modelled values of the magnetic field strengths from AC and DC cables assumed a 1m burial depth.
Table 11.29 Averaged magnetic field strength values from AC and DC cables buried 1 m (Normandeau et al. 2011)
Distance (m) above sea bed
0 5
10
0m AC 7.85 0.35 0.13
0m DC 78.27 2.73 0.83
Magnetic Fields Strength (µT) Horizontal distance (m) from cable 4m AC 1.47 0.29 0.12
4m DC 5.97 1.92 0.74
10m AC 0.22 0.14 0.08
10m DC 1.02 0.75 0.46
225. The areas affected by EMFs generated by the worst case scenario cabling associated with the East Anglia THREE project are expected to be small, being limited to the area of the East Anglia THREE windfarm site and the offshore cable corridor, restricted to the immediate vicinity of the cables within the range of metres. In addition, EMFs are expected to attenuate quickly in both the horizontal and vertical planes with distance from the source. The magnitude of the effect therefore considered to be low.
226. With regards to receptor sensitivity, a number of organisms in the marine environment are known either to be sensitive to electromagnetic fields or have the potential to detect them (Gill & Taylor 2001; Gill et al. 2005). These organisms can be categorised into two groups based on their mode of magnetic field detection, which may be induced electric field detection or direct magnetic field detection.
227. The first group are those species that are electro-receptive, the majority of which are elasmobranchs (sharks, skates and rays), although it also includes holocephalans (chimaeras, e.g. ratfish) and agnathans (i.e. lampreys). These can detect the presence of a magnetic field either indirectly by detection of the electrical field induced by the movement of water through a magnetic field or directly by their own movement through that field. The magnetic field could be the Earth’s geomagnetic field or a magnetic field produced by a power cable. In natural scenarios, induction of the electric field usually results from organisms positioning themselves in tidal currents and animals may time activities such as foraging or migration by detecting diurnal cues resulting from varying tidal flows.
228. The second group is believed to use magnetic particles (magnetite) within their own tissues in magnetic field detection (Kirshvink 1997). Whilst the exact mechanism of
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 11 Fish and Shellfish Page 75
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