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Strategic Environmental Assessment (SEA) of Draft Plan for Offshore Wind Energy in Scottish Territorial Waters: Volume 1: Environmental Report


4 Sources of Potential Environmental Effects

4.1 Introduction

Offshore wind developments could create a wide range of environmental effects throughout the project life-cycle. This SEA considers the stages of a project including pre-construction, construction, operation and decommissioning.

The actual effect will depend upon the specific location, the timing and approach to activities, the sensitivity as well as the simple presence of receptors and also the pressures on the existing system from other forms of activity. Consequently, the SEA considers the full range of potential effects that could affect SEA receptors (The Potential Impact Tables - Tables 1 to 8 in Appendix 4.1). Effects are considered in this chapter in their generic form to avoid repeating explanations of effect types and pathways for short, and medium to long term options considered in Chapter 8.

Potential effects have been derived from a literature review of relevant studies and on expert professional opinion based upon typical current turbine technologies and installation techniques. The experience and lessons learnt from wind development to date have helped provide a greater understanding of potential effects. In the following section potential effects are identified and are classified as scheme level or strategic in the Potential Effects Tables provided in Appendix 4.1. Those of strategic importance have been taken forward for assessment by this SEA. This has ensured that all potential strategic level effects including those which may be relevant at both a strategic and scheme level have been captured in the assessment. Additional site specific studies such as EIA may identify additional effects relevant at a project rather than strategic level.

4.2 Description of Potential Effects Tables

Tables 1 to 8 in Appendix 4.1 show the potential effects, which have been grouped by work phase:

  • pre-construction - survey and site investigation;
  • construction - site preparation and installation of turbines, associated infrastructure, cabling and buoyage etc;
  • operation and maintenance - the period during which the turbines are actually generating electricity; and
  • decommissioning - the phase during which turbines and or infrastructure is removed and or 'disabled' and left in-situ.

It is acknowledged that due to the scale of offshore wind developments and the potential for upgrades in equipment and technology, multiple work phases may take place all at the same time within one wind farm site. These effects may be cumulative, perhaps combined with those of different wind farms or alternative developments, to interact and have greater significance than they would in isolation.

Effects have been classified in terms of a Source-Pathway-Receptor relationship, i.e. the Source or activity generating the effect, the Pathway or link between the source and the Receptor impacted by the effect.

Effects have also been classified in terms of their Duration - temporary or permanent, their Scale - local/regional, transboundary or global; and in terms of how they should be Managed - either at project or at a strategic level. Overall effects are classified as either positive or negative and each effect identified is accompanied by a short explanatory text commentary on the importance of the effect.

A process or activity-based approach has been used in identifying effects, and effects have been determined to a level of accuracy, commensurate with the level of plan available. This is not as detailed as might be found at EIA level - e.g. piling is identified as a Source activity, the Pathway for the effect being underwater noise and the Receptors identified as marine mammals and fish. The assessment does not go so far as to assess specific noise frequencies, or distances over which the effect may propagate as may be expected for an EIA.

In this way the Potential Impact Tables sign-post effects associated with wind development in STW likely to be strategically significant and defer consideration of specific project scale issues to the appropriate stage.

4.3 Summary of Potential Effects

4.3.1 Introduction

A summary of the potential effects identified in Tables 1 to 8 in Appendix 4.1 is provided below. They include a range of effects identified prior to classification as of strategic or scheme level significance.

4.3.2 Climatic factors (Table 1 in Appendix 4.1)

Wind farms are associated with being beneficial to climate change due to the production of carbon free energy during the operation phase. However, it is acknowledged that there is a carbon cost associated with wind farms manufacture, construction, maintenance and decommissioning activities. The overall carbon balance varies from project to project depending on distance from manufacturing point, installation and maintenance support ports, turbine and foundation design. Hence at a strategic level it is not possible to carry out a lifecycle carbon assessment. However, it has been assumed that there is a positive benefit over the lifetime of each wind farm and that, in comparison to other sources, wind has one of the lowest carbon footprints 9.

4.3.3 Water Resources (Table 2 in Appendix 4.1)

Effects on water quality during construction are likely to include reduced water quality due to factors such as increased suspended sediment load and associated turbidity due to sediment disturbance/mobilisation and the potential for pollution incidents. These impacts are likely to be temporary (i.e. during the construction phase only). There is also the potential for the physical presence of the structures (i.e. during operation) to affect local currents, wave climate and water column mixing which could have a range of effects on water quality, and secondary factors such as sedimentation and erosion in the near field and far field.

4.3.4 Geology, Sediments and Coastal Processes (Table 3 in Appendix 4.1)

Effects on geology, sediments and coastal processes occur during construction and decommissioning when there is direct disturbance to the seabed and sediments. The presence of new offshore wind development and associated potential effects on hydrodynamics and the existing wave climate may change patterns of deposition and erosion. This in turn could affect geology, sediments and coastal processes both within and beyond the wind farm site boundary during the longer term.

