16.3 Post Wind Farm Modelling
16.3.1 Simulated Automatic Identification System
Anatec’s AIS Simulator software was used to gain an insight into the potential re-routed commercial traffic following the installation of the wind farm structures within the Proposed Development array area. The AIS Simulator uses the mean positions of the main commercial routes identified within the Proposed Development array area study area and the anticipated shift post wind farm, together with the standard deviations and average number of vessels on each main commercial route to simulate tracks.
A plot of 28 days of simulated AIS (matching the total duration of the vessel traffic surveys) within the Proposed Development array area study area, based on the deviated main commercial routes, is presented in Figure 16.4 Open ▸ .
It is noted that the simulated AIS represents a maximum design scenario based on routes passing at a minimum mean distance of 1 nm from the Proposed Development array area.
Figure 16.4 Post Wind Farm Simulated Base Case AIS Tracks within the Proposed Development Array Area Study Area (28 Days)
16.3.2 Vessel to Vessel Collision Risk
Using the post wind farm routeing as input, Anatec’s COLLRISK model has been run to estimate the anticipated vessel to vessel collision risk within the Proposed Development array area study area.
A heat map based on the geographical distribution of collision risk within a density grid for post wind farm base case is presented in Figure 16.5 Open ▸ .
Figure 16.5 Post Wind Farm Vessel to Vessel Collision Risk Heat Map within the Proposed Development Array Area Study Area
Assuming base case traffic levels, the annual collision frequency post wind farm was estimated to be 9.69×10-4, corresponding to a return period of approximately one in 1,032 years. This represents a 15% increase in collision frequency compared to the pre wind farm base case result.
The increase in vessel to vessel collision risk was greatest along the southern and eastern edges of the Proposed Development array area. The change in vessel to vessel collision risk between the base case pre wind farm and post wind farm scenarios is presented in a heat map in Figure 16.6 Open ▸ .
Figure 16.6 Change in Vessel to Vessel Collision Risk within the Proposed Development Array Area Study Area
16.3.3 Powered Vessel to Structure Allision Risk
Based upon the vessel routeing identified within the Proposed Development array area study area, the anticipated re-routeing as a result of the presence of the Proposed Development, and the assumptions that relevant embedded mitigation measures are in place (see section 17), the frequency of an errant vessel under power deviating from its route to the extent that it may come into proximity with a wind farm structure associated with the Proposed Development is considered to be low.
From consultation with the shipping industry, it is also assumed that commercial vessels would be highly unlikely to navigate between wind farm structures due to the restricted sea room and will instead be directed by the aids to navigation located in the region and those present at the Proposed Development. During the construction and decommissioning phases this will primarily consist of the buoyed construction area, while during the operation and maintenance phase this will primarily consist of the lighting and marking of the wind farm structures themselves.
Using the post wind farm routeing as input, together with the maximum design scenario and local meteorological ocean data, Anatec’s COLLRISK model was run to estimate the likelihood of a commercial vessel alluding with one of the wind farm structures within the Proposed Development array area whilst under power. In order to maintain a maximum design scenario, the model did not consider one structure shielding another.
A plot of the annual powered allision frequency per structure for the base case is presented in Figure 16.7 Open ▸ , with the chart background removed to increase the visibility of those structures with lower allision frequencies.
Figure 16.7 Base Case Powered Allision Risk per Structure
Assuming base case vessel traffic levels, the annual powered allision frequency was estimated to be 1.52×10-4, corresponding to a collision return period of approximately one in 6,581 years.
The greatest powered vessel to structure allision risk was associated with structures along the western edge of the Proposed Development array area, where multiple main commercial routes pass at the minimum 1 nm distance. The greatest individual allision risk was associated with one of the structures on the western edge of the Proposed Development array area (approximately 2.72×10-5, or one in 36,701 years).
