2013
Scheingross, Joel S.; Winchell, Eric W.; Lamb, Michael P.; Dietrich, William E.
Influence of bed patchiness, slope, grain hiding, and formdrag on gravel mobilization in very steep streams Journal Article
In: Journal of Geophysical Research-Earth Surface, vol. 118, no. 2, pp. 982–1001, 2013.
Abstract | Links | BibTeX | Tags: ERCZO, gravel mobilization, steep streams
@article{Scheingross2013,
title = {Influence of bed patchiness, slope, grain hiding, and formdrag on gravel mobilization in very steep streams},
author = {Joel S. Scheingross and Eric W. Winchell and Michael P. Lamb and William E. Dietrich},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Scheingross_2013JournGeophyRes-EarthSurf.pdf},
doi = {10.1002/jgrf.20067},
year = {2013},
date = {2013-06-10},
journal = {Journal of Geophysical Research-Earth Surface},
volume = {118},
number = {2},
pages = {982–1001},
abstract = {Steep streams are a major portion of channel networks and provide a link to transport sediment from hillslopes to lower gradient rivers. Despite their importance, key unknowns remain, perhaps foremost of which is evaluating in steep streams empirical laws for fluvial sediment transport developed for low-gradient rivers. To address this knowledge gap, we painted sediment in situ over 3 years to monitor incipient sediment motion and sediment-patch development in five small (drainage areas of 0.04–2 km2) and steep (slopes of 5–37%) tributaries of Elder Creek, California, United States. We found that channel beds organized into size-sorted sediment patches which displayed active fluvial transport of gravel annually, consistent year-to-year patch median grain sizes, partial transport of bed material, and significantly higher values of critical Shields stress for incipient sediment motion compared to that observed for lower gradient rivers. The high critical Shields stresses (up to ≈0.5 for the median grain size) agree within a factor of ~3 to theoretical predictions which account for slope-dependent hydraulics, grain hiding, and sediment patches. For grains of approximately the same size as the roughness length scale, slope-dependent hydraulics and bed patchiness are the dominant controls on critical Shields stress values, while grain hiding is important for grains larger or smaller than the roughness length scale. Form drag exists in our monitored tributaries but has a smaller influence than the above effects. Our field observations show fluvial processes contribute to sediment mobilization in steep channels which are often considered to be dominated by debris flows.},
keywords = {ERCZO, gravel mobilization, steep streams},
pubstate = {published},
tppubtype = {article}
}
Steep streams are a major portion of channel networks and provide a link to transport sediment from hillslopes to lower gradient rivers. Despite their importance, key unknowns remain, perhaps foremost of which is evaluating in steep streams empirical laws for fluvial sediment transport developed for low-gradient rivers. To address this knowledge gap, we painted sediment in situ over 3 years to monitor incipient sediment motion and sediment-patch development in five small (drainage areas of 0.04–2 km2) and steep (slopes of 5–37%) tributaries of Elder Creek, California, United States. We found that channel beds organized into size-sorted sediment patches which displayed active fluvial transport of gravel annually, consistent year-to-year patch median grain sizes, partial transport of bed material, and significantly higher values of critical Shields stress for incipient sediment motion compared to that observed for lower gradient rivers. The high critical Shields stresses (up to ≈0.5 for the median grain size) agree within a factor of ~3 to theoretical predictions which account for slope-dependent hydraulics, grain hiding, and sediment patches. For grains of approximately the same size as the roughness length scale, slope-dependent hydraulics and bed patchiness are the dominant controls on critical Shields stress values, while grain hiding is important for grains larger or smaller than the roughness length scale. Form drag exists in our monitored tributaries but has a smaller influence than the above effects. Our field observations show fluvial processes contribute to sediment mobilization in steep channels which are often considered to be dominated by debris flows.
2012
Yager, E. M.; Dietrich, W. E.; Kirchner, J. W.; McArdell, B. W.
