Significance of the Effect

85. Overall, the severity of consequence is deemed to be minor and the frequency of occurrence is considered to be frequent. The effect will, therefore, be of tolerable adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

86. No shipping and navigation mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in Table 13.15   Open ▸ ) is not significant in EIA terms.

Decommissioning Phase

Severity of Consequence

87. 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, as presented in Figure 13.8   Open ▸ and detailed in Table 13.16   Open ▸ .
88. Therefore, the most likely consequences associated with the maximum adverse scenario are as per the equivalent construction phase impact.
89. The severity of consequence is therefore considered to be minor.

Frequency of Occurrence

90. The impact will be present throughout the decommissioning phase which will last for up to eight years. Since the anticipated deviations associated with the main commercial routes and the volumes of vessel traffic on such routes are the same as for the equivalent construction phase impact, it is again anticipated that vessels will be exposed to the impact on a daily basis.
91. The frequency of occurrence is therefore considered to be frequent.

Significance of the Effect

92. Overall, the severity of consequence is deemed to be minor and the frequency of occurrence is considered to be frequent. The effect will, therefore, be of tolerable adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

93. No shipping and navigation mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in Table 13.15   Open ▸ ) is not significant in EIA terms.

Increased Vessel to Vessel Collision Risk Between a Third-party Vessel and a Project Vessel

Construction Phase

Severity of Consequence

94. Up to 10,964 return trips by construction vessels (excluding site preparation activities) 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, designated routes to and from construction ports and liaison with Project vessels for the other Outer Firth of Forth developments. Project vessels will also carry AIS and be compliant with relevant Flag State regulations including the COLREGs. This includes installation vessels working within the Proposed Development export cable corridor which as vessels Restricted in their Ability to Manoeuvre (RAM) are covered by COLREGs rule 18.
95. 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 but not yet fully commissioned surface piercing structures. Such safety zones will protect project vessels involved in construction which may be RAM and, if on-site, guard vessels will assist with monitoring safety zones.
96. Any lessons learnt from construction vessel movements associated with the Seagreen construction phase will be considered. Details of construction activities, including the presence of safety zones and any advisory safe passing distances, as defined by risk assessment, will be suitably promulgated to maximise awareness of ongoing construction activities.
97. Additionally, the use of 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. This includes the buoyed construction area which will be agreed with the NLB and within which Project vessels undertaking construction activities associated with the Proposed Development array area will generally be located. As per the impact on vessel displacement, it is anticipated that third-party vessels will not enter the buoyed construction area and therefore the level of exposure for Project vessels located on-site will be very low.
98. 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 the carriage of AIS by such vessels will also assist with identifying their movements.
99. 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 ten year period since, reflecting the increasing awareness of offshore wind farm developments and improved application of the various measures outlined above.
100. 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. The maximum adverse scenario 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 the third-party vessel involved was a small craft which may have weaker structural integrity than a commercial vessel. The Project’s Marine Pollution Contingency Plan will be implemented to minimise the environmental effects should pollution occur.
101. The severity of consequence is therefore considered to be moderate.

Frequency of Occurrence

102. The impact will be present throughout the construction phase which will last for up to eight years. With the mitigation 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 ensuring that the likelihood of the encounter developing into a collision incident is very low.
103. The frequency of occurrence is therefore considered to be extremely unlikely.

Significance of the Effect

104. Overall, the severity of consequence is deemed to be moderate and the frequency of occurrence is considered to be extremely unlikely. The effect will, therefore, be of broadly acceptable adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

105. No shipping and navigation mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in Table 13.15   Open ▸ ) is not significant in EIA terms.

Operation and Maintenance Phase

Severity of Consequence

106. Up to 2,323 return trips per year by operation and maintenance 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.
107. 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 and, if on-site, guard vessels will assist with monitoring safety zones.
108. Any lessons learnt from operation and maintenance vessel movements associated with the Seagreen operation and maintenance phase will be considered, noting that Seagreen is expected to be fully commissioned in November 2023 (Seagreen Wind Energy Ltd., 2020). 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 to maximise awareness of ongoing major maintenance activities.
109. Additionally, the use of lighting and marking as required by the NLB and the MCA will further maximise awareness, both in day and night conditions including in restricted visibility. As per the equivalent construction phase impact, 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 array. 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 identifying their movements.
110. 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 ten-year period since, reflecting the increasing awareness of offshore wind farm developments and improved application of the various measures previously outlined.
111. 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. The maximum adverse scenario 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 Project’s Marine Pollution Contingency Plan will be implemented to minimise the environmental effects should pollution occur.
112. The severity of consequence is therefore considered to be moderate.

