A Conceptual Model of Energy Partitioning in the Collision of Saltating Grains with an Unconsolidated Sediment Bed

Abstract

Abstract Grain-bed collision is a key component of saltation, but substantial uncertainty remains regarding many aspects of this process. Previous empirical work is used to develop a conceptual model of this process that accounts for the partitioning of impact energy between rebounding grains and the bed. The model envisions two distinct collision regimes: (i) a quasi-elastic regime at low impact speeds and (ii) an inelastic regime at high impact speeds. In the quasi-elastic regime, colliding grains retain a constant proportion of their kinetic energy, and thus rebound at speeds that are proportional to the impact speed and shear velocity. In the inelastic regime, colliding grains retain a fixed and limited amount of kinetic energy, transferring any excess above this limit to the bed. Rebound speeds are thus constant and independent of both impact speed and shear velocity. Impact energy transferred to the bed is expended in “deformation” (i.e., ejection, rearrangement, etc. of bed grains). These two colli...