Flooding <ul><li>What is meant by a river flood? </li></ul><ul><li>A river floods when the level of the water  </li></ul><...
<ul><li>Floodplain </li></ul><ul><li>Rivers regularly flood. When they do so they </li></ul><ul><li>deposit some of their ...
Floodplain Notice how brown the water is. It is this colour because of the silt it is carrying..
Our school is on the floodplain of the River Thames but is protected by flood defences Edge of floodplain The Thames Dagen...
Floodplain worksheet <ul><li>Complete the floodplain worksheet </li></ul>
Flood hydrographs <ul><li>These are used to show the relationship  </li></ul><ul><li>between rainfall and the discharge of...
TIME DISCHARGE (cumecs) FLOOD HYDROGRAPH
TIME days or hours DISCHARGE (cumecs) FLOOD HYDROGRAPH Bankfull level Lag time Peak discharge Peak rainfall
Key terms <ul><li>Peak rainfall </li></ul><ul><li>Peak discharge </li></ul><ul><li>Lag time </li></ul><ul><li>Bankfull lev...
<ul><li>A hydrograph shows us the difference between the peak rainfall and peak discharge. This difference is called  lag ...
<ul><li>There is a lag time because ___________ </li></ul><ul><li>__________________________________ </li></ul><ul><li>___...
Deforestation and flooding Rock Trees River Soil
<ul><li>When it rains water falls to the ground. In a forested  </li></ul><ul><li>drainage basin the trees _______________...
Rock Concrete Drains Urbanisation and flooding River
TIME DISCHARGE (cumecs) FLOOD HYDROGRAPH Bankfull level Lag time Peak discharge Peak rainfall
<ul><li>Explain why there a time lag between peak  </li></ul><ul><li>rainfall and peak discharge?  </li></ul><ul><li>Use y...
 
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Flooding

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Flooding

  1. 1. Flooding <ul><li>What is meant by a river flood? </li></ul><ul><li>A river floods when the level of the water </li></ul><ul><li>exceeds bankfull and flows onto the </li></ul><ul><li>floodplain. </li></ul>
  2. 2. <ul><li>Floodplain </li></ul><ul><li>Rivers regularly flood. When they do so they </li></ul><ul><li>deposit some of their load. This material is </li></ul><ul><li>known as silt . </li></ul><ul><li>The land on either side of a river that floods </li></ul><ul><li>is known as its floodplain. </li></ul>Floodplain Higher land
  3. 3. Floodplain Notice how brown the water is. It is this colour because of the silt it is carrying..
  4. 4. 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
  5. 5. Floodplain worksheet <ul><li>Complete the floodplain worksheet </li></ul>
  6. 6. Flood hydrographs <ul><li>These are used to show the relationship </li></ul><ul><li>between rainfall and the discharge of a river </li></ul><ul><li>Discharge is the volume of water flowing </li></ul><ul><li>past a point in a river during a period of time. </li></ul><ul><li>It is usually measured in cubic metres per </li></ul><ul><li>second i.e. cumecs </li></ul>
  7. 7. TIME DISCHARGE (cumecs) FLOOD HYDROGRAPH
  8. 8. TIME days or hours DISCHARGE (cumecs) FLOOD HYDROGRAPH Bankfull level Lag time Peak discharge Peak rainfall
  9. 9. Key terms <ul><li>Peak rainfall </li></ul><ul><li>Peak discharge </li></ul><ul><li>Lag time </li></ul><ul><li>Bankfull level </li></ul><ul><li>Write out simple definitions of these terms. </li></ul>
  10. 10. <ul><li>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. </li></ul><ul><li>A rise in discharge on the graph is called the rising limb ; the falling limb shows a decrease in discharge. </li></ul><ul><li>The flood hydrograph below shows: </li></ul><ul><li>rainfall peaking at six hours </li></ul><ul><li>discharge peaking at 11 hours </li></ul><ul><li>lag time - the time between peak rainfall and peak discharge - is five hours. </li></ul>
  11. 11. <ul><li>There is a lag time because ___________ </li></ul><ul><li>__________________________________ </li></ul><ul><li>__________________________________ </li></ul><ul><li>Extension for the clever ones </li></ul><ul><li>There are two peaks to my hydrograph </li></ul><ul><li>because __________________________ </li></ul><ul><li>__________________________________ </li></ul><ul><li>__________________________________ </li></ul><ul><li>__________________________________ </li></ul>
  12. 12. Deforestation and flooding Rock Trees River Soil
  13. 13. <ul><li>When it rains water falls to the ground. In a forested </li></ul><ul><li>drainage basin the trees ___________________________ </li></ul><ul><li>_______________________________________________ </li></ul><ul><li>_______________________________________________ </li></ul><ul><li>_______________________________________________ </li></ul><ul><li>_______________________________________________ </li></ul><ul><li>_______________________________________________ </li></ul><ul><li>_______________________________________________ </li></ul><ul><li>Less water reaches the river and the water that does arrive </li></ul><ul><li>takes a long time to reach it. This means that the river has </li></ul><ul><li>A chance to discharge the rainwater and so flooding is less </li></ul><ul><li>likely. </li></ul>intercept transpiration roots
  14. 14. Rock Concrete Drains Urbanisation and flooding River
  15. 15. TIME DISCHARGE (cumecs) FLOOD HYDROGRAPH Bankfull level Lag time Peak discharge Peak rainfall
  16. 16. <ul><li>Explain why there a time lag between peak </li></ul><ul><li>rainfall and peak discharge? </li></ul><ul><li>Use your diagram of the drainage basin to </li></ul><ul><li>help you. </li></ul>
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