Flooding
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Flooding

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Good for Avery Hill Water Landforms and people

Good for Avery Hill Water Landforms and people

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Flooding Flooding Presentation Transcript

  • Flooding
    • What is meant by a river flood?
    • A river floods when the level of the water
    • exceeds bankfull and flows onto the
    • floodplain.
    • Floodplain
    • Rivers regularly flood. When they do so they
    • deposit some of their load. This material is
    • known as silt .
    • The land on either side of a river that floods
    • is known as its floodplain.
    Floodplain Higher land
  • Floodplain Notice how brown the water is. It is this colour because of the silt it is carrying.. View slide
  • Our school is on the floodplain of the River Thames but is protected by flood defences Edge of floodplain The Thames Dagenham Park Dagenham Heathway View slide
  • Floodplain worksheet
    • Complete the floodplain worksheet
  • Flood hydrographs
    • These are used to show the relationship
    • between rainfall and the discharge of a river
    • Discharge is the volume of water flowing
    • past a point in a river during a period of time.
    • It is usually measured in cubic metres per
    • second i.e. cumecs
  • TIME DISCHARGE (cumecs) FLOOD HYDROGRAPH
  • TIME days or hours DISCHARGE (cumecs) FLOOD HYDROGRAPH Bankfull level Lag time Peak discharge Peak rainfall
  • Key terms
    • Peak rainfall
    • Peak discharge
    • Lag time
    • Bankfull level
    • Write out simple definitions of these terms.
    • A hydrograph shows us the difference between the peak rainfall and peak discharge. This difference is called lag time . The greater the lag time, the less chance there is of a flood; while a short lag time shows that water has reached the river channel quickly.
    • A rise in discharge on the graph is called the rising limb ; the falling limb shows a decrease in discharge.
    • The flood hydrograph below shows:
    • rainfall peaking at six hours
    • discharge peaking at 11 hours
    • lag time - the time between peak rainfall and peak discharge - is five hours.
    • There is a lag time because ___________
    • __________________________________
    • __________________________________
    • Extension for the clever ones
    • There are two peaks to my hydrograph
    • because __________________________
    • __________________________________
    • __________________________________
    • __________________________________
  • Deforestation and flooding Rock Trees River Soil
    • When it rains water falls to the ground. In a forested
    • drainage basin the trees ___________________________
    • _______________________________________________
    • _______________________________________________
    • _______________________________________________
    • _______________________________________________
    • _______________________________________________
    • _______________________________________________
    • Less water reaches the river and the water that does arrive
    • takes a long time to reach it. This means that the river has
    • A chance to discharge the rainwater and so flooding is less
    • likely.
    intercept transpiration roots
  • Rock Concrete Drains Urbanisation and flooding River
  • TIME DISCHARGE (cumecs) FLOOD HYDROGRAPH Bankfull level Lag time Peak discharge Peak rainfall
    • Explain why there a time lag between peak
    • rainfall and peak discharge?
    • Use your diagram of the drainage basin to
    • help you.
  •