2005, Subacoustech, North Hoyle, Measurements of underwater noise during construction and operation of offshore wind farms

The series of studies commissioned by COWRIE Ltd conducted primarily by Subacoustech Ltd, Nedwell et al., and CEFAS between 2003 and 2007, aimed to measure and interpret underwater noise generated during the construction and operation of UK offshore windfarms (including North Hoyle, Scroby Sands, Kentish Flats, Barrow, and Burbo Bank), and to evaluate the potential impacts on marine mammals and fish. Multiple methodologies were employed, including in-situ underwater noise measurements using calibrated hydrophones, behavioral response studies, field transects, environmental modeling, and literature reviews. Findings consistently show that operational windfarm noise is minimal, often indistinguishable from ambient levels and poses negligible risk to marine fauna. In contrast, pile driving during construction produces significantly higher noise levels, creating temporary injury risk zones within a few hundred metres, with effects attenuating rapidly with distance due to environmental factors. Key recommendations include ongoing monitoring, use of frequency- and species-specific metrics (such as dBht), mitigation strategies like acoustic deterrents and soft start procedures during construction, and adherence to defined safety criteria (e.g., 130 dBht for marine mammal protection). The studies support the adequacy of current mitigation guidelines and highlight the importance of contextual noise assessments across varying environments to minimize ecological impacts during offshore windfarm development.