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Amplified erosion above waterfalls and oversteepened bedrock reaches

Haviv, I.; Enzel, Y.; Whipple, K. X; Zilberman, E.; Stone, John; Matmon, A.; Fifield, Keith

Description

None of the conventional bedrock erosion laws can predict incision immediately upslope of a waterfall lip where the flow is accelerating toward a freefall. Considering the expected increase in flow velocity and shear stress at the lip of a waterfall, we determine erosion amplification at a waterfall lip as [equation], where [equation] is the erosion rate at the upstream end of the flow acceleration zone above a waterfall, Fr is the Froude number at this setting, and n ranges between 0.5–1.7....[Show more]

dc.contributor.authorHaviv, I.
dc.contributor.authorEnzel, Y.
dc.contributor.authorWhipple, K. X
dc.contributor.authorZilberman, E.
dc.contributor.authorStone, John
dc.contributor.authorMatmon, A.
dc.contributor.authorFifield, Keith
dc.date.accessioned2011-07-12T00:49:14Z
dc.date.available2011-07-12T00:49:14Z
dc.identifier.issn0148-0227
dc.identifier.urihttp://hdl.handle.net/1885/8115
dc.description.abstractNone of the conventional bedrock erosion laws can predict incision immediately upslope of a waterfall lip where the flow is accelerating toward a freefall. Considering the expected increase in flow velocity and shear stress at the lip of a waterfall, we determine erosion amplification at a waterfall lip as [equation], where [equation] is the erosion rate at the upstream end of the flow acceleration zone above a waterfall, Fr is the Froude number at this setting, and n ranges between 0.5–1.7. This amplification expression suggests that erosion at the lip could be as much as 2–5 times higher relative to erosion at a normal setting with identical hydraulic geometry. Utilizing this erosion amplification expression in numerical simulations, we demonstrate its impact on reach-scale morphology above waterfalls. Amplified erosion at the lip of a waterfall can trigger the formation of an oversteepened reach whose length is longer than the flow acceleration zone, provided incision wave velocity (Vi) at the upstream edge of the flow acceleration zone is higher than the retreat velocity of the waterfall face. Such an oversteepened reach is expected to be more pronounced when Vi increases with increasing slope. The simulations also suggest that oversteepening can eventually lead to steady state gradients adjacent to a waterfall lip provided Vi decreases with increasing slope. Flow acceleration above waterfalls can thus account, at least partially, for prevalent oversteepened bedrock reaches above waterfalls. Using the cosmogenic isotope Cl-36, we demonstrate that incision wave velocity upstream of a waterfall at the Dead Sea western escarpment is probably high enough for freefall-induced oversteepening to be feasible.
dc.format11 pages
dc.publisherAmerican Geophysical Union
dc.rightshttp://www.agu.org/pubs/authors/usage_permissions.shtml "Permission to Deposit an Article in an Institutional Repository Adopted by Council 13 December 2009 AGU allows authors to deposit their journal articles if the version is the final published citable version of record, the AGU copyright statement is clearly visible on the posting, and the posting is made 6 months after official publication by the AGU." - from publisher web site (as at 5/7/11)
dc.sourceJournal of Geophysical Research 111 (2006): F04004/1-11
dc.source.urihttp://www.agu.org/pubs/crossref/2006/2006JF000461.shtml
dc.subjectwaterfall, knickpoint, bedrock incision, erosion, landscape evolution, Dead Sea
dc.titleAmplified erosion above waterfalls and oversteepened bedrock reaches
dc.typeJournal article
local.identifier.citationvolume111
dcterms.dateAccepted2006-06-14
dc.date.issued2006-10-24
local.identifier.absfor040601 - Geomorphology and Regolith and Landscape Evolution
local.identifier.ariespublicationU4155331xPUB3
local.publisher.urlhttp://www.agu.org/
local.type.statusPublished Version
local.contributor.affiliationHaviv, I, Hebrew University of Jerusalem
local.contributor.affiliationEnzel, Y, Hebrew University of Jerusalem
local.contributor.affiliationWhipple, K X, Hebrew University of Jerusalem
local.contributor.affiliationZilberman, E., Geological Survey of Israel
local.contributor.affiliationStone, John O, University of Washington
local.contributor.affiliationMatmon, A, Hebrew University of Jerusalem
local.contributor.affiliationFifield, L Keith, College of Physical and Mathematical Sciences, ANU
local.bibliographicCitation.startpageF04004-1-11
local.identifier.doi10.1029/2006JF000461
dc.date.updated2015-12-08T02:46:06Z
local.identifier.scopusID2-s2.0-34147155443
CollectionsANU Research Publications

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