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What’s New in Sedimentation and River Mechanics

What’s New in Sedimentation and River Mechanics. Pierre Julien Spring 2001. 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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What’s New in Sedimentation and River Mechanics

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  1. What’s New in Sedimentation and River Mechanics Pierre Julien Spring 2001

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

  3. Rhine River flood in 1998

  4. Bovenrijn Waal 1.5 0.6 Center Left Right 1.0 0.4 primary dune height (m) 0.5 0.2 0.0 0.0 2500 5000 7500 10000 2000 4000 6000 8000 Discharge (m3/s) Discharge (m3/s) Primary dune height vs discharge

  5. Bovenrijn Waal 0.6 Center 0.3 Left Right 0.4 0.2 Roughness height (m) 0.2 0.1 0.0 0.0 2500 5000 7500 10000 2000 4000 6000 8000 Discharge (m3/s) Discharge (m3/s) Roughness height vs discharge

  6. Bovenrijn Waal 0.05 0.05 center Left Right 0.04 0.04 Darcy-Weisbach f 0.03 0.03 0.02 0.02 2500 5000 7500 10000 2000 4000 6000 8000 Discharge (m3/s) Discharge (m3/s) Darcy-Weisbach f vs discharge

  7. Bovenrijn Waal 0.04 0.04 Center Left Right Manning n Manning n 0.03 0.03 0.02 0.02 2500 5000 7500 10000 2000 4000 6000 8000 Discharge (m3/s) Discharge (m3/s) Manning n vs discharge

  8. Downstream hydraulic geometry

  9. Cochiti Dam N Rio Grande Santa Fe River

  10. Peak Annual Discharge

  11. Annual Average Daily Sediment Concentration

  12. 1.1 1.9 2.1 2.6 3.1 4.1 3.5 26 Subreaches 4.6 284 Cross sections 4 Reaches

  13. Cross section CO-2

  14. Cross section CO-18

  15. Cross section CO-24

  16. Reach 2 Reach 1 Reach 3 Reach 4 Change in Mean Bed Elevation

  17. Bed material size

  18. Sinuosity

  19. Active channel width

  20. Planform geometry 1935 1972 1992 N

  21. Planform Adjustments Braided Meandering

  22. Lateral Adjustments

  23. Equilibrium? Hydraulic Geometry Equations

  24. Hydraulic Geometry Equations (Julien & Wargadalam 1995) 1992 1918

  25. Modeling Lateral Movement Deviation from Equilibrium

  26. Modeling Width Change Deviation from equilibrium width

  27. Exponential Model Results

  28. 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.

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