Hydrodynamic Processes Controlling Sand Bank Mobility and Long-Term Base Stability: A Case Study of Arklow Bank

Author:

Creane Shauna123ORCID,O’Shea Michael12ORCID,Coughlan Mark345ORCID,Murphy Jimmy12ORCID

Affiliation:

1. School of Civil & Environmental Engineering, University College Cork, College Road, T12 K8AF Cork, Ireland

2. SFI Research Centre for Energy, Climate and Marine (MaREI), Beaufort Building, Environmental Research Institute, University College Cork, Ringaskiddy, P43 C573 Cork, Ireland

3. Gavin and Doherty Geosolutions, Unit A2, Nutgrove Office Park, Rathfarnham, D14 X627 Dublin, Ireland

4. School of Earth Sciences, Science Centre West, University College Dublin, Belfield, D04 N2E5 Dublin, Ireland

5. SFI Research Centre for Applied Geosciences (iCRAG), O’Brien Centre for Science East, University College Dublin, D04 N2E5 Dublin, Ireland

Abstract

Offshore sand banks are an important resource for coastal protection, marine aggregates, and benthic habitats and are the site of many offshore wind farms. Consequently, a comprehensive understanding of the baseline processes controlling sand bank morphodynamics is imperative. This knowledge will aid the development of a long-term robust marine spatial plan and help address the environmental instability arising from anthropogenic activities. This study uses a validated, dynamically coupled, two-dimensional hydrodynamic and sediment transport model to investigate the hydrodynamic processes controlling the highly mobile upper layer of Arklow Bank, while maintaining overall long-term bank base stability. The results reveal a flood and ebb tidal current dominance on the west and east side of the bank, respectively, ultimately generating a large anticlockwise residual current eddy encompassing the entire bank. This residual current flow distributes sediment along the full length of the sand bank. The positioning of multiple off-bank anticlockwise residual current eddies on the edge of this cell is shown to influence east–west fluctuations of the upper slopes of the sand bank and act as a control on long-term stability. These off-bank eddies facilitate this type of movement when the outer flows of adjacent eddies, located on both sides of the bank, flow in a general uniform direction. Whereas they inhibit this east–west movement when the outer flows of adjacent eddies, on either side of the bank, flow in converging directions towards the bank itself. These residual eddies also facilitate sediment transport in and out of the local sediment transport system. Within Arklow Bank’s morphological cell, eight morphodynamically and hydrodynamically unique bank sections or ‘sub-cells’ are identified, whereby a complex morphodynamic–hydrodynamic feedback loop is present. The local east–west fluctuation of the upper slopes of the bank is driven by migratory on-bank stationary and transient clockwise residual eddies and the development of ‘narrow’ residual current cross-flow zones. Together, these processes drive upper slope mobility but maintain long-term bank base stability. This novel understanding of sand bank morphodynamics is applicable to bedforms in tidally dominated continental shelf seas outside the Irish Sea.

Funder

Irish Research Council

Marine Institute

Science Foundation Ireland

Publisher

MDPI AG

Subject

General Earth and Planetary Sciences

Reference36 articles.

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