Preprints
https://doi.org/10.5194/egusphere-2023-1375
https://doi.org/10.5194/egusphere-2023-1375
23 Aug 2023
 | 23 Aug 2023

Influence of cohesive clay on wave–current ripple dynamics captured in a 3D phase diagram

Xuxu Wu, Jonathan Malarkey, Roberto Fernández, Jaco Baas, Ellen Pollard, and Daniel Parsons

Abstract. Wave–current ripples that develop on seabeds of mixed non-cohesive sand and cohesive clay are commonplace in coastal and estuarine environments. However, laboratory research on ripples forming in these types of mixed-bed environments is relatively limited. New large-scale flume experiments seek to address this by considering two wave-current conditions with initial clay content, C0, ranging from 0 to 18.3 %. The experiments record ripple development and pre- and post-experiment bed clay contents, to quantify clay winnowing. The experiments are combined with previous data to produce a consistent picture of larger and smaller flatter ripples over a range of wave-current conditions and C0. Specifically, the results reveal a sudden decrease in the ripple steepness for C0 > 10.6 %, likely associated with hydraulic conductivity. Accompanying the sudden change in steepness is a gradual linear decrease in wavelength with C0 for C0 > 7.4 %, which may be significant for paleoenvironmental reconstruction. Moreover, for a given flow, the initiation time, when ripples first appear on a flat bed, increases with increasing C0. This, together with the fact that the bed remains flat for the highest values of C0, demonstrates that the threshold of motion increases with C0. The inferred threshold enhancement, and the occurrence of large and small ripples, is used to construct a new three-dimensional phase diagram of bed characteristics involving the wave and current Shields parameters and C0, which has important implications for morphodynamic modelling. Winnowing occurs for both flat and rippled beds, but the rate is two orders of magnitude smaller for flat beds.

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Journal article(s) based on this preprint

30 Jan 2024
| Highlight paper
Influence of cohesive clay on wave–current ripple dynamics captured in a 3D phase diagram
Xuxu Wu, Jonathan Malarkey, Roberto Fernández, Jaco H. Baas, Ellen Pollard, and Daniel R. Parsons
Earth Surf. Dynam., 12, 231–247, https://doi.org/10.5194/esurf-12-231-2024,https://doi.org/10.5194/esurf-12-231-2024, 2024
Short summary Editor
Xuxu Wu, Jonathan Malarkey, Roberto Fernández, Jaco Baas, Ellen Pollard, and Daniel Parsons

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1375', Sjoukje de Lange, 13 Sep 2023
    • AC2: 'Reply on RC1', Xuxu Wu, 11 Nov 2023
  • RC2: 'Comment on egusphere-2023-1375', Anonymous Referee #2, 03 Oct 2023
    • AC3: 'Reply on RC2', Xuxu Wu, 11 Nov 2023
  • AC1: 'Comment on egusphere-2023-1375', Xuxu Wu, 11 Nov 2023

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1375', Sjoukje de Lange, 13 Sep 2023
    • AC2: 'Reply on RC1', Xuxu Wu, 11 Nov 2023
  • RC2: 'Comment on egusphere-2023-1375', Anonymous Referee #2, 03 Oct 2023
    • AC3: 'Reply on RC2', Xuxu Wu, 11 Nov 2023
  • AC1: 'Comment on egusphere-2023-1375', Xuxu Wu, 11 Nov 2023

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Xuxu Wu on behalf of the Authors (24 Nov 2023)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (27 Nov 2023) by Kieran Dunne
ED: Publish as is (28 Nov 2023) by Tom Coulthard (Editor)
AR by Xuxu Wu on behalf of the Authors (05 Dec 2023)

Journal article(s) based on this preprint

30 Jan 2024
| Highlight paper
Influence of cohesive clay on wave–current ripple dynamics captured in a 3D phase diagram
Xuxu Wu, Jonathan Malarkey, Roberto Fernández, Jaco H. Baas, Ellen Pollard, and Daniel R. Parsons
Earth Surf. Dynam., 12, 231–247, https://doi.org/10.5194/esurf-12-231-2024,https://doi.org/10.5194/esurf-12-231-2024, 2024
Short summary Editor
Xuxu Wu, Jonathan Malarkey, Roberto Fernández, Jaco Baas, Ellen Pollard, and Daniel Parsons
Xuxu Wu, Jonathan Malarkey, Roberto Fernández, Jaco Baas, Ellen Pollard, and Daniel Parsons

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Latest update: 02 Sep 2024
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

The transition between ripples and dunes dependent upon sediment and flow conditions has been classically represented with a phase space diagram differentiating between the different bedforms based on these drivers. This work, importantly, introduces the role of clay content within the sediment and shows how this shifts these fundamental long standing relationships.
Short summary
The seabed can change its shape from flat to undulating, known as ripples; the change rate depends on whether the bed is composed of sticky mud. This study, based on experiments, shows a strong reduction in ripple size when the initial mud content over 10.6 %. This could help geologists better interpret the ancient sea conditions. We present a new model to predict ripple size by considering sticky mud. It should help engineers to describe the behavior of the seabed when sticky mud is present.