4.3.5 Biodiversity, Flora and Fauna (Table 4 in Appendix 4.1)

Effects on biodiversity, flora and fauna can occur at all stages of a wind energy project. However, the greatest number of significant effects are likely to be experienced during the construction stage of the scheme. Adverse effects may include the displacement or disturbance of birds, mammals, fish, benthic communities and flora through a combination of factors including noise, vibration, visual and light intensity changes, water quality changes, habitat disturbance and/or the presence of structures and vessels.

Effects may be direct or indirect, the former being for example actual losses of habitat or flora and fauna in the footprint of works; the latter includes factors such as reduced water quality, or increased environmental stress. Commonly direct effects are easier to mitigate and apply metrics to, indirect effects may be harder to assess and mitigate as the sources of effects or their significance may be harder to determine. Many potential effects are commonly mitigated through standard procedures. Notwithstanding this, they must still be identified to ensure they are fully recognised and subsequently addressed.

In terms of fisheries, there is the potential for disturbance of mobile species, disruption and or damage to habitats and spawning grounds, reduced access to fishing grounds and displacement of activity to existing fishing grounds with consequent increase in fishing intensity. Additional cabling and sea bed infrastructure may cause fouling or prevent access to some areas.

It is important to consider the nature of the period of the effect; some will be permanent, for example, loss of seabed habitat and associated ecological assemblages in the footprint of structures. Other effects may be temporary in nature, for example disturbance due to sea bed preparation or piling. The duration of temporary effects is relevant along with the potential for interactions with other sites and or activities which may have cumulative in-combination effects.

There is the potential for some benefits for biodiversity to arise from this type of development, including the creation of artificial habitat for marine organisms resulting from the presence of new structures and conservation through exclusion of fishing. The permanence of these potentially beneficial effects has to be considered in terms of infrastructure (and artificial habitat and ecological assemblages), which may be removed during decommissioning.

4.3.6 Landscape, Seascape and Visual Amenity (Table 5 in Appendix 4.1)

There are unlikely to be any significant effects on landscape, seascape character or visual amenity during the pre-construction stage. However, temporary effects on landscape character, seascape character or visual amenity are likely to be experienced during construction and decommissioning as a result of the presence of plant and vessels. Long term effects on seascape/coastal landscape character and visual amenity are likely to result from the presence of wind farms and associated navigation lighting during operation.

4.3.7 Population and Human Health (Table 6 in Appendix 4.1)

A combination of beneficial and adverse strategic effects on population and human health may be experienced. Adverse effects may include disturbance to, or loss of coastal and marine recreational areas and activities with associated effects on the enjoyment and potentially the safety of marine users. Issues such as shadow flicker and noise disturbance have not been assessed as they are considered to be relevant at a scheme rather than strategic level.

Visitors may be affected through disturbance and displacement of marine fauna including fish and marine mammals or local and migrating birds, prevention of navigation or access to some areas, reduced visual amenity due to the presence of the turbines. Wind farms may also reduce the areas through which yachts and other leisure craft can pass. The converse may also be true with wind farms effectively creating visitor opportunities, e.g. sight-seeing boat trips or improved angling near wind energy developments.

4.3.8 Cultural Heritage (Table 7 in Appendix 4.1)

The majority of the effects on submerged cultural heritage and the historic environment will occur during construction and decommissioning when direct disturbance to the seabed could occur, potentially resulting in the loss or damage of cultural heritage features including wrecks, submerged archaeological features/landscapes and artefacts. The presence of new offshore wind development also has the potential to affect hydrodynamics and the existing wave climate, which in turn could affect sediment dynamics and consequently archaeological assets.

It is possible that there may also be effects upon cultural heritage receptors above the surface, for example WHS or Listed Buildings. Effects may occur as a result of interrupting views from such locations, to locations or changing the setting of sites or buildings.

4.3.9 Material Assets (Table 8 in Appendix 4.1)

Potentially significant impacts on material assets may occur at all stages in the development of offshore wind developments. There is the potential to physically affect existing or planned activities and operations. Marine renewable industry, shipping and navigation issues are covered within this ER whilst other sector issues are considered within the Plan (such as commercial fishing). Navigation has been included as it may result in displacement issues and disturbance to shipping. 10 Key factors to consider will include:

  • impacts on navigation and safety through conflict with shipping routes, displacement of other vessels into shipping routes and increased collision risk;
  • interference with international shipping, designated international shipping routes and international treaties and agreements for example by affecting rights of innocent passage and rights to enter ports;
  • the cumulative effects of the scale of offshore wind development envisaged to meet the 2020 targets, both within STW and outside of the 12nm limit.

Resolution of these issues is only likely to be achievable through a combination of high level government decisions to set guiding principles and early and robust engagement of developers and the shipping industry at a regional or project level. Consequently, both this ER and the draft Plan outline the main existing characteristics of shipping around Scotland along with the key mechanisms for managing traffic in order to inform future engagement but does not try to resolve these issues.

The presence of wind farms and associated infrastructure and cables may also conflict with existing, planned or potential future use of the sea, sea bed or marine area for other resources and energy generation purposes.