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 ● ● ● ● 4 The potential environmental impacts that could occur during the installation and maintenance of subsea cables. Impacts are described and discussed for intertidal habitats, subtidal ecology, natural fish resources, commercial fisheries, marine mammals, ornithology, shipping and navigation, seascape and visual character, and marine and coastal archaeology. Impacts are divided into those that could cause potentially significant impacts and those that may arise but are unlikely to cause significant effects. Mitigation measures that can be used to reduce the level of significance of environmental effects. Examples of good practice measures that could be adopted during all phases of project planning and used in conjunction with mitigation measures to reduce potential disturbance from cabling activities; and Knowledge gaps identified during this review, including gaps in understanding of the actual environmental impacts resulting from cable burial activities. The key impacts relating to cable laying in the marine environment occur during the installation process. Cable burial and other protection measures (i.e. outer protective cable armouring, concrete and frond mattresses, rock dumping, and grout / sand bags) are used in order to reduce the risk of damage to the cable and to ensure the safety of other users of the sea. Where cables are not afforded adequate protection, damage can occur through abrasion (i.e. on rocky seabed types) and interaction with human activities such as snagging or entanglement from bottom trawl fishing gear, anchoring or navigational dredging. Dependant upon prevailing conditions of depth, seabed morphology, hydrodynamics and geology, a range of cable burial technology is available to developers, such as cable ploughs, tracked burial machines, free swimming remotely operated vehicles (ROVs) and burial sleds. Induced changes to the prevailing physical conditions of an area, such as the suspension, dispersal and subsequent deposition of seabed sediments, changes to seabed morphology and the direct impacts associated with the presence and operation of cable burial equipment can lead to a range of potential environmental impacts. The nature, extent and significance of these impacts will be a function of site specific characteristics (i.e. seabed type, tidal and wave conditions) and the chosen installation method. The key potential environmental impacts, which can, in specific circumstances, be associated with cable burial, include: ● ● ● Disturbance to sessile, encrusting, and attached fauna and flora which can be dislodged/disturbed; Smothering of sessile species due to increased sediment deposition and sidecast; Damage to the filtering mechanisms of certain species, the gills of sensitive fish species and eggs and larvae from increases in suspended sediment and subsequent deposition;
● ● ● ● ● ● ● ● ● ● The potential release of contaminants, previously retained in the sediment; Disturbance to important fisheries habitats such as spawning grounds, nursery grounds, feeding grounds, over-wintering areas for crustaceans, migration routes and shellfish beds; Disturbance to sensitive habitats, such as saltmarshes, biogenic reefs and eel grass beds; Noise and vibration impacts to fish and marine mammals; Electromagnetic field generation impacts to benthic species, fish and marine mammals; Risk of collision of marine mammals with cable installation vessels / support vessels; marine mammals may be disturbed by the presence of vessels and cable burial equipment; and, cable entanglement with marine mammals; Marine and coastal bird species, particularly at sites of importance to nature conservation, may be disturbed by the presence of vessels and human activities; Navigational risks such as collision with cable installation vessels; Direct loss or disturbance to artefacts of importance to marine and coastal archaeology and cultural heritage; and Seascape and visual impacts related to the cable installation activities and the presence of cable installation vessels; and possible sea surface aesthetic effects arising from sediment plumes, particularly in areas of chalk bedrock. This study concludes that, although cabling can cover large areas of seabed, the associated environmental impacts are highly transitory, localised in extent and temporary in duration. Although the corridor for cable installation impacts can be long, the footprint of impact is narrow, generally restricted to 2-3m width. For the majority of installation scenarios, the seabed and associated fauna and flora would be expected to return to a state similar to the pre-disturbance conditions. Exceptions could occur in hard clays and rock seabed types, where the cable trench would not naturally backfill, requiring intervention to backfill as part of construction works or else leaving permanent scarring of the seabed. The environmental impacts associated with the installation, operation and maintenance of cables associated with offshore wind farms must be considered in the context of other influencing factors. Natural perturbations such as storm activity can have a significant effect on the structure and functioning of the seabed, as can other activities such as oil and gas exploration and infrastructure, telecommunication cable installations, certain fishing activities, aggregate extraction, and other sources of change to the physical environment. In many cases, such influencing factors may lead to related environmental impacts of greater extent, duration and significance than those observed or suspected to arise as a result of the installation of offshore wind farm cable infrastructure. 5
Page 1: REVIEW OF CABLING TECHNIQUES AND EN
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Page 9 and 10: Abbreviations AIS Automatic Identif
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Review of Cabling Techniques and En
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4 Physical change 4.1 Introduction
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6 Good practice measures This secti
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7 Gaps in understanding Research fo
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References Introduction Sinden, G.
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Appendix A: Standards and codes of
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Printed in UK on recycled paper. De
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