16.2.3 Decommissioning Phase

  1. Since the methods used to remove infrastructure are expected to be similar to those used for installation, this impact is expected to be similar in nature to the equivalent construction phase impact. In particular, a buoyed decommissioning area analogous to the buoyed construction area will be in place. However, it is noted that the deviations will be well established by the decommissioning phase, and that vessels will likely be more familiar with the Array than during the construction phase.
  2. Details would be promulgated to facilitate advanced passage planning including in adverse conditions. In particular, vessels would be able to account for forecast for adverse conditions within their passage planning. Under COLREGS (IMO, 1972/77), vessels are also required to take appropriate measures with regards to determining a safe speed, taking into account various factors including the state of visibility, the state of the wind, sea, and current as well as the proximity of navigational hazards.
  3. Most likely consequences are minor alterations to existing adverse weather routeing noting the data indicates a preference for inshore routeing in such conditions. As a worst case vessels may be required to pass further offshore than preferred leading to large deviations in adverse conditions and safety concerns.

16.2.3.1  Frequency of Occurrence

  1. The frequency of occurrence is considered to be extremely unlikely based on the available sea room, the outputs of the modelling, and consideration of historical incident data.

16.2.3.2  Severity of Consequence

  1. The severity of consequence is considered to be serious.

16.2.3.3  Significance of the Risk

  1. Overall, the frequency of occurrence is considered to be extremely unlikely and the severity of consequence is deemed to be serious. The risk will therefore be of tolerable significance.

16.2.3.4  Additional Mitigation and Residual Risk

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

16.3 Increased Vessel to Vessel Collision Risk (Third-Party To Project Vessels)

16.3.1 Construction Phase

  1. Up to 7,902 return trips by construction vessels (and site preparation vessels) may be made throughout the construction phase and will include vessels which are Restricted in their Ability to Manoeuvre (RAM). Project vessels will be managed by marine coordination, including the use of traffic management procedures such as the designation of entry and exit points to and from the buoyed construction area. Project vessels will also carry AIS and be compliant with relevant Flag State regulations, including the COLREGs, and comply with the procedures set out in the VMP (which will be a condition of consent).
  2. Safety zones will be applied for including up to 500 m around structures where vessels are undertaking construction work and 50 m around partially completed or completed surface piercing structures prior to commissioning of the wind farm. Such safety zones will protect project vessels involved in construction which may be RAM. If on-site as deemed necessary via risk assessment, guard vessels will also assist with monitoring safety zones and alerting third party traffic to their presence.
  3. Details of construction activities, including the presence of safety zones and any use of advisory safe passing distances, as defined by risk assessment, will be suitably promulgated to increase awareness of ongoing construction activities.
  4. Additionally, the use of IALA G1162 (IALA, 2021b) compliant lighting and marking including lights, marks, sounds, signals and other aids to navigation as required by the NLB and the MCA will further increase awareness, both in day and night conditions including in restricted visibility. This includes the buoyed construction area which will be agreed with the NLB and within which project vessels undertaking construction activities will most likely be located during construction activities. As per the impact on vessel displacement, it is anticipated that third-party vessels are unlikely to frequently enter the buoyed construction area and therefore the level of exposure for project vessels located on-site will be very low.
  5. In restricted visibility, there is an increased risk of visual impediment to third-party vessels in relation to identifying project vessels entering and exiting the buoyed construction area. However, the COLREGs regulate vessel movements in adverse weather conditions including the requirement for all vessels operating in reduced visibility to maintain a safe speed which will allow more time for reacting to encounters. COLREGs also covers the movement of project vessels and manages any encounters, and the carriage of AIS by such vessels will also assist with identifying their movements.
  6. It is noted that there will be a need to tow floating substructures out of port during the construction phase. Feedback received at the Hazard Workshop (see section 4.3.3) was that good seamanship and watchkeeping in compliance with COLREGS were key mitigations. Procedures for vessels towing substructures will also be considered in the VMP. All vessels involved in towing procedures will be lit and marked as required under COLREGS. Precise plans for fabrication and wet storage locations are unknown at this stage. Where enabling works are required within port limits to facilitate fabrication and storage these will be subject to the relevant assessment and licensing for the port works. Wet storage within the site boundary will be limited.
  7. The impact will be present throughout the construction phase which may last for up to eight years. With the embedded mitigation measures noted in section 18.1 implemented, it is considered unlikely that a close encounter between a third-party vessel and a project vessel will occur. In the event that such an encounter does occur, collision avoidance action would be implemented by the vessels as per the COLREGs, thus seeking to ensure that the likelihood of the encounter developing into a collision incident is very low.
  8. From historical incident data, there has been only one collision incident involving a third-party vessel and project vessel in the UK, occurring in a harbour in 2011 and resulting in moderate vessel damage but no harm to any People On Board (POB). No collision incidents have occurred in the period since (in excess of ten years), reflecting the increasing awareness of offshore wind farm developments and improved application of the various measures outlined above.
  9. The most likely consequences in the event of a collision incident between a project vessel and third‑party vessel are minor contact between the vessels resulting in minor damage to property and minor reputational effects on business but no perceptible effect on people. Although considered less likely collision between third party vessels could involve one of the vessels foundering resulting in PLL and the environmental consequence of pollution. Such a scenario would be more likely if the third-party vessel involved was a small craft which may have weaker structural integrity than a commercial vessel. The Applicant’s MPCP will be implemented to reduce the environmental effects should pollution occur.

