encountered, with poor quality footage obtained at some sites, despite numerous attempts made on different days, and states of the tide.
1.4 Grab Sampling 36.
37.
Following recovery of the sea bed video, a quantitative sea bed sample was collected using a 0.1m2 Hamon grab.
The position of each grab sample was fixed at the time when the winch wire went slack indicating that the grab was on the sea bed. Upon retrieval, the sample was checked to ensure adequate quality. Samples of five litres and above were considered acceptable. Samples with a volume less than this were generally rejected and the stations re‐sampled up to a maximum of three times. Where samples of less than five litres were continually achieved then best judgement was used to accept samples of lesser quality.
38.
Once a sample had been accepted, it was emptied into a hopper and photographed (Appendix I). The sediment was also described and any conspicuous fauna were recorded. A sub‐sample was then taken and placed in a plastic bag for subsequent PSD analysis. The volume taken depended upon the nature of the sediment (as described in BS1377; part two; 1990), but was generally between 500g and 1500g.
39.
The remaining sediment was then gently washed over a 1mm sieve with the material retained on the sieve transferred into a pre‐labelled container and preserved with 4% buffered formaldehyde/seawater solution. These were then stored for return to Fugro EMU benthic laboratories for determination of faunal content.
40.
Single grab samples were successfully collected at all of the proposed 49 stations for determination of faunal content and particle size analysis. At Sites 18 and 36 a sample volume of four litres was accepted after three attempts at each site.
1.5 Epibenthic Trawling 41.
42.
Of the 13 trawl sites proposed, 12 were successfully sampled. Sampling at site T03 was precluded as a result of potential Sabellaria spinulosa reef being present in the video footage across this site.
Each trawl tow was approximately 500m in length and conducted at a speed of 1 to 2knots. The start and end of each tow was fixed within the HydroPro navigation software and an appropriate layback applied based on length of warp deployed and
Benthic Characterisation Report November 2013
East Anglia THREE and FOUR Offshore Cable Corridor
