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Drainage Basins

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Grade 12 Geomorphology. SA Curriculum. Drainage Basins.

Grade 12 Geomorphology. SA Curriculum. Drainage Basins.

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  • The section on Groundwater in the textbook is out of the syllabus – direct, indirect drainage, acquifers (Gravel, sandstone, conglomerate), acquicludes (clay, shale, Granite), springs and artesian wells. Meteoric water (ground water) Magmatic water, Connate water (found is Sed rocks)
    Pg 111, 112 and 113.
  • Gradient more runoff and less infiltration if there is a steep slope. Less runoff therefore the drainage density will be lower.
    Low drainage density 1km of river flowing in 1 km sq drainage basin.
    Extremely high drainage density (eg. Badlands) 700 km of river flowing in 1 km sq drainage basin
  • Stream order helps to conceptually organize the streams in a watershed.
    As streams increase in order, they also increase in length, exponentially;
    World-wide, about 70-75% of stream miles occur as headwater (first order) streams.

Transcript

  • 1. Grade 12 Geomorphology The Drainage Basin System What is a drainage basin? How does the drainage basin system operate? Factors affecting run-off and infiltration in a drainage basin. Drainage Basin Management. Stream Order. Laminar and Turbulent flow. 1 of 29 © Boardworks Ltd 2005
  • 2. What is a drainage basin? Mouth Where the river flows into the sea, or sometimes a lake. Tributary A river which joins a larger river. Watershed The boundary dividing one drainage basin from another- a ridge of high land. Confluence The point at which two rivers join. 2 of 29 Catchment The area from which water drains into a particular drainage basin. Source The upland area where the river begins. © Boardworks Ltd 2005
  • 3. 3 of 29 © Boardworks Ltd 2005
  • 4. Drainage Basin Terminologies Drainage Basin An area of land drained by a river and it’s tributaries Watershed The boundary between 2 drainage basins Interfluve High lying area between 2 stream in the same drainage basin Water table Level at which saturation occurs in the soil Groundwater Water stored in rocks following percolation Confluence Where two tributaries join Consequent stream Subsequent stream 4 of 29 Main stream Main tributary © Boardworks Ltd 2005
  • 5. Do you know your drainage basin terminology? Click here for online Click here for online test test Source: http://www.boardworks.co.uk/ Source: http://www.boardworks.co.uk/ 5 of 29 © Boardworks Ltd 2005
  • 6. Watershed The drainage basin of the Afon Caerfanell, a tributary of the River Usk, South Wales. the watershed can be clearly seen on this photograph 6 of 29 © Boardworks Ltd 2005
  • 7. The confluence of two rivers 7 of 29 © Boardworks Ltd 2005
  • 8. Match the label to the correct letter Watershed c Confluence Tributary b Source d a Source: http://www.boardworks.co.uk/ Source: http://www.boardworks.co.uk/ 8 of 29 © Boardworks Ltd 2005
  • 9. Sketch the river showing its catchment Add the following labels – Watershed, Confluence, Tributary Source: http://www.boardworks.co.uk/ Source: http://www.boardworks.co.uk/ 9 of 29 © Boardworks Ltd 2005
  • 10. 2 5 1 4 3 10 of 29 © Boardworks Ltd 2005
  • 11. Learning objectives The Drainage Basin System What is a drainage basin? How does the drainage basin system operate? Factors affecting run-off and infiltration in a drainage basin. Drainage Basin Management. Stream Ordering. Laminar and Turbulent flow. 11 of 29 © Boardworks Ltd 2005
  • 12. All rain falling within a drainage basin ends up in the river system. How does it get there? 12 of 29 © Boardworks Ltd 2005
  • 13. OVERGROUND Raindrops might fall directly into a river or stream - Water runs downhill over the ground towards a river or stream SURFACE RUNOFF CHANNEL FLOW 13 of 29 © Boardworks Ltd 2005
  • 14. UNDERGROUND Raindrops INFILTRATE soil and rock. The water then moves underground towards a stream or river (uppermost level of saturated 14 of 29 © Boardworks Ltd 2005
  • 15. Which route to the river is quicker - surface runoff or infiltration / groundwater flow? ANSWER: Rain travelling as surface runoff will get to rivers and streams much more quickly, reaching a river or stream with little delay,within a short time-span. Water that infiltrates and travels underground travels much more slowly, finally reaching a river or stream bit by bit over a much longer period of time. Which situation is a river more likely to be able to cope with, without flooding? 15 of 29 © Boardworks Ltd 2005
  • 16. How does the drainage basin system operate? A drainage basin system is a part of the world’s hydrological (water) cycle: The hydrological cycle is a closed system. The drainage basin is an open system. You should be able to explain why once you have seen the following slides! Water Cycle animation 16 of 29 © Boardworks Ltd 2005
  • 17. The water cycle – more detailed http://www.managingwholes.co m/flash/watercycle.htm Source: http://www.boardworks.co.uk/ Source: http://www.boardworks.co.uk/ 17 of 29 © Boardworks Ltd 2005
