Assessing the visual impact of wind farms: a comprehensive local solution



As with any power infrastructure, wind farms have a visual impact which needs to be considered when assessing the environmental impact of the plant. There is a common opinion that wind turbines are erected without any consideration of the visual impact, but this is not the case as a detailed assessment of this factor is carried out. A locally produced guideline for VIA has been produced and is being employed.

The visual impact of infrastructure has long been a source of contention in this country.  Blocks of flats on top of a ridge in Pretoria East, residential structures on top of koppies, and other blights on the landscape, have all proceeded despite objections from affected people in the area, either via political influence or abuse of weaknesses in existing regulations. Quite often the accusation has been made that planning and construction proceeded without any attention being paid to the visual impact of the project.

Table 1: Categories of development [2].
Categories of development
Category 1 Nature reserves, nature related recreation, camping, picnicking, trails and minimal visitor facilities.
Category 2 Low key recreation/resorts/residential development/ small scale agriculture/nurseries, narrow roads and small scale infrastructure.
Category 3 Low density resort/residential/golf or other sport estates/low to medium scale infrastructure.
Category 4 Medium density residential. Sports facilities and stadia, small scale commercial facilities, office parks, one stop petrol stations, light industry, medium scale infrastructure.
Category 5 High density township/residential development, retail and office complexes, industrial facilities, refineries, treatment plants, power stations, wind energy farms, power lines, freeways, toll roads, large scale infrastructure, large scale agriculture and plantations, quarrying and mining.

The visual impact of infrastructure forms a part of any EIA and is subject to legislation.

Wind turbines are increasing in blade and mast size, with the obvious increased visual impact, and this means stricter application of assessments. The height of the wind turbine compared to the height of other features in the area has an influence on the visual impact.

Objections to large structures such as mobile phone towers, electricity pylons and other large structures are common, and justified. Large wind farms can
have significant visual impacts for affected receptors, particularly those related to the tourism industry. Scenic resources also form part of the ‘National estate’ and are therefore protected by heritage legislation. Wind energy producers need to understand these issues when planning a wind farm to be successful in their applications.

Many wind farm applications worldwide have been rejected because of visual aspects. This seems to be common in England and Scotland, which are understandably lands of great scenic beauty. Objections to wind farms are based on a number of common issues, included alleged health problems, threat to wild life, and in some cases claims
that they are stealing the wind, but the visual aspects seems to be the most common, the most reasonable and also the most assessable.

In spite of there being unrealistic objections, there is no doubt that some planners have attempted to steamroller any objection to wind, and to play down the impact of wind farms on a community or a place. Common arguments are based on the greater common good and financial benefits. One argument offered is that they are symbolic of the change to clean energy and should therefore be accepted irrespective of their impact. No doubt an obsession with renewable energy, and the profit motive has clouded the vision and dulled the sensibilities of numerous people, who fail to see any problems with wind turbines.

Assessment methods, standards and practices

Although there are a number of accepted impact assessment methods and standards in use, there appears to be a wide variation in interpretation and application. In an attempt to develop a “best practice” approach for visual specialists, EIA practitioners and authorities involved in the EIA process, a visual Guideline document has been established by the Department of Environmental Affairs and Development Planning (DEA and DP) of the provincial government of the Western Cape (PGWC), [3] which cover the VIA portion of an EIA on any project, not specifically related to wind farms. These guidelines are applied in a specific manner when assessing wind farms.

Table 2: Category of impact [2].
Categories of impact expected
Very high visual impact Potential significant effect on wilderness quality or scenic resources. Fundamental change in the visual character of the area. Establishes a major precedent for development in the area.
High visual impact Potential protrusion on protected landscapes or scenic resources. Noticeable change in visual character of the area. Establishes a new precedent for development in the area
Moderate  visual impact Potentially has some effect on protected landscapes or scenic resources. Some change in the visual character of the area. Introduces new development or adds to existing development in the area.
Minimum visual impact Potentially low level of intrusion on landscapes or scenic resouces. Limited change in the visual character of the area.Low key development, similar to existing development in the area.

Even with a VIA there are many interrelated problems [1]:

  • The sites selected for wind farms, based on wind potential, are often in conflict with scenic and heritage resources, as well as protected wilderness areas. There is an inherent conflict between renewable energy resources and landscape. Wind turbines not placed in urban areas but in the country, which naturally increases the chance of encroaching on country or scenic areas which are valued. High wind sites are often located on ridges or high places, which are seen as local scenic places.
  • Unlike heritage resources, for which there is a national data base and rating system, as well as legislation, there is no similar data base for our scenic resources, or even what constitutes a scenic resource. Scenic value and “sense of place” can be very subjective.
  • Although guidelines are available for visual specialists, there are still wide discrepancies in approaches to visual assessments and rating of scenic resources.

