Flora and fauna
As it is difficult to say what the negative impact on the environment will be, Belwind will conduct a 6 year environment monitoring study. This will pinpoint the precise impact and allows Belwind to provide environmental compensations.
Belwind already provides a number of compensations. An emergency vessel allows the authorities to respond quickly and adequately in case of offshore environmental pollution. Belwind has also earmarked a number of financial guarantees to restore the site to its original condition after decommissioning.
Underwater noise emissions
The level of underwater noise emissions produced by the turning wind turbines on the Bligh Bank is very difficult to predict. This sound level will certainly be much lower than during the construction phase (driving piles into the seabed, dredging), but is long-term.
And the masts will also cause some noise. The flow of the water will be slightly different and waves will hit the mast. The offshore support vessels will also cause more noise.
Evaluating the possible impact of underwater noise involves too many uncertainties and unknown factors. It is possible that underwater noise emissions have an impact on the growth, reproduction and survival of organisms, finding prey and on communication or the use of certain areas.
That is why Belwind has already applied several measures to reduce underwater sound emissions and to avoid the exposure of marine life to noise.
Preventative measures that avoid exposure of marine mammals to noise:
1. During periods when marine mammals are in the area or the spawning period of certain fish which could experience disruption, all work is suspended.
2. When marine mammals are near the site the works are stopped or we don't start.
3. Acoustic devices, such as pingers and seal scares, drive away any marine mammals from the site.
4. Pile driving according to a ramp-up procedure, whereby the maximum sound level is only reached after half an hour or an hour.
Noise reduction measures
1. Modification of the pile driving system: modification of the pile hammer, longer contact between pile hammer and pile, use less energy during het pile driving (see Schultz – von Glahn, et al, 2006; Nehls et al, 2007).
2. Drilling instead of pile driving - see http://www.we-at-sea.org dated 30 October 2007. It is no yet clear whether this is technically feasible at sea.
3. Vibro-piling instead of pile driving.
4. Covering the pile with an absorbing layer (polyethylene foam). This can reduce the sound level depending on the frequency by 5 to 20 dB. The diameter of the pile during the experiment was 2.2 metres, the depth of the water was 8.5 metres (Schultz – von Glahn et al , 2006).
5. Provision of an air bubble curtain around the pile during the pile driving. Although the use of an air bubble curtain is sometimes disputed, noise reductions of 3 to 30 dB in certain frequencies have been demonstrated (e.g. Würzig et al, 2000, Laughlin, 2007, Vagle, 2003).
6. The current can seriously affect the efficiency of an air bubble curtain. If the air bubbles' rate of ascent is 0.3 m/s, and the current amounts to 1 knot, the air bubbles have travelled 34 m on the surface. A system that keeps the air bubbles within a restricted area is more expensive but can reduce the impact of the current, and reduce the sound by 10 - 20 dB (David, 2006, Laughlin, 2007; Nehls, 2007). Sources for air bubbles can be provided at different depths around the pile.
In addition to these measures, Belgium has accepted, in the context of ASCOBANS (Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas), that the parties will prevent any significant disturbance, in particular acoustic (Conservation and Management plan enclosed with the Agreement).
The grey and common seal rookery closest to the wind farm site on the Bligh Bank are on the Dutch coast (Zeeland), at a distance of approximately 80 km.
It has already been sufficiently proven that big pressure differences, such as those caused by strong sources of sound can be potentially very harmful for marine mammals, irrespective of the relationship between the sound frequency and the frequency marine mammals use to communicate, find their way and forage.
According to most researchers, seals are less sensitive to noise than porpoises (in Gordon et al, 2007). Seals like to hug the coast where they have resting places and rookeries, and are found less frequently out at sea, including the wind farm area.
(Source: Environment impact evaluation Belwind, December 2007)
Is the construction of an offshore wind farm harmful to fish?During the construction of offshore wind farms high noise levels are measured, comparable to underwater explosions.
During the construction of the wind farm of Egmond aan Zee measures were taken to scare away the porpoises before they started driving piles into the seabed. This was done with so-called "pingers", acoustic devices that produce an underwater noise that they do not find pleasant but does not harm them . During the construction of this farm no fish mortality or an increase in the number of dead fish on the coast were detected.
During the construction of Belwind, pingers were also used, a ramp-up procedure was strictly followed (whereby the pile driving intensity is gradually increased) and we continuously monitored the proximity of marine mammals. During construction no marine mammals were detected near the Bligh Bank, nor was any fish mortality detected over the construction period.
Is the sound of turning offshore wind turbines harmful to marine life?
Wind farms emit underwater noise. Because the impact of noise on animals is not yet clear, we cannot say whether this is harmful to the environment. Choosing the location of wind farms does take into account the impact of noise on marine life.The big distance to the closest seal rookery, and the absence of notifications or reports (over the last 80 years) of porpoises or other mammals around the Bligh Bank, leads us to believe that the impact will be minimal.
The impact on nature and environment is being studied at the offshore wind farm of Egmond aan Zee, which has been technically operational since 2007 and is used as a demonstration project by the government. Eight underwater microphones pick up the sound signals of porpoises allowing the movements of these marine mammals to be measured. Twelve seals have been equipped with a transmitter. The information we learn from this will be used for the construction of other wind farms.
How do birds react to offshore wind turbines?
Birds can fly into wind turbines. Contrary to what many people think, modern wind turbines hardly kill more birds than older, smaller ones. This is apparent from a survey conducted for utility company Nuon, in co-operation with the Dutch Bird Protection Agency.