Note 5

A Visual Impact Assessment (VIA) is a specific study that focuses on assessing the visual and aesthetic impacts of a proposed project. This type of assessment is not a stand-alone study but should be part of the study that assesses impacts on the OUV of a World Heritage property (Environmental and Social Impact Assessment, or Heritage Impact Assessment study) – in the most likely case when it is relevant for its values. VIAs are largely used for assessing the impacts of proposed infrastructure projects in relation to cultural World Heritage properties inscribed for their architectural and landscape values. It is to be noted that visual qualities are primarily related to the integrity of a World Heritage property. World Heritage properties that are inscribed on the World Heritage List under the category of cultural landscapes might be especially vulnerable to wind energy developments.

➔ See World Heritage essentials

What should be considered in relation to the World Heritage property/properties?

The visual and aesthetic impacts of wind energy facilities on the landscape are one of the main challenges faced by the wind energy development. The perception of these facilities in a landscape depends on several factors: typology of the site, morphology of the landscape, social factors, the extension of infrastructural development in the area and the level of acceptance by local communities.

Wind energy projects not only need to consider the possible compatibility or incompatibility of wind turbines and ancillary facilities with the attributes that convey the OUV of a World Heritage property, but also need the willingness and support of the people and local communities to live with and adapt to the proposed changes of their environment. Visual aspects, in this respect, play an important role in the acceptance of these projects.

The assessment of the visual impacts of a wind energy project relates directly to the visual qualities of the OUV of properties within their aspect of integrity. From the point of view of World Heritage protection and management, the project should not compromise or marginalize the visual characteristics and attributes of a World Heritage property.

For a VIA in the World Heritage context, consideration should be given to:

1. the overall sensitivity of a World Heritage property and its setting to changes in general;
2. the sensitivity of the property to wind energy facilities that includes measuring qualitative and quantitative visual changes, considering particularly the installation of tall facilities like wind turbines or industrial set ups like sub-stations and power grids (for potential dimensions of the parts of a wind farm and ancillary facilities ➔ see Wind energy essentials);
3. the extent to which a property and its setting can adapt and support change while ensuring the protection of its OUV.

Information related to visual sensitivity of a World Heritage property and its attributes can be collected through the process of vulnerability studies/sensitivity mapping (➔ see Note 2). This process looks at the connection between the property’s OUV and its key panoramas and vistas, as well as intangible connections and ways in which people and communities perceive the property and its surrounding.

Further information on how the visual sensitivity of a World Heritage property could be identified

A visual impact assessment needs to include a detailed map showing the location of all attributes conveying OUV, all relevant vistas and panoramas, the physical location of the proposed development and any ancillary or annexed facility as well as other existing developments that might need to be considered to assess possible impacts and cumulative impacts. Nevertheless, depending on the characteristics of the property and its OUV, some attributes may be difficult to trace and map, and should therefore be considered beyond their physical location on a map.

➔ See Note 6

The information related to the World Heritage property and the planned wind energy development need to be combined for assessing the potential impacts:

Visualization of impacts

The digital visualization of wind energy projects to support assessing their impact is at the core of VIAs. The production of a digital visualization requires adequate data, technical material and software. Good simulations or models are:

• spatially accurate and realistic, simulating the expected appearance of the proposed project and the actual appearance of the property and its setting;
• representing different views, including different viewpoints, day time/night time differences, weather conditions, lighting conditions, seasons and others;
• visually clear and accurate including all necessary details of the proposed project and the property;
• defendable and able to withstand scientific scrutiny.

Importance of visual simulations in engagement with rights-holders and other stakeholders

Accurate and realistic simulations are key during the consultation process in general but are especially important during the engagement with rights-holders and other stakeholders as they allow for people and communities to better understand and contextualize the project in relation to their environment and the World Heritage property.

