Floods: What are floods?

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.’

Recap Causes of

Floods

Rainfall Snowmelt Storm

surge

Failure of

man-made

structure

‘Rainfall refers to droplets of water that

fall to the ground.’

4

Recap: Characteristics of rainfall

Floods: How Can Cities Prepare For Floods?5

Rainfall

character-

istics

Rainfall

intensity

Rainfall

durationRainfall

frequency

1. Thunderstorm

2. Increase in amount of water

3. Overflow flooding

Recap: How rainfall can lead to river flooding?

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

‘Snowmelt is surface runoff that results from melting snow.’

Floods: How Can Cities Prepare For Floods?8

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

Explain the causes of floods

Storm surge

Failure of man-made structures

Lesson Objective

Storm surge

Floods: How Can Cities Prepare For Floods?11

‘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.’

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?12

How a storm surge causes floods

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?13

How a storm surge causes floods

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

Play the whole video

Link: https://www.youtube.com/watch?v=txt8wUznyJM

How hurricane causes storm surge?

Play from start to 0.34.

Link: https://www.youtube.com/watch?v=XTvkrLESrwU

How a storm surge looks like in real life?

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

river.

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

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?

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?

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)

Cause: Snowmelt

Causes: Heavy rainfall & Failure of dams

Causes: Storm surge & heavy rainfall

Causes of floods & how it lead to flooding

Storm surge

Failure of man-made structures

Recap

Recap

Causes of

Floods

Snowmel

tRainfall

Storm

surge

Failure of

man-

made

structure