Review of Cabling Techniques and Environmental Effects Applicable

Review of Cabling Techniques and Environmental Effects Applicable to the Offshore Wind
Farm Industry – Technical Report
zone is very likely to be undertaken during periods of low tide, and as such the
potential for resuspension of material is reduced. Some of the disturbed material
will, however enter into suspension during the flood tide but the extent of this
will depend on the sediment type and cohesiveness. Resuspension of sediment
is not likely to be of concern where cabling occurs within cohesive or coarse
sediments, but can be significant when cabling is undertaken in non-cohesive
fine sediments or chalks. Potential effects of suspended sediment are detailed
in Section 5.2.2.
Within fine sediments there are also issues to consider in relation to potential
contaminant release. Contaminants, such as oils and heavy metals, generally
attach to fine sediments but certain chemicals can persist in coarser sediments.
Disturbance of sediment can release associated contaminants into the water
column. If contaminants reach a certain level they can cause effects on certain
species or can bioaccumulate through the food chain. However, the effects of
contaminant release on the environment tend to be localised and would only be of
concern near industrialised areas. Investigation of potentially contaminated sites
that may lie within the cable route would be considered during the screening and
scoping phase. If nearby sites are identified where there is evidence of historic
contamination, sediment sampling will be necessary in order to determine the
level of concentration within the sediment. Predictions can then be made as to
whether the release of contaminants could have an adverse effect.
Settlement of material
Settlement of suspended material has the potential for smothering to occur
that could cause the burial of important or sensitive species and habitats (see
Section 5.2.2). Given that the installation generally occurs during low tide, it is
only likely to be the fine sediments that have been disturbed, which may become
suspended in the water column during the flood tide.
5.3.3 MITIGATION MEASURES
Access to a site requires careful planning to avoid any sensitive features, which
can be marked to ensure effective avoidance by construction plant and staff.
Such features include rare or notable plants for example on shingle banks or
saltmarsh, the presence of biogenic reef areas and the presence of important
sessile (non-mobile) communities or species. Vegetated shingle areas should be
avoided, or a process of translocation agreed.
Horizontal directional drilling (within Section 3.8.6) is an appropriate form of
mitigation to avoid damage, particularly in the intertidal and landfall areas
where habitats may be more sensitive (e.g. chalk cliffs, saltmarsh, etc.). This
methodology has been proposed for the Thanet offshore wind farm due to the
inter alia geological features of the area and the presence of saltmarsh habitat
(Thanet Offshore Wind, 2005).
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