Caues And Impacts Of Flooding

Question 1

How does prolonged rainfall cause flooding?

Answer 1

After a long period of rain, ground becomes saturated, further rainfall can’t infiltrate, increases surface runoff, increases discharge.

Question 2

How does heavy rainfall cause flooding?

Answer 2

Can lead to rapid surface runoff if rainfall is too intense for infiltration to occur.

Can lead to sharp rise in discharge, called a flash flood

Question 3

What is another factor that can increase river discharge?

Answer 3

Melting snow and ice

Question 4

What are the 5 physical factors that increase the risk of flooding?

Answer 4

Sparse vegetation/deciduous trees 
Impermeable ground
Circular drainage basins
High drainage density 
Steep slopes

Question 5

How does sparse vegetation/deciduous trees increase the risk of flooding?

Answer 5

Sparse vegetation means little rainfall is intercepted, more rain reaches the ground, increases volume of water reaching the river, increases discharge

Deciduous trees have no leaves in winter, same affect as sparse vegetation - little rainfall intercepted.

Question 6

How does impermeable ground increase the risk of flooding?

Answer 6

Clay soils and rocks such as granite and shale are impermeable - doesn’t allow infiltration of surface water, increases surface runoff, increases discharge

If ground has been baked by heat of summer or is frozen, same thing happened, can’t infiltrate, increasing runoff and discharge

Question 7

How does circular drainage basins increase the risk of flooding?

Answer 7

Water draining into the main river channel will all arrive in a short space of time, as all points in basin are a similar distance from river, increases discharge.

Question 8

How does a high drainage density increase the risk of flooding?

Answer 8

Drainage basins with a high drainage basin (lots of streams) drain quickly, have short lag times. Lots of water flows from streams into main river in short space of time, increasing discharge

Question 9

How does steep slopes increase the risk of flooding?

Answer 9

If drainage basin has steep sided valleys, water will reach river channel faster as water flows more quickly down steep slope, increases discharge.

Question 10

What are the 5 human factors that increase the risk of flooding?

Answer 10

Urbanisation
Deforestation
Flood management strategies
Agriculture
Climate change

Question 11

How does urbanisation increase the risk of flooding?

Answer 11

Urban areas have large areas or impermeable tarmac and concrete, when it rains runoff is very rapid

Gutter and drains quickly take runoff to rivers

Both things reduce lag time and so increase discharge

Question 12

How does deforestation increase the risk of flooding?

Answer 12

Clearing trees and plants reduces interception and evapotranspiration, increases volume of water reaching channel, increases discharge.

Deforestation leaves soil loose, soil is eroded by rainwater and carried to river, raises river bed, reduces channel capacity, takes less water for river to flood.

Question 13

How do flood management strategies increase the risk of flooding?

Answer 13

Can end up making flooding worse, if dams fail they release a huge volume of water all at once - giving huge increase in discharge.

Question 14

How does agriculture increase the risk of flooding?

Answer 14

Overgrazing leaves areas with less vegetation, has same affect as deforestation.

Overgrazing and ploughing also increases soil erosion.

Question 15

How does climate change increase the risk of flooding?

Answer 15

Can increase rainfall and more storms could arise in some areas, could increase flooding

Question 16

What 3 areas does flooding affect?

Answer 16

People
Economy
Environment

Question 17

What are the social impacts of flooding?

Answer 17

People and animals can be killed

Floodwater is often contaminated with sewage, can lead to a lack of clean drinking water

Contaminated water can also put people at risk of diseases

Possessions an be damaged by floodwater or lost

People can be made homeless as their properties are inundated and damaged

Question 18

What are the economic impacts of flooding?

Answer 18

Businesses often have to shut down as premises are inundated and overt supplies are affected

Rescue work and repairs are usually costly. Insurance premiums go up after floods

Unemployment levels often rise as businesses shut down because they can’t recover from the flooding

Public transport, roads and bridges can be destroyed

Crops can be destroyed, can lead to a rise in price of food

Question 19

What are the negative environmental impacts of flooding?

Answer 19

Floodwater contaminated with sewage and rubbish can pollute rivers

River banks are eroded

Question 20

What are the positive impacts of flooding?

Answer 20

River sediment is deposited on the flood plain, makes land more fertile.

Wetlands can be created, e.g. marshes and ponds, which are habitats for many species.

Question 21

What countries have a greater social impact of flooding? (Rich/poor)

Answer 21

Higher in poorer countries because flood defences are poorer, people are less able to evacuate, sanitation systems aren’t as good and buildings are a poorer quality

Question 22

What countries receive the biggest ABSOLUTE economic effect? (rich/poor)

Answer 22

Higher in richer countries as they have more high value buildings and infrastructure.

Question 23

What countries receive the biggest RELATIVE economic effect? (Rich/poor)

Answer 23

Higher in poorer countries, the buildings and crops that are damaged are worth less money, thus affects the economy more because they have less money to recover from it

Question 24

What is a flood return interval (RI)?

Answer 24

People can predict from records how often a flood of a certain magnitude may occur

Question 25

What would the RI of a small flood be?

Answer 25

RI of 1-2 years

They happen more often so are more frequent

Question 26

What would the RI of a huge flood be?

Answer 26

RI of 100 years

Floods of very large magnitude don’t happen very often - they’re not very frequent

Question 27

What are the two main causes of flooding

Answer 27

Prolonged rainfall

Heavy rainfall