In contrast to Newtonian fluids, some naturallyoccurring materials (i.e., fluids with strength) willnot deform until yield stress has been exceeded (Fig.2); once the yield stress is exceeded the deformationPis linear. Such materials with strength are consideredto be Bingham plastic. For Bingham plastics, thecriterion for initiation of turbulence is based on boththe Reynolds Number, R, and the Bingham Number,B (Fig. 2). Although debris flows can develop turbulence (Enos, 1977), such flows are not diagnostic ofmost debris flows that are laminar (i.e., no fluidmixing across streamlines). Johnson (1970) favored aBingham plastic rheologic model for debris flows.