Glossary

Acronyms

Acronyms

Units

Units

1.             Introduction

1. Introduction

1.1.        Overview of the Array

1.1. Overview of the Array

1. In January 2022, Ossian Offshore Wind Farm Limited (Ossian OWFL) (hereafter referred to as the ‘Applicant') was awarded an Option to Lease Agreement to develop Ossian, an offshore wind farm within the E1 East Plan Option (PO) Area as part of the ScotWind Leasing Round. This project (hereafter referred to as ‘Ossian’) is a joint venture between SSE Renewables Limited (SSER), Copenhagen Infrastructure Partners (CIP) and Marubeni Corporation.
2. Ossian is a proposed offshore wind farm located off the east coast of Scotland, approximately 80 km south-east from the nearest point of Aberdeen (see Figure 1.1   Open ▸ ). The Array is located within the site boundary and includes the offshore infrastructure required to generate electricity including the wind turbines (including their floating substructures, as well as the mooring and anchoring systems), the fixed bottom Offshore Substation Platforms (OSPs), and inter-array and interconnector cables. The Array is the subject of this Report to Inform Appropriate Assessment (RIAA).
3. In March 2024, as part of the ongoing National Grid Holistic Network Design Follow Up Exercise (HNDFUE), National Grid Electricity System Operator (ESO) published their Transitional Centralised Strategic Network Plan (TCSNP) in the ‘Beyond 2030’ report (National Grid ESO, 2024). Beyond 2030 sets out National Grid ESO’s recommendations to achieve a decarbonised electricity network.
4. The proposed grid design aims to facilitate transmission of a number of offshore wind farm projects. Within this publication it was confirmed that Ossian will be offered two grid connection locations in Lincolnshire, one at Weston Marsh and one at the Lincolnshire Connection Node.
5. Onshore and offshore route optioneering work has now commenced to determine appropriate offshore and onshore export cable corridors, and locations for proposed substation locations. As part of this Ossian has initiated engagement with key stakeholders in Lincolnshire to inform early design and site selection considerations
6. Therefore, the Proposed offshore export cable corridor(s) and Proposed onshore transmission infrastructure (comprising the Proposed onshore export cable corridor(s), Proposed onshore converter station and the Proposed landfall location(s)) will be subject to separate consent applications in due course, including separate Likely Significant Effects (LSE2) Screening Reports and associated RIAAs. In-combination effects of the Proposed offshore export cable corridor(s) and Proposed onshore transmission infrastructure will be considered insofar as practicable on the basis of available information in the in-combination assessment forming part of the RIAA.

Figure 1.1: Location of the Site Boundary, where the Array will be Located

1.2.        Habitats regulations appraisal overview

1.2. Habitats regulations appraisal overview

7. Following the departure of the United Kingdom (UK) from the European Union (EU) on 31 December 2020 (EU Exit), the UK is no longer an EU Member State. Notwithstanding, the Habitats Regulations, which implemented the EU Habitats Directive (92/43/EEC) in the UK,, continues to form the legislative basis for the domestic HRA regime. The changes implemented by EU Exit Regulations have implemented only minor changes to the HRA regime compared to before EU Exit. These changes are not considered to have material implications on the requirement or process for a HRA in relation to the Array.
8. The Habitats Regulations require that an Appropriate Assessment must be carried out on all plans and projects that are likely to have a significant effect on a European site. European sites include Special Areas of Conservation (SACs), candidate SACs (cSACs), Sites of Community Importance (SCI), Special Protection Areas (SPAs) and, as a matter of policy (Scottish Government, 2020), possible SACs (pSACs), potential SPAs (pSPAs) and Ramsar Sites (listed under the Ramsar Convention on Wetlands of International Importance – where also designated as a European site).
9. In this RIAA, and in accordance with EU Exit guidance issued by the Scottish Government, the term “European site” has been retained to refer to the above sites protected in European Member States, Scotland and the rest of the UK (Scottish Government, 2020). However, where these sites are located in the UK, they now form part of the National Site Network. Post EU-Exit, the Habitats Regulations continue to refer to Annexes I and II of the Habitats Directive and Annex I of the Birds Directive and as such, reference is made to the annexes of the Habitats and Birds Directives in this report.

1.3.        Purpose of this RIAA

1.3. Purpose of this RIAA

10. This RIAA has been prepared by RPS and Niras on behalf of the Applicant to support the HRA of the Array in the determination of the implications upon European sites. This RIAA builds upon the Array HRA Stage One LSE2 Screening Report (appendix 1A), completed in March 2023, and the subsequent advice from stakeholders received in the Ossian Array Scoping Opinion from May to June 2023 (Marine Directorate – Licensing Operations Team (MD-LOT, 2023)). This RIAA represents Stage Two of the HRA process and assesses the LSE2s of the Array as they relate to the integrity of the relevant European sites. This RIAA will provide the competent authority with the information required to undertake a HRA Stage Two Appropriate Assessment (see section 2.3 for more detail on the HRA process).
11. The scope of this RIAA covers all relevant European sites and relevant qualifying interest features where LSE2s have been identified due to impacts arising from the Array. This includes both ‘offshore’ European site and features (seaward of Mean High Water Springs (MHWS) and ‘onshore’ European sites (landward of Mean Low Water Springs (MLWS) where appropriate.  

1.4.        Progress to Date

1.4. Progress to Date

12. A Array HRA Stage One LSE2 Screening Report has been produced for the Array in accordance with the Habitats Regulations (appendix 1A). The purpose of the LSE2 Screening exercise was to determine whether the Array could result in a LSE2 on any European site, with reference to its conservation objectives. The LSE2 Screening exercise determined that LSEs from impacts associated with the Array could not be discounted at Stage One, and European sites where LSE2s could not be ruled out were carried forward to Stage Two.
13. The Array HRA Stage One LSE2 Screening Report (appendix 1A) presents the LSE2 Screening exercise, the purpose of which is summarised below:

• Identification of the relevant European sites which may include features (e.g. Annex I habitats, ornithology features, Annex II diadromous fish, and Annex II marine mammals) which may be sensitive or vulnerable to potential impacts arising from all phases of the Array;
• Consideration of the features of relevant European sites and identification of those which are not considered likely to be at risk of significant effects arising from the array, either alone or in-combination with other plans and projects, so that they could be eliminated from further assessment within the HRA process;
• Consideration of features of relevant European sites and identification of those which are considered likely to be at risk of significant effects so that they could be carried forwards to HRA Stage Two Appropriate Assessment in this RIAA; and
• Consideration of which of the potential impacts arising from the Array (alone or in-combination with other plans and projects) were likely to result in LSE2s to features of European sites and which impacts could be eliminated from further assessment in the HRA process[1].

14. The HRA process is iterative. Since the Array HRA Stage One LSE2 Screening Report was shared with consultees in March 2023, aspects of the design of the Array have evolved (see section 4). Consultation representation and advice with respect to the Array HRA Stage One LSE2 Screening Report were received along with the Ossian Array Scoping Opinion in June 2023 (MD-LOT, 2023). The potential implications of design changes on the LSE2 Screening exercise have been considered and a summary of the LSE2 Screening exercise for the Array is provided in the relevant sections of this RIAA (i.e. Part 2 for SACs and Part 3 for SPAs). Any changes to the LSE2 Screening outcomes presented in the Array HRA Stage One LSE2 Screening Report (appendix 1A) have been made as a result of consultation are highlighted in the relevant Parts of the RIAA, with all consultation to date presented, where relevant to SACs and SPAs, in Part 2 and Part 3, respectively.

1.5.        Structure of this RIAA

1.5. Structure of this RIAA

15. For clarity and ease of navigation, this RIAA has been structured and reported in the below ‘Parts’, as follows:

• Executive Summary;
• Part 1 (this document): Introduction ;
• Part 2: SAC assessments; and
• Part 3: SPA and Ramsar site assessments.

