The Irish Sea bed load parting zone: Is it a mid-sea hydrodynamic phenomenon or a geological theoretical concept?

Creane, Shauna; O’Shea, Michael; Coughlan, Mark; Murphy, Jimmy

doi:10.1016/j.ecss.2021.107651

Cited by 3 publications

(8 citation statements)

References 103 publications

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“…Additionally, high-resolution modelling of residual tidal currents reveals a residual anticlockwise eddy over the submarine channel, Wicklow Trough [56,57], similar to the trend identified in Creane et al [14] and Creane et al [15] (Figure 13b). This potentially acts as a sediment accumulation/deposition zone for eroded sediment from the encompassing shallower Codling Platform [14]. When analysing the one-year accumulative total load sediment transport vectors, a predominant southward sediment transport pathway is evident, streamlined through the Wicklow Trough towards the northern tip of Arklow Bank and partially through source pathways 1 and 2 (Figure 13c).…”

Section: Sediment Budgetsupporting

confidence: 72%

“…The external sediment sources at the northern section of the bank can be linked to a sediment transport pathway originating from the on-land headland, Wicklow Head, whereby a south-eastward residual transport pathway is evident, originating from Wicklow Head and entering Arklow Bank's main morphological cell through source pathway numbers 1 and 2 (Figure 13b) [14]. Additionally, high-resolution modelling of residual tidal currents reveals a residual anticlockwise eddy over the submarine channel, Wicklow Trough [56,57], similar to the trend identified in Creane et al [14] and Creane et al [15] (Figure 13b). This potentially acts as a sediment accumulation/deposition zone for eroded sediment from the encompassing shallower Codling Platform [14].…”

Section: Sediment Budgetmentioning

confidence: 99%

“…These pathways comprise a combined 20.31% of total external sediment sources. In this way, the Wicklow Trough has the potential to focus sediment transport from the bed load parting zone [14] to Arklow Bank. This is consistent with the work of Coughlan et al [58], in which areas of active erosion and sediment transport were identified in the Wicklow Trough through the use of geophysical and geological datasets.…”

Section: Sediment Budgetmentioning

confidence: 99%

“…The south Irish Sea is a tidally-dominated shallow shelf sea environment that exhibits a highly complex hydrodynamic and morphodynamic regime influenced by a tidal symmetry zone and bed load parting zone extending approximately from Ardanary on the Irish coastline to Anglesey on the United Kingdom's coastline [14] (Figure 1). Additionally, the presence of a tidal node oscillation zone extending from the coastline at Courtown for approximately 39 km provides additional complexity to the hydrodynamics of the region [14] (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

“…When developing robust hydrodynamic and morphological models for offshore environments, the utilisation of the most efficient mesh resolution after considering specific study aims and objectives, site-specific environmental considerations, computational power and run time, and project budget and timeline is imperative to achieving the best results. Depending on these variables, various mesh types (unstructured or structured) [28] and resolution have been utilised to model regional scale hydrodynamic and sediment trans-port trends [14,16,29], and specific bedform dynamics such as sand waves under both two-dimensional (2D) [30], two-dimensional vertical (2DV) [31], and three-dimensional (3D) modelling techniques [32,33], and sand banks [20,[34][35][36][37][38]. Performing a mesh sensitivity analysis is a useful technique in the decision-making process.…”

Section: Introductionmentioning

confidence: 99%

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Morphological Modelling to Investigate the Role of External Sediment Sources and Wind and Wave-Induced Flow on Sand Bank Sustainability: An Arklow Bank Case Study

