installation of the offshore cabling has the potential to disturb sediments from the sea bed surface to depths of up to 5m over a width of 10m. The assessment of changes in suspended sediment concentrations during offshore export cable installation has been considered in Chapter 7 Marine Geology, Oceanography and Physical Processes.
194. Overall sediment release volumes are predicted to be low and confined to near the sea bed (rather than higher in the water column) along the alignment of the offshore export cables, and the rate at which the sediment is released into the water column from the jetting process would be relatively slow. Sand sized particles would settle out within 1km of the jetting operations whereas mud particles would be advected a greater distance and persist in the water column from hours to days.
195. In water depths greater than 20mLowest Astronomical Tide (LAT), peak suspended sediment concentrations would be typically less than 100mg/l, except in the immediate vicinity of the release location.
196. In shallow water depths nearer to shore (less than 5m LAT) the potential for dispersion is more limited and therefore the concentrations are likely to be greater, approaching 400mg/l at their peak. This is far greater than typical background values of up to 170mg/l which have been recorded in the vicinity of the coast at Great Yarmouth (ABPmer 2012b).
197. Considering the findings of the relative assessments within Chapter 7 Marine Geology, Oceanography and Physical processes the magnitude of the impact is considered to be low in the offshore section of the cable corridor and medium in the nearshore section where water depths are shallower.
198. Of the biotopes which have been identified as present within the offshore cable corridor through the East Anglia ONE export cable corridor survey, the East Anglia THREE survey and through the East Anglia Zone survey, none are considered to be sensitive to increased suspended sediment concentrations or smothering by deposition of material (Table 10.16). Therefore, the sensitivity of biotopes in the offshore cable corridor is considered as low in accordance with Table 10.6.
199. Furthermore, none of the habitats identified would be considered rare or of high value in accordance with Table 10.7.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
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