1.6.        Structure of this Document

1.6. Structure of this Document

16. As stated in paragraph 15, this document constitutes Part 1 of the RIAA, and provides an introduction to the Array and the HRA process. This document is structured as follows:

• Section 1: Introduction (this section) which describes the Array and establishes the requirement for, the purpose, and the structure of the RIAA;
• Section 2: The HRA Process, which sets out the process, principles, tests, and guidance applied to the RIAA;
• Section 3: Consultation, which provides a summary of the relevant consultation undertaken to date; and
• Section 4: Information on the Array, which provides information about the design of the Array relevant to the RIAA, including relevant maximum design parameters and any design updates since the Array HRA Stage One LSE2 Screening.  

2.             The HRA Process

2. The HRA Process

2.1.        Legislative Context

2.1. Legislative Context

17. The EU Habitats Directive (92/43/EEC) on the conservation of natural habitats and of wild fauna and flora, protects habitats and species of European nature conservation importance. Together with Council Directive (2009/147/EC) on the conservation of wild birds (the ‘Birds Directive’), the Habitats Directive establishes a network of internationally important sites, designated for their ecological status. This network of designated sites is comprised of the following:

• SACS, which are designated under the Habitats Directive and promote the protection of flora, fauna and habitats; and
• SPAs, which are designated under the Birds Directive in order to protect rare, vulnerable and migratory birds.

18. SACs are designated for the conservation of Annex I habitats (including priority habitat types which are in danger of disappearing) and Annex II species (including diadromous fish and marine mammals). SPAs are designated for the conservation of Annex I birds and other regularly occurring migratory birds and their habitats. The habitats and species that a European site is designated for are referred to as its ‘qualifying interest features’. The conservation objectives of a European site are set for each qualifying interest feature of each site.  and aim to ensure that a qualifying habitat or species is maintained or restored in a favourable conservation status (FCS) .
19. As introduced in section 1.2, although the UK is no longer an EU Member State, the Habitats Directive as implemented by the Habitats Regulations continue to provide the legislative backdrop for HRA in the UK. The HRA process implemented under the Habitats Regulations continues to apply (subject to minor changes effected by the EU Exit Regulations) and the UK is currently bound by HRA judgments handed down by The Court of Justice of the European Union (CJEU) prior to 31 December 2020.
20. In addition to sites formally defined as European sites in the Habitats Regulations, Scottish Planning Policy acknowledges that Ramsar sites are afforded the same protection where they are also designated as a European site (Scottish Government, 2020). The Scottish Government also states that authorities should afford the same level of protection to proposed SACs and SPAs (i.e. sites which have been approved by Scottish Ministers for formal consultation but which have not yet been designated) as they do to sites which have been designated (Scottish Government, 2020).
21. Under the Habitats Regulations, before granting approval (i.e. planning permissions, licenses and consents) for a development that is likely to have a significant effect on a European site, an Appropriate Assessment must be made by the Competent Authority. This assesses the proposed plan or project’s potential for adverse effects on integrity of the site in view of that European site’s conservation objectives.

2.2.        European Sites (Post EU Exit)

2.2. European Sites (Post EU Exit)

22. The National Site Network  is comprised of European sites in the UK that already existed (i.e. were established under the Habitats or Birds Directives) on 31 December 2020 (or proposed to the European Commission before that date) and any new sites designated under the Habitats Regulations under an amended designation process.

2.3.        The HRA Process

2.3. The HRA Process

23. The HRA process is generally recognised as a progressive, multi-stage process built around the wording of Articles 6(3) and 6(4) of the Habitats Directive, with the outcome at each stage defining the requirement for, and scope of the next. These stages are summarised in Figure 2.1   Open ▸ .
24. Article 6(3) of the Habitats Directive requires that: “Any plan or project not directly connected with or necessary to the management of the site but likely to have a significant effect thereon either individually or in combination with other plans or projects, shall be subject to appropriate assessment of its implications for the site in view of the site’s conservation objectives. In the light of the conclusions of the assessment of the implications for the site and subject to the provisions of paragraph 4, the competent national authorities shall agree to the plan or project only after having ascertained that it will not adversely affect the integrity of the site concerned and if appropriate, after having obtained the opinion of the general public”.
25. Therefore, Article 6(3) provides a two-stage process:

• the first stage, which involves a screening for LSE2; and
• the second stage arises where, having screened the Array, the relevant competent authority determines that an Appropriate Assessment is required, in which case it must then carry out that Appropriate Assessment ( Figure 2.1   Open ▸ ).

26. This RIAA is concerned with the second stage of the process (i.e. the Appropriate Assessment), which seeks to assess and decide whether a plan or project, alone or in combination with other projects or plans, will have an adverse effect on the integrity of a European site. This RIAA also summarises the conclusions of the Array HRA Stage One LSE2 Screening Report (appendix 1A), and updates made to the screening conclusions, since this was published in March 2023, to account for feedback received from stakeholders during consultation.
27. Article 6(4) is the third stage of the HRA process which provides for a derogation from the strict protection of European sites in certain circumstances. Where the RIAA has concluded that an adverse effect on the integrity of a European site cannot be excluded, the project will proceed to the third stage. The third stage derogation process comprises three tests which must be passed in sequence for consent to be granted  (see Figure 2.1   Open ▸ ):

• Test 1: Assessment of Alternative Solutions – there are no feasible alternative solutions that would be less damaging or avoid damage to the site.
• Test 2: Assessment of Imperative Reasons of Overriding Public Interest (IROPI) - the proposal needs to be carried out for imperative reasons of overriding public interest; and
• Test 3: The necessary compensation measures can be secured.

28. The documents prepared regarding Test 3 of the Derogation, i.e. the proposed compensation measures in relation to the Array are presented as part of the Derogation Case which includes:

• Appendix 1: Ecological Evidence Report;
• Appendix 2: Compensation Plan;
• Appendix 2, Annex A: Compensation Stakeholder Consultation; and
• Appendix 3: Compensation Implementation and Monitoring Plan.

29. The EU-Exit Regulations establish management objectives for the National Site Network. These are called the network objectives. The objectives in relation to the National Site Network are to:

• maintain or restore Annexed habitats and species listed in the Habitats Directive to FCS; and
• contribute to ensuring the survival and reproduction of certain species of wild birds in their area of distribution and to maintaining their populations at levels which correspond to ecological, scientific and cultural requirements, while taking account of economic and recreational requirements.

Figure 2.1: Stages in the HRA Process (adapted from the European Commission (2021))

2.4.        Guidance

2.4. Guidance

30. Following the UK’s departure from the EU, reference to EC guidance on the interpretation of HRA concepts continues to apply. The EU Exit Habitats Regulations in Scotland state that in the longer term, guidance may be updated and/or new guidance may be produced, to replace guidance by the European Commission (Scottish Government, 2020). However, at the time of writing, existing guidance continues to apply and should still be used. Therefore, this RIAA is undertaken in accordance with the following guidance documents:

• “Habitats Regulations Appraisal (HRA) of Local Development Plans (LDPs) - Guidance for planning authorities in Scotland” (NatureScot, 2023);
• “European Site Casework Guidance: How to consider plans and projects affecting Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)” (NatureScot, 2022);
• “The Habitats Regulations Assessment Handbook” (Tyldesley et al., 2021);
• “Assessment of plans and projects in relation to Natura 2000 sites - Methodological guidance on Article 6(3) and (4) of the Habitats Directive 92/43/EEC” (European Commission, 2021);
• “Guidance document on wind energy developments and EU nature legislation” (European Commission, 2020);
• “Guidance Note: The handling of mitigation in Habitats Regulations Appraisal – the People Over Wind CJEU judgement” (Scottish National Heritage (SNH, now NatureScot) (2019));
• “Managing Natura 2000 sites. The provisions of Article 6 of the 'Habitats' Directive 92/43/EEC” (European Commission, 2018);
• “Habitats Regulations Appraisal (HRA) on the Firth of Forth A Guide for developers and regulators” (SNH (2016));
• “Marine Scotland Consenting and Licensing Guidance for Offshore Wind, Wave and Tidal Energy Applications” (Scottish Government, 2018);
• “HRA Advice Sheet 1 (Version 1) - Aligning Development Planning procedures with Habitats Regulations Appraisal requirements” (Scottish Government, 2012);
• “Guidance document on Article 6(4) of the 'Habitats Directive' 92/43/EE. Clarification on the Concepts of: Alternative Solutions, Imperative Reasons of Overriding Public Interest, Compensatory Measures, Overall Coherence, Opinion of the Commission” (European Commission, 2007); and
• “Nature and Biodiversity Cases Ruling of the European Court of Justice” (European Commission, 2006).

