is described. The measurements included moored instruments (current meters, ADCP), shipborne ADCP transects, and drifters. Eulerian and Lagrangian current measurements provided a detailed description of the hydrodynamics. Results showed the presence of strong currents near the headland, reversal of currents veering towards the bank during the flood and ebb, and the formation of a transient eddy around the bank at slack water. Throughout the tidal cycle, secondary currents were present at the headland, with secondary flow near the seabed directed towards the headland and surface secondary flow directed away from the headland. Near the bank, near-bed secondary flows were directed towards the centre of the bank on both flanks at both the flood and ebb phases of the tide. Based on the detailed hydrodynamic data, a conceptual model for sediment transport pathways near the sandbank is proposed. The sandbank appears to be part of a sand circulation cell where the sand circulates around the bank with exchanges between the sandbank and the headland. [Copyright &y& Elsevier]

Linear sandbanks are located globally in areas where there are strong currents and an abundance of sand. In the recent years, these sandbanks have become of strategic interest as a potential source of marine aggregates (sand and gravel) and mineral deposits. They form the seaward boundary of the nearshore zone and therefore are important for the stability of the coastal system. They also commonly reach the sea surface and thus pose a threat to navigation. Headland-associated linear sandbanks are a specific type of sandbanks 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 re-produced in the numerical simulations. Numerical results have shown that residual eddies are not representative of the sediment transport and that secondary currents enhance the convergence of sediment towards the sandbank. Maintenance processes have been investigated. 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. [ABSTRACT FROM AUTHOR]