Exploring a semimechanistic episodic Langevin model for bed load transport: Emergence of normal and anomalous advection and diffusion regimes

Niannian Fan, Arvind Singh, Michele Guala, Efi Foufoula-Georgiou, Baosheng Wu

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

Bed load transport is a highly stochastic, multiscale process, where particle advection and diffusion regimes are governed by the dynamics of each sediment grain during its motion and resting states. Having a quantitative understanding of the macroscale behavior emerging from the microscale interactions is important for proper model selection in the absence of individual grain-scale observations. Here we develop a semimechanistic sediment transport model based on individual particle dynamics, which incorporates the episodic movement (steps separated by rests) of sediment particles and study their macroscale behavior. By incorporating different types of probability distribution functions (PDFs) of particle resting times Tr, under the assumption of thin-tailed PDF of particle velocities, we study the emergent behavior of particle advection and diffusion regimes across a wide range of spatial and temporal scales. For exponential PDFs of resting times Tr, we observe normal advection and diffusion at long time scales. For a power-law PDF of resting times (i.e., f(Tr)Tr-ν), the tail thickness parameter ν is observed to affect the advection regimes (both sub and normal advective), and the diffusion regimes (both subdiffusive and superdiffusive). By comparing our semimechanistic model with two random walk models in the literature, we further suggest that in order to reproduce accurately the emerging diffusive regimes, the resting time model has to be coupled with a particle motion model able to produce finite particle velocities during steps, as the episodic model discussed here.

Original languageEnglish (US)
Pages (from-to)2789-2801
Number of pages13
JournalWater Resources Research
Volume52
Issue number4
DOIs
StatePublished - Apr 1 2016

Bibliographical note

Publisher Copyright:
© 2016. American Geophysical Union. All Rights Reserved.

Keywords

  • advection
  • diffusion
  • episodic Langevin equation
  • normal/anomalous
  • resting time
  • velocity

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