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Seabed surveys underway for Norfolk duo

By: Tom Russell 18/09/2020 Vattenfall

General Grid Windfarms

A jack-up vessel is working close to shore off a Norfolk beach collecting seabed data to shape the design of Vattenfall’s Norfolk Vanguard and Norfolk Boreas developments. The 500-tonne Haven Seariser 2 is on the nearshore off Happisburgh while its geotechnical engineering team take samples.

The rig is a 29-metre-long barge fitted with long support legs jacked down onto the seafloor. It is gathering borehole samples, down to a maximum of 30 metres. The process will build an understanding of seabed sediment layering to decide the installation methodology for the wind farms’ main transmission cables at their landfall at Happisburgh.

Several larger vessels are working further offshore carrying out similar sampling in a four-month campaign by geodata experts Fugro.

Onshore site investigations have also begun around where the onshore substation will be built near Necton.

Offshore data will feed into planning the most efficient turbine locations within the array, appropriate foundation design, as well as the final cable route from the turbines to connect into the National Grid at the onshore project substation.

Teams are collecting samples to learn about the properties of soil types at the site and are also completing cone penetration testing (CPT).

These samples will be sent for testing in Fugro’ss soil testing laboratories in Wallingford, UK, and Nootdorp in the Netherlands. Data collected will be used to shape a ‘ground model’ for the wind farm and final cable design. Other laboratories carrying out specialised testing include GEO’s laboratory in Denmark.

Haven Seariser 2 is expected to be in place for another two weeks or so, with timing dependant on weather, work progress and operations.

Andy Galbraith, Vattenfall’s Head of Geoscience, said: “The information gathered during these site investigation surveys will be used to fine tune the design of the export cable and associated installation techniques.

“Horizontal directional drilling will be considered for installing the cable underneath the beach and the area of the shore which is submerged at high tide and exposed at low tide.. These surveys will help determine the best technique to use.”

“A jack up vessel provides a very stable sampling environment compared to other offshore drilling rigs and this is important to preserve the quality of the samples. It also helps that the current weather conditions are favourable for the campaign.”

Vattenfall recently secured consent for its Norfolk Vanguard project off the Norfolk coast. It is hoping to secure consent for the nearby Norfolk Boreas project in November. The two arrays would have a combined capacity of 3.6 GW and could be operational from the mid-2020s. The projects' combined capacity is expected to meet the equivalent annual electricity demand today of 2.6 million UK households.

Onshore construction of Vattenfall’s Norfolk Projects is due to start in 2122-23, with the prospect of many local jobs supported in local construction companies and relevant contractors. Offshore works are due to start in the mid to late 2020s.

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Seabed surveys underway for Norfolk duo

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