Physical Causes of River Flooding

Refers to AQA AS Geography

Chapter 1 - Rivers, floods and management

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  • 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.
    • 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.
      • 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.

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