The Environmental Fluid Dynamics Lecture Series Presents a Seminar

1. The Environmental Fluid Dynamics Lecture Series Presents a Seminar Professor Gary Parker W.H. Johnson Professor of Engineering and also Geology University of Illinois Champaign Urbana Tuesday, January 21 Rm. 117 Hayes-Healy 11am-12noon Emplacement of Massive Turbidities Linked to Extinction of Turbulence in Turbidity Currents (by Mariano Cantero, Tzu-haoYeh and Gary Parker) ABSTRACT Turbulent flows that carry suspended sediment are naturally self-stratifying. Such sediment settles toward the bed with a flux that is linearly dependent upon fall velocity. Maintenance of this sediment in suspension requires a balancing upward Reynolds flux, further dictating that mean suspended sediment concentration should decrease upward. Since higher concentration implies larger density, the implication is that sediment suspension generates its own stable stratification. In the case of rivers, this self-stratification can act to damp turbulence, so decreasing the ability of the flow to maintain the suspension. The flow itself, however, is not extinguished, because the driving force of the flow results from the downstream component of gravity acting on the water, rather than the sediment phase. Turbidity currents, i.e. dense bottom currents driven by suspended sediment, have many similarities to river flows. They differ, however, in that the driving force of the flow acts directly on the sediment. In this case, sufficient self-stratification can kill the entire flow, causing the emplacement of a massive deposit of sediment. Conditions for this extinguishing of the flow can be reached as, for example, a turbidity current traverses ever-lower slopes. These results are demonstrated using direct numerical simulations of channel flows and turbidity currents.