River processes


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this slide helps IGCSE to be able to revise and grasp the main topic of rivers

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River processes

  1. 1. River features? Are facial features the same thing for rivers? 1
  2. 2. River Features Rivers are eroding, transporting and depositing constantly. The river can be divided into 3 sections – Upper Course at the Source, Middle Course and Lower Course at the Mouth of the river. The river displays different characteristics at each section. 2
  3. 3. River Structure 3
  4. 4. Upper valley characteristics “V”shape valley, mostly vertical erosion Interlocking spurs Narrow, shallow channel, low velocity and discharge Large rocks that come from upstream and from valley sides 4
  5. 5. Interlocking spurs, Robinson, Lake District An upper course valley often has interlocking spurs, and steep valley sides 5
  6. 6. River load in upper course Why are they rounded? 6
  7. 7. River load in upper course Why are they rounded? Boulders are large and semi-rounded, due to attrition within the load and abrasion with the stream bed and banks 7
  8. 8. Waterfall formation Look at the diagram, How is a waterfall formed? 8
  9. 9. Upper Course: Waterfalls & Gorges Waterfall and Gorge 1 (OBLIQUE AERIAL VIEW) EROSION TYPE: Vertical and Headward 9
  10. 10. High Force waterfall, R. Tees Waterfall creates gorge as it recedes upstream by eroding the base and neck Plunge pool 10
  11. 11. Upper Course: Potholes Pothole s EROSION TYPE: Vertical (by EDDY CURRENTS) Boulders broken off by erosion that sit on the river bed create swirling eddy currents as the water flows past as the river is not strong enough yet to move the boulders by TRACTION. These eddies swirl the boulder round and erode a pothole in the river bed by ABRASION. 11
  12. 12. Potholes, human scale!! 12
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  14. 14. Middle course, R. Tees HOW DOES THIS DIFFER FROM THE UPPER SECTION? 14
  15. 15. Middle course, R. Tees Valley opens out, more gentle slopes, wider valley bottom First signs of meanders River channel wider, deeper, greater velocity and discharge 15
  16. 16. Meandering Rivers WHAT IS A MEANDER? 16
  17. 17. Middle Course: Meanders Meanders 1 (Aerial View) Meanders are formed because the current swings to the outside of a bend and concentrates the erosion there. Deposition occurs on the inside of the bed where there is not enough energy to carry load. EROSION TYPE: Lateral
  18. 18. Middle Course: Meanders 2 Meanders 2 (Profile View / Cross Section X - Y) EROSION TYPE: Lateral This cross section clearly shows the eddy current (near ’X’) formed by the velocity of the river being concentrated on the outside of the bend. These UNDERCUT the bank causing the formation of a RIVER CLIFF. On the inside (NEAR ‘Y’), a SLIP-OFF-SLOPE is formed where current is too slow to carry any load.
  19. 19. Meander, R. Lavant, Chichester WHICH WAY IS THIS MEANDER MOVING? Slip-Off Slope Pebble deposits on the inner meander bend where there is low energy Floodplain River Cliff 19
  20. 20. WHERE IS EROSION TAKING PLACE? River Cliff F A E B Slip-off slope C } Meander loop D WHERE IS DEPOSTION TAKING PLACE? 20
  21. 21. What happens to the river when it moves to the middle course Gradient becomes less steep River continues to erode vertically a bit but more LATERAL erosion now occurs in MEANDERS The meanders MIGRATE. What do you think that means? Name three effects it have on the valley. 21
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  23. 23. Lower Course: Severn Valley HOW DOES IT DIFFER FROM THE MIDDLE COURSE? 23
  24. 24. Lower Severn Valley Very wide floodplain Very gentle valley side gradients Well developed meanders with bars in the channel indicating high sediment load 24
  25. 25. Lower Course: Ox-bow lake Ox-Bow Lake 1 (Aerial View) EROSION TYPE: Lateral Ox-bow lakes are formed when two meander RIVER CLIFFS are being eroded towards each other. These will eventually meet, causing the river to then flow across the bottom of the diagram.
  26. 26. Lower Course: Ox-bow lake 2 Ox-Bow Lake 2 (Aerial View)
  27. 27. Ox Bow lake on Mississippi 27
  28. 28. The Nile Delta from space River Nile 28
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