River Flooding[1]


Published on

Published in: Technology, Education
1 Like
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

River Flooding[1]

  1. 1. River flooding Why do rivers flood?
  2. 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. 3. Flooding <ul><li>On your table, circle the most important processes that may cause flooding </li></ul>
  4. 4. Homework <ul><li>Investigate a major flood event in the UK </li></ul><ul><li>Include: </li></ul><ul><li>Location </li></ul><ul><li>Causes </li></ul><ul><li>Effects (e.g. deaths, costs, damages) </li></ul><ul><li>E.g. floods in Wales 2009 </li></ul>
  5. 5. The Flood / Storm Hydrograph <ul><li>Hydrographs are used to show the relationship between precipitation and discharge (the amount of water passing in the river channel) . </li></ul><ul><li>Hydrographs are used to predict whether a river is likely to flood . </li></ul><ul><li>Discharge is measured in Cumecs (cubic metres of water per second). </li></ul><ul><li>Lag Time is the delay between peak precipitation and peak river discharge. </li></ul><ul><li>Short Lag Times means water enters the river system very quickly following rainfall </li></ul><ul><li>Long Lag Times means water takes a longer time to enter the river system following rainfall </li></ul>
  6. 6. Lag times <ul><li>So a lag time changes depending on the characteristics of the river basin </li></ul><ul><li>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) </li></ul><ul><li>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. </li></ul><ul><li>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. </li></ul>
  7. 7. Questions <ul><li>Question 5 (a,b,c) Page 75 </li></ul><ul><li>P76/77. Which hydrograph do you think is for a rural location? Which is urban? Why? </li></ul>
  8. 8. Question 5 (a,b,c) Page 75 <ul><li>The discharge of the river in cumecs in response to precipitation </li></ul><ul><li>8 m 3 /sec </li></ul><ul><li>12 hours </li></ul>
  9. 9. What are the causes of flooding? <ul><li>Make a copy of the diagram on page 76 </li></ul><ul><li>Colour classify each cause into either physical or human . </li></ul><ul><li>Complete activities 2-4 </li></ul><ul><ul><li>2. 2 marks </li></ul></ul><ul><ul><li>3. 3 marks </li></ul></ul><ul><ul><li>4. 2 marks </li></ul></ul>
  10. 10. Answers <ul><li>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. </li></ul><ul><li>3. Using permeable surfaces in urban areas, ploughing across hills instead of up and down, planting trees </li></ul><ul><li>4. The lag time is shorter and the peak discharge higher in urban areas when compared to rural areas. </li></ul>
  11. 11. Causes of Flooding <ul><li>Precipitation - Heavy rainfall over a long period = creates saturated soil and surface run-off </li></ul><ul><li>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. </li></ul><ul><li>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. </li></ul><ul><li>Deforestation - When trees are cut down this reduces interception, transpiration and storage by the trees. This results in increased surface run-off </li></ul><ul><li>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. </li></ul>
  12. 12. What are the impacts of river flooding?
  13. 13. What are the impacts of river flooding?
  14. 14. Landforms revision <ul><li>Right, now for something creative </li></ul>
  15. 15. Ready, Steady, Dough… <ul><li>Work in pairs/groups to make a play-dough model showing how meanders and ox-bow lakes form </li></ul><ul><li>You could make paper labels to add to it </li></ul><ul><li>Now present your model to another group </li></ul><ul><li>You should explain your model and the processes involved </li></ul><ul><li>The listening group should tell you one thing they like and suggest one thing to improve </li></ul>
  16. 16. Poster task <ul><li>In pairs or groups, create a poster to show what you have learnt about rivers. </li></ul><ul><li>Include: </li></ul><ul><li>- Types of erosion </li></ul><ul><li>- Upper / middle / lower course features </li></ul><ul><li>- Landforms </li></ul>