Abstract
Project and Export Cable Route – Offshore Survey
Bibby HydroMap were commissioned by Xodus Group in June 2015 to carry out a geophysical and environmental survey at Holyhead Deep, Holyhead, Wales. CMACS Ltd were subcontracted by Bibby HydroMap to assist on the environmental study.
The survey was required to investigate the seabed and sub-surface conditions in order to plan any subsequent geotechnical investigations and assist with the design and placement of tidal generation units and associated foundation structures including an export subsea cable linked to a land based substation facility and a transformer positioned on the seabed.
The survey was carried out between 9 June and 5 July 2015.
The main objectives of the surveys were as follows:
Geophysical Survey:
- To provide detail of the seabed conditions and bathymetry of the area
- To identify any debris, potential hazards and obstructions
- To identify any cable/ pipeline crossings as well as the presence of any existing subsea structures within the survey area
- To identify the presence of any points of archaeological and cultural heritage interest
- To produce laterally continuous interpretation of subsoil conditions where possible within the uppermost 5m below seabed
Integrate the above data to optimise the installation of the subsea structures, cable route layout and planning of future geotechnical investigations
Environmental Survey:
- To document the seabed environment, habitats and species of conservational interest
- To ensure that all potential seabed biotopes and their distribution are sufficiently sampled in order to produce final habitat and biotope maps
In order to meet these objectives, multibeam bathymetry, side scan sonar, sub-bottom profiling and magnetometer data were acquired on site.
During the latter stages of the survey, an additional ‘Route Development Area’ survey was requested by the Client. This was undertaken within the inner section of the route bend between KP2.500 and KP4.500, across an area of approximately 0.58 km². Bathymetry and backscatter data were acquired at this location, with the backscatter data used for seabed features interpretation.
Volume 1 is the Operations Report, which details the operational parameters, locations, times and techniques utilised during the survey carried out by MV Chartwell and MV Eagle. This volume, Volume 2, presents the preliminary results of the survey undertaken within the PDA and proposed export cable route. The preliminary Results Report encompasses the geophysical survey; the Environmental survey, provided by CMACS, will be included in the final report.