Abstract
Subacoustech Environmental has undertaken a study on behalf of Mainstream Renewable Power to assess the impact of underwater noise produced during pile driving operations during the installation of wind turbines at the Neart na Gaoithe (NNG) Wind Farm site, situated in the Firth of Forth.
The levels of underwater noise from the installation of jacket piles have been assessed and estimated using a proprietary underwater sound propagation model, INSPIRE (currently version 3.3.0), that enables the behaviour of noise with range from the piling to be estimated for varying water depths, pile sizes, blow energies and piling locations based on an existing database of measurements of piling noise. The model is validated against Subacoustech’s existing database of measurements of piling noise. The INSPIRE model has been used to calculate the expected noise level on 180 transects radiating outwards from the piling location at the NNG Wind Farm site and the results interpreted to yield impact range contours.
The modelled results suggest that marine species may suffer a lethal effect, where peak to peak pressure levels exceed 240 dB re. 1 µPa, out to a range of less than 10 m. Physical injury, where peak to peak pressure levels exceed 220 dB re. 1 µPa, is likely to occur out to a maximum range of 50 m or 60 m depending on the piling scenario modelled.
The possibility of traumatic hearing injury has been assessed using the 130 dBht(Species) criteria, for which the largest estimated ranges are for humpback whale, with 130 dBht ranges of up to 780 m during the fully driven scenario and 690 m during the drill-drive scenario.
Behavioural impacts on marine species have been assessed using the 90 and 75 dBht(Species) criteria. The results show that the largest impact ranges are predicted for herring, harbour porpoise and humpback whale, with a maximum 90 dBht impact range for herring of 34 km, 20 km for the harbour porpoise and 41 km for the humpback whale for the worst case fully driven NNG scenario.
The accumulated exposure to sound for marine mammals has been assessed using M-Weighted SELs assuming an animal fleeing the noise source. The largest ranges are calculated for the 186 dB criteria for Pinnipeds. For piling operations at a single location a maximum range of 8.4 km is likely to be needed at the onset of the impact piling for the NNG drill-drive scenario to avoid a damaging exposure to sound using the Southall criteria. Lower ranges are predicted for all the criteria using the 198 dB threshold. The largest impact range calculated was found to be 47.3 km for the 186 dB criteria for Pinnipeds for the cumulative scenario of NNG drill-drive, Inch Cape and Seagreen.