Causes of Flooding

Question 1

What are the physical causes of flooding?

6

Answer 1

1. Sparse vegetation/deciduous trees
2. Impermeable ground
3. Circular drainage basins
4. High drainage density
5. Steep slopes
6. Heavy/prolonged rainfall

Question 2

What are the human causes of flooding?

5

Answer 2

1. Urbanisation
2. Deforestation
3. Flood management strategies
4. Agriculture
5. Climate change

Question 3

Explain sparse vegetation/deciduous trees.

Answer 3

Less interception - more rain reaches the ground.

Increases the volume of water reaching the river - discharge increase.

Question 4

Explain impermeable ground.

Answer 4

Clay soils and some rocks (granite) are impermeable.
Increases surface runoff and discharge.
Can happen with hard baked or frozen ground.

Question 5

Explain circular drainage basins.

Answer 5

Water arrives in a short space of time - all points in the basin are a similar distance from the river.
Discharge increase.

Question 6

Explain high drainage density.

Answer 6

Drains quicker - short lag times.
Lots of water flows from the streams into the main river in a short amount of time.
Discharge increase.

Question 7

Explain steep slopes.

Answer 7

Steep sided valleys - quicker water arrival due to gradient.

Discharge increase.

Question 8

Explain urbanisation.

Answer 8

Large areas of impermeable tarmac and concrete - increase runoff.
Gutters and drains increase runoff.
Decrease lag time - increase discharge.

Question 9

Explain deforestation.

Answer 9

Clearing trees reduce interception and evapotranspiration - bigger water volume - discharge increase.
Loose soil - eroded by rainwater/carried to the river - river bed raised.
Less channel capacity - takes less water for the river to flood.

Question 10

Explain flood management strategies.

Answer 10

Dam and levee failure - mass flooding.

Question 11

Explain agriculture.

Answer 11

Overgrazing leaves areas with less vegetation.

Increase soil erosion.

Question 12

Explain climate change.

Answer 12

Could cause an increase in rainfall and storms - increased flooding.

Question 13

What are the main causes of flooding?

Answer 13

Heavy and prolonged rainfall.

Question 14

Explain heavy rainfall.

Answer 14

Rapid surface runoff if the rainfall is too intense for infiltration to occur.
Sharp rise in river discharge - flash flood.

Question 15

Explain prolonged rainfall.

Answer 15

Ground becomes saturated - water can’t infiltrate soil.

Increase runoff and discharge.

Question 16

Flooding definition.

Answer 16

When the discharge of a river is so high that the river spills over its banks onto the flood plain.

Question 17

Explain melting snow and ice.

Answer 17

Huge increase in the river’s discharge e.g melting snow in the Himalayas contributes to annual summer flooding of the River Ganges in Bangladesh.