Isabel de Cala
Relating the Flow Processes and Bedforms of Steady-State and Waning Density Currents
de Cala, Isabel; Ohata, Koji; Dorrell, Robert; Naruse, Hajime; Patacci, Marco; Amy, Lawrence A.; Simmons, Steve; McLelland, Stuart J.; McCaffrey, William D.
Dr Robert Dorrell R.Dorrell@hull.ac.uk
University Research Fellow
Lawrence A. Amy
Dr Steve Simmons S.Simmons@hull.ac.uk
Dr Stuart McLelland S.J.McLelland@hull.ac.uk
Deputy Director of the Energy and Environment Institute
William D. McCaffrey
© Copyright© 2020 de Cala, Ohata, Dorrell, Naruse, Patacci, Amy, Simmons, McLelland and McCaffrey. The interaction between turbidity currents and mobile substrates can lead to the development of different types of bedforms. Although much research has been conducted on bedform development beneath open channel flows, research into bedform development beneath waning gravity currents is relatively rare. Analysis of density current-related bedform development has therefore relied upon open channel flow phase diagrams. We report on an experimental study designed to assess the development of bedforms under steady and waning saline density currents. The experimental density currents developed stepped density profiles in which a higher-density basal zone was separated from the ambient fluid by a zone of intermediate density; any bedforms that developed were contained within the bottom layer of the current. Under different conditions ripples, dunes, downstream migrating antidunes and long wavelength antidunes were observed to form and could be distinguished based on their interactions and phase relationships with the upper surface of the lower denser layer of the current. Due to limited mixing between the upper and lower layer of the current and maintenance of current momentum, currents set with slowing discharge flow rates maintained a steady flow velocity in the lower layer of the flow. As a result, sustained bedform formative conditions were achieved within this lower layer, while waning current conditions effected the rest of the flow. Under waning currents, it was seen how pre-existing bed states can determine the subsequent evolution of bedforms. This illustrates the limitations of existing phase diagrams as they do not account for trajectory or rate of passage of flows through different bedform phase spaces. In order to establish a reliable quantitative association between the flow regime and the type of bedform development, it is critical to adopt an appropriate Froude number calculation method for stratified flow. The updated density current phase diagram indicates supercritical flow can be achieved at lower flow velocities than for open channel flows due to the effects of reduced gravity. Bedform depositional structures found in outcrop and on the modern sea floor provide data that helps to interpret the hydrodynamic and sedimentological character of the current that formed them. Therefore, understanding the processes involved in bedform development beneath density currents will enable more accurate estimation of the properties of flows.
de Cala, I., Ohata, K., Dorrell, R., Naruse, H., Patacci, M., Amy, L. A., …McCaffrey, W. D. (2020). Relating the Flow Processes and Bedforms of Steady-State and Waning Density Currents. Frontiers in Earth Science, 8, https://doi.org/10.3389/feart.2020.535743
|Journal Article Type||Article|
|Acceptance Date||Aug 28, 2020|
|Online Publication Date||Oct 22, 2020|
|Publication Date||Oct 22, 2020|
|Deposit Date||Nov 6, 2020|
|Publicly Available Date||Nov 9, 2020|
|Journal||Frontiers in Earth Science|
|Peer Reviewed||Peer Reviewed|
|Keywords||Bedforms; Saline density current; Turbidity current; Dunes; Ripples; Antidunes; Experimental|
Copyright© 2020 de Cala, Ohata, Dorrell, Naruse, Patacci, Amy, Simmons, McLelland and McCaffrey. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
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