ScottishPower Renewables (SPR) and Seabed Scour Control Systems (SSCS) visit HR Wallingford’s Fast Flow Facility where the frond mat scour tests are being carried out.
The East Anglia ONE Offshore Windfarm (EA ONE), which is approximately 30 miles southeast of Lowestoft, is entering its construction phase. When fully operational, the EA ONE windfarm will comprise 102 turbines, mounted on piled jacket foundations, for which the need to install effective scour protection has been identified.
HR Wallingford is carrying out physical modelling in its Fast Flow Facility to test the scour development and the performance of a frond mat scour protection system to protect the jacket piles for EA ONE, taking into account the foundation design, the seabed characteristics and metocean conditions.
Initial tests, undertaken at a scale of 1:2, are some of the largest scour tests ever undertaken in a laboratory, and highlight the power and scale of the Fast Flow Facility, which at 75 m long and 8 m wide can hold a million litres of water, and can generate waves up to 1 m high and flows of over 2 m/second.
In the tests, jacket legs are protected with weighted frond mats. The mats are composed of high tensile strength, polypropylene, buoyant, frond lines. The frond mats are designed to mimic naturally formed seaweed, providing additional drag and slowing the flow of water. This reduction in velocity reduces the sediment carrying capacity of the water, resulting in a reduction in the erosion rate of material around the jacket legs, or in deposition. The weight and time development of sediment build-up of the sediment bank will depend on the local conditions and seabed composition.
A series of three full tidal cycles (including both flood and ebb tides) are 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.
Samantha Dawson, Business Development Manager Renewables, at HR Wallingford, said: ”At HR Wallingford we have an active programme of research in the prediction and analysis of scour around marine structures, with world class modelling facilities, including the Fast Flow Facility. This gives us a controlled environment in which to evaluate and select the best-performing scour protection systems for a specific site, like EA ONE, and the conditions in which it operates.”