31. This RIAA has also been undertaken in accordance with the following publications that seek to explain the changes made to the Habitats Regulations from 1 January 2021:

• “EU Exit: The Habitats Regulations in Scotland” (Scottish Government, 2020);
• “Department for Environment, Food and Rural Affairs (Defra) Policy Paper - Changes to the Habitats Regulations 2017” (Defra, 2021); and
• “Habitats Regulations Assessments: protecting a European site” (Defra et al., 2023)

32. The Statutory Nature Conservation Bodies (SNCBs) have produced conservation advice for European sites under their statutory remit. This conservation advice provides information on sites and features and guidance on how to achieve FCS. Conservation advice is discussed further, where relevant, in Part 2 and Part 3 of the RIAA.

2.5.        Relevant Case Law

2.5. Relevant Case Law

33. The case law that defines key assessment parameters (such as the definition of “integrity” and “significance”, the consideration of ex situ effects and the consideration of mitigation measures) are discussed in the sections 2.5.1 to 2.5.3. 

2.5.1.    Consideration of Mitigation Measures

2.5.1. Consideration of Mitigation Measures

34. In case C-323/17 ‘People Over Wind and Sweetman v Coillte Teoranta’ (April 2018) (Sweetman 2), the CJEU ruled that mitigation measures could not be taken into account at the screening stage. This judgment was taken into account in undertaking the screening exercise for the Array and no mitigation measures (secondary or additional mitigation) were considered in the HRA Stage One LSE2 Screening Report (appendix 1A).

2.5.2.    Adverse Effects on the Integrity of European Sites

2.5.2. Adverse Effects on the Integrity of European Sites

35. The European Commission’s guidance on managing Natura 2000 sites (2018) advises that the purpose of the Appropriate Assessment is to assess the implications of the plan or project in respect of a European site’s conservation objectives, either individually or in combination with other plans or projects. The conclusions should enable the relevant competent authorities to ascertain whether the plan or project will adversely affect the integrity of the European site concerned. The focus of the Appropriate Assessment is therefore specifically on the species and/or the habitats for which the European site is designated.
36. The European Commission (2018) also emphasises the importance of using the best scientific knowledge when carrying out the Appropriate Assessment in order to enable the competent authorities to conclude with certainty that there will be no adverse effects on the integrity of the European site. This guidance notes that it is at the time of the decision authorising implementation of the project that there must be no reasonable scientific doubt remaining as to the absence of adverse effects on the integrity of the European site in question.
37. The CJEU confirmed in its ruling in Case C-258/11 that “Article 6(3) of the Habitats Directive must be interpreted as meaning that a plan or project not directly connected with or necessary to the management of a site will adversely affect the integrity of that site if it is liable to prevent the lasting preservation of the constitutive characteristics of the site that are connected to the presence of a priority natural habitat whose conservation was the objective justifying the designation of the site in the list of SCIs, in accordance with the directive. The precautionary principle should be applied for the purposes of that appraisal”. The European Commission (2018) advises that the logic of such an interpretation would also be relevant to non-priority habitat types and to habitats of species.
38. The “integrity of the site” can be usefully defined as the coherent sum of the European site’s ecological structure, function and ecological processes, across its whole area, which enables it to sustain the habitats, complex of habitats and/or populations of species for which the site is designated (European Commission, 2018). In Sweetman, Ireland, Attorney General, Minister for the Environment, Heritage and Local Government v An Bord Pleanála) (C-258/11) (Sweetman 1) it was determined that the ecological structure and function of a European site would be adversely affected with reference to the site’s overall ecological functions and “the lasting preservation of the constitutive characteristics of the site.” In a dynamic ecological context, it can also be considered as having the sense of resilience and ability to evolve in ways that are favourable to conservation (European Commission, 2018).
39. The European Commission (2018) notes that if the competent authority considers the mitigation measures are sufficient to avoid the adverse effects on site integrity identified in the Appropriate Assessment, they will become an integral part of the specification of the final plan or project or may be listed as a condition for project approval.
40. The European Commission (2020) advises that it is for the competent authorities, in the light of the conclusions made in the Appropriate Assessment on the implications of a plan or project for the European site concerned, to approve the plan or project. This decision can only be taken after they have made certain that the plan or project will not adversely affect the integrity of the site. That is the case where no reasonable scientific doubt remains as to the absence of such effects.
41. The European Commission (2020) also reaffirms that the authorisation criterion laid down in the second sentence of Article 6(3) of the Habitats Directive integrates the precautionary principle and makes it possible to effectively prevent the European sites from suffering adverse effects on their integrity as the result of the plans or projects. A less stringent authorisation criterion could not as effectively ensure the fulfilment of the objective of site protection intended under that provision. The onus is therefore on demonstrating the absence of adverse effects rather than their presence, reflecting the precautionary principle. It follows that the Appropriate Assessment must be sufficiently detailed and reasoned to demonstrate the absence of adverse effects, in light of the best scientific knowledge in the field.
42. In accordance with the decision of the CJEU in the Waddenzee (C-127-02), the measure of significance is made against the conservation objectives for which the European sites were designated.

2.5.3.    Consideration of Ex situ Effects

2.5.3. Consideration of Ex situ Effects

43. The European Commission (2018) advises that Article 6(3) and Article 6(4) safeguards be applied to European sites subject to LSE2s from any development pressures, including those which are external to those European site(s).
44. The CJEU developed this point when it issued a ruling in case C-461/17 (“Brian Holohan and Others v An Bord Pleanála”) that determined inter alia that Article 6(3) of Directive 92/43/EEC must be interpreted as meaning that an Appropriate Assessment must on the one hand, catalogue the entirety of habitat types and species for which a European site is protected, and, on the other, identify and examine both the implications of the proposed project for the species present on that site, and for which that site has not been listed, and the implications for habitat types and species to be found outside the boundaries of that site, provided that those implications are liable to affect its conservation objectives.
45. In that regard, consideration has been given at Screening (and where necessary, based on the outcomes of that Screening) in this RIAA to implications for habitats and species located both inside and outside of the European sites with reference to their conservation objectives, where effects upon those habitats and/or species are liable to affect the conservation objectives of the sites concerned.

3.             Consultation to Date

3. Consultation to Date

46. To date, consultation has been undertaken with relevant statutory stakeholders during key stages of the pre-application phase of the Array.
47. Consultation was undertaken with MD-LOT, NatureScot, and Natural England, alongside various other stakeholders, such as the Scottish Fishermen’s Federation (SFF) and the Scottish Environmental Protection Agency (SEPA). Consultation feedback was received in November 2022, following information presented at the Array EIA Scoping Workshop. Following this, consultation representation and advice with respect to the Array HRA Stage One LSE2 Screening Report were received along with the Ossian Array Scoping Opinion in June 2023 (MD-LOT, 2023). Consultation applicable to this RIAA has been taken into consideration, as appropriate, and is summarised, where relevant to SACs and SPAs, in Part 2 and Part 3 of this RIAA, respectively.
48. Based on the outcomes of the Array HRA Stage One LSE2 Screening Report, no potential significant transboundary effects, either alone or in-combination, were predicted for the Array. Therefore, no transboundary consultation has been carried out with respect to this RIAA.

4.             Information on the Array

4. Information on the Array

49. This section provides an outline of the Array and describes the activities likely to be associated with the construction, operation and maintenance, and decommissioning phases of the Array. It summarises the design and components of the Array infrastructure, based on conceptual design information and refinement of the Array parameters.

