River processes and landforms

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An introduction: to support AS Geography (Edexcel B)

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River processes and landforms

  1. 1. Channel processes and features Valley slope processes and landforms RIVER STUDIES
  2. 2. Satellite view of river drainage, Middle East
  3. 3. Microscale drainage basin
  4. 4. Upper valley characteristics
  5. 5. Upper valley characteristics
  6. 6. Upper valley characteristics “ V”shape valley , vertical erosion dominant
  7. 7. Upper valley characteristics “ V”shape valley , vertical erosion dominant Interlocking spurs
  8. 8. Upper valley characteristics “ V”shape valley , vertical erosion dominant Interlocking spurs Slumping and landslides - very active hillslopes
  9. 9. Upper valley characteristics “ V”shape valley , vertical erosion dominant Interlocking spurs Slumping and landslides - very active hillslopes Terracettes formed by soil creep
  10. 10. Upper valley characteristics “ V”shape valley , vertical erosion dominant Interlocking spurs Slumping and landslides - very active hillslopes Terracettes formed by soil creep Narrow, shallow channel, low velocity and discharge
  11. 11. Upper valley characteristics “ V”shape valley , vertical erosion dominant Interlocking spurs Slumping and landslides - very active hillslopes Terracettes formed by soil creep Narrow, shallow channel, low velocity and discharge Large bedload derived from upstream and from valley sides
  12. 12. Interlocking spurs, Robinson, Lake District A typical upper course valley with interlocking spurs, steep valley sides and active slope processes
  13. 13. Choked runnel, N. Pennines Ephemeral stream or runnel - water present only during high rainfall events
  14. 14. Choked runnel, N. Pennines Debris brought downslope towards channel - dropped when water disappears after storm Ephemeral stream or runnel - water present only during high rainfall events
  15. 15. Choked runnel, N. Pennines Debris brought downslope towards channel - dropped when water disappears after storm Ephemeral stream or runnel - water present only during high rainfall events Vertical erosion creating steep, bare slopes vulnerable to further erosion - an example of positive feedback in a slope system
  16. 16. River load in upper course Load is dumped in summer due to the low discharge unable to carry the c ________ and c __________ of load at higher flow levels
  17. 17. River load in upper course Load is dumped in summer due to the low discharge unable to carry the capacity and competence of load at higher flow levels
  18. 18. River load in upper course Load is dumped in summer due to the low discharge unable to carry the capacity and competence of load at higher flow levels
  19. 19. River load in upper course Boulders are large and semi-rounded, due to attrition within the load and abrasion with the stream bed and banks Load is dumped in summer due to the low discharge unable to carry the capacity and competence of load at higher flow levels
  20. 20. Rapids in the Upper Tees Valley
  21. 21. Rapids in the Upper Tees Valley Rapids are mini-waterfalls Protruding bands of more resistant strata create steps over which rapids fall - the river bed is ungraded
  22. 22. Rapids in the Upper Tees Valley Rapids are mini-waterfalls Protruding bands of more resistant strata create steps over which rapids fall - the river bed is ungraded Shallow, slow flowing river due to large amount of friction.
  23. 23. Rapids in the Upper Tees Valley Rapids are mini-waterfalls Protruding bands of more resistant strata create steps over which rapids fall - the river bed is ungraded Shallow, slow flowing river due to large amount of friction. Wetted perimeter is large compared to cross sectional area of water - resulting in a low ????????????
  24. 24. Rapids in the Upper Tees Valley Rapids are mini-waterfalls Protruding bands of more resistant strata create steps over which rapids fall - the river bed is ungraded Shallow, slow flowing river due to large amount of friction. Wetted perimeter is large compared to cross sectional area of water - resulting in a low hydraulic radius (low efficiency)
  25. 25. High Force waterfall, R. Tees
  26. 26. High Force waterfall, R. Tees Huge step in river bed due to igneous intrusion of dolerite into the limestone.
  27. 27. High Force waterfall, R. Tees Huge step in river bed due to igneous intrusion of dolerite into the limestone. Plunge pool where the dolerite wall is undercut, causing rockfalls and recession of the waterfall upstream
  28. 28. High Force waterfall, R. Tees Huge step in river bed due to igneous intrusion of dolerite into the limestone. Waterfall creates gorge as it recedes upstream by eroding the base and neck Plunge pool where the dolerite wall is undercut, causing rockfalls and recession of the waterfall upstream
  29. 29. High Force waterfall, R. Tees Huge step in river bed due to igneous intrusion of dolerite into the limestone. The long profile will be graded over time Waterfall creates gorge as it recedes upstream by eroding the base and neck Plunge pool where the dolerite wall is undercut, causing rockfalls and recession of the waterfall upstream
  30. 30. Headward erosion, Offa’s Dyke This is amazing!!
