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Fake seaweed tested to provide scour protection

East Anglia One large scale test 1 frond mats

Leaf-like mats, which mimic natural seaweed, are being tested to see if they can provide scour protection for offshore windfarm foundations in the southern North Sea.

Consultant HR Wallingford is working with ScottishPower Renewables (SPR) to test the performance of the mats for the piled jacket foundations at the East Anglia One offshore windfarm.

The mats are composed of high tensile strength polypropylene, buoyant, frond (leaf-like) lines. They have been designed to mimic seaweed providing additional drag and slowing the flow of water. This reduction in velocity reduces the sediment carrying capacity of the water, reducing the erosion rate of material around the jacket legs, or in deposition.

The consultant said the weight and time development of the sediment bank build up would depend on the local conditions and seabed composition.

It is carrying out physical modelling in its fast flow testing facility to assess the performance of the mats against scour with the jacket legs protected with weighted frond mats. It said this testing would take into account the specific foundation design, seabed characteristics and environmental conditions such as wind, wave and climate conditions.

A series of three full tidal cycles is being simulated to allow the mats to accumulate sediment. Storm conditions are also being run, in which a 1:1 year, 1:10 year, and 1:50 year storm are simulated.

The company said the initial tests, undertaken at a scale of 1:2, were some of the largest scour tests ever undertaken in a laboratory. The facility is 75m long and 8m wide, can hold 1M.l of water, can generate waves up to 1m high and flows of over 2m/s.

HR Wallingford business development manager renewables Samantha Dawson said: “It is very important to be able to predict and analyse the scour that occurs around marine structures such as the jacket piles of the foundations for the EA One windfarm.

”The controlled environment of a flume like the Fast Flow Facility allows us to model and test at different scales, both existing and innovative scour protection systems, simulating the seabed and metocean conditions of the particular site where they might be deployed.”

The East Anglia One offshore windfarm is approximately 48km southeast of Lowestoft and is entering its construction phase.

When fully operational, it will comprise 102 turbines, mounted on piled jacket foundations, for which the need to install effective scour protection has been identified.

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