Granular physics of sediment transport

by Douglas Jerolmack

Aula Conversi (Dipartimento di Fisica - Ed. G. Marconi)

Aula Conversi

Dipartimento di Fisica - Ed. G. Marconi

Fluid-sheared granular transport sculpts landscapes and undermines infrastructure, yet predicting the onset of sediment transport remains notoriously unreliable. For almost a century, this onset has been treated as a discontinuous transition at which hydrodynamic forces overcome gravity-loaded grain-grain friction. Many studies have emphasized the confounding role of large-scale fluctuations in fluid stress as a result of turbulence. Recently, however, researchers have begun to recognize the importance of particle-particle interactions in determining both the rheology of and river patterns resulting from bed-load transport. After examining the dynamics of fluid-driven sediment transport under a laminar shear flow, over a wide range of time scales, we propose a new phase diagram that unites fluid-driven sediment transport with a broader class of granular systems, while presenting challenges to current models for both. Finally, we show some consequences of these granular dynamics on the transport of river sediment tracers in natural rivers.