16.3.4 Drifting Vessel to Structure Allision Risk
Using the post wind farm routeing as input, together with the worst-case indicative array layout and meteorological ocean data, Anatec’s COLLRISK model was run to estimate the likelihood of a commercial vessel alluding with one of the wind farm structures within the Proposed Development array area. The model is based on the premise that propulsion on a vessel must fail before drifting will occur. The model takes account of the type and size of the vessel, the number of engines and the average time required to repair but does not consider navigational errors caused by human actions.
The exposure times for a drifting scenario are based upon the vessel hours spent within the Proposed Development array area study area. These have been estimated based on the vessel traffic levels, speeds, and revised routeing patterns. The exposure is divided by vessel type and size to ensure that these specific factors, which based upon analysis of historical incident data have been shown to influence incident rates, are taken into account for the modelling.
Using this information, the overall rate of mechanical failure in proximity to the Proposed Development array area was estimated. The probability of a vessel drifting towards a wind farm structure and drift speed are dependent on the prevailing wind, wave and tidal conditions at the time of the incident. Therefore, three drift scenarios were modelled, each using the meteorological ocean data provided in section 8.
- Wind;
- Peak spring flood tide; and
- Peak spring ebb tide.
The probability of vessel recovery from drift is estimated based upon the speed of the drift and hence the time available before arriving at a wind farm structure. Vessels which do not recover within this time are assumed to allide. Conservatively, no account is made for another vessel (including a vessel associated with the Proposed Development) rendering assistance.
After modelling the three drifting scenarios, the wind dominated scenario was established to produce the worst-case results. A plot of the annual drifting allision frequency per structure for the base case is presented in Figure 16.8 Open ▸ , with the chart background removed to increase the visibility of those structures with a low allision frequency.
Figure 16.8 Base Case Drifting Allision Risk per Structure
Assuming base case vessel traffic levels, the annual drifting allision frequency was estimated to be 7.69×10-5, corresponding to a return period of approximately one in 12,999 years.
The greatest drifting vessel to structure allision risk was associated with structures along the southern and eastern edges of the Proposed Development array area, at both of which main commercial routes pass at the minimum mean distance of 1 nm from the Proposed Development array area. The greatest individual allision risk was associated with one of the structures on the southern edge of the Proposed Development array area (approximately 4.82×10-6, or one in 207,650 years).
It is noted that historically there have been no reported drifting allision incidents with wind farm structures in the UK. While drifting vessels do occur every year in UK waters, in most cases the vessel has been recovered prior to any allision incident occurring (such as by anchoring, restarting engines, or being taken in tow).
16.3.5 Fishing Vessel to Structure Allision Risk
Using the vessel traffic survey data as input, Anatec’s COLLRISK model was run to estimate the likelihood of a fishing vessel alluding with one of the wind farm structures within the Proposed Development array area.
A fishing vessel allision is classified separately from other allisions since fishing vessels may be either in transit or actively fishing within the Proposed Development array area (unlike the transiting commercial traffic characterised by the main commercial routes). Additionally, fishing vessels could be observed internally within the Proposed Development array area (i.e., between structures) as well as externally. Anatec’s model uses vessel numbers, sizes (length and beam), array layout and structure dimensions. The likelihood of a major allision incident has been calibrated against historical maritime incident data and historical AIS vessel traffic data within operational wind farm arrays. Given that not all fishing vessels broadcast on AIS, the vessel density observed is scaled up to account for non-AIS fishing vessels, with the scaling factor dependent on the distance of the array offshore.
A plot of the annual fishing vessel allision frequency per structure for the base case is presented in Figure 16.9 Open ▸ .
Figure 16.9 Base Case Fishing Vessel Allision Risk per Structure
Assuming base case traffic levels, the annual fishing vessel to structure allision frequency was estimated to be 2.29×10-1, corresponding to a return period of approximately one in 4.4 years.
The fishing vessel to structure allision risk was distributed throughout the Proposed Development array area, with fishing activity observed throughout. The greatest individual allision risk was associated with a structure (an offshore substation platform) in the north-east of the Proposed Development array area (approximately 2.19×10-2 or one in 45.6 years).
It is noted that this allision risk result does not give an indication of the consequences of an allision incident which would most likely (based on historical incident data) involve a minor contact with no material damage, injuries to persons or pollution.
