Bedform facies in western Torres Strait and the influence of hydrodynamics, coastal geometry, and sediment supply on their distribution

• Six bedforms facies are presented in the form of a map for western Torres Strait
• Coastal Geometry influence north/south variations in bedform morphology
• Hydrodynamics influence the east/west variations in bedform morphology
• Bedform sequences indicate sediment is trapped in the central part of the strait
• The sand ribbon facies is previously unreported in the scientific literature

This study uses outputs from hydrodynamic and bedload transport models combined with satellite imagery, aerial photography, and bathymetric data to understand the distributions and mechanisms maintaining six spatially extensive bedform facies in western Torres Strait. Changes in bedform morphology occur along north–south variations in coastal geometry and east–west variations in hydrodynamic regime. Numerous islands create an environment that favours the formation of banner banks in the south, while other sandbank morphologies occur on an extensive and comparatively ‘flat’ basement to the north. The western side of Torres Strait experiences net bedload transport that is directed to the west throughout the year and favours the formation of bedforms that prefer unidirectional bedload transport regimes (i.e. barchan-shaped sandbanks and sand ribbons). The eastern side of the strait experiences seasonal changes in the direction of net bedload transport and maintains ‘S’ and ‘V’ shaped sandbanks.Sediment availability also influences the bedform facies. Western Torres Strait experiences net westward bedload transport through the Strait. However, sandbanks (indicating high sediment availability) are found in the central shallow and high current velocity areas, while sand ribbons (indicating low sediment availability) are a distal facies on the western side of the Strait. This sequence of bedforms indicates that sediments are preferentially trapped within the central portion of the Strait and not transported further west into the Gulf of Carpentaria.