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River Flooding[1]
 

River Flooding[1]

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

    • River flooding Why do rivers flood?
    • 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
    • Flooding
      • On your table, circle the most important processes that may cause flooding
    • Homework
      • Investigate a major flood event in the UK
      • Include:
      • Location
      • Causes
      • Effects (e.g. deaths, costs, damages)
      • E.g. floods in Wales 2009
    • 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
    • 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.
    • Questions
      • Question 5 (a,b,c) Page 75
      • P76/77. Which hydrograph do you think is for a rural location? Which is urban? Why?
    • Question 5 (a,b,c) Page 75
      • The discharge of the river in cumecs in response to precipitation
      • 8 m 3 /sec
      • 12 hours
    • 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
    • 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.
    • 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.
    • What are the impacts of river flooding?
    • What are the impacts of river flooding?
    • Landforms revision
      • Right, now for something creative
    • 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
    • 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