Floods

Question 1

What are river floods?

Answer 1

They occur when the volume of water in a river channel increases beyond the capacity of the channel.Water thus overflows the riverbanks and onto the floodplain.

Question 2

What are flash floods?

Answer 2

It takes place suddenly and lasts for a short period of time.It can be caused by heavy rainfall.

Question 3

What are coastal floods?

Answer 3

Floods that occur along the coast.Low-lying coastal areas are prone to coastal floods.Coastal floods are caused by intense storms.Strong winds during these storms generate large waves known as storm surges.Storm surges bring about higher water levels and cause coastal floods.

Question 4

What are the rainfall characteristics(causes of floods)?

Answer 4

Rainfall intensity-rate of which rain falls(mm/h)
Rainfall duration-duration of the rain event
Rainfall frequency-no of times a certain amount of rain falls within a period of time

Question 5

What is snowmelt?(causes of floods)?

Answer 5

Surface runoff that results from melting snow.Volcanic eruption can also cause snowmelt.The snowmelt flows over the land into rivers.The snowmelt increases the amount of water in the river and causes the river to overflow its banks.

Question 6

What are storm surges?(causes of floods)

Answer 6

A sudden rise for the sea level in which water is piled up against a coastline beyond normal high-tide conditions. During a storm, strong winds push water towards the coast and create huge waves, giving rise to a storm surge.

Question 7

What does the failure of man-made structures like dams and levees do?(causes of floods)

Answer 7

Failure of dams and levees can result in floods.Dam failure can be disastrous for people living downstream.The failure of levees and flood walls also have disastrous impacts on cities.

Question 8

How will floods result to injuries, spread of diseases and loss of lives?(impacts of floods)

Answer 8

People may be injured by objects and debris washed along by fast-moving floodwaters.Floodwaters may cause buildings to collapse and injure or kill people. When people are caught in the flood for a long period of time, they can suffer from hyperthermia with symptoms such as constant shivering, confusion and loss of coordination.’
After a flood, diseases may spread.Water supplies may be contaminated by chemical spills from factories and sewage. People will be exposed to contaminated drinking water & diseases like cholera and dysentery to spread.

Question 9

How do floods impact houses?(impacts of floods)

Answer 9

Floodwaters can cause damage to property and can sweep houses away.During floods, people would have to evacuate to emergency shelters for long periods of time after the floods while trying to rebuild their homes.

Question 10

How do the supply of clean water get disrupted due to floods?(impacts of floods)

Answer 10

The supply of clean water may be disrupted due to damaged water pipes.Sewage pipes may also burst, causing sewage to flow and contaminate water supplies.

Question 11

What will happen after the floods damaged the machinery and equipment?(impacts of floods)

Answer 11

The machinery and equipment may be submerged in water and cause damage to the motors and other electrical components.As such, factories are unable to operate at full capacity and suffer economic losses.companies may lose profits and have to spend money to buy new equipment.People may lose their jobs.

Question 12

What will happen to the transport infrastructure after a flood?(impacts of floods)

Answer 12

During a flood, transport infrastructure can become impassable because they may be submerged.The force of floodwater may be so powerful that it weakens the transport infrastructure. Cities may need to spend considerable amounts of time and money to repair the damaged infrastructure.

Question 13

How do floods affect the energy supply?

Answer 13

By affecting its distribution.The distribution of electricity can affect the ability of factories and companies to produce goods and services.Power lines may be damaged and power outages may occur during floods.These power failures can last for weeks before they are restored.Factories and companies are unable to operate due to the lack of electricity.This may result in a loss of employment and income for individuals and companies.

Question 14

What is zoning?(Mitigation measures)

Answer 14

A way in which the government plans the physical development of the land and its uses.Flood-prone areas are often zoned as low-value developments such as parks for recreational activities.With the use of zoning, cities are likely to suffer fewer economic losses in the event of floods.