Creane,

O’Shea,

Coughlan

et al. 2023

JMSE

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Offshore anthropogenic activities such as the installation of Offshore Renewable Energy (ORE) developments and sediment extraction for marine aggregates have been shown to disrupt current flow, wave propagation, and sediment transport pathways, leading to potential environmental instability. Due to the complexity of the interconnected sediment transport pathways in the south-western Irish Sea combined with an increase in planned anthropogenic activities, the assessment of this risk is imperative for the development of a robust marine spatial plan. Subsequently, this study uses two-dimensional morphological modelling to build upon previous studies to assess the dependency of Arklow Bank’s local sediment transport regime on external sediment sources. Additionally, scenario modelling is used to identify vulnerable areas of this offshore linear sand bank to wind and wave-forcing and to examine the nature of this impact. A sediment budget is estimated for Arklow Bank, whereby seven source and nine sink pathways are identified. New evidence to support the exchange of sediment between offshore sand banks and offshore independent sand wave fields is also provided. The areas of the bank most vulnerable to changes in external sediment sources and the addition of wind- and wave-induced flow are analogous. These high vulnerability zones (HVZs) align with regions of residual cross-flow under pure current conditions. The restriction of sediment sources off the southern extent of Arklow Bank impacts erosion and accretion patterns in the mid- and northern sections of the bank after just one lunar month of simulation. Where tidal current is the primary driver of sand bank morphodynamics, wind- and wave-induced flow is shown to temporarily alter sediment distribution patterns. Wind and wave-induced flow can both accelerate and decelerate the east-west fluctuation of the upper slopes of the bank, yet the nature of this impact is inconsistent due to the misalignment of the directionality of these two forces. The methods and new knowledge derived from this study are directly applicable to tidally-dominated environments outside the Irish Sea.

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Section: Sediment Budgetsupporting

confidence: 72%

Section: Sediment Budgetmentioning

confidence: 99%

Section: Sediment Budgetmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Morphological Modelling to Investigate the Role of External Sediment Sources and Wind and Wave-Induced Flow on Sand Bank Sustainability: An Arklow Bank Case Study

Creane,

O’Shea,

Coughlan

et al. 2023

JMSE

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Development and Dynamics of Sediment Waves in a Complex Morphological and Tidal Dominant System: Southern Irish Sea

et al. 2022

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With the recent push for a transition towards a climate-resilient economy, the demand on marine resources is accelerating. For many economic exploits, a comprehensive understanding of environmental parameters underpinning seabed morphodynamics in tidally-dominated shelf seas, and the relationship between local and regional scale sediment transport regimes as an entire system, is imperative. In this paper, high-resolution, time-lapse bathymetry datasets, hydrodynamic numerical modelling outputs and various theoretical parameters are used to describe the morphological characteristics of sediment waves and their spatio-temporal evolution in a hydrodynamically and morphodynamically complex region of the Irish Sea. Analysis reveals sediment waves in a range of sizes (height = 0.1 to 25.7 m, and wavelength = 17 to 983 m), occurring in water depths of 8.2 to 83 mLAT, and migrating at a rate of 1.1 to 79 m/yr. Combined with numerical modelling outputs, a strong divergence of sediment transport pathways from the previously understood predominantly southward flow in the south Irish Sea is revealed, both at offshore sand banks and independent sediment wave assemblages. This evidence supports the presence of a semi-closed circulatory hydrodynamic and sediment transport system at Arklow Bank (an open-shelf linear sand bank). Contrastingly, the Lucifer–Blackwater Bank complex and associated sediment waves are heavily influenced by the interaction between a dominant southward flow and a residual headland eddy, which also exerts a strong influence on the adjacent banner bank. Furthermore, a new sediment transfer system is defined for offshore independent sediment wave assemblages, whereby each sediment wave field is supported by circulatory residual current cells originating from offshore sand banks. These new data and results improve knowledge of seabed morphodynamics in tidally-dominated shelf seas, which has direct implications for offshore renewable developments and long-term marine spatial planning.

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

et al. 2023

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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.

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The Irish Sea bed load parting zone: Is it a mid-sea hydrodynamic phenomenon or a geological theoretical concept?

Cited by 3 publications

References 103 publications

Morphological Modelling to Investigate the Role of External Sediment Sources and Wind and Wave-Induced Flow on Sand Bank Sustainability: An Arklow Bank Case Study

Morphological Modelling to Investigate the Role of External Sediment Sources and Wind and Wave-Induced Flow on Sand Bank Sustainability: An Arklow Bank Case Study

Development and Dynamics of Sediment Waves in a Complex Morphological and Tidal Dominant System: Southern Irish Sea

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

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