East Anglia ONE
EMF Assessment
B fields upon the same species, nor upon the round crab (Rhithropanopeus harrisii), an isopod (Saduria entomon) or the mussel (Mytilus edulis). Equally, demonstrations of B fields ranging between 1-100µT delaying embryonic development in sea urchins (Zimmerman et al 1990), and of high frequency AC EMF causing cell damage to barnacle larvae and interfering with their settlement (Leya et al 1999), contrasts with anecdotal evidence of benthic invertebrates living directly upon DC electrodes (Nielsen 1986) with no apparent effects (Walker 2001; Swedpower 2003). No similar information exists for invertebrates living upon or over AC cables, as far as CMACS is aware, other than diver observations of some algae and anemones colonising an exposed J-tube2 (Bunker 2004). The J-tube was otherwise bare, but this may have been due to scour. It would seem, therefore, that DC B fields cause fewer biological effects upon these taxa than AC B fields, although this assumption should be made tentatively owing to the sheer lack of relevant studies.
A number of marine invertebrate species that inhabit the southern North Sea are magnetically sensitive, including important commercial taxa (Parker-Humphreys 2004). Site specific surveys undertaken at the EAONE project area recorded lobster, edible crabs and squid (MESL 2010 & 2011), and International Beam Trawl Survey Data (IBTS) also recorded brown shrimp and cockles (DATRAS 2011) in the relevant ICES rectangles (33F1, 33F2 & 32F1). Surveys undertaken by CMACS at nearby wind farm sites (Gabbard and London Array) also recorded brown shrimp, many crabs (including some edible), queen scallops, common whelk, edible mussel, cuttlefish and squid (CMACS 2005; RPS 2005).
B fields expected to be generated by AC cables within the EAONE site (assumes array and HVAC export cables of 33kV to 220kV) will be below background geomagnetic field magnitude (assuming burial of greater than 0.5m). Should the cutting edge 275kV cables be used (which is unlikely), the B fields are more likely to reach background levels, especially if they are deployed separately, whereby markedly stronger fields are likely to be generated.
Background levels will be reached by B fields generated by all HVDC designs likely to be utilised at EAONE, but will attenuate below the geomagnetic field at distances of approximately 1m (bundled) and 5m (separated) for 320kV cables, a few meters (bundled) and 10m (separated) for 500kV cables and slightly further still for 600kV cables (bundled and separated). The deeper cables are buried, the weaker the B fields encountered by most marine fauna will be (except borrowing species such as polychaetes and bivalve molluscs). Bundling cables, rather than utilising separation deployment, will also markedly reduce the distance at which organisms are likely to encounter B fields stronger than the background field. Where cables are covered with rocks or mattresses, invertebrates are highly likely to colonise any interstitial spaces, and may therefore come into direct contact with the cables. They could therefore potentially be exposed to strong B fields of approximately 5000µT or more when considering HVDC cabling.
In summary, the potential for effects upon invertebrates’ navigation and/or for physiological effects may therefore exist within tens of meters of separated HVDC
2 J-tubes convey AC cables away from wind turbines; they are normally buried, but had apparently been exposed by scour in this case.
J3184 EAONE v2 25
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