ENVIRONMENTAL STATEMENT BARDOLINO DEVELOPMENT

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Bardolino Development Environmental Statement Underwater noise can have a severe effect in the immediate vicinity of high level pressure sources, such as that caused by piling. At greater distances from the source, the noise would decrease and its effects would diminish (Nedwell et al., 2004, 2005). Pile-driving generates signals of a very high source level and broad bandwidth (Richardson et al., 1995). Piling operations create underwater noises of a frequency and level that are audible to seals (pinnipeds), toothed whales, dolphins and porpoises (odontocetes) and baleen whales (mysticetes) (Richardson et al., 1995; Nedwell and Howell, 2004; Nedwell et al., 2004). Noise from piling can enter the marine environment by four pathways, the most significant of which is thought to be by transmission of vibration through the pile itself directly into the water column. The noise produced during piling is dependent on the several factors including the type of equipment used, the size of the pile, the water depth and the characteristics of the seabed (Nedwell et al., 2004). The potential impact of piling noise on sensitive receptors depends on the actual level of noise received by the receptor at a certain distance from the source, and the animal’s sensitivity and response to that noise. The minimum level of noise that each species of marine mammal is able to detect (the hearing threshold) varies with the frequency of the noise. Audiograms illustrate the range of frequencies that a species is able to detect, and the frequency range over which the species’ hearing is most acute. For an underwater noise to have an effect on an animal it must have a frequency spectrum that is detectable by the particular species, and loud enough to be audible. Audiograms have been obtained for four of the species of marine mammal which are known to be present in the area of the Bardolino development, namely harbour porpoise, bottlenose dolphin, killer whale and minke whale. Table 6.9 shows the hearing ranges and peak frequencies for these species. Table 6.9: Hearing characteristics of some species or groups of marine mammals likely to be present at the Bardolino location Species Hearing range (Hz) Approximate peak frequency (Hz) Harbour porpoise 200-200,000 100,000-200,000 30-60 Bottlenose dolphin 100-300,000 50,000-80,000 40-50 Killer whale 500-200,000 10,000-30,000 30-45 Minke whale 10-10,000 300-400 30-40 Source: Nedwell et al. (2004), Richardson et al. (1995) Noise modelling Threshold at peak frequency (dB re 1µPa) Propagation of sound can be modelled to predict the sound level at any distance from the noise source. A common method is the Source Level – Transmission Loss model (Nedwell and Howell, 2004). The Source Level refers to the level of sound measured at one metre from the noise source, expressed in dB re 1 µPa @ 1m. As an acoustic signal travels through the ocean, it becomes distorted due to multi-path effects and weak due to various loss mechanisms (Jensen et al., 1994). The standard measure of the change in signal strength in underwater acoustics is called Transmission Loss. It is calculated as the sum of a loss due to geometrical spreading and a loss due to attenuation. Spreading Loss is a measure of the signal weakening as it propagates outward from a source. There are two main geometrical spreading laws to be considered in underwater acoustic modelling (see Jensen et al., 1994; Richardson et al., 1995), namely spherical spreading and cylindrical spreading. Spherical spreading is characterised by multi-directional propagation with loss of energy that is inversely proportional to the square of the distance from the source, whereas cylindrical spreading, which is typical of noise propagation in shallow waters, has a loss of energy inversely proportional to the distance from the source. For “shallow waters” (i.e. water depths of less than 200m), the cylindrical model should be applied (Jensen et al., 1994). The following equation was used to model noise propagation: Page 6-24 April 2008
Bardolino Development Environmental Statement SPL(r) = SPL(source) –N log(r) SPL=SL-TL where SPL is Sound Pressure Level, r is distance from the source, N is the transmission loss coefficient, SL is the source level and TL is the transmission loss (both measured in dB). The model scenario was based on a sound level at source of 194 dB @ 1m at a frequency at source selected as the frequency at which the species shows most sensitivity within the range of 300-1000 Hz, and a single noise source was considered (Nedwell et al., 2005). The transmission loss coefficient was assumed to have a value of 22 (reflecting depth of water). Absorption loss coefficient was calculated using the formula from Erbe & Farmer (2000): α = 2 2 −3 0. 11 f 44 f −4 2 3. 3× 10 + + + 3. 0 × 10 f 2 2 1+ f 4100 + f The scenario details for the model runs are provided in Table 6.10. Table 6.10: Scenario details for the model runs to assess the potential impacts during piling operations at the Bardolino location Scenario Species Sound level at source (dB at 1m) Frequency at which species shows most sensitivity (Hz) Threshold value for species derived from audiogram (dB) Predicted level at which TTS may occur (dBht) 1 Harbour porpoise 194 1,000 80 140 2 Bottlenose dolphin 194 700 91 140 3 Killer whale 194 500 100 140 4 Minke whale 194 400 34 124 Source: Nedwell et al., 2005 Thresholds for response to noise: For the purposes of assessing the potential effects of the proposed Bardolino development on marine mammals, the EIA focused on determining which activities might produce noises loud enough to result either in an animal displaying a “strong avoidance reaction”, or to cause a temporary change in hearing ability (a “temporary threshold shift (TTS)). The threshold for “strong avoidance” was selected because it is the lowest level at which overt behavioural changes occur. The TTS level was selected because it is the least damaging of the possible physical effects and would be found over the largest area in which physical effects might occur. It is therefore the most precautionary physical threshold. Noise modelling results Figures 6.1 to 6.4 show the results of the modelling which demonstrate the variation in perceived sound level with distance from the noise source for the four marine mammals studied (BMT Cordah, 2008a). April 2008 Page 6-25
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Page 181 and 182: 13 th March 2008 Dear Sir or Madam,
Page 183 and 184: To: Paul Wood Shell U.K Limited, Se
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What risks to marine mammals do pil
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Noise propagation modelling. Noise
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If, for any reason, piling operatio
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APPPENDIX 1 MARINE MAMMAL RECORDING
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ENVIRONMENTAL STATEMENT BARDOLINO DEVELOPMENT

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