Underwater radiated noise and impact assessment of marine piling operations during offshore windfarm construction

Abstract

In UK waters numerous large scale offshore wind farm developments have been constructed typically using large hollow steel mono-pile foundations with pile diameters varying from a few meters to greater than 6 m diameter and lengths 60-80 m. Piles may be driven 20-30 m into the seabed in water depths from a few meters to greater than 30 m. Typically percussive piling construction operations are used with many thousands of individual strikes over periods of several hours resulting in repetitive high amplitude impulsive sound within the water column that has potential for impact on marine life. Data is presented for in-situ measurements made during installation a range of mono-pile diameters used on offshore windfarms. Full piling sequences were recorded at fixed ranges using fixed autonomous data loggers and sampled range dependent boat based measurements. Simultaneous recordings at multiple ranges varying from 10’s meters to 10’s km were made. Data is analyzed in terms of received levels, spectral and temporal components. Using range dependent propagation loss modeling equivalent mono-pole source levels are estimated. Level dependence on range, hammer energy, etc. are discussed. A Monte Carlo approach is used to obtain total cumulative exposure (SEL) risk for single foundation to whole windfarm construction scenarios.