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Field investigation of ridge-runnel dynamics on an intertidal mudflat

Field investigation of ridge-runnel dynamics on an intertidal mudflat
Field investigation of ridge-runnel dynamics on an intertidal mudflat
Flow-parallel linear ridge–runnel (R–R) bedforms composed of mainly cohesive sediments have been investigated at an intertidal site located at Hills Flats in the Severn Estuary, UK. It is argued that the sequences of sand–mud laminae in the ridge sediments indicate strongly that R–R are depositional bedforms. Faint R–R topography scoured in the underlying soft bedrock and parallel rows of coarser particle now found at the base of ridges are evidence of secondary vortices that may have provided a catalyst for mud ridge growth. Bed shear stress remains below the erosion threshold for all but the most recent and weak surficial mud deposits which are removed by evorsion [mechanical erosion by turbulent flows that may also carry sand and/or gravel] during Spring tidal flow ca. 60 cm/s. Differences in flow characteristics between ridges and runnel are minor. Corrasion [to erode or be eroded by abrasion] by sparse coarse sediment largely prevents net deposition in the runnels. Over time a slight imbalance between mud deposition and erosion rates allows slow growth of the ridges suggesting that these mudflats may be especially sensitive to slight changes in the local hydrodynamic regime and/or sediment supply
bedforms, tidal flats, cohesive sediment, ridge–runnel morphology, incipient threshold, evorsion and corrasion, coherent structures, hydrodynamics, severn estuary, 51°40.45?N: 2°33.24?W
0272-7714
213-229
Williams, Jon J.
8d4fa85f-eb90-47ca-8115-c34793fad602
Carling, Paul A.
8d252dd9-3c88-4803-81cc-c2ec4c6fa687
Amos, Carl L.
d0a18a13-bccd-4fdc-8901-aea595d4ed5c
Thompson, Charlie
2a304aa6-761e-4d99-b227-cedb67129bfb
Williams, Jon J.
8d4fa85f-eb90-47ca-8115-c34793fad602
Carling, Paul A.
8d252dd9-3c88-4803-81cc-c2ec4c6fa687
Amos, Carl L.
d0a18a13-bccd-4fdc-8901-aea595d4ed5c
Thompson, Charlie
2a304aa6-761e-4d99-b227-cedb67129bfb

Williams, Jon J., Carling, Paul A., Amos, Carl L. and Thompson, Charlie (2008) Field investigation of ridge-runnel dynamics on an intertidal mudflat. Estuarine, Coastal and Shelf Science, 79 (2), 213-229. (doi:10.1016/j.ecss.2008.04.001).

Record type: Article

Abstract

Flow-parallel linear ridge–runnel (R–R) bedforms composed of mainly cohesive sediments have been investigated at an intertidal site located at Hills Flats in the Severn Estuary, UK. It is argued that the sequences of sand–mud laminae in the ridge sediments indicate strongly that R–R are depositional bedforms. Faint R–R topography scoured in the underlying soft bedrock and parallel rows of coarser particle now found at the base of ridges are evidence of secondary vortices that may have provided a catalyst for mud ridge growth. Bed shear stress remains below the erosion threshold for all but the most recent and weak surficial mud deposits which are removed by evorsion [mechanical erosion by turbulent flows that may also carry sand and/or gravel] during Spring tidal flow ca. 60 cm/s. Differences in flow characteristics between ridges and runnel are minor. Corrasion [to erode or be eroded by abrasion] by sparse coarse sediment largely prevents net deposition in the runnels. Over time a slight imbalance between mud deposition and erosion rates allows slow growth of the ridges suggesting that these mudflats may be especially sensitive to slight changes in the local hydrodynamic regime and/or sediment supply

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More information

e-pub ahead of print date: 9 April 2008
Published date: 20 August 2008
Keywords: bedforms, tidal flats, cohesive sediment, ridge–runnel morphology, incipient threshold, evorsion and corrasion, coherent structures, hydrodynamics, severn estuary, 51°40.45?N: 2°33.24?W
Organisations: Ocean and Earth Science, Environmental Processes & Change

Identifiers

Local EPrints ID: 69365
URI: https://eprints.soton.ac.uk/id/eprint/69365
ISSN: 0272-7714
PURE UUID: bc5a2ef0-a74f-4d13-b561-6e271e384599

Catalogue record

Date deposited: 05 Nov 2009
Last modified: 19 Jul 2019 23:47

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