Causes of flooding

Question 1

Rainfall

Answer 1

1. Long spells of heavy rain/ melting snow- more water in the river
2. Antecedent rainfall- the ground is saturated. Water can’t infiltrate and becomes surface run-off

Question 2

Weather

Answer 2

1. Sunshine and high temperatures, increases evaporation- lead to heavy sudden rainfall
2. After very dry weather the ground become hard, any rainfall can’t infiltrate. It runs straight into rivers or collects on the surface and floods
3. Frozen ground doesn’t allow infiltration

Question 3

Relief

Answer 3

Where slopes are steep, water doesn’t infiltrate because its flowing too fast, a more gentle slope means infiltration is more likely.

Question 4

Rocks and soils

Answer 4

Impermeable rocks and soils don’t allow infiltration.

Question 5

Deforestation

Answer 5

Trees use water in photosynthesis, and intercept precipitation. If trees are chopped down, water reaches the ground faster and saturates it, so surface run-off increases.

Question 6

Building

Answer 6

Concrete and tarmac are impermeable- water flows quickly across them into drains, which flow into rivers

Question 7

Farming

Answer 7

Ploughing creates vertical channels which allow rainfall to flow straight downhill into rivers

Question 8

Soil erosion

Answer 8

Deforestation leaves the soil bare. Rain washes the soil into rivers. This clogs the rivers up, causing them to flood.