Barchan Dune (Subaqueous)

A subaqueous barchan dune is a crescent-shaped, flow-transverse sand bedform whose horns point downstream, the underwater analogue of the aeolian barchan. It forms under unidirectional or strongly asymmetric tidal flow where sand supply is limited, so isolated crescents develop on a non-erodible or starved bed rather than a continuous dune field. The gentle stoss side faces upstream, the steep lee slip face faces downstream, and the whole form migrates downcurrent as sand avalanches down the lee. In the Ashley (1990) scheme it is a 3-D dune defined by crescentic, barchanoid crest shape. Barchan trains mark the dominant transport direction on swept shelf and channel floors.