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Williams J. J; Carling P. A. and Bell, P. S., 2007. Dynamics of Intertidal Gravel Dunes. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 673 – 677. Gold Coast, Australia, ISSN 0749.0208 The paper examines the dynamics of intertidal gravel dunes located at Hills Flat in the Severn Estuary, UK. Here a veneer of shale gravel (D50 = 4 mm) is locally deformed by strong tidal currents to form a series of flow transverse dunes with average heights and wavelengths of 0.6 m and 7.0 m, respectively. Incipient threshold values were much higher than expected owing to a coarse armor layer with D50 = 9 mm on the surface of the dune. More than 80 % of dune migration occurred during the first three days of the spring flows tide. During mobilisation and translation of the dune fine suspended sediment were released and concentrations were approximately one order of magnitude greater than the background level for this site. In a narrow range of hydraulic conditions highly localised and ephemeral secondary dunes were observed. Migration of the primary dune was accomplished without a measurable change in the dune volume supporting the view that the bedforms exist in quasi-equilibrium. [ABSTRACT FROM AUTHOR]