16.4 Risk Results Summary
The previous sections modelled two scenarios, namely the pre and post wind farm scenarios with base case traffic levels. In order to incorporate the potential for future traffic growth, pre and post wind farm scenarios have also been modelled for future case traffic levels (both 10% and 20% increases). Table 16.1 Open ▸ summarises the results of all six scenarios.
Overall, the base case collision and allision frequency due to the presence of the Proposed Development was estimated to increase by approximately 1.95×10-1 (equating to an additional collision or allision every 5.1 years).
Table 16.1 Summary of Annual Collision and Allision Risk Results
17 Embedded Mitigation Measures
As part of the design process for the Proposed Development, a number of embedded mitigation measures have been adopted to reduce the risk of hazards identified, including those relevant to shipping and navigation. These measures have and will continue to evolve over the development process as the EIA progresses and in response to consultation.
These measures typically include those that have been identified as good or standard practice and include actions that will be undertaken to meet existing legislation requirements. As there is a commitment to implementing these measures, and also to various standard sectoral practices and procedures, they are considered inherently part of the design of the Proposed Development.
The embedded mitigation measures within the design relevant to shipping and navigation are outlined in Table 17.1 Open ▸
Table 17.1 Embedded Mitigation Measures Relevant to Shipping and Navigation
17.2 Design Specifications Noted in Marine Guidance Note 654
The individual wind turbines and other structures will have functions and procedures in place for generator shut down in emergency situations, as per MGN 654 (MCA, 2021).
18 Project in Isolation Risk Assessment
This section outlines the final shipping and navigation hazards for the Project in isolation which have been identified based upon:
- Baseline data;
- Consultation;
- Hazard log[12]; and
- Modelling/numerical assessment.
For each hazard, a description of the hazard is given alongside the causes, relevant users. As per section 0, hazards associated with navigation, communications, and position fixing equipment (with the exception of interference with magnetic position fixing equipment) have been screened out of the FSA. Hazards associated with vessels engaged in fishing are considered in volume 2, chapter 12.
To avoid replication of text the risk assessment has been undertaken in volume 2, chapter 13 in line with EIA requirements but does follow the FSA methodology. Table 18.1 Open ▸ summarises the output of the risk assessment undertaken with consideration of the embedded mitigation measures outlined in section 17. Any additional mitigation measures required above those outlined in section 17 are also summarised.
Table 18.1 Summary of Outputs of Risk Assessment
19 Cumulative Risk Assessment
19.1 Navigation Corridor Safety Case
This section considers the gap between the Proposed Development array area and Inch Cape as a navigation corridor and, where appropriate, uses available guidance to provide a safety case for the corridor from a navigational perspective.
Figure 19.1 Open ▸ presents an overview of the gap between the Proposed Development array area and Inch Cape. For the purposes of this subsection, Inch Cape is represented by the array area boundary published by Crown Estate Scotland, noting that a final array layout has not been published at the time of writing. Therefore, as a worst case, it is assumed that build out of Inch Cape could maximise use of the full array area.
Figure 19.1 Overview of Gap Between Proposed Development Array Area and Inch Cape
The length of the gap is dependent upon where it is measured from, with the length increasing towards the eastern extent. At this extreme of the gap, the length is approximately 4.2 nm. Towards the western extent the length of the gap is approximately 3.3 nm (measured north-south from the eastern boundary of Inch Cape) and in a central location is approximately 3.7 nm.
The width of the gap is approximately 4.1 nm at the northern extent and approximately 8.0 nm at the southern extent, with the former representing the minimum overall width.
19.1.1 Navigational Features
The charted water depth within the gap between the Proposed Development array area and Inch Cape varies between 40 and 60 m below CD. There are no existing surface or seabed features within or in proximity to the gap such as aids to navigation, charted wrecks or submarine cables and pipelines.