Frequency of Occurrence

113. The impact will be present throughout the operation and maintenance phase which will 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.
114. The likelihood of an encounter is decreased compared to in the construction phase given that much fewer project vessels will generally be on-site at any time, although this is somewhat balanced by the much longer duration of the operation and maintenance phase.
115. The frequency of occurrence is therefore considered to be negligible.

Significance of the Effect

116. Overall, the severity of consequence is deemed to be moderate and the frequency of occurrence is considered to be negligible. The effect will, therefore, be of broadly acceptable adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

117. No shipping and navigation mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in Table 13.15   Open ▸ ) is not significant in EIA terms.

Decommissioning Phase

Severity of Consequence

118. 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, safety zones will be applied for and decommissioning activities will generally be located within the buoyed decommissioning area.
119. Therefore, the most likely consequences associated with the maximum adverse scenario are as per the equivalent construction phase impact.
120. The severity of consequence is therefore considered to be moderate.

Frequency of Occurrence

121. The impact will be present throughout the decommissioning phase which will last for up to 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.
122. The frequency of occurrence is therefore considered to be extremely unlikely.

Significance of the Effect

123. Overall, the severity of consequence is deemed to be moderate and the frequency of occurrence is considered to be extremely unlikely. The effect will, therefore, be of broadly acceptable adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

124. No shipping and navigation mitigation is considered necessary because the predicted impact in the absence of mitigation is not significant in EIA terms.

Increased Vessel to Vessel Collision Risk Between Third Party Vessels

Construction Phase

Severity of Consequence

125. Anticipated deviations for the main commercial routes identified from the vessel traffic data have been defined, as described in the construction phase impact for vessel displacement. An illustration of the anticipated shift in the mean positions of the main commercial routes within the Proposed Development array area shipping and navigation study area for the maximum adverse scenario is presented in Figure 13.8   Open ▸ . For the displaced routes, the increase in distance from the pre wind farm scenario is detailed in Table 13.16   Open ▸ .
126. Although a deviation will be required for seven out of the 14 main commercial routes identified, the level of deviation is relatively low (less than 1.0 nm) for five of them. The two routes with larger deviations (Routes 5 and 14) involve passing around the south-eastern corner of the buoyed construction area, where they did not previously pass. This creates a pinch point where encounters between commercial vessels are more likely to occur and was confirmed by collision risk modelling (see Figure 16.5 in the NRA). Other pinch points include at the south-western corner of the buoyed construction area.
127. With the main commercial route deviations in place, the base case annual vessel to vessel collision frequency for commercial vessels is estimated to be 9.69×10-4, corresponding to a return period of approximately one in 1,031 years. This represents a 15% increase in collision frequency compared to the pre wind farm base case scenario.
128. The return period of one in 1,031 years is considered below average compared to that estimated for other UK offshore wind farm developments and 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. This will reduce the effects of the aforementioned pinch points and reduce the likelihood of encounters.
129. Following consultation with the UK Chamber of Shipping and Forth Ports, it was confirmed that occasional vessel traffic movements associated with jack-ups, semi-submersibles and other platforms occur in the region. One such case (involving a Floating Production Storage and Offloading (FPSO) vessel) was identified in the long-term vessel traffic data (see appendix E of the NRA) and in such instances the vessel will often be under tow and RAM. Therefore, the collision risk associated with the vessel would be greater given the inability to take swift collision avoidance action in the event of an encounter. This will be particularly pertinent where such movements occur within the gap between the Proposed Development array area and Seagreen.
130. In the unrealistic scenario that Inch Cape is not built, there is potential for a small number of vessels to utilise the gap between the Proposed Development array area and Seagreen. There is an increased collision risk given the proximity to surface piercing structures to both port and starboard, reducing sea room for any collision avoidance action. The potential for fishing gear to be present within this gap is also highlighted, although the gap will be known to commercial fishing operators and they will be able to choose whether to deploy gear depending on the level of risk. Additionally, pots should always be marked appropriate to minimise the risk to other vessels and the gear.
131. During consultation the MCA highlighted the need to consider the potential squeeze of small craft into the routes of larger commercial vessels. Given that recreational traffic is primarily located inshore of the Proposed Development array area (as indicated by the Forth Yacht Clubs Association), the effect on recreational vessels is expected to be limited.
132. Commercial fishing vessel traffic is more likely to be affected since active fishing vessel activity is located within the proposed buoyed construction area and based on experience at previously under construction offshore wind farms (including the nearby NnG), it is anticipated that commercial fishing vessels will choose not to navigate internally within the buoyed construction area. Transits out of Eyemouth may interact with the pinch points previously noted for commercial vessels.
133. 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. The maximum adverse scenario 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 vessels involved was a small craft which may have weaker structural integrity than a commercial vessel. The Project’s Marine Pollution Contingency Plan will be implemented to minimise the environmental effects should pollution occur.
134. The severity of consequence is therefore considered to be moderate.

