Phillips, Colin BMartin, Raleigh LJerolmack, Douglas J2023-05-222023-05-222013-04-162015-11-12https://repository.upenn.edu/handle/20.500.14332/33050Sediment 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 superdiffusive, 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.Copyright © 2013 by the American Geophysical Union.bed load transporthydrograph unsteadinessanomalous diffusionsediment tracer particlesAtmospheric SciencesClimateEarth SciencesEnvironmental SciencesPhysical Sciences and MathematicsArticle