Review of Cabling Techniques and Environmental Effects Applicable

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Review of Cabling Techniques and Environmental Effects Applicable to the Offshore Wind Farm Industry – Technical Report particular significance, given that each of these animals is afforded a high level of individual protection under a suite of national and international legislation and signatory agreements 3 (Defra, 2005). As such, potential adverse impacts upon a single individual of a species of marine mammal must be considered as being of significance and, therefore, there is a requirement to apply practicable and financially feasible mitigation measures in order to be compliant with the legislation (in particular, the Habitats Directive). 5.6.1 POTENTIALLY SIGNIFICANT EFFECTS Cable laying operations have the potential to impact upon marine mammals through: ● ● ● ● 126 Collision with the vessel or support vessels; Noise and visual disturbance from the vessel and cable burial system; 4 Contact with any fuels and chemicals that may be accidentally released during the operation; and Interactions or entanglement with the cable or other lines between the vessel and the installation tool. Collision risk While there are no accurate records of the number of incidents of accidental collisions between marine mammals and shipping in UK waters (e.g. Hammond et al., 2003), it is considered that a direct relationship exists between shipping intensity, vessel speed and the number and severity of collisions, certainly in the case of whales (Laist et al., 2001). Certain assumptions can be made about the risk of collision with marine mammals (Sakhalin Energy Investment Company Limited, 2005; Laist et al., 2001): ● ● ● ● ● All types and sizes of vessels can hit marine mammals; Vessels over 80m in length cause most severe or lethal injuries; Serious injuries to mammals rarely occur if struck by vessels travelling at speeds of less than 10 knots; Mammals struck by vessels are usually not seen prior to impact, or are seen too late to avoid impact; and The risk of collision increases in poor visibility. Collisions between marine mammals and the cable burial vessel are considered to be unlikely. The cable burial vessel whilst working in the shallow water locations, is likely to only make very slow progress while laying and burying cable, with a burial rate of 1000m of installed cable per hour and therefore would 4 Such accidental releases are likely to be similar in extent, duration and significance as for other parameters and is not discussed in this section.
Potential impacts and mitigration measures not be travelling at over 10 knots during installation operations, thus reducing the risk of fatal injury, should a collision occur. Visual disturbance Marine mammals may be disturbed by the presence of vessels and human activities, particularly in sensitive locations such as in close proximity to seal haul out sites and marine mammal foraging areas. Such disturbance, during sensitive periods (such as the breeding and pupping season of seals), may lead to significant impacts such as the abandonment of young and reduced reproductive success (Brown and Prior, 1997). Underwater noise There is increasing concern over the impacts of underwater noise as a result of anthropogenic activities upon marine life in general. This issue is of greater relevance to marine mammals, given both their physiological capacity for detecting and responding to sound, and the high levels of protection that they are afforded. The sources and intensities of sound associated with offshore wind farm construction and the related impact on marine life has been investigated by Nedwell et al. (2003) and Nedwell & Howell (2004). Further useful information is provided in Jansy et al. (2005) and Madsen et al. (2006). The impact of noise on marine mammals can be divided into three levels: ● ● ● Those that cause fatal injury; Those that cause non-fatal injury such as deafness and other auditory damage such as temporary threshold shift (TTS); and Those that cause behavioural change (e.g. avoidance, cessation of feeding etc.). Similarly to the impacts of underwater noise on fish, available information suggests that species of marine mammal will show a strong avoidance reaction to sound levels of 90 dB ht (species) and above. It is, however, considered highly unlikely that cable installation would produce noise at a level that would cause a behavioural reaction in marine mammals. For a more detailed discussion of the dB ht (species) measurement, an example of where the measurement has been applied to cable installation and the likely levels of effect on both marine mammals and fish, see Section 5.4.2. Entanglement The risk of marine mammals becoming entangled in a cable under low tension, or in any other lines used to connect the installation tool to the vessel, is considered to be extremely limited. Most seals and cetaceans would be expected to avoid areas of human activity and significant disturbance and, as 127
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REVIEW OF CABLING TECHNIQUES AND EN
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Review of Cabling Techniques and En
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Abbreviations AIS Automatic Identif
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TTS Temporary Threshold Shift TWA T
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3 Cable types and 18 installation t
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Page 82 and 83: 4 Physical change 4.1 Introduction
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Page 144 and 145: References Introduction Sinden, G.
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