Extract of presentation "River morphology: the science of sustainability", held in Lalitpur, Nepal, 15 March 2012

1. River morphology:
the science of sustainability
Erik Mosselman (extract of original presentation)
A joint meeting on river morphology, sediment transport,
catchment hydrology and flood forecasting issues
Himalaya Hotel, Lalitpur, Nepal, 15 March 2012

2. Nepal, 1985

3. Nepal, 1985

5. Fundamental concept: the Exner principle
∂zb dqs ∂u
+ =0
∂t du ∂x
erosion
sedimentation erosion sedimentation
top view side view
of flow in channel with uniform width
of flow over horizontal bed

6. Application: river narrowing for navigation
constriction

7. Application: river narrowing for navigation
constriction

8. Application: river narrowing for navigation
long-term equilibrium
constriction

9. Application: river narrowing for navigation
Bed degradation: advantage of lower flood levels?

10. Application: river narrowing for navigation
navigation bottleneck

11. Application: river narrowing for navigation
River bed degradation:
• Limited depth above fixed layers
• Restrictions for sluices and river
port entrances
• Instability of banks and hydraulic
structures
• Shift in discharge distribution at
bifurcations
• and for the Netherlands…
angry Germans!

12. Application: river narrowing for navigation
Johann Gottfried Tulla
In derrule, no
As a Regel,
keinriver or
Fluß oder
Bach derin the
stream Welt
brauchtneeds
world mehr
als ein Bett
more than one
bed

13. Application: river narrowing for navigation
Oberrhein below Basel
1828 1872 1963

14. Application: river narrowing for navigation
Narrowing produced up to 10 m bed degradation

15. Application: river narrowing for navigation

16. Application: river narrowing for navigation
Navigation
impossible …
Construction of
lateral canal:
Grand Canal
d’Alsace

17. Application: river narrowing for navigation

18. Application: river narrowing for navigation

19. Application: river narrowing for navigation

20. Application: river narrowing for navigation
Lesson learned:
River narrowing to improve navigability:
• effective on a short term
• leading to expensive measures to maintain navigability
on a long term
• due to river morphology

21. Application: water withdrawal for irrigation
water withdrawal

22. Application: water withdrawal for irrigation
water withdrawal

23. Application: water withdrawal for irrigation
water withdrawal
long-term equilibrium

24. Application: water withdrawal for irrigation
water withdrawal

25. Application: water withdrawal for irrigation
sedimentation:
• rise in bed levels
• rise in water levels
water withdrawal

26. Application: water withdrawal for irrigation
sedimentation:
• rise in bed levels
• rise in water levels
• raised embankments

27. Application: water withdrawal for irrigation
sedimentation:
• rise in bed levels
• rise in water levels
• raised embankments

28. Application: water withdrawal for irrigation
sedimentation:
• rise in bed levels
• rise in water levels
• raised embankments

29. Application: water withdrawal for irrigation
sedimentation:
• rise in bed levels
• rise in water levels
• raised embankments
flooding

30. Application: water withdrawal for irrigation
Effect of water withdrawal
made worse in case of barrages and subsidence
flooding

31. Application: water withdrawal for irrigation
Lesson learned:
Water withdrawal for irrigation:
• lowers water levels on a short term
• raises flood water levels on a long term
• due to river morphology

32. Both applications
Lesson learned:
Morphological effects on long term:
• opposite to initial effects, hence easily overlooked
• involving high costs

33. There is more to river morphology …
RIVER MORPHOLOGY
Bed sediment
River shape composition
Bed Bed Bank Bank
degradation aggradation retreat advance

34. Nepalese river morphologists
Sanjay Giri

35. Nepalese river morphologists
Lochan Devkota
Umesh Singh

36. Nepalese river morphologists

37. Nepalese river morphologists