Review of Cabling Techniques and Environmental Effects Applicable
Review of Cabling Techniques and Environmental Effects Applicable
Review of Cabling Techniques and Environmental Effects Applicable
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<strong>Review</strong> <strong>of</strong> <strong>Cabling</strong> <strong>Techniques</strong> <strong>and</strong> <strong>Environmental</strong> <strong>Effects</strong> <strong>Applicable</strong> to the Offshore Wind<br />
Farm Industry – Technical Report<br />
introduction <strong>of</strong> an essentially ‘alien’ substrate cannot be considered as a beneficial<br />
impact. As previously mentioned, another alternative is to use concrete or frond<br />
mattresses as a protective measure for cables. Frond mattresses will encourage<br />
the accumulation <strong>of</strong> sediment <strong>and</strong>, in an area that comprises s<strong>of</strong>t sediments this<br />
is likely to be preferable as it is more in keeping with the natural environment.<br />
Mobile species, in the vicinity <strong>of</strong> the cable route <strong>and</strong> inter-array area, may avoid<br />
the footprint <strong>of</strong> the impact. Sessile species, however, would be damaged or killed<br />
during excavation through direct contact with the installation device, burial <strong>and</strong><br />
dislodgement. The significance <strong>of</strong> the impact would depend on a number <strong>of</strong><br />
factors including:<br />
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104<br />
The nature <strong>and</strong> geology <strong>of</strong> the seabed where the cable is to be laid. The<br />
geology needs to be ascertained to at least the depth <strong>of</strong> cabling to ensure<br />
that where sediments overlay bedrock within the depth <strong>of</strong> cabling activity, the<br />
effect <strong>of</strong> cabling through all habitat types is assessed;<br />
The nature <strong>of</strong> the assemblage <strong>of</strong> species within the footprint <strong>of</strong> the works (e.g.<br />
species abundance, richness <strong>and</strong> diversity in the study area, <strong>and</strong> the value<br />
<strong>of</strong> this assemblage in the context <strong>of</strong> the wider seabed area within which the<br />
cabling operation is to occur); <strong>and</strong><br />
The sensitivity, importance <strong>and</strong> recoverability <strong>of</strong> the species/communities<br />
including any seasonal variation e.g. spawning activity <strong>and</strong> over-wintering<br />
species.<br />
In terms <strong>of</strong> the recovery <strong>of</strong> the seabed following disturbance, studies have shown<br />
that initial recolonisation takes place rapidly following a disturbance event with<br />
certain species returning almost immediately to the disturbed site. The length <strong>of</strong><br />
time taken for recovery will be dependent on a number <strong>of</strong> characteristics including<br />
the nature <strong>of</strong> the seabed, the community types present, the duration <strong>and</strong> footprint<br />
<strong>of</strong> the proposed activity <strong>and</strong> the degree <strong>of</strong> disturbance already experienced at<br />
the site. There are a number <strong>of</strong> activities that can cause disturbance including<br />
severe storms, bottom fishing <strong>and</strong> aggregate extraction. Studies have shown<br />
that in shallow water <strong>and</strong> estuarine environments where disturbance is more<br />
frequent <strong>and</strong> opportunistic species are more likely to dominate the community<br />
structure, recovery occurs rapidly whereas in deeper water undisturbed areas<br />
the recovery to a more stable community could take many years. The degree<br />
<strong>of</strong> existing disturbance is therefore <strong>of</strong> importance in assessing this effect <strong>and</strong> in<br />
deeper water environments the impact <strong>of</strong> other activities, such as fishing, should<br />
be taken into consideration.<br />
Rates <strong>of</strong> recovery <strong>of</strong> invertebrate communities appear to be associated with the<br />
rate <strong>of</strong> recovery <strong>of</strong> the seabed sediment characteristics. Experiments undertaken<br />
to record recovery given different intensities <strong>of</strong> disturbance revealed that when<br />
sediment was removed to a depth <strong>of</strong> 10cm recovery <strong>of</strong> the faunal component<br />
occurred within 64 days <strong>of</strong> the disturbance. However, when sediment was<br />
removed to 20cm depth, recovery was not complete until after 107 days but had<br />
occurred within 208 days <strong>of</strong> the disturbance. Thus recovery at more intensely