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

Nepal, 1985

Nepal, 1985

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

constriction

Application: river narrowing for navigation

constriction

Application: river narrowing for navigation

constriction

long-term equilibrium

Application: river narrowing for navigation

Bed degradation: advantage of lower flood levels?

Application: river narrowing for navigation

navigation bottleneck

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

1828 1872 1963

Oberrhein below Basel

Application: river narrowing for navigation

Narrowing produced up to 10 m bed degradation

Application: river narrowing for navigation

Application: river narrowing for navigation

Navigation impossible …

Construction of lateral canal:

Grand Canal d’Alsace

Application: river narrowing for navigation

Application: river narrowing for navigation

Application: river narrowing for navigation

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

Application: water withdrawal for irrigation

water withdrawal

Application: water withdrawal for irrigation

water withdrawal

long-term equilibrium

Application: water withdrawal for irrigation

water withdrawal

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

Nepalese river morphologists

Sanjay Giri

Nepalese river morphologists

Umesh Singh

Lochan Devkota

Nepalese river morphologists

Nepalese river morphologists