Review of Cabling Techniques and Environmental Effects Applicable

7 Gaps in understanding
Research for this report has highlighted a number of gaps in available data
and in understanding of the actual impacts resulting from cable burial activities
associated with the offshore wind farm industry. The general lack of understanding
is due to the physical and biological effects of cable burial being very site
specific, particularly with regard to sites with different sediment characteristics.
What makes this even more difficult to interpret is that the majority of sites will
experience a large variation of sediment types along the cable routes. There has
also been a deficit in the monitoring of cable burial activities in the past as the
impacts are regarded as secondary in terms of scale when compared with those
from the installation and operation of the wind turbines.
There is limited centralised knowledge sharing both with the offshore wind farm
industry and from other more established marine cabling industries such as
subsea telecommunications and the oil and gas sector. Information that does
exist is not widely disseminated, reviewed or synthesised for a wider audience
or made publicly available.
There is limited documentation and research carried out to date on the
quantification of material disturbed and brought into suspension from cable
burial operations, in particular, from burial methods using jetting, cutting,
dredging and excavating tools. This lack of basic information on the volumes of
sediment brought into suspension limits the potential of modelling techniques
and establishing the fate of sediment plumes. Research from other industries
can be used for predicting potential effects but the scale of impacts is quite
different (as identified in Section 4.4) and the effect will depend on the sensitivity
of the receptor and the site conditions. Should the generation of a sediment
plume be considered to be an area of concern, in situ monitoring of a number
of different techniques and tools in one location, together with further plume
modelling would be required in order to draw comparisons under the same site
specific conditions. Confidence in the modelling could be attained by comparing
predicted versus in situ results. The sediment monitoring requirements included
in FEPA licences for UK Round 1 and potentially Round 2 offshore wind farm
applications will also provide valuable data for the quantification of the impact
of cable burial operations.
In addition, there is a general lack of understanding of the biological response
to sediment plumes, arising from any activities that disturb the seabed, such
as the sensitivity and tolerance of species and habitats to different levels of
sediment plumes and different plume durations. Additional research in this area
is therefore necessary in order to further this knowledge base to enable accurate
predictions of sensitivity to be determined. There are, however difficulties in
undertaking research to fill these gaps such as the problem associated with
site specific differences changing the scale of the effects and the adaptability of
species in different environments and at different times of the year. Targeted
research involving the testing of different cable burial devices and tools in the
same conditions (seabed types, wave and tidal conditions) could overcome
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