Underwater noise generated from marine piling

Marine piling impact piling is a source of high-amplitude impulsive sound that can travel a considerable distance in the water column and has the potential for impact on marine mammals and fish. It involves steel piles being driven into the seabed using powerful hydraulic hammers, and is a commonly used construction method for fixing structures to the sea-bed in the offshore industry, and for the installation of offshore wind turbines in shallow coastal waters such as those around the UK. This paper describes methodologies developed for measurement of marine piling including estimation of the energy source level. Measurement results are presented of measurements made during the construction of an offshore windfarm, involving piles of typically 5 m in diameter driven by hammers with typical strike energies of around 1000 kJ. Acoustic data were recorded as a function of range from the source using hydrophones deployed form a vessel, allowing the transmission loss to be confirmed empirically. The use of fixed acoustic enabled recording of the entire piling sequence, including the increasing pulse energy during the soft start. The methodology of measurement is described along with the method of estimation of the energy source level.