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 5.9.1 POTENTIAL EFFECTS Cable installation activities will have a physical impact on the environment (see Section 4) and may, therefore, alter its visual appearance. The key issues of concern are the effects upon unspoilt landscapes and seascapes, designated and valued landscapes/seascapes and effects on visual amenity. The severity of the visual and landscape impacts arising from cable installation activities will be related to the value and use of the area and the scale of the alteration of the appearance. There will be trenching or ploughing activities taking place in the intertidal zone and adjacent coastal area necessary for the burial of the cable, which will be visible. However, the impacts to the landscape and seascape will be localised and short term. There will be landscape and visual impacts as a result of the presence of electricity substations and overhead transmission lines and poles connecting the offshore wind farm to the local electricity grid on land, and temporary disturbance of the seascape arising from the presence of subsea cable burial machinery and vessels. 5.9.2 MITIGATION MEASURES Visual and seascape impacts can only be effectively mitigated at the landfall site and will include usual good construction practice, such as limiting the area to be disturbed; maintaining tidy and compact site compounds and ensuring full restoration of the site in consultation with the relevant authorities (Natural England, Environment Agency or the Local Planning Authority). In addition, potential effects of cabling activities in the intertidal zone and adjacent coastal area may be minimised by timing trenching activities to avoid sensitive periods such as busy tourist seasons. 5.10 Marine and Coastal Archaeology The potential archaeological resource that may be impacted by cable installation activities includes submerged palaeo-landscapes, including evidence of former human habitation or climate change; wrecks and related maritime remains and terrestrial archaeology, including in situ sites and / or findspots. Potentially significant effects include: ● ● 134 Direct loss or disturbance by cable installation activities; and Indirect disturbance via changes in sedimentation, such as increased erosion or accretion. The protection of archaeological, cultural heritage and wrecks are provided by a number of Legislative Acts. The principal protection for underwater heritage in
Potential impacts and mitigration measures the UK’s territorial waters is provided by the Protection of Wrecks Act 1983. More recently, the Natural Heritage Act (2002) has enabled English Heritage to assume responsibility for maritime archaeology in English coastal waters. Specifically the Joint Nautical Archaeology Policy Committee (JNAPC) brings together a wide range of organisations with a direct and active interest and expertise in the marine historic environment. Relevant guidance provided by English Heritage and others includes: ● ● ● ● ● England’s Coastal Heritage; Identifying and Protecting Palaeolithic Remains: Archaeological Guidance for Planning Authorities and Developers; Military Aircraft Crash Sites: archaeological guidance on their significance and future management; Joint Nautical Archaeology Policy Committee, 2006, Maritime Cultural Heritage and Seabed Development JNAPC Code of Practice for Seabed Development; and Wessex Archaeology (in consultation, 2006) Historic Environment Guidance Note for the Offshore Renewable Energy Sector. 5.10.1 POTENTIALLY SIGNIFICANT EFFECTS Direct loss or disturbance Cable installation activities including the anchoring of vessels can disturb the seabed in ways which could damage or destroy historic artefacts and submerged archaeological sites and features. In addition, indirect disturbance may occur from the longer term changes in the scouring and sedimentation patterns arising from cable installation and cable protection methods, exposing previously buried sites to degradation, destabilisation and corrosion. Archaeological remains and artefacts are a finite and non-renewable resource and, as such, cannot be replaced or recover from damage caused to physical properties or archaeological context. All direct impacts upon archaeology would be permanent and, therefore, of significance. However, the scale of significance would depend upon the strength of the impact ranging from low, if the material is simply dislodged from its resting place, to high, if the material is crushed or damaged by the installation equipment. Unlike aggregate extraction where the sediment is brought to the surface increasing the likelihood of identifying archaeological finds, the excavated sediment from cable burial machines is not brought to the surface. The sediment is ploughed or jetted to the side of the trench and thus there is no opportunity, at present, to investigate the occurrence of archaeological remains during cable installation activities, unless they are identified by the sonar systems, cable 135
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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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4 Physical change 4.1 Introduction
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