4.1.        Project Design Envelope

4.1. Project Design Envelope

50. The Project Design Envelope (PDE) approach (also known as the 'Rochdale Envelope') (Scottish Government, 2022) has been followed by the Applicant, meaning that parameters for the Array included in this section present the maximum extent of the design in order to assess the maximum adverse effects of the Array. The ‘maximum design envelope’ (e.g. the Maximum Design Scenario (MDS)) presented in this section defines the maximum range of design parameters. Through the MDS approach the Applicant has determined the maximum impacts that could occur for given receptor groups, selecting these from within the range of the ‘maximum design envelope’ to define the MDS for that receptor group and potential impact pathway. As a result, the predicted effects assessed in Part 2 and Part 3 of this RIAA will be no greater for any alternative parameters .
51. The final detailed design will be further developed post-consent, as additional information becomes available from site investigations and commercial availability of technologies. It should be noted that the final detailed design for the Array will be within the PDE parameters presented in this section. This is a standard approach for large scale energy projects such as the Array.
52. The PDE approach allows for flexibility in the final Array design to account for supply chain constraints and selection of the most appropriate technology for the site and conditions, while allowing for an appropriate assessment of the Array on designated sites in view of their conservation objectives, as reported within the RIAA. The PDE presents a range of potential parameter values up to and including the maximum Array design parameters.
53. The Array PDE has been designed to allow for sufficient flexibility in the final project design options and further refinement during the final design stage, where the full details of a project are not known at the point of Application submission. For each of the impacts assessed within Part 2 and Part 3 of this RIAA, the PDE has been reviewed and the MDS has been identified from the range of potential options for each parameter. The MDS approach allows the Applicant to retain some flexibility in the final design of the Array and associated offshore infrastructure, but certain maximum parameters are set and are assessed in this RIAA.
54. The MDSs, as per the PDE, are presented in Part 2 and Part 3 of this RIAA. Anything less than that set out within this section and assessed within Part 2 and Part 3 of this RIAA will have a lesser impact.
55. The PDE describes a range of parameters that apply to a Project technology design scenario (e.g. largest wind turbine option). In this example, wind turbine size and wind turbine number are inherently correlated so if larger wind turbines are selected, fewer wind turbines are likely to be required. Therefore, each design parameter set out in this section is not considered independently. The PDE has been used to develop the MDS for each impact pathway in order to determine the parameters (or combination of parameters) which are likely to result in the maximum effect (e.g. the MDS) on a particular receptor. It should be noted, however, that the largest parameters set out in this section will not necessarily comprise the MDS for any given receptor group and each of the impacts assessed in Part 2 and Part 3 of the RIAA.
56. Since the submission of the Array EIA Scoping Report (Ossian OWFL, 2023) and the Array HRA Stage One LSE2 Screening Report (appendix 1A), the Applicant has developed and refined the PDE for the RIAA using the results of early engineering studies and information gained through consultation with stakeholders. A full description of PDE refinements for the Array is provided within volume 1, chapter 4 of the Array EIA Report, however, a summary is provided in Table 4.1   Open ▸ .

Table 4.1: Overview of PDE Refinements for the Array

57. The HRA process includes derogation provisions which may require the Applicant to provide measures to compensate for the adverse effects on the integrity of European sites resulting from the Array, either alone, or in combination with other plans and projects. The Applicant has undertaken an appraisal of the potential impacts of the compensatory measures proposed (without prejudice to the HRA to be conducted by the competent authority). An EIA Likely Significant Effect (LSE1) and HRA LSE2 Assessment has been undertaken on the proposed compensation measures for the Array and are provided as part of the Application.

4.2.        Location and Site Information

4.2. Location and Site Information

58. The Array will be located within the site boundary, located off the east coast of Scotland, approximately 80 km south-east of Aberdeen from the nearest point, and comprising an area of approximately 859 km2 ( Figure 1.1   Open ▸ ).  
59. In January 2022, as part of the ScotWind Leasing Round, the Applicant was awarded an Option to Lease Agreement to develop Ossian, an offshore wind farm project within the E1 PO Area (see volume 1, chapter 4 of the Array EIA Report for further information on the site selection process).

4.2.1.    Water depths and seabed within the Array

4.2.1. Water depths and seabed within the Array

60. A geophysical survey covering the area within the site boundary was conducted between March 2022 and July 2022 to collect geophysical and bathymetric data. Across the site boundary, the maximum water depth was recorded at 88.7 m LAT, and the shallowest area was recorded at 63.8 m LAT. The seabed across the site boundary slopes gently downwards in an approximately north-west to south-east direction (Ocean Infinity, 2022).
61. Seabed sediments within the site boundary are significantly dominated by deep circalittoral sand, with one area of limited extent comprised of deep circalittoral coarse sediment within the northern part of the site (European Marine Observation and Data Network (EMODnet), 2023). The geophysical survey indicated that the seabed comprises mainly of sand, with areas of gravel in the west of the site boundary (Ocean Infinity, 2022). The seabed within the site boundary is generally flat, with mega-ripples and sand waves observed in the north-west of the site. Furrows were observed occasionally across the site boundary, more commonly in the west (Ocean Infinity, 2022).
62. Further details of the bathymetry and seabed composition are presented within volume 2, chapters 7 and 8 of the Array EIA Report.

4.3.        Array Infrastructure

4.3. Array Infrastructure

4.3.1.    Overview

4.3.1. Overview

63. The main components of the Array will include:

• up to 265 floating wind turbines (each comprising a tower section, nacelle, hub and three rotor blades) and associated floating foundations;
• mooring and anchoring systems for each floating foundation;
• connectors and ancillaries for mooring and anchoring systems, including buoyancy elements and clump weights;
• up to six large OSPs, or up to three large OSPs and up to 12 small OSPs with fixed jacket foundations;
• scour protection for wind turbine anchoring systems;
• scour protection for small and large OSP fixed foundations as required;
• a network of dynamic/static inter-array cabling linking the individual floating wind turbines to OSPs, and interconnector cables between OSPs (approximately 1,261 km of inter-array cabling and 236 km of interconnector cabling); and
• discrete condition monitoring equipment (such as sensors, cameras, dataloggers etc.), as required for safe and efficient operation of the Array infrastructure.

4.3.2.    Floating Wind Turbines

4.3.2. Floating Wind Turbines

64. The Array will comprise up to 265 floating wind turbines, however, the final number of wind turbines will be dependent on the capacity of individual wind turbines used, as well as the environmental and engineering survey results.
65. A range of wind turbine parameters are provided which account for varying generating capacities of wind turbines considered within the PDE. This allows a degree of flexibility to account for anticipated technological developments in the future whilst allowing the MDS to be defined for each potential impact within the RIAA. Therefore, the wind turbine parameters presented in this section, and for which consent is being sought, represent the maximum wind turbine parameters as presented in the PDE, such as maximum rotor blade diameter and maximum blade tip height.
66. Table 4.2   Open ▸ presents the range of parameters considered for the wind turbines and considers both the maximum number of wind turbines and the largest wind turbines described within the PDE. Therefore, the parameters in combination do not represent a realistic design scenario, rather they represent the most adverse parameters of a range of wind turbine models that may be available post-consent/at the time of the Array construction.
67. Floating wind turbines will comprise a tower section, nacelle, hub and three rotor blades, and will be attached to a floating foundation. A schematic of a typical floating wind turbine is presented in Figure 4.1   Open ▸ .
68. The maximum rotor blade diameter will be no greater than 350 m, with a maximum blade tip height of up to 399 m above LAT and minimum blade clearance of 36 m above LAT. The hub height will be no greater than 224 m above LAT. The Applicant will develop and agree a scheme for wind turbine lighting and navigation marking with the relevant consultees post-consent decision for approval by Scottish Ministers after consultation with appropriate consultees.
69. The wind turbine layout will be developed to effectively make use of the available wind resource and suitability of seabed conditions, whilst ensuring that the environmental effects and potential impacts on other marine users (e.g., fisheries and shipping routes) are reduced. If required by consent conditions, confirmation of the final layout of the wind turbines will occur at the final design stage (post-consent) in consultation with relevant stakeholders and submitted to the MD-LOT for approval. Indicative array layouts are presented in Figure 4.2   Open ▸ and Figure 4.3   Open ▸ for 265 wind turbine locations plus 15 OSP locations and 130 wind turbine locations plus 15 OSP locations, respectively. The OSPs could be sited at any of the locations shown in the figures and will be determined at the final design stage (post-consent). Further information on OSPs is provided in section 4.3.4.

