Offshore wind energy - draft sectoral marine plan: strategic environmental assessment

Strategic environmental assessment (SEA) identifies the likely significant environmental impacts of plans and policies and proposed reasonable alternatives to them.

3 Approach to the Assessment

3.1 Purpose of the Assessment

3.1.1 The purpose of this SEA is to assess the potential for likely significant environmental effects that may arise from adoption of the Draft Plan. This will allow corresponding mitigation measures to be identified where necessary and highlight opportunities for enhancement in cases where beneficial effects are likely.

3.2 Relationship Between this SEA and Previous Assessments

3.2.1 A considerable amount of work has already been undertaken to explore the potential wider environmental effects of activities associated with offshore wind development. Of particular relevance are the SEAs that were previously undertaken for the 2011[72] and 2013[73] Sectoral Marine Plans for Offshore Wind. This SEA builds upon the assessment methodology, information and findings of the respective Environmental Reports that were produced as part of these assessments. This is to help ensure consistency in the strategic assessment of offshore wind energy development in Scotland.

3.2.2 The latest evidence regarding environmental effects of offshore wind farm development and mitigation of effects from available research and monitoring results has also informed this assessment. These include outputs from the ScotMER (formerly SpORRAn) process and other research programmes, such as ORJIP and the DECC/BEIS Offshore Energy SEA[74]..

3.2.3 Other relevant sources of information include the SEAs that have been prepared to assess the designation and management of four MPAs[75], the designation of marine pSPAs[76], proposed fisheries management measures in MPAs and SACs[77], and Wild Seaweed Harvesting[78], as well as the ongoing SEA of the plan to improve protection given to Priority Marine Features (PMFs) outside the MPA network[79] and the SEA of the plan to designate a deep sea marine reserve in Scottish waters[80].

3.3 Scope of the Plan to be Assessed

3.3.1 Marine Scotland will deliver an overarching Sustainability Appraisal (SA) through four key, complementary initiatives: the SEA; a Habitats Regulations Appraisal (HRA); a socio-economic impact assessment (SEIA); and public consultation on the Draft Plan.

3.3.2 The SEA and development of the Draft Plan have been undertaken alongside each other in order for the results of the SEA, together with the results of the HRA and SEIA, to inform the development of the final Draft Plan.

3.4 Scope of the Assessment

3.4.1 Following a review of previous offshore wind plan SEAs[81], [82], as well as relevant academic and grey literature, the Screening and Scoping Report[83] proposed that the following SEA topics should be scoped into the assessment:

  • Biodiversity, Flora, and Fauna;
  • Population and Human Health;
  • Soil (namely, Marine Geology and Coastal Processes);
  • Water Quality;
  • Climatic Factors;
  • Cultural Heritage; and
  • Landscape, Seascape, and Visual Amenity.

3.4.2 Consultation responses on the Screening and Scoping Report have been reviewed and where appropriate have been built into the assessment scope and methodology.

3.4.3 The assessment has included consideration of the likely significant effects resulting from the Draft Plan on the marine and coastal environments where relevant. The potential effects associated with all offshore wind development stages, including pre-construction (e.g. UXO survey/clearance) and decommissioning phases, have also been assessed. As a broad assumption, decommissioning phases have been assumed to be of the same magnitude as construction impacts for all receptors unless specified otherwise.

3.4.4 At this stage, it is considered that significant environmental effects on 'Air Quality' are unlikely to arise through the implementation of the Draft Plan. As such, this topic has been scoped out of the assessment.

3.4.5 The SEA topic of 'Material Assets' encompasses a broad range of subtopics that include both built and natural assets and relevant issues have been assessed under corresponding SEA topic areas. For example, potential effects that relate to nursery and spawning grounds of commercial fish have been covered under the topic of 'Biodiversity, Flora, and Fauna'. Similarly, infrastructure with regard to the promotion of a diverse and decarbonised energy sector has been given consideration under the topic of 'Climatic Factors'. SEPA advised that the potential re-use of existing energy infrastructure, particularly in relation to North Sea Oil and Gas Rig Decommissioning should be assessed by this SEA. This issue is not possible to assess in detail at this stage due to the uncertainty around project locations and for the most part existing infrastructure has been excluded from the areas under assessment. However, it is recognised as a potential opportunity that will need to be considered in the future. 'Material Assets' has therefore been scoped out of the assessment. This reflects the approach taken in previous offshore wind plan SEAs[84], [85].

3.4.6 The effects on other marine users, such as the potential displacement of commercial fishing activity, recreational boating, and tourism, have been considered by the accompanying SEIA. Issues of navigational safety and collision risk for vessels have been covered, as far as possible, within the topic of 'Population and Human Health'.

