River Profiles

3,575 views

Published on

Geomorphology: River Profiles, fluvial landforms, river capture/stream piracy

Published in: Education, Technology
0 Comments
6 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
3,575
On SlideShare
0
From Embeds
0
Number of Embeds
62
Actions
Shares
0
Downloads
159
Comments
0
Likes
6
Embeds 0
No embeds

No notes for slide

River Profiles

  1. 1. River Profiles and Fluvial Landforms River Capture / Stream Piracy
  2. 2. Learningobjectives Processes of River Transportation River Profiles : Long Profile River Profiles : Cross Profile Fluvial Landforms River Abstraction / Stream Piracy.
  3. 3. Processes of river transportation Schuters: Pg.165
  4. 4. Learningobjectives Processes of River Transportation River Profiles : Long Profile River Profiles : Cross Profile Fluvial Landforms River Abstraction / Stream Piracy.
  5. 5. Longitudinal Profile: River from Source to Mouth
  6. 6. V-shaped valley Vertical erosion (Turbulent flow) Waterfalls Rapids Gorges Pot-holes Interlocking spurs Asymmetrical channel Meanders Transportation Floodplains Slip-off slopes Truncated spurs Large channel Deposition Braiding Ox-bow lakes Large flood plains Levees Deltas River Channels Pg.127 Click for video Longitudinal Profile is the profile of a river from it’s Source to it’s Mouth. Youthful stage Mature stage Old age stage
  7. 7. Stages of Stream Development Initial Stage: Fast moving stream, narrow valley Mature Stage: Meanders develop, widening floodplain Old Age Stage: Wide floodplain, yazoo streams, and oxbow lakes develop
  8. 8. 1 2 3 4 5 6 7 8 9
  9. 9. Back Upper Course where alternate layers of hard and soft rock is found!
  10. 10. Back Middle Course!
  11. 11. CC- Woolyboy Back Meanders
  12. 12. CC- Photo Paul Back Estuary
  13. 13. Back Deposition
  14. 14. CC- Geoff Edwards Back Erosion
  15. 15. CC- Aerial Photography Back Middle
  16. 16. CC- Martin Third Back Flood plain
  17. 17. CC- ecstaticist Back Lower Course
  18. 18. Ronnie Raindrop’s journey… Instructions Copy the following 14 slides (slides 17-29) into a new PowerPoint presentation and complete the following : 1. Rearrange the slides so that they show the correct order as you travel down a river. Remember that a river has an Upper, Middle and Lower stage. By the way the numbers don’t go in order! 2. On each slide write what Ronnie can see (fluvial erosional and depositional landforms and the process at work) on his journey. You could use text boxes or speech bubbles to do this. 3. Add your name and form to the title slide. 4. Delete this instruction slide. 5. Print out your work and staple it. 6. Finally, hand it to your teacher. Well done, mission complete…
  19. 19. 1 Source / Origin of River Youthful stage Watershed Catchment area Orographic uplift Formation of clouds
  20. 20. 7 Youthful stage V-Shaped Valley Vertical erosion Turbulent flow
  21. 21. 5 Waterfall Youthful stage Turbulent flow Alternate layers of hard and soft rock
  22. 22. 2 Rapids Youthful stage Turbulent flow Large bed load
  23. 23. 6 Interlocking spurs Youthful stage Turbulent flow Large bed load
  24. 24. 11 Temporary Base Level of erosion
  25. 25. 3 Mature stage Meandering river Large channel Asymmetrical channel
  26. 26. 10 Old Age stage Meandering river Asymmetrical channel
  27. 27. Old Age stage Meandering river River flood plain 8
  28. 28. 4 Old age stage Meandering river Ox-bow lake
  29. 29. 9 Old Age stage Braided river Velocity of river is reduced Deposition occurs
  30. 30. 12 Ultimate Base Level of erosion Lowest level to which a river can erode Mouth of the river
  31. 31. Profiles Cross Profile Longitudinal Profile Cross Profile Is the profile of a river from Bank to Bank Longitudinal Profile is the profile of a river from it’s Source to it’s Mouth.
  32. 32. Ungraded vs. Graded Streams Graded stream: Balance between transport capacity and sediment load. Maintained by altering the shape of the channel and stream profile. Rate of erosion = Rate of Deposition Smooth concave profile Ungraded profile / stream: Rate of erosion is not equal to rate of deposition Rough concave profile
  33. 33. Graded Streams
  34. 34. Long Profile 1) Name the typical shape that the river strives to achieve. Smooth concave profile. [Graded profile] Dotted line on profile 2) What is the real shape it accepts? An uneven, concave profile, steep at the source and gentle at the mouth. 3) Name (a) a temporary (local) and (b) a permanent (ultimate) base level of erosion. (a) Dam (b) sea (the lowest level to which a river can erode) 4) Name three ways in which the above river may be rejuvenated. Dam wall bursting. Rising of the land. Sinking of the sea. 5) Name 3 factors that disrupted the above longitudinal profile. Rapids, waterfall and dam 6) Where does erosion occur fastest? Give a reason for your answer. In the middle section, stream volume and load have increased. Erosion is thus faster.
