Page 103 - Alderney Regional Environmental Assessment of Renewable Energy: Environmental Report

Alderney Regional Environmental Assessment of Renewable Energy:
Environmental Report
5.3.2.10Electromagnetic field
Electromagnetic fields (EMF) arise from the power cables associated with tidal energy power
cabling as a result of the current passing along the conductor and the voltage differential
between the conductor and earth ground, which is nominally at zero volts. The nature and
strength of the fields produced, depends on the system voltage and the current passing
through. The effects on the surrounding environment depend on the cable construction,
configuration and orientation in space.
Export cables from tidal devices transmitting high voltage alternating current (AC) and direct
current (DC) generate an EMF comprising two components: firstly, an electric field contained
within the cable by armouring and, secondly, a magnetic field that can be detected outside of
the cable (Gill, 2005). The EMF levels generated are typically well below those detectable by
humans, but many species of fish are electrosensitive and rely upon subtle bioelectrical
emissions in the marine environment in order to catch prey and avoid predators. Research by
COWRIE and Scottish Natural Heritage indicates that electro-sensitive species of fish,
particularly elasmobranches, can detect the levels of induced electric field generated by a
cable. Other fish species such as salmon, eels and sea trout may also be able to detect the
magnetic fields associated with cables, depending on cable design. The overall impact on fish
populations associated with EMF from cables is uncertain (Gill, 2005). The resulting
behavioural responses could include avoidance of the area, attraction towards the export cable
or disruption of migratory patterns.
Based on the limited information available, sensitivity is considered to be at worst moderate
and due to the limited area potentially affected, as a result of the cabling required for a single
tidal array, exposure is considered to be low resulting in an insignificant to minor adverse
impact. A minimum of approximately 367km of cable length will be required for the full build out
of the Draft Plan (see Section 2.2.2). Overall, this is considered to result in a moderate level of
exposure to change and an insignificant to moderate adverse impact.
5.3.2.11 Mitigation
The following mitigation works will need be applied, as appropriate, to minimise any potentially
significant (i.e. moderate or major) impacts of the Draft Plan on fish and shellfish:
Collision/Entrapment Risk:
ƒ Undertake iterative reviews of the Draft Plan taking account of information available
from other trial deployments elsewhere and monitoring data collected during
implementation of early developments under the Plan. Co-operation with regulators in
France and the Channel Islands should be pursued to ensure that as much as possible
can be learnt from early deployments of tidal energy devices.
Noise/Vibration Disturbance:
ƒ Avoid construction during sensitive seasons, e.g. breeding/peak egg laying/spawning
seasons, in feeding grounds and during migration times of migratory fish;
ƒ Good construction practice to minimising noise and vibration; and
ƒ Minimise use of high noise emission activities such as piling.
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