Transition between two bed-load transport regimes: Saltation and sheet flow

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43 Scopus citations


In the saltation regime where bed-shear stress is low, bed load moves by sliding, rolling, and saltating along the bed, while in the sheet-flow regime where bed-shear stress is high, it travels by a combination of saltation and sheet flow. In this paper a theoretical model is developed for predicting the onset of the sheet-flow regime as shear stress increases. This model is based on a new variable Pb representing the proportion of grains on the bed that are entrained as bed load. The model yields the equation Pb=2.56θG3 in which G=1-θc/θ, θ=dimensionless bed-shear stress; and θc=critical value of θ at which grains begin to move. The equation shows that θt, which is the value of θ at the onset of the sheet-flow regime and is assumed to occur when Pb=1, is around 0.5 with the exact value controlled by θc. For example, when θc=0.045, θt=0.52. The theoretical model is verified by performing a nonlinear regression analysis on data from 285 flume experiments. Additional flume experiments with a high-speed video (HSV) system result in consistent values of θ for the onset of the sheet-flow regime, which support the theoretical model. The HSV images further reveal that: (1) the sheet-flow regime is characterized by granular sheets or laminations; and (2) a zone of mixed saltation and rolling grains exists not only in the saltation regime but also in the sheet-flow regime.

Original languageEnglish (US)
Pages (from-to)340-349
Number of pages10
JournalJournal of Hydraulic Engineering
Issue number3
StatePublished - Mar 2008


  • Bed load
  • Saltation
  • Sediment transport
  • Sheet flow

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Water Science and Technology
  • Mechanical Engineering


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