Flocculation of the fine particulate portion of drilling mud during discharge into the ocean provides a pathway for an impact on the benthic environment in that the higher settling velocity of flocculated particles leads to higher concentrations near the sea floor. The benthic boundary layer transport model, bblt, has been developed for predicting the dispersion and transport of suspended sediment in the benthic boundary layer on the continental shelf. Past bblt applications aimed at impact zone assessment of drill mud discharges on the Atlantic Canadian shelf have used a constant settling velocity to describe particle settling. However, recent observations on the shelf suggest that natural floes break up when the turbulent shear stress exceeds 0.1 Pa. We incorporate a variable settling velocity into the bblt model to investigate how stress-dependant flocculation affects the magnitude and frequency of high drill mud concentrations near the sea floor. Applications to the Hibernia drill site on the Grand Banks and the Cohasset site near Sable Island are considered.
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