Problems in Linking the Threshold Condition for the Transport of Cohesionless and Cohesive Sediment Grain

Abstract

The threshold condition for the incipient transport of sediment linking cohesionless to cohesive size ranges is revisited using known concepts. The functional dependence of the threshold or critical shear stress on the principal parameters characterizing the sediment bed is examined, while recognizing that the actual relationships among these parameters remain largely unknown. For marine muds, until further experimental evidence is obtained, it is argued that erosion shear stress formulations for cohesionless sediment transport should be restricted to sediments containing grains larger than about 20 um, and empirical erosion shear strength formulations be applied to sediments smaller than this size. Given this limit, the classical definition of silt size range (2 um to 62um) based on the plastic properties of soil does not appear to be very useful in delineating the domains of cohesion-dominated and cchesionless sediment transport.