2019 CSCE Annual Conference - Laval (Greater Montreal)

2019 CSCE Annual Conference - Laval (Greater Montreal) Conference


Title
Mitigation of underwater sound levels with bubble curtains during resurfacing operations of the piers at the port of Gros-Cacouna

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Author(s)
Mr. Djibril Sy, GKM Consultants (Presenter)
Mr. Vincent Le Borgne, GKM Consultants
Mr. Énias Antoine, GKM Consultants
Mr. Shayn Levoy, Canadian Pond
Mr. Mario Paris, Canadian Pond
Abstract

Protection of marine mammals in the vicinity of human activities has been a growing concern in Canada over the past decade. Construction activities, oil and gas exploitation, container boats can all have direct impacts on marine mammals such as beluga whales and dolphins. As part of maintenance of the installations of the port of Gros-Cacouna, Quebec, the sidewalls of the piers were resurfaced on a total depth of 9 m. Cofferdam were built 2 meter away from the piers to allow access to the sidewalls in “dry dock”. The resurfacing operations required the removal of a 25 cm thick layer of concrete from the sidewalls with power tools. Using an OceanSonics hydrophone, it was confirmed that the main sources of underwater noise in the harbour were jackhammers, gas-powered concrete saws and air hoses. It was required to maintain ambient sound levels below a median value of 102 dB re 1 µPa immediately outside the harbour. The project requirements additionally specified that if it were impossible to remain below this value at all times, sound-emitting activities were to be performed only during the October 1st to March 31st period. Other sound level parameters such as SELcum and SPLpeak were measured and monitored over the course of the project.

Because the stringent requirements for the protection of wildlife proved difficult to attain, a 30 m long BubbleTubing® was deployed in a crescent shape at approximately 5 m from the cofferdam to provide additional sound level control. The BubbleTubing® produces a dense “curtain” of rising bubbles that interacts with sound. Experimental results from this field project showed a global attenuation of the order of 10 dB. These results are analyzed in light of a controlled test phase conducted previously in 2018 in the Bedford Basin located in Halifax, Nova-Scotia. This case studies demonstrates that a bubble curtain can be an asset to protect marine mammals from underwater construction work.