Frequency of Occurrence

135. 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 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 maximise awareness of ongoing construction activities, thus allowing third-party vessels to passage plan in advance.
136. The frequency of occurrence is therefore considered to be extremely unlikely.

Significance of the Effect

137. Overall, the severity of consequence is deemed to be moderate and the frequency of occurrence is considered to be extremely unlikely. The effect will, therefore, be of broadly acceptable adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

138. No shipping and navigation mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in Table 13.15   Open ▸ ) is not significant in EIA terms.

Operation and Maintenance Phase

Severity of Consequence

139. Based on experience at existing operational offshore wind farms, it is anticipated that commercial vessels will generally choose not to navigate internally within the Proposed Development array area. Therefore, the anticipated deviations for the main commercial routes defined for the construction phase (around the buoyed construction area) are directly applicable for the operation and maintenance phase, as presented in Figure 13.8   Open ▸ and detailed in Table 13.16   Open ▸ .
140. Since the size and location of the buoyed construction area and operational Proposed Development array area will be almost identical, the pinch points highlighted for the equivalent construction phase impact are again applicable.
141. Based on experience at existing operational offshore wind farms, it is anticipated that commercial fishing vessels and recreational vessels may choose to navigate internally within the Proposed Development array area, particularly in favourable weather conditions. Such navigation may result in an additional encounter and collision risk associated with these small craft exiting the Proposed Development array area. Although, 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 Proposed Development array area.
142. 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. The maximum adverse scenario 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 Project’s Marine Pollution Contingency Plan will be implemented to minimise the environmental effects should pollution occur.
143. The severity of consequence is therefore considered to be moderate.

Frequency of Occurrence

144. 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 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 Proposed Development which will maximise awareness of the Proposed Development and any ongoing major maintenance activities, thus allowing third-party vessels to passage plan in advance.
145. The frequency of occurrence is therefore considered to be extremely unlikely.

Significance of the Effect

146. Overall, the severity of consequence is deemed to be moderate and the frequency of occurrence is considered to be extremely unlikely. The effect will, therefore, be of broadly acceptable adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

147. No shipping and navigation mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in Table 13.15   Open ▸ ) is not significant in EIA terms.

Decommissioning Phase

Severity of Consequence

148. 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, presented in Figure 13.8   Open ▸ and detailed in Table 13.16   Open ▸ .
149. Therefore, the most likely consequences associated with the maximum adverse scenario are as per the equivalent construction phase impact.
150. The severity of consequence is therefore considered to be moderate.

Frequency of Occurrence

151. The impact will be present throughout the decommissioning phase which will last for up to 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 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.
152. The frequency of occurrence is therefore considered to be extremely unlikely.

Significance of the Effect

153. Overall, the severity of consequence is deemed to be moderate and the frequency of occurrence is considered to be extremely unlikely. The effect will, therefore, be of broadly acceptable adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

154. No shipping and navigation mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in Table 13.15   Open ▸ ) is not significant in EIA terms.