Table 4.2: Maximum Design Envelope: Floating Wind Turbines

Figure 4.1: Schematic of a Typical Floating Wind Turbine

Figure 4.2: Preliminary Array Layout Comprising up to 265 Wind Turbines and up to 15 OSP Locations

Figure 4.3: Preliminary Array Layout Comprising up to 130 Wind Turbines and up to 15 OSP Locations

70. A number of consumables will be required throughout the Array’s lifecycle to improve operation, productivity and reduce wear on parts of wind turbines. These may include:

• grease;
• synthetic oil;
• hydraulic oil;
• gear oil;
• lubricants;
• nitrogen;
• water/glycerol;
• transformer silicon/ester oil;
• diesel fuel;
• Sulphur Hexafluoride; and
• glycol/coolants.

71. Required quantities of each consumable will be dependent upon the final design of the wind turbine selected. Potential release of any chemicals into the marine environment via an accidental pollution event during the construction, operation and maintenance and decommissioning phases will be reduced as far as reasonably practicable through implementation of appropriate controls and mitigation as set out in an Environmental Management Plan (EMP), including a Marine Pollution Contingency Plan (MPCP), and the Decommissioning Programme. An outline EMP, including an outline MPCP, is presented in volume 4, appendix 21 of the Array EIA Report.

4.3.3.    Floating Wind Turbine Foundations and Support Structures

4.3.3. Floating Wind Turbine Foundations and Support Structures

72. The Array will comprise floating wind turbines supported by floating foundations which require mooring and anchoring systems to maintain station. The following subsections describe the MDS for the floating foundations, mooring systems, and anchoring systems.

                        Floating foundations

73. An overview of the floating foundation options considered for the Array is provided in Figure 4.4   Open ▸ and Table 4.3   Open ▸ . Each floating technology has varying dimensions as a result of the differing approach to meeting the unique engineering challenges associated with floating wind turbines, floating structure site specific design, wind turbine sizes and project specific requirements. The final floating foundation design may look different to those pictured but will follow the same design principles. The following floating foundation solutions are being considered for the Array:

• Semi-submersible: A buoyancy stabilised platform which floats semi-submerged on the sea surface whilst anchored to the seabed. The structure gains its stability through the buoyancy force associated with its large footprint (relative to the spar solution) and geometry, which ensures the wind loadings on the floating foundation and wind floating turbine are countered/dampened by the equivalent buoyancy force on the opposite side of the structure. Other configurations, similar to semi-submersibles with regards to footprint, draft and mooring arrangement, like buoy floaters, are also being considered.  It should be noted that semi-submersible foundations are applicable for use with catenary, semi taut and taut mooring systems.
• Tension Leg Platform (TLP): A TLP is a semi-submerged buoyant structure, anchored to the seabed with tensioned mooring lines (tendon). The combination of the structure buoyancy and tension in the anchor and mooring system provides the platform stability. This system stability (as opposed to the stability coming from the floating foundation itself) allows for a smaller and lighter floating foundation.

Figure 4.4: Indicative Floating Foundation Options for the Array

Table 4.3: Maximum Design Envelope: Floating Foundations

                        Mooring systems

74. The floating foundations are connected to the seabed via mooring and anchoring systems. Mooring lines run from the floating foundations, through the water column, to an anchoring system which maintains station of the floating foundation. The mooring line will connect to the floating foundation at a point below the splash zone, nominally set at 5 m below the sea surface. The point at which the mooring line reaches the seabed is referred to as the touchdown point.
75. Four mooring system options are currently being considered within the PDE, namely:

• catenary - catenary mooring lines typically comprise free hanging chains, secured to the seabed using anchors. Some designs may include the addition of clump weights to enhance the stiffness and restoring capacity.;
• semi taut - semi taut mooring lines typically use mixed materials, for example, chain and synthetic rope, secured to the seabed with anchors. Ancillary components like buoyancy modules may be required to achieve desired configuration.;
• taut - taut mooring lines use mostly synthetic ropes connected to small sections of chain at the seabed and at the top section, to prevent abrasion damage to the fibre ropes. Taut mooring lines are usually kept under tension and have a narrower mooring footprint; and
• tendons - tendons may also be used, which are tensioned mooring lines running vertically from the floating foundation to the seabed, and are only applicable for use with TLP floating foundations.

76. For catenary and semi-taut mooring systems sections of the mooring lines will lie on the seabed. During normal operations systems will be designed to minimise the excursion of floating foundations as far as practicable. However, during stronger winds and heavy sea states when floating foundations move to the edge of the excursion limits mooring lines on the windward side of the turbine will experience increased tension and may lift from the seabed. Mooring lines on the leeward side of the turbine would slacken and drop to the seabed ( Figure 4.5   Open ▸ ). The greatest changes would be anticipated with the catenary mooring system followed by the semi taut mooring systems. 
77. For the taut system it is anticipated that mooring lines would only interact with the seabed during extreme weather conditions. For the tendons option, mooring lines are tensioned, meaning that they run vertically from the floating foundation straight to the seabed, therefore, the mooring lines would not interact with the seabed and would not extend horizontally beyond the floating foundation footprint, unlike the catenary, semi taut and taut options ( Figure 4.6   Open ▸ , Figure 4.7   Open ▸ and Figure 4.8   Open ▸ , respectively).
78. It should be noted that the final mooring line solution selected may vary across the site, and will be dependent upon the anchoring solution chosen (see paragraph 79). A schematic of the different mooring systems is provided in Figure 4.6   Open ▸ , Figure 4.7   Open ▸ and Figure 4.8   Open ▸ , respectively .
79. The mooring system will be limited to a maximum of six and nine mooring lines per wind turbine for the 130 and 265 turbine scenarios respectively. Mooring line radius is not expected to exceed 700 m, and maximum length of mooring line per foundation will be up to 750 m. A maximum of 680 m of mooring line per foundation will rest on the seabed during normal operations. The maximum design envelope for the mooring system options is presented in Table 4.4   Open ▸ .

Figure 4.5: Indicative Schematic of Example Semi-Submersible Floating Foundation with Catenary Mooring System Option During Normal Operations and Extreme Conditions

Figure 4.6: Indicative Schematic of Catenary Mooring System Option for Floating Wind Turbines on Example Semi-Submersible Floating Foundation

Figure 4.7: Indicative Schematic of Taut Mooring System Options for Floating Wind Turbines on Example Semi-Submersible Floating Foundation

Figure 4.8: Indicative Schematic of Taut Mooring System Options for Floating Wind Turbines on Example Semi-Submersible Floating Foundation

Table 4.4: Maximum Design Envelope: Mooring Systems

                        Anchoring systems

80. Anchoring systems fix the mooring lines to the seabed and may include various solutions, such as driven piles, or embedded anchor types such as suction anchors and Drag Embedment Anchors (DEA). A brief description of the various anchoring types that are considered are presented in Table 4.5   Open ▸ .

Table 4.5: Description of Anchoring Options Considered in the Maximum Design Envelope

81. The Applicant is considering installation of up to nine anchors per floating foundation within the PDE. The final anchoring solution selected may vary across the site and will take account of the seabed conditions, detailed analysis of geotechnical data to inform engineering design, and environmental impacts. A range of scenarios has been identified based on preliminary analysis of geophysical and geotechnical data to identify possible anchoring solutions arrangements which could be installed for the purposes of undertaking a robust assessment. The Applicant has undertaken preliminary geotechnical surveys to determine feasibility of the proposed scenarios.  Geotechnical samples were not taken at every turbine location; therefore, flexibility is retained within the PDE to ensure there will be feasible anchoring solutions across the site. This will be informed by detailed geotechnical surveys and engineering design to identify the most appropriate anchor technology.
82. The final design may vary from the specific scenarios outlined but the environmental impacts will be no greater than the maximum design scenario impacts resulting from these scenarios and will be confirmed post-consent within the suite of consent plans. The scenarios assessed within this RIAA are as follows:

• Anchoring Option 1 - use of driven piles to anchor all floating foundations;
• Anchoring Option 2 - use of DEAs to anchor all floating foundations;
• Anchoring Option 3 – use of a mix of driven piles and DEAs to anchor up to 65% and 35% of the floating foundations, respectively;
• Anchoring Option 4 – use of a mix of driven piles and suction anchors to anchor up to 65% and 35% of the floating foundations, respectively; and
• Anchoring Option 5 - use of driven piles, shared between the floating foundations (equating to up to 70% of the total number of piles required for Anchoring Option 1).

