Scottish Marine and Freshwater Science Volume 4 Number 5: Modelling of Noise Effects of Operational Offshore Wind Turbines including noise transmission through various foundation types

7 Conclusion

• Noise emitted from operational wind turbines is directionally dependent on the wind; however the sound level characteristics differ for each of the foundation types.
• Wind turbines founded on monopiles emit high noise into the marine environment at low frequency (<500 Hz). Monopiles are ~10 dB louder than equivalent gravity bases and ~50 dB louder than equivalent jackets at low frequency.
• At high frequencies (>500 Hz) jackets emit higher noise levels than gravity bases or monopiles. However, the sound pressure level produced by all three foundation types at high frequency is close to or below the background noise.
• Noise levels from operating windfarms are likely to be audible to marine mammals, particularly under scenarios where wind speeds increase.
• Jacket foundations appear to generate the lowest marine mammal impact ranges when compared to gravity and monopile foundations.
• Low-frequency specialists minke whales are most likely to be affected and are predicted to respond to the wind farm out to ranges of up to ~18 km.
• Seal species (harbour and grey) and bottlenose dolphins were not considered to be at risk of displacement from the operational turbines.
• In assessing behavioural responses, we recommend the use of reversed audiogram weighting and a probabilistic approach to assessing noise impacts. We believe the limited data available on sensation levels and the precautionary nature of M-weighting indicate that the RA weighting approach may be more realistic.
• Atlantic salmon and European eels can detect monopiles at greater ranges than gravity bases, while they do not sense jackets in the far-field. Shad and sea trout do not sense any of the foundation types in the far-field.