Vessel to Structure Allision Risk

Construction Phase

Severity of Consequence

155. There are three distinct forms of allision risk which are considered – powered allision risk, drifting allision risk and internal allision risk.
156. Powered allision risk may be caused by human/navigational error, unfamiliarity with the Proposed Development and/or a failure of an aid to navigation. 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. In doing so, vessels are unlikely to navigate close enough to a structure to create an allision risk. Masters will also have experience navigating in proximity to NnG and Seagreen (which will be operational by the time of the construction phase) which will further reduce the risk of an allision incident associated with the Proposed Development.
157. This assertion (in terms of sufficient sea room being available) is also applicable within the gap between the Proposed Development array area and Seagreen given that the width of this gap varies between 2.8 and 6.0 nm. Usage is expected to be very low (only one main commercial route is anticipated to regularly utilise the gap) and sufficient sea room is available to allow a vessel navigating within the gap to maintain a minimum distance of 1 nm from wind farm structures (including pre-commissioned structures), minimising allision risk.
158. 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.
159. 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.
160. 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.
161. During consultation the MCA highlighted the need to consider the risk to drifting recreational craft in adverse weather or tidal conditions. A sailing vessel in such a situation could be exposed to an additional allision risk from its mast with wind turbine blades. Emergency action, such as the lowering of the sails, may prevent an allision occurring and the minimum blade clearance of 22 m above MHWS (see Table 13.15   Open ▸ ) is aligned with the minimum clearance the RYA recommend for minimising allision risk (RYA, 2019); indeed the Applicant is committed to a minimum blade clearance of 37 m above LAT. There is also potential for effects such as wind shear, masking and turbulence to occur, with previous studies of offshore wind farm developments concluding that wind turbines do reduce wind velocity downwind of a wind turbine (MCA, 2008) noting no negative effects on recreational craft reported. It is also noted that no practical issues have been raised by recreational users to date when operating in proximity to existing offshore wind farm developments.
162. As per the impact on vessel displacement, it is anticipated that third-party vessels will not enter the buoyed construction area and therefore internal allision risk is not considered relevant during this phase.
163. The most likely consequences in the event of an allision incident (powered or drifting) 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. The maximum adverse scenario could involve the vessel foundering resulting in PLL and the environmental consequence of pollution. The Project’s Marine Pollution Contingency Plan will be implemented to minimise the environmental effects should pollution occur.
164. The consequences are less likely to be severe for a drifting allision incident given that the speed at which the impact occurs (and subsequent energy of the impact) will generally be dictated by the wind and/or tidal speeds.
165. The severity of consequence is therefore considered to be moderate.

Frequency of Occurrence

166. The impact will be present throughout the construction phase which will last for up to eight years and will cover a greater spatial extent as more structures are installed. For powered allision incidents, 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. If on-site, guard vessels will assist with monitoring safety zones. 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. The NLB stated during consultation that further discussions on lighting and marking will be appropriate once final layouts are under consideration. The final array layout will be agreed through the DSLP which will include consultation with the MCA and NLB. With these designed in measures in place, it is considered unlikely that a powered allision incident will occur.
167. 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). Moreover, under SOLAS obligations (IMO, 1974), other nearby vessels including project vessels (via marine coordination) may be able to render assistance. There is also a possibility that a drifting vessel could regain power prior to alliding with a structure. Therefore, it is considered very unlikely that a drifting allision incident will occur.
168. The frequency of occurrence is therefore considered to be extremely unlikely.

Significance of the Effect

169. Overall, the severity of consequence is deemed to be moderate and the frequency of occurrence is considered to be extremely unlikely. The effect will, therefore, be of broadly acceptable adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

170. No shipping and navigation mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in Table 13.15   Open ▸ ) is not significant in EIA terms.

