Table 2. Observed and calculated critical stresses (T_c), in Pascals (Pa), for artificial sand and oil agglomerates (aSOAs) with observed incipient motion. T_Shields, _inst.is the stress at the observed time of incipient motion, T_Shields, _max. is the maximum stress in the oscillatory flow prior to the observed time of incipient motion, T_c, _high is the calculated shear stress using an unmodified Shields parameter, and T_Shields, _medium and T_Shields, _low are modified critical shear-stress values for exposed particles in a mixed-grain-size bed (see Plant and others, 2013).