Sand wave field : the Obel Sands, Bristol Channel, UK

The OBel Sands, an area of sand waves up to 19 m high, cover an extensive area, >1,000 km2, in the Outer Bristol Channel off the coast of Wales. The sand wave field can be divided into a northern half with a dense concentration of bedforms on a sand substrate, and southern half with isolated sand waves on a coarse substrate. In both areas, the sand waves are generally asymmetric in cross profile, with steep west-facing lee slopes associated with the Channel’s ebb tides. The sand waves commonly have abundant megaripples and secondary sand waves on their slopes; these dynamic environments maintain little or no epifauna. The infaunal assemblages are varied and primarily related to sediment composition, sediment stability, and depth. Species richness is highest in coarse sediment between isolated sand waves and on the nearby platform. These areas generally support a rich epifauna.