19.1.2 Potential Users
From the vessel traffic baseline, five of the main commercial routes identified in section 11.2 (Routes 1, 9, 10, 13 and 14) could be candidates for potential use of a navigation corridor. This is a worst case assumption in terms of usage and in reality, it is anticipated that vessels would be more likely to make an alternative choice such as passing inshore (with appropriate draughts/cargoes) of Inch Cape or offshore of the Proposed Development array area as noted in the regular operator response from Evergas (see section 4.2). This is considered further in section 15.6.
Overall, there is an average of three to four transits per day by potential navigation corridor users on the main commercial routes. Applying a conservative 20% increase in commercial vessel movements for the future case scenario (as outlined in section 15.1), an average of four to five transits per day by potential navigation corridor users is considered throughout the rest of this section.
The average length of potential navigation corridor users was 87 m with a 90th percentile length of 131 m. The 90th percentile length is considered throughout the rest of this section.
19.1.3 Application of Marine Guidance Note 654
There are multiple methods within MGN 654 that the MCA may require developers to demonstrate when calculating the safe width of a proposed navigation corridor. Those methods are demonstrated in the following paragraphs.
MGN 654 states that:
The possibility of ships overtaking cannot be excluded and should be taken into consideration. Consequently, the assumption should be that four ships should safely be able to pass each other… Between overtaking and meeting vessels, a distance of two ship’s lengths is normally maintained as a minimum passing distance.
Therefore, the overtaking width for the navigation corridor, based on the 90th percentile length, is 0.42 nm (786 m)[13].
To determine the overall corridor width, the suitable distance between the outermost vessels and the array areas is required. The Shipping Route Template indicates that 1 nm is the “minimum distance to a parallel IMO routeing measure” and is widely accepted in the industry as a minimum passing distance from an offshore wind farm.
Therefore, the minimum overall width for the navigation corridor, based on the 90th percentile length is 2.4 nm.
Additionally, MGN 654 states that:
Experience also shows that in heavy sea conditions it is much harder to turn the vessel around and [it] may not be possible to achieve a dead stop and deviations from track are common. Therefore 20° or more, are common and must be considered in developing corridors through OREIs.
Applying this 20-degree rule to the minimum navigation corridor length of 3.3 nm (the shortest north-south length) gives a corresponding width requirement of 1.2 nm.
19.1.4 Application of Permanent International Association of Navigation Congresses Guidance
The Guidance on the Interaction between Offshore Wind Farms and Maritime Navigation (Permanent International Association of Navigation Congresses (PIANC), 2018) provides a methodology for calculating the width of corridor required to make a round turn to starboard in the event of a head-on encounter between two vessels. Although this methodology is designed for a Traffic Separation Scheme running parallel to an offshore wind farm, it is considered relevant and useful for corridor design, noting that vessels will have greater flexibility to alter course in the event that collision avoidance is required than would be the case within an IMO routeing measure.
As illustrated in Figure 19.2 Open ▸ , the calculation assumes an initial deviation of 0.3 nm, turning circle of six vessel lengths diameter and 500 m safety margin.
Figure 19.2 Sea Space Required for a Full Round Turn to Starboard (PIANC, 2018)
Applying the calculation to the navigation corridor gives a total width requirement of 2.0 nm, with the breakdown of the distances considered illustrated in Figure 19.3 Open ▸ .
Figure 19.3 Application of PIANC Guidance to Navigation Corridor Between Proposed Development Array Area and Inch Cape
19.1.5 Application of Maritime Institute Netherlands Guidance
A study undertaken by the Maritime Institute Netherlands (MARIN) and referenced in both the PIANC guidance and The Shipping Industry and Marine Spatial Planning (MSP) – A Professional Approach (Nautical Institute, 2013) states that the width of a navigation corridor should consider:
- Number of vessels: based on AIS study, keeping in mind the future development during the lifespan of the structures;
- Maximum size of vessels: same as point 1 re: future development;
- Number of vessels overtaking:
- <4,400 vessels per year: 2 vessels side to side.
- >4,400 vessels and <18,000 vessels: 3 side to side.
- >18,000 vessels: 4 vessels side to side.
- Room per vessel: 2 ship lengths.
