Managing Unexploded Ordnance (UXO) Risks in Offshore Wind Farm Operations & Maintenance – SSE Renewables
Company Information
SSE Renewables operates the Greater Gabbard offshore wind farm. Greater Gabbard is located around 20km off the coast of Suffolk, England and is operated and maintained from its operations and maintenance base at Lowestoft, Suffolk. The 504MW offshore wind farm has been in operation since 2012, generating enough low-carbon renewable energy each year to power the equivalent of over 400,000 UK homes. Greater Gabbard was a pioneering project for the UK offshore wind industry and for many years the 140-turbine site was the largest wind farm under development world-wide.
Project Aim
This project will introduce the student to:
- The history of unexploded ordnance (UXO) in the UK, particularly from World War II.
- The technical processes used today to manage UXO risks at offshore wind farms, using evidence from real offshore operations, including Greater Gabbard (in operation) and North Falls (in development).
The aim is to help the student understand why UXOs still pose a risk and how modern offshore teams assess, monitor, and safely remove or manage them.
During WWI and WWII, the UK and surrounding waters saw intense military activity, including:
- Aerial bombing campaigns, which left behind many bombs that failed to detonate.
- Naval minefields, laid by both Allied and German forces.
- Weapon disposal, shipwrecks, and wartime dumping, especially in the North Sea.
Studies indicate as many as 500,000 legacy UXO items may still be present in UK waters.
Changing seabed conditions can shift buried ordnance. For example, seabed migration of up to 25 m has been recorded at Greater Gabbard, increasing the chance of uncovering or moving UXO. This means consistent risk management is required to ensure ongoing risk to operations remain ALARP (As Low As Reasonably Practicable).
Technical Overview of UXO Management at Offshore Wind Farms
A. Historical Risk Assessment
UXO risk management always begins with historical research.
Desk studies examine:
- Military records
- Historical charts
- Records of wartime events in the area
- Known dumping or battle sites
Such studies form the basis of identifying potential UXO risk zones.
B. Geophysical Surveys
Offshore surveys are used to locate buried metal objects. These include:
- Magnetometry
- Side‑scan sonar
- Multibeam echo‑sounders
- Sub‑bottom profilers
These technologies help map the seabed and identify targets for investigation.
C. Risk Categorisation
UXO threats are ranked from “highly likely” to “highly unlikely,” based on:
- Type of munition
- Historical activity
- Seabed conditions
- Survey data
For example, a confirmed UXO (cUXO) at Greater Gabbard was categorised and managed based on its proximity to offshore infrastructure.
D. Investigation and Identification
- ROVs (Remotely Operated Vehicles) are the preferred tool for underwater inspection.
- Divers may be used in shallow depth when ROV access is limited.
- UXO specialists assess whether the ordnance is “safe to move.”
E. UXO Relocation and Disposal
If a UXO poses a risk:
- It may be relocated to a designated sandbank or safe detonation zone.
Example: A WWII UXO at Greater Gabbard in 2024 was relocated prior to disposal planning. - Disposal is carried out by qualified Explosive Ordnance Disposal (EOD) teams.
In some cases, if burial in sediment reduces the danger, the UXO may be left in place and monitored.
What You Will Do
• Work with the Site Operations and Control Room team to identify key operational risks
• Work with Engineers and Geoscientists to understand maintenance activities and required outputs
• Speak with the Safety, Health and Wellbeing Advisor to understand the top risks of offshore work
• Work with the Commercial team to understand commercial risks related to new technology deployment
• Research technologies such as unmanned survey vessels and advanced monitoring systems
Science, Engineering and Technical Understanding
• Understanding wind turbine operation and maintenance
• Evaluating monitoring and inspection technologies
• Assessing risk reduction through engineering solutions
• Interpreting technical information to support decisions
Planning and Organisation
You will plan your work in stages, manage your time effectively, justify decisions made during the project, and document challenges and solutions.
Skills Developed
• Engineering and problem solving
• Research and data analysis
• Teamwork and communication
• Independent working
• Understanding safety and risk in offshore environments
Final Outputs
Task 1: Research Portfolio
- Summarise how WWII activities led to UXO in the UK.
- Create an infographic showing types of WWII ordnance found offshore.
Task 2: UXO Detection Methods
- Compare different geophysical survey techniques.
- Explain why ROVs are preferred for underwater investigation.
Task 3: Case Study – Greater Gabbard
Use real examples from your site:
- A 2024 confirmed UXO relocation.
- A buried UXO monitored in place.
Reflection and Evaluation
Your report could include:
• Evidence-based conclusions
• Discussion of assumptions and limitations
• Reflection on learning and project development
• Consideration of how the project could be improved or extended
https://www.crestawards.org/resources/crest-gold-student-guide