Due to extensive utilisation for, eg harbour piers and coast protection facilities, rock reefs have become a rare natural element in Denmark. And this is a shame for the large variety of flora and fauna that lives on and by the reefs.
Now, lobsters, crabs and a neumber of fish species will benefit from the large offshore wind farm project by Anholt, which DONG Energy is constructing in 2012-2013.
5,000 large boulders at the size of approx one metre and some even the size of three to four metres in diameter are in the way of the wind farm’s many cables, and supporting legs and anchors of the vessels that are used for construction. And DONG Energy has decided to use the many boulders for creating new artificial reefs.
Birte Hansen, Environment & Consents Manager, Renewables :
“Even though boulder extraction is prohibited today, it hasn’t given us back the ruined reefs. By Anholt, it’s necessary to remove a lot of large boulders due to construction. But instead of just rearranging the boulders, we have decided to use the boulders to build close to 30 artificial reefs with various sizes of caverns.”
Quick move in
Experience from even small artificial reefs, for instance erosion protection by Nysted and Horns Rev 1 offshore wind farms shows that fish and shellfish are very quick to occupy the new reefs and caverns.
“ Already within two years, a large number of species are occupying the reefs. We call it colonisation. Then comes a couple of years when the different species of animals and plants particularly attached to reefs compete for the position, and after 5-6 years, a mutual long-term balance is achieved ,” says Birthe Hansen.
The caverns of the reefs will attract lobsters, crabs and a number of codfish, and large algae will grow such as seaweed forests on the rocks.
Reefs in place on New Year’s Eve
Removal of the many boulders has not started yet. At the moment, the work is going out to tender and the contractor has not yet been selected. But as construction of Anholt Offshore Wind Farm must begin on 1 January 2012, many of the boulders must be removed and a large part of the reefs built by then.
Facts
Anholt Offshore Wind Farms will be located halfway between the island of Anholt and Grenaa. 111 wind turbines will be erected, each with a capacity of 3.6MW. Foundations must be driven 16-30m into the seabed. The area is approx 5 x 20km with a water depth of 14-20m.
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Source: DONG Energy, July 15, 2011;