2013, National Physical Laboratory, Modelling of Underwater Noise Resulting from Greater Gabbard Offshore Wind Farm Operation

Description

The Food and Environment Protection Act (FEPA) Licence (33097/07/0) for the Greater Gabbard Offshore Wind Farm (GGOWF) required the subsea noise during the operational phase of the wind farm to be measured to assess ‘various frequencies across the sound spectrum at a selection of locations immediately (adjacent to), within and outside the array at varying distances’. The full wording of licence condition 9.9 is stated below: ‘The Licence Holder must make provision during the construction phase of the wind farm to install facilities to enable subsea noise and vibration from the turbines to be assessed and monitored during the operational phase of the wind farm. Before completion of the construction phase the Licence Holder must specify how it proposes to measure subsea noise and vibrations to the Licensing Authority in order to fulfil the monitoring requirement outlined in Annex 1 attached to this Licence. The specification must include assessment of various frequencies across the sound spectrum at a selection of locations immediately, within and outside the array at varying distances.’ Although the licence condition sates ‘monitoring’ as a requirement, in situ measurements alone may not necessarily result in an increase of understanding of the potential noise resulting from GGOWF, compared with background or ambient noise in the area. Evidence from the Gunfleet Sands offshore wind farm (Nedwell et al., 2011) suggests that the type of wind turbine operating at GGOWF is not very ‘noisy’ compared with typical coastal ambient noise. This may particularly be the case around the GGOWF site where the density of surface vessel activity is relatively high. The more pertinent question for larger offshore wind farms, such as GGOWF, is what effect, ‘many’ turbines, operating together over such a large area have on the resulting noise levels. This is more challenging to investigate within the specified requirements of the licence, particularly for GGOWF, where there is substantial variation in bathymetry and acoustic sediment properties across the site. This is particularly challenging for GGOWF due to its geographic make up (i.e. Inner Gabbard and Galloper sites).