Scope of work
Nexans, as the export cable EPCI contractor, engaged the services of Global Maritime to conduct a Cable Burial Risk Assessment (CBRA) to assess external threats to the planned Empire Wind 1 export cables ahead of installation and to recommend mitigations to these external threats through defining recommended burial or protection by alternative means along the export cable routes. The following works were carried out to support Nexans pre-installation design works, to be presented to the wind farm developer, Equinor, the Certified Verification Agent, DNV, and the local regulator, BOEM:
- Review of the site conditions within the export cable corridor
- Definition of a Stable Seabed Level (SSBL) to be used as reference for the CBRA burial recommendations and definition of pre-sweeping works
- Cable hazard Identification
- Probabilistic assessment of anchor strike risk
- Cable Burial Risk Assessment (CBRA) and recommendations for cable depth of lowering along the export cable route.
Challenges
- Previously performed CBRA provided to Nexans from the developer stated the target depth of lowering was very deep – and this may make the project uneconomically viable.
- The United States Arme Corps of Engineers (USACE) and US Coast Guard (USCG) provide onerous burial requirements in certain areas of federal navigation locations, federally maintained areas and anchoring grounds.
- The route consisted of seabed mobility, such as sandwaves, that needed to be incorporated into the total burial depth, with the overall depth able to be achieved by pre-sweeping and conventional burial tools, other than in specific areas where a Vertical Injector could be utilized.
Outcome – Results and Deliverables
Though the spatial 3-dimensional CBRA approach taken by Global Maritime, including the definition of stable seabed level and the input from our internal master mariners, our CBRA was able to show that the risk to the cable was considered acceptable for reduced depths to make the project viable. Not only this, but the presentation methods and simple ability to visualize the change in risk was able to be used to convince the CVA and BOEM that reduced burial requirements can be used, saving both Equinor and Nexans a lot of time, effort and money for the installation of the cables.
