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The morphodynamics and internal structure of intertidal fine-gravel dunes: Hills Flats, Severn Estuary, UK

Carling, P.A., Radecki-Pawlik, A., Williams, J.J., Rumble, B., Meshkova, L., Bell, P. and Breakspear, R. (2006) The morphodynamics and internal structure of intertidal fine-gravel dunes: Hills Flats, Severn Estuary, UK Sedimentary Geology, 183, (3-4), pp. 159-179. (doi:10.1016/j.sedgeo.2005.07.007).

Record type: Article


In the macrotidal Severn estuary, UK, the dynamics of intertidal fine-gravel dunes were investigated. These dunes are migrating
across a bedrock platform. Systematic observations were made of hydraulic climate, geometry, migration rates and internal sedimentary structures of the dunes. During spring tides, the ebb flow is dominant, dunes grow in height and have ebb orientated geometry with bedrock floors in the troughs. During neap tides, a weak flood flow may dominate. Dunes then are flood orientated or symmetrical. Neap dune heights decrease and the eroded sediment is stored in the dune troughs where the bedrock becomes blanketed by muddy gravel. During spring tides, instantaneous bed shear stresses reach 8 N m2, sufficient to disrupt a 9 mmgravel armour layer. However, a sustained bed shear stress of 4 N m2 is required to initiate dune migration at which time the critical depth-mean velocity is 1 m s1. Ebb and flood inequalities in the bed shear stress explain the changes in dune asymmetry and internal structures. During flood tides, the crests of the dunes reverse such that very mobile sedimentary dcapsT overlie a more stable dune dcoreT. Because ebb tides dominate, internal structures of the caps often are characterised by ebb orientated steep openwork foresets developed by strong tidal currents and some lower angle crossbeds deposited as weaker currents degrade foresets. The foresets forming the caps may be grouped into cosets (tidal bundles) and are separated from mud-infused cores of crossbeds that lie below, by reactivation and erosion surfaces blanketed by discontinuous mud drapes. The cores often exhibit distinctive muddy toe sets that define the spacing of tidal cosets.

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Submitted date: 4 March 2005
Published date: 25 July 2006
Additional Information: Estuarine gravel dunes condition sediment transport and hydraulic roughness, effecting storm-driven sea-levels. Understanding of process and stratigraphy will aid identification of hydraulics and bedforms in the geological record. This paper is one of two by the authors that presents the first systematic study of gravel bedform hydro- morphology and stratigraphy.
Keywords: gravel dunes, intertidal zone, sedimentary process, sedimentary structures, severn estuary


Local EPrints ID: 37717
ISSN: 0037-0738
PURE UUID: 866ab051-65c4-419e-b934-f1261656d3fa

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Date deposited: 25 May 2006
Last modified: 17 Jul 2017 15:41

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Author: P.A. Carling
Author: A. Radecki-Pawlik
Author: J.J. Williams
Author: B. Rumble
Author: L. Meshkova
Author: P. Bell
Author: R. Breakspear

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