Quantifying Hydrograph Unsteadiness and Sediment Cobble Dispersion

Project Description: 

Sediment transport is an intrinsically stochastic process, and measurement of bed load in the environment is further complicated by the unsteady nature of river flooding. Here we present a methodology for analyzing sediment tracer data with unsteady forcing. We define a dimensionless impulse by integrating the cumulative excess shear velocity for the duration of measurement, normalized by grain size. We analyze the dispersion of a plume of cobble tracers in a very flashy stream over two years. The mean and variance of transport distance collapse onto well-defined linear and power-law relations, respectively, when plotted against cumulative dimensionless impulse. Data suggest that the asymptotic limit of bed load tracer dispersion is super diffusive, in line with a broad class of geophysical flows exhibiting strong directional asymmetry (advection), thin-tailed step lengths and heavy-tailed waiting times. The impulse framework justifies the use of quasi-steady flow approximations for long-term river evolution modeling.

Research Location: 
Core Area(s) and/or Keywords: 

Sediment Transport, Geomorphology, Hydrograph

Source of Funding: 
NSF CZO Program
Relevant Publications: 

Phillips, C. B., R. L., Martin, and D. J., Jerolmack (2013) Impulse framework for unsteady flows reveals super-diffusive bed load transport, Geophysical Research Letters. DOI:10.1002/grl.50323

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Contact Information
Person(s) Completing This Form: 
Colin B. Phillips
Colin B. Phillips, Douglas J. Jerolmack
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