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Clean Current and the Environment
The
potential impact of Clean Current’s tidal turbine technology on marine life
can be divided into impacts created by the deployment phase and
impacts due to the operation of the unit. During the deployment
phase of the Race Rocks Project, every effort was employed to mitigate the effects of drilling
on the surrounding ecosystem. Pile driving best practices were
followed and
drill cuttings were collected and then transported back to the
mainland for disposal. Work was
scheduled on the seabed and on the land to avoid seasons of wildlife
nesting and migration. The permanent footprint of the unit on the
seabed is minimal, as the tidal generator is supported on a single
32” diameter pile grouted into the bedrock. As installations
will occur in areas of high tidal currents, it is also an area rich in
nutrients. Any damage caused during the installation of the pile
is likely to regenerate quickly.
There are several potential
environmental concerns that arise during the operation of a tidal
turbine. The effects on the regional tidal ecosystem with regard
to sediment suspension and deposition have been analyzed for large
tidal farm installations by Triton Consultants¹ and found to be
negligible. Clean Current has employed several features to mitigate
the risk of potential injury to marine mammals due to the rotation
of the turbine blades. Key features are: a) a large central hole
(over 1 metre diameter for the ¼ scale demonstration unit) that
provides a safe passage through the unit; b) fixed guide vanes both upstream and down
stream of the rotor. Small floating sea life such as jellyfish may
flow through the blades and be damaged.
The unit has been designed to
rotate only when the current velocities exceed 2 knots (1 m/s). This
minimum operation velocity means that the rotor is spinning about
two thirds of the time at a typical tidal current location
(including Race Rocks). Another concern is the impact of the
acoustic signature on fish and cetaceans in particular. The rotation
speed of the turbine varies between 20 and 70 rpm depending on
current speed and unit size. As a result, a very low frequency noise
(<100 Hz) will be produced. Cetaceans are not sensitive to low
frequency noise (peak sensitivity for Killer Whales is 20 kHz) and
their echo communication is at a much higher frequency (10-80 kHz).
The amplitude of the sound is anticipated to be low. A detailed
acoustic signature of the unit will be performed shortly after
deployment.
¹”Green Energy Study for British Columbia, Phase 2: Mainland,
Tidal Current Energy”, Triton Consultants Ltd., October 24, 2002
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