Hummocky sedimentary structures within rippled beds due to combined orbital waves and transverse currents
Hummocky sedimentary structures within rippled beds due to combined orbital waves and transverse currents
Hummocky cross-stratification is commonly observed in the marine offshore transition to lower shoreface environments. However, to date, the origins of hummocky cross-stratification and its associated hummocky bedforms and hydrodynamic processes remain controversial and enigmatic. In the present study, a large-scale flume experiment was conducted to study the formation of hummocky bedforms. In the central test area of the flume, combined flow with water waves, with period of 2 s and velocity of 0.34 m s-1, progressed at a right angle to a current with velocity of 0.17 m s-1, whereas a wave alone condition pertained upstream and downstream of the test area. The combined-flow ripples in the test area had smaller dimensions than wave ripples, but their cross-section geometries were very similar. Most importantly, the experimental results, for the first time, revealed that humps occur with lengths up to approximately 40 mm beneath combined flow ripples. The formation of these structures appears to relate to the enhanced turbulence for the combined flow, because the turbulence kinetic energy for combined flow was ca 50% higher than that under the wave-only condition. Moreover, the observed small-scale humps in the present experiment had comparable cross-section geometries with hummock-like bedforms previously reported in laboratories and fields under storm conditions. Additionally, these humps could scale up to large-size hummocks under waves with longer period and faster velocity than the present conditions. The present experiment indicates that waves perpendicular to a current do generate hummock-like structures in association with ripples and therefore provide a new perspective for future study of the origins of hummocky cross-stratification.
Combined wave and current, combined-flow ripple, enhanced turbulence, hummocky bedforms, large-scale flume experiment., combined-flow ripple, Combined wave and current, enhanced turbulence, hummocky bedforms, large-scale flume experiment
573-589
Wu, Xuxu
6bb85514-40e4-4db5-8418-5bd00acde81b
Carling, Paul A.
8d252dd9-3c88-4803-81cc-c2ec4c6fa687
Parsons, Daniel
254b9145-8299-4c55-98ed-d37a8cdcb782
February 2024
Wu, Xuxu
6bb85514-40e4-4db5-8418-5bd00acde81b
Carling, Paul A.
8d252dd9-3c88-4803-81cc-c2ec4c6fa687
Parsons, Daniel
254b9145-8299-4c55-98ed-d37a8cdcb782
Wu, Xuxu, Carling, Paul A. and Parsons, Daniel
(2024)
Hummocky sedimentary structures within rippled beds due to combined orbital waves and transverse currents.
Sedimentology, 71 (2), .
(doi:10.1111/sed.13145).
Abstract
Hummocky cross-stratification is commonly observed in the marine offshore transition to lower shoreface environments. However, to date, the origins of hummocky cross-stratification and its associated hummocky bedforms and hydrodynamic processes remain controversial and enigmatic. In the present study, a large-scale flume experiment was conducted to study the formation of hummocky bedforms. In the central test area of the flume, combined flow with water waves, with period of 2 s and velocity of 0.34 m s-1, progressed at a right angle to a current with velocity of 0.17 m s-1, whereas a wave alone condition pertained upstream and downstream of the test area. The combined-flow ripples in the test area had smaller dimensions than wave ripples, but their cross-section geometries were very similar. Most importantly, the experimental results, for the first time, revealed that humps occur with lengths up to approximately 40 mm beneath combined flow ripples. The formation of these structures appears to relate to the enhanced turbulence for the combined flow, because the turbulence kinetic energy for combined flow was ca 50% higher than that under the wave-only condition. Moreover, the observed small-scale humps in the present experiment had comparable cross-section geometries with hummock-like bedforms previously reported in laboratories and fields under storm conditions. Additionally, these humps could scale up to large-size hummocks under waves with longer period and faster velocity than the present conditions. The present experiment indicates that waves perpendicular to a current do generate hummock-like structures in association with ripples and therefore provide a new perspective for future study of the origins of hummocky cross-stratification.
Text
Wu et al. 2023
- Accepted Manuscript
Restricted to Repository staff only until 8 October 2024.
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More information
Accepted/In Press date: 18 September 2023
e-pub ahead of print date: 8 October 2023
Published date: February 2024
Additional Information:
Funding Information:
The authors acknowledge reviewers Dr Mads E. Jelby and Dr Chris Stevenson, as well as the Associate Editor Prof. Kyle M. Straub, for their constructive feedback. The authors also acknowledge the contribution of Brendan Murphy, whose help throughout the study made our setup, data collection, and clean‐up efforts smooth and trouble‐free. Participation of XW and DP was made possible thanks to funding by the European Research Council under the European Union's Horizon 2020 research and innovation program (grant 725955).
Publisher Copyright:
© 2023 International Association of Sedimentologists.
Keywords:
Combined wave and current, combined-flow ripple, enhanced turbulence, hummocky bedforms, large-scale flume experiment., combined-flow ripple, Combined wave and current, enhanced turbulence, hummocky bedforms, large-scale flume experiment
Identifiers
Local EPrints ID: 483634
URI: http://eprints.soton.ac.uk/id/eprint/483634
ISSN: 0037-0746
PURE UUID: a9e698f6-52d5-423b-843e-de3f5624e524
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Date deposited: 02 Nov 2023 17:59
Last modified: 17 Mar 2024 05:23
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Author:
Xuxu Wu
Author:
Daniel Parsons
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