13.8. Key Parameters for Assessment

13.8.1. Maximum Design Scenario

44. The Maximum Design Scenario (MDS) identified in Table 13.6   Open ▸ are those expected to have the potential to result in the greatest effect on an identified receptor or receptor group. These scenarios have been selected from the details provided in volume 1, chapter 3 of the Array EIA Report. Effects of greater significance are not predicted to arise should any other development scenario, based on details within the Project Description (volume 1, chapter 3) (e.g. different infrastructure layout), to that assessed here, be taken forward in the final design scheme.

Table 13.6: Maximum Design Scenario Considered for Each Potential Impact as Part of the Assessment of LSE1 on Shipping and Navigation

13.8.2. Impacts Scoped Out of the Assessment

45. The shipping and navigation pre-Scoping workshop and the Array EIA Scoping Report (Ossian OWFL, 2023) process were used to facilitate stakeholder engagement on topics to be scoped out of the assessment (see Table 13.3   Open ▸ ).
46. On the basis of the baseline environment and the Project Description outlined in volume 1, chapter 3 of the Array EIA Report, no impacts are proposed to be scoped out of the assessment for shipping and navigation. It is noted that impacts to vessel communication and position fixing equipment have been assessed in the NRA (volume 3, appendix 13.1), noting it has been considered within the assessment of collisions and allisions in section 13.11.

13.9. Methodology for Assessment of Effects

13.9.1. Overview

47. The shipping and navigation assessment of effects has followed the Formal Safety Assessment (FSA) methodology since this is the internationally recognised approach for assessing the impact to shipping and navigation receptors, and is the approach required under the MCA’s methodology (Annex 1 of MGN 654). The following guidance documents have been considered:

• MGN 654 (Merchant and Fishing) Safety of Navigation: Offshore Renewable Energy Installations (OREIs) – Guidance on UK Navigational Practice, Safety and Emergency Response and its annexes (MCA, 2021a);
• MGN 372 Amendment 1 (Merchant and Fishing) Guidance to Mariners Operating in the Vicinity of UK OREIs (MCA, 2022);
• International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA) O-139 on The Marking of Man-Made Offshore Structures (IALA, 2021a);
• IALA G1162 The Marking of Offshore Man-Made Structures (IALA, 2021b);
• The RYA Position on Offshore Renewable Energy Developments: Paper 1 (of 4) – Wind Energy (RYA, 2019a); and
• Regulatory Expectations on Moorings for Floating Wind and Marine Devices (MCA and Health and Safety Executive (HSE), 2017).

13.9.2. Criteria for Assessment of Effects

48. The criteria for determining the likely significance of effects for shipping and navigation are derived from a two-stage process that considers the severity of consequence and frequency of occurrence. This section describes the criteria applied in this chapter to assign values to each of these two factors.
49. The criteria for defining severity of consequence in this chapter are outlined in Table 13.7   Open ▸ . For the level of assistance required to manage environmental damage, the tiers indicated relate to the incident response matrix provided in the National Contingency Plan (NCP) (MCA, 2014).

Table 13.7: Definition of Terms Relating to the Severity of Consequence (MCA, 2014)

50. The criteria for defining frequency of occurrence in this shipping and navigation Array EIA Report chapter are outlined in Table 13.8   Open ▸ .

Table 13.8: Definition of Terms Relating to the Frequency of Occurrence

51. The significance of the effect upon shipping and navigation is determined by correlating the severity of consequence and frequency of occurrence, as shown in in Table 13.9   Open ▸ .
52. For the purposes of this assessment:

• a level of effect of Unacceptable will be considered a ‘significant’ effect in terms of the EIA Regulations;
• a level of effect of Broadly Acceptable will be considered ‘not significant’ in terms of the EIA Regulations; and
• a level of effect of Tolerable will be considered ‘not significant’ in terms of the EIA Regulations assuming the risks have been reduced to As Low As Reasonably Practicable (ALARP) through application of mitigation.

Table 13.9: Matrix Used for the Assessment of the Significance of the Effect

53. Additionally, differences in terminology between this chapter (which uses EIA terminology) and the NRA (which uses FSA terminology) are summarised in Table 13.10   Open ▸ . Further details of the EIA methodology are provided in volume 1, chapter 6.

