Physical Causes of River Flooding
Refers to AQA AS Geography
Chapter 1 - Rivers, floods and management
- Created by: Bethany
- Created on: 10-05-13 15:35
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- Physical Causes of River Flooding
- When does flooding occur?
- When a river's discharge exceeds the capacity of the channel to carry that level of discharge.
- When the river overflows it banks.
- When the river overflows it banks.
- When a river's discharge exceeds the capacity of the channel to carry that level of discharge.
- Physical causes
- Excessive levels of precipitation over a prolonged period of time.
- Soil becomes saturated
- When water table reaches ground surface, there is an increase in overland flow/ runoff.
- Intense Precipitation over a short period of time
- Especially significant if ground is baked after a long period without rainfall.
- This reduces infiltration capacity so ground cannot soak up rainfall quickly enough.
- More water reaches river than in normal circumstances.
- e.g. Boscastle, Cornwall, 2004.
- 200m of rain in 24 hours, most between 12 and 5pm. 100mm/h between 3 and 4 pm for short periods of time.
- Over 60 properties submerged under floodwater, 70-80 cars swept away.
- 200m of rain in 24 hours, most between 12 and 5pm. 100mm/h between 3 and 4 pm for short periods of time.
- Especially significant if ground is baked after a long period without rainfall.
- Melting of snowfall
- Infiltration capacity is reduced when the subsoil is still frozen.
- Climatic Hazards
- e.g. Cyclones in Bangladesh, hurricanes in Gulf of Mexico, deep low-pressure systems in mid-latitudes.
- The nature of the drainage basin
- Some drainage basins more likely to flood than others
- Relief
- vegetation
- Soil type
- Geology
- In drainage basins with dense forest, interception and uptake from plants reduce risk of flooding during times of heavy rainfall.
- Some drainage basins more likely to flood than others
- Excessive levels of precipitation over a prolonged period of time.
- When does flooding occur?
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