Reconnaissance cable route survey & detailed survey

ServiceReconnaissance cable route survey and detailed survey
LocationTenerife, Canary Islands
Water depth5-1160 m
Project duration40 days (November – December 2019
IndustrySubmarine Power Cable
scope of work

In November 2019, ACSM has been awarded by a major power cable company to execute preliminary inspections and surveys to support the design of a submarine electrical interconnection cable between Tenerife and La Gomera, in the Canary Islands. The scope of the work consisted in providing reconnaissance cable route survey and various engineering studies along the two alternative routes identified, for a total of 68 kms.

The activities provided were as per follows:

Cable Route Survey (divided in nearshore and offshore):

  • Reconnaissance survey.
  • Geophysical detailed survey.
  • Geotechnical survey.
  • Route engineering.
  • Hydro-sedimentary study.
  • Navigation and fishing study.
  • Cable Burial Risk Assessment

VESSEL

OSV “NAUTILUS”
As survey vessel platform, ACSM deployed the owned offshore support vessel NAUTILUS. The NAUTILUS is designed to the highest standards required for the offshore industry and ideally suited for a broad range of pre-engineering activities, construction support and IMR operations. At 75 metres long, with a cruising speed of 10 knots and accommodation for 44 personnel, ACSM Nautilus is a robust, practical and efficient vessel for all inspection and survey requirements. The stern A-frames allowed to deploy geotechnical sampling The vessel also has integrated ROV control, online inspection, survey and offline processing/review offices and client offices.
Partenza nautilus

ROV

CMROV ROV
The DP2 NAUTILUS has a permanent mobilized Work Class ROV of 400Hp that can be used for both survey and inspection purposes. The system is 1500 m depth rated.
The Cable Maintenance ROV (CMROV) is a free swimming or tracked hydraulic ROV with 300kW/400HP providing an efficient and cost-effective solution for maintaining and installing regional and intercontinental submarine cable systems. This type of ROV has an extensive track record for operating globally in extreme environmental conditions and a variety of seabed soils.

SURVEY EQUIPMENT

  • Alty/Bathy
  • Gyro and INS
  • Survey Mux
  • DVL
  • Norbit MBES
  • SSS/SBP Edgetech 4200
  • 6 Sensors Gradiometer
  • CPT Roson 100
  • Piston Corer

METHODOLOGY

The subsea cable route survey between Tenerife and La Gomera consisted in 4 different phases:
  • Reconnaissance survey – (MBES)
  • Detailed surveys (both inshore and offshore) – (MBES, SSS, SBP)
  • Benthic habitat video inspections – (Video Inspection)
  • Geotechnical survey – (CPT, VC, Grabs)
The reconnaissance bathymetric survey was undertaken in agreement with the client representative on board, along a corridor of about 1,000 m wide in order to define two different paths for the electrical submarine interconnections.
Once defined the two survey routes, a detailed geophysical survey along two corridors, 80 m wide, was performed. During the survey have been collected accurate bathymetric soundings using multibeam echosounder (MBES), seabed images using side scan sonar in order to map seabed features and shallow geological profiles using a sub-bottom profiler to determine the shallow geological units. Additionally, in dedicated areas of interest have been performed video footages.
Client was satisfied about the offshore works and extremely pleased to have received the final report with reasonable time from the end of the operations.
RESULTS
Survey Scope achieved:
ACSM successfully conducted geophysical survey and geotechnical samplings along the two alternative proposed routes with the aim to identify possible natural or man-made hazards that may represent obstructions during the cable laying operations. The offshore operations were carried out smoothly and with zero LTI.
Geophysical and Geotechnical interpretation:
The marine survey in the channel between Tenerife and La Gomera islands highlighted the presence of quite complex geological-morphological area, due to the volcanic activities, the mass transport deposits along the volcanic building sides and the limited distance between the islands.
Client satisfaction:
Client was satisfied about the offshore works and extremely pleased to have received the final report with reasonable time from the end of the operations.

Turning complex subsea challenges into safe and efficient operations