The following example is provided, noting that a separation of one vessel length between the flank vessels and the array is assumed:
For example: a traffic lane that accommodates 18,000 vessels per year with a maximum size of 400 m should be at least 3,200 m (1.72 nm) wide.
Applying this calculation to the Proposed Development, the number of potential navigation corridor users per day was estimated as three to four, which corresponds to approximately 1,240 vessels per year. Under the MARIN guidance this leads to an assumption that two vessels should be able to pass side by side through the corridor. Therefore, the overall corridor width (inclusive of the separation between the flank vessels and the array) is 0.28 nm (524 m). Applying the MGN 654 Shipping Route Template value of 1 nm between the flank vessels and the array, the overall corridor width is 2.1 nm.
19.1.6 Application of International Regulations for Preventing Collisions at Sea
The COLREGs are the rules and regulations that help regulate vessel traffic movements throughout the world. It is therefore important that the navigation corridor does not prevent a vessel from being able to comply with these regulations. Although the COLREGs do not make specific provision for a separation between offshore wind farms such as a navigation corridor, they do lay down rules for navigating within a narrow channel which may be somewhat applicable.
Rule 9a states:
A vessel proceeding along the course of a narrow channel or fairway shall keep as near to the outer limit of the channel or fairway which lies on her starboard side as is safe and practicable.
However, a vessel should not enter the gap unless it is confident that it can alter course and manoeuvre as required to comply with the collision regulations and avoid a collision. Course alterations within the gap should not be required under most circumstances given that vessels will be able to navigate straight through on a generally north-south bearing.
Rule 9b states:
A vessel of less than 20 m in length or a sailing vessel shall not impede the passage of a vessel which can safely navigate only within a narrow channel or fairway.
Furthermore, Rule 9c states:
A vessel engaged in fishing shall not impede the passage of any other vessel navigation within a narrow channel or fairway.
Although the COLREGs give priority to vessels navigating within a narrow channel it is still prudent for the purpose of minimising the navigational risk to consider any dense activity involving relevant small craft.
From analysis of non-commercial vessel traffic (see section 10.1.2 and Appendix E), it can be seen that there is moderate fishing vessel activity within and in proximity to the navigation corridor including active fishing as well as transits. Recreational vessel activity within and in proximity to the navigation corridor is relatively low, primarily consisting of north-south transits. However, from consultation there is potential for recreational users to be discouraged from navigating in the area (see 27 July 2022 entry in Table 4.1 Open ▸ ).
The shape of the navigation corridor is suitable for identifying small craft whilst making passage through the navigation corridor. Although not a conventional parallelogram in shape, the navigation corridor is shaped such that vessels have a clear view of any small craft located at the other end or side of the corridor, including in low visibility.
19.1.7 Effect of Non-Transit Users
As noted in section 10.1.2.3 and Appendix E, there are moderate volumes of fishing activity located in proximity to the navigation corridor. A fishing vessel engaged in fishing activities may be unable to make a manoeuvre in sufficient time to avoid an oncoming commercial vessel making passage through the corridor. However, the considerable minimum spacing between structures in proximity to the corridor within the Proposed Development array area (minimum spacing of 1,000 m) and the Inch Cape array area (consented minimum spacing of 1,278 m (ICOL, 2018)) will assist with earlier detection by passing vessels of any smaller craft present within or on the other side of the corridor.
For vessels associated with the Proposed Development, any movements within or in proximity to the corridor will be made in line with the designed-in mitigation measures (see section 17) including compliance with the COLREGs and MGN 372 (MCA, 2008).
A similar mitigation measure is provided in the Inch Cape EIA Report (ICOL, 2018) in relation to vessels associated with Inch Cape works:
Appropriate marine coordination (through a dedicated marine coordination function) of the Development’s own vessels will be implemented in order to ensure that construction vessels do not create additional risk to third parties.
With these mitigation measures in place, it is not anticipated that vessels (either for the Proposed Development or Inch Cape) will have any detrimental effect on the ability of navigation corridor users to make passage safely.
