Floods: What are floods?

Play from start to 2.40 minutes

Link: http://study.com/academy/lesson/what-are-floods-causes-types-prevention.html

Recap: Video – Flood Types and Causes

Recap: What are Floods?

Floods : How Can Cities Prepare For Floods?3

‘Floods are overflows of large amounts of water onto land that is normally dry.’

Types of Floods

Coastal Floods River Floods Flash Floods

Recap

Causes of

Floods

Snowmelt Rainfall Storm

surge

Failure of

man-made

structure

Explain the causes of floods

Snowmelt

Rainfall

Lesson Objective

It is important to find out the root cause or causes of the flood so that the government can do something to

prevent it.

Why is it important to know the causes of floods?

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

Floods: How Can Cities Prepare For Floods?8

Demonstration with the help of the visualiser.

Ice melting experiment

Ground Rules

1. Stay in our group. You are not allowed to move/walk to another group unless you are given permission.

2. Keep your volume down.

3. Do not play with the ice or water.

4. Anyone who is deem and seen disruptive will not be allowed to participate for future experiments.

Ice melting experiment

Grouping 1. 8 Groups in total – 1 group consists of 5 people. 2. When you are ready in our groups, one representative

(group leaders) will raise their hands and will collect the materials.

Materials needed 1. Bag of Ice 2. 8 rectangle transparent plastic container3. Textbook or anything with a bit of height to tilt the

container.

Ice melting experiment

Instructions

1. Place some ice cubes at one end of the plastic container.

2. Tilt your plastic container with the help of a textbook or something to elevate it slightly.

3. Note: The corner with the ice should be elevated.

4. After you are done get back to your sit.

5. Wait and observe for the ice to melt. You should be observing water flowing down from the other end of the plastic container. (It will take about 4 minutes or more for the ice to melt)

Whole experiment set up should take no more than 2 minutes.

Ice melting experiment

How snowmelt can lead to flooding?

During winter, ice and snow form on the ground and on the mountains.

How snowmelt can lead to flooding?

When spring arrives and the temperature rises, the ice and snowmelts.

How snowmelt can lead to flooding?

The snowmelt flows over the land into rivers, increasing the amount of water in the river.

This causes the river to overflow its banks and floodthe surrounding areas.

‘Rainfall refers to droplets of water that

fall to the ground.’

17

How is rain formed? Water vapour in the

atmosphere condenses to form water droplets.

The water droplets form clouds.

4. When the water droplets become too heavy, they fall as rain.

Characteristics of rainfall

Floods: How Can Cities Prepare For Floods?19

Rainfall

character-

istics

Rainfall

intensity

Rainfall

durationRainfall

frequency

Definition:

The duration of the rain event (Time)

How long does the rain last?

Example: 3 hours

Rainfall Duration

Floods: How Can Cities Prepare For Floods?20

Definition:

The rate at which rain falls, measured in millimetres per hour (mm/h)

Rainfall intensity

Rainfall intensities in increasing order:

Rainfall intensity

Floods: How Can Cities Prepare For Floods?22

LOW intensity

HIGH intensity

Formula

Rainfall intensity (mm/h) = 𝑻𝒐𝒕𝒂𝒍 𝒂𝒎𝒐𝒖𝒏𝒕 𝒐𝒇 𝒓𝒂𝒊𝒏𝒘𝒂𝒕𝒆𝒓 𝒎𝒎

𝑫𝒖𝒓𝒂𝒕𝒊𝒐𝒏 𝒐𝒇 𝒓𝒂𝒊𝒏𝒇𝒂𝒍𝒍 (𝒉)

Example:

Total amount of rainwater: 1000mm

Duration: 2hours

Rainfall intensity (mm/h) = 𝟏𝟎𝟎𝟎 𝒎𝒎

𝟐(𝒉)

Rainfall intensity is 500mm/h

Calculation of rainfall intensity

Demonstration

Rainfall Intensity experiment

Materials needed

1. 1 Pail, 1 scoop

2. A pail of water

Grouping (optional)

1. 8 Groups in total – 1 group consist of 5 people.

Rainfall intensity demonstration

Ground Rules

1. Stay in our seat. You are not allowed to move/walk unless you are given permission.

2. Keep your volume down.

3. Do not play with the water when you are experimenting. (E.g. no sprinkling of water etc.)

4. Anyone who is deem and seen disruptive will not be allowed to participate for future experiments.

Rainfall intensity demonstration

Instructions

1. Teacher will demonstrate two scenarios

A. Scoop a full scoop of water and pour it back to the pail. Assuming that I am pouring that amount of water in one minute. This is to represent high rainfall intensity.

B. Fill half of the scoop with water and pour it back to the pail. Assuming that I am pouring that amount of water in one minute. This is to represent low rainfall intensity.

Students can come to the front to feel the intensity of the water when it is being poured back.

Rainfall intensity demonstration (5mins)

Definition:

The probability of occurrence of a certain amount of rain falling within a certain period of time

Example: 1-in-50-year storm in England in June 2012.

Rainfall Frequency

Floods: How Can Cities Prepare For Floods?28

1. When a thunderstorm occurs, it will cause an increase in amount of water.

How rainfall can lead to river flooding?

2. If the water level in the river is at its peak (Level A), further increase in the amount of water will overflow over the land. Land that is normally dry will be flooded.

How rainfall can lead to river flooding?

1. A tropical storm is a storm with high intensity and prolonged rainfall (long duration). Such storms bring in heavy rain and strong winds.

2. Tropical storms may develop into tropical cyclones also known as hurricane and typhoon.

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

3. When a tropical cyclone occurs, there will be an increase in rainfall.

4. Since most tropical cyclone occurs near the coast, the increase in amount of water into the existing water bodies will lead to coastal flooding.

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

Textbook Page 164

Read : “Flooding possible as snow melt finally starts” (1 minute)

Answer the questions that are on the worksheet.

Practice Time!

1. What will be the possible cause of the flood?

Snowmelt

Title of article 1: Flooding possible as snow melt finally starts. (TB Pg 164)

2. Explain how the cause will contribute to the flood?

Balmy weather (warm weather) is expected in the next 10 days.

When there is an increase in temperature, the snowand ice will melt.

The snowmelt flows over the land into rivers, increasing the amount of water in the river.

This causes the river to overflow its banks and flood the surrounding areas.

Title of article 1: Flooding possible as snow melt finally starts. (TB Pg 164)

Causes of floods & how it lead to flooding

Snowmelt

Rainfall

Recap