Floods are caused by overflow of large amounts of water onto dry land. The main causes of floods discussed are heavy rainfall, snowmelt, storm surge, and failure of man-made structures like dams. Heavy rainfall can lead to river or coastal flooding when intense or prolonged rainfall overwhelms drainage systems. Snowmelt flooding occurs when spring temperatures rise and melt large amounts of accumulated snow and ice. Storm surge flooding results from rising sea levels during storms that pile water against coastlines beyond normal high tide levels. Failure of dams or levees can also cause flooding when structures are unable to contain or regulate water flow due to issues like heavy rainfall or structural weaknesses.

1. Floods: What are floods?

2. Recap: What are Floods?
Floods : How Can Cities Prepare For Floods?2
‘Floods are overflows of large amounts of water onto
land that is normally dry.’

3. Recap Causes of
Floods
Rainfall Snowmelt
Storm
surge
Failure of
man-made
structure

4. ‘Rainfall refers to droplets of water that
fall to the ground.’
4

5. Recap: Characteristics of rainfall
Floods: How Can Cities Prepare For Floods?
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Rainfall
character-
istics
Rainfall
intensity
Rainfall
duration
Rainfall
frequency

6. 1. Thunderstorm
2. Increase in amount of water
3. Overflow  flooding
Recap:
How rainfall can lead to river flooding?

7. 1. Tropical cyclone (coastal areas)
2. Increase in rainfall/ amount of
water  coastal flooding
Recap:
How rainfall can lead to coastal flooding?
A rollercoaster on a pier was destroyed by Hurricane Sandy
in the state of New Jersey, United States of America
Photo: EPA/Master Sgt. Mark Olsen/US Air Force

8. ‘Snowmelt is surface runoff that results from
melting snow.’
Floods: How Can Cities Prepare For Floods?
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9. Recap: How snowmelt can lead to flooding?
1. Winter  Ice and snow formed
2. Spring  Temperature rises, ice and
snow melts.
3. Increase in amount of water in the
river.
4. Overflow banks flooding

10. Explain the causes of floods
Storm surge
Failure of man-made structures
Lesson Objective

11. Storm surge
Floods: How Can Cities Prepare For Floods?
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‘A storm surge is a sudden rise of the sea
level in which water is piled up against a
coastline beyond normal high-tide
conditions.’

12. How storm surge lead to coastal flooding?
1. During a storm, strong winds push water towards the
coast and create huge waves, giving rise to a storm
surge
Floods: How Can Cities Prepare For Floods?
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How a storm surge causes floods

13. How storm surge lead to coastal flooding?
2. Due to the force of the huge waves moving inland,
coastal areas that was once dry will be flooded.
Floods: How Can Cities Prepare For Floods?
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How a storm surge causes floods

14.  Play from the start to 0.58 minutes.
 Pause at 0.10minutes to show high tide
 Observe the rise in sea level & the damage on the coast (0.33).
 Speculate: What will happen to the house and the trees?
 Click to 0.48 to show the impact end at 0.58.
 Link: https://www.youtube.com/watch?v=SyPkImZoWoE
Storm surge animation

15. Play the whole video
Link: https://www.youtube.com/watch?v=txt8wUznyJM
How hurricane causes storm
surge?

16. Play from start to 0.34.
Link: https://www.youtube.com/watch?v=XTvkrLESrwU
How a storm surge looks like
in real life?

17. A dam is a barrier built across a river to retain
and store water, generate hydropower or
regulate the amount of water flowing in a
river.

18.  The failure of man-made structures such as dams and levees can
result in floods, due to heavy rainfall and structural weaknesses
(cracks).
Failure of man-made structures

19. 1. When a dam fails to retain and store water, it will not be able
to regulate the amount of water flowing in the river.
2. This will cause water to overflow the river banks leading to
flooding.
How dam failure lead to flooding?

20.  Example 1: Banqiao Dam, August 1975 in Zhumadian City,
Henan Province, China
 Heavy rainfall  Dam failure  Flooding
 Link: https://www.youtube.com/watch?v=ctPLXim9WG8
 Example 2: Teton Dam, June 1976, Idaho, United States of
America.
 Structural weaknesses(cracks)  Dam failure  Flooding
 Link: https://www.youtube.com/watch?v=cdOGPBnfoKE
How dam failure lead to flooding?

21. Instructions
1. Read the following articles.
2. State the four causes of floods in the boxes.
3. Underline the keywords that explain how
the causes lead to floods.
Activity (Part 2 of worksheet 5.3A)

23.  Cause: Snowmelt

24.  Causes: Heavy rainfall &
Failure of dams

25.  Causes: Storm surge &
heavy rainfall

26. Causes of floods & how it lead to flooding
Storm surge
Failure of man-made structures
Recap

27. Recap
Causes of
Floods
Snowmel
t
Rainfall
Storm
surge
Failure of
man-
made
structure