19.1.8 Radar Interference
For vessels transiting through the navigation corridor there may be a potential for increased exposure to radar interference. This is considered fully in section 13.8 as part of the wider assessment of risks associated with navigation, communication and position fixing equipment and is not considered to have a significant effect. In particular, it is very unlikely that vessels will navigate within 0.5 nm of a wind turbine (the distance at which intolerable risks can be experienced).
19.1.9 Consultation
The cumulative scenario has been highlighted throughout the scoping and EIA process for the Proposed Development. For example, the shipping and navigation section of the Scoping Report included a targeted question for consultees in relation to the scope of the cumulative assessment and what effects may be seen at a cumulative level (RPS Energy, 2021). This was mirrored in the round of Regular Operator consultation undertaken (see Appendix D) and the cumulative scenario was a key consideration during the Hazard Workshops that involved representatives for multiple shipping and navigation users.
Comments received relating to the proposed navigation corridor – which are provided in Table 4.1 Open ▸ – are summarised in the following paragraphs.
19.1.9.1 Maritime and Coastguard Agency
The MCA commented during a consultation meeting that any navigation corridors would need to be in accordance with MGN 654 and local consultation with regular users and ports is key for any navigation corridor assessment. The MCA also stated during the first Hazard Workshop that an adjustment to the north-west boundary of the Proposed Development array area should be considered to allow vessels more space when navigating between the Proposed Development array area and Inch Cape.
19.1.9.2 UK Chamber of Shipping
The MCA’s suggestion for an adjustment to the boundary of the Proposed Development array area (as presented at the first Hazard Workshop) was echoed by the UK Chamber of Shipping in email correspondence, noting that vessels may choose to pass east or west of both the Proposed Development array area and Inch Cape rather than use the navigation corridor.
19.1.9.3 Fishermen’s Mutual Association
The FMA commented during the first Hazard Workshop that fishing vessels will be forced into the navigation corridor and have to share the space with commercial vessels. The consequences of a collision incident between a commercial vessel and a fishing vessel could be significant noting that the bend in the navigation corridor (as presented at the first Hazard Workshop) increases the probability of a collision incident occurring.
The FMA also indicated that vessels may be wary of utilising the navigation corridor in adverse weather, adding in the second Hazard Workshop that larger tankers may face increased risks due to the Marr Bank, particularly in adverse weather.
19.1.9.4 Northern Lighthouse Board
NLB commented during the first Hazard Workshop that large vessels would be more comfortable transiting east of the Proposed Development with only smaller vessels likely to utilise the navigation corridor (as presented at the first Hazard Workshop). NLB also highlighted in a Scoping Opinion response that the potential ‘funnelling’ of vessel traffic between offshore wind farm developments was of particular interest.
19.1.9.5 Royal Yacht Association Scotland
RYA Scotland commented during the first Hazard Workshop that if commercial traffic chooses to make passage through the navigation corridor (as presented at the first Hazard Workshop) then recreational users may be discouraged from navigating in that area. However, during the second Hazard Workshop, RYA Scotland acknowledged that some recreational vessels may choose to cut across the eastern extent of the Inch Cape array area, thus avoiding the potential for increased interaction in the navigation corridor.
RYA Scotland indicated during the second Hazard Workshop that the refinement of the Proposed Development array area reduces the level of concern for recreational users. Additionally, the alignment of the western boundary of the Proposed Development array area with the western boundary of Seagreen is a positive change since it is now clearer how vessels will transit the area, which will assist with passage planning.
19.1.9.6 Scottish Whitefish Producers Association
The Scottish Whitefish Producers Association indicated during the second Hazard Workshop that the refinement of the Proposed Development array area is beneficial. This is particularly important given that the overall size of the Proposed Development array area will require careful passage planning for any internal navigation within the array.
19.1.9.7 Forth Ports
Forth Ports commented during the second Hazard Workshop that the proximity of the other offshore wind farms in the region could form a ‘crossroads’ which may create a pinch point. Additionally, the region is known to experience significant adverse weather and (prior to the construction of Inch Cape) vessels transiting east-west to/from the River Tay will need to navigate through the gap between the Proposed Development array area and Seagreen.