  31. 31. Headward erosion, Offa’s Dyke Spring erodes ground over which it flows and lubricates base of cliff, causing slumping and headward erosion
  32. 32. Headward erosion, R. Colorado
  33. 33. Headward erosion, R. Colorado River seeps out from spring at base and undermines steep cliff, causing rockfalls and headwall recession
  34. 34. Headward erosion, R. Colorado Rivers erode in a headward direction, eating back into plateau River seeps out from spring at base and undermines steep cliff, causing rockfalls and headwall recession
  35. 35. Potholes in R. Wharfe Smooth sculpturing of rock by abrasion, showing evidence of water levels during high discharge events Vertical erosion is dominant
  36. 36. Close-up of potholes
  37. 37. Close-up of potholes
  38. 38. Close-up of potholes Circular potholes due to eddying motion when river energy is high
  39. 39. Close-up of potholes Circular potholes due to eddying motion when river energy is high Potholes will join together by abrasion , and deepen by vertical erosion
  40. 40. Close-up of potholes Circular potholes due to eddying motion when river energy is high Load is picked up and used to scour or abrade pothole. Load itself becomes rounded by attrition Potholes will join together by abrasion , and deepen by vertical erosion
  41. 41. Potholes, human scale!!
  42. 42. Middle course, R. Tees
  43. 43. Middle course, R. Tees Valley opens out, more gentle slopes, wider valley bottom
  44. 44. Middle course, R. Tees Valley opens out, more gentle slopes, wider valley bottom First signs of meanders
  45. 45. Middle course, R. Tees Valley opens out, more gentle slopes, wider valley bottom First signs of meanders Floodplain
  46. 46. Middle course, R. Tees Valley opens out, more gentle slopes, wider valley bottom First signs of meanders Floodplain River channel wider, deeper, greater velocity and discharge
  47. 47. Meander, R. Lavant, Chichester
  48. 48. Meander, R. Lavant, Chichester Floodplain
  49. 49. Meander, R. Lavant, Chichester Floodplain Point bar deposits on the inner meander bend where there is low energy
  50. 50. Meander, R. Lavant, Chichester Floodplain Steep bank known as the river bluff or cliff , caused by concentrated erosion due to the Point bar deposits on the inner meander bend where there is low energy
  51. 51. Meander, R. Lavant, Chichester Floodplain Steep bank known as the river bluff or cliff , caused by concentrated erosion due to the thalweg Point bar deposits on the inner meander bend where there is low energy
  52. 52. Meander, R. Lavant, Chichester Floodplain Steep bank known as the river bluff or cliff , caused by concentrated erosion due to the thalweg and Point bar deposits on the inner meander bend where there is low energy helicoidal flow
  53. 53. Meander, R. Lavant, Chichester Floodplain Steep bank known as the river bluff or cliff , caused by concentrated erosion due to the thalweg and Point bar deposits on the inner meander bend where there is low energy helicoidal flow pool riffle pool Pools develop at meander bends and riffles in the stretches between bends
  54. 54. Meander on the R. Colorado
  55. 55. Meander on the R. Colorado Meander incised into plateau due to rejuvenation
  56. 56. Meander on the R. Colorado Meander incised into plateau due to rejuvenation Different strata show evidence of past climates or hydrological events
  57. 57. Meander on the R. Colorado Meander incised into plateau due to rejuvenation Different strata show evidence of past climates or hydrological events. Stratum with large boulders must have formed in wetter conditions when higher river discharge carried a greater competence of load
  58. 58. Migrating meanders, R. Gongola, Nigeria
  59. 59. Migrating meanders, R. Gongola, Nigeria Former course marked by white sediments Current channel is braided
  60. 60. Lower Severn Valley
  61. 61. Lower Severn Valley Well developed meanders with bars in the channel indicating high sediment load Very wide floodplain Very gentle valley side gradients
  62. 62. River terraces, R. Agri, S. Italy
  63. 63. River terraces, R. Agri, S. Italy River has been rejuvenated causing renewed vertical erosion - base level has dropped either due to rising land or falling sealevel
  64. 64. River terraces, R. Agri, S. Italy Flat terraces represent former floodplains River has been rejuvenated causing renewed vertical erosion - base level has dropped either due to rising land or falling sealevel
  65. 65. Flooding in the Severn Valley
  66. 66. Flooding in the Severn Valley Floodplain can be mapped into risk zones high to low
