River Incision into Bedrock

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River Incision into Bedrock

• Interaction of a suite of processes
• Plucking, Abrasion (bedload suspended load),
  Cavitation (?), Weathering
• Vortices shed off macro-roughness drive processes
  
• Relation to mean bed shear stress?
• Critical stress for incision/flood frequency
• Adjustment of channel morphology / bed state
• How non-linear? Relation to Climate?

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Plucking in Action during Flood
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Macro-Abrasion
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Study Sites in South Africa
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Impact Abrasion
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Plucking
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Fluting by suspended load
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Flat-Bottom Channel Morphology
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Weathering
Wetting and Drying in clay-rich shales
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Relative Hardness of Clasts in Transport -deposit
ed contemporaneously
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King Range, MTJ Region, CA
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San Gabriel Mnts, Southern CA
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Siwalik Hills Anticline Himalaya Foreland, Nepal
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Bagmati Transect
Bakeya Transect
Data from Lave and Avouac, 2000, JGR
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Modeled Erosion Rates
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Siwalik Hills, Nepal
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Howard and Kerby, 1983, GSA Bulletin Site Map
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Howard and Kerby, 1983, Seasonal Surveys
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Stochastic-threshold incision model(Tucker
Bras, 2000)

• E KRKCKtcAmSn
• KRKR(physical parameters, ?, g, ke, width,
  lithology)
• KCKC (climate parameters, P, Tr, Tb)
• KtcKtc (Rc/P?tc/P, A, S varies from 0 to 1)
• Key unknown parameters tc, ke, and a (or n)
• From the basic postulate, Eke(tba-tca)

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Mixed Bedrock-Alluvial Stream (Appalachians, VA)
Concavity Index indistinguishable from
detachment-limited bedrock channels
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a 1.5
No threshold
Tucker and Bras, 2000, WRR
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Ktc at steady state
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Model effect on relief-uplift rate relation
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Mixed Bedrock-Alluvial Stream (Appalachians, VA)
Concavity Index indistinguishable from
detachment-limited bedrock channels
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q .69
q .42
q .49
Available data suggests DL and TL streams have
similar concavities
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