River management strategies include channelization through river realignment and re-sectioning, and bank protection through embankments and vegetation management. These strategies have limitations such as causing flooding downstream, accumulating sediments, destroying habitats, and being costly to implement and maintain.

1. Topic: Rivers 3
River Management Strategies
• Two types:
1. Channelisation Strategies:
• River re‐alignment
• River re‐sectioning
2. Bank protection strategies:
• Dykes/ Embankments
• Vegetation planting/
clearing
• Effectiveness of strategies

2. River Channel Management
Why manage river
channels?

6. Flooding occurs when:
1. Clearance of vegetation increase surface
runoff sudden increase in river volume
2. Period of heavy and continuous rainfall
river exceeds carrying capacity
These may be triggered by:
• Global warming
– Extreme weather phenomena called El Nino and
La Nina effect

7. HENCE THERE IS A NEED TO MANAGE
RIVERS. QUESTION IS, HOW?

8. River Channel Management
Strategies
Two types of strategies
1. Channelisation Strategies:
Change the river
• River re‐alignment channel shape/
• River re‐sectioning length, etc.
2. Bank protection strategies:
• Dykes/ Embankments Make changes to
• Vegetation planting/ clearing the river banks

9. 1. Channelisation
Strategies
• River re‐alignment
• River re‐sectioning

10. 1.1 River Re‐alignment
• Straightening of river channel to increase
speed of river water to flow away from an
area more quickly & wash away sediments
accumulated on river bed reduce flooding
in that area
Source:
http://www.defra.gov.uk/enviro
n/fcd/policy/mrcomp/Image6.gi
f

11. River re‐alignment
E.g. Mississippi
River (USA) has
Straightening
been shortened
of river = river
by 240 km to
re-alignment
reduce threat of
flooding.

12. 1.2 River Re‐sectioning
• Widening and deepening of river channel.
• Increase channel’s ability to hold water
decrease likelihood of floods
Or,
• Smoothening of river beds and banks with
cement and granite less friction allow
water to flow away more quickly reduce
likelihood of floods
• E.g. Singapore River ay Boat Quay

13. River re‐sectioning
Widen &
Deepen river
= River
Re- Sectioning

14. 2. Bank Protection
Strategies
• Dykes/ embankments
• Vegetation planting/ clearing

15. 2.1 Bank Protection (Embankments)
1. Dykes/ Artificial levees : Walls of sand, stone
or concrete built along rivers increase
river capacity to hold water reduce
flooding
2. Protects banks from erosion by force of
running water reduced sediments flowing
into river increase river capacity less
flood
• E.g. Artificial embankments along river of
Pasir Ris Park, Singapore

16. Embankments:
Dykes/ Levees
Dykes

17. Dykes

18. 2.2.1 Vegetation Planting
• Roots of trees and plants holds soil together
stabilise river banks
• Vegetation also slows down rate of surface runoff
prevent large amount of water entering river
at any one time
• Reduced surface runoff less sediments
transported river channel does not become
shallower reduce flood occurrence
• E.g. Joint effort to protect mangroves along
Mekong River.

19. Vegetation Planting

20. 2.2.2 Vegetation Clearing
• Weight of vegetation may add stress to river
banks and cause them to collapse
• Fallen trees or branches in the river bed
cause obstruction to river flow
– Reduce speed of flow of river
– Increase likelihood of flooding
• E.g. Vegetation clearance done on Geylang
River near Tanjong Rhu, Singapore.

21. Vegetation Clearing

22. WHAT ARE THE LIMITATION(S) OF
THIS STRATEGIES?

23. Limitations of River Channel Management
Strategies
1. Causes flooding downstream
2. Accumulation of sediments
3. Loss of marine life and wetlands
4. High cost of building and maintenance

24. Effectiveness of River Channel
Management Strategies
1. Flooding downstream
Increase in speed of river due to
channelisation may result in flooding
downstream
Hence, flooding is not reduced. They can still
occur in another part of the river.

25. Recall: River re‐alignment strategy
Increase in
speed of flow
due to re-
alignment
upstream may
cause flooding
downstream.

26. Recall: River re‐sectioning strategy
Increase in
speed of flow
due to re-
sectioning
upstream may
cause flooding
downstream.

27. Effectiveness of River Channel Management
Strategies
2.1 Accumulation of sediments
• Channelisation allows rivers to flow at higher
speed.
• Sediments, previously deposited on river bed
are carried downstream into sea/ ocean.
• Result: less sunlight reach seabed, affect
growth of marine life such as coral reefs

28. Recall: River re‐alignment strategy
Accumulation
of sediments

29. Effectiveness of River Channel Management
Strategies
2.2 Accumulation of sediments
• Bank protection measures such as dykes
causes sediments to accumulate behind these
structures
• Sediments build‐up over time river channel
become shallower still flood with
continuous rain
• Higher dykes need to be built/ money spent to
dig out accumulated sediments

30. Recall: Building of dykes
Sediments
accumulated behind
structures makes the
river shallower
E.g. Build up of sediments along lower
course of Yellow River, China, making
the channel shallower over the years.

31. Effectiveness of River Channel Management
Strategies
3. Loss of marine life and wetlands
1.Too much vegetation prevents sunlight from
reaching river bed kill aquatic life affect
aquatic food chains
2.Changing river course, lining of banks with
concrete destroys plants and animal habitats
3.Channelisation leads to disappearance of
wetlands. i.e. river flows over smaller area with
shortening of river course

32. Recall: River re‐alignment strategy
Loss of Loss of
wetlands wetlands

33. Effectiveness of River Channel Management
Strategies
4. High cost of building and maintenance
• Expensive to build and maintain river
defenses
• Resources and manpower needed for river
realignment and re‐sectioning.
• Aesthetically unappealing

34. In summation…
Name of strategy/ Flooding Accumulation Loss of Expensive to
Limitation(s) Downstream of Sediments wetlands & build &
marine life maintain
Re‐alignment √ √ √ √
Channelisation
(downstream)
Re‐sectioning √ √ √ √
(downstream)
Building of √ (behind √
embankments structures)
Bank protection
Clearing Vegetation √
Planting Vegetation √