Review of Cabling Techniques and Environmental Effects Applicable

Review of Cabling Techniques and Environmental Effects Applicable to the Offshore Wind
Farm Industry – Technical Report
introduction of an essentially ‘alien’ substrate cannot be considered as a beneficial
impact. As previously mentioned, another alternative is to use concrete or frond
mattresses as a protective measure for cables. Frond mattresses will encourage
the accumulation of sediment and, in an area that comprises soft sediments this
is likely to be preferable as it is more in keeping with the natural environment.
Mobile species, in the vicinity of the cable route and inter-array area, may avoid
the footprint of the impact. Sessile species, however, would be damaged or killed
during excavation through direct contact with the installation device, burial and
dislodgement. The significance of the impact would depend on a number of
factors including:
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The nature and geology of the seabed where the cable is to be laid. The
geology needs to be ascertained to at least the depth of cabling to ensure
that where sediments overlay bedrock within the depth of cabling activity, the
effect of cabling through all habitat types is assessed;
The nature of the assemblage of species within the footprint of the works (e.g.
species abundance, richness and diversity in the study area, and the value
of this assemblage in the context of the wider seabed area within which the
cabling operation is to occur); and
The sensitivity, importance and recoverability of the species/communities
including any seasonal variation e.g. spawning activity and over-wintering
species.
In terms of the recovery of the seabed following disturbance, studies have shown
that initial recolonisation takes place rapidly following a disturbance event with
certain species returning almost immediately to the disturbed site. The length of
time taken for recovery will be dependent on a number of characteristics including
the nature of the seabed, the community types present, the duration and footprint
of the proposed activity and the degree of disturbance already experienced at
the site. There are a number of activities that can cause disturbance including
severe storms, bottom fishing and aggregate extraction. Studies have shown
that in shallow water and estuarine environments where disturbance is more
frequent and opportunistic species are more likely to dominate the community
structure, recovery occurs rapidly whereas in deeper water undisturbed areas
the recovery to a more stable community could take many years. The degree
of existing disturbance is therefore of importance in assessing this effect and in
deeper water environments the impact of other activities, such as fishing, should
be taken into consideration.
Rates of recovery of invertebrate communities appear to be associated with the
rate of recovery of the seabed sediment characteristics. Experiments undertaken
to record recovery given different intensities of disturbance revealed that when
sediment was removed to a depth of 10cm recovery of the faunal component
occurred within 64 days of the disturbance. However, when sediment was
removed to 20cm depth, recovery was not complete until after 107 days but had
occurred within 208 days of the disturbance. Thus recovery at more intensely