Differentiating between underwater construction noise of monopile and jacket foundations for offshore windmills: a case study from the Belgian part of the North Sea.

Steel monopiles, jackets requiring four steel pinpiles, and gravity-based foundations were applied in offshore wind farms in the Belgian part of the North Sea. This paper compares the underwater noise generated during the piling activities of steel monopiles at the Belwind wind farm (Blighbank) with that of jacket pinpiles at the C-Power project (Thorntonbank). Underwater noise was measured at various distances from the pile driving location. The underwater noise was quantified by its zero to peak sound pressure level (L(z-p)), unweighted sound exposure level (SEL), cumulative SEL, and 1/3 octave spectra. No significant differences in L(z-p) could be demonstrated (monopile L(z-p): 179-194 dB  re 1  μPa, jacket L(z-p): 172-189 dB  re 1  μPa). SEL showed no statistical difference between monopile and jacket and varied between 145 and 168 dB  re 1  μPa(2)s. Furthermore, near identical spectra were measured for both types of piling. Piling of the jacket pinpiles took, however, about 2.5 times the time of the monopile. When standardised to megawatt installed per foundation both types of piling scored near equally. As an illustration, the radius of major behavioural disturbance (L(p-p) = 155 dB  re 1  μPa) in the harbour porpoise Phocoena phocoena was estimated by a model at 16 km for monopiles and at 8 km for jacket.