The objectives of the export cable route survey were to:
- Determine water depths reduced to LAT;
- Identify seabed features and obstructions;
- Determine the seabed sediments and sub-seabed lithology, topographical and geological features that could impact on the satisfactory installation and trenching of the cable such as wrecks, boulders, exposed bedrock, seabed gas seepage, pockmarks, adverse gradients, sand waves, slumping or channelling;
- Determine the physical and engineering properties of the seabed sediments;
- Collect data to assist assessment of archaeological features;
- Collect geotechnical samples including vibrocores (VC) and cone penetrometer tests (CPT), to identify and classify the material in order to further aid cable burial assessment studies.
All lines were run simultaneously acquiring multibeam echo sounder, side scan sonar, pinger and sparker sub bottom profilers, Automatic Ground Discrimination System (AGDS) and magnetometer data. Multibeam infill data was also acquired, in order to achieve 100% seabed coverage. Land topographical surveys and depth probing (air lancing) were also carried out at each landfall corridor.
The geophysical survey was undertaken using Bibby HydroMap's own dedicated survey vessel, MV Lia. Data acquisition comprised simultaneous recording of Reson 7125 multibeam echo sounder, Klein 3000 high resolution side scan sonar data, with piggy backed marine magnetometer (surface towed in shallow water) and ‘pinger’ and ‘sparker’ sub bottom profilers.
Vibrocoring and CPT operations were undertaken using a 3rd party vessel, Forth Fighter. The vessel, built in 1985 (rebuilt 2001) is a multicat design with dimensions of 23.50m length, 7.5m beam and a draft of 1.50m. Forth Fighter is powered by 2 x Man 320hp engines and fixed Kort Nozzles, which makes her very manoeuvrable and well suited to holding station.
Spec Sheet: Lia