Table 13.10: Summary of Differences in Terminology Between EIA and NRA

13.10. Measures Adopted as Part of the Array

54. As part of the Array design process, a number of designed in measures have been proposed to reduce the potential for impacts on shipping and navigation (see Table 13.11   Open ▸ ). They are considered inherently part of the design of the Array and, as there is a commitment to implementing these measures, these have been considered in the assessment presented in section 13.11 (i.e. the determination of significance assumes implementation of these measures). These designed in measures are considered standard industry practice for this type of development.

Table 13.11: Designed in Measures Adopted as Part of the Array

13.11. Assessment of Significance

55. Table 13.6   Open ▸ summarises the impacts arising from the construction, operation and maintenance and decommissioning phases of the Array, as well as the MDS against which each impact has been assessed. An assessment of the likely significance of the effects of the Array on the shipping and navigation receptors caused by each identified impact is given below.

Increased Vessel to Vessel Collision Risk Resulting from Displacement (Third‑Party to Third‑Party)

                        Construction phase

56. There will be no restrictions on entry to the Array other than through any active safety zones. However, it is considered likely that commercial vessels will deviate to avoid the Array during construction, which will be marked as a buoyed construction area as directed by NLB. This aligns with input received in the Hazard Workshop including from commercial vessel representation, and operational experience of other UK wind farms including the nearby Seagreen 1 Offshore Wind Farm and Neart na Gaoithe Offshore Wind Farm.
57. Anticipated deviations for the main commercial routes identified from the vessel traffic data have been defined. The full methodology for main route deviations is provided in volume 3, appendix 13.1, section 13.4.1, with reasonable worst case deviation assumptions established in line with industry experience and consultation feedback.
58. Deviations from the pre wind farm scenario (current baseline) would be required for seven out of the 11 main commercial routes identified (routes 4, 5, 7, 8, 9, 10 and 12 as per Figure 13.4   Open ▸ ). However, it should be noted that the busiest routes (routes 4 and 5 in Figure 13.4   Open ▸ , which have six vessels per week and two to three vessels per week, respectively) would have very low deviation (less than 0.1 nm) while the routes with larger deviation (routes 7 and 8 in Figure 13.4   Open ▸ , which would have a deviation of 5.7 nm and 4.9 nm, respectively) are quieter routes (with only one to two vessels per week each). Further, worst case assumptions have been made in terms of deviations as set out in volume 3, appendix 13.1, section 13.4.1.
59. It is noted that one regular commercial ferry operator was identified in the area, namely Smyril Line, who run a service between the Faroe Islands, Iceland and Rotterdam.
60. With the main commercial route deviations in place, the base case annual vessel to vessel collision frequency for commercial vessels is estimated to be 5.42×10-4, corresponding to a return period of approximately one in 1,845 years. This represents a 31% increase in collision frequency compared to the pre wind farm base case scenario (see volume 3, appendix 13.1).
61. The return period of one in 1,845 years is reflective of the low volume of vessel traffic in the area compared to elsewhere in the UK. Experience from previous under construction offshore wind farms indicates that Masters regularly choose to transit greater than 1 nm from construction works, and there is sufficient sea room available for vessels to do so around the Array (see volume 3, appendix 13.1).
62. Smaller vessel types (e.g. fishing, recreation) may still choose to transit through the Array during construction, noting this would be at the discretion of individual vessels. In this regard it should be considered that there is limited experience of deployment of large scale floating offshore wind projects, and as such vessels may be less likely to transit through floating structures than those on fixed foundations (this assumption aligns with consultation input, see section 13.5). However, there is considered to be sufficient sea room to accommodate any vessels that chose to avoid the Array without notably increasing vessel density around the site boundary, given that the nearest baseline offshore wind farm (Seagreen 1 Offshore Wind Farm) is approximately 27 nm inshore of the Array.
63. The impact will be present throughout the construction phase which will last for up to eight years. Given that third-party vessels are expected to be compliant with relevant Flag State regulations including the COLREGs, the likes of collision avoidance action seek to ensure that the likelihood of an encounter developing into a collision incident is low. This is furthered by the promulgation of information and charting of the buoyed construction area which will increase awareness of ongoing construction activities, thus allowing third-party vessels to passage plan in advance (see section 13.10).
64. Based on the incident data studied for the NRA, the most likely consequences in the event of a collision incident between third-party vessels 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 Potential Loss of Life (PLL) and the environmental consequence of pollution. Such a scenario would be more likely if one of the vessels 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 impacts should pollution occur (volume 4, appendix 21, annex A).

