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Intrawave observations of sediment entrainment processes above sand ripples under irregular waves

O'Hara Murray, R.B.; Thorne, P.D.; Hodgson, D.M.. 2011 Intrawave observations of sediment entrainment processes above sand ripples under irregular waves. Journal of Geophysical Research, 116. C01001. 10.1029/2010JC006216

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Abstract/Summary

Measurements of intrawave sediment entrainment processes are reported above ripples under irregular waves generated in a large-scale flume facility. The data consist of substantive observations of small-scale processes collected at high spatial and temporal resolution under irregular wave forcing, typical of coastal environments. Acoustic measurements were made of water velocities, bed forms, and suspended sediment concentration over plane and rippled beds. During each rippled bed experiment, measurements were taken over the crests of steep sided ripples, above which flow separation was considered likely to occur. Above the ripple crests, a strong intrawave variation in the near-bed suspended sediment, indicative of vortex formation and shedding, was observed to dominate wave half cycles where the orbital diameter was greater than 1.2 times the ripple wavelength lambda. The irregular waves were parameterized with a significant wave height H-s and a significant orbital diameter d(0s). Thus, during irregular wave conditions and over steep ripples where d(0s)/lambda > 1.2, vortex shedding was deemed as the dominant sediment entrainment process. Furthermore, the percentage of wave half cycles where vortex shedding was observed, was found to scale as 26 d(0s)/lambda. These results demonstrate, for under irregular waves, the existence of a clear suspended sediment structure consistent with vortex shedding, previously observed under regular waves

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1029/2010JC006216
Programmes: Oceans 2025 > Shelf and coastal processes
ISSN: 0148-0227
Additional Information. Not used in RCUK Gateway to Research.: Murray, R. B. O'Hara Thorne, P. D. Hodgson, D. M. European Union ; Natural Environment Research Council ; University of Liverpool This work was supported by the European Union, through its access to large-scale facilities, and by the Natural Environment Research Council and the University of Liverpool for PhD funding. The authors thank J. J. Williams at Associated British Ports, U. K., who coordinated the Deltaflume experiments and Paul S. Bell and Benjamin D. Moate at the National Oceanography Centre for help with analyzing the flow and ripple data. We thank Stephen S. Flint at the School of Environmental Sciences, University of Liverpool, for his support. The constructive reviews from Peter Nielsen at the University of Queensland, Australia, and an anonymous reviewer are also much appreciated. We especially thank Alan G. Davies at the School of Ocean Science, Bangor University, Wales, for his many useful conversations and suggestions. Amer geophysical union Washington
Additional Keywords: OSCILLATORY FLOW; GENERATED RIPPLES; VORTEX RIPPLES; SUSPENDED SEDIMENTS; TRANSPORT MODELS; NORTH CAROLINA; BEDFORMS; BEDS; PREDICTION; GEOMETRY
NORA Subject Terms: Marine Sciences
Date made live: 02 Mar 2011 15:56
URI: http://nora.nerc.ac.uk/id/eprint/13685

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