River management in very short form!

Channelisation: Re-alignment and resectioning

Realignment:
Purpose=straightening of the river
Pros=to increase water speed, remove sediments faster and reduce flooding
Cons=Expensive and high manpower, destroy natural environment
Example=Singapore River

Resectioning:
Purpose=widening and deepening of the river
Pros=to hold more water, increase water speed, remove sediments faster and reduce flooding
Cons=Expensive and high manpower, destroy natural environment
Example=Singapore River
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Bank Protection: Planting vegetation (soft engineering) & building dykes, revetments and gabions (hard engineering)

Planting vegetation:
Purpose=plant plants along river banks
pros=cheap and roots help to prevent soil erosion.
Cons= Slower water speed
Example= Kallang River

Building dykes, revetments and gabions:
In case you are not sure what is the difference, dykes are simply rocks, sand or concrete walls. Gabions are small rocks in wire cages, and revetments are rocks cemented together.
Purpose= Artificial man made bank walls.
pros=long lasting, faster water flow due to less friction
cons=expensive and high manpower
example=Kallang River