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Surface Particle Sizes on Armoured Gravel Streambeds: Effects of Supply and Hydraulics


Whiting, P.J.;King, John G. 2003. Surface particle sizes on armoured gravel streambeds: effects of supply and hydraulics. Earth Surface Processes and Landforms, 28: 1459-1471.

Most gravel-bed streams exhibit a surface armour in which the median grain size of the surface particles is coarser than that of the subsurface particles. This armour has been interpreted to result when the supply of sediment is less than the ability of the stream to move sediment. While there may be certain sizes in the bed for which the supply is less than the ability of the stream to transport these particles. These sizes of particles the 'supply limited' and 'hydraulically limited' in their transport, respectively, and can be differentiated in dimensionless sediment transport rating curves by size fractions. The supply- and hydraulically limited sizes can be distinguished also by comparing the size of particles of the surface and subsurface. Those sizes that are supply-limited are winnowed from the bed and are under-represented in the surface layer. Progressive truncation of the surface and subsurface size distributions from the fine end and rrecalculation until the size distributions are similar (collapse), establishes the break between supply- and hydraulically limited sizes. At sites along 12 streams in Idaho ranging in drainage area from about 100 to 4900 km2, sediment transport rating curves by size class and surface and subsurface size distributions were examined. The break between sizes that were supply- and hydraulically limited as determined by examination of the transport rate and surface and subsurface size distributions was similar. the collapse size as described by its percentile in teh cumulative size distribution averaged D36 of the surface and D73 of the subsurface. The discharge at which the collapse size began to move averaged 88 per cent of bankfull discharge. The collapse size decreased as bed load yield increased and increased with a degree of selective transport.

Keywords: armour, sediment supply, sediment transport, gravel


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http://www.fs.fed.us/rm/pubs_other/rmrs_2003_whiting_p001.pdf

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Title: RMRS Other Publications: Surface Particle Sizes on Armoured Gravel Streambeds: Effects of Supply and Hydraulics
Electronic Publish Date: January 18, 2004
Expires: Indefinite
Last Update:
January 18, 2004

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