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The role of physical cohesion on ripple dynamics under combined wave and current flow

The role of physical cohesion on ripple dynamics under combined wave and current flow
The role of physical cohesion on ripple dynamics under combined wave and current flow
We present the results of flume experiments, conducted in the Total Environment Simulator at the University of Hull, that aim to provide a fuller understanding of the influence of physical cohesion (abiotic clay content) on ripple development under combined wave and current flow Experiments including three runs were performed with wave-dominated combined flows, with maximum orbital velocity of 0.3 m/s and depth-averaged current velocity of 0.2 m/s. The bed in each run consisted of three channels side-by-side with common flow conditions. Run 1 as a control experiment used three beds of well-sorted sand (D50 = 440 ). Beds with homogenous mixing Kaolinite clay with the same sand were in Run 2 and 3, with initial cohesive clay contents ranging from 6% to 13.4%. A suite of state-of-the-art instruments was deployed to quantify the interactions of near-bed hydrodynamics and sediment transport over rippled beds formed by combined waves and currents. An Ultrasonic Ranging System (URS) was mounted on an automated traverse to acquire cross-section profiles of the evolving bed, capturing the development of the ripples and quantifying how planform geometries (2D or 3D) evolved. URS transducers at fixed positions were also used to detect ripple migration and thus determine bedload transport rates. Moreover, sediment cores were collected from ripple crests and troughs in each channel during the experiments to quantify how clay content varied with time and depth as the ripples evolved. The experimental results show the significant influence of the amount of initial cohesive clay in the substrate on ripple evolution under combined flows. Higher cohesive clay contents in the bed dramatically slowed down the rate of ripple development and evolution. Furthermore, the dimensions and steepness of the ripples decreased with increasing clay content, particularly for bed clay contents above 10%. The implications of the results for bed roughness calculations and the process interpretation of interference ripples in sedimentary environments will be discussed.
Wu, Xuxu
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Fernandez, Roberto
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Parsons, Daniel R.
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Baas, Jaco
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Malarkey, Jonathan
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Manning, A.J.
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McLelland, S.J.
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Simmons, S
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Baar, A.W.
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Bastianon, E
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Roggatz, C
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Murphy, B
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Kassem, Hachem
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Wu, Xuxu
688e0888-0b13-47f2-b222-cd5315834ed2
Fernandez, Roberto
65dcecb9-9a9f-4d12-8285-7b6842217cb4
Parsons, Daniel R.
59f2673a-9c73-437a-8865-52d52830a3aa
Baas, Jaco
b0769c25-0a5a-460d-9c7d-5b4d53e5d09a
Malarkey, Jonathan
47695191-3894-4aaa-ba15-e47cef46ac8c
Manning, A.J.
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McLelland, S.J.
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Simmons, S
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Baar, A.W.
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Bastianon, E
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Roggatz, C
643c3e8c-cde6-43ad-afd7-c60964d92299
Murphy, B
e334d833-5112-403b-a1e6-be00c5bfca42
Kassem, Hachem
658efa7a-a02c-4b29-9d07-5d57e95a4b51

Wu, Xuxu, Fernandez, Roberto, Parsons, Daniel R., Baas, Jaco, Malarkey, Jonathan, Manning, A.J., McLelland, S.J., Simmons, S, Baar, A.W., Bastianon, E, Roggatz, C, Murphy, B and Kassem, Hachem (2020) The role of physical cohesion on ripple dynamics under combined wave and current flow. American Geophysical Union, Fall Meeting 2020, New Orleans, LA, USA, New Orleans, United States. 01 - 17 Dec 2020.

Record type: Conference or Workshop Item (Other)

Abstract

We present the results of flume experiments, conducted in the Total Environment Simulator at the University of Hull, that aim to provide a fuller understanding of the influence of physical cohesion (abiotic clay content) on ripple development under combined wave and current flow Experiments including three runs were performed with wave-dominated combined flows, with maximum orbital velocity of 0.3 m/s and depth-averaged current velocity of 0.2 m/s. The bed in each run consisted of three channels side-by-side with common flow conditions. Run 1 as a control experiment used three beds of well-sorted sand (D50 = 440 ). Beds with homogenous mixing Kaolinite clay with the same sand were in Run 2 and 3, with initial cohesive clay contents ranging from 6% to 13.4%. A suite of state-of-the-art instruments was deployed to quantify the interactions of near-bed hydrodynamics and sediment transport over rippled beds formed by combined waves and currents. An Ultrasonic Ranging System (URS) was mounted on an automated traverse to acquire cross-section profiles of the evolving bed, capturing the development of the ripples and quantifying how planform geometries (2D or 3D) evolved. URS transducers at fixed positions were also used to detect ripple migration and thus determine bedload transport rates. Moreover, sediment cores were collected from ripple crests and troughs in each channel during the experiments to quantify how clay content varied with time and depth as the ripples evolved. The experimental results show the significant influence of the amount of initial cohesive clay in the substrate on ripple evolution under combined flows. Higher cohesive clay contents in the bed dramatically slowed down the rate of ripple development and evolution. Furthermore, the dimensions and steepness of the ripples decreased with increasing clay content, particularly for bed clay contents above 10%. The implications of the results for bed roughness calculations and the process interpretation of interference ripples in sedimentary environments will be discussed.

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More information

Published date: 7 December 2020
Venue - Dates: American Geophysical Union, Fall Meeting 2020, New Orleans, LA, USA, New Orleans, United States, 2020-12-01 - 2020-12-17

Identifiers

Local EPrints ID: 449767
URI: http://eprints.soton.ac.uk/id/eprint/449767
PURE UUID: 36caa81c-2718-48ee-9999-4ac57483bb36
ORCID for Hachem Kassem: ORCID iD orcid.org/0000-0002-5936-6037

Catalogue record

Date deposited: 16 Jun 2021 16:30
Last modified: 17 Jun 2021 01:44

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Contributors

Author: Xuxu Wu
Author: Roberto Fernandez
Author: Daniel R. Parsons
Author: Jaco Baas
Author: Jonathan Malarkey
Author: A.J. Manning
Author: S.J. McLelland
Author: S Simmons
Author: A.W. Baar
Author: E Bastianon
Author: C Roggatz
Author: B Murphy
Author: Hachem Kassem ORCID iD

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