83. Anchoring Option 1 is considered the most likely anchoring solution for the project at this stage, with Anchoring Options 2 to 5 considered as alternative options which may be used depending upon the results of engineering and environmental studies. A description of the maximum design envelope for each Anchoring Option is presented in Table 4.6   Open ▸ to Table 4.10   Open ▸ . Images of the anchoring solutions are presented in Figure 4.9   Open ▸ . Shared anchors will be considered by the project subject to appropriate layout design. This has the potential to reduce the overall number of anchors required within the site boundary. The maximum length of mooring line detailed within Table 4.4   Open ▸ may be exceeded for the shared anchor solution, however, the overall length of anchor chain required across the array, including length of chain on the seabed, would be reduced by utilising shared anchors.
84. Considering all Anchoring Options, the maximum seabed footprint per foundation is 900 m2 and maximum seabed footprint for the Array is 159,000 m2. Scour protection may be required for the anchoring systems with up to 8,511 m2 of scour protection to be installed per foundation, and up to 1,503,612 m2 of scour protection to be installed across the Array.

Table 4.6: Maximum Design Envelope: Anchoring Option 1

Table 4.7: Maximum Design Envelope: Anchoring Option 2

Table 4.8: Maximum Design Envelope: Anchoring Option 3

Table 4.9: Maximum Design Envelope: Anchoring Option 4

Table 4.10: Maximum Design Envelope: Anchoring Option 5

Figure 4.9: Schematic of Anchoring Options

                        Emerging anchor technologies

85. The Applicant is engaging with a number of suppliers who are developing innovative solutions to address some of the challenges associated with anchoring of floating offshore wind turbines. A number of emerging anchoring technologies are being considered by the Applicant.
86. These anchor technologies have the potential to increase efficiency by using less materials to achieve similar or higher loading capacities, reduce installation times and transportation requirements, mitigate supply chain constraints and further mitigate environmental effects. Innovative solutions currently being considered include using helical micro piles to fix an anchor plate to the seabed. These include helical piles that are installed through a bespoke installation tool, or drilled and grouted micro piles installed using a drilling template.
87. The Applicant will aim to use these technologies where they are feasible (depending on availability, certification, ground conditions and design performance) and where there are opportunities to reduce environmental impacts. These technologies will be presented in post-consent plans outlining how the construction and deployment falls within parameters assessed within the RIAA.

                        Connectors and ancillaries

88. The use of a number of different connectors and ancillaries may be required for the mooring and anchoring systems which alter the mooring system behaviour, for example, to reduce dynamic loads, and to reduce mooring line radius which limits movement of the floating foundation. The following connectors and ancillaries may be used:

• Long Term Mooring (LTM) connectors (shackles or H-links): these are used to securely connect different mooring line sections and the mooring lines to the anchoring systems.
• Clump weights: these may be added near the touchdown point of the mooring line to reduce the mooring line radius and provide additional weight. These are commonly used with catenary mooring lines and are usually installed over the chain links.
• Buoys or buoyancy elements: commonly used with semi taut mooring lines, these are used to suspend portions of the mooring line within the water column. The depth of these buoyancy elements within the water column can be altered, which allows the correct tension to be obtained.
• In-line tensioners: these may be added to the mooring line in order to install mooring lines with the correct tension.

89. The maximum design envelope for mooring line connectors and ancillaries is presented in Table 4.11   Open ▸ and a schematic is presented in Figure 4.10   Open ▸ and Figure 4.11   Open ▸ .

Table 4.11: Maximum Design Envelope: Connectors and Ancillaries

Figure 4.10: Indicative Schematic of Mooring Line Connectors and Ancillaries Showing LTM Connectors, Clump Weights, and In-Line Tensioners

Figure 4.11: Indicative Schematic of Mooring Line Connectors and Ancillaries Showing LTM Connectors and Buoyancy Modules

4.3.4.    Offshore Substation Platforms

4.3.4. Offshore Substation Platforms

90. The OSPs will transform the electricity generated by the wind turbines to a higher voltage and/or to direct current allowing the power to be efficiently transmitted directly to shore or to a wider offshore grid network.
91. The Applicant has defined two options for OSP arrangements to be assessed within the appropriate assessment. The exact number and size of OSPs will be subject to National Grid ESO final design recommendations and detailed design, however, the overall size, footprint, piling parameters and key design features will remain within the representative OSP design scenarios considered. The following OSP arrangement scenarios have been considered:

• OSP Option 1: up to six large High Voltage Alternating Current (HVAC)/High Voltage Direct Current (HVDC) OSPs; or
• OSP Option 2: a combined option comprising:

–           up to three large HVAC/HVDC OSPs; and

–           up to 12 small HVAC OSPs.

92. The following subsections describe the maximum design envelope for the topsides and foundations for these options.

                        Offshore platform topsides

93. Up to six large OSP topsides will be installed with maximum dimensions of up to 121 m (length) by 89 m (width) and will be approximately 93 m in height (above LAT), excluding the helideck, lightning protection and antenna structure ( Table 4.12   Open ▸ ).
94. Should OSP Option 2 be selected at the final design stage, up to 12 small OSPs will be installed (alongside three large OSPs with same dimensions as mentioned previously), up to 41 m in length, 37 m in width and 50 m in height, excluding helideck, lightning protection and antenna structure ( Table 4.13   Open ▸ ). The final solution chosen, and the topside sizes, will be dependent on the final electrical set up for the Array.

Table 4.12: Maximum Design Envelope: OSP Option 1 Topsides

Table 4.13: Maximum Design Envelope: OSP Option 2 Topsides

                        Offshore platform foundations

95. The OSPs will be installed on fixed jacket foundations and will be located within the Array. For large OSPs, the fixed jacket foundations will have up to 12 legs, whereas fixed jacket foundations for small OSPs will have up to six legs. Up to two piles will be required per leg for both large and small OSPs.
96. For OSP Option 1, this results in a maximum of 24 piles required per foundation. Up to 144 piles will require piling for up to six large OSPs ( Table 4.14   Open ▸ ). For OSP Option 2, a maximum of 24 piles will be required per foundation for three large OSPs and a maximum of 12 piles will be required per foundation for 12 small OSPs, resulting in a total number of up to 216 piles requiring piling ( Table 4.15   Open ▸ ). It should be noted that diameter of piles required for large OSP fixed jacket foundations are 4.5 m, whereas small OSP fixed jacket foundations will require piles with a diameter of 3 m.
97. Table 4.14   Open ▸ and Table 4.15   Open ▸ describe the maximum design envelope for OSP Option 1 and OSP Option 2, respectively.

Table 4.14: Maximum Design Envelope: OSP Option 1 Fixed Jacket Foundations

Table 4.15: Maximum Design Envelope: OSP Option 2 Fixed Jacket Foundations

4.3.5.    Scour Protection for Foundations

4.3.5. Scour Protection for Foundations

98. Natural hydrodynamic and sedimentary processes can lead to seabed erosion and ‘scour hole’ formation around anchor and mooring systems, and foundation structures. Scour hole development is influenced by the shape of the foundation structure, seabed sedimentology and site-specific metocean conditions such as waves, currents, and storms. Employing scour protection can mitigate scour around foundations. Commonly used scour protection types include:

• concrete mattresses: cast of articulated concrete blocks, several metres wide and long and linked by a polypropylene rope lattice, which are placed on and/or around structures to stabilise the seabed and inhibit erosion; or
• rock: the most frequently used scour protection method. Layers of graded stones placed on and/or around structures (e.g. foundation structures) to inhibit erosion, or rock filled mesh fibre bags which adapt to the shape of the seabed/structure as they are lowered on to it.

