Contract Details

Cumulative Impact of Wind Turbine Generation: Methodology

The methodology which will be employed in this contract will address the three objectives of the research (ref. tender Specification Document):

1. The primary considerations/issues when assessing cumulative impact;
2. How those issues can be practically applied when considering planning applications for wind turbine developments;
3. How the information can be incorporated in unitary authority development plans.

The methodology will include the suggestions of:

1. Review existing methods of landscape evaluation and designation as the background against which new proposals are to be viewed (CCW1);
2. Review existing methods of visual impact assessment, and their application to cumulative impact (CCW2);
3. Produce worked examples of visual impact assessment in the case of wind turbine installations (CCW3);
4. Make recommendations for the most appropriate method of assessing cumulative visual and landscape impact, in the context of the planning system (CCW4).

Philosophy of Methodology:

The philosophy behind this programme of work is to provide the contract outputs in consultation with the Countryside Commission for Wales (CCW) following an established procedure of "Project Planning." This provides a formal approach to identifying the key requirements of CCW when responding to planning applications for wind energy developments and provides a basis for assessing the appropriate scale of input data and presentation of output. In addition, estimates of reliability are provided, where possible, in the worked examples of Task 4.

Tasks 2 and 3 provide the context for the worked examples including the reviews of landscape evaluation, designation and visual impact assessment and a description and discussion of the impacts of error from different sources on the viewshed and subsequently on the assessment of visual impact.

Task 4 provides different examples of the type of analysis that may be expected in a visual impact assessment, the nature of the outputs and how they may be presented using a World Wide Web browser.

Task 5 will provide recommendations in such a manner that they may be summarised according to the format of Appendix 3 ("A checklist for wind turbine power station development proposals") of the CCW Policy Document (CCW, 1992).

Countryside Council for Wales (1992), Wind turbine power stations: policy document. Countryside Council for Wales, Bangor, pp 39.

Programme of Work:

1. Task 1. Project Planning.
   • Definition of a planning methodology, which explicitly addresses the questions of information production, accuracy and linkage between tasks. Clarification of the information produced and needed by each participant and definition of protocols for selection of scales and content of digital data.
   • This is undertaken using a "product description" which is a detailed proforma relating to the types of output required (maps, photographs, lists, tables) and indications of the desired levels of reliability and presentation of reliability (for example, numerical or diagrammatic). The output is a specification of the visual impact assessment to be carried out. The execution of this Task will be in conjunction with CCW.
2. Task 2. Review of existing methods of landscape evaluation (CCW1).
   • This review will encompass all methods of landscape evaluation and it will critically appraise the methods and their implementations with respect to the output of Task 1. The review will be based upon existing research into the principles of such evaluations and the type of models that may be employed.
   • Designations of landscape (such as National Parks, National Nature Reserves, Sites of Special Scientific Interest, Environmentally Sensitive Areas and Areas of Outstanding Natural Beauty) will be discussed with respect to their status in planning applications in relation to wind farms.
   • This task will also look at the classifications of landscape as used by statutory bodies, such as the Landscape Character Classification developed by Scottish Natural Heritage and their role in planning applications related to the development of a wind farm.
   • The contents of this Task will be undertaken with due regard to Chapter 7, para 2 of the CCW Policy Document "Wind turbine power stations" (1992). Discussion of the role of designations in Task 2 will take account of the importance of the spatial context of designated areas with respect to the visual impact of changes taking place beyond the de jura boundary.
3. Task 3. Review existing methods of visual impact assessment (VIAs) (CCW2).
   • This Task will draw upon previous review work undertaken by MLURI and RGU on visual impact assessments and it will be supplemented by work undertaken by the University of Leicester on the uncertainty in Digital Elevation Models (DEMs) and the potential impact of such uncertainty on the VIA.
   • Issues of the location of a development will be discussed, with respect to the potential impacts on the visual quality and amenity of an area. Specific examples relate to the question of the line of sight, how far it may extend, whether wind turbines will be visible and if so from what type of location and how visible will they be (e.g. will they "break the skyline" as described in CCW, 1992)
   • This Task will make reference to the recommended approaches outlined by the Landscape Institute and where Geographic Information Systems may play a larger role in the analysis of a proposal as part of a VIA.
4. Task 4. Produce worked examples of visual impact assessments (CCW3).
   • Worked examples will be produced to illustrate the nature of the measures of visual impact that may be included in an overall assessment of the development.
   • The examples will relate to a hilltop location. This may be altered in discussion with CCW if an alternative type of geographic location is preferred (eg. an offshore development). In general, the issues of the extent of visibility and scale will be the primary focus, with discussion as to how they relate to the effects on the landscape of the construction of the site (eg. a new access road).

• The variables which will be considered include:
  1. Differing levels of visibility of the base of a turbine, spindle height and top of the locus of rotation of the rotar.
  2. Initially using map scales to be negotiated with CCW following Task 1 bit likely to include 1:10 000 and 1:50 000. Access to extracts of DEM data for Wales will be in negotiation with CCW.
• The outputs which will be demonstrated include:
  1. Zones of visual influence of a single turbine and of a group of turbines, ranking the land according to the number of turbines visible at different distances from the development, using two scales of DEM. OUTPUT: maps and tables.
  2. Tabulation of proportion of transport routes which are visible with respect to zones of visual influence (within a negotiated areal extent) calculated for different heights up the turbine. OUTPUT: tables.
  3. Tabulation of the visibility levels of selected view points (such as houses or car parks) with respect to zones of visual influence and an assessment of the development with respect to the observers horizon and thus the skyline. OUTPUT: tables.
  4. A census of visibility of the terrain, deriving an absolute measure of visibility of the location of a theoretical proposal for a development with respect to other proposals. The census of visibility is an assessment for each DEM cell of the total number of other DEM cells that are visible. This produces a national estimate of the visibility levels of different proposed or existing developments, allows for comparisons between locations in an objective manner and provides for an interpretation of the degree of opennes or enclosure of the land.. OUTPUT: map and tables.
  5. Photo-montages of a view of a wind turbine at different distances from the turbine, groups of turbines and turbines of different structural characteristics and turbines with different backdrops (eg. skyline or hillside). OUTPUT: photograph.
  6. Creation of a 3D model of the landscape (in a Silicon Graphics computing environment) within which a model of a single turbine is placed. The model of the landscape will use data from an OS DEM and photographic information for the provision of textural features. OUTPUT: photographs and animated sequence of views in "html" readable form.
  7. Illustrations of the impact of error in the DEM on line of sight and the results of the derivation of the zones of visual influence. OUTPUT: maps and tables.
  8. The worked examples will be presented in a format compatible for use with a WWW browser. OUTPUT: html file.

5. Task 5. Recommendations for the most appropriate methods of assessing cumulative visual and landscape impact (CCW4).

• This task will set out a recommended approach to assessing the visual impact of wind farms. Issues that will be discussed will include:
  1. A procedure for identifying what is required on a case-by-case basis;
  2. The implications of selecting different scales of input data (such as DEM);
  3. The impact of error in DEM, observer location and target point, with respect to calculations of visibility;
  4. The selection of algorithms on products derived from DEMs.
  5. The role of different approaches to assessing visual impact, with reference to the worked examples.
  6. The role of landscape evaluation procedures with respect to visual impact.
  7. The potential role of Geographic Information Systems and visualisations in public enquiries.

In conclusion, this Task will set out a flow chart to guide selection of method or methods for use in a visual impact assessment of a wind farm development.