                        Frequency of occurrence

65. 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.

                        Severity of consequence

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

                        Significance of the effect

67. Overall, the severity of consequence is deemed to be serious and the frequency of occurrence is considered to be extremely unlikely. The effect will, therefore, be of tolerable significance and ALARP, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

68. No secondary shipping and navigation mitigation is considered necessary because the likely effect, in the absence of mitigation beyond the designed in measures outlined in Table 13.11   Open ▸ , is of tolerable significance and ALARP which is not significant in EIA terms.

                        Operation and maintenance phase

69. Based on experience at existing operational offshore wind farms and consultation undertaken (see section 13.5), it is anticipated that commercial vessels will generally choose not to navigate internally within the Array. Therefore, the anticipated deviations discussed for the construction phase are directly applicable to the operation and maintenance phase, and it is likely that the deviations already established during construction will continue into the operation and maintenance phase. On this basis, the risk of third-party to third-party vessel collision for commercial vessels is considered analogous during the operation and maintenance phase as during the construction phase.
70. It is anticipated that commercial fishing vessels and recreational vessels may choose to navigate internally within the Array (and this may be more likely during the operation and maintenance phase than in the construction phase given there will be no construction buoys or construction activities) based on experience at existing operational offshore wind farms, particularly in favourable weather conditions. Such navigation may result in an additional encounter and collision risk associated with these small craft exiting the Array. However, with the application of good seamanship and given the high minimum spacing between wind turbines (1,000 m), there is not expected to be a visual obstruction to vessels passing at the edge of the Array. It is also noted that most small vessels this far offshore would be expected to be broadcasting on AIS. This assumption aligns with both consultation input (section 13.5), and the vessel traffic survey data collected (section 13.7.1).
71. The impact will be present throughout the operation and maintenance phase which will last for up to 35 years. Given that third-party vessels are expected to be compliant with Flag State regulations including the COLREGs, the likes of collision avoidance action seek to ensure that the likelihood of an encounter developing into a collision incident is low. This is furthered by the promulgation of information and charting of infrastructure associated with the Array which will increase awareness of the Array and any ongoing major maintenance activities, thus allowing third-party vessels to passage plan in advance (see section 13.10).
72. The most likely consequences of the impact 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 one of the third‑party vessels involved was a small craft and the other a commercial vessel since the small craft may have a weaker structural integrity than the commercial vessel. The Array’s MPCP will be implemented to minimise the environmental effects should pollution occur.

                        Frequency of occurrence

73. 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.

                        Severity of consequence

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

                        Significance of the effect

75. Overall, the severity of consequence is deemed to be serious and the frequency of occurrence is considered to be extremely unlikely. The effect will therefore be of tolerable significance and ALARP, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

76. No secondary shipping and navigation mitigation is considered necessary because the likely effect, in the absence of mitigation beyond the designed in measures outlined in Table 13.11   Open ▸ , is of tolerable significance and ALARP which is not significant in EIA terms.

                        Decommissioning phase

77. 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 resulting in the anticipated deviations for the main commercial routes defined for the construction phase being directly applicable for the decommissioning phase. On this basis, the risk of third-party to third-party vessel collision for commercial vessels is considered the same during the decommissioning phase as during the construction phase. 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.
78. The impact will be present throughout the decommissioning phase which is expected to be of similar duration to the construction phase (i.e. maximum of eight years). Given that third-party vessels are expected to be compliant with Flag State regulations including the COLREGs, the likes of collision avoidance action seek to ensure that the likelihood of an encounter developing into a collision incident is low. This is furthered by the promulgation of information and charting of the buoyed decommissioning area which will maximise awareness of ongoing decommissioning activities, thus allowing third-party vessels to passage plan in advance.
79. The most likely consequences associated with the MDS are as per the equivalent construction phase and operation and maintenance phase impacts.

                        Frequency of occurrence

80. 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.

