Bubble Curtain for Sound Attenuation in Gros-Cacouna, Québec

Marine protection using Bubble Curtain during refection of the pier at Gros-Cacouna

In 2018, the sidewalls of the piers of Gros-Cacouna in Quebec, Canada needed to be resurfaced. Although a Cofferdam was used leaving 2 metres of dry space to work to reduce the underwater sound, the power tools were still producing too much noise for the sensitive species of beluga whales living nearby in the St-Lawrence River. It was required to keep the underwater sound level below a median value of 102 dB right outside the harbour.

The belugas being a protected species, in the call for tender, the Quebec government required that sound levels be monitored and reduced, lowering the impact on this protected species of marine mammal, which is very sensitive to strong sound, especially those at low frequency. The consultant firm GKM Consultants were hired to monitor the underwater sound level to ensure the regulations were met.

2 metres of Cofferdam

How does a bubble curtain work?

The use of Bubble Tubing® linear air diffusers immersed in water creates an efficient bubble curtain which buffers and acts as a sound and pressure barrier. Bubble curtains can attenuate the transmission and intensity of underwater noise comparatively to earmuffs protecting hearing from loud noises. Strategically positioned, these bubble curtains can attenuate various shock waves that are created by underwater activity such as pile driving, dredging, underwater explosions, rock blasting or drilling for oil exploration. Bubble curtains will allow the free passage of vessels during construction and prevent marine wildlife from becoming entrapped inside a closed construction site enabling them to leave the area towards a safe zone, even at the last minute. Bubble curtains are a sensible and durable solution for the environment.

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Product Sold:

• Custom bubble curtain systems using 1 inch I.D. Bubble Tubing®.
  • Double curtain of 100 ft (30 m) for a total of 200 ft (60 m) of weighted Bubble Tubing® linear diffuser.
  • 100 ft (30 m) of Torpedo self sinking air feeder lines.
  • All other required hardware.

Bubble Tubing® is a third party certified, industrial linear air diffuser typically used for aeration, de-icing and bubble curtains. It is designed and manufactured in Canada to our highest standards and specifications.

Air bubble diffusers such as Bubble Tubing® produce a large homogenous dispersion of small air bubbles which are typically between one (1) to ten (10) mm in diameter.  These precise bubble sizes and density ensure that coalescence is avoided and that an even distribution of bubbles will rise from the bottom to the surface of waterways, rivers, lakes or reservoirs to act as curtains.

Compressed air enters the network of bubble curtains through manifolds with flow meters to create the expected results that contractors are searching for to meet environmental requirements. The nature of the Bubble Tubing® prevents it from clogging or fouling which is typically found in porous hose or competing diffusers.

Installation:

Using an OceanSonics hydrophone when the demolition work started, it was registered that the noise was exceeding the acceptable limit outside of the perimeter. Data were hard to retrieve because of the lack of real-time data transmitting tools. The hydrophone was installed, and data were only analyzed at the end of the working day. Even though data retrieval was a challenge, a sound mitigation system was still required to respect sound limits.

Different solutions were considered such as working only 1 team at a time and using lower impact power tools. Those solutions would have significantly increased work time and therefore increase the cost of the project. That’s why a bubble curtain was considered as a mitigation tool. GKM Consultant being familiar with the technology for having previously worked with it successfully decided on a bubble curtain by Bubble Tubing® technology. Once the bubble curtain in a crescent shape was installed at 5 metres off the cofferdam, construction work could resume.

Bubble curtain installed 5 m from the cofferdam during the repair work

R&D Validations:

CanadianPond.ca Products Ltd. invested in a third-party study (GKM Consultants) to prove the efficacy of a bubble curtain (Bubble Tubing®) for sound attenuation. This study was conducted in the Bedford Basin back in 2018 in Nova Scotia. During this study it was well demonstrated that the use of a bubble curtain can reduce the sound travelling in water by up to 80 dB. The bubble curtain was effective at reducing low frequencies and high frequencies.

Results of sound attenuation tests performed by third-party as part of the research and development. Abscissa in logarithmic scale

Conclusion:

To call this case a success, the following 3 frequency bands needed to be aligned; the frequency bands emitted during the work, the frequencies to which the animals are sensitive to and frequency on which the curtain is effective should all be on the same spectrum, in this case, somewhere in the low frequency’s spectrum. Analysis done with the data retrieved from the OceanSonic hydrophone showed that the bubble curtain using Bubble Tubing® technology was able to sufficiently reduce the dB level to keep the sound level acceptable for the beluga in the St-Lawrence River.

Efficacy of the curtain:

Bubble Tubing® technology successfully demonstrated its effectiveness during this project as a bubble curtain for sound attenuation. It was found that a 3 to 5 dB sound reduction was registered during the process of this marine work. 3 to 5 dB reduction also means a pressure reduction generated by sound up to 44% in fresh water which is significant especially for marine mammals sensitive to underwater noise. The bubble curtain allowed the marine construction sound to drop below the limit the government set for the construction company which was 102 dB and resume work in a timely manner. Bubble Tubing® helped take care of the Beluga in the St-Lawrence River.

Regulations on sound attenuation are increasingly common around the globe. We’ve encountered a quite large range of dB reduction between 5 dB to 20 dB reduction requirement for mitigation method. Those targets vary depending on species such as: tortoise and turtles to protect and the region.

Do you have an project ? Contact us, it will be our pleasure to help you in the development of your project.

Link :

GKM Consultant article on the subject : Click here