ENVIORNMENTAL

Noise (And Other Issues)

Environmental issues related to installing flexible mooring lines and CoRMaT device



Although tidal energy devices are considered as "green energy" it is important to point out the negative impact of such devices on the environment.
Different types of impact relate to different stages of the process [Brian Polagye et al, 2010]:

Installation:

  • Seabed disturbance - direct impact on benthic organisms,
  • Increased traffic and therefore increased risk of collision,
  • Water quality change (due to contamination from antifouling paints and accidental release of hydraulic fluids
  • Noise, depending on the type of installation but can exceed the hearing threshold for many of the marine creatures

    • Operation:

  • Collision risk
  • The risk of interfering with nursery/migratory routes
  • Contamination
  • Electromagnetic field interference for EMF sensitive fish
  • Noise



    • Summary of Effects on Marine Life is represented in the table below: [The Scottish Government, 2007]

    Noise seems to be one of the main areas of concern related to offshore devices. This is because vision, touch, smell and taste are limited underwater so most forms of marine life use sound as their primary mode of communication. Noise impact during the operational phase of CoRMaT turbine will cause disturbance and detraction for the marine animals, which, in turn will lead to habitat loss and avoidance but wonÕt cause any injuries or hearing loss. It also has been noticed in some studies that marine animal are trying to avoid the source of noises below PTS and TTS thresholds which can have a significant impact on feeding in case of arrays because the areas will be avoided altogether even if there is enough space to swim in between the devices.

    Terminology:

  • PTS - permanent threshold shift or permanent hearing loss
  • TTS - temporary threshold shift or temporary hearing loss
    • During the operational phase pile driving is the most brutal type of installation from the noise point of view. During this phase the pressure level can reach up to 250 dB re 1microPa1(2-3 times hire than hearing threshold), which can lead to PTS or TTS depending on the distance from the object and time of influence.
    In-water threshold of hearing for fish, man, and marine mammals is represented below [Scottish Marine Renewables, 2007]

    In conclusion, we have developed some recommendations with regards of minimising the risk of environmental impact.