Question 15

Benefits of zoning?(Mitigation measures)

Answer 15

It creates green spaces like parks and fields which help to reduce the impact of flood damage.

Question 16

Challenges of zoning?(Mitigation measures)

Answer 16

• Zoning may limit the development of available land because only certain land uses are permitted.
• Zoning is difficult to carry out because of competing land uses and because people may not abide by the recommended land use.

Question 17

What are the elevated properties?(mitigation measures)

Answer 17

A measure is to elevate properties to a certain height.

Question 18

Benefits of elevated properties?(mitigation measures)

Answer 18

Development is protected against floods up to the highest of the minimum platform level.

Question 19

Challenges of elevated properties?(mitigation measures)

Answer 19

It is challenging to implement the minimum platform level because of the increased cost of development.

Question 20

What are levees and flood walls?(mitigation measures)

Answer 20

They are barriers against the floods and protect development from floodwater.

Question 21

Benefits of levees and flood walls?(Mitigation measures)

Answer 21

Cheaper to build levees and flood walls to mitigate and prevent floods as compared to raising the height of the surrounding lava.

Question 22

Challenges of levees and flood walls?(Mitigation measures)

Answer 22

Regular maintenance is required to ensure that levees and flood walls are strong enough to hold back floodwater.

Question 23

What is channel improvement?(Mitigation measures)

Answer 23

Changes made to the river channel or canal to increase its capacity to hold water or to enable the water to flow quickly.

Question 24

Benefits of channel improvement?(mitigation measures)

Answer 24

Channel improvement makes it possible for moderate-value and high-value developments to take place on the land adjacent to river channels and canals.

Question 25

Challenges of channel improvement?(mitigation measures)

Answer 25

May create problems for areas upstream or downstream of the improved area.

Question 26

What do the forecasting and warning system do?(mitigation measures)

Answer 26

To reduce flood risks

Question 27

Benefits of forecasting and warning system?(mitigation measures)

Answer 27

Provides useful information so that there is time for people to take action to minimise flood damage.

Question 28

Challenges of forecasting and warnings system?(mitigation measures)

Answer 28

Cities may not have the expertise and technology to collect accurate data and make accurate flood forecasts.

Question 29

What are evacuation drills?(Mitigation measures)

Answer 29

A form of preparedness measure where people practise the steps to leave a place in a safe and orderly way during an emergency.

Question 30

Benefits of evacuation drills?(mitigation measures)

Answer 30

• People are educated on what to do when a flood warning is received.
• Evacuation drills will enable cities to improve their flood evacuation plans.

Question 31

Challenges of evacuation drills?(mitigation measures)

Answer 31

Limited participation will reduce the effectiveness of an evacuation drill.

Question 32

How does the height of land above sea level affect how cities are more prone to floods than others?

Answer 32

It is an important factor that determines how likely a place will flood.The mean sea level is the midpoint between the mean low tide and the mean high tide.

Question 33

How do the proximity to water bodies affect how cities are more prone to floods than others?

Answer 33

Cities which are located nearer to water bodies, such as coastal cities or cities with a river running through them, are more prone to floods.

Question 34

How does the permeability of surface cover lead to flooding?

Answer 34

Permeability refers to the ease with which water can infiltrate or seep into the ground.When permeability is high, there will be more infiltration and less surface runoff. When permeability is low, there will be less infiltration and more surface runoff.When surface runoff is high, chances of floods occurring will be higher.

Question 35

How does the channel capacity lead to floods?

Answer 35

Floods may occur when there is too much rain and the capacity of the channel is exceeded.

Question 36

Why does a city need a good network of canals and drains?

Answer 36

A city’s ability to drain water quickly is very important because it has a high proportion of built-up areas.The concrete surfaces in the built-up areas are impermeable, resulting in large amounts of surface runoff during a rain event.In cities, a network of canals is built to remove surface runoff from the area.The canals and rivers would have to be able to cope with the high surface runoff or a flood will occur.