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Effects of hydraulic roughness on surface textures of gravel-bed rivers

Water Resources Research

By:
,
DOI: 10.1029/1999WR900138

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Abstract

Field studies of forest gravel-bed rivers in northwestern Washington and southeastern Alaska demonstrate that bed-surface grain size is responsive to hydraulic roughness caused by bank irregularities, bars, and wood debris. We evaluate textural response by comparing reach-average median grain size (D50) to that predicted from the total bank-full boundary shear stress (??0(bf)), representing a hypothetical reference condition of low hydraulic roughness. For a given ??0(bf), channels with progressively greater hydraulic roughness have systematically finer bed surfaces, presumably due to reduced bed shear stress, resulting in lower channel competence and diminished bed load transport capacity, both of which promote textural fining. In channels with significant hydraulic roughness, observed values of D50 can be up to 90% smaller than those predicted from ??0(bf). We find that wood debris plays an important role at our study sites, not only providing hydraulic roughness but also influencing pool spacing, frequency of textural patches, and the amplitude and wavelength of bank and bar topography and their consequent roughness. Our observations also have biological implications. We find that textural fining due to hydraulic roughness can create usable salmonid spawning gravels in channels that otherwise would be too coarse.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Effects of hydraulic roughness on surface textures of gravel-bed rivers
Series title:
Water Resources Research
DOI:
10.1029/1999WR900138
Volume
35
Issue:
11
Year Published:
1999
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
3507
Last page:
3521
Number of Pages:
15