ENVIRONMENTAL STATEMENT BARDOLINO DEVELOPMENT

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Bardolino Development Environmental Statement 6.6.5 Adequacy of proposed mitigation measures Although benthic fauna would inevitably be physically impacted by the installation and presence of the production manifold, production tree and valve skid, the effects would be confined to three very small areas of seabed totalling some 100 m 2 . This represents a tiny fraction of the available seabed in the Blocks covering the Bardolino development. Except for the very small areas beneath them, the quality of the sediments would not be altered by the installation of the structures. The use of a DP vessel to deploy the manifold will avoid the potential impact of anchor scars. A post-lay survey of the seabed will be conducted by Shell to verify that the structures are installed according to plan, and are over-trawlable. The subsea structures and their protective structures would be designed to ensure that they do not impede fishing activities and would withstand fishing interaction loads and dropped object loads. Shell will notify the Hydrographic Office, which will issue Notices to Mariners to advise fishing and shipping traffic of the potential hazards to navigation that would be associated with the project. Mariners will be advised of specific periods and locations in which vessel operations should be avoided. Contact information will be provided and details of guard vessels will be given. Guard vessels would be on station during installation to alert shipping and fishing vessels of potential navigational hazards. Page 6-18 April 2008
Bardolino Development Environmental Statement 6.7 NOISE ARISING FROM THE <strong>BARDOLINO</strong> <strong>DEVELOPMENT</strong> ACTIVITIES 6.7.1 Likely magnitude and duration In general terms, sound can be characterised with reference to two features, the frequency at which it is emitted (measured in hertz (Hz)) and the strength or intensity of the sound (measured in decibels (dB)). Noise from various sources may combine or cancel to produce a pattern of noise in the marine environment that is characterised by variations in frequency and noise level. Noise levels in the marine environment are attenuated by distance (dispersion in 3 dimensions), and by absorption by the water. The degree of absorption is roughly in proportion to the square of the frequency. The main sources of sound associated with the proposed project are: • a semi-submersible drilling rig; • a standby vessel; • 3 anchor handling tug vessels (AHTVs); • a guard vessel; • a DP pipelay vessel (which utilises thrusters to maintain its position); • a trenching / backfill vessel; • a rock dump vessel; • a survey / umbilical vessel; • a dive support vessel (DSV) to tie-in and commission pipeline; and, • piling the subsea structures. The characteristics of the noises produced by different types of vessels and activities are shown in Table 6.6. Table 6.6: Examples of underwater noise levels produced by different types of vessel or different types of activity Source Source levels of underwater noise (dB re 1µPa at 1m)* (predominant frequency if known) Drilling from semi-submersible 154 (100 to 500Hz) Tug / Barge 140 to 170 Trenching 159 to 174 (500 Hz) Supply / Support Vessel 170 to 180 (500Hz) DP pipelaying vessel 177 (500-1,000Hz) Pile driver 206 Helicopters (various) & at various altitudes 101 to 109** Key: dB re1µPa at 1m – unit of Sound Pressure Levels measured at a 1m range from source * Most data taken from 1/3-octave band centre frequencies (50-2000Hz) ** Measured at the water surface Source: Richardson et al., 1995; Evans and Nice, 1996. The noise resulting from normal operations of the drilling rig and associated vessels, including the DP vessel, would be steady and continuous, and sudden changes in the frequency or levels of noise would be unlikely. Marine mammals are the most sensitive receptor for underwater noise from offshore operations. Animals moving into or through the area may experience a growing level of noise as they approach the development and pipelaying operations. Marine mammals would therefore have time to react to this noise and move away from the source of disturbance. Given the relatively low density of marine mammals in the area, and the ability of the mammals to move away from sources of noise, it is unlikely that April 2008 Page 6-19
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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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