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Intertidal gravel dune dynamics in the Severn Estuary

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Period: September 2005 till 2007
Status: Completed

Geographical term: ANE, British Isles, Severn Estuary [Marine Regions]

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Fieldwork undertaken in 2004 and 2005 at Hills Flats in the Severn Estuary has focused on the dynamic behaviour of inter-tidal gravel dunes. The work has been undertaken in collaboration with Professor Paul Carling at the University of Southampton, Dr Paul Bell at the Proudman Oceanographic Laboratory and the British Geological Survey. In addition to detailed studies of internal dune structures, attention has been given to the relationships between the strong tidal flows and the movement of individual dunes and the entire dune field. The relatively short periods of reversing flow produces gravel dunes that do not conform well to theory for dunes developed on sandy substrates. Although there is evidence to support the view that the present dunes are in equilibrium with the imposed flow, they cannot attain maximum steepness owing to time constraints imposed by the duration of competent tidal flows. There is no evidence to indicate that sediment supply to the dunes is restricted. Owing to the exposed bedrock platform between the dunes, their geometry and dynamic behaviour might reflect some unknown effects of this unusual composite roughness. These facts should be born in mind when using empirical predictors for dunes developed in similar sediments in inter-tidal or shallow tidal environments. This must be considered also when attempting to interpret inter-tidal depositional environments in the geological record.

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