Yr 11 Rivers Revision 2009


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Yr 11 Rivers Revision 2009

  1. 1. Yr 11 Rivers Revision 1 st May 2009
  2. 2. Examiner’s tips…. <ul><li>Read through each question and highlight or underline the command word – what is the question asking you to do? </li></ul>
  3. 3. Command words Write down what you can see Describe… Give reasons for (how?/why?) Explain… Add labels with details Annotate Write down similarities and differences Compare… Make a list (e.g. bullet points) List… Write down State…
  4. 4. How are answers marked ? <ul><li>Point marking – a mark is given for each specific point made, usually worth 4 or less marks e.g. ‘Give 3 reasons for…..’ </li></ul><ul><li>Level marking – an overall level is given for the depth of the answer as a whole . </li></ul><ul><ul><li>Level 1 – Basic and simple statements </li></ul></ul><ul><ul><li>Level 2 – clear answers, some detail </li></ul></ul><ul><ul><li>Level 3 – detailed, supporting evidence given/used. </li></ul></ul>
  5. 5. The Water Cycle
  6. 12. With the aid of diagram (s) Explain the formation of waterfalls <ul><li>Alternating bands of hard and soft rock </li></ul><ul><li>Rapids </li></ul><ul><li>River erodes the softer, less resistant bands of rock </li></ul><ul><li>Hard rock undercut </li></ul><ul><li>Soft rock worn away through processes of hydraulic action (force of running water, compresses air in cracks in rock and leads to rock weakening and crumbling) and abrasion (action of running water and it’s load, wearing away at channel sides) </li></ul><ul><li>Plunge pool is formed at base of waterfall </li></ul><ul><li>Overhang eventually collapses providing more material for river to further deepen plunge pool </li></ul><ul><li>Process continues repeating, eventually river erodes further back upstream, leading to the formation of a gorge downstream </li></ul>
  7. 14. Meander bend on the River Conwy A B A cross section through a meander River Cliff FEATURE Slip off slope Erosion PROCESS Deposition Deep DEPTH Shallow Fast SPEED OF FLOW Slow CONCAVE CONVEX
  8. 15. A cross section through a meander
  9. 16. 2007 Q2 (b) Explain why the meander cross-section has this shape <ul><li>The meander cross section is asymmetrical . The river cliff is formed on the outer bend of the meander. This is where the water is deeper and moves more quickly . Hydraulic action and abrasion wear away at the side of the channel, undercutting the river bank to form a river cliff. </li></ul><ul><li>The slip-off slope is formed on the inside bend by deposition of alluvium. Because the water is shallow and moving more slowly at this point the river load gets deposited to form a gentle slope. </li></ul>
  10. 18. So … putting it all together
  11. 19. River features: Ox – bow lakes <ul><li>With the aid of diagrams, explain the formation of an oxbow lake (6 marks) (AQAA04) </li></ul><ul><li>Form from a meander </li></ul><ul><li>erosion on outside bend especially by hydraulic power </li></ul><ul><li>deposition on inside bends where water is shallower and lower velocity </li></ul><ul><li>neck narrows, breaks through in time of flood </li></ul><ul><li>deposition seals ox bow lake </li></ul><ul><li>eventual loss of lake to form meander scar </li></ul>
  12. 20. Storm Hydrographs
  13. 21. Rising limb Falling limb Peak discharge Peak rainfall storm flow normal (base) flow Hydrographs I = Lagtime
  14. 22. What factors increase The risk of flooding? * Impermeable rock * Hard dry soil * Very wet soil *steep slopes * Cutting down trees Building in the drainage basin * Many tributaries
  15. 23. Flood protection *Dams hold back flood waters *reservoirs store floodwater *straighten channels Increases speed of flow *Dredging Makes channel deeper so can hold more water *levees and embankments Prevents river from overflowing *land use zoning Restricts development to uses unaffected by flooding *afforestation Increases interception etc, reduces run off
  16. 24. Management of water quality and amenities River pollution *nitrates from fertilisers causes eutrophication Water taken from river for cooling in power stations is returned warmer and de-oxygenates water Poisonous / smelling waste from industrial sites Domestic sewage containing dissolved chemicals such as phosphorous from washing powder
  17. 25. Rainfall map of t Rainfall map of the United Kingdom   Fig 1. - Annual precipitation over Great Britain he United Kingdom   Fig 1. - Annual precipitation over Great Britain Heaviest rainfall Areas with most cloud cover Lowest summer temperatures – less loss of water due to evaporation or transpiration Areas with low population density WATER SURPLUS WATER DEFICIT Demand > Supply Rainfall is lower Evaporation and transpiration is high 1/3 UK population lives in SE IN THE WEST IN THE EAST
