for oil spill modelling and dispersant product testing was of such limited extent and sufficiently long ago that no traces remain in surface sediments.
8.5.2 Suspended Sediment Concentration 66.
For full details of concentrations of suspended sediments naturally present within the East Anglia THREE site and offshore cable corridor, see Chapter 7 Marine Geology, Oceanography and Physical Processes. For ease of reference, a short summary of the findings is provided below.
67.
Suspended sediments across the East Anglia Zone are typically in the range 1 to 35mg/l, with the highest values typically found along the western margin and during winter months. Concentrations do, however, increase towards the coast at Great Yarmouth and have been recorded up to 170mg/l. These elevated concentrations are thought to be generated from eroding areas of cliff line along the English east coast. A metocean survey undertaken within the East Anglia THREE site recorded suspended sediment concentrations to be in the range of 3 to 13.5mg/l throughout the winter of 2012/13. Surface values are typically less than those experienced close to, and at, the sea bed. In terms of sea bed sediment, grab sample analysis revealed that 90% of the East Anglia Zone consists of either sand, slightly gravelly sand or gravelly sand. The remaining areas are primarily characterised by sand gravel, with localised areas of muddy sand and (slightly) gravelly muddy sand.
68.
The sea bed across the East Anglia THREE site is characterised predominantly by sand. The median sediment grain size (d50) of a series of grab samples ranges from 0.21 to 0.36mm (medium sand) with a single sample containing a d50 of 0/07mm (very fine sand).
8.5.3 Site Specific Survey 69.
In order to inform the baseline for sediment quality, a site specific survey was carried out in 2013 (reported in Fugro EMU 2013). The locations of the stations for which contaminant analysis was undertaken are shown in Figure 8.1.
70.
Sediment contaminant data is summarised in Tables 8.10 and 8.11. Data highlighted in yellow indicate concentrations of contaminants over either Cefas Action Level 1 (Table 8.10) or Canadian Sediment Quality Guideline TEL (Table 8.11). Red indicates concentration greater than Cefas Action Level 2 or Canadian Sediment Quality Guideline PEL.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 8 Marine Water and Sediment Quality Page 22
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