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Particle friction angles in steep mountain channels

Prancevic, Jeff P. and Lamb, Michael P. (2015) Particle friction angles in steep mountain channels. Journal of Geophysical Research. Earth Surface, 120 (2). pp. 242-259. ISSN 2169-9003. http://resolver.caltech.edu/CaltechAUTHORS:20150420-142138201

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Abstract

Sediment transport rates in steep mountain channels are typically an order of magnitude lower than predicted by models developed for lowland rivers. One hypothesis for this observation is that particles are more stable in mountain channels due to particle-particle interlocking or bridging across the channel width. This hypothesis has yet to be tested, however, because we lack direct measurements of particle friction angles in steep mountain channels. Here we address this data gap by directly measuring the minimum force required to dislodge sediment (pebbles to boulders) and the sediment weight in mountain channels using a handheld force gauge. At eight sites in California, with reach-averaged bed angles ranging from 0.5° to 23° and channel widths ranging from 2 m to 16 m, we show that friction angles in natural streams average 68° and are 16° larger than those typically measured in laboratory experiments, which is likely due to particle interlocking and burial. Results also show that larger grains are disproportionately more stable than predicted by existing models and that grains organized into steps are twice as stable as grains outside of steps. However, the mean particle friction angle does not vary systematically with bed slope. These results do not support systematic increases in friction angle in steeper and narrower channels to explain the observed low sediment transport rates in mountain channels. Instead, the spatial pattern and grain-size dependence of particle friction angles may indirectly lower transport rates in steep, narrow channels by stabilizing large clasts and channel-spanning steps, which act as momentum sinks due to form drag.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1002/2014JF003286 DOIArticle
http://onlinelibrary.wiley.com/doi/10.1002/2014JF003286/abstractPublisherArticle
ORCID:
AuthorORCID
Lamb, Michael P.0000-0002-5701-0504
Additional Information:© 2015 American Geophysical Union. Received 17 JUL 2014; Accepted 14 JAN 2015; Accepted article online 16 JAN 2015; Published online 16 FEB 2015. Preliminary measurements for this study were performed by Eric Kleinsasser. We would like to thank Brian Fuller, Luca Malatesta, Joel Scheingross, and Alison Piasecki for their help with field measurements. Field data and calculated friction angles can be found in the supporting information. Funding for this work was provided by NSF grants EAR-0922199 and EAR-1349115, the Terrestrial Hazards Observation and Reporting center at Caltech, and the Keck Institute for Space Studies. We thank Michael Church, Mark Schmeeckle, and an anonymous reviewer for their insightful reviews that improved this paper.
Group:Keck Institute for Space Studies
Funders:
Funding AgencyGrant Number
NSFEAR-0922199
NSFEAR-1349115
Caltech Terrestrial Hazards Observation and Reporting CenterUNSPECIFIED
Keck Institute for Space Studies (KISS)UNSPECIFIED
Record Number:CaltechAUTHORS:20150420-142138201
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20150420-142138201
Official Citation:Prancevic, J. P., and M. P. Lamb (2015), Particle friction angles in steep mountain channels, J. Geophys. Res. Earth Surf., 120, 242–259, doi:10.1002/2014JF003286
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56785
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:20 Apr 2015 21:54
Last Modified:23 Nov 2016 00:47

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