Pile driving: noise levels coming closer to emission limits

Thursday, 12 July, 2012 - 14:30

Researchers within the Evaluation of Pile Driving Noise Mitigation Systems (ESRa) program have published the results of tests conducted in the Baltic Sea. Last August, five sound mitigation concepts were tested at the so-called Brodtner pile (Neustadt Bay), in a water depth of nine metres. The systems – all of them were prototypes – worked with air-filled enveloping bodies, multi-layer hose curtains, bubble curtains and combinations of acoustic cladding and bubble curtains. According to the authors, each of the noise reduction technologies – used under almost identical ambient conditions – withstood the harsh conditions at sea and demonstrated a significant noise mitigation effect. After correction of site-specific effects, “the mitigation effect totalled up to nine decibel in the relevant range”. In Germany, a rather demanding maximum noise emission limit of 160 decibel at a distance of 750 metres around the source is part of the building permits issued by the Federal Maritime and Hydrographic Agency. According to the study, the five prototype systems brought the noise level much closer to the German emission limit.

Other European countries have less strict regulations for offshore projects. In Great Britain as well as Denmark e.g. so called pingers are used for expelling protected species like harbour porpoise from the construction grounds. In addition boat patrols observe the sea area around the construction sites in order to possibly interrupt the works to protect the whales.

Supporters of the research done are eight builders and operators of German offshore wind projects like Bard, DONG Energy, EnBW, EWE and Stadtwerke München.

RWE Innogy is using bubble curtains as a means to protect wildlife around its current construction site “Nordsee Ost”, 30 km north off Heligoland. There, these days construction works have begun to install 48 multi megawatt turbines. On the sea ground as well as in different water depths tubular rings with nozzles are installed surrounding the foundation. By introducing compressed air a bubble curtain is established that is mitigating the noise of the piling and drilling works. “This is a state of the art technology concerning noise mitigation that can be easily handled”, says Konrad Böcker from RWE Innogy.

So far however, the offshore industry cannot guarantee a sound level constantly complying with the German limit value. That’s why the ESRa study states that “more research and development is required in order to meet the limit reliably in the future”.

Volker Uphoff

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