Grain-scale mechanics of sediment transport
Studies of large-scale landscape evolution ultimately depend on rate laws for erosion and sediment transport mechanisms that operate at the scale of sediment grains. Several recent projects in the group focused on building a better understanding of grain-scale processes.
Eric Deal and Santiago Benavides are collaborating with Prof. Jeremy Venditti (Simon Fraser University) and Prof. Ken Kamrin and Qiong Zhang (MIT Mechanical Engineering) to study granular phenoma in bed-load sediment transport.
Many studies have examined how sediment grain size affects the sediment entrainment threshold and transport rate, but few have considered the role of grain shape. Eric Deal used laboratory flume experiments with a variety of grain shapes to show that grain shape has a large effect on bedload transport rates. He developed a shape-independent sediment transport law that accounts for grain shape effects on fluid drag and granular friction.
- Deal, E.A., J.G. Venditti, S.J. Benavides, R. Bradley, Q. Zhang, K. Kamrin, and J.T. Perron. Grain shape effects in bed load sediment transport. In review. Preprint
Sediment transport by wind or water near the threshold of grain motion is dominated by rare and seemingly random transport events. This intermittency makes it difficult to calibrate sediment transport laws, or to define an unambiguous threshold for grain entrainment, both of which are crucial for predicting sediment transport rates. Santiago Benavides developed a model that describes this intermittency and found that the noisy statistics of sediment transport contain useful information about the sediment entrainment threshold and the variations in driving fluid stress.
- Benavides, S.J., E.A. Deal, M. Rushlow, J.G. Venditti , Q. Zhang, K. Kamrin, and J.T. Perron (2022). The impact of intermittency on bed load sediment transport. Geophysical Research Letters, 49, e2021GL096088. https://doi.org/10.1029/2021GL096088.
Another project investigated feedbacks between wave-driven flows, sand transport, and ripples like the ones you see at the beach. Jaap Nienhuis and Justin Kao showed that the spacing between ripple crests is set by the maximum length of the flow separation zone downstream of the crests, which gives rise to the well-known relationship between ripple size and wave orbital diameter.
Taylor Perron did a series of wave tank experiments with a team that included Kim Huppert, Abby Koss, Andy Wickert (U. Minnesota) and Paul Myrow (Colorado College), and demonstrated how wave ripple patterns found in ancient rocks form as wave conditions change.
- Nienhuis, J.H., J.T. Perron, J.C.T. Kao and P.M. Myrow (2014), Wavelength selection and symmetry breaking in orbital wave ripples, J. Geophys. Res., 119, 2239-2257, http://doi.org/10.1002/2014JF003158.
- Perron, J.T., P. Myrow, K.L. Huppert, A. Koss and A. Wickert (2018). Ancient record of changing flows from wave ripple defects. Geology, 46, 875-878, http://doi.org/10.1130/G45463.1.
- Myrow, P., D. Jerolmack and J.T. Perron (2018). Bedform disequilibrium. Sedimentology, 88, 1096-1113, http://doi.org/10.2110/jsr.2018.55.
- Lamb, M.P., W.W. Fischer, T.D. Raub, J.T. Perron and P.M. Myrow (2012), Origin of giant wave ripples in Snowball Earth cap carbonate. Geology, 40, 827–830, http://doi.org/10.1130/G33093.1.