Types of Rivers

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Grade 12 Geomorphology. SA curriculum. Types of Rivers.

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Types of Rivers

  1. 1. Learningobjectives Types of Rivers Drainage Patterns River Channel Patterns
  2. 2. The hydrologic cycle ga.water.usgs.gov/edu/charts/waterdistribution.gif
  3. 3. Types of Rivers • Rivers are very dependent on climate and their characteristics are closely related to the precipitation and evaporation regimes in their drainage areas. • Four types: – Perennial or permanent rivers – Periodic rivers – Episodic rivers – Exotic www.aquatic.uoguelph.ca/rivers/chintro.htm
  4. 4. Permanent / Perennial Rivers • Rivers that flow all year e.g. Orange (Gariep), Kunene, Zambezi. • River channel reaches water table throughout the year. • Orange River used to be non-perennial before the construction of the Gariep Dam.
  5. 5. Periodic / Non-Perennial Rivers • Only flow during the rainy season e.g. Berg River (seen below) • Water table must rise enough to feed the river when it is not raining
  6. 6. Episodic Rivers • Only flow for short periods after heavy rain e.g. Nassob (Namibia). • May have some permanent pools where bed intercepts water table. • It is an important water source in desert regions.
  7. 7. Exotic Rivers • Rise in humid areas with high rainfall and flow through dry areas. • Gariep river rises in the Drakensberg moutains (high rainfall) and flows through the Northern Cape (dry region).
  8. 8. Relationship between the water tables and types of rivers Schuters: Pg.155 Orange River Rivers
  9. 9. Learningobjectives Types of Rivers Drainage Patterns River Channel Patterns
  10. 10. Drainage Patterns Schuters Pg.150 and 151
  11. 11. Dendritic drainage pattern •Occurs in regions where the rock is uniform in its resistance to erosion. •Shaped like the branches of a tree. •Consequent and subsequent streams meet at acute angles.
  12. 12. Rectangular drainage pattern • Rectangular drainage patterns have rt.-angled bends in the tributaries and the main streams. • Streams are not parallel to each other. Rectangular drainage pattern
  13. 13. Trellis drainage pattern • Occurs in regions the sedimentary rock is folded or where there are alternate layers of hard and soft rock. • The main stream and tributaries join at rt. angles. • Streams are parallel with short tributaries.
  14. 14. Trellis Drainage Pattern
  15. 15. Trellis Drainage Pattern
  16. 16. Radial drainage pattern • The stream flows down a dome shaped feature e.g. an isolated hill volcanic dome spitskop.
  17. 17. Deranged drainage pattern • A deranged pattern is found in a region that is geological young. • Haphazard shape. • Streams entering lakes and marshes in a haphazard pattern.
  18. 18. • Common drainage patterns that are structurally controlled
  19. 19. Superimposed (Inherited) Streams / Drainage A stream establishes its course in rock layers. The covering rock is removed and the stream imposes its course on underlying rock of a completely different structure. River is younger than the structures they flow through. E.g. The Vaal river in the vicinity of Parys (in the Free State) breaks through two quartzite hills instead of following a course around them.
  20. 20. Copyright © Houghton Mifflin Company. All rights reserved. Geology, 14b–20 Figure 14-12a Superposed Streams
  21. 21. Copyright © Houghton Mifflin Company. All rights reserved. Geology, 14b–21 Figure 14-12b Superposed Streams (cont’d)
  22. 22. Copyright © Houghton Mifflin Company. All rights reserved. Geology, 14b–22 Figure 14-12c Superposed Streams (cont’d) Source: Jeff Lepore/Photo Researchers Inc.
  23. 23. Antecedent Streams / Drainage A stream existed on an earlier landscape which was subsequently raised.  The stream was able to maintain its original course in spite of uplift (or the formation of a mountain or a ridge).  Antecedent streams are therefore older than the structures they flow through.  e.g. The lower part of the Orange river retained its course and eroded downwards at the same rate that the mountains of the escarpment formed.  The stream cut through the obstruction as it formed.
  24. 24. Copyright © Houghton Mifflin Company. All rights reserved. Geology, 14b–24 Figure 14-13a Antecedent Streams
  25. 25. Copyright © Houghton Mifflin Company. All rights reserved. Geology, 14b–25 Figure 14-13b Antecedent Streams (cont’d)
  26. 26. Superposed Stream Development of Water gap Folded Units Erosion and downcutting through young horizontal units Identify this Stream Pattern
  27. 27. Superimposed and Antecedent Streams • Superimposed streams is one whose valley and direction of flow were developed much later than the underlying structure, and the river possessed sufficient stream power to cut through these underlying structures. • An antecedent stream is one whose path of flow within a valley was established before the mountainous structure was uplifted
  28. 28. Schuters Pg.174
  29. 29. Schuters pg 179 Schuters pg 179 Drainage Basin Development
  30. 30. Schuters Pg.151* Answers 1) Trellis 2) Dendritic Tree pattern, tributaries joins main stream at acute angles..
  31. 31. Activity 13: Identifying drainage patterns Pg.135
  32. 32. Learningobjectives Types of Rivers Drainage Patterns River Channel Patterns (Stream flow Characteristics)
  33. 33. River Channel Patterns / Stream flow characteristics Identify the stream flow characteristic of the following river: Meandering Stream  River winds from side to side  River flows over loose silt and clay  The banks are fairly stable  The river starts to wind due to irregularities in the channel (corkscrew action)  Lateral shifting takes place (meanders shift downstream)  Fastest flow speeds occur on the outer bank (undercut slope) resulting in erosion  Slowest flow occurs on the inner bank (slip-off) slope resulting in deposition
  34. 34. Schuters: Pg.170 Features of erosion and deposition Schuters: Pg.170 Click here for animation
  35. 35. 1) Describe what happens on the outside of the bend 2) Describe what happens on the inside of the bend 3) What causes the corkscrew motion?
  36. 36. Meandering rivers http://www.aquatic.uoguelph.ca/rivers/chphys.htm A meander becomes more pronounced as the streamline shifts between the river banks. Formation of an oxbow lake
  37. 37. • Small meanders – steep gradient – coarse particles Gradient • Big meanders – gentle gradient – fine particles
  38. 38. Meanders in the Amazon Basin
  39. 39. McKenzie River meanders and glacial lakes
  40. 40. Identify the stream flow characteristic of the following river: Braided stream  The velocity of the river is reduced and this causes the river to split and rejoin many times  The river flows over loose sandy alluvium  The banks of the river are unstable and lateral erosion occurs easily  As a result of the wide channel, the river flows slowly and large deposits of alluvium form islands in the middle of the river. River Channel Patterns / Stream flow characteristics
  41. 41. • Braided Pattern = steep slope + high stream power + coarse bed materials changes to gentle gradient and slows down depositing material Braided channel earthsci.org/teacher/basicgeol/stream/stream.html#Erosion%20by%20Streams
  42. 42. Braided River
  43. 43. Braided geometry, Matanuksa River, Alaska
  44. 44. Braided River, Shyok River, India
  45. 45. Identify the stream flow characteristic of the following river: Straight Stream Rock-controlled channel o The river flows in straight and twisting sections o It is characterized by many rocky banks, rapids and waterfalls o The rock barriers on the sides and riverbed prevent the river from determining its own channel pattern River Channel Patterns / Stream flow characteristics
  46. 46. Identify the drainage pattern and describe the underlying topography.

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