Motion of sediment at the bed of rivers

Edward Silberman Fellowship Award Ceremony
2018-2019 Edward Silberman Fellowship Recipient: Santosh Kumar, PhD Student in Mechanical Engineering (advisor: Jiarong Hong)
Keynote Speaker: Mark Schmeeckle, Professor in the School of Geographical Sciences and Urban Planning, Arizona State University

Abstract: The movement of sediment at the bed of a river or a laboratory flume can be viewed by the human eye and recorded by high-speed cameras. Velocimetry techniques can simultaneously record details of the turbulent fluid. It is, thus, surprising that many of the details of this sediment movement, which shapes much of earth’s surface, remains unknown or controversial. Bed load sediment is often thought to move in a series of hops called saltation. However, tracking of particles using high-speed video reveals that saltation models do a poor job of predicting the full distribution of grain motions; many grains move more slowly and for shorter distances than by saltation. The video particle tracking results also show that the temporal variability of grain motion due to turbulence is large at all mean transport rates. New field and lab evidence also suggests that the detailed structure of grain-to-grain contacts within the bed plays a key role in determining sediment transport rates. Furthermore, grain contact structure differs dramatically at different locations and at different times. Laboratory measurements as well as detailed numerical simulations of turbulence and particle motion will be presented to explain what is known about bed load motion in rivers and how that leads to the formation of ripples, dunes, bars, and channels.