INDUSTRY NEWS
During the development of Round 1 and 2 offshore wind farm projects, there was a general presumption that concrete gravity bases result in a considerable loss of seabed. However, increasingly, the impact of the area being ‘over-shadowed’ by the total foundation structure, for example the seabed area located under the lattice of a steel jacket and not just under one of the feet, is considered to represent the real loss of seabed. In this respect, the research carried out by MarineSpace found that steel jackets or tripods can result in larger seabed disturbance and loss than gravity concrete bases. This loss can only increase as the deeper waters of Round 3 necessitate larger foundations.
INSTALLATION IMPACT The larger foundations required for deeper waters of Round 3 have a further environmental impact. Steel monopiles, tripod and jacket foundations typically rely on piles being hammered or drilled into position. The impact of installation is significant and this can have a severe detrimental effect upon marine life. In the shallow waters of Rounds 1 and 2 monopiles may be struck between 1000-7000 times depending on seabed conditions. With a weight of 225 T and delivering blow forces between 200 – 500 kJ per strike, piling hammers can a significant noise and vibration impact during an installation period that can take up to 4 - 7 days per foundation, excluding any weather downtime.
“No piling is required for gravity concrete bases. They are lowered into position,” explained Andrew Minson, Executive Director of MPA The Concrete Centre. “The avoidance of piling noise installation is a major benefit of concrete gravity bases as the impact on marine life from piling noise is likely to lead to planning conditions being applied resulting in project delays and increased costs. With this in mind, retaining concrete gravity bases as an option through the planning process is a prudent priority for developers.”
Monopiles, steel jackets, tripods and floating platforms all require drilling or hammer piling to secure then to the seabed. The noise and vibration impact of this will increase due to increased size of the foundations necessary for Round 3 deep water locations.
HABITATS DIRECTIVE AND THE MARINE STRATEGY FRAMEWORK DIRECTIVE The resultant sound pressure waves from piling, drilling and hammering could be at levels high enough to cause death, damage and displacement of marine animals, sensitive fish species and some fish eggs and larvae. Domestic and international environmental legislation, such as the Habitats Directive and the Marine Strategy Framework Directive, now reflect the serious consideration of these possible effects. By comparison, any concrete gravity bases that require site preparation works will generate noise associated
with the dredging activity. Evidence from marine aggregate extraction operations demonstrates that dredging noise levels are barely detected above those associated with general dredger navigation and are no more noisy than merchant shipping sailing in the local area.
OTHER CONSIDERATIONS Other environmental impacts to be considered include the impact of tidal currents, which for all options was found to be minimal, and the potential colonisation by marine life of new ‘reef’ areas. This reef effect is common to all foundations types and may result in local changes to biodiversity and habitat provision.
“Overall, the report found that the environmental impact from concrete gravity bases are broadly comparable to other foundation types with one major exception”, said Minson. “The installation of concrete gravity bases is far more quiet and less disruptive than other foundation types. This offers a very significant advantage to those offshore developers choosing concrete gravity bases for Round 3 projects.”
MPA The Concrete Centre
www.concretecentre.com
Click to view more info
wind market. We are now looking forward to these vessels entering service and continuing our support to deliver state of the art designs which are designed specifically to meet our customers’ requirements.”
BMT Nigel Gee
www.bmtng.com
www.windenergynetwork.co.uk
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