Modelling for bird collision risk in offshore wind

17th December 2019

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Sinead Petersen of Xodus Group discusses the challenges associated with bird collision risk modelling for cumulative impact assessment

Worldwide, wind power generation has been one the fastest-growing industries within the renewable energy sector. Due to its rapid growth in the UK, there is growing concern over offshore wind's cumulative impact on the marine environment. One of the main concerns is the cumulative impact associated with seabird collision risks with wind. The UK is of particular interest as the surrounding coastal waters feature a number of Special Protected Areas (SPAs) – areas protected under the EU Birds Directive (Directive 2009/147/EC).

Some species of seabird are thought to collide and/or be displaced by offshore wind farm developments. However, for the majority of the time, species such as Arctic skua (Stercorarius parasiticus), Manx shearwater (Puffinus puffinus), little auk (Alle alle) and Atlantic puffin (Fratercula arctica) fly near the sea surface, not at turbine. Some species-specific models, considering flight height as a factor, are now being produced to better reflect the proportion of populations potentially at higher risk. In addition, migratory pathways towards seabird breeding grounds, overwintering sites and areas close to SPAs are considered to be higher risk in terms of collisions.

The majority of collision models involve calculating the probability of a collision occurring between a wind turbine and a seabird, assuming no evasive action or behaviour has taken place, and measuring the number of birds within a 'risk window'. Using this information, the number of collisions expected to take place is estimated.

Within EU and UK legislation there is a requirement to carry out a cumulative impact assessment (CIA) as part of an environmental impact assessment (EIA). However, a common consensus is that there is a lack of detailed guidance, particularly on the assessments (ie collision risk modelling), within the EIA process that restricts the ability to show a detailed and 'true' picture of the potential impacts of wind turbines on seabird populations. There is a concern that CIA is constrained by a lack of understanding of the effect wind farms are having on seabirds. Despite the monitoring measures in place, uncertainty remains around the potential impact that the large development of offshore turbines entering the marine environment may have on seabirds.

In the UK, before applying for consent to construct an offshore wind farm, the developer must monitor the bird densities within their development site to inform their EIA. Data can be collected using a variety of different camera techniques and survey types, including aerial, boat and visual surveys. Further monitoring is sometimes necessary for consent to be granted by the regulatory body. However, this process relies heavily on assumptions, as mortality from collision is estimated using collision risk models. This uncertainty has been explicitly recognised for a number of years. On top of this issue, the data is often confidential to the project and therefore cannot be used by other developers to inform their own CIA. As a result, CIA is often restricted spatially and temporally, and geographical boundaries are not always specified.

As a potential solution to this issue, Masden et al. (2010) suggested CIA should be the responsibility of the regulatory body rather than the developer. This will remove the confidentiality issue regarding data availability between developments and allow for a more strategic approach with a greater amount of data. Overall, this would increase the accuracy of cumulative collision risk modelling. However, changes to data collection methods will still need to be made. Until a standardised method is developed and utilised, CIA will provide the same amount of value as it does presently.

Collision risk models are a valuable tool for EIA and have the potential to benefit the CIA process if they are adapted to become more strategic. For this to be accomplished in an effective manner, collision risk models will need to be modified to account for larger scale developments. Data for surrounding developments could also become available to developers if the responsibility for data collection was moved to the relevant regulatory body, as suggested by Masden et al. in their paper 'Cumulative impact assessments and bird/wind farm interactions: Developing a conceptual framework'. Not only would the data be available for all developers, but the methodology used for data collection would be consistent across all projects. This could result in projects becoming more comparable and increase the reliability of the CIA process.

Sinead Petersen is a graduate environmental consultant in the Environment Team at Xodus Group, London.

Image credit: iStock


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