Background

Reconnaissance survey of an English Channel subsea cable route from Alderney island to Britain Jurassic coast including the clearance of multiple landing options.

Requirement

The survey included multi-beam, synthetic aperture sonar (seabed sonar imagery), sub-bottom profiler and ground truth along the 135km cable route and associated potential landfalls.

Challenges

• Acquisition: ensure high data quality and full coverage along 135km route length characterized by water depth comprised between 10 and 180m.
• Interpretation: process and interpretation of each dataset, prior to compilation for a better understanding and validation of local geomorphology interpretation of such English Channel transect.
• Alignment charts and comprehensive charting to support the search for the corridor position of least impact.

Survey Solution

• iXplorer 24/24 without refuelling
• Synthetic aperture sonar Shadow, positioned by USBL, to ensure high resolution seabed imagery over a wide corridor
• Sub-bottom profiler Echoes 3500 to obtain high resolution seismic data, with 20-30m observed penetration depth below the seafloor, for shallow geology description
• Multibeam R2Sonic 2024 for morpho-bathymetry
• Ground truth with grab sampler, positioned by USBL, to support the geophysical interpretation.
• Compilation of geophysical dataset (sonar imagery, sub-bottom profiler) through the use of Delph Software Suite. Alignement charts and illustration under a GIS structure
• Team of surveyors, geophysicists, cartographers and coastal engineers to ensure onboard, processing and reporting.

Outcome

Survey project along the English Channel transect highlighted interesting dataset successfully combined together for a regional morpho/sedimentology and subsurface geology understanding in order to identify the optimum routes for future cable installation.