Emu Ltd was commissioned by SeaGeneration (Wales) Ltd to undertake a geophysical survey of the proposed tidal energy farm, located in The Skerries, off the north west coast of Anglesey. The aim of the survey was to determine and report on the subsurface and seabed conditions in order to facilitate the construction of the tidal energy farm. The survey was performed using swath bathymetry, sidescan sonar imaging, magnetometor, shallow seismic (boomer) and the collection of seabed samples for ground truthing. Survey lines were run using a line plan which amounted to approximately 90 line kilometres. The survey was carried out using the vessel FPV Morven between the 12th and the 22nd August 2008 utilising: • A fully motion aided Reson 8101 multibeam echosounder • An SES Sonar Mag digital sidescan sonar system and Edgetech 4200 digital sidescan sonar system, positioned with a Sonardyne Scout USBL • A Geometrics G-882 marine caesium vapour magnetometer • An Applied Acoustics AA200 boomer system • A stainless steel Shipek grab. Bathymetry data were reduced to Chart Datum at Holyhead using GPS tidal elevations recorded on board the survey vessel. The site of the proposed tidal energy farm has variable depths over the surveyed area. Depths range from 0 m to 50 m below Chart Datum (CD). Depth variations across the site appeared to correspond not only to exposed bedrock but also fingers of mobile and static sediment within the area. Coarse sand and bedrock dominated the central and western region of the surveyed area. Surrounding this area were regions that contained cobbled silt, gravelly pebbly cobbles, sandy gravel and cobbly sand. Bedforms with a maximum wave height of 2 m have been identified in the surveyed area and have their long axis generally orientated NNW-SSE. Pockets of sediment infilling the surface topography of the bedrock were clearly identified in the seismic data. The distribution and thickness of these sediment deposits have been mapped. As expected very little seismic penetration into the bedrock was achieved.
Appendix H GIS Data
Side Scan Sonar Data