  35. 35. Cross Profile 1) What type of river channel will produce a symmetrical cross profile? Straight stream 2) Which 2 factors determine the different cross profiles that a river may display? Climate and Geological conditions 3) Which 2 erosive processes are responsible for eroding the valley sides. Mass wasting and undercutting 4) Account for the shape of the cross profile on a bend. Outer bend (undercut slope) is characterized by erosion since the water flows faster. Inner bend (slip-off slope) is characterized by deposition, since the water flows slowly.
  36. 36. Learningobjectives Processes of River Transportation River Profiles : Long Profile River Profiles : Cross Profile Fluvial Landforms River Abstraction / Stream Piracy.
  37. 37. Cross Profile Schuters: Pg.167* Notes Oxford: Pg.122
  38. 38. Cross Profile - Answers
  39. 39. • Velocity varies within the channel – Highest velocity is in the center of the channel – Drag slows water along the bottom, banks, and top (water-air interface)
  40. 40. Channel shape and velocity Schuters: Pg.167
  41. 41. Activity 6: Channel shape and velocity Pg.122
  42. 42. Schuters: Pg.163
  43. 43. Learningobjectives Processes of River Transportation River Profiles : Long Profile River Profiles : Cross Profile Fluvial Landforms River Abstraction / Stream Piracy.
  44. 44. 1) Meanders / Ox-bow Lake Fluvial Landforms  River reaches flat land  Begins to meander  Velocity is highest on the outer bend - erosion – undercut bank – river cliff Velocity is lower on the inside bend - deposition – slip-off slope – gradual slope.
  45. 45. Channel shape is based on the velocity of the stream and resistance of rock it is cutting into. Water in streams tends to move quicker in the center of the stream and slower towards the outside. Outside of meander is called a Undercut slope and is associated with erosion.Inside of meander is called a Slip-off slope and is associated with deposition.
  46. 46. Formation
  47. 47. Fluvial Landforms
  48. 48. Fluvial Landforms : Incised / Intrenched Meander
  49. 49. Incised / Intrenched Meanders
  50. 50. Fluvial Landforms 2) Waterfalls  Forms when resistant layer of rock prevents vertical erosion  Softer underlying layers are eroded  Resistant layer is undermined and collapses. Waterfall retreats upstream. Forms a Gorge or Ravine.
  51. 51. Copyright © Houghton Mifflin Company. All rights reserved. Geology, 14b–52 Fluvial Landforms Formation of a Waterfall
  52. 52. Fluvial Landforms 3) Levees  Form on the floodplain on the lower course  Flooding causes overflowing of banks  Heavier deposits occur repeatedly on the banks Deposits are built up to raised banks known as levees May be artificially raised and strengthened as flood protection Swamps may form on the floodplain
  53. 53. Deposition and Erosion of River Bars Flood: Increased discharge and erosion! Normal Flow Post-flood; new bars deposited
  54. 54. Deposits
  55. 55. The Aswan Dam and the Nile DeltaFluvial Landforms 4) Deltas  A large and constant supply of silt.  A slow flowing river with water all year  No strong tidal effect in the sea A calm, shallow sea with: No rapid subsidence of the sea floor No strong currents in the sea When a river enters the sea or a lake the gradient is gentle and the flow speed of the river is reduced resulting in the deposition of sediments causing the river channel to become blocked. Requirements for a Delta to form
  56. 56. The Irrawaddy River Delta This river delta in Burma is one of the world’s great rice producing regions Fertile mud and sand have been deposited here during the last 2 million years mangrove forest Sediment plumes
  57. 57. Development of Delta
  58. 58. Fluvial Landforms after rejuvenation
  59. 59. Rejuvenation is when the river flows faster due to the following:  Global drop in sea level Uplift of land  Increase in rainfall River Capture Rejuvenation results in:  Incised rivers (rivers cut into the plain) River Terraces Knickpoints
  60. 60. How Terraces Form Incised River
  61. 61. Stream Terraces - Jackson Hole, WY
  62. 62. Fluvial Landforms : After Rejuvenation Name the landforms that may develop after a river has been rejuvenated. Intrenched Meander  These are formed when rejuvenation occurs in a stream which is already meandering  The stream now meanders in a deep, steep-sided gorge eg. Fish River Canyon and lower course of the Breede River Valleys within Valleys  When streams are rejuvenated fairly rapidly and the base level drops substantially, a valley can be formed within a valley. Terraces • When rejuvenation of a river flowing on a wide valley floor (flood plain) occurs, a new valley is carved into the old one and parts of the earlier valley remain as terraces. E.g. Canyons • Terraces may be: Matched Unmatched • Such terraces can be seen along the banks of the Vaal river in the vicinity of Bloemhof, Christiana and Delport.
