Departmental Papers (EES)

Document Type

Journal Article

Date of this Version

3-2012

Publication Source

Journal of Geophysical Research: Earth Surface

Volume

117

Issue

F1

Start Page

F01018

DOI

10.1029/2011JF002075

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.

Copyright/Permission Statement

Copyright © 2012 by the American Geophysical Union.

Comments

This article has a correction that can be found through the DOI: 10.1029/2012JF002608

Keywords

anomalous diffusion, bed load transport, sediment transport

Additional Files

correction.pdf (32 kB)
Correction

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Date Posted: 11 November 2016

This document has been peer reviewed.