The incidence and nature of bedload transport during flood flows in coarse‐grained alluvial channels

The incidence and nature of bedload transport during flood flows in coarse‐grained alluvial... A continuous record reveals that the incidence of bedload in a coarse‐grained river channel changes from flood to flood. Long periods of inactivity encourage the channel bed to consolidate sufficiently so that bedload is largely confined to the recession limb of the next flood‐wave. But when floods follow each other closely, the bed material is comparatively loose and offers less resistance to entrainment. In this case, substantial amounts of bedload are generated on the rising limb. This is confirmed by values of bed shear stress or stream power at the threshold of initial motion which can be up to five times the overall mean in the case of isolated floods or those which are the first of the season. This produces a complicated relationship between flow parameters and bedload and explains some of the difficulties in establishing bedload rating curves for coarse‐grained channels. Besides this, the threshold of initial motion is shown to occur at levels of bed shear stress three times those at the thresholds of final motion. This adds further confusion to attempts at developing predictive bedload equations and clearly indicates at least one reason why equations currently in use are unsatisfactory. Bedload is shown to be characterized by a series of pulses with a mean periodicity of 1.7 hours. In the absence of migrating bedforms, it is speculated that this well‐documented pattern reflects the passage of kinematic waves of particles in a slow‐moving traction carpet. The general pattern of bedload, including pulsations, is shown to occur more or less synchronously at different points across the stream channel. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Earth Surface Processes and Landforms Wiley

The incidence and nature of bedload transport during flood flows in coarse‐grained alluvial channels

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Publisher
Wiley
Copyright
Copyright © 1985 John Wiley & Sons, Ltd
ISSN
0197-9337
eISSN
1096-9837
D.O.I.
10.1002/esp.3290100107
Publisher site
See Article on Publisher Site

Abstract

A continuous record reveals that the incidence of bedload in a coarse‐grained river channel changes from flood to flood. Long periods of inactivity encourage the channel bed to consolidate sufficiently so that bedload is largely confined to the recession limb of the next flood‐wave. But when floods follow each other closely, the bed material is comparatively loose and offers less resistance to entrainment. In this case, substantial amounts of bedload are generated on the rising limb. This is confirmed by values of bed shear stress or stream power at the threshold of initial motion which can be up to five times the overall mean in the case of isolated floods or those which are the first of the season. This produces a complicated relationship between flow parameters and bedload and explains some of the difficulties in establishing bedload rating curves for coarse‐grained channels. Besides this, the threshold of initial motion is shown to occur at levels of bed shear stress three times those at the thresholds of final motion. This adds further confusion to attempts at developing predictive bedload equations and clearly indicates at least one reason why equations currently in use are unsatisfactory. Bedload is shown to be characterized by a series of pulses with a mean periodicity of 1.7 hours. In the absence of migrating bedforms, it is speculated that this well‐documented pattern reflects the passage of kinematic waves of particles in a slow‐moving traction carpet. The general pattern of bedload, including pulsations, is shown to occur more or less synchronously at different points across the stream channel.

Journal

Earth Surface Processes and LandformsWiley

Published: Jan 1, 1985

References

  • Bed load transport by natural rivers
    Bagnold, Bagnold
  • The dynamics of a river bend: a study in flow and sedimentary processes
    Bridge, Bridge; Jarvis, Jarvis
  • Threshold of sediment motion under unidirectional currents
    Miller, Miller; McCave, McCave; Komar, Komar
  • Measurement of hydraulic and sediment transport variables in a small recirculating flume
    Rathbun, Rathbun; Guy, Guy
  • An electromagnetic device for automatic detection of bedload motion and its field applications
    Reid, Reid; Brayshaw, Brayshaw; Frostick, Frostick

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