Selective gravel entrainment and the empirical evaluation of flow competence

Selective gravel entrainment and the empirical evaluation of flow competence ABSTRACT The concept of flow competence is generally employed to evaluate velocities and bed stresses of river floods from the sizes of the largest sediment particles transported. For the most part, this evaluation has been empirical, combining data from a number of separate flood events in different river systems. Those data are re‐examined and compared with empirical equations for the selective entrainment of gravel from deposits of mixed sizes. It is found that the competence relationships trend counter to those obtained for selective entrainment, indicating that the competence evaluations are affected by varying degrees of selective size entrainment. Individual data sets which have been employed to establish the flow‐competence relationships either show no trend on their own or yield a trend which runs counter to the competence equation, instead being more compatible with the selective‐entrainment relationships. In most instances, the empirical competence equations greatly overestimate the hydraulics of flood flows, and it is suggested that the better established selective entrainment equations be used for competence evaluations as well. Empirical equations are available for this purpose, relating the dimensionless Shields entrainment function or the bed shear stress to the diameter of the largest grain moved and to the median diameter of the deposit as a whole. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Sedimentology Wiley

Selective gravel entrainment and the empirical evaluation of flow competence

Sedimentology, Volume 34 (6) – Dec 1, 1987

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Publisher
Wiley
Copyright
Copyright © 1987 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0037-0746
eISSN
1365-3091
DOI
10.1111/j.1365-3091.1987.tb00599.x
Publisher site
See Article on Publisher Site

Abstract

ABSTRACT The concept of flow competence is generally employed to evaluate velocities and bed stresses of river floods from the sizes of the largest sediment particles transported. For the most part, this evaluation has been empirical, combining data from a number of separate flood events in different river systems. Those data are re‐examined and compared with empirical equations for the selective entrainment of gravel from deposits of mixed sizes. It is found that the competence relationships trend counter to those obtained for selective entrainment, indicating that the competence evaluations are affected by varying degrees of selective size entrainment. Individual data sets which have been employed to establish the flow‐competence relationships either show no trend on their own or yield a trend which runs counter to the competence equation, instead being more compatible with the selective‐entrainment relationships. In most instances, the empirical competence equations greatly overestimate the hydraulics of flood flows, and it is suggested that the better established selective entrainment equations be used for competence evaluations as well. Empirical equations are available for this purpose, relating the dimensionless Shields entrainment function or the bed shear stress to the diameter of the largest grain moved and to the median diameter of the deposit as a whole.

Journal

SedimentologyWiley

Published: Dec 1, 1987

References

  • Threshold of coarse sediment transport in broad and narrow natural streams
    Carling, Carling
  • A comparison between Shields' threshold criterion and the movement of loosely packed gravel in a tidal channel
    Hammond, Hammond; Heathershaw, Heathershaw; Langhorne, Langhorne
  • Threshold of sediment motion in unidirectional currents
    Miller, Miller; McCave, McCave; Komar, Komar

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