Boom system and its use to attenuate underwater sound or shock wave transmission

A method of attenuating underwater transmission of sound or shock waves comprising:

• surrounding a site of underwater activity with a boom system comprising:
• a support system,
• a curtain comprising a sheet of flexible material which allows water to flow theretbrough, the curtain being suspended from the support system such that an upper end thereof is positioned above the water level and a lower end thereof positioned above the floor of the body of water,
• a skirt comprising a sleeve formed of a deformable material which resists folding but is not a geosynthetic material and a ballast positioned within the sleeve, the skirt being connected to the lower end of the curtain or to the support system, wherein the curtain and the skirt together extend substantially the entire water column, with the ballast-weighted skirt resting against the floor of the body of water, thereby defining a perimeter, and
• a gas injection system comprising a plurality of outlets which surround the site of underwater activity, the plurality of outlets being positioned between the site of underwater activity and the perimeter;
• injecting gas into the water through the plurality of outlets to form a gas curtain during performance of an underwater activity capable of generating sound or shock waves, whereby the curtain minimizes dissipation of the gas curtain to improve the efficacy of sound or shock wave attenuation as compared to a gas curtain in the absence of the curtain and skirt.