Operation and Maintenance Phase

Severity of Consequence

171. Again, there are three distinct forms of allision risk which are considered – powered allision risk, drifting allision risk and internal allision risk.
172. Powered allision risk may be caused by human/navigational error, unfamiliarity with the Proposed Development and/or a failure of an aid to navigation. Experience from previous operational offshore wind farms indicates that Masters regularly choose to transit greater than 1 nm from the array, and there is sufficient sea room available for vessels to do so. In doing so, vessels are unlikely to navigate in close enough proximity to a structure to create an allision risk. Masters will also have experience navigating in proximity to the nearby NnG and Seagreen (which will also be operational by the time of the operation and maintenance phase) which will further reduce the risk of an allision incident.
173. With the main commercial route deviations in place, the base case annual powered vessel to structure allision frequency is estimated to be 1.52×10-4, corresponding to a return period of approximately one in 6,581 years. This is below average compared to that estimated for other UK offshore wind farm developments. The greatest powered vessel to structure allision risk was associated with structures along the western edge of the array, where multiple main commercial routes pass at the minimum 1 nm distance. As discussed above, Masters may choose to transit at greater than 1 nm from the array, which would reduce the powered allision risk considerably.
174. From historical incident data, there has been two reported instances of a third-party vessel alliding with an operational wind farm structure in the UK. Both of these incidents involved a fishing vessel, with a RNLI lifeboat attending on both occasions and a helicopter deployed in one case. Given that the Proposed Development array area is located in the Outer Firth of Forth where there is varied vessel traffic including transits in and out of the Firth of Forth, there will likely be a heightened level of awareness meaning that such an incident is unlikely to occur at the Proposed Development array area.
175. 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 structure and this is only the case where the adrift vessel is located in proximity to the array and the wind and/or tide directs the vessel towards a structure.
176. With the main commercial route deviations in place, the base case annual drifting vessel to structure allision frequency is estimated to be 7.69×10-5, corresponding to a return period of approximately one in 12,999 years. This is below average compared to that estimated for other UK offshore wind farm developments. The greatest drifting vessel to structure allision risk was associated with structures along the eastern and western edges of the array, where multiple main commercial routes pass at the minimum 1 nm distance. As discussed above, Masters may choose to transit at greater than 1 nm from the array, which would reduce the drifting allision risk considerably.
177. From historical incident data, there have been no reported instances of a drifting allision involving a third-party vessel with an operational wind farm structure in the UK. It is also noted that RNLI incident data indicates that cases of machinery failure (which may result in a drifting vessel) typically occur inshore of the Proposed Development array area at a distance within which a recovery could be expected prior to an allision occurring.
178. During consultation, the MCA highlighted the need to consider the risk to drifting recreational craft in adverse weather or tidal conditions. As per the equivalent construction phase impact, blade allision is possible for a sailing vessel with a mast, but the sails could be lowered and the minimum blade clearance of 22 m above MHWS (see section Table 13.15   Open ▸ ) is aligned with the minimum clearance the RYA recommend for minimising allision risk (RYA, 2019); indeed the Applicant is committed to a minimum blade clearance of 37 m above LAT. Effects such as wind shear, masking and turbulence could occur but previous studies conclude that no negative effects on recreational craft are reported.
179. As per the impact on vessel displacement, it is anticipated that commercial fishing vessels and recreational vessels may choose to navigate internally within the array, particularly in favourable weather conditions. Therefore, an internal allision risk exists for such smaller craft.
180. The base case annual fishing vessel to structure allision frequency is estimated to be 2.29×10-1, corresponding to a return period of approximately one in 4.4 years. This is high compared to that estimated for other UK offshore wind farm developments and is reflective of the widespread fishing vessel activity and number of structures. This frequency does not account for the presence of safety zones of up to 500 m around structures where vessels are undertaking major maintenance work which will assist with ensuring that vessels are aware of the presence of structures.
181. For internal navigation it is also noted that the array layout forms a grid pattern with two lines of orientation for wind turbines (as requested by MGN 654), including an angle favourable for the steady volume of fishing vessel transits in and out of Eyemouth. This will further assist safe navigation by small craft, with the need for changes in course minimised. However, the offshore substation platforms/offshore convertor station platforms are out of alignment with the wind turbines (noting that the array layout assessed is indicative at the time of the assessment and represents the MDS) which may result in extra care being required when navigating within the relevant rows of the array. Comfort with internal navigation will likely increase throughout the lifetime of the Proposed Development and appropriate lighting and marking will be in place to maximise awareness of the substation locations. The final array layout will be agreed through the DSLP will include consultation with the MCA and NLB.
182. The most likely consequences in the event of an allision incident (powered or drifting) are as per the equivalent construction phase impact, namely minor damage to property. The maximum adverse scenario could involve the vessel foundering resulting in PLL and the environmental consequence of pollution. The Proposed Development’s Marine Pollution Contingency Plan (MPCP) will be implemented to minimise the environmental effects should pollution occur.
183. The consequences are less likely to be severe for a drifting allision incident given that the speed at which the impact occurs (and subsequent energy of the impact) will generally be dictated by the wind and/or tidal speeds. Likewise, a vessel navigating internally within the array is likely to be transiting at lower speeds, reducing the severity of impact.
184. The severity of consequence is therefore considered to be moderate.

Frequency of Occurrence

185. The impact will be present throughout the operation and maintenance phase which will last for up to 35 years. For powered allision incidents, major maintenance safety zones will be in place and assist with ensuring that vessels are aware of the presence of structures. If on-site, guard vessels will assist with monitoring safety zones. Furthermore, the use of lighting and marking as required by the NLB and the MCA and promulgation of information will allow vessels to passage plan a safe route in advance, with the NLB stating during consultation that further discussions on lighting and marking will be appropriate once final layouts are under consideration. With these designed in measures in place, it is considered unlikely that a powered allision incident will occur.
186. For drifting allision incidents, the adrift vessel would initiate its emergency response procedures to avoid a CPA with a structure potentially 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). Moreover, under SOLAS obligations (IMO, 1974), other nearby vessels including project vessels (via marine coordination) may be able to render assistance. It is, however, noted that the number of project vessels on-site will be substantially lower than during the construction phase. There is also a possibility that a drifting vessel could regain power prior to alliding with a structure. Therefore, it is considered unlikely that a drifting allision incident will occur.
187. The frequency of occurrence is therefore considered to be remote.