  67. 67. Flooding in the Severn Valley Floodplain can be mapped into risk zones high to low Floods can be beneficial - they renew soil fertility by depositing sediment on floodplain
  68. 68. Flooding in the Severn Valley Floodplain can be mapped into risk zones high to low Floods can be beneficial - they renew soil fertility by depositing sediment on floodplain Floods result in large amounts of sediment transported in the channel
  69. 69. Padstow estuary Estuaries are tidal, dominated by marine sediments At low tide, mudflats are exposed
  70. 70. Alluvial fan, Buttermere, Lake District
  71. 71. Alluvial fan, Buttermere, Lake District
  72. 72. Alluvial fan, Buttermere, Lake District Lake Buttermere acts as a local baselevel for the stream, leading to deposition of load in a triangular shape - an alluvial fan This is the same process that forms major deltas at the coast e.g. R. Nile
  73. 73. Braided river, Swiss Alps
  74. 74. Braided river, Swiss Alps
  75. 75. Braided river, Swiss Alps Daytime snowmelt in summer produces flashy regime Vast amounts of sediment supplied from frost-shattered valley sides
  76. 76. Braided river, Swiss Alps Daytime snowmelt in summer produces flashy regime Vast amounts of sediment supplied from frost-shattered valley sides Channel course can change daily due to changes in discharge and loose sediments
  77. 77. Summary of channel characteristics (1) Processes
  78. 78. Summary of channel characteristics (1) Processes
  79. 79. Summary of channel characteristics (1) Processes
  80. 80. Summary of channel characteristics (1) Processes
  81. 81. Summary of channel characteristics (2) Landforms
  82. 82. Summary of channel characteristics (2) Landforms <ul><li>Rapids </li></ul><ul><li>Waterfall </li></ul><ul><li>Pothole </li></ul>
  83. 83. Summary of channel characteristics (2) Landforms <ul><li>Rapids </li></ul><ul><li>Waterfall </li></ul><ul><li>Pothole </li></ul><ul><li>Meander </li></ul><ul><li>Bluff/cliff </li></ul><ul><li>Point bar </li></ul><ul><li>Pool </li></ul><ul><li>Riffle </li></ul>
  84. 84. Summary of channel characteristics (2) Landforms <ul><li>Rapids </li></ul><ul><li>Waterfall </li></ul><ul><li>Pothole </li></ul><ul><li>Meander </li></ul><ul><li>Bluff/cliff </li></ul><ul><li>Point bar </li></ul><ul><li>Pool </li></ul><ul><li>Riffle </li></ul><ul><li>Knick point </li></ul><ul><li>Braids </li></ul><ul><li>Alluvial fan </li></ul><ul><li>Delta </li></ul>
  85. 85. Summary of channel characteristics (3) Concepts and technical terms
  86. 86. Summary of channel characteristics (3) Concepts and technical terms <ul><li>Discharge </li></ul><ul><li>Regime </li></ul><ul><li>- flashy </li></ul><ul><li>- regular </li></ul><ul><li>Capacity </li></ul><ul><li>Competence </li></ul>
  87. 87. Summary of channel characteristics (3) Concepts and technical terms <ul><li>Discharge </li></ul><ul><li>Regime </li></ul><ul><li>- flashy </li></ul><ul><li>- regular </li></ul><ul><li>Capacity </li></ul><ul><li>Competence </li></ul><ul><li>Hydraulic radius </li></ul><ul><li>- cross sectional </li></ul><ul><li>area </li></ul><ul><li>- wetted </li></ul><ul><li>perimeter </li></ul>
  88. 88. Summary of channel characteristics (3) Concepts and technical terms <ul><li>Discharge </li></ul><ul><li>Regime </li></ul><ul><li>- flashy </li></ul><ul><li>- regular </li></ul><ul><li>Capacity </li></ul><ul><li>Competence </li></ul><ul><li>Hydraulic radius </li></ul><ul><li>- cross sectional </li></ul><ul><li>area </li></ul><ul><li>- wetted </li></ul><ul><li>perimeter </li></ul><ul><li>Long profile </li></ul><ul><li>Graded profile </li></ul><ul><li>Rejuvenation </li></ul><ul><li>Base level </li></ul>
  89. 89. Summary of channel characteristics (3) Concepts and technical terms <ul><li>Discharge </li></ul><ul><li>Regime </li></ul><ul><li>- flashy </li></ul><ul><li>- regular </li></ul><ul><li>Capacity </li></ul><ul><li>Competence </li></ul><ul><li>Hydraulic radius </li></ul><ul><li>- cross sectional </li></ul><ul><li>area </li></ul><ul><li>- wetted </li></ul><ul><li>perimeter </li></ul><ul><li>Long profile </li></ul><ul><li>Graded profile </li></ul><ul><li>Rejuvenation </li></ul><ul><li>Base level </li></ul><ul><li>Thalweg </li></ul><ul><li>Helicoidal </li></ul><ul><li>flow </li></ul><ul><li>Meander </li></ul><ul><li>migration </li></ul>
  90. 90. Summary of valley characteristics
  91. 91. Summary of valley characteristics
  92. 92. Summary of valley characteristics
  93. 93. Summary of valley characteristics

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