Review of Cabling Techniques and Environmental Effects Applicable

Review of Cabling Techniques and Environmental Effects Applicable to the Offshore Wind
Farm Industry – Technical Report
particular significance, given that each of these animals is afforded a high level
of individual protection under a suite of national and international legislation
and signatory agreements 3 (Defra, 2005). As such, potential adverse impacts
upon a single individual of a species of marine mammal must be considered as
being of significance and, therefore, there is a requirement to apply practicable
and financially feasible mitigation measures in order to be compliant with the
legislation (in particular, the Habitats Directive).
5.6.1 POTENTIALLY SIGNIFICANT EFFECTS
Cable laying operations have the potential to impact upon marine mammals
through:
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Collision with the vessel or support vessels;
Noise and visual disturbance from the vessel and cable burial system;
4 Contact with any fuels and chemicals that may be accidentally released
during the operation; and
Interactions or entanglement with the cable or other lines between the vessel
and the installation tool.
Collision risk
While there are no accurate records of the number of incidents of accidental
collisions between marine mammals and shipping in UK waters (e.g. Hammond
et al., 2003), it is considered that a direct relationship exists between shipping
intensity, vessel speed and the number and severity of collisions, certainly in the
case of whales (Laist et al., 2001). Certain assumptions can be made about the
risk of collision with marine mammals (Sakhalin Energy Investment Company
Limited, 2005; Laist et al., 2001):
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All types and sizes of vessels can hit marine mammals;
Vessels over 80m in length cause most severe or lethal injuries;
Serious injuries to mammals rarely occur if struck by vessels travelling at
speeds of less than 10 knots;
Mammals struck by vessels are usually not seen prior to impact, or are seen
too late to avoid impact; and
The risk of collision increases in poor visibility.
Collisions between marine mammals and the cable burial vessel are considered
to be unlikely. The cable burial vessel whilst working in the shallow water
locations, is likely to only make very slow progress while laying and burying
cable, with a burial rate of 1000m of installed cable per hour and therefore would
4 Such accidental releases are likely to be similar in extent, duration and significance as for other parameters and is
not discussed in this section.