Tools for visualizing and assessing the impact of proposed and planned wind energy infrastructures in relation to a World Heritage property and its setting could include:

• digital terrain models (DGM) and digital surface models (DOM) which allow showing precise distances and heights between the property, the viewpoints and the potential placement of the wind turbines, including the topography in-between;
• Photo simulation and photomontage: photographic-based assessments, like photomontage and modelling, should provide clear technical information concerning the position of the camera and the focal length used for the images used in the montage. This information is vital to prove the reliability of the recommendations derived from the visual impact study;
• Viewpoint photography;
• 3D modelling and digital simulations;
• Colour and light-based methods;
• Zone of visual influence maps;
• Line of sight technique which is a digital and GIS-based assessment that applies an accurate representation of the shape of wind energy facilities to better understand the visual perception of these facilities by the human eye. It considers the distortion of the perceived shape and size of facilities caused by the location of the observer and calculates the possible obscuring of facilities caused by terrain morphology. This also allows including information of other existing facilities to represent the landscape more accurately;
• Landscape sensitivity assessments;
• Landscape quality assessments;
• Viewshed analysis in a GIS (or visual envelop) map: a digital evaluation model based on GIS data which is used to determine which parts of a landscape are visible or not visible from a particular vantage point.

Assessing visual impacts

Potential visual impacts should be evaluated by considering the visual sensitivity of the property combined with the potential magnitude and significance of the impact on the property’s OUV.

The assessment should be based on two key sets of information concerning:

1. Characteristics of the World Heritage property related to identified key visual aspects, scenic views and panoramas, including information on:

• the topography of the property and the connections within the property, and between the property and its setting;
• attributes conveying the OUV of the property and values that are not part of the OUV but have a role to support it;
• key observation points (KOPs) including sensitive areas, panoramas and viewsheds that can support the protection of the OUV.

2. visual characteristics of the proposed wind energy installation, including information on the wind turbines and, if applicable, the ancillary facilities:

• scale of the wind energy project;
• location of the wind energy facilities;
• form of the wind turbines and other facilities;
• height (hub and with blades) of the wind turbines and other facilities;
• rotor diameter of the wind turbines;
• colour, including possible colour contrast of the wind turbines with the surrounding land- or seascape;
• texture/material of the wind turbines and other facilities;
• glare of the wind turbines;
• lighting of the wind turbines;
• motion of wind turbines;
• number and distribution of the wind turbines within an area;
• visual lines and axes of the facilities (paths followed by the eye when perceiving obstructions and abruptions in a landscape).

There are multiple methodologies for the identification of possible visual impacts and many more for the evaluation of these impacts. There is no standard nor a universally or unilaterally agreed methodology to assess the visual impacts of wind energy facilities on a World Heritage property. Therefore, the decision in favour of a specific VIA methodology should be justified by technical considerations about the OUV of the World Heritage property and the proposed wind energy project. Nevertheless, as already mentioned, visual impacts of wind energy projects should never be assessed in isolation but be considered within the scope of a fully fledged World Heritage focused impact assessment and together with other impacts, including environmental, cultural heritage, social and economic impacts.

The methodology applied in the assessment should be described clearly and with specific reference to the evaluation criteria considered during the process. There are various possible typologies of assessments with consolidated scientific and technical requirements, and should all consider with quantitative and qualitative methodologies:

• the extent of the visibility of a wind energy facility (like maximum vertical angle of visibility, horizontal angle of visibility);
• the distance of the project and its element that are visible (and wind turbines, other features of the project) from identified key observation points and viewpoints;
• the number of visible wind turbines and other features of the project (at a given vertical angle and above);
• the significance of the viewshed;
• the character of the landscape or seascape, and the surroundings of the installation (natural or man-influenced surroundings with their visual sensitivity relevant for the OUV of the property).

The degree of impacts will need to consider the level of visual intrusion and obstruction in relation to identified sensitive areas or key panoramas and vistas.

Assessing the level of impacts

Examples of potential visual impacts of wind turbines on the OUV of World Heritage properties are listed as below

Case Study

• See case studies in World Heritage and Wind Energy Planning (2021)
• In 2013, the Landscape Institute for Environmental Management and Assessment (IEMA) published a Guidelines for Landscape and Visual Impact Assessment (GLVIA3).This is a key resource for those involved in assessing visual impacts or reviewing an impact assessment report including specific references to the assessment of visual and landscape impacts. Although the guidance is not a World Heritage specific document and does not focus on the OUV of World Heritage properties, it nevertheless could serve as key guidance for the assessment of a property’s visual sensibility and for the identification and evaluation of possible visual impacts.

• A useful document prepared by the NGO Kompetenzzentrum Naturschutz und Energiewende facilitate wind energy project planning in Germany (available in German).
• A study on visual integrity has been prepared for the Dutch Water Defence Lines World Heritage property (the Netherlands) on assessing visual impacts.