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Influence of bed patchiness, slope, grain hiding, and form drag on gravel mobilization in very steep streams

Scheingross, Joel S. and Winchell, Eric W. and Lamb, Michael P. and Dietrich, William E. (2013) Influence of bed patchiness, slope, grain hiding, and form drag on gravel mobilization in very steep streams. Journal of Geophysical Research. Earth Surface, 118 (2). pp. 982-1001. ISSN 2169-9003. doi:10.1002/jgrf.20067.

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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 km^2) 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.

Item Type:Article
Related URLs:
URLURL TypeDescription DOIArticle
Scheingross, Joel S.0000-0002-7220-8084
Lamb, Michael P.0000-0002-5701-0504
Additional Information:© 2013 American Geophysical Union. Received 30 July 2012; revised 21 March 2013; accepted 25 March 2013; published 10 June 2013. Support for this work came from the National Center for Earth-Surface Dynamics, NASA BioMars Grant to W.E.D., the Charles H. Ramsden Endowed Fund to J.S.S., and NSF EAR-0922199 grant to M.P.L. J.S.S. was partially supported by a NSF Graduate Research Fellowship. We thank Toby Minear for assistance with terrestrial LiDAR scanning. Airborne laser swath mapping data were provided by the National Center for Airborne Laser Mapping. Jonathan Perkins, Peter Nelson, Kathleen Swanson, Jasper Oshun, Eric Kleinsasser, Alessandro Uccelli, Sam Peach, Ben Mackey, Colin Phillips, Evan Scheingross, Matt Stuckey, and Clark Winchell assisted with field work. We thank Peter Steel for facilitating land access and logistical support at the University of California’s Angelo Coast Range Reserve. This manuscript greatly benefited from constructive reviews by Dieter Rickenmann, André Zimmermann, and an anonymous reviewer, as well as editing by Alexander Densmore and John Pitlick.
Funding AgencyGrant Number
National Center for Earth-Surface DynamicsUNSPECIFIED
Charles H. Ramsden Endowed FundUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Subject Keywords:incipient motion; steep streams; partial transport; form drag; patches
Issue or Number:2
Record Number:CaltechAUTHORS:20131101-110701809
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Official Citation:Scheingross, J. S., E.W.Winchell, M. P. Lamb, and W. E. Dietrich (2013), Influence of bed patchiness, slope, grain hiding, and form drag on gravel mobilization in very steep streams, J. Geophys. Res. Earth Surf., 118, 982–1001, doi:10.1002/jgrf.20067
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42190
Deposited By: Tony Diaz
Deposited On:01 Nov 2013 18:28
Last Modified:10 Nov 2021 16:19

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