How we mitigate underwater noise with FaunaGuard and Bubble Curtain

‘We deliver, We innovate and We share’; these are the mottos of CrossWind. This powerful slogan easily lends itself for the construction of the Hollandse Kust Noord offshore wind park. ‘Delivery’ of the first foundations has taken place through offshore installation vessel Innovation. One matter which should also not be overlooked, is that we ‘Share’ the offshore wind park area with many marine compatriots such as fish, seals and porpoises.

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16/01/2023

Article by Jesper Elzinga, Environmental Engineer at Van Oord

Our underwater neighbours can be adversely affected by the underwater noise produced by the hydraulic impact hammer installing the monopiles. In order to keep marine life out of harm’s way we’ve proactively taken a number of underwater noise mitigation measures.

Our first line of defense for marine fauna is Van Oord’s FaunaGuard module. The FaunaGuard is an acoustic deterrent device which emits specialised safe acoustics into the marine surroundings to temporarily deter marine fauna from the construction area. For this project we make use of three modules, namely the Fish, Seal and Porpoise module. Where the deterrence of porpoises and seals have been field tested by Van Oord before, fish deterrence will be tested at the HKN site by deploying specialised frames to monitor fish activity. The FaunaGuard is activated 30 minutes prior to monopile installation to warn marine fauna the works are about to commence and allow them to move away from the construction area.

"The harbour porpoise is the most common marine mammal in the North Sea with a very sensitive hearing"

- Marin van Regteren, Marine Environmental Specialist at CrossWind

The FaunaGuard protects marine life from the most immediate potential effects of underwater noise. In order to protect marine life from more subtle effects such as behavioural alterations on individual and population level, we ensure to reduce the amount of underwater noise travelling from the installation site. To do so, we make use of two measures: the hydro sound damper (HSD) and the big bubble curtain. The HSD consists of a net which is fitted with foam and air elements to reflect and absorb underwater noise. The HSD net is deployed all around the monopile from the vessel deck level until the bottom of the sea and is considered a near to pile noise mitigation system.

The big bubble curtain consists of a thick air hose which is deployed on the seafloor in a circle at around 150m from the monopile installation. Air compressors are used to blow air through the air hose which then creates a bubble curtain noise barrier underwater which blocks the majority of the remaining noise otherwise travelling from the site. Jesper Elzinga is Environmental Engineer at Van Oord for this project and was on board of the big bubble curtain vessel for the start-up phase of the monopile installations. According to Jesper ‘The underwater noise levels so far are favourable compared to our predictions during the design phase of the project. I am proud to be able to contribute to this project due to the care we take to protect our marine fauna. It’s a true example of marine ingenuity!’

"Harbour porpoises, with their calves, are often seen in operational windfarms"

- Marin van Regteren, Marine Environmental Specialist at CrossWind

Image by Flying Focus