Multibeam sonar survey of a nearshore banner bank, Helwick Sands, Bristol Channel

What is it about?

Surveys in 2001 and 2002 of Helwick Sands characterised the changing pattern of sand dunes over this headland-connected "banner" bank, a sand bank formed by tidal currents south of the Gower peninsular at Port Eynon Point. Measurements made from the data showed that the heights of dunes increases with water depth, as found in studies carried out elsewhere. Dunes migrated to the west (ebb-dominated) on the south flank and to the east (flood-dominated) on the north flank of Helwick Sands, as expected from dune asymmetry. Movements over the 11 months between the surveys varied from 8 m to 50 m.

Featured Image

Photo by Anna Sullivan on Unsplash

Photo by Anna Sullivan on Unsplash

Why is it important?

This was a preliminary study developed further in our Continental Shelf Research paper in 2014, going into more detail in considering the origin of dunes over the crest of the bank - unusually, these connect with dunes on the flanks of the bank, despite dunes their travelling in opposite directions. It appears that the strong wave agitation here enhances mobility of sand along dune crests, producing unusually rapid evolution of dunes. The article also describes a simple method developed to isolate the mobile sand layer, assumed to overlying a surface interpolated between dune troughs. This allowed us to look at changes in dune cross-sectional area between the surveys.