A wide range in the standard of visual impact assessments (VIA) that are carried out.The guideline lists some of the current problems associated with visual and aesthetic assessments undertaken as part of the EIA process include the following [4]:

  • A lack of understanding of the landscape processes that are responsible for specific visual qualities or scenic resources of the area.
  • A lack of clarity in the methodology and determination of impact ratings, as well as inconsistency between different assessments.
  • A lack of objectivity, or conflict of interests, especially where the assessment is carried out by the same firm that is representing the proponent.
  • The risk that the ratings of impacts are tempered by the fact that the proponent is paying for the VIA.

Guidelines

The guidelines have simplified the process by means of a matrix formed by the visual rating of the area and the category of development involved. Table 1 shows the categories of development covered in the guideline.

Table 3: Impact matrix [2].
Type of environment Type of development (see box 2) Low to high intensity
Category 1 development Category 2 development Category 3 development Category 4 development Category 5 development
Protected/wild areas of international, national, or regional significance Moderate visual impact expected High visual impact expected High visual impact expected Very visual impact expected Very visual impact expected
Areas or routes of high scenic, cultural, historical significance Minimal visual impact expected Moderate visual impact expected High visual impact expected High visual impact expected Very high visual impact expected
Areas or routes of medium scenic, cultural, historical significance Little or no visual expected Minimal visual impact expected Moderate visual impact expected High visual impact expected High visual impact expected
Areas or routes of low scenic, cultural, historical significance disturbed Little or no visual impact expected. Possible benefits Little or no visual impact expected Minimal visual impact expected Moderate visual impact expected High visual impact expected
Disturbed or degraded site / run-down urban area / wasteland Little or no visual impact expected. Possible benefits Little or no visual impact expected. Possible benefits Little or no visual impact expected Minimal visual impact expected Moderate visual impact expected

From Table 1 it can be seen that wind farms fall into category 5.

Table 2 lists the degree of impact expected

The impact matrix is shown in Table 3

From Table 3 can be seen that wind turbines should normally range from moderate to very high visual impact, and would justify a visual impact assessment in all cases.

How is a VIA carried out and how is the impact evaluated?

A VIA will consist if the following typical components:

  • Identification of landscape types, landscape character and sense of place, generally based on geology, landforms, vegetation cover and land use patterns.
  • Identification of viewsheds, and view catchment areas, generally based on topography.
  • Identification of important view points and view corridors within the affected environment, including sensitive receptors.
  • Indication of distance radii from the proposed project to the various view points and receptors.
  • Determination of the visual absorption capacity (VAC) of the landscape, usually based on vegetation cover or urban fabric in the area.
  • Determination of the relative visibility, or visual intrusion, of the proposed project.
  • Determination of the relative compatibility or conflict of the project with the surroundings.
  • A comparison of the existing situation with the probable effect of the proposed project, through visual simulation, generally using photo-montages.

Viewsheds

A viewshed can be defined as an area or place from which all or part of the proposed construction can be seen, and which is occupied or visited regularly by people or receptors.

Important part of the process is the identification of viewsheds, as the whole visual impact rests on these areas. The visual impact assessment is based on views from the viewsheds and not a general site within the radius of impact. So a wind farm may be considered a high impact when viewed from a site which does not fall within the viewshed, but this will not affect the VIA unless the site has potential for future development.

Receptors can include private game and wildlife parks (not declared as national parks), tourism and accommodation operators, tourist traffic on roads in the area hiking camping and outdoor sports facilities in the area, and the permanent residents of the area.

A number of tools and techniques are available for determining visibility and for describing relevant landscape and project characteristics. Establishing the viewshed is made easy today by means of GIS, and specific viewshed programs are available keyed to wind turbine tower projects. The use of 3D imaging is also becoming popular. Field analysis is essential to verify actual visibility. It also is possible to do a “partial viewshed analysis,” which examines the visibility of specific turbines, or to look at a particularly sensitive viewing point on the ground to examine an area of potential visibility [4].

Field observation of wind facilities in a study conducted in the USA revealed that the facilities were visible at distances of 58 km in both daytime and night-time views, and were found a major focus of visual attention at distances of up to 19km. Turbine blade movement was often visible at 39 km [5].