3.4.7 A summary of the scope of the assessment and associated potential effects is presented in Table 2.

Table 2 SEA topics scoped into the assessment

SEA Topic Potential Effects
Biodiversity, Flora, and Fauna
  • Loss of and/or damage to marine and coastal habitats, including benthic and intertidal habitats (for example, due to smothering of benthic habitats and substratum loss);
  • Effects on key receptors and prey species, including disturbance, noise effects, EMF exposure, collision risk, habitat exclusion, and barriers to wildlife movement;
  • Positive effects arising from habitat enhancement, such as the creation of artificial reefs, new roosting structures and exclusion of habitat damaging activity;
  • Effects of pollution releases on both species and habitats; and
  • Effects from introduction and spread of Invasive Non-Native Species (INNS).
Population and Human Health
  • Effects arising from noise, vibration, light, dust and shadow flicker effects from all phases of development;
  • Effects on residential amenity stemming from construction/installation/operational activities;
  • Issues of navigational and aviation safety and collision risk; and
  • Effects on marine and coastal recreation and access
Soil (Marine Geology and Coastal Processes)
  • Effects on subsea geology, sediments, and coastal processes arising from changes in hydrodynamics and the existing wave regime.
Water Quality
  • Effects on ecological status;
  • Effects on water quality (for example, due to increases in suspended sediment loads and turbidity as well as an increase in pollution incidents); and
  • Effects of the presence of structures on local currents, wave regimes, and water column mixing, as well as secondary effects on sedimentation and erosion beyond the sites.
Climatic Factors
  • Contribution to supporting a diverse and decarbonised energy sector; and
  • Coastal facilities may be at risk from climate change.
Cultural Heritage
  • Loss of and/or damage to historic environment features and their settings, including coastal and marine archaeology and historic MPAs.
  • Both temporary and longer term effects on landscape and coastal character and visual receptors arising from the presence of structures including any ancillary infrastructure.

3.5 Consideration of Reasonable Alternatives

3.5.1 The development of the draft Plan has been an iterative process that has been informed throughout by relevant environmental information and has given regular consideration to reasonable alternatives. These alternatives are confined to the consideration of alternative offshore wind opportunities, in line with the focus of the draft Plan.

3.5.2 The initial Areas of Search scoping work identified prospective Areas of Search, in line with the objective of the plan to identify locations for potential future offshore wind development in the period up to 2050 in Scottish waters, through a consideration of multiple constraints that would restrict potential for sustainable offshore wind development or where offshore wind development would be likely to negatively affect the environment, other sectors or users of the sea. These initial AoS have been refined following consideration of feedback received through the initial consultation on the AoS, extended engagement with key stakeholders, preparation of the RLG, cross-sectoral steering group feedback and updated analysis resulting in the identification of 17 DPO areas in which offshore wind energy could potentially be sustainably pursued. Section 1.2 above describes how these areas were identified and where others were removed from the process.

3.5.3 An assessment of reasonable alternatives has been undertaken at each of the assessment stages described in detail in Section 3.6. The first stage of the assessment has involved setting out the potential environmental effects associated with a range of alternative offshore wind technologies that could be implemented in Scottish marine waters.

3.5.4 The second stage has been to apply the potential environmental effects identified in the first stage to spatial and locational constraints identified in the baseline data for each of the DPOs. The DPOs (see Figure 4) themselves constitute reasonable alternatives as they represent different options for fulfilling the objectives of the Draft Plan, based on varying levels of constraint and opportunity as described above.

3.5.5 The third stage in the assessment has been to determine the potential cumulative environmental effects associated with development in multiple DPOs at a regional and national scale. For the assessment of cumulative effects at regional and national scales, three scenarios, relating to different realistic scales of possible future offshore wind development within the DPOs, have been considered. These three scenarios give indicative low, medium and high development scenarios of installed capacity within the DPOs at a regional and subsequently national scale. The SEA and SEIA use these scenarios to inform the assessment of a broad range of impact scenario.

3.6 Assessment Methodology

3.6.1 The assessment has involved the following stages:

  • Stage 1: Identify the range of environmental effects associated with alternative offshore wind technologies;
  • Stage 2: Identify environmental effects of applying the range of effects identified in Stage 1 to the alternative DPOs; and
  • Stage 3: Assessment of potential cumulative effects, including those associated with the alternative scenarios for different scales of possible future offshore wind development within the DPOs.

Stage 1: Identify the Range of Environmental Effects Associated with Alternative Offshore Wind Technologies

3.6.2 Stage 1 of the assessment has been to identify the range of potential environmental effects that could result from alternative offshore wind technologies and subsea cables during all project phases of offshore wind development (i.e. pre-construction, construction, operation and maintenance, and decommissioning).

