ENVIRONMENTAL STATEMENT BARDOLINO DEVELOPMENT

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Bardolino Development Environmental Statement the noise resulting from the pipeline installation would have any measurable or long-term effect on marine mammals frequenting the area. Inspection of the data in Table 6.6, and assessment of the range of noise sources, and their magnitude and duration, indicates that the noise from piling would be the most significant potential source of underwater noise affecting marine mammals. Consequently the rest of this section examines this noise and its potential effects in greater detail. 6.7.2 Noise produced development activities Noise generated during piling operations Piling operations create underwater noises of a frequency and level that are audible to seals, toothed and baleen whales, and fish (Richardson et al., 1995; Nedwell & 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 production manifold would be secured to the seabed by means of four piles. Each pile would be 610 mm in diameter and 20 m long, and would be driven to the required depth in the seabed by an underwater vibro-hammer. It would take about 12 hours to install the four manifold piles. The valve skid would be secured to the seabed by means of four piles, and these would be of smaller diameter and length than those used to install the production manifold. Again, each pile would be installed separately using a vibro-hammer, and it would take about 12 hours to drive the 4 valve skid piles. There are no specific measurements available for the noise levels that would be produced during operations to fix such piles in a sandy clayey seabed in a water depth of approximately 85 m. From noise measurements of other piling operations taken under different circumstances, however, there appears to be a correlation between the diameter of the pile being driven and the Source Noise Level (SL) (Nedwell et al., 2005). The best fit line shows; SL = 24.3D +179 dB re 1µPa @ 1 m where D is pile diameter in metres. Application of this equation would suggest that the source noise level for a 0.61 m (610 mm) diameter pile might be approximately 194 dB re 1µPa @ 1 m. The frequency profile for piling noise is rather “flat” with no obvious peak, but maximum pressure levels are attained over the range 300 - 1,000 Hz (Nedwell et al., 2005). The larger piles used to secure the production manifold will produce a higher source level than those required to secure the valve skid, so modelling has been undertaken for the production manifold piling as this represents the worst case event. Acoustic propagation modelling was conducted for the production manifold pile driving at the Bardolino field, using accepted formulae, to calculate the noise propagation in the marine environment. This was combined with audiograms for marine mammals to predict the distances at which strong avoidance and a Temporary Threshold Shift (TTS) would occur in the species which are most likely to be exposed to the noise from piling. The technique employed reflects the current state of knowledge regarding underwater noise and its impact on marine species. During piling the noisiest vessel that is likely to be under way and in close proximity to the piling operations would be a DP vessel. The decibel scale used to measure sound is a logarithmic scale, therefore the presence of several sources of noise at any location at any one time leads to only a small increase in the total source level of noise at the site. The estimated noise level from this DP vessel operating at the site would be 180 dB re 1µPa dB @ 1 m. The difference between the source level noise for piling (194 dB) and source level noise for the vessel (180 dB) is more than 10 dB, so the presence of this additional noise Page 6-20 April 2008
Bardolino Development Environmental Statement source would make no significant contribution to the total source noise level at the site during the piling operations (Norton, 1989). Noise generated during pipeline installation operations The underwater noise that is produced by vessels arises from two sources – propeller cavitation and the propulsion machinery inside the vessel. Vessel noise may be considered to be a continuous, rather than transient noise source, which is a combination of broadband noise and tonal sounds at specific frequencies (Richardson et al., 1995). The noise that would be generated by the vessels would be determined by the types and numbers of vessels that are present at the site at any one time. Because the decibel scale used to measure sound is a logarithmic scale, the presence of several sources of noise at any location at any one time leads to only a small increase in the total source level of noise at the site. Published data on the sound source levels and frequencies for different types of vessels are provided in Table 6.6. Sound levels and frequency characteristics are depended on ship size and speed, with variations among vessels of similar classes (Richardson et al., 1995). Noise from shipping is roughly related to vessel size; larger ships have larger, slower rotating propellers, which produce louder, lower frequency sounds. Broadband source levels of ships between 55 and 85 m are generally around 170-180 dB re 1 µPa @ 1 m (Richardson et al., 1995), with most energy below 1 kHz. The use of bow thrusters can increase broadband sound levels by 11 dB and includes higher frequency tonal components up to 1 kHz (Richardson et al., 1995). There are currently two pipeline options which would require the operation of a number of different vessel types in the Bardolino area over a total period of 6 weeks. All would be typical of the vessels routinely used in the UK North Sea for oil and gas operations and other activities. • A dynamically positioned (DP) reel lay vessel would be used to lay the piggy-backed pipelines simultaneously onto the seabed. • Trenching would be carried out using a seabed plough towed by an anchor handling tug vessel (AHTV). • Rock dumping would be achieved by the careful placement of graded crushed rock over the pipelines, using a dedicated rock dumping vessel. • A DP dive support vessel (DSV) would be in the field for several different phases, such as tie-in spools and hydro-testing. • Guard vessels would be on site throughout the pipeline operations. • A DP survey vessel would be used to ensure that the pipes were laid in the correct location and that trenching activities were performed satisfactorily. The noise produced by subsea trenching operations depends on the equipment used and the nature of the seabed sediments. A trenching noise spectrum reported in Richardson et al. (1995) has peak levels of 178 dB re 1µPa @ 1 m at 160 Hz, with an overall source level 185 dB re 1µPa @ 1 m; this is similar to the data reported by Nedwell et al. (2004). These levels are for mechanical dredging operations, and may be noisier than the proposed pipeline installation operations for the Bardolino development which would use a towed plough. During the pipeline installation operations the vessels that are likely to be present in the area include DP pipelay vessel (180 db), AHTV for trenching (170 dB), dive support vessel (180 dB), guard vessel (180 dB), survey vessel (180 dB) and rock dump vessel (180 dB) (Table 6.6). The estimated noise level from this combination of vessels operating simultaneously at April 2008 Page 6-21
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ENVIRONMENTAL STATEMENT BARDOLINO D
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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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