10.14. Transboundary Effects

  1. A screening of transboundary impacts has been carried out and has identified that there were no likely significant transboundary effects with regard to marine mammal receptors from the Array upon the interests of EEA states.
  2. Potential transboundary effects could occur where elevations in underwater sound, particularly during construction piling, could ensonify large areas causing wide-ranging disturbance of marine mammals. The closest transboundary state, Norway, is 151.8 km away and therefore would not overlap with the zone of influence predicted for the Array. In addition, the underwater sound modelling is highly precautionary, and it is considered highly unlikely that sound propagating at tens of kilometres from the Array would be detected above background levels. For example, considering the NMFS threshold of 160 dB re 1 μPa (rms) for strong disturbance, the disturbance range for all marine mammals is out to a maximum of ~11 km from the Array. Even for harbour porpoise, as the most sensitive species, the 143 re 1µPa2s SELss threshold for significant disturbance extents out to ~46.5 km from the Array and therefore does not reach the nearest EEA border. Whilst marine mammals are highly mobile and there is potential for individual animals to cross into EEA states, it is considered unlikely that piling would lead to significant transboundary effects.
  3. For the assessment of injury and disturbance from UXO clearance a precautionary 100 km screening buffer area was used, whilst for site-investigation surveys, vessel use and other noise producing activities, collision, operational noise and entanglement a buffer of 50 km was used. For effects on marine mammals due to EMFs from subsea electrical cabling in the water column, given the localised effect and transient nature of marine mammals a 10 km buffer was used. Therefore, given the closest transboundary EEA state is 151.8 km away, these effects are unlikely to have any interactions with transboundary sites, and it is concluded that there would be no likely significant transboundary effects with regard to marine mammal receptors from the Array.