                        Severity of consequence

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

                        Significance of the effect

82. Overall, the severity of consequence is deemed to be serious and the frequency of occurrence is considered to be extremely unlikely. The effect will therefore be of tolerable significance and ALARP, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

83. No secondary shipping and navigation mitigation is considered necessary because the likely effect, in the absence of mitigation beyond the designed in measures outlined in Table 13.11   Open ▸ , is of tolerable significance and ALARP which is not significant in EIA terms.

Displacement from Adverse Weather Routeing

84. Some vessels and vessel operators may wish to transit alternative routes during periods of adverse weather. Adverse weather includes wind, wave and tidal conditions as well as reduced visibility due to fog.

                        Construction phase

85. No specific adverse weather routeing was observed within the baseline vessel traffic data studied, however the long term 12 month AIS analysis within the NRA (volume 3, appendix 13.1) showed a minor weighting towards summer months for cargo vessels, tankers, and oil and gas vessels in terms of traffic volumes. This may indicate that such vessels prefer to pass further inshore of the shipping and navigation study area in adverse conditions (which may be more likely during winter months).
86. Adverse weather can hinder a vessel’s standard route, its speed of navigation, and/or its ability to enter the destination port. Adverse weather routes are assessed to be significant course adjustments to mitigate vessel motion in adverse weather conditions. When transiting in adverse weather conditions, a vessel is likely to encounter various types of weather and tidal phenomena, which may lead to severe roll motions, potentially causing damage to cargo and equipment, and/or discomfort and danger to persons on board. The sensitivity of a vessel to these phenomena will depend on the actual stability parameters, hull geometry, vessel type, vessel size and speed.
87. The following key points of relevance to adverse weather were raised during consultation (see section 13.5):

• Smyril Line stated that vessels would likely not transit through offshore wind farms in adverse weather conditions.
• It was suggested at the Hazard Workshop that vessels would likely seek to make the most direct safe transit possible during adverse weather.
• Wilson Ship Management indicated transit choice through the area would depend on weather conditions, and stated preference for passing inshore.

88. There is open sea area inshore of the site boundary (the closest baseline wind farm is Seagreen 1 Offshore Wind Farm, located 27 nm inshore) and therefore the buoyed construction area is not considered as hindering any preference for inshore routeing.
89. Details would be promulgated to facilitate advanced passage planning including in adverse conditions. 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. In particular, vessels would be able to account for forecast for adverse conditions within their passage planning.
90. 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.

                        Frequency of occurrence

91. 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.

                        Severity of consequence

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

                        Significance of the effect

93. Overall, the severity of consequence is deemed to be serious and the frequency of occurrence is considered to be extremely unlikely. The effect will therefore be of tolerable significance and ALARP, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

94. No secondary shipping and navigation mitigation is considered necessary because the likely effect, in the absence of mitigation beyond the designed in measures outlined in Table 13.11   Open ▸ , is of tolerable significance and ALARP which is not significant in EIA terms.

                        Operation and maintenance phase

95. As noted in the equivalent construction phase discussion, no specific adverse weather routeing was observed within the baseline vessel traffic data studied, however the long term 12 month AIS analysis within the NRA showed a minor weighting towards summer months for cargo vessels, tankers, and oil and gas vessels in terms of volume.
96. There is open sea area inshore of the site boundary (the closest operational wind farm is Seagreen 1 Offshore Wind Farm, located 27 nm inshore) and therefore the Array is not considered as hindering any preference for inshore routeing. During the operation and maintenance phase, vessels may be more likely to pass through the Array than during the construction phase, however based on consultation input (see section 13.5) it is unlikely that vessels would choose to transit through the Array during adverse weather conditions.
97. All infrastructure will be shown on appropriate Admiralty Charts ensuring vessels can passage plan to account for the Array. 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.
98. 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.

                        Frequency of occurrence

99. 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.

                        Severity of consequence

100. The severity of consequence is therefore considered to be serious.

                        Significance of the effect

101. Overall, the severity of consequence is deemed to be serious and the frequency of occurrence is considered to be extremely unlikely. The effect will therefore be of tolerable significance and ALARP, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

102. No secondary shipping and navigation mitigation is considered necessary because the likely effect, in the absence of mitigation beyond the designed in measures outlined in Table 13.11   Open ▸ , is of tolerable significance and ALARP which is not significant in EIA terms.

                        Decommissioning phase

103. 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.
104. 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.
105. 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.

