The thickness of the transport layer in stratified geomorphic flows

River Flow 2010

This paper is aimed at the development of a model for the thickness of the transport layer in stratified geomorphic flows such as sheet-flows or immature debris flows occurring, for instance, as a consequence of dam failure. These are flows with high geomorphic potential, occurring at or generating high shear stresses, whose ultimate driving mechanism is gravity. The micromechanical characteristics of the sediment and viscous flow-grain interactions are of paramount importance in the definition of the constitutive equations that relate stresses and shear rates within the flow. The model was derived from the granular flow theory based on Chapman-Enskog’s dense gas kinetic theory. A 2DV conceptual model was employed to render the flow structure in a flow in the absence of longitudinal pressure gradients. The 2DV model was further simplified to obtain an implicit formula for the thickness of the transport layer. The role of the flux of fluctuating particle energy and of the granular temperature is clarified. Results of the simplified formula are discussed and compared with the result of the complete model. Solutions of hyperbolic instantaneous dam-break problems over mobile beds, incorporating the present model of the transport layer thickness, are presented.