New guidance for offshore wind industry on geophysical surveys for unexploded ordnance and boulders
08 April 2020
The Carbon Trust’s Offshore Wind Accelerator (OWA) has today published guidance for the geophysical surveying for unexploded ordnance (UXO) and boulders, supporting subsea cable installation by improving the efficiency and effectiveness of surveys.
The new guidance is the most comprehensive of its kind, and the first dedicated to the offshore wind industry. It aims to optimise surveys by equipping offshore wind developers and surveyors with information to facilitate the creation and utilisation of data according to best practise, a consistent structure and improved survey result documentation.
UXO and boulders present risks to subsea cables, as well as the operations and equipment required for their installation, maintenance, and decommissioning. Data generated by geophysical surveys undertaken in the planning stages of offshore wind farms form a key part of the knowledge base for risk evaluation and management of these operations - and can cost millions of pounds.
Faults in survey design can lead to the need to repeat surveys, or unexpected damage to equipment. Mitigating these risks is critical to minimise resulting project delays and increased costs.
The development of this guidance builds on previous OWA guidance for cable installation, the Cable Burial Risk Assessment (CBRA) Methodology, published in 2015, which provides a risk-based assessment to optimise the Depth of Lowering of subsea cables.
The guidance was developed with support from Cathie UK, a geoscience and geotechnical consultancy and Ordtek, unexploded ordnance specialists.
Jan Matthiesen, director, offshore wind, the Carbon Trust, commented: "After an initial review of the technologies available and past issues with surveying it became clear the equipment was not the issue, but the design. By publishing this work we are providing industry with the tools to optimise this critical part of the planning process for offshore wind farms.”