Mechanisms for the formation of headland-associated linear sandbanks

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.