• Marine

Safeguarding salmon farms from construction noise

Scan Tech AS in Norway has developed a new high-performance bubble curtain technology designed to protect marine life from the noise produced by underwater seismic testing and construction activities.

Bubble curtains are used underwater to protect marine life from loud noises during subsea operations. A perforated hose is laid on the sea floor, through which air is forced, rising – as a curtain of tiny bubbles – to the surface. Most systems successfully reduce noise by 11-15 decibels (maximum 18 decibels) but Scan Tech’s new system has been independently proven to be able to reduce noise by 35 decibels.

Chris Stevens managing director at Scan Tech AS says:

‘This is a significant improvement over any other system. Not only that, but it uses only a quarter of the air – another environmental saving.’

Eighteen months ago, the Scan Tech team was asked to provide bubble curtain technology for the Norwegian Department of Environment and Roads which has commissioned an undersea tunnel network to replace the ferry crossings which link parts of the coast. This powerful bubble curtain has been designed to minimise the impact on local salmon farms of the seismic shocks produced by tunnels’ construction.

Ordinary construction noises and pressure waves travel much more easily underwater and do so without losing much of their energy. This can be enough to harm and even kill marine life. However, air bubbles compress in response to sound, absorbing acoustic energy and when formed into a curtain, they reflect and refract the sound, effectively keeping it within the curtained area.

Chris explains:

‘Traditional bubble curtains can be difficult to deploy as the hoses need to be tethered to the sea bed with chains and concrete weights which are prone to being shifted by currents. Accurately placing the hoses can lead to costly extra vessel-days on any project. However, our system does not use chains, just a special self-sinking hose.’

He says its superior performance is linked to the unique array and size of the bubbles it creates and the extent to which they absorb and reflect/refract the sound waves.

‘The technology was monitored by an independent research institute associated with Norway’s national technical university (NTNU) which measured the level of noise reaching the fish farm, and to everybody’s surprise and delight, the system showed the best protection of any other system by a large margin.’

The system takes air from Scan Tech's specially designed low emission offshore compressors which can be adapted to ensure only air of medical cleanliness goes into the sea.

As a result of this performance, Scan Tech has been approached by potential clients in the oil and gas and renewables markets keen to protect marine life from noise associated with subsea construction. The team has begun work with a renewable major, scaling-up the technology for use around turbines off the coast of Norway and worldwide.

Chris adds:

‘Scaling up brings with it the challenges of handling a couple of kilometres of hose, as well as storage, deployment, and recovery. Happily, Scan Tech's lifting division has years of experience in deploying wires and hoses, buoys and clump-weights, so can contribute to making this a complete system for our clients.’

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