Significance of the Effect

188. Overall, the severity of consequence is deemed to be moderate and the frequency of occurrence is considered to be remote. The effect will, therefore, be of tolerable adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

189. No shipping and navigation mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in Table 13.15   Open ▸ ) is not significant in EIA terms.

Decommissioning Phase

Severity of Consequence

190. 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 and it is anticipated that third-party vessels will not enter. Therefore, the internal allision risk is not considered relevant during this phase.
191. Pre-decommissioning or partially removed structures will be similar in nature to pre-commissioning or partially completed structures, and the movement of third-party vessels around the buoyed decommissioning area is anticipated to be similar to that during the construction phase. Therefore, powered and drifting allision risk is anticipated to be similar in nature to that determined for the equivalent construction phase impact, including the most likely consequences and consequences associated with the maximum adverse scenario.
192. The severity of consequence is therefore considered to be moderate.

Frequency of Occurrence

193. The impact will be present throughout the decommissioning phase which will last for up to eight years and will cover a lesser spatial extent as more structures are removed. For powered allision incidents, safety zones of up to 50 m around partially removed surface piercing structures will be in place and assist with ensuring that vessels are aware of the presence of structures. If on-site, guard vessels will assist with monitoring safety zones. Furthermore, the use of lighting and marking as required by the NLB and the MCA (including for partially removed structures), charting of the buoyed decommissioning area and promulgation of information will allow vessels to passage plan a safe route in advance. With these designed in measures in place, it is considered unlikely that a powered allision incident will occur.
194. For drifting allision incidents, the adrift vessel would initiate its emergency response procedures to avoid a 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). Moreover, under SOLAS obligations (IMO, 1974), other nearby vessels including project vessels (via marine coordination) may be able to render assistance. There is also a possibility that a drifting vessel could regain power prior to alliding with a structure. Therefore, it is considered very unlikely that a drifting allision incident will occur.
195. The frequency of occurrence is therefore considered to be extremely unlikely.

Significance of the Effect

196. Overall, the severity of consequence is deemed to be moderate and the frequency of occurrence is considered to be extremely unlikely. The effect will, therefore, be of broadly acceptable adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

197. No shipping and navigation mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in Table 13.15   Open ▸ ) is not significant in EIA terms.

Reduced Access to Local Ports

Construction Phase

Severity of Consequence

198. Up to 10,964 return trips by construction vessels (excluding site preparation activities) 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, designated routes to and from construction ports and liaison with project vessels for the other Outer Firth of Forth developments. Project vessels will also carry AIS and be compliant with Flag State regulations including the COLREGs.
199. Anticipated deviations for the main commercial routes identified from the vessel traffic data have been defined, as described in the construction phase impact for vessel displacement. An illustration of the anticipated shift in the mean positions of the main commercial routes within the Proposed Development array area shipping and navigation study area for the maximum adverse scenario is presented in Figure 13.8   Open ▸ . For the displaced routes, the increase in distance from the pre wind farm scenario is detailed in Table 13.16   Open ▸ .
200. The closest port or harbour to the Proposed Development array area is Arbroath Harbour, located approximately 23 nm (43 km) to the north-west, on the east coast of Scotland. Given the relative distance to ports in the area and the anticipated deviations for the main commercial routes, it is not anticipated that there will be any substantial effect on vessel approaches to and from the Firth of Forth or other local ports above and beyond the deviations outlined for the vessel displacement impact.
201. There are no pilot boarding locations associated with Forth, Tay and Montrose ports/harbours within the Outer Firth of Forth; pilot boarding stations associated with the Tay and Montrose are located in the close approaches to the respective ports. Additionally, during consultation, Forth Ports noted that their VTS system does not extend as far out as the Proposed Development array area and they do not have VTS authority over that area (even in an advisory capacity).
202. Offshore export cables installation may result in some disruption for those vessels crossing the Proposed Development export cable corridor in and out of the Firth of Forth, Firth of Tay and Montrose due to the presence of vessels which may be RAM, such as a cable laying vessel. However, the offshore export cables are expected to be installed in phases which will restrict any disruption to only a small portion of the total Proposed Development export cable corridor.
203. Any lessons learnt from construction vessel movements associated with the Seagreen construction phase will be considered and details of construction activities including the presence of safety zones and any advisory safe passing distances, as defined by risk assessment, will be suitably promulgated to maximise awareness of ongoing construction activities.
204. The most likely consequences of the impact are increased journey times and distances due to the presence of the buoyed construction area and project vessels, as per the vessel displacement impact. The maximum design scenario may include disruption to schedules, but this is considered highly unlikely given the international nature of routeing in the area and the ability to passage plan to minimise timing impacts. No effect is anticipated on port related services such as pilotage.
205. The severity of consequence is therefore considered to be minor.