3.6.3 This initial stage has drawn on a number of different sources of information, including the results of previous assessment work highlighted in Section 3.2, research studies including those undertaken for Marine Scotland and by the offshore wind energy industry, guidance for the environmental assessment of offshore wind projects, general findings from available environmental impact assessments (EIAs) of offshore wind development projects and emerging monitoring information from existing installations where relevant. The evidence base and outcomes of this initial assessment stage are documented in Appendix B.

Stage 2: Identify Environmental Effects of Applying the Range of Effects Identified in Stage 1 to the Alternative DPOs

3.6.4 Stage 2 of the assessment has been to assess each of the alternative DPOs and possible subsea cable routes against the environmental baseline, reflecting on the sensitivity of environmental features within these areas and the potential environmental pressures associated with offshore wind farm development identified in the Stage 1 assessment, to determine the likely significance of any environmental effects. The second stage in the assessment has involved developing evidence-based assumptions on how the wider environment might be affected by such development and then describing and quantifying any likely significant positive or negative environmental effects associated with the realistic maximum scale of development in each DPO.

3.6.5 The particular importance of accessing the best available spatial data on mobile species' distribution and functional use of the sea space (e.g. seabirds and marine mammals) is recognised as these have been significant issues for previous offshore wind projects. Focused reviews on these topics have been undertaken to inform both the SEA and HRA of the Draft Plan. These reviews have drawn on best available information, including outputs from the ScotMER process, ORJIP and the DECC/BEIS Offshore Energy SEA[86].

3.6.6 Stage 2 of the assessment has comprised a combination of desk-based review and Geographic Information System (GIS) analysis. The outcomes have been presented in tables for each DPO, as illustrated in Table 3. The first column presents the SEA topic scoped into the assessment. The second column highlights the key relevant headline baseline information for a DPO, rather than all of the detail considered in the assessment. This provides a means for the relevant environmental baseline and problems to be a key component of the assessment. This approach is known as a 'baseline-led assessment' and sets the context of the DPO within their receiving environment.

Table 3 Example assessment table

SEA Topic Key Baseline Evidence Potential for Effects Characteristics Mitigation Available and Potential Residual Effects

3.6.7 The third column discusses the potential effects of offshore wind development on the receiving environment. This is based on the realistic maximum scale of development within each DPO taking account of the likely scale of overall development under the Plan. Table 4 sets out the likely scale of maximum development at each DPO. These assumptions are consistent with those used in the accompanying SEIA. For individual DPOs, in line with the broad parameters for the Plan, it has been assumed that the minimum scale of development within any DPO is 100 MW.

3.6.8 The fourth column describes the characteristic of the effect. This provides a summary of the relevant dimensions of effects set out in Schedule 3 (6) of the Environmental Assessment (Scotland) Act 2005. This includes the timescale of effects, whether effects are permanent or temporary, positive or negative, and whether there are particular secondary, cumulative or synergistic effects where these could be determined and relevant to the assessment of significance.

3.6.9 The final column considers the potential mitigation that might be available to prevent, reduce and as fully as possible offset any significant adverse effects, and assesses the residual risk to environmental receptors through the application of judgement informed by the criteria in Table 5. i.e. judgement is used to balance where partial criteria for a magnitude level is met. The results of these assessments are set out in Appendix C.

Table 4 Realistic maximum scale of development within each DPO

Region DPO Area km² Potential Installed Capacity (GW) Realistic Maximum Development Scenario for each DPO (GW)
East E1 3816 19.1 3
E2 1287 6.4 2
E3 474 2.4 1
North East NE1 776 3.9 2
NE2 464 2.3 1
NE3 339 1.7 1
NE4 440 2.2 1
NE5 496 2.5 1
NE6 699 3.5 2
NE7 1027 5.1 3
NE8 401 2.0 1
North N1 1163 5.8 2
N2 560 2.8 2
N3 1106 5.5 2
N4 200 1.0 1
West W1 1107 5.5 2
South West SW1 292 1.5 1

Table 5 Assessment criteria

Type Magnitude Indicative Criteria
Negative/Positive Major Large spatial scale (size/number);
Major intensity (level/magnitude);
Long-term (duration/frequency);
High sensitivity of features;
and/or Low tolerance/reversibility of features.
Moderate Medium spatial scale;
Moderate intensity;
Moderate sensitivity of features;
and/or Moderate tolerance/reversibility of features.
Minor Small spatial scale;
Low intensity; Short-term;
Low sensitivity of features;
and/or High tolerance/reversibility of features.
Adverse/Beneficial Negligible There is likely to be a change, but the level will be indiscernible from baseline conditions.

