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2008, EMU, Skerries Tidal Site, Marine Geophysical Survey

2008, EMU, Skerries Tidal Site, Marine Geophysical Survey

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Geophysical

Description

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.

Dataset

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Seismic Data

Appendix H GIS Data

Side Scan Sonar Data

Bathymetry Data

Magnetometer Data

Report

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Report

Appendices