Flood Risk Factors
Geography: Edexcel IGCSE, topic 1.1.16
Factors Affecting Flood Risk
When the amount of water in a river is greater than the river's capacity, flooding will happen. Increasing river level is caused by increasing river discharge. There are human and physical factors that can increase discharge, and therefore cause flooding:
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Precipitation
- Heavy rainfall causes high runoff because the water arrives so quickly that there isn't enough time for it to infiltrate the soil.
- Prolonged rainfall makes the soil become saturated, and so any more rainfall will run off instead of infiltrating.
Geology
- Runoff is higher in areas that are mainly made up of impermeable soil (e.g. clay) or impermeable rock (e.g. granite).
Relief
- Rainfall will reach the river channel quicker in a steep-sided valley.
Land use
- Buildings and roads are usually made of impermeable materials. More impermeable surfaces mean more runoff and more discharge.
- Trees intercept water and store water that they take up from the ground. Removing trees will, therefore, increase flooding risk as more water will be finding its way into the river channel.
Test yourself on Flood Risk Factors
Runoff is high in areas dominated by impermeable surfaces. Which of the following have impermeable surfaces?
Which of the following would increase the risk of flooding?