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16.6 Loss of Station

16.6.1 Construction phase

The MCA require under their Regulatory Expectations on Moorings for Floating Wind and Marine Devices (MCA and HSE, 2017) that developers arrange TPV of the mooring systems by an independent and competent person/body. The Regulatory Expectations state that TPV is a “continuous activity”, and that if any modifications to a system occur or if new information becomes available with regard to its reliability, additional TPV would be required. This TPV will facilitate management of any risk of failure of the mooring lines.
On this basis, the potential for loss of station is considered unlikely, noting that for a total loss of station, all moorings would be required to fail (based on the MDS there may be up to six mooring lines per foundation). There have been no reports to date of loss of stations from floating UK offshore wind farms.
The Regulatory Expectations (MCA and HSE, 2017) also require the provision of continuous monitoring either by GPS or other suitable means. The Applicant will put such a system in place, with each wind turbine continuously monitored to ensure any failure is quickly identified, and with capability of being tracked in the event of a loss of station as detailed in MGN 654.
The most likely consequences are failure of a single mooring line leading to a larger excursion zone than typical. As a worst case, total mooring line failure could lead to a drifting platform leading to a collision.

The frequency of occurrence is considered to be negligible based on the embedded mitigation in place in terms of TPV, monitoring and tracking.

Overall, the severity of consequence is deemed to be serious and the frequency of occurrence is considered to be negligible. The risk will, therefore, be of broadly acceptable significance.

No additional shipping and navigation mitigation is considered necessary because the likely risk in the absence of further mitigation (beyond the embedded mitigation measures outlined in section 18.1) is ALARP and not significant in EIA terms.

The same mitigations in terms of TPV and monitoring details for the construction phase will apply during the operation and maintenance phase, based on the requirements of the Regulatory Expectations on Moorings for Floating Wind and Marine Devices (MCA and HSE, 2017) and MGN 654 (MCA, 2021).
On this basis, the potential for loss of station is considered unlikely, noting that for a total loss of station, all moorings would be required to fail (based on the MDS there may be up to six mooring lines per foundation), and in the event that mooring lines did fail, monitoring and tracking procedures will be in place.
The most likely consequences are failure of a single mooring line leading to a larger excursion zone than typical. As a worst case, total mooring line failure could lead to a drifting platform leading to a collision.

The frequency of occurrence is considered to be negligible based on the embedded mitigation in place such as TPV of project infrastructure, and implementation of a continuous discrete monitoring system.

Overall, the severity of consequence is deemed to be serious and the frequency of occurrence is considered to be negligible. The risk will, therefore, be of broadly acceptable significance.

No additional shipping and navigation mitigation is considered necessary because the likely risk in the absence of further mitigation (beyond the embedded mitigation measures outlined in section 18.1) is ALARP and not significant in EIA terms.

The decommissioning phase is considered to be generally analogous to the construction phase in reverse and therefore the likelihood of loss of station during the decommissioning phase is considered to be the same as for the construction phase.

The frequency of occurrence is considered to be negligible based on the embedded mitigation in place such as TPV of project infrastructure, and implementation of a continuous discrete monitoring system.

Overall, the severity of consequence is deemed to be serious and the frequency of occurrence is considered to be negligible. The risk will, therefore, be of broadly acceptable significance.

No additional shipping and navigation mitigation is considered necessary because the likely risk in the absence of further mitigation (beyond the embedded mitigation measures outlined in section 18.1) is ALARP and not significant in EIA terms.