The Physical Basis for Anomalous Diffusion in Bed Load Transport

Loading...
Thumbnail Image
Penn collection
Departmental Papers (EES)
Degree type
Discipline
Subject
anomalous diffusion
bed load transport
sediment transport
Earth Sciences
Environmental Sciences
Geomorphology
Hydrology
Physical Sciences and Mathematics
Sedimentology
Funder
Grant number
License
Copyright date
Distributor
Author
Martin, Raleigh L
Schumer, Rina
Contributor
Abstract

Recent studies have observed deviation from normal (Fickian) diffusion in sediment tracer dispersion that violates the assumption of statistical convergence to a Gaussian. Nikora et al. (2002) hypothesized that particle motion at short time scales is superdiffusive because of inertia, while long-time subdiffusion results from heavy-tailed rest durations between particle motions. Here we test this hypothesis with laboratory experiments that trace the motion of individual gravels under near-threshold intermittent bed load transport (0.027 < τ* < 0.087). Particle behavior consists of two independent states: a mobile phase, in which indeed we find superdiffusive behavior, and an immobile phase, in which gravels distrained from the fluid remain stationary for long durations. Correlated grain motion can account for some but not all of the superdiffusive behavior for the mobile phase; invoking heterogeneity of grain size provides a plausible explanation for the rest. Grains that become immobile appear to stay at rest until the bed scours down to an elevation that exposes them to the flow. The return time distribution for bed scour is similar to the distribution of rest durations, and both have power law tails. Results provide a physical basis for scaling regimes of anomalous dispersion and the time scales that separate these regimes.

Advisor
Date Range for Data Collection (Start Date)
Date Range for Data Collection (End Date)
Digital Object Identifier
Series name and number
Publication date
2012-03-01
Journal title
Journal of Geophysical Research: Earth Surface
Volume number
Issue number
Publisher
Publisher DOI
Journal Issue
Comments
This article has a correction that can be found through the DOI: 10.1029/2012JF002608
Recommended citation
Collection