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 />
a negative impact for commercial fisheries, the introduction <strong>of</strong> hard substrate<br />
creates habitat diversity, which can benefit some commercial resources e.g.<br />
crustacean fisheries.<br />
Mobilised sediment may settle on fishing gear (e.g. mon<strong>of</strong>ilament gill nets)<br />
<strong>and</strong> reduce their efficiency. The significance <strong>of</strong> this depends on background<br />
turbidity levels <strong>and</strong> given the dynamic hydrographic conditions <strong>of</strong> much <strong>of</strong> the<br />
UK coastline this is likely to be insignificant.<br />
Snagging<br />
The extent <strong>of</strong> the physical disturbance to the seabed along the cable route will<br />
depend on the prevailing geological conditions, which determine the cable<br />
installation techniques that can be used. For s<strong>of</strong>t sediment, natural infilling<br />
or assisted infilling by the cable burial tool should ensure that no debris to<br />
potentially snag a fishing net is left on the seabed. However in rocky substrata<br />
or in clay, chunks <strong>of</strong> debris could potentially cause fishing nets to snag.<br />
Snagging can also occur where stretches <strong>of</strong> cable are exposed for example<br />
over rocky substrata, spanning s<strong>and</strong> waves or at any location where cable is<br />
surface laid prior to any post lay burial operation. However, there should not be<br />
a problem for the latter point, as the fishermen should be respecting exclusions<br />
zones until all cable burial operations are complete. Shifting sediment can also<br />
expose previously buried sections <strong>of</strong> cable.<br />
Seabed hazards resulting from the trenching <strong>of</strong> the cable route, including any<br />
exposed sections <strong>of</strong> the cable itself, can interfere with benthic fishing gear,<br />
particularly beam trawl, otter trawl <strong>and</strong> drift netting. Static gear also has the<br />
potential to become snagged on subsea cables. The small 1m long anchors used<br />
by inshore vessels to secure static gear are found to penetrate s<strong>and</strong> to a depth <strong>of</strong><br />
around 0.2m (less in coarser sediments). These may drag in strong currents <strong>and</strong><br />
become snagged on cable. The risk lies in attempting to recover the gear, which<br />
is <strong>of</strong>ten through the use <strong>of</strong> grappling hooks. The cable route assessment should<br />
however take on board all <strong>of</strong> these potential hazards <strong>and</strong> the design depth <strong>of</strong><br />
burial for the cables should provide suitable mitigation against the measured<br />
risks.<br />
Danger arises where vessels, unknowingly snagged on a cable attempt to heave<br />
the gear free from the seabed obstruction. This can lift the cable clear <strong>of</strong> the<br />
seabed, exposing more cable that causes a significant downward pull from the<br />
weight <strong>of</strong> cable.<br />
The recovery <strong>of</strong> snagged gear is not recommended <strong>and</strong> fishing operations will<br />
be compensated by cable operators if provided with evidence <strong>of</strong> such instances.<br />
Such claims are only compensated providing that the fishermen have not<br />
operated within restricted fishing or anchorage zones.<br />
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