| Clean Current and the Environment The 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, every effort will be employed to mitigate the effects of drilling and/or blasting on the surrounding ecosystem. Pile driving best practices will be followed including the use of shock wave monitoring (hydrophone) or bubble curtains as required. Work will be scheduled on the seabed and on the land to avoid seasons of wildlife nesting and migration. The permanent footprint of the unit will be minimal, as the tidal generators will be supported on a single pile fastened to the bedrock. As installations occur in areas of high tidal currents, it is also an area rich in nutrients. Any damage caused during the installation of the piles will be quickly regenerated. The electrical cables from the unit will come onto the land through a hole drilled below the inter-tidal zone; therefore avoiding any interference with this sensitive zone. There are several potential environmental concerns that arise during the operation of a tidal turbine. The effects on the regional tidal ecosystem with regards 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) an acoustic sensor in the inlet to lock the rotor if a large object enters the duct and c) 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; however, sound attenuation panels (closed cell foam) will be installed in the duct structure. 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. |