Review of Cabling Techniques and Environmental Effects Applicable
Review of Cabling Techniques and Environmental Effects Applicable
Review of Cabling Techniques and Environmental Effects Applicable
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Potential impacts <strong>and</strong> mitigration measures<br />
There are two mechanisms by which fish <strong>and</strong> shellfish may be displaced from<br />
the installation area. One is direct avoidance <strong>of</strong> the burial site in response to<br />
noise, the turbidity plume or both. This will be a local effect <strong>of</strong> short duration that<br />
will cease once the cable has been installed (see Sections 4.3 <strong>and</strong> 4.4). The other<br />
is in response to sea bed habitat alteration that may well downgrade the cable<br />
route as a feeding area. Due to the short duration <strong>of</strong> construction activity <strong>and</strong> the<br />
small width <strong>of</strong> habitat affected by cable laying, the likely impact on commercial<br />
fishing is expected to be small.<br />
The temporary displacement <strong>of</strong> fish stocks through disturbance or habitat<br />
alteration is predicted in the <strong>Environmental</strong> Statements for the Horns Rev <strong>and</strong><br />
the Nysted wind farms, Denmark. The short term nature <strong>of</strong> this impact has been<br />
corroborated by subsequent monitoring studies. The most recent monitoring<br />
report available from 2004 concludes for Nysted that:<br />
“the direct <strong>and</strong> indirect impacts <strong>of</strong> the earthwork [conducted from September<br />
2002 to February 2003] on eelgrass, macroalgae <strong>and</strong> invertebrates were<br />
limited in space <strong>and</strong> time <strong>and</strong> a full recovery <strong>of</strong> the populations close to<br />
the cable trench is expected in the near future.” (Elsam Engineering &<br />
ENERGI E2, 2005).<br />
For Horns Rev, which forms part <strong>of</strong> Denmark’s important commercial s<strong>and</strong>eel<br />
fishery, the 2004 monitoring report found that “There is no indication that<br />
the construction <strong>of</strong> the wind farm has had a marked effect on the sediment<br />
composition in the wind farm area. There was no indication <strong>of</strong> an increase in<br />
the content <strong>of</strong> silt/clay <strong>and</strong> very fine s<strong>and</strong> in the impact area from 2002 to 2004.<br />
S<strong>and</strong>eels are very sensitive to changes in the content <strong>of</strong> these sediment sizes <strong>and</strong><br />
will completely ab<strong>and</strong>on the area if the weight fraction <strong>of</strong> the silt/clay content<br />
rises above 6%.” Sediment movement resulting from cable laying was found to<br />
be insignificant in the relatively dynamic environment <strong>of</strong> the wind farm.<br />
There is concern amongst the fishing industry <strong>of</strong> the potential impacts on fish<br />
stocks <strong>of</strong> EMF emitted by operating power cables (see Section 5.4). This is<br />
particularly important to small vessel operators as these vessels have a limited<br />
operating area from their home port <strong>and</strong> therefore may be unable to still target<br />
highly displaced resources. Monitoring <strong>of</strong> the earliest-established <strong>of</strong>fshore<br />
wind farms, Horns Rev <strong>and</strong> Nysted, have to date found no significant impact <strong>of</strong><br />
either the export cable or the inter-array cables on fish stock displacement. The<br />
creation <strong>of</strong> significant areas <strong>of</strong> hard substrate through placement <strong>of</strong> the turbines<br />
<strong>and</strong> associated rock armour has, however, led to a changed (moderately<br />
increased) epibenthic productivity (macroalgae <strong>and</strong> benthic invertebrates) that<br />
has attracted commercial fish species within the turbine array. There has been<br />
no reported reaction <strong>of</strong> these fish species to the presence <strong>of</strong> cables with localised<br />
emissions <strong>of</strong> EMF.<br />
The permanent alteration <strong>of</strong> the seabed will be most pronounced with the use<br />
<strong>of</strong> rock dumping to protect cables when burial is not feasible <strong>and</strong> the installation<br />
<strong>of</strong> concrete mattresses at cable crossings. While this is seen as predominantly<br />
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