Question

What are the key issues in identifying and dealing with cumulative impacts?

In answering this query it is firstly useful to understand the key issues with regard to cumulative effects.

The purpose of SPG is to steer development to areas with the lowest sensitivity to wind farm development over 20MW in size.  This is likely to concentrate development in relatively localised geographic areas leaving spaces between such broad areas of search (BAS) where limited or no development of wind energy is possible.

Cumulative impacts occur when multiple, i.e. 2 or more wind farms, are visible either in combination, in succession or sequentially.

Current guidance from SNH (Cumulative Effect of Windfarms, 2005) defines these terms as follows:

• In combination: 'where several windfarms are within the observer's arc of vision at the same time.'

• In succession: 'where the observer has to turn to see the various windfarms.'

• Sequential effects: 'when the observer has to move to another viewpoint to see different developments.'

These terms can be used to inform siting and layout guidelines for development within BAS and used to assess areas that should be afforded protection and to judge how much development might be appropriate in other areas.

In the context of SPG there are three potential scenarios that will give rise to the types of cumulative impacts mentioned above:

1. Cumulative impacts between two broad areas of search (BAS);
2. Cumulative impacts between BAS and areas outside them; and,
3. Cumulative impacts of wind farms within a single BAS.

The three scenarios are related and should not be treated in isolation.  For example, cumulative impacts between two BAS could be heightened by the presence of poorly sited and designed small schemes within the areas between BAS.

The overall effect of inappropriately sited multiple wind farm development could be to create the perception of a landscape dominated by wind farms with few or no locations from which a wind farm is not a prominent feature.

Practical Application and Decision Making

Broad areas of search should be planned with the existing pattern of development with the intention of encouraging clusters of wind farms where appropriate.  The principles of developing wind farm clusters are fairly well established however, and SNH's Siting and Designing Windfarms in the Landscape provides up to date thinking on this issue.

Most people agree that clustering and spacing windfarms is a sound idea and the principle was endorsed at the Clyde/Harestanes PLI.  The SNH windfarm footprint map illustrates that an element of clustering and spacing is already occurring, due to the various constraints on wind farm development, which could be usefully be reinforced through a spatial framework endorsed by the SPG.

There remains some debate about how big the 'spaces' should be which may be resolved in the forthcoming 'Designing Windfarms in the landscape' guidance.

There is a more subtle question of how LA's can apply the cluster and space concept to their spatial frameworks.  If you have two clusters of wind farms, or two very large wind farms, and you wish to maintain a space between them, then by definition you need to identify the area lying between them as an area 'afforded significant protection' in your spatial framework.

This obviously involves a level of local decision making and analysis and will eventually rely on a somewhat subjective decision to identify a suitable space between two clusters.

The paragraph on cumulative impacts in SPP gives a steer:

"When considering cumulative impact, planning authorities should take account of existing wind farms, those which have permission and valid applications for wind farms which have not been determined. Decisions should not be unreasonably delayed because other schemes in the area are at a less advanced stage in the application process. The weight that planning authorities attach to undetermined applications should reflect their position in the application process. Cumulative impact will largely relate to the scale and proximity of further development. The
factors that will be taken into account when considering cumulative impact should be set out in the development plan or supplementary guidance."

This gives justification to Local Authorities identifying an 'area of significant protection' between clusters of wind farms in order to protect a coherent pattern of wind farm development and thereby reduce the potential for adverse cumulative impacts.

As spatial frameworks are intended to be the basis for determining applications then they also have to take account of wind farms with permission and valid applications.

These matters are considered in further detail in SNH's Siting and Designing Windfarms in the Landscape which may assist in developing criteria for the SPG.

SPG Good Practice Guidance

The approach recommended in the Guidance will help in identifying appropriate sizes and scales of turbine, layouts and designs that could be accommodated within the different landscapes in the Planning Authority Area.  Through the identification of key viewpoints and routes it should be possible to identify locations that are particularly sensitive to the encroachment of wind energy development and against which criteria could be applied to manage potential impacts within tolerable levels. 

Whilst the SNH guidance deals primarily with layout and design of wind farms it sets out some key principles that could be informed by detailed studies using an approach similar to that outlined in the Good Practice Guidance.

SNH Workshop, Designing Windfarms in the Landscape 2^nd March 2009

An understading of these two factors, and the different potential impacts should influence the location of BAS and judgements regarding the size of areas of significant protection and the amount of development that could be achieved outside BAS.

It was suggested at the workshop that criteria for identifying thresholds against which to assess individual and multiple wind farm applications should be used.  The criteria could relate to key viewpoints, footpaths, beauty spots or picnic areas frequented by people.

Design frameworks for BAS were discussed and considered to be useful guide for developers particularly where a number of different developers put forward proposals within the same BAS.  Design frameworks could provide a consistency in the design and layout of multiple wind farms within a single BAS, potentially reducing cumulative impacts and increasing the likelihood of consent.  Design frameworks are often used successfully for large housing sites, where there are a number of different developers, in order to achieve consistency in design and layout. 

It was considered that developers need to work together to a certain extent to achieve good design and layout of multiple schemes.

The edges of BAS were considered to be important as these are likely to be the most visible parts of the area.