Unification of Aeolian and Fluvial Sediment Transport Rate from Granular Physics.

One of the physically least understood characteristics of geophysical transport of sediments along sediment surfaces is the well-known experimental observation that the sediment transport rate Q is linearly dependent on the fluid shear stress τ applied onto the surface in air, but is nonlinearly dependent on τ in water. Using transport simulations for a wide range of driving conditions, we show that the scaling depends on the manner in which the kinetic fluctuation energy of transported particles is dissipated: via predominantly fluid drag and quasistatic contacts (linear) versus fluid drag and quasistatic and collisional contacts (nonlinear). We use this finding to derive a scaling law (asymptotically Q∼τ^{2}) in simultaneous agreement with measurements in water and air streams.