Air curtains for windfarm constructions
Protection of underwater marine life during construction
In the beginning of September 2022, a significant milestone was achieved in the construction of the Hollandse Kust Zuid wind farm with all 140 monopiles successfully installed into the Dutch North Seabed. These monopiles serve as the foundation for the turbines.
Using ship cranes, the monopiles were lifted vertically and lowered to the seabed at depths ranging from 17 to 28 meters, penetrating the scour protection and underlying seabed due to their weight. Each pile was driven to its final depth using a hydraulic impact hammer.
One of the key elements closely monitored during the piling process was the protection of underwater marine life. The North Sea is home to several protected species, such as harbor porpoises, which use sound for communication and hunting. Underwater noise from construction activities can disturb these animals. The underwater noise from piling had to stay below certain thresholds to minimize the impact on marine life. These thresholds vary by season and wind farm site.
To reduce noise levels, the contractor Seaway Heavy Lift employed a Double Big Bubble Curtain (DBBC). This technology consists of two separate rings of perforated hoses that blow air from the seabed to the water surface, creating ‘shields’ of air bubbles around the monopile. These bubble curtains significantly reduce underwater noise from piling activities. The bubble curtains consistently kept the actual underwater noise during both campaigns below the thresholds.
The use of double bubble curtains proved to be more effective than initially anticipated, resulting in noise levels well below the threshold. Although a single bubble curtain would have sufficed during the summer season, Vattenfall continued using the double bubble curtain to further minimize noise levels and limit the project’s impact on the marine environment.
In order to better understand the actual impact of piling noise on fish, the scientific research project Apelafico, funded by the Dutch organization for scientific research NWO, reached out to Vattenfall to conduct research during piling. The aim was to collect information on the response of pelagic fish to piling noise and test a deterrent device developed to deter fish before piling.
In addition, Vattenfall voluntarily placed four monitoring frames in the HKZ area during the second installation campaign. The aim was to measure noise levels and fish activity at various distances from the piling activities. The fish deterrent device was used at several piling locations, providing specific information about the response of fish.
During construction of other wind farm projects, Vattenfall also utilizes alternative methods for noise reduction.
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