  63. 63. A Question of Rivers 1 2 3 4 5 6 7 8 9
  64. 64. 1 a) Which stage of the river will this type of erosion take place in? b) Which type of erosion is responsible for the formation of these circular depressions?
  65. 65. a)The circular depressions are little pot holes and they develop in the Youthful stage of the river. Small stones are swirled around in them when the river is flowing higher and faster than it is at present. b) The pot holes are eroded by the abrasive action of the swirling stones. 1
  66. 66. 2 What is required for incision of the river to occur? Drag and drop the following labels in the correct position: Fall in sea level Waterfall retreats cutting a lower valley New flood plain forms River bluffs
  67. 67. 2Rejuvenation is required for incision of the river to occur.
  68. 68. 3 Identify the physical features by dragging and dropping the following labels in the correct position: meanders broad, flat flood plain ox bow lake limit of tidal influence embankments/levees
  69. 69. ox bow lake limit of tidal influence meanders broad, flat flood plain embankments/levees 3
  70. 70. 4 What river feature occupies the centre of this photo? How does the river change downstream of the feature?
  71. 71. This feature is a confluence. It occurs where a tributary joins the main stream or river. Downstream of a confluence , the river increases in width. The discharge of a river (the volume of water it is carrying) also increases significantly. 4
  72. 72. 5 What features identify this stretch of river as part of its upper course? interlocking spurs steep valley sides steep long profile absence of flood plain large bed load Drag and drop the following labels in the correct position.
  73. 73. interlocking spurs steep valley sides absence of flood plain steep long profile large bed load 5
  74. 74. 6 Why has a waterfall developed here? Label the following: a band of hard rock interrupts the river’s course An overhang develops where the softer rock below is eroded. In time this will collapse. relatively softer rock plunge pool
  75. 75. a band of hard rock interrupts the river’s course An overhang develops where the softer rock below is eroded. In time this will collapse. relatively softer rock plunge pool 6
  76. 76. 7 How would you know that this valley was not carved by the river which flows in it today?
  77. 77. This valley is a U-shaped valley in the Scottish Highlands. It was eroded by ice during the Ice Age. It is much too large and deep to have been carved by the small river which now flows in it. The river is called a ‘misfit’ as it is not in keeping with the scale of its valley. Although the river is in a highland valley, it displays features of a valley in its lower course (meanders). This is because the valley floor is so flat. 7
  78. 78. 8 Identify the physical features by dragging and dropping the following labels in the correct position: small tributary no flood plain steep valley sides Perennial Straight stream steep long profile of a tributary
  79. 79. steep valley sides small tributary no flood plain steep long profile of a tributary 8 Perennial Straight stream
  80. 80. 9 Describe and explain the differences between the sides (banks ) of the river
  81. 81. 9 On the inside of the meander water is flowing more slowly. This results in deposition and the formation of the slip-off slope or river beach. On the outside of the meander water is flowing more quickly. This results in erosion and the formation of a undercut slope or river cliff.
  82. 82. Learningobjectives Processes of River Transportation River Profiles : Long Profile River Profiles : Cross Profile Fluvial Landforms River Abstraction / Stream Piracy.
  83. 83. Abstraction of a Drainage Basin  A watershed remains in the same position only if the rates of erosion on either side are equal  The river (B) flowing down the steeper gradient erodes faster and moves the watershed back from position 1 to 2  Water falling on the area between 1 and 2 will thus no longer flow down gradient B, as it had previously done, but will be captured to fall into the catchment area belonging to A Factors favouring river abstraction
  84. 84. Factors favouring river abstraction Schuters pg 176
  85. 85. Activity 14: Abstraction of the eastern escarpment Pg.136
  86. 86. Activity 15: Identifying river capture Pg.137
  87. 87. Copyright © Houghton Mifflin Company. All rights reserved. Geology, 14b–88 Stream Piracy
  88. 88. Stream Piracy
  89. 89. Stream Piracy Schuters pg 177
  90. 90. Schuters pg 178
  91. 91. Schuters pg 178

×