Fig. 1: Viewshed of proposed SA windfarm [3].

A typical viewshed plot established using GIS is shown in Fig.1.

Evaluation using photo montage

Photomontage involves placing the proposed wind turbines in a photograph taken from a viewshed an assessing the impact. The montage will consider visibility, haze, etc., and attempt to replicate the wind farm as it would appear under the conditions prevailing when the photo was taken. To give complete coverage, the photo needs to be taken at the worst case, i.e. maximum visibility, minimum haze and atmospheric disturbance, maximum scenic effect, etc.

An example is given in Fig.2

Daily and seasonal changes

The only problem with using photo-montage is that a static image at a particular point in time is used. To get a full assessment, changes in the view on with daily and seasonal variations need to be taken into account. For instance, if the viewshed contains a winter sports resort, the view in winter when there is reduced foliage greenery is of prime importance.

Rotation, flicker and blade glint

The VIA process defined in the guideline appears to be based on the static visual effect, and no specific mention is made of the visual effect of blade rotation, which could significantly add to the impact of the wind farm. The processes listed as static do not take dynamic effects into account. These involve:

  • Rotation of the blades at different speeds
  • Rotation of the turbine about the horizontal axis with change in wind direction, which could give a different aspect.

Flicker is a time-based phenomenon which causes visual effects to be repeated at regular basis. One of the possible disturbing factors mentioned in the guide is the regular movement of traffic in a gap exposing the road. The same could apply to wind turbines, either by a repeated flashed reflection off the blades (blade glint) or in the case of partial vision, the regular appearance and disappearance of the blades, which more disturbing than a permanent view of rotating blades.

Fig.2: Photo montage showing proposed wind farm [5].

Shadow flicker occurs when the sun is shining directly behind a wind turbine and the turning blades cast moving or flickering shadows on nearby residences or public use areas. This occurs only during low sun angles, but it can present an annoyance to nearby residents and people temporarily occupying a site. Shadow flicker can be a health risk if the shadow flicker reaches certain frequencies. Modern turbines turn too slowly to trigger optical epileptic seizures, but combined shadows from overlapping turbine blades could increase the
overall frequency.

Case studies

The proposed Inyanda Roodeplaat wind energy facility near port Elizabeth “The very high significance rating for the potential visual and landscape impacts identified in this report indicates that the proposed site for the Inyanda Roodeplaat WEF is not ideal in terms of landscape and visual considerations” [3]. The proposed site was near both nature reserves and game farms.

The proposed Umsinde Emoyeni wind energy facility, was subjected to a VIA and received the following rating. “Given the scale of the proposed WEF, as well as the height of the wind turbines, a significant transformation of the study area can be expected, and this resulted in high potential visual impact significance for both phases before mitigation.” [4]. The WEF site was located in an area renowned for its wide open spaces, serenity, quiet and starry skies at night, the rural landscape being relatively intact and free of visual intrusions, such as powerlines.

Conclusion

The guideline provides a useful starting point for a fair VIA, but there is still considerable discussion and argument on the interpretation. One extreme view says that everyone has to make sacrifices for the sake of the environment, and the other says that it is essential to retain sites with a sense of place.  There remain a number areas which are heavily dependent on subjective opinions, and there is an inherent variability in ratings between observers because of their differing perceptions of the wind facilities and other landscape elements. Opinions of the receptors and the assessor will differ.  One person may see wind turbines as graceful, and another will be repulsed by them. For people who live, work, and recreate in a region, the landscape consists of layers of meaning that may not be understood by a developer or a professional conducting a visual assessment. It is important to ensure the independence of the person or organisation doing the assessment.

References

[1]  B Oberholzer :“Visual, Aesthetics and Scenic Resources in relation to Wind Energy Farms”, Windac 2107, November 2017.
[2] B Oberholtzer :“Guideline for involving visual and aesthetic specialists in EIA processes”, CSIR Report No ENV-S-C 2005 053 F, Provincial Government of the Western Cape, Department of Environmental Affairs & Development Planning, Cape Town.
[3]  H Holland: “Visual impact assessment:  Inyanda-Roodeplaat Wind Energy Facility”, SRK Consulting.
[4]  B Oberholzer: “Visual Impact Assessment for Emoyeni Wind Farm Project (Pty) Ltd”, Arcus consultancy services.
[5]  R Sullivan: “Wind turbine visibility and visual impact threshold distances” Argonne National Laboratory

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