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A comparison between Shields' threshold criterion and the movement of loosely packed gravel in a tidal channel

A comparison between Shields' threshold criterion and the movement of loosely packed gravel in a... ABSTRACT Observations of the threshold of movement of loosely packed gravel in a tidal current are described. For gravel with equivalent ‘spherical’ diameters D in the range 0.2 ≲D≲ 5.0cm the critical friction velocity u*c, corresponding to the initiation of sediment transport, is given by u*c=7.0 D0.2. At large values of D within the quoted range, the value u*c is significantly lower than would be obtained by a Shields experiment (u*c∞D0.5). By comparing our values of u*c with those obtained under well‐controlled laboratory conditions, the discrepancy with Shields is shown to be due to the open spacing between, and exposure of, individual pebbles on the seabed. By comparing our results with those from upland gravel streams and flume experiments, it is suggested that Shields assumed an excessively large water depth to particle size ratio as a constraint within which the critical sediment entrainment number 0c is valid. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Sedimentology Wiley

A comparison between Shields' threshold criterion and the movement of loosely packed gravel in a tidal channel

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References (19)

Publisher
Wiley
Copyright
Copyright © 1984 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0037-0746
eISSN
1365-3091
DOI
10.1111/j.1365-3091.1984.tb00722.x
Publisher site
See Article on Publisher Site

Abstract

ABSTRACT Observations of the threshold of movement of loosely packed gravel in a tidal current are described. For gravel with equivalent ‘spherical’ diameters D in the range 0.2 ≲D≲ 5.0cm the critical friction velocity u*c, corresponding to the initiation of sediment transport, is given by u*c=7.0 D0.2. At large values of D within the quoted range, the value u*c is significantly lower than would be obtained by a Shields experiment (u*c∞D0.5). By comparing our values of u*c with those obtained under well‐controlled laboratory conditions, the discrepancy with Shields is shown to be due to the open spacing between, and exposure of, individual pebbles on the seabed. By comparing our results with those from upland gravel streams and flume experiments, it is suggested that Shields assumed an excessively large water depth to particle size ratio as a constraint within which the critical sediment entrainment number 0c is valid.

Journal

SedimentologyWiley

Published: Feb 1, 1984

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