Research Document - 2004/119

Assessing Ballast Water Exchange Zones on the Scotian Shelf and Gulf of Maine

By Brickman, D., B.D. Petrie, P.C. Smith

Abstract

This paper assesses the risk of various alternate ballast water exchange zones in the Scotian Shelf (SS) and Gulf of Maine (GoM) region of Maritime Canada. The authors assembled available drifter data to look at drift and dispersion on the shelf. These data were too sparse to formulate useful advice about particular traffic corridors. Therefore, a numerical circulation model of the SS/GoM was used to assess dispersion along various vessel routes on the shelf. Model output formed the basis of the advice on ballast water exchange in Maritime Canada.

The preferred option for alternative ballast water exchange would occur off the shelf (beyond the 1000 m isobath). This is based on the existence of a persistent shelfbreak current that acts as a barrier to onshelf transport.

Recognizing that ships transiting the north-south coastal route often do not normally travel offshelf, we propose the following:

• For ships that can travel beyond the 1000 m isobath without a major course diversion, we recommend that they do so. Vessels should exchange in waters deeper than 1000 m, west of Sable Island and the Gully and away from the entrance to N.E. Channel. The nominal coordinates of this zone, starting from the most southeast point and proceeding counter-clockwise, are as follows: (-60.0,43.0), (-60.25,43.40), then following the 1000 m isobath to (-62.90,42.75), (-66.0,41.25), then following the 1000 m isobath to (-69.25,39.90) (-68.75,39.38);
• For ships that can not reach the 1000 m isobath without a major diversion:
  • Traffic transiting to/from the Bay of Fundy should exchange in the Gulf of Maine, in water deeper than 100 m;
  • Traffic crossing the Gulf of Maine and using a coastal route on the Scotian Shelf should exchange in the Gulf of Maine, in water deeper than 100 m;
  • Considering that safe, complete ballast water exchange requires between 350 and 400 nautical miles, the full length of the alternate ballast water exchange zones may be necessary.

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