Review of Cabling Techniques and Environmental Effects Applicable

Review of Cabling Techniques and Environmental Effects Applicable to the Offshore Wind
Farm Industry – Technical Report
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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:
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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;