  18. 26. Water storage <ul><li>Porous – rock with spaces between the particles which make up the rock </li></ul><ul><li>Permeable – rock which allows water to pass through the pore spaces </li></ul><ul><li>Pervious – rock which allows water to pass through via cracks </li></ul><ul><li>Impermeable – rock which does not allow water to pass through </li></ul><ul><li>Groundwater - water stored underground in areas of permeable rock </li></ul>
  19. 28. <ul><li>Rock types found in Greater London basin are: </li></ul><ul><li>Sandstone, chalk and limestone which are permeable </li></ul><ul><li>Clay which is impermeable </li></ul><ul><li>Rain falling on the Chiltern Hills and North Downs soaks in through the permeable chalk. The Chalk layer is called an aquifer because ground water supplies can be taken from it. </li></ul><ul><li>The water table reaches the surface in places where the water comes out as springs </li></ul>
  20. 29. <ul><li>Where the water table is always below the surface a well has to be dug to reach the ground water. </li></ul><ul><li>Water table rises in winter when there is plenty of rainfall, low evaporation and transpiration </li></ul><ul><li>Water table falls in summer when there is less rainfall and higher rates of evaporation </li></ul><ul><li>To ensure there is water in the well all year round the bottom of the well must be below the lowest summer level of the water table </li></ul><ul><li>When the wells were first dug the water table was so high above the bottom of the wells that it flowed out without being pumped = artesian well </li></ul>Today Greater London needs more water than the ground water can yield so extra supplies come from: Pumping (abstraction) from River Thames Waste water from factories and homes is purified and reused.
  21. 30. Upland reservoirs – Kielder (N.E) <ul><li>2006 Many urban areas get their water from upland reservoirs. </li></ul><ul><li>Using an example of an upland reservoir that you have studied, explain the physical and human advantages of its location. </li></ul>
  22. 31. Detailed elaborated or linked statements with precise reference to case study exemplar. Must cover both physical and human advantages of the location. Expect reasonable balance between the two for full marks <ul><li>. </li></ul><ul><li>PHYSICAL Kielder Water is in the relatively narrow valley of the River North Tyne so the size and cost of building the dam was relatively small. </li></ul><ul><li>PHYSICAL The local geology is shale, which is impermeable so the water does not drain away. </li></ul><ul><li>PHYSICAL The high rainfall of over 1000mm meant that there was an ample supply of water. </li></ul><ul><li>HUMAN The area was sparsely populated so when the valley was flooded there was not too much disruption to the local population. </li></ul><ul><li>HUMAN The water could be used in the densely populated industrial areas of North East England which are near by. </li></ul><ul><li>HUMAN The population of the north east could also use the reservoir for leisure pursuits such as fishing and sailing </li></ul>
  23. 32. What causes flooding? Impermeable rock deforestation Arable farming Building on floodplains Heavy rainfall Lots of tributaries Marshy areas Very wet soil Hard dry soil steep slopes
  24. 33. Flood protection *Dams hold back flood waters *reservoirs store floodwater *straighten channels Increases speed of flow *Dredging Makes channel deeper so can hold more water *levees and embankments Prevents river from overflowing *land use zoning Restricts development to uses unaffected by flooding *afforestation Increases interception etc, reduces run off
  25. 34. How can the risk of flooding be reduced? <ul><li>Control the WATER Build a dam to trap and store water. </li></ul><ul><li>Pump water into a temporary storage lake or build reservoirs </li></ul>Control LAND USE Stop people building on the floodplain Plant trees to increase interception and infiltration
  26. 35. How can the risk of flooding be reduced? <ul><li>Alter the RIVERS CHANNEL </li></ul><ul><li>Straighten it – to speed up flow of water </li></ul><ul><li>Widen and deepen it </li></ul><ul><ul><li>Levees and embankment </li></ul></ul><ul><ul><li>Dredging </li></ul></ul><ul><li>Build BARRIERS </li></ul><ul><li>Build up the banks with earth or concrete to make embankments to keep water IN </li></ul><ul><li>Build flood walls to keep water OUT </li></ul>
  27. 36. Wider channel Concrete walls
  28. 37. Dam
  29. 38. Channel Diversion
  30. 39. Homes On Stilts
  31. 40. Re-planting Trees
  32. 41. Channel Straightening
  33. 44. What do you know about drainage basins?