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2 thoughts on “Tidal power supply coming to Puget Sound

  1. If these two tidal turbines are placed in Admiralty Inlet they will create noise and an obstruction to travel. Both should be avoided if possible, so from the point of view of the orcas and other marine life it would be better if they were not put there. If the project is built out and dozens of turbines are placed in Admiralty Inlet the noises and obstructions could become significant, and other effects could become serious, including reducing tidal currents and therefore reducing the flushing of Puget Sound, which could increase pollution levels.

    These are issues to worry about, and the project is without precedent so these are predicted estimates, but these two turbines are not expected to generate more noise that the average, every day background ambient noise levels at that location. The turbines are expected to generate about 120 dB, which will dissipate and be masked by ambient noises beyond a few hundred meters.

    The only mention of 180 dB in the FERC license is: “The terms and conditions require Snohomish PUD to: (1) cease operating and obtain NMFS approval to resume operations if sound levels exceed 180 dB any distance from the turbines or if sound levels of 120 dB propogate to a distance of 750 meters or more from the turbines; ”

    Quoting the FERC license:

    p. 43 –
    In regard to turbine noise, the EA concluded that the nature of the noise coming from the relatively slow turbines and passive mechanics was not likely to harm or displace whales or fish.[1] Staff determined that outside of a few hundred meters from the operating turbines, the chance of marine mammals, including killer whales, from distinguishing the turbines from background noise was less than 25 percent.

    p. 44 –
    If the maximum allowable area of 750 meters around the turbines was affected by noise emanating from the project, that affected area would occupy less than 15 percent of the cross section of Admiralty Inlet, leaving the remainder of the inlet available for whale passage or foraging. If killer whales were to respond negatively to noise levels, a behavioral change of this degree will not have a detrimental energy cost to a highly mobile killer whale.

    Northwest National Marine Renewable Energy Center
    University of Washington, Seattle, WA 98195
    Estimated Received Noise Levels for Marine Mammals from
    OpenHydro Turbines in Admiralty Inlet, Washington
    Technical Report: UW-2011-01
    January 2011
    Mean ambient noise levels in the project area are 117 ± 3 dB re 1 Pa. Broadband noise levels rarely (< 2.5% of the time) fall below 100 dB re 1 Pa and rarely (1/2 mile away from the turbines) would mask the turbine noise most of the time. Orca calls are also typically louder than the noise the turbines will generate. Holt et al. (2007) studied noise effects on the call amplitude of southern resident killer whales and found that with increasing background noise,source level increased, ranging from 130-160 dB re1 Pa.

    Howard Garrett

  2. This article acknowledged concern from tribal fishers but does not address at all any adverse impacts upon other waterway users such as recreational boaters and fishers. Will there be total exclusionary zones? Will there be no fishing zones as 15 pound downrigger weights might not be compatible with turbine blades (despite the 150 installation depth the size of the turbine and mounting base could put the top at 100-120 feet which is clearly within trolling depth)? And is there a risk to fishers if their gear were to become entangled in the turbines?

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