Patch dynamics and stability in steep, rough streams Journal Article
In: Journal of Geophysical Research-Earth Surface, vol. 117, no. F2, 2012.
Abstract | Links | BibTeX | Tags: patch dynmics, stability, steep streams
@article{Yager2012,
title = {Patch dynamics and stability in steep, rough streams},
author = {E. M. Yager and W. E. Dietrich and J. W. Kirchner and B. W. McArdell},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Yager_2012_JournGeophysRes.pdf},
year = {2012},
date = {2012-04-18},
journal = {Journal of Geophysical Research-Earth Surface},
volume = {117},
number = {F2},
abstract = {The beds of steep streams are typically composed of relatively immobile boulders
and more mobile patches of gravel and cobbles. Little is known about how variability in
flow and sediment flux affect the area, thickness, composition, and grain mobility of
sediment patches. To better understand patch dynamics, we measured flow, sediment
transport, and bed properties in two steep channels. Patches close to the thalweg varied in
area, thickness, and grain size, whereas those outside the thalweg did not. Local variations
in transport of several orders of magnitude occurred, even on a patch with a spatially
homogeneous grain size distribution. During moderate flow events, partial to selective
transport dominated on the entire channel bed and all individual patches. Tracer particles
moved freely between different patch classes (e.g., fine and coarse patches exchanged
particles), and relatively fine sediment on all patch classes began motion at the same shear
stress. Therefore, the selective transport observed for the entire bed was not a result
of the preferential transport of only fine patches, but the high relative mobility of finer
sediment on all patches. Our results suggest that local flow and sediment supply,
and not spatial grain size variations, were the primary drivers of local bed load transport
variability. The use of reach-averaged flow properties to understand local patch dynamics
may not be applicable.},
keywords = {patch dynmics, stability, steep streams},
pubstate = {published},
tppubtype = {article}
}
The beds of steep streams are typically composed of relatively immobile boulders
and more mobile patches of gravel and cobbles. Little is known about how variability in
flow and sediment flux affect the area, thickness, composition, and grain mobility of
sediment patches. To better understand patch dynamics, we measured flow, sediment
transport, and bed properties in two steep channels. Patches close to the thalweg varied in
area, thickness, and grain size, whereas those outside the thalweg did not. Local variations
in transport of several orders of magnitude occurred, even on a patch with a spatially
homogeneous grain size distribution. During moderate flow events, partial to selective
transport dominated on the entire channel bed and all individual patches. Tracer particles
moved freely between different patch classes (e.g., fine and coarse patches exchanged
particles), and relatively fine sediment on all patch classes began motion at the same shear
stress. Therefore, the selective transport observed for the entire bed was not a result
of the preferential transport of only fine patches, but the high relative mobility of finer
sediment on all patches. Our results suggest that local flow and sediment supply,
and not spatial grain size variations, were the primary drivers of local bed load transport
variability. The use of reach-averaged flow properties to understand local patch dynamics
may not be applicable.
and more mobile patches of gravel and cobbles. Little is known about how variability in
flow and sediment flux affect the area, thickness, composition, and grain mobility of
sediment patches. To better understand patch dynamics, we measured flow, sediment
transport, and bed properties in two steep channels. Patches close to the thalweg varied in
area, thickness, and grain size, whereas those outside the thalweg did not. Local variations
in transport of several orders of magnitude occurred, even on a patch with a spatially
homogeneous grain size distribution. During moderate flow events, partial to selective
transport dominated on the entire channel bed and all individual patches. Tracer particles
moved freely between different patch classes (e.g., fine and coarse patches exchanged
particles), and relatively fine sediment on all patch classes began motion at the same shear
stress. Therefore, the selective transport observed for the entire bed was not a result
of the preferential transport of only fine patches, but the high relative mobility of finer
sediment on all patches. Our results suggest that local flow and sediment supply,
and not spatial grain size variations, were the primary drivers of local bed load transport
variability. The use of reach-averaged flow properties to understand local patch dynamics
may not be applicable.