River Flooding[1]
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River Flooding[1] Presentation Transcript

  • 1. River flooding Why do rivers flood?
  • 2. Copy the table + sort the following hydrological cycle processes into the right sections Surface Runoff Precipitation Condensation Infiltration Throughflow Transpiration Soil Moisture Lake Stream Flow Interception Groundwater Groundwater flow Outputs Flows Stores Inputs
  • 3. Flooding
    • On your table, circle the most important processes that may cause flooding
  • 4. Homework
    • Investigate a major flood event in the UK
    • Include:
    • Location
    • Causes
    • Effects (e.g. deaths, costs, damages)
    • E.g. floods in Wales 2009
  • 5. The Flood / Storm Hydrograph
    • Hydrographs are used to show the relationship between precipitation and discharge (the amount of water passing in the river channel) .
    • Hydrographs are used to predict whether a river is likely to flood .
    • Discharge is measured in Cumecs (cubic metres of water per second).
    • Lag Time is the delay between peak precipitation and peak river discharge.
    • Short Lag Times means water enters the river system very quickly following rainfall
    • Long Lag Times means water takes a longer time to enter the river system following rainfall
  • 6. Lag times
    • So a lag time changes depending on the characteristics of the river basin
    • What kinds of things might cause rainfall to enter the river more slowly or more quickly? (Tip – think about factors that slow down infiltration or increase surface run-off)
    • Short lag times = are caused by steep slopes , impermeable rock, sparse vegetation and a small drainage basin. These mean surface run-off is high so water enters the river quickly following precipitation.
    • Long lag times = are caused by gentle slopes, permeable rock, dense vegetation and a large drainage basin. These mean surface run-off is lower, there is more interception and infiltration so water takes longer to get to the river channel.
  • 7. Questions
    • Question 5 (a,b,c) Page 75
    • P76/77. Which hydrograph do you think is for a rural location? Which is urban? Why?
  • 8. Question 5 (a,b,c) Page 75
    • The discharge of the river in cumecs in response to precipitation
    • 8 m 3 /sec
    • 12 hours
  • 9. What are the causes of flooding?
    • Make a copy of the diagram on page 76
    • Colour classify each cause into either physical or human .
    • Complete activities 2-4
      • 2. 2 marks
      • 3. 3 marks
      • 4. 2 marks
  • 10. Answers
    • 2. The UK’s population is still rising, for example from migration, and new housing is needed. There is little space in the UK and land is cheap on floodplains.
    • 3. Using permeable surfaces in urban areas, ploughing across hills instead of up and down, planting trees
    • 4. The lag time is shorter and the peak discharge higher in urban areas when compared to rural areas.
  • 11. Causes of Flooding
    • Precipitation - Heavy rainfall over a long period = creates saturated soil and surface run-off
    • Flash Floods - Hot dry areas where the land is baked hard causes flooding if there is an intense burst of heavy rainfall - water cannot infiltrate and results in rapid run-off.
    • Snowmelt - When temperatures rise and snow melts the stored precipitation is released as run off as infiltration will be low as the ground is still frozen.
    • Deforestation - When trees are cut down this reduces interception, transpiration and storage by the trees. This results in increased surface run-off
    • Urbanisation - When land is urbanised vegetation is removed and the land is covered in concrete and tarmac. These surfaces are impermeable and increase surface run-off.
  • 12. What are the impacts of river flooding?
  • 13. What are the impacts of river flooding?
  • 14. Landforms revision
    • Right, now for something creative
  • 15. Ready, Steady, Dough…
    • Work in pairs/groups to make a play-dough model showing how meanders and ox-bow lakes form
    • You could make paper labels to add to it
    • Now present your model to another group
    • You should explain your model and the processes involved
    • The listening group should tell you one thing they like and suggest one thing to improve
  • 16. Poster task
    • In pairs or groups, create a poster to show what you have learnt about rivers.
    • Include:
    • - Types of erosion
    • - Upper / middle / lower course features
    • - Landforms