Amplified erosion above waterfalls and oversteepened bedrock reaches
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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.author | Haviv, I. | |
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dc.contributor.author | Enzel, Y. | |
dc.contributor.author | Whipple, K. X | |
dc.contributor.author | Zilberman, E. | |
dc.contributor.author | Stone, John | |
dc.contributor.author | Matmon, A. | |
dc.contributor.author | Fifield, Keith | |
dc.date.accessioned | 2011-07-12T00:49:14Z | |
dc.date.available | 2011-07-12T00:49:14Z | |
dc.identifier.issn | 0148-0227 | |
dc.identifier.uri | http://hdl.handle.net/1885/8115 | |
dc.description.abstract | 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. 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.format | 11 pages | |
dc.publisher | American Geophysical Union | |
dc.rights | http://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.source | Journal of Geophysical Research 111 (2006): F04004/1-11 | |
dc.source.uri | http://www.agu.org/pubs/crossref/2006/2006JF000461.shtml | |
dc.subject | waterfall, knickpoint, bedrock incision, erosion, landscape evolution, Dead Sea | |
dc.title | Amplified erosion above waterfalls and oversteepened bedrock reaches | |
dc.type | Journal article | |
local.identifier.citationvolume | 111 | |
dcterms.dateAccepted | 2006-06-14 | |
dc.date.issued | 2006-10-24 | |
local.identifier.absfor | 040601 - Geomorphology and Regolith and Landscape Evolution | |
local.identifier.ariespublication | U4155331xPUB3 | |
local.publisher.url | http://www.agu.org/ | |
local.type.status | Published Version | |
local.contributor.affiliation | Haviv, I, Hebrew University of Jerusalem | |
local.contributor.affiliation | Enzel, Y, Hebrew University of Jerusalem | |
local.contributor.affiliation | Whipple, K X, Hebrew University of Jerusalem | |
local.contributor.affiliation | Zilberman, E., Geological Survey of Israel | |
local.contributor.affiliation | Stone, John O, University of Washington | |
local.contributor.affiliation | Matmon, A, Hebrew University of Jerusalem | |
local.contributor.affiliation | Fifield, L Keith, College of Physical and Mathematical Sciences, ANU | |
local.bibliographicCitation.startpage | F04004-1-11 | |
local.identifier.doi | 10.1029/2006JF000461 | |
dc.date.updated | 2015-12-08T02:46:06Z | |
local.identifier.scopusID | 2-s2.0-34147155443 | |
Collections | ANU Research Publications |
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