bathymetry, with the larger predicted impact distances generally occurring to the west (south-west to north-west) of East Anglia THREE. The effect of this on the behavioural disturbance ranges for harbour porpoise can be seen in Plate 9.5. The same image also shows the possible spatial extent of the piling noise, in terms of the harbour porpoise zones of likely avoidance (164dB re 1 μPa2·s) and possible avoidance (145dB re 1 μPa2·s), with regard to a single pile strike using the 3,500kJ hammer blow energy. It should be noted that the longest stated impact distances only occur along limited transects from the source. Plate 9.6 shows an example of a noise footprint which may be expected for a 3,500 kJ hammer energy used at East Anglia THREE for the harbour porpoise behavioural disturbance criteria adopted from Lucke et al. (2009). The footprint indicates the possible spatial extent of the piling noise in terms of harbour porpoise behavioural disturbance, with no regard for specific temporal construction sequencing across the project (see Section 9.4 for more detail). For lower hammer energies, harbour porpoise would be expected to exhibit disturbance (or possible avoidance behaviour) at shorter ranges, as indicated in Table 9.6. Overall, it is important to note that possible avoidance is not expected to lead to all individuals avoiding the area, nor are all individuals expected to display an equal level of avoidance, as indicated by the work of Brandt et al. (2011) in Belgium.


104. Applying the Marine Mammal Exposure Criteria for mid-frequency cetaceans it may be predicted that an avoidance range of less than about 4km is likely and that a possible avoidance range of between 8km and 12km may occur for a 3,500kJ hammer blow energy. Behavioural disturbance ranges for mid-frequency cetaceans are illustrated in Plate 9.7 for a 3,500kJ hammer blow energy.


105. Applying the Marine Mammal Exposure Criteria for low-frequency cetaceans it may be assumed that, for a 3,500kJ hammer blow energy, an avoidance of about 20km to 35km would be likely and that an avoidance range of between about 42km and 93km may be possible. These behavioural disturbance ranges for low-frequency cetaceans are illustrated in Plate 9.8 from which it can be seen that the longest stated impact distances only occur along limited transects from the source. At lower hammer energies the ranges may be expected to be shorter as indicated in Table 9.8.


106. The noise levels present in the water will also depend on the depth of the receptor as described in Section 9.4 and marine mammals near the surface will be exposed to lower noise levels with correspondingly smaller impact ranges. For example, an animal with its ears just below the water line would be exposed to substantially


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm Appendix 9.1 Underwater Noise Modelling 42


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