Frequency of Occurrence

206. The impact will be present throughout the construction phase which will last for up to eight years. The busiest main commercial route identified within the Proposed Development array area shipping and navigation study area accessing a local port for which an increased passage distance is required is Route 5, with an average of one vessel per day. In total, across all the routes accessing a local port for which an increased passage distance is required, there is an average of two vessels per day. Additionally, a proportion of the non-commercial vessel traffic may also be affected, noting that an average of one to two unique fishing vessels per day were recorded within the Proposed Development array area shipping and navigation study area throughout the vessel traffic surveys. Fishing vessel routeing out of Eyemouth is of particular note.
207. Therefore, it is anticipated that vessels will be exposed to the impact on a daily basis, particularly commercial vessels such as tankers and cargo vessels which constitute the majority of the vessel traffic, including those assigned to the main commercial routes.
208. The frequency of occurrence is therefore considered to be frequent.

Significance of the Effect

209. Overall, the severity of consequence is deemed to be minor and the frequency of occurrence is considered to be frequent. The effect will, therefore, be of tolerable adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

210. No shipping and navigation mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in Table 13.15   Open ▸ ) is not significant in EIA terms.

Operation and Maintenance Phase

Severity of Consequence

211. Up to 2,323 return trips per year by operation and maintenance 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.
212. Based on experience at existing operational offshore wind farms, it is anticipated that commercial vessels will generally choose not to navigate internally within the Proposed Development array area. Therefore, the anticipated deviations for the main commercial routes defined for the construction phase (around the buoyed construction area) are directly applicable for the operation and maintenance phase, as presented in Figure 13.8   Open ▸ and detailed in Table 13.16   Open ▸ .
213. As noted for the equivalent construction phase impact, the closest port or harbour to the Proposed Development array area is Arbroath Harbour (23 nm (43 km)). Again, given the relative distance to ports in the area and the anticipated deviations for the main commercial routes, it is not anticipated that there will be any substantial effect on vessel approaches to and from the Firth of Forth or other local ports above and beyond the deviations outlined for the vessel displacement impact.
214. As noted for the equivalent construction phase impact, there are no pilot boarding locations associated with the Forth, Tay and Montrose within the Outer Firth of Forth, and pilot boarding stations associated with the Tay and Montrose are located in the close approaches to the respective ports. Additionally, during consultation, Forth Ports noted that their VTS system does not extend as far out as the Proposed Development array area and they do not have VTS authority over that area (even in an advisory capacity).
215. Disruption within the Proposed Development export cable corridor will be more limited during the operation and maintenance phase, due to the more limited nature of operation and maintenance works consisting of temporary and intermittent activities such as inspections, surveys, repairs and reburials.
216. Any lessons learnt from operation and maintenance vessel movements associated with the Seagreen operational phase will be considered and 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 to maximise awareness of ongoing operation and maintenance activities.
217. The most likely consequences of the impact are as per the equivalent construction phase impact, namely increased journey times and distances. The maximum adverse scenario may include disruption to schedules, but this is considered highly unlikely given the international nature of routeing in the area and the ability to passage plan to minimise timing impacts. No effect is anticipated on port related services such as pilotage.
218. The severity of consequence is therefore considered to be minor.

