As observed in several recent cases (e.g., DBL-152, Enbridge-Kalamazoo), under certain circumstances, spilled oil can sink to the bottom of a water body. Once on the bottom, the oil can move or even remobilize into the water column. The critical shear stress (CSS) is used to accurately predict the movement of sunken oil along and off the bottom. Unfortunately, shear stress has only been measured for one sunken oil (Hibernian Crude API = 34). The Coastal Response Research Center (CRRC) at the University of New Hampshire (UNH) has an annular flume equipped with high-definition cameras and an acoustic velocimeter that can be used to estimate CSS by measuring the instantaneous, three-dimensional water current velocities at which sunken oils move and erode as visible oil droplets. The results reported are for an Alberta bitumen, tested at temperatures between 5° and 28°C in freshwater.

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