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

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

3. Rhine River flood in 1998

4. Primary dune height vs discharge

5. Roughness height vs discharge

6. Darcy-Weisbach f vs discharge

7. Manning n vs discharge

8. Downstream hydraulic geometry

10. Cochiti Dam Santa Fe River Rio Grande N

12. Peak Annual Discharge

13. Annual Average Daily Sediment Concentration

14. 1.1 1.9 2.1 4.6 3.5 4.1 3.1 2.6 26 Subreaches 284 Cross sections 4 Reaches

15. Cross section CO-2

16. Cross section CO-18

17. Cross section CO-24

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

19. Bed material size

20. Sinuosity

21. Active channel width

22. 19351972 1992 N Planform geometry

23. Planform Adjustments BraidedMeandering

24. Lateral Adjustments

25. Equilibrium? Hydraulic Geometry Equations

26. 19181992 (Julien & Wargadalam 1995)

27. Modeling Lateral Movement Deviation from Equilibrium

28. Modeling Width Change Deviation from equilibrium width

29. Exponential Model Results

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