Particle Sorting: From Rotating Drums To Riverbeds

Kimberly Hill, Assistant Professor of Civil Engineering, University of Minnesota

As gravel particles travel along a riverbed, one might predict that the apparently random movement and interparticle collisions might lead to a relatively uniform size distribution. However, this is not the case. In stream and river beds particles are often segregated, in situations including downstream fining, armouring, and gravel patch formation. There are many open questions regarding the physical mechanisms that drive and maintain the segregation structures. Within the last few decades, driven both by industrial need and interest in pattern formation, particle sorting has been studied in very simple systems, such as rotating drums, revealing distinct mixing and sorting mechanisms and brilliant patterns that arise as a result of the interplay of these mechanisms. This talk will include an overview of experiments and theory involving pattern formation in rotating drums. Then, an analogy will be made between these patterns and some sorting effects observed in riverbeds and debris flows.

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