99. The type and volume of scour protection required will vary depending on the various wind turbine anchoring options and offshore platform options considered, and the final parameters will be decided once the design of these is finalised. This decision will consider a range of aspects including geotechnical data, meteorological and oceanographical data, water depth, foundation type, maintenance strategy, and cost.
100. Table 4.16   Open ▸ presents the maximum design envelope for scour protection required for the Anchoring Options described in section 4.3.3. It should be noted that Anchoring Option 2 is not included within Table 4.16   Open ▸ as there is no requirement for scour protection for this option. DEAs are fully embedded within the seabed (see Table 4.5   Open ▸ ) and, therefore, erosion around the structure is unlikely to occur, minimising the need for scour protection.
101. Table 4.17   Open ▸ presents the maximum design envelope for the OSP Options described in section 4.3.4.

Table 4.16: Maximum Design Envelope: Scour Protection for Anchoring Options[7]

Table 4.17: Maximum Design Envelope: Scour Protection for OSP Options

4.3.6.    Subsea Cables

4.3.6. Subsea Cables

                        Inter-array cables

102. Inter-array cables carry the electrical current produced by wind turbines to an OSP. So as not to hinder the movement of the floating foundations, it is proposed that dynamic inter-array cables will be used. There are several cable designs which may be used, however, the most likely to be used for the Array is a ‘lazy-S’ configuration which allows extension of the cables in response to the floating foundation movements. Buoyancy modules are attached to the dynamic inter-array cable to support the weight of the cable and provide the ‘lazy-S’ configuration in the water column (as demonstrated in Figure 4.12   Open ▸ ). Bend stiffeners help to reduce the fatigue in the inter-array cables and are typically used where the cable exits the floating foundation and at touch down points of the cable on the seabed.
103. Where the dynamic cable transitions to static, the transition length (dynamic touch down) would typically have protection around the cable to protect the cable from abrasion and fatigue. Tether clamps and anchor may also be required ( Figure 4.12   Open ▸ ) to limit the movement at the touch down area. A tether clamp is designed to secure subsea lines to an anchor on the seabed and usually comprises a steel housing that is bolted over the cable with a padeye to secure a chain to a weighted anchor on the seabed. Where the static cable is laid on the seabed it will be protected in line with the outputs of the Cable Burial Risk Assessment (CBRA). It is anticipated that cable burial methods will be used to protect cables, with external cable protection employed where target burial depths cannot be achieved. A schematic of the dynamic/static inter-array cabling system is presented in Figure 4.12   Open ▸ .

Figure 4.12: Typical Indicative Schematic of the Dynamic/Static Inter-array Cable System (Subject to Detailed Design Configuration)

104. Different approaches and techniques are available for burial of the inter-array cables laid on the seabed. The final choice of burial or external cable protection methods will be subject to a review of the seabed conditions and the CBRA. Equipment which will be used to achieve cable burial is described in paragraph 154.
105. External cable protection methods will be required in areas where cable burial is unachievable, for example, where there are pre-existing cables or pipelines, or areas of exposed bedrock. A hard protective layer, such as rock or concrete mattresses, may be used to protect exposed cables. The need for this additional external protection will be subject to whether minimum target cable burial depths recommended for protection from the external threats can be achieved. Factors such as seabed conditions and sedimentology, naturally occurring physical processes and any potential interactions with human activities such as vessel anchoring and bottom-trawl fishing gear, will influence the requirement for additional protection. Site preparation activities may be required to provide relatively flat seabed surface for installation of cables and enable burial of inter-array cables to target burial depths.
106. The cable burial methodology and potential external cable protection will be identified at the final design stage (post-consent). The maximum design envelope for the inter-array cables is presented in Table 4.18   Open ▸ . Figure 4.13   Open ▸ presents a schematic of the dimensional characteristics set out in Table 4.18   Open ▸ .

Table 4.18: Maximum Design Envelope: Inter-Array Cables

Figure 4.13: Indicative Inter-Array Cable Dimensional Characteristics

                        Subsea junction boxes

107. Subsea junction boxes may be installed on the seabed which serve as a single connection point for inter-array cables from several wind turbines. There are several configurations which may be used to connect inter-array cables into the subsea junction boxes as depicted in Figure 4.14   Open ▸ . These comprise the following:

• Daisy-chain – two inter-array cables are required per wind turbine, which connect wind turbines together in sequence. The wind turbines located at either end of the grouping are connected to a single subsea junction box via the second inter-array cable exiting each of the two wind turbines. Once reaching the subsea junction box, a single static inter-array cable exits, to connect into the OSP.
• Fishbone – each wind turbine is connected to a single subsea junction box via one inter-array cable. Lengths of static inter-array cable connect the subsea junction boxes together in sequence and then a single static inter-array cable exits the final subsea junction box in the sequence to connect into the OSP.
• Star – several wind turbines are connected to a single subsea junction box via one inter-array cable per wind turbine. A single static inter-array cable exits the subsea junction box, to connect into the OSP.
• Fishbone and star hybrid – several wind turbines are connected to a single subsea junction box via one inter-array cable per wind turbine. Lengths of static inter-array cable then connect multiple subsea junction boxes together in sequence. A single static inter-array cable exits the final subsea junction box in the sequence to connect into the OSP.

Figure 4.14: Schematic of Indicative Inter-Array Cable String Configurations utilising Junction boxes (Subject to Detailed Design Configuration)

108. The maximum design envelope for inter-array cables, presented in Table 4.18   Open ▸ , takes into account these potential configurations and, therefore, allows flexibility in design should any of these configurations be employed alongside the subsea junction boxes.
109. The maximum design envelope for the subsea junction boxes is presented in Table 4.19   Open ▸ . At this stage, the design of the subsea junction boxes is conceptual, therefore, some parameters included are estimated; this is indicated in Table 4.19   Open ▸ as appropriate. In addition, the parameters presented in Table 4.19   Open ▸ take into account the junction boxes associated with the various inter-array cable configurations, therefore, the parameters represent a conservative estimate which is considered to be the maximum design scenario. The parameters included within the maximum design envelope for the subsea junction boxes account for ongoing development of this technology and allows flexibility in the future.

Table 4.19: Maximum Design Envelope: Subsea Junction Boxes

                        Interconnector cables

110. Interconnector cables connect OSPs to one another and provide redundancy should there be any failures within the electrical transmission system. It is expected that these cables will be a combination of HVAC and HVDC. The maximum design envelope is presented in Table 4.20   Open ▸
111. Up to 236 km of interconnector cables will be installed within the Array. It is anticipated that cables will be protected via burial methods and will be buried at a minimum target depth of 0.4 m (subject to CBRA). External cable protection will be used in areas where minimum target burial depth cannot be achieved. Site preparation activities may also be required to provide relatively flat seabed surface for installation of cables and enable burial of interconnector cables to target depths.

Table 4.20: Maximum Design Envelope: Interconnector Cables

                        External cable protection

112. Where minimum target cable burial dept h cannot be achieved, external cable protection methods will   be employed to restrict movement and prevent exposure over the lifetime of the Array. This will protect cables from activities such as fishing, anchor placement or dropped objects, and limit effect of heat and/or electromagnetic fields. External cable protection systems include concrete mattresses, rock placement, cast iron shells or polyurethane/polyethylene sleeving. The final solution(s) chosen at final design stage (post-consent) will be dependent upon seabed conditions and any potential interactions with human activities which may occur within the Array. Table 4.21   Open ▸ presents the maximum design envelope for external cable protection for inter-array cables and interconnector cables.

Table 4.21: Maximum Design Envelope: External Cable Protection Parameters

                        Concrete mattressing  

113. Concrete mattresses comprising high strength concrete blocks and Ultraviolet (UV) stabilised polypropylene rope may be used as a means of external cable protection for inter-array and interconnector cables and at cable crossings. The standard size of units is 6 m x 3 m x 0.3 m with standard density, however, size, density, and shape of units may be modified (within the parameters presented in Table 4.21   Open ▸ ) for example, by tapering edges of units for use in high current environments, or using denser concrete, so that they are engineered for and bespoke to the locality in which they are installed.
114. 69. Concrete mattresses are installed above the cables using a Dynamic Positioning (DP1) vessel and free swimming installation frame. The mattresses are lowered to the seabed and the installation frame is released in a controlled manner once in the correct position to deploy the mattress on the seabed. This installation process is repeated for each mattress along the length of cable that requires external protection. Dependant on expected scour, mattresses may be gradually layered in a stepped formation on top of each other.

