EIA and the design of onshore wind farms

Andrew Mitchell of RPS Group outlines how constraints analysis and design evolution in environmental impact assessment (EIA) can ensure onshore wind developments are designed sensitively

Without sensitive design, onshore wind farms can have the potential to result in significant environmental effects. One function of EIA is to inform the design and layout such that, where possible, adverse environmental effects are avoided or reduced. It is, therefore, a key role of the EIA practitioner to provide advice that seeks to avoid significant adverse effects at an early stage.

At the outset of a project, it is usual for a developer to identify preferred parameters in terms of numbers of turbines or maximum rated output – as such factors can be important to the financial viability of a wind farm site. However, specific client requirements for the positioning and spacing of turbines are uncommon.

The EIA process can usefully focus on identifying environmental constraints to inform the design evolution process. Through EIA it is possible to ensure the turbine layout is sensitive to the specific site, avoiding significant environmental effects as far as practicable, and incorporating opportunities for enhancement.

A range of factors influence the number of turbines suitable for a particular site and where they should be located, including technical requirements for spacing to ensure efficiency. Such factors may include:

  • The presence of designated sites

    Where possible, turbines should avoid locations within designated sites. In some cases, it may be advisable to avoid locations adjacent or close to designated sites, for example where turbines would have a significant effect on views from nearby protected landscapes.

  • Residential properties

    There is no absolute buffer for residential properties but the findings of the noise assessment, visual amenity and shadow flicker should be considerations in turbine siting.

  • Views

    A zone of theoretical visibility model and wirelines should be used to consider turbine arrangement and height to minimise visibility from sensitive receptors. Use of such tools at the siting stage can allow realignment of turbines to reduce undesired effects such as turbine clustering and blade overlap.

  • Habitats and species

    The results of ecological surveys should inform turbine siting such that priority habitats, migration routes and features supporting bats are avoided. A buffer should be provided to woodland or bat roosts.

  • Peat

    Where present, peat can be a significant consideration. A robust approach to surveying and turbine siting will be required to meet the requirements of statutory consultees. Areas of significant peat resource should be avoided where possible.

  • Water resources

    Watercourses should be avoided, with a buffer implemented, where feasible to avoid pollution. Groundwater resources should also be considered.

  • Public rights of way

    Rights of way can be an important factor at sites intersected by such routes. Minimum and preferred buffers are published for bridleways.

  • Telecommunications and radar

    The location of airports and radar systems should be considered at an early stage, together with microwave fixed links and scanning telemetry.

  • Known utilities and roads

    An appropriate offset buffer from the alignment of utilities and roads may be applied to protect existing infrastructure from physical interference and take into account the theoretical topple-distance of wind turbines.

A design workshop is a good way to consider the input from all relevant topics and to reach consensus on the most appropriate layout. The input of statutory and other consultees may be necessary and valuable, depending on the site and its particular characteristics. Civil engineering design work to confirm both viability and environmental effects is worth considering at an early stage.

Once a layout is selected, work on assessing the identified project can commence. However, it is important to recognise that the design and mitigation process should be ongoing and iterative. Where technical specialists provide feedback regarding a likely effect and measures that could address this, consideration should be given to adoption of such measures as part of the project.

The use of an iterative, site-specific and constraints-led design approach will ensure that effects are avoided where reasonably possible to do so.

The measures adopted as part of the project and the iterative design process should be clearly set out in the nvironmental statement to ensure that the process is clearly demonstrated to decision makers.

Such sensitive design and assessment of a project incorporating measures to avoid and minimise effects will not only provide the most environmentally appropriate design for the site but will also provide the most robust environmental statement, with the best chance of successful passage through the planning system.

Only through completing this process from an early stage and clearly reporting it in the environmental statement can a project truly claim to be sensitively designed and appropriately assessed.

This article was written as a contribution to the EIA Quality Mark’s commitment to improving EIA practice.

Andrew Mitchell is an associate director at RPS Group

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