Stage 3: Assessment of Potential Cumulative Effects, including those Associated with the Scenarios for Different Scales of Possible Future Offshore Wind Development within the DPOs

3.6.10 The third stage of the assessment has been the cumulative assessment. This has firstly identified the potential effects of development in multiple DPOs at a regional scale and determining where these may have significant environmental effects, taking account of the likely scales of development under the plan at a regional level. Three scenarios have been reviewed against each region (Table 6), taking into account the potential for a greater or lesser proportion of the total (national, see Section 3.6.11) scale of development to be present in a particular region.

Table 6: Regional scenarios

Region Total DPO Area (km²) Maximum Potential Installed Capacity (GW) Low Development Scenario (GW) Medium Development Scenario (GW) High Development Scenario (GW)
East 5577 27.9 1 2 3
North East 4641 23.2 1.5 3 4.5
North 3030 15.1 1 2 3
West 1107 5.5 0.5 1 2
South West 292 1.5 0.3 0.6 1

3.6.11 A national scale assessment of the potential effects of possible future offshore development within the DPOs in the period 2020 to 2050 has also been undertaken by considering the following three scenarios at a national level:

  • Low Development Scenario: 3 GW Installed Capacity;
  • Medium Development Scenario: 5 GW Installed Capacity; and
  • High Development Scenario: 10 GW Installed Capacity.

3.6.12 This is to help to identify possible capacity constraints and how different scales of development within DPOs might give rise to differing levels of environmental effect at a national scale. These scenarios enable the assessment to consider whether the magnitude of an effect is altered by smaller or larger areas of development, or whether an effect is related simply to the presence of devices and independent of the areas of development. It should be noted that although Scottish Government provided direction, the scenarios used are hypothetical and are not a formal commitment or statement of policy. The reasoning behind the selection of 10 GW as the high development scenario is discussed in the Draft Plan.

3.6.13 The cumulative assessment has then investigated the combined effects of the Plan at a regional and national scale alongside other plans and projects. Consideration has been given to the competition for space between different sectors and within sectors. Given the significant uncertainty regarding the scale or design of development, this stage has not sought to quantify impacts, rather it has identified current and future developments that would require integration into a cumulative assessment at a project level.

3.6.14 The cumulative effects assessment has been qualitative in nature and has assessed the potential for cumulative effects. However, recognising the uncertainties of where and when development might occur under the plan, there will also be a requirement for a more detailed cumulative assessment to be undertaken at a project level, at which point there is likely to be additional information on other development locations and timings.

3.6.15 The final stage of the assessment has also involved summarising the overall effects of the Draft Plan against the SEA objectives set out in

3.6.16 Table 7. These objectives, which are based on those which were developed for previous offshore wind plan SEAs[87], [88], have been updated following advice from the Consultation Authorities during the scoping phase of the Draft Plan (Section 1.3). This 'objective led approach' provides a useful measure to draw together and comment on the combined performance of the Draft Plan.

Table 7 SEA objectives

SEA Topic SEA Objective
Biodiversity, Flora, and Fauna
  • To safeguard marine and coastal ecosystems, including species, habitats, and their interactions;
  • To avoid adverse effects on both designated and non-designated habitats and species (note: this work has been developed in parallel with the HRA work); and
  • To avoid the introduction and spread of INNS.
Population and Human Health
  • To maintain the accessibility of natural areas for recreation;
  • To minimise or prevent the discharge of pollutants into the natural environment; and
  • To avoid adverse effects on human health and safety.
Soil (Marine Geology and Coastal Processes)
  • To avoid exacerbating coastal erosion and maintain the integrity of coastal processes;
  • To maintain and protect the character and integrity of the seabed, including avoiding the pollution of seabed strata/bottom sediments; and
  • To avoid significant adverse physical damage to coastal geodiversity sites from coastal infrastructure.
Water Quality
  • To avoid pollution of the coastal and marine water environment; and
  • To maintain or work towards achieving good ecological status.
Climatic Factors
  • To contribute to a diverse and decarbonised energy sector;
  • To ensure that adaptation to predicted climate change impacts are taken into account (for example, through consideration of resilience and changing environmental sensitivity); and
  • To preserve marine carbon stocks and carbon sequestration potential (note: this objective is closely linked to the SEA topic of 'Biodiversity, Flora, and Fauna').
Cultural Heritage
  • To protect and, where appropriate, enhance, the historic marine environment;
  • To avoid damage to known and unknown coastal and marine archaeology; and
  • To avoid adverse effects on the character and setting of historic sites and buildings.
  • To avoid or minimise adverse effects on landscape, seascape, and visual amenity, including designated sites;
  • To promote the protection of seascape and coastal landscapes; and
  • To avoid or minimise adverse visual effects.

