Review of Cabling Techniques and Environmental Effects Applicable

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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 140
Gaps in understanding part of this problem but the different levels of adaptability of species will need to be assessed on each occasion. This more generalised research requirement is much wider ranging than is necessary for cable burial alone as it involves a number of industries with an interest in the marine environment. The need for further studies and monitoring to investigate the potential impacts needs to be put into context with the amount of sediment that is put into suspension during cabling in comparison to other activities (i.e. certain fishing techniques and dredging activity) and natural events (i.e. severe storms). 141
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REVIEW OF CABLING TECHNIQUES AND EN
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Review of Cabling Techniques and En
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Abbreviations AIS Automatic Identif
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TTS Temporary Threshold Shift TWA T
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3 Cable types and 18 installation t
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4 Physical change 4.1 Introduction
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