Whats New in Sedimentation and River Mechanics

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Whats New in Sedimentation and River Mechanics

• Pierre Julien
• Spring 2001

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Objectives

• Bedforms and resistance to flow during floods.
• Effects of dams on hydraulic geometry.
• River response to deviations from equilibrium
  geometry of alluvial rivers.

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Rhine River flood in 1998
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Primary dune height vs discharge
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Roughness height vs discharge
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Darcy-Weisbach f vs discharge
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Manning n vs discharge
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Downstream hydraulic geometry
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Cochiti Dam
N
Rio Grande
Santa Fe River
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Peak Annual Discharge
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Annual Average Daily Sediment Concentration
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284 Cross sections 4 Reaches
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Cross section CO-2
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Cross section CO-18
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Cross section CO-24
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Change in Mean Bed Elevation
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Bed material size
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Sinuosity
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Active channel width
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Planform geometry
1935
1972
1992
N
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Planform Adjustments
Braided
Meandering
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Lateral Adjustments
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Equilibrium?
Hydraulic Geometry Equations
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Hydraulic Geometry Equations (Julien
Wargadalam 1995)
1918
1992
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Modeling Lateral Movement
Deviation from Equilibrium
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Modeling Width Change
Deviation from equilibrium width
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Exponential Model Results
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Conclusions

• Bedforms affect resistance to flow and Manning n
  can increase during floods.
• The effects of Cochiti Dam on the Rio Grande are
  primarily degradation and armouring. There is
  relatively little effect on channel width.
• The rate of change in channel width is
  proportional to the deviation from the
  equilibrium channel width.