Use of swath bathymetry in the investigation of sand dune geometry and migration around a near shore 'banner' tidal sandbank

Banner tidal sandbanks in the Bristol Channel have been repeatedly surveyed with a multibeam sonar to study the geometry and migration patterns of superimposed dunes. The data presented in this paper constitute one of the first studies concerned with sediment transport around a banner sandbank (Helwick Sands in the Bristol Channel) using repeated swath- bathymetry. The data reveal that the dunes maintain their shapes over a period of 11 months, and that they migrate in opposite directions on the alternate sides of the bank. Curiously, dunes connect over the crest of the bank despite opposing sediment transport directions on the flanks. Dune height increases with water depth as found in similar environments. We suggest how the morphology of the dunes results from the complex interaction between surface waves and tidal currents that occurs within the proximity of the headland. © The Geological Society of London 2007.