CHARACTERIZATION OF IMPACT PILE DRIVING SIGNALS AND FIN WHALE VOCALIZATIONS AT THE BLOCK ISLAND WIND FARM SITE

Abstract

Offshore wind farm development is rapidly expanding and with that comes the need for assessment of the potential short and long term environmental impacts. As a by-product of the construction, operation, and eventual decommissioning of offshore wind farms, sound is generated both in air and underwater through various activities and mechanisms. With the rate of wind farm development continuing to increase worldwide, regulatory agencies, industry, and scientists are attentive to the potential physiological and behavioral effects these sounds might have on marine life living in the surrounding environment. The impact pile driving used to install the wind turbine foundations is of particular concern due to the intense, impulsive sound that is radiated into the surrounding environment. Piles driven vertically into the seabed generate an azimuthally symmetric underwater sound field whereas piles driven on an angle will generate an azimuthally dependent sound field. Variations in the radiated sound field along opposing azimuths resulted in differences in measured sound exposure levels of up to 10 dB and greater due to the pile rake as the sound propagated in range. This difference in sound levels is significant and should be considered when performing acoustic propagation modeling during the environmental assessment stage of the wind farm development. Environmental assessments are performed to determine how far in range the sound will travel and what potential effect the sound will have on marine animals typically found in the development area. Fin whales are known to traverse the area where the Block Island Wind Farm (BIWF) was constructed and they were recorded vocalizing not long after the foundations for the turbines were installed. Fin whale 20-Hz pulses were recorded for an extended duration and multiple modal arrivals in the received signals were used to localize and track the fin whale. The characteristics of the received signal were then used to invert for the environmental parameters that supported the observed acoustic propagation.