                        Frequency of occurrence

106. 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.

                        Severity of consequence

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

                        Significance of the effect

108. Overall, the severity of consequence is deemed to be serious and the frequency of occurrence is considered to be extremely unlikely. The effect will therefore be of tolerable significance and ALARP, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

109. No secondary shipping and navigation mitigation is considered necessary because the likely effect, in the absence of mitigation beyond the designed in measures outlined in Table 13.11   Open ▸ , is of tolerable significance and ALARP which is not significant in EIA terms.

Increased Vessel to Vessel Collision Risk (Third‑Party to Project Vessels)

                        Construction phase

110. 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 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 NSVMP (which will be a condition of consent).
111. 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 works 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.
112. 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 maximise awareness of ongoing construction activities.
113. 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 maximise awareness, both in day and night conditions including in restricted visibility. An outline LMP is provided in volume 4, appendix 26. This will include details of 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.
114. 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.
115. 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 13.5) 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.
116. The impact will be present throughout the construction phase which may last for up to eight years. With the designed in measures noted above 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.
117. 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.
118. 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 Array’s MPCP will be implemented to reduce the environmental effects should pollution occur.

                        Frequency of occurrence

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

                        Severity of consequence

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

                        Significance of the effect

121. Overall, the severity of consequence is deemed to be serious and the frequency of occurrence is considered to be extremely unlikely. The effect will therefore be of tolerable significance and ALARP, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

122. No secondary shipping and navigation mitigation is considered necessary because the likely effect, in the absence of mitigation beyond the designed in measures outlined in Table 13.11   Open ▸ , is of tolerable significance and ALARP which is not significant in EIA terms.

                        Operation and maintenance phase

123. 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.
124. 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.
125. 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 maximise awareness of ongoing major maintenance activities.
126. 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.
127. 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.
128. 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 13.5) 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.
129. The impact will be present throughout the operation and maintenance phase which may last for up to 35 years. With the designed in measures noted above 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.
130. 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.
131. 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 allision 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 minimise the environmental effects should pollution occur.

                        Frequency of occurrence

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

                        Severity of consequence

133. The severity of consequence is therefore considered to be serious.

                        Significance of the effect

134. Overall, the severity of consequence is deemed to be serious and the frequency of occurrence is considered to be extremely unlikely. The effect will therefore be of tolerable significance and ALARP, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

135. No secondary shipping and navigation mitigation is considered necessary because the likely effect, in the absence of mitigation beyond the designed in measures outlined in Table 13.11   Open ▸ , is of tolerable significance and ALARP which is not significant in EIA terms.

                        Decommissioning phase

136. Since the numbers and types of vessel 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, project vessels will be managed by marine coordination, applications will be made for statutory safety zones, and decommissioning activities will generally be located within the buoyed decommissioning area.
137. The impact will be present throughout the decommissioning phase which is expected to be of similar duration to the construction phase (i.e. maximum of eight years). With the designed in measures previously noted implemented, it is considered unlikely that an encounter between a third-party vessel and a project vessel will occur. As per the equivalent construction phase impact, in the event that such an encounter does occur, collision avoidance action would be implemented by the vessels as per the COLREGs, thus ensuring that the likelihood of the encounter developing into a collision incident is very low.

                        Frequency of occurrence

138. The frequency of occurrence is considered to be extremely unlikely based on the available searoom, consideration of historical incident data, and the designed in measures in place to manage project vessel movements and activities.

                        Severity of consequence

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

                        Significance of the effect

140. Overall, the severity of consequence is deemed to be serious and the frequency of occurrence is considered to be extremely unlikely. The effect will therefore be of tolerable significance and ALARP, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

141. No secondary shipping and navigation mitigation is considered necessary because the likely effect, in the absence of mitigation beyond the designed in measures outlined in Table 13.11   Open ▸ , is of tolerable significance and ALARP which is not significant in EIA terms.

Vessel to Structure Allision Risk

142. The spatial extent of the impact is considered small given that a vessel must be in close proximity to a structure in the Array for an allision incident to occur. The forms of allision considered are:

• powered allision;
• drifting allision; and
• internal allision.

