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 such, would be unlikely to venture close enough to the cable burial vessel to become entangled. A review of relevant published literature and discussions with installation contractors has not identified any reports of marine mammals of any kind becoming entangled during cable burial operations. 5.6.2 MITIGATION MEASURES Visual and other construction related disturbance, in relation to hauled out seals, can be effectively mitigated by avoiding cable installation operations in the vicinity of known haul out sites during sensitive periods, such as the breeding season (late June to early July for common seal and late July to early December for grey seals (although this varies with position around the UK). Wherever possible, seal haul out sites should be avoided during the planning of the cable route in order to completely remove the potential for disturbance to occur. Further study is required to assess the noise levels produced by the range of available cable burial devices and tools in the types of seabed sediments encountered in UK waters. This can be achieved through real time monitoring of cable installation, such as at North Hoyle, or through specific experimentation and computer modelling. Only once sufficient, reliable data is available can the disturbance caused by cable installation be understood and effectively mitigated. As a precautionary measure, given the conservation significance of the species involved, it may be necessary, as a minimum, to employ Marine Mammal Observers on the installation vessel and to have a protocol in place to delay installation activities from occurring if marine mammals are detected within a predetermined distance from the installation vessel. Such a need would be identified through consultation with the relevant nature conservation body and the JNCC (JNCC, 2004). 5.7 Ornithology Concerns and issues relating to birds, in the context of offshore wind farms are primarily concentrated on the wind turbine array. The installation of both the export and inter-array cabling is of significantly lower concern. Potentially significant effects of cable installation on birds are limited. The main area of concern would be: ● ● 128 Disturbance of normal behaviour in the intertidal; and Disturbance of normal behaviour at sea. Other effects on birds would be limited to: ● Prey availability.
5.7.1 POTENTIALLY SIGNIFICANT EFFECTS Disturbance of normal behaviour in the intertidal Potential impacts and mitigration measures In the intertidal zone, the impact of disturbance upon birds may be significant. The presence of construction plant and activity is likely to cause temporary disturbance to birds which would otherwise be foraging, loafing and roosting. The significance of the impact depends upon a number of factors, including the importance of the intertidal site to birds, the duration of intertidal works and the season in which the works are programmed. Such disturbance would be particularly significant if the intertidal area in question is designated as an SPA. Disturbance of normal behaviour at sea The installation of export cables involves activity in shallow coastal waters that can provide favourable foraging habitat for a wide range of seabird species, particularly in areas of shallow sandbanks. Noise levels and the presence of vessels and machinery associated with the installation process may impact on the use of the area by foraging birds, or those ‘rafting’ on the sea, through disturbance of normal behaviour. However, given the transient nature of cable installation, such disturbance will be highly limited, both spatially and temporally and would not be of major concern. 5.7.2 OTHER EFFECTS Prey availability Impacts on the seabed, and within the water column, that cause direct removal or displacement (i.e. due to noise) of fish and benthos, may indirectly impact birds through a reduction of prey availability in favoured foraging habitat. Offshore, foraging seabirds target a range of different fish species, particularly in shallow coastal waters. If installation activity causes the movement of prey species out of the area, this is likely to result in a related displacement of bird species that would follow the prey. The impact of displacement would be limited in both extent and duration and not considered as being significant, unless the cable is to be installed in an area that supports an important prey resource that has a limited distribution in the wider study area and is associated with a sea area considered to be suitable for the designation of offshore SPAs 5 . Similarly, in the intertidal zone, there may be a short term decrease in prey abundance caused by the direct loss of flora and fauna in the footprint of the installation device. The significance of this impact would depend on the availability of similar prey within the intertidal, outside the installation footprint. 5 http://www.jncc.gov.uk/page-1414 129
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REVIEW OF CABLING TECHNIQUES AND EN
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TTS Temporary Threshold Shift TWA T
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