A spatiotemporal analysis of seabed morphodynamics in a constrained flow environment: A case study of an open tunnel valley in the Western Irish Sea

Seabed morphodynamics examines the processes that change the seabed topography. It is a dynamic system of sediment being eroded, transported, and deposited over different spatial and temporal scales. These dynamics have consequences for the siting of offshore engineering infrastructure such as renewable energy cables and foundations, as well as changes in seafloor habitats. Therefore, understanding seabed morphodynamics supports sustainable marine spatial planning.

Continental shelves can exhibit a range of geomorphological features that are composed of or covered in mobile sediment. These features can be subjected to sediment dynamic processes, creating an evolving seabed landscape. The Western Irish Sea is defined by sediment banks forming bathymetric highs, open tunnel valleys forming bathymetric lows, and sediment wave assemblages, amongst others. Previous studies in the area (Creane et al., 2021, 2022, 2023a, 2023b) have shown the influence of sediment banks on sub-regional hydrodynamic and sediment transport regimes. In particular, highlighting the system of sediment exchange between neighbouring banks and sediment wave assemblages. It has also been suggested that an open tunnel valley, the Wicklow Trough, is a potential source of sediment for the Arklow Bank, a sediment bank neighbouring it. To date, there is an absence of work conducted on the role of open tunnel valleys on such sub-regional systems and their potential role as a sediment sink or source in association with surrounding seabed features. As such, the Wicklow Trough offers an ideal site to investigate the influence of large-scale bathymetric lows on sub-regional seabed morphodynamics and flow regimes, as well as an opportunity to define the relationship between the Wicklow Trough and Arklow Bank.

The Wicklow Trough has a length of 18 km, a width of 2 km, and a maximum depth of 82 m, with an internal morphology composed of enclosed deeps, ridges, and sediment wave assemblages. The Western Irish Sea has been mapped and ground-truthed by the INFOMAR programme, providing sub-regional available data and context of the Wicklow Trough in the surrounding seabed. Localised repeat bathymetry surveys within the Wicklow Trough have provided data to measure local changes in morphology through sediment wave migration. In addition, extensive sediment samples provided an understanding of sediment grain size distribution, with Acoustic Doppler Current Profile (ADCP) data providing an insight into current flow. The compilation of results and data is presented here and will form a foundational understanding for a local and sub-regional hydrodynamic and morphodynamic numerical model. The findings of which will have important implications for understanding the role of large bathymetric lows in sub-regional flow regimes and sediment transport pathways.