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PRODID:-//Memento EPFL//
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SUMMARY:The influence of extreme events on sediment transport\, channel be
 d conditions\, and the accuracy of bedload transport calculations
DTSTART:20110609T121500
DTSTAMP:20260917T025018Z
UID:136eb1cb79a606f34e628c17ba983608e29448b55423fee5cb20604c
CATEGORIES:Conferences - Seminars
DESCRIPTION:Assistant Prof. Elowyn YAGER\, Department of Civil Engineering
 \, Center for Ecohydraulics Research\, University of Idaho\, USA\nThe sedi
 ment supply to steep streams is highly episodic and is partially a functio
 n of the magnitude and timing of landslides and debris flows. In these cha
 nnels\, clusters and steps of large boulders move only during extreme flow
  events\, and significantly alter the flow hydraulics and the transport of
  the more mobile gravel. Bedload flux predictions are often inaccurate in 
 these streams because they do not account for the influence of the immobil
 e boulders and the highly variable sediment supply. We measured bedload tr
 ansport rates\, grain-size\, and the boulder-step characteristics (e.g. pr
 otrusion) in the Erlenbach torrent (10% slope)\, Switzerland\, over a peri
 od of 6 years. This period encompassed two extreme events that reorganized
  boulder steps. Bedload fluxes increased and bed grain sizes fined after e
 ach extreme event because of greater hillslope sediment supply\, reduced b
 ed armoring and particle interlocking. The boulder step protrusion was a p
 ower function of the bedload flux\; protrusion increased with lower sedime
 nt availability and with time elapsed since the last extreme event. We pre
 viously developed a bedload transport equation that accounts for the influ
 ence of boulder steps on the flow hydraulics. We now incorporate a functio
 n for protrusion\, to estimate the sediment availability during any flow e
 vent. Sediment transport predictions were within an order of magnitude of 
 the measured values if they used a time-dependent protrusion. Use of a con
 stant protrusion caused the predicted bedload fluxes to systematically ove
 r- or under- estimate the measured values. This suggests that protrusion m
 ay be used as a proxy for the relative sediment availability and that bedl
 oad flux predictions may be improved using stochastic functions for bed ro
 ughness and sediment supply. Elowyn Yager obtained her PhD in Geology at t
 he University of California\, Berkeley in 2006. After a postdoc at Arizona
  State University\, she joined the faculty of Civil Engineering at the Uni
 versity of Idaho\, where she is currently assistant professor at the Cente
 r for Ecohydraulics Research. Her research focuses on understanding the me
 chanics of sediment transport\, hillslope erosion\, and channel morphology
  using field measurements\, laboratory flumes and numerical models. She st
 udies the interaction between flow turbulence and sediment motion\, the in
 fluence of vegetation on bedload transport and flow hydraulics\, and the c
 oupling between hillslope sediment supply and channel conditions.
LOCATION:GC C30
STATUS:CONFIRMED
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