The main objectives of the geophysical survey were as follows:
- To provide an accurate bathymetric chart of the site extension;
- To chart natural seabed features and any obstructions, manmade objects, debris or wrecks;
- To produce isopachyte charts to show sediment thickness of the upper, loose, and any mobile material, and of any other significant reflector levels which might impact on the engineering design
- Locate and identify sites of near surface soft materials pertinent to jack up operations;
- To provide a detailed geological interpretation to show facies variations and structural feature changes via appropriate maps and sections;
- To correlate magnetic anomalies and sonar contacts to identify items that may require further physical surveying
The survey was undertaken using Bibby HydroMap's own dedicated survey vessel, MV Chartwell, a 24hr operations vessel.
Data acquisition comprised simultaneous recording of Reson 7101 multibeam echo sounder, Klein 3000 high resolution side scan sonar data, with piggy backed marine magnetometer and ‘Boomer’ sub bottom profiler. The line spacing for the extension survey was set at 150m for main lines (26 total), with cross lines at 1500m. A total of 7 cross lines were acquired perpendicular to the main line orientation at 1500m spacing. This ensured that the cross line data could be tied into the original survey results where cross lines were acquired at 750m line spacing.
The UXO investigation comprised a 200m box area, with 41 main lines spaced at 5m and orientated at 71°/251°, and 3 cross lines orientated perpendicular to the main lines. The objective of the survey was to locate any potential obstructions (natural or anthropogenic) to the installation of a met mast. The same equipment spread was utilised, with changes made to the settings of the boomer and multibeam to increase data resolution. The magnetometer was flown as close to the bed as possible, with flying height controlled generally between 0m and 2m above seabed.
A Fisheries Industry Representative (FIR) was assigned to the project for the duration of the survey to ease any conflict between active fisheries parties and Bibby Hydromap. The project was carried out under CDM Regulations 2007, with Bibby Hydromap appointed Principal Contractor and Designer.
Related Pages: Hydrographic and Geophysical Survey