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Variability of bed mobility in natural, gravel‐bed channels and adjustments to sediment load at local and reach scales

Water Resources Research

By:
, ORCID iD , , ORCID iD , and
https://doi.org/10.1029/2000WR900238

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Abstract

Local variations in boundary shear stress acting on bed‐surface particles control patterns of bed load transport and channel evolution during varying stream discharges. At the reach scale a channel adjusts to imposed water and sediment supply through mutual interactions among channel form, local grain size, and local flow dynamics that govern bed mobility. In order to explore these adjustments, we used a numerical flow model to examine relations between model‐predicted local boundary shear stress (тj( and measured surface particle size (D50) at bank‐full discharge in six gravel‐bed, alternate‐bar channels with widely differing annual sediment yields. Values of тj and D50 were poorly correlated such that small areas conveyed large proportions of the total bed load, especially in sediment‐poor channels with low mobility. Sediment‐rich channels had greater areas of full mobility; sediment‐poor channels had greater areas of partial mobility; and both types had significant areas that were essentially immobile. Two reach‐mean mobility parameters (Shields stress and Q*) correlated reasonably well with sediment supply. Values which can be practicably obtained from carefully measured mean hydraulic variables and particle size would provide first‐order assessments of bed mobility that would broadly distinguish the channels in this study according to their sediment yield and bed mobility.

Additional publication details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Variability of bed mobility in natural, gravel‐bed channels and adjustments to sediment load at local and reach scales
Series title:
Water Resources Research
DOI:
10.1029/2000WR900238
Volume:
36
Issue:
12
Year Published:
2000
Language:
English
Publisher:
American Geophysical Union
Contributing office(s):
Western Ecological Research Center
Description:
13 p.
First page:
3743
Last page:
3755