‘footprint’ approach is used to assess the maximum area over which likely and possible avoidance can occur in harbour porpoise. The noise footprint can be considered as containing the possible impact ranges for a given threshold which might occur, irrespective of the timing, specific location or number of piling vessels operating within the project boundary (Appendix 9.1). Therefore, the footprint area may be greater than the combined area for two concurrent piling vessels, but is considered to approximate to the worst case scenario in this assessment.
237. Monopile foundations will result in the worst spatial impact (i.e. will use the maximum hammer energy). With regard to the worst case temporal impact, the maximum duration of piling noise during construction of the off shore windfarm will result from the use of jackets (with four piles each), and only a single piling vessel operating at any one time.
238. For jacket foundations 1,800kJ is the maximum hammer energy that will be used, with a maximum of four piles per jacket. However, noise propagation modelling has not been completed for this hammer size, so the 2,000kJ hammer is used as a proxy.
239. As only a single piling vessel will result in the greatest temporal impact, the area of impact will be considered based on the location where the greatest ranges of impact are predicted.
240. Appendix 9.1 provides details on the ambient noise levels expected in the East Anglia THREE site. The ambient noise level is also highly likely to depend on the distance to shipping lanes, fishing areas, dredging areas or other areas where potential noise sources are operating. In the North Sea, the contribution of shipping noise to ambient levels has been shown to be significant (Ainslie et al. 2009). Natural environmental contributors to the ambient noise level in and around East Anglia THREE and the East Anglia Zone in general, will likely be from the wind (sea-state) with contributions from rain noise and biological noise. The primary anthropogenic contributors to the ambient noise level in the North Sea include shipping (e.g. fishing, cargo, cruise ship, ferries, and aggregate extraction) and oil and gas related activities. However, the ambient noise environment around the East Anglia THREE site would likely be dominated by local shipping (see section12.6.1.2 for current shipping levels) and sea-state.
241. The metrics used in the noise assessment are consistent with the Marine Strategy Framework Directive and include peak-to-peak pressure level and Sound Exposure Level (SEL). Sound Pressure Level (SPL) is used to describe the level of a continuous type noise such as shipping or operational wind turbine noise.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 12 Marine Mammal Ecology Page 66
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