16.3.1.1  Frequency of Occurrence

  1. The frequency of occurrence is considered to be extremely unlikely based on the available sea room, consideration of historical incident data, and the embedded mitigation in place to manage project vessel movements and activities.

16.3.1.2  Severity of Consequence

  1. The severity of consequence is considered to be serious.

16.3.1.3  Significance of Risk

  1. Overall, the frequency of occurrence is considered to be extremely unlikely and the severity of consequence is deemed to be serious. The risk will therefore be of tolerable significance.

16.3.1.4  Additional Mitigation and Residual Risk

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

16.3.2 Operation and Maintenance Phase

  1. Up to 508 return trips annually from vessels may be made throughout the operation and maintenance phase and will include vessels which are RAM. As per the construction phase, project vessels will be managed by marine coordination, carry AIS and be compliant with relevant Flag State regulations.
  2. Also, safety zones will be applied for including up to 500 m around structures where vessels are undertaking major maintenance work. Such safety zones will protect project vessels involved in major maintenance which may be RAM. If on-site (determined via risk assessment of major maintenance activities), guard vessels will assist with monitoring safety zones and alerting third‑party traffic to their presence.
  3. Similarly to the construction phase, details of major maintenance activities including the presence of safety zones and any advisory safe passing distances, as defined by risk assessment, will be suitably promulgated (e.g. via Notice to Mariners, Kingfisher) to increase awareness of ongoing major maintenance activities.
  4. Additionally, the use of lighting and marking (IALA G1162 compliant (IALA, 2021b)) as required by the NLB and the MCA will further increase awareness, both in day and night conditions including in restricted visibility. In restricted visibility there is an increased risk of visual obstruction to third-party vessels in relation to identifying project vessels entering and exiting the project. However, the COLREGs regulate vessel movements in adverse weather conditions, allowing more time to react to encounters. The carriage of AIS by project vessels will also assist with third‑party vessels identifying their movements.
  5. As per the equivalent construction phase impact, there has been only one collision incident involving a third-party vessel and project vessel in the UK, occurring in a harbour in 2011 and resulting in moderate vessel damage but no harm to any POB. No collision incidents have occurred in the period since (in excess of ten years), reflecting the increasing awareness of offshore wind farm developments and improved application of the various measures previously outlined.
  6. It is noted that there may be a need to tow floating substructures to/from port during the operation and maintenance phase for maintenance purposes (noting this is only likely to be needed for major component replacement). Feedback received at the Hazard Workshop (see section 4.3.3) was that good seamanship and watchkeeping in compliance with COLREGS were key mitigations. Procedures for vessels towing substructures will also be considered in the VMP. All vessels involved in towing procedures will be lit and marked as required under COLREGS.
  7. The impact will be present throughout the operation and maintenance phase which may last for up to 35 years. With the embedded mitigation measures noted in section  18.1 implemented, it is considered unlikely that an encounter between a third-party vessel and a project vessel will occur. In the event that such an encounter does occur, collision avoidance action would be implemented by the vessels as per COLREGs, thus ensuring that the likelihood of the encounter developing into a collision incident is very low.
  8. The likelihood of an encounter is decreased compared to in the construction phase given that fewer project vessels will generally be on-site at any time.
  9. The most likely consequences in the event of a collision incident between a project vessel and third-party vessel are as per the equivalent construction phase impact, namely minor contact and damage to property and minor reputational effects on business, but no perceptible effect on people. Although considered less likely collision between third party vessels could involve one of the vessels foundering resulting in PLL and the environmental consequence of pollution. Such a scenario would be more likely if the third-party vessel involved was a small craft which may have weaker structural integrity than a commercial vessel. The Array’s MPCP will be implemented to reduce the environmental effects should pollution occur.

16.3.2.1  Frequency of Occurrence

  1. The frequency of occurrence is considered to be extremely unlikely based on the available sea room, consideration of historical incident data, and the embedded mitigation in place to manage project vessel movements and activities.

16.3.2.2  Severity of Consequence

  1. The severity of consequence is considered to be serious.

16.3.2.3  Significance of the Risk

  1. Overall, the frequency of occurrence is considered to be extremely unlikely and the severity of consequence is deemed to be serious. The risk will therefore be of tolerable significance.

16.3.2.4  Additional Mitigation and Residual Risk

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