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
Fundamental concept: the Exner principle
erosion
top viewof flow over horizontal bed
sedimentation sedimentation erosion
side viewof flow in channel with uniform width
d0
db sz q u
t u x
∂ ∂+ =∂ ∂
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!
Application: river narrowing for navigation
In der Regel, kein Fluß oder Bach der Welt braucht mehr als ein Bett
Johann Gottfried Tulla
As a rule, no river or
stream in the world needs
more than one bed
Application: river narrowing for navigation
Navigation impossible …
Construction of lateral canal:
Grand Canal d’Alsace
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
Application: water withdrawal for irrigation
water withdrawal
sedimentation:
• rise in bed levels
• rise in water levels
Application: water withdrawal for irrigation
sedimentation:
• rise in bed levels
• rise in water levels
• raised embankments
Application: water withdrawal for irrigation
sedimentation:
• rise in bed levels
• rise in water levels
• raised embankments
Application: water withdrawal for irrigation
sedimentation:
• rise in bed levels
• rise in water levels
• raised embankments
Application: water withdrawal for irrigation
sedimentation:
• rise in bed levels
• rise in water levels
• raised embankments
flooding
Application: water withdrawal for irrigation
flooding
Effect of water withdrawal
made worse in case of barrages and subsidence
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
Both applications
Lesson learned:
Morphological effects on long term:
• opposite to initial effects, hence easily overlooked
• involving high costs
There is more to river morphology …
RIVER MORPHOLOGY
River shapeBed sedimentcomposition
Beddegradation
Bedaggradation
Bankretreat
Bankadvance