143. These are discussed separately for each phase, with a combined impact significance ranking provided.

                        Construction phase

                        Powered allision

144. Powered allision risk may be caused by human/navigational error, unfamiliarity with the Array and/or a failure of an aid to navigation.
145. Experience from previous under construction offshore wind farms indicates that Masters regularly choose to transit greater than 1 nm from construction works. In doing so, vessels are unlikely to navigate close enough to a structure to create an allision risk. There is a distance of 27 nm between the Array and Seagreen 1 Offshore Wind Farm, the closest baseline offshore wind farm, which provides notable sea room for safe navigation.
146. Based on the NRA (volume 3, appendix 13.1) modelling, with the main commercial route deviations in place and assuming all structures are installed, the base case annual powered vessel to structure allision frequency is estimated to be 6.91×10-3, corresponding to a return period of approximately one in 145 years.
147. The impact will be present throughout the construction phase which may last for up to eight years and will cover a greater spatial extent as more structures are installed. Safety zones of up to 50 m around partially completed or completed but not yet fully commissioned surface piercing structures will be in place and assist with ensuring that vessels are aware of the presence of structures. Where identified as necessary via risk assessment (which will include consideration of the other mitigation measures in place), a guard vessel may also be used, which will alert passing vessels to the presence of the ongoing construction activities. Furthermore, the use of lighting and marking as required by the NLB and the MCA (including for partially completed structures), charting of the buoyed construction area and promulgation of information will allow vessels to passage plan a safe route in advance. It should also be noted that commercial vessels are expected to comply with international and Flag State regulations (including the COLREGs and SOLAS). Consultation with the NLB to establish agreement on lighting and marking will be undertaken post-consent. With these designed in measures in place, it is considered unlikely that a powered allision incident will occur.
148. From historical incident data, there have been no reported instances of a powered allision involving a third-party vessel with a pre-commissioned wind farm structure in the UK.
149. The most likely consequences in the event of a powered allision incident are minor damage to property with the vessel able to resume passage and undertake a full inspection at the next port. However, this will depend on multiple factors including the energy of the impact, structural integrity of the vessel and the sea state at the time. Given the potential for a non-steel construction, commercial fishing vessels and recreational vessels are considered more vulnerable. Although considered less likely an allision could involve the vessel foundering resulting in PLL and the environmental consequence of pollution. The Array’s MPCP will be implemented to reduce the environmental effects should pollution occur.

                        Drifting allision

150. Drifting allision risk may be caused by mechanical or technical failure, adverse weather and/or a navigational system error. A vessel adrift may only develop into an allision situation if in proximity to a pre-commissioned structure. This is only the case where the adrift vessel is located in proximity to the buoyed construction area and the wind and/or tide directs the vessel towards a structure.
151. As discussed in relation to powered allision risk, it is likely that commercial vessels will deviate to avoid the buoyed construction area. As such, it is likely that associated allision risk would be highest to pre-commissioned structures on the periphery of the Array. Smaller vessels may still choose to transit through, and as such may come in proximity to internal structures.
152. Based on the NRA (volume 3, appendix 13.1) modelling, with the main commercial route deviations in place, the base case annual drifting vessel to structure allision frequency is estimated to be 2.16×10-4, corresponding to a return period of approximately one in 4,619 years.
153. For drifting allision incidents, the adrift vessel would initiate its emergency response procedures to avoid a Closest Point of Approach (CPA) with a structure resulting in an allision. This may include emergency anchoring following a check of the relevant nautical charts (thus ensuring that the anchor deployment does not lead to other impacts such as anchor snagging on a subsea cable), noting this would depend on the vessel and water depths. These measures may also include the use of thrusters (depending on availability and power supply). Moreover, under SOLAS obligations (IMO, 1974), other nearby vessels including project vessels (via marine coordination) may be able to render assistance, depending on the type and size of vessel.
154. From historical incident data, there have been no reported instances of a drifting allision involving a third-party vessel with a pre-commissioned wind farm structure in the UK.
155. Should a drifting allision occur, the consequences will be similar to those noted for the case of a powered allision including the unlikely worst case of foundering and pollution. In the highly unlikely scenario of a drifting allision incident resulting in pollution, the implementation of the MPCP will reduce the environmental risk. Additionally, a drifting vessel is likely to be moving at a reduced speed compared to a powered vessel dependent on conditions, thus reducing the energy of the impact, including in the case of a recreational vessel under sail.