Title: Segregation dynamics in fluid-driven annular couette flow: contribution of subsurface processes to surface armoring in an idealized riverbed

Author (Poster): Behrooz Ferdowsi, University of Pennsylvania

Abstract:

We study the granular physics of erosion, deposition and sediment transport in a bidisperse fluid-driven sheared granular systems. The experiments are performed in an idealized laboratory river developed at PennSed at the University of Pennsylvania. The setup consists of an annular flume of immersed granular bed, sheared in free surface condition by a rotating top plate. The setup allows us to investigate armoring in riverbeds. Armoring is the development of the coarse surface in gravel bedded rivers and can be related to segregation in granular systems. By imaging the slow granular dynamics deep into the bed. we monitor the subsurface to surface evolution of the granular bed. We observe that segregation in our system takes place due to 1) fluid-induced shear at the first few particle diameter depth (active layer) and 2) creep (slow rearrangement of grains deep in the bed). The two segregation mechanisms tend to have significantly different timescales.