Frequency of Occurrence

219. The impact will be present throughout the operation and maintenance phase which will last for up to 35 years. Since the anticipated deviations associated with the main commercial routes accessing a local port and the volumes of vessel traffic on such routes are the same as for the equivalent construction phase impact, it is again anticipated that vessels will be exposed to the impact on a daily basis. However, with lower levels of project vessel, restrictions on port access due to project vessel activity can be expected to be lower in frequency than during the construction phase.
220. The likelihood of non-commercial vessels being affected is lower than for the equivalent construction phase impact given that, based on experience at existing operational offshore wind farms, it is anticipated that small craft may choose to navigate internally within the array, particularly in favourable weather conditions. This will minimise disruption to routeing to and from local ports, particularly out of Eyemouth where there is a notable volume of fishing vessel activity.
221. The frequency of occurrence is therefore considered to be reasonably probable.

Significance of the Effect

222. Overall, the severity of consequence is deemed to be minor and the frequency of occurrence is considered to be reasonably probable. The effect will, therefore, be of tolerable adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

223. No shipping and navigation mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in Table 13.15   Open ▸ ) is not significant in EIA terms.

Decommissioning Phase

Severity of Consequence

224. 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, the number of return trips per year by decommissioning vessels will be similar and 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, as presented in Figure 13.8   Open ▸ and detailed in Table 13.16   Open ▸ .
225. Therefore, the most likely consequences associated with the maximum adverse scenario are as per the equivalent construction phase impacts.
226. The severity of consequence is therefore considered to be minor.

Frequency of Occurrence

227. The impact will be present throughout the decommissioning phase which will last for up to eight years. Since the anticipated deviations associated with the main commercial routes accessing a local port and the volumes of vessel traffic on such routes are the same as for the equivalent construction phase impact, it is again anticipated that vessels will be exposed to the impact on a daily basis.
228. One notable difference in the decommissioning phase compared to the construction phase is that subsea cables are anticipated to be left in situ (although best practice will be followed at the time of decommissioning). This will reduce the likelihood of disruption for those vessels crossing the Proposed Development export cable corridor in and out of the Firth of Forth, Firth of Tay and Montrose.
229. The frequency of occurrence is therefore considered to be frequent.

Significance of the Effect

230. Overall, the severity of consequence is deemed to be minor and the frequency of occurrence is considered to be frequent. The effect will, therefore, be of tolerable adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

231. No shipping and navigation mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in Table 13.15   Open ▸ ) is not significant in EIA terms.

Reduction of Under Keel Clearance

Operation and Maintenance Phase

Severity of Consequence

232. Up to 661 nm (1,225 km) of inter-array cables, 51 nm (94 km) of interconnector cables and eight offshore export cables with total length 471 nm (872 km) will be in place during the operation and maintenance phase. The target minimum burial depth for subsea cables will be 0.5 m with a maximum cable protection height of 3 m (excluding crossings). Cable burial is the preferred option of safeguarding the subsea cables, with up to 15% of all subsea cables anticipated to require cable protection.
233. There is an overlap between the offshore export cables for NnG and the Proposed Development export cable corridor. Where the crossing occurs, there will be a maximum cable protection height of 3.5 m against a water depth between 34 m and 43 m below CD. Therefore, the change in navigable water depth is likely to be up to 10%.
234. Seagreen 1 makes landfall at Carnoustie on the east coast of Scotland with no spatial overlap with the Proposed Development export cable corridor. Likewise, the inter-array cables for NnG and Seagreen 1 will be located entirely within the respective array areas, resulting in no spatial overlap with the Proposed Development export cable corridor.
235. A cable burial risk assessment will be undertaken to determine the implementation and monitoring of cable protection.
236. During consultation, the MCA raised that cable burial depth requires consideration and noted the requirements of MGN 654 (MCA, 2021). The Applicant intends to follow the guidance provided in MGN 654 where possible, and in particular cable protection will not change the charted water depth by more than 5% where possible. This also aligns with the RYA’s recommendation that the “minimum safe under keel clearance over submerged structures and associated infrastructure should be determined in accordance with the methodology set out in MGN 543 [now superseded by MGN 654]” (RYA, 2019). In the case of the crossing of the Proposed Development export cable corridor and the offshore export cables for NnG, any reduction in navigable water depth greater than 5% will be discussed with the MCA and the NLB post consent as per MGN 654.
237. Should an underwater allision occur, the most likely consequences are minor damage to property and minor reputational effects on business but no perceptible effect on people. The maximum adverse scenario may include the vessel foundering resulting in PLL and the environmental consequence of pollution. The Project’s Marine Pollution Contingency Plan will be implemented to minimise the environmental effects should pollution occur.
238. The severity of consequence is therefore considered to be moderate.