                        Rock placement

115. Rock placement may also be utilised as a form of external cable protection for inter-array and interconnector cables and at cable crossings. Rock is placed on top of cables either by creating a berm or using rock bags ( Figure 4.15   Open ▸ ).
116. Installation of rock placement in the form of berm creation will utilise a vessel with equipment such as a ‘fall pipe’ so that rock can be placed close to the seabed. Rock may be placed to a maximum height of 3 m and 20 m width (see Table 4.21   Open ▸ ). The berm created via rock placement will be designed to provide protection from anchor strike and anchor dragging, and to reduce risk of snagging by towed fishing gear as far as practicable in line with best practice guidance. Depending on expected scour, the cross-section of the berm may vary, and the length of the berm will be dependent on the length of the cable which requires protection.
117. Alternatively, pre-filled rock bags may be used which will be placed above the inter-array and interconnector cables or cable crossings using installation beams. Rock bags consist of various sized rocks contained within a rope or wire net which are lowered to the seabed and deployed on to the seabed once in the correct position. Rock bags have typical dimensions of 0.7 m in height and 3 m diameter; the number of rock bags which may be required will be dependent on the length of cable which requires protection.

Figure 4.15: Rock Cable Protection Methods (Left: Rock Placement; Right: Rock Bags)

                        Cable crossings

118. Up to 12 inter-array cable crossings and up to 12 interconnector cable crossings may be installed across the Array. Cable crossings may comprise several different methods as demonstrated in Table 4.22   Open ▸ , and additional cable protection will be installed at cable crossings. Table 4.22   Open ▸ presents the maximum design envelope for cable crossings, and accounts for additional protection required.

Table 4.22: Maximum Design Envelope: Cable Crossing Parameters

4.4.        Site Preparation Activites

4.4. Site Preparation Activites

119. Prior to the construction phase of the Array, a number of site preparation activities will be required to be undertaken. It is assumed that site preparation works will continue throughout the construction phase as required, therefore, these works may be undertaken at any point within the construction programme. A summary of site preparation activities is provided in this section.

4.4.1.    Pre-Construction surveys

4.4.1. Pre-Construction surveys

120. Pre-construction surveys, including geophysical and geotechnical surveys, may be carried out to provide further information of:

• seabed conditions and morphology;
• soil conditions and properties;
• presence or absence of any potential obstructions or hazards; and
• to inform detailed design for the Array.

121. Geophysical surveys will be undertaken within the Array to provide further information of Unexploded Ordnance (UXO), bedforms and mapping of boulders, bathymetry, topography and sub-surface layers. Geophysical survey techniques to be employed include Multibeam Echosounder (MBES), magnetometer, Side-Scan Sonar (SSS), Sub-Bottom Profiler (SBP) and Ultra-High Resolution Seismic (UHRS).
122. Geotechnical surveys will be carried out at specific locations within the Array and will employ techniques such as Cone Penetration Tests (CPTs), vibrocores, box cores, piston cores and boreholes.

4.4.2.    Clearance of Unexploded ORdnance

4.4.2. Clearance of Unexploded ORdnance

123. The possibility exists for UXO originating from World War I or World War II to be present within the Array. Due to the health and safety risks posed by UXO and potential interactions with planned locations of installed infrastructure and vessel activities, it is necessary for UXO to be surveyed and managed carefully before the construction phase and installation of offshore infrastructure commences.
124.  A desk-based study of the Array (Ordtek, 2022) reviewed the relevant military history in the vicinity of the Array and the likelihood of encountering UXO. Based on known military activity the desk-based study concluded that there was a low background risk of UXO within the Array, and the likelihood of encountering different types of UXO within the Array was considered to be unlikely, meaning that it would be unusual for UXOs to be encountered within the Array. However, due to existing evidence of use in the wider area, potential for unrecorded activities such as munitions dumping, and potential for burial and migration of UXO due to natural seabed processes, the potential presence of UXOs cannot be discounted (Ordtek, 2022).
125. Methodologies considered within the PDE to avoid/clear UXOs are as follows:

• avoid and leave in situ;
• micrositing of offshore infrastructure to avoid UXO;
• relocation of UXO to avoid detonation;
• low order technique (e.g. deflagration); and
• high order detonation (with associated mitigation measures). 

126. Due to the health and safety risks that UXOs pose, the Applicant would seek to either avoid UXOs entirely, avoid UXOs via micrositing, or relocate UXO where practicable. If methods cannot be employed to avoid UXOs, a specialist contractor will clear UXOs in advance of further site preparation and construction works taking place.  The preferred clearance method for UXO is use of a low order technique with a single donor charge of 0.25 kg Net Explosive Quantity (NEQ) for each clearance event. Up to 0.5 kg NEQ clearance shot will be required for neutralisation of residual explosive material at each location. Detailed design work would be required to confirm planned locations of infrastructure, prior to conducting any UXO surveys. The Applicant have assumed that up to 15 UXOs may require clearance based upon the desk-based study (Ordtek, 2022) and experience from other offshore wind farms in the region such as the Seagreen 1 Offshore Wind Farm. As a risk remains that unintended high order detonation may occur, 10% of clearance events have been assumed to have the potential to result in high order detonation.
127. Table 4.23   Open ▸ presents the maximum design envelope for UXO clearance.

Table 4.23: Maximum Design Envelope: Unexploded Ordnance Parameters

4.4.3.    Sand Wave Clearance

4.4.3. Sand Wave Clearance

128. Existing sand waves may need to be cleared in some areas of the Array prior to the installation and burial of inter-array and interconnector cables. There are two main reasons for undertaking sand wave clearance:

• To provide a relatively flat seabed surface for cable installation and so that cable burial tools can work effectively: if cables are installed up or down a slope over a certain angle, or where the cable burial tool is working on a camber, the ability to meet target burial depths may be impacted.
• In order for cables to be buried at the target burial depth and remain buried for the operational lifetime of the Array (35 years): as sand waves are generally mobile in nature, the cable must be buried beneath the level where natural sand wave movement could uncover it. Therefore, for this to be achieved, mobile sediments may need to be removed before cables are installed and buried.

129. No large bed forms were observed as being prevalent across the site. It is expected based on geophysical data that if sand wave clearance is required it will be undertaken in specific discrete areas of the Array (e.g. along inter-array and interconnector cables) and could occur throughout the construction phase.
130. Sand wave clearance techniques could include pre-installation ploughing which flattens sand waves and pushes sediment from wave crests into adjacent troughs to level the seabed may be employed. It is not anticipated that large scale dredging would be required within the site boundary.
131. Table 4.24   Open ▸ presents the maximum design envelope for sand wave clearance. A geophysical survey campaign will be completed prior to construction which will allow the final parameters for sand wave clearance to be defined.

Table 4.24: Maximum Design Envelope: Sand Wave Clearance Parameters

4.4.4.    Boulder Clearance

4.4.4. Boulder Clearance

132. Boulder clearance may be required in some areas of the Array prior to installation of offshore infrastructure, in particular, along inter-array cables and interconnector cables. A boulder is defined as being over 256 mm (Wentworth Scale) in diameter and/or length. A DP1 vessel is likely to be used to undertake the boulder clearance campaign.
133. Boulder clearance is required to aid cable installation and increase the success rate for achieving minimum target burial depth during cable burial, therefore, reducing the risk of further cables burial works and/or the need for cable protection. Boulder clearance also reduces the risk of cable damage during installation and subsequent burial. It may also be required in the vicinity of the OSP jacket foundation locations (including within the jack-up vessel zone around the OSP foundation locations), to avoid disruption to installation activities and to ensure stability for the jack-up vessel. The maximum design envelope for boulder clearance in the Array is presented in Table 4.25   Open ▸ .
134. Boulders may be cleared using a plough or boulder grab, however, the geophysical and pre-construction surveys, and the parameters of any boulders present (e.g. size, density and location of boulders), will inform the methodology to be used. It is possible that more than one method of boulder clearance may be deployed across the Array. Cleared boulders will be relocated to an appropriate location within the site boundary.

Table 4.25: Maximum Design Envelope: Boulder Clearance Parameters