Ground Modelling for Tonn Nua – South Coast DMAP
Example of 3D model provided for Tonn Nua showing some of the elements included: the top of bedrock, seabed lithology and morphology, DCEE geotechnical data, INFOMAR samples, and INFOMAR and NMS shipwrecks
Project:
Ground Modelling for Tonn Nua – South Coast DMAP
Date:
During 2024 & 2025
Location:
North Celtic Sea – South Coast DMAP area – Tonn Nua
Client:
Multiple
Business Sectors:
Offshore Wind – Ireland
Services (Technical Disciplines):
- Geological Desk Studies
- Geological & Geotechnical Ground Models
Project Objectives/Outcomes:
The South Coast Designated Maritime Area Plan (SC-DMAP) of the Northern Celtic Sea is Ireland’s first marine spatial plan for offshore renewable energy. The SC-DMAP adopts a plan-led approach and identifies four development sites (Figure 1) which will contribute towards the government objective of 5 GW of installed offshore wind capacity by 2030. GDG/Venterra, in collaboration with BVG Associates, was involved in the works carried out for the identification of the optimal areas for development – full report can be found here.
Tonn Nua is one of the four DCEE-designated maritime areas within the SC-DMAP region, located off county Waterford. The site is anticipated to support 900 MW of offshore wind energy and is scheduled for completion in the early 2030s.
Figure 1: SC-DMAP maritime areas
Our ground modelling team at GDG/Venterra was commissioned by several developers in the region to provide desktop studies and ground modelling services for the Tonn Nua site throughout the multiple stages of DCEE geophysical data release to inform and de-risk the offshore wind auction process.
These studies made use of academic and publicly available datasets (from our collaborations with Irish universities and public sources – e. g. INFOMAR, BGS), along with governmental data released by DCEE which included several geophysical survey datasets and, most recently, geotechnical data. Following the release of each dataset, GDG/Venterra were required to carry out updates of the seabed and subsurface interpretation to ensure a thorough and seamless integration of all available data. Geological units interpreted on the available seismic data were associated with geotechnical parameters based on the analysis of the newly released geotechnical data and a soil zonation of the entire site was undertaken. Hazards and geohazards were identified and analysed along with areas of outstanding uncertainty.
Based on our assessment of the available data and literature, the seabed at the site is mainly covered by coarse sediments with isolated areas of sand, and it displays features such as sand waves (Figure 2), sediment ridges, and eskers (associated with the latest ice sheet advance in the region).
Figure 2: Example of the Tonn Nua seabed morphology on MBES bathymetry and backscatter along with the updated seabed lithology interpretation.
In the subsurface, several units were separated representing the bedrock and Quaternary sedimentary cover (Figure 3). The bedrock was interpreted as predominantly Palaeozoic in age and consisting of a series of lithologies. Limestone was the main rock lithology interpreted based on the available borehole data and literature with additional mudstone and sandstone domains delineated in the northwestern and eastern parts of the site. A sliver of Palaeogene limestone/sandstone was also interpreted along the southern boundary of the site.
Figure 3: Example of interpreted seismo-stratigraphic units in section (left) and 3D (right) views.
Glacial sediments were interpreted directly on top of the Palaeogene to Palaeozoic bedrock, notably including thick till deposits, comprising high to ultra-high strength clays and dense to very dense sands. Overlying these older units, lacustrine to outwash plain (medium to very high strength / medium to very dense) and subglacial or proglacial fluvial (low strength) deposits were interpreted. A veneer of Holocene marine sands and gravels was inferred across the site based on literature.
The geohazards identified within the site include elements such as shallow bedrock, boulders, coarse sediments, over-consolidated deposits, and buried channels. Due to the risks that these elements pose to foundations and cables, a comprehensive assessment of each hazard was performed and mitigation actions proposed. These will represent the main inputs for future risk analyses carried out to establish the risk levels at the site. Additionally, man-made obstructions such as shipwrecks, marine traffic, fishing grounds, and more were collated and discussed and recommendations were provided for minimising their impact on project development.
The findings of this assessment represented the base for a suite of recommendations for studies and surveys to be completed at the site to further de-risk the area and support the client during the future development process.
The ground modelling work carried out by GDG/Venterra for Tonn Nua has provided a robust geological framework crucial for risk assessment and design. Our experience with Irish waters academic and publicly available data has ensured improved coverage and interpretation reliability and aligns with industry standards and stakeholder expectations for data-driven decision-making. The results of our studies were compiled into interactive 3D ground models enabling an effortless visualisation of the seabed and subsurface conditions and supporting the safe siting of turbines, infrastructure, and cable corridors (Figure 4).
Figure 4: Example of 3D model provided for Tonn Nua showing some of the elements included: the top of bedrock, seabed lithology and morphology, DCEE geotechnical data, INFOMAR samples, and INFOMAR and NMS shipwrecks.
The works carried out by our team on Tonn Nua and in the wider Celtic Sea demonstrate our capacity to support the successful delivery of proposed projects in the region, such as those arising from the future DCEE Lí Ban, Manannán, and Danu sites auctions, with preliminary interpretations already completed for Lí Ban.
As part of the data collation and work carried out so far in Tonn Nua, our team can provide access to additional academic data for the region to refine the subsurface interpretation, integrating all the data available so far for the site. Our knowledge of the Tonn Nua ground conditions and our experience in survey design and management makes us the best choice to support future geophysical and geotechnical campaigns, provide data review services, and undertake updated integrated ground models for the site. In collaboration with our sister companies, our expertise also covers coastal and marine processes, UXO, and risk management. Our work in ground modelling naturally bridges over to the engineering design services offered by our Design team, thus offering provision of a wide range of technical services which support the full timeline of a windfarm.
Our Role:
Geoscience Consultancy – Ground Modelling Services
Geoscience Ireland Contact:
Roxana Stanca roxana-mihaela.stanca@venterra-group.com