19.1.9.8 Regular Operators
In Regular Operator responses, both HAV Ship Management and North Star Shipping indicated that there were no concerns with the safety of their vessels foreseen when considering the cumulative scenario. In contrast, Evergas indicated that their vessels would deviate around the south and east of the Proposed Development array area since this would be safer than utilising the navigation corridor (as presented at the first Hazard Workshop) or making passage inshore of Inch Cape given the difficult situation that would develop in the event of machinery failure.
19.1.10 Refinement of Proposed Development Array Area
As detailed in section 6.1.1.1 and noted in some of the consultation feedback, the extent of the Proposed Development array area has been refined markedly during the NRA process, including at the north western corner. This change was primarily driven by the need to increase the width of the gap between the Proposed Development array area and Inch Cape in line with the feedback received in the first Hazard Workshop.
The minimum width of the gap has been increased from approximately 2.1 nm to 4.1 nm, with the shape of the gap also changing to become closer to a conventional parallelogram. This increase in width assists in ensuring that there is sufficient sea room available for vessels to safely navigate through the gap including in the event of collision avoidance action being required (as indicated by the various width calculations undertaken in the previous subsections). Additionally, the shape of the gap has become closer to a conventional parallelogram in shape, such that vessels should have a clearer view of each other when approach and navigating within the gap, further reducing the collision risk.
19.1.11 Embedded Mitigation Measures
The following mitigation measures will assist in ensuring that the navigational risk associated with the navigation corridor between the Proposed Development array area and Inch Cape is ALARP:
- Compliance with MGN 654 and its annexes where applicable as part of the Design Specification and Layout Plan;
- Lighting and marking of the Proposed Development array area in agreement with NLB and in line with IALA Recommendation O-139 (IALA, 2021 (a)) and Guidance G1162 (IALA, 2021 (b));
- Marine coordination and communication to manage vessel movements;
- Compliance of all vessels associated with the Proposed Development with international marine regulations as adopted by the Flag State, notably the COLREGs (IMO, 1972/77) and SOLAS (IMO, 1974);
- Promulgation of information for vessel routes, timings and locations, Safety Zones and advisory passing distances as required via Kingfisher Bulletins; and
- The buoyed construction area size and location will consider the need to maintain safe navigation through the navigation corridor, noting that this will be determined post consent in agreement with NLB.
It is noted that no part of the navigation corridor is within the Order Limits for the Proposed Development or Inch Cape. Therefore, no infrastructure associated with either development (including subsea cables) will be located within the navigation corridor.
19.1.12 Summary and Conclusion
This safety case has considered the following in relation to the navigation corridor between the Proposed Development array area and Inch Cape:
- Relevant navigational features within or in proximity to the navigation corridor;
- Number, size and speed of potential navigation corridor users;
- Relevant guidance and legislation including MGN 654, PIANC guidance and MARIN guidance as well as the COLREGs;
- Non-transit users and activities;
- Radar interference;
- Consultation undertaken with relevant stakeholders including Regular Operators; and
- Embedded mitigation measures.
Table 19.1 Open ▸ summarises the outcome of the various width calculations undertaken based on relevant guidance.
Table 19.1 Summary of Navigation Corridor Width Calculations
With the provision outlined in section 17 in place, the navigation corridor (which has a minimum width of 4.1 nm) satisfies the various width calculations.
The size of vessels identified as potential corridor users are generally small to moderate, as indicated by the 90th percentile length of 131 m. However, the presence of fishing vessels in proximity to the corridor, including active fishing activities, mean that collision risk is increased but is managed by the navigation corridor’s design being in compliance with MGN 654 which minimises the likelihood of an encounter and allows compliance with COLREGs. This includes in adverse weather conditions noting that the 20-degree rule provided in MGN 654 is designed to account for “deviations from track” in poorer conditions.
On this basis, the navigation corridor can be considered to meet safety of navigation expectations.