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 It is currently unknown which invertebrate species could be affected but magnetic sensitivity has been demonstrated for the following: Decapoda (Crangon crangon), Isopoda (Idotea baltica) and Amphipoda (Talorchestia martensii and Talitrus saltator) (Greater Gabbard Offshore Winds Ltd., 2005). In all cases, magnetic sensitivity is understood to be associated with orientation and direction finding ability such that the animal may become disorientated; depending on the magnitude and persistence of the confounding magnetic field the impact could be a trivial temporary change in swimming direction or a more serious impact on migration (Greater Gabbard Offshore Winds Ltd., 2005). Although there has been no targeted monitoring specifically to investigate whether distributions of crustaceans and molluscs have been affected by the presence of submarine power cables and associated magnetic fields, monitoring to meet other specific objectives relating to offshore wind farms has not revealed any evidence to show such an effect. There are therefore uncertainties regarding the significance of this potential impact. However, it is not expected that the impact would be of significance, since the species that could be affected are known to be mobile and, as such, are able to avoid impacted areas. Generally the habitats that they inhabit are widespread and the effects of magnetic fields are usually highly localised around the cable. Potential heating effects The effect of radiated heat from cables buried in the seabed has been considered by the Connecticut Siting Council (CSC, 2001) as part of the ‘Cross Sound Cable Interconnector’ project, a high voltage DC buried cable system between New England and Long Island New York. The CSC estimated a rise in temperature at the seabed immediately above the buried cable of 0.19 o C and an associated increase in seawater temperature of 0.000006 o C. The potential rise in temperature is therefore considered to be impossible to detect against natural fluctuations in the surrounding sediments. Cable coating effects The leaching of chemicals and substances from cable coatings and cable sheaths are likely to have a minimal impact on the surrounding environment. Burial of the cable will further reduce possible environmental effects. Research conducted on the environmental impact of a submarine cable used to transmit hydrophonic data to shore from an acoustic hydrophone array in Monterey Bay, California reported no apparent effect on infaunal abundance (Kogan et al., 2003). Where the cable had become exposed, colonisation had occurred by encrusting species such as anemones, echinoderms and sponges (Figure 5.1), with fish congregating near the cable in places. At present, no specific regulations or standards exist for submarine cable coatings with respect to environment impacts arising from their constituents 108
Potential impacts and mitigration measures (UKCPC and Nexans Norway A/S, pers. comm.). However, cable manufacturers may be certified to ISO 14001 ‘Environmental System Management Certification’ and as part of this certification, manufacturers are required to demonstrate effective ways to minimise environmental risks. Figure 5.1: Submarine cable 3.2 cm wide colonised by Metridium farcimen anemones (Kogan et al., 2003) 5.2.4 MITIGATION MEASURES Where cable installation activities are proposed within sensitive locations and the significance of the impact is considered to be high it may be possible to mitigate the effect by altering the cable route or micro-siting of the cables to avoid localised areas. Micro-siting of the cables was a measure that was recommended in the ES for Thanet offshore wind farm in order to avoid dense aggregations of the reef-building worm Sabellaria spinulosa (Thanet Offshore Wind, 2005). Baseline information on the distribution of sensitive habitats and species within the construction area can be effectively used to plan the positioning of anchor arrays. In this way, exclusion zones for anchoring can be established if necessary. Disturbance due to anchors can be further reduced by using tenders to lift the anchors rather than dragging them across the seabed. Where there are species that are particularly sensitive to increases in suspended sediment occurring close to positions of cable burial, it is recommended that 109
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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
Page 140 and 141: 6 Good practice measures This secti
Page 142 and 143: 7 Gaps in understanding Research fo
Page 144 and 145: References Introduction Sinden, G.
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Printed in UK on recycled paper. De
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