Coastline Surveys Completes Geotechnical Investigation for Navitus Bay

Navitus Release

Navitus Release 2013

Coastline Surveys has completed a geotechnical investigation of the seabed cable route at the proposed Navitus Bay offshore wind park, off the South coast of England.

Coastline Surveys, the Falmouth-based marine data consultancy, was delighted to be chosen to extend previous phases of work as the main contractor on such a high profile project. The team have provided geotechnical expertise to examine the viability of the proposed cable route that will transport energy from the wind park to shore.

Mike Unsworth, Project Manager for Navitus Bay, said: “We have worked with Coastline Surveys during previous phases of the project. The team’s thorough knowledge of the project, combined with their geotechnical expertise and extensive experience of working along the south coast, made them the obvious choice for this latest piece of work.

Utilising its own 24m survey vessel, MV Flatholm, along with their C-COREHP vibrocorer, Coastline Surveys successfully completed sampling at 22 locations along the planned route for the cable. The route runs from the shoreline to approximately 12 miles off shore.

A key requirement for Navitus Bay was the acquisition of high quality samples for environmental and potential archaeological analysis.

On investigating the ocean floor, the team expected to find marine sands overlaying bedrock, with a range of depths throughout the area. It soon became clear that the site was made up of a variety of soil conditions ranging from soft silts to dense sand and clays.

Navitus Bay required undisturbed quality samples where possible, but particularly around the palaeochannels, where fine grained material and peat deposits were also expected.

Coastline Survey’s C-COREHP unit has a real-time Penetrometer fitted to it, to monitor the rate of penetration during sampling. This was especially invaluable in areas of softer loose sediments as it allowed the geotechnical team to recover high quality samples with reduced disturbance.

The stiff clays and dense sands that the team encountered presented a different kind of challenge. The class leading power and weight of the C-COREHP unit meant the team were able to achieve good depths in these conditions, penetrating the ground up to one metre into the underlying stiff clay in some locations.  The penetrometer was particularly useful in these difficult conditions allowing the team to realise when they wouldn’t be able to recover any more sediment. As a result, the team were able to terminate their tests when appropriate, saving time and costs whilst preserving sample integrity.

Lab testing and reporting was completed at Coastline’s facility in Lowestoft. The Geotechnical logs, soil descriptions and core photography provided to Navitus Bay were of sufficient quality and standard to assist with identification of archaeological features.

Mike Unsworth added: “The breadth and depth of knowledge of the ocean floor that the geotechnical investigation has given us is vital to the technical development of Navitus Bay.

We are very pleased with the high standard of work provided by Coastline Surveys, and hope to work with the team again in the future.

The work was largely conducted in challenging environmental conditions with strong tidal currents and the requirement for shallow water operations close to the shoreline. However, the experience of the team, which includes extensive investigations on the nearby marine aggregate dredging licences, enabled them to complete the workscope in two highly-productive twelve hour days.

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May 2013