3.7 Identifying Mitigation and Monitoring Proposals

3.7.1 Potential measures to mitigate adverse effects or enhance benefits associated with the Draft Plan and development within the DPOs have been identified. This has built on the recommendations that were made in the previous offshore wind plan SEAs[89],[90], and strategic work undertaken to fill data gaps and uncertainties, and to assist with mitigating potentially significant adverse environmental effects.

3.7.2 In identifying potential regional environmental sensitivities associated with development within the DPOs and requirements for mitigation measures, alternative technology (and construction method) choices have been identified as key mitigation measures. The 'avoid/ reduce (or minimise)/ offset' hierarchy has also been applied to the consideration of appropriate mitigation measures.

3.7.3 Monitoring proposals have focused on the significant environmental effects that have been identified during the course of the work undertaken to develop DPOs, as well as following implementation of mitigation measures where appropriate. Where possible, existing data sources and indicators will be linked with relevant indicators to minimise resourcing requirements for additional data collection.

3.8 Assumptions, Data Gaps and Limitations

3.8.1 Where data gaps or a lack of evidence exist, then uncertainty is introduced into the Draft Plan and into the prediction of environmental effects. Given these uncertainties, a clear and transparent approach has been adopted for the assessment, documenting any assumptions, data gaps and limitations. Many of these gaps, limitations and difficulties have informed the development of recommendations as set out in Section 6.

Understanding of Scotland's Marine Environment

3.8.2 Whilst a great deal of research has been undertaken on Scotland's marine and coastal environments through public bodies, and by academic institutions and the offshore wind sector, it is widely acknowledged that significant data gaps remain in the understanding of the current and future marine environment. For example, the spatial and temporal distributions of mobile features are not fully characterised, and there are uncertainties regarding the presence of submerged marine structures and buried assets, including underwater archaeology features. Key data gaps and issues are highlighted in the environmental baseline review (Section 4).

Consideration of Possible Technologies

3.8.3 There is uncertainty concerning the nature of potential future technologies for offshore wind that will be deployed which creates uncertainties for the assessment of potentially significant effects. The DPOs provide space both for conventional fixed bottom installations in shallower water (<60 m) and for deeper water (floating) technologies. It is currently unclear how quickly and to what extent deep water technologies might become cost competitive and thus what the balance between technologies might be.

3.8.4 There is also uncertainty concerning construction methods, particularly for deep water technologies, where a variety of options for foundation substructures, might be considered. For example, deep water wind projects may require less percussive piling (and less intensive piling) than some existing offshore wind technologies (monopiles, jackets) and thus underwater noise during construction could be less of an issue compared to conventional projects. However, construction methods for some deep-water technologies could still entail some level of piling.

3.8.5 In order to account for these uncertainties within the assessment, a 'Design Envelope' approach has been adopted to the consideration of potential effects associated with alternative offshore wind technologies, recognising that this will be conservative.

Consideration of Supporting Activities

3.8.6 There remains a degree of uncertainty surrounding the potential effects of some supporting activities as a result of the precise location of activities being unknown. For example, the location of any dredging that might be required to provide fill for gravity base foundations.

3.8.7 Where possible, the potential and general environmental effects of these activities have been identified through a review of the outcomes from the consenting process for past and present projects but have a limited spatial focus as acknowledged in the appropriate sections of this report.

Taking Account of Cable Routes

3.8.8 There is currently a high level of uncertainty concerning the possible location and number of export cables associated with potential development within the DPOs. These requirements will depend on the scale and location of development within the DPOs and the future development of grid connection points (both onshore and possibly offshore). Some information is available from National Grid[91] on potential and planned grid reinforcement which indicates locations where capacity may be available in the future, but this only extends to the medium term and does not take into account potential further offshore wind development in Scottish waters. It remains challenging to predict the precise routes for export cable corridors.

3.8.9 Given these uncertainties, the approach adopted in this study has not considered in detail the potential cable corridors but has more broadly considered the environmental sensitivities of inshore areas. Where sensitive features need to be avoided, this has been identified as a potential mitigation requirement.

Cumulative Effects Assessment

3.8.10 Cumulative effects assessments present significant methodological challenges owing to limitations of data availability from other plans and projects, and uncertainties in the manner in which the DPOs will be developed. The approach to assessing the cumulative effects of the Plan alone and in combination with other plans and projects is set out in Section 3.6.



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