  • 18. The Water Cycle 18 of 29 © Boardworks Ltd 2005
  • 19. The water cycle – definitions! Source: http://www.boardworks.co.uk/ Source: http://www.boardworks.co.uk/ 19 of 29 © Boardworks Ltd 2005
  • 20. The drainage basin Source: http://www.boardworks.co.uk/ Source: http://www.boardworks.co.uk/ 20 of 29 © Boardworks Ltd 2005
  • 21. Drainage basin system precipitation interception evapotranspiration infiltration surfa c e ru n throu ghflow percolation water table 21 of 29 off river groundwater flow © Boardworks Ltd 2005
  • 22. Drainage basin terms Source: http://www.boardworks.co.uk/ Source: http://www.boardworks.co.uk/ 22 of 29 © Boardworks Ltd 2005
  • 23. Drainage basin system inputs stores and flows precipitation interception outputs river runoff surface water storage evaporation surface runoff transpiration infiltration soil water storage throughflow percolation groundwater storage Source: http://www.boardworks.co.uk/ Source: http://www.boardworks.co.uk/ 23 of 29 groundwater flow © Boardworks Ltd 2005
  • 24. Page 114 Click for video Click for video 24 of 29 © Boardworks Ltd 2005
  • 25. Drainage basin system Source: http://www.boardworks.co.uk/ Source: http://www.boardworks.co.uk/ 25 of 29 © Boardworks Ltd 2005
  • 26. Learning objectives The Drainage Basin System What is a Drainage Basin? How does the drainage basin system operate? Factors affecting run-off and infiltration in a Drainage Basin. Laminar and Turbulent flow. Drainage Basin Management. Stream order. What is a flood hydrograph? What factors influence the shape of a flood hydrograph? 26 of 29 © Boardworks Ltd 2005
  • 27. Factors influencing Drainage Density Low density (Coarse texture) are: Factors affecting drainage density  Medium density (Medium texture) gradient, vegetation, rock type, soil type, evaporation, amount of rainfall, type of rainfall and  High density (Fine texture) man.  Very high density (Superfine texture) How do the above factors influence drainage density? 27 of 29 © Boardworks Ltd 2005
  • 28. Factors affecting Drainage Density 28 of 29 © Boardworks Ltd 2005
  • 29. Drainage Density and Texture Schuters pg 145 29 of 29 © Boardworks Ltd 2005
  • 30. 30 of 29 © Boardworks Ltd 2005
  • 31. Factors affecting Drainage Density What is: a)Porosity b)Permeability? Which rock will cause the most overland flow and why? Which rock might slow down the passage of water the most? 31 of 29 © Boardworks Ltd 2005
  • 32. Factors affecting Drainage Density Which one might be pervious? Which one would slow down the passage of water the most? Which one would be most likely to flood? 32 of 29 © Boardworks Ltd 2005
  • 33. A number of factors will effect how quickly water gets to a river. If water returns to a river too quickly it may result in flooding. Look at the following slides (35-39) How do you think they affect how quickly water returns to the river? Explain how each of these factors will affect drainage density. Insert you answer in a textbox. 33 of 29 © Boardworks Ltd 2005
  • 34. 1 34 of 29 © Boardworks Ltd 2005
  • 35. 2 35 of 29 © Boardworks Ltd 2005
  • 36. 3 36 of 29 © Boardworks Ltd 2005
  • 37. 4 37 of 29 © Boardworks Ltd 2005
  • 38. 5 38 of 29 © Boardworks Ltd 2005
  • 39. Flood Controls •  Reduce run-off in the upper areas of the river by ensuring that the slopes are covered with vegetation. Use terraces and contour ploughing in farmlands to help control surface runoff. Build dams to control the flow of water through an area. Don’t build settlements in areas below the floodline. Flooding in Australia 39 of 29 Build levees that can withstand the pressure and high water levels. Build larger channels and divert water away from certain areas. Powerpoint Coastal flooding © Boardworks Ltd 2005
  • 40. Activity 4: Causes and impacts of floods Pg.119 (5) (3) (3) (5) 40 of 29 © Boardworks Ltd 2005
  • 41. Factors Influencing Infiltration – Schuters Pg 144 41 of 29 © Boardworks Ltd 2005
  • 42. Activity 1: Direct and indirect run-off 42 of 29 Oxford Pg.116 © Boardworks Ltd 2005
  • 43. Learning objectives What is a drainage basin? How does the drainage basin system operate? Factors affecting run-off and infiltration in a drainage basin. Drainage Basin Management. Stream Order. Laminar and Turbulent flow. What is a flood hydrograph? What factors influence the shape of a flood hydrograph? 43 of 29 © Boardworks Ltd 2005
  • 44. Mgeni Drainage Basin 44 of 29 Schuters pg 182 and 183 © Boardworks Ltd 2005
  • 45. Learning objectives What is a Drainage Basin? How does the drainage basin system operate? Factors affecting run-off and infiltration in a Drainage Basin. Drainage Basin Management. Stream Order. Laminar and Turbulent flow. What is a flood hydrograph? What factors influence the shape of a flood hydrograph? 45 of 29 © Boardworks Ltd 2005
  • 46. Stream order • A method of classifying or ordering the hierarchy of natural channels. • Strahler (1957) is the most widely used system. • See GIS stream ordering www.usda.gov/stream_restoration/chap1.html 46 of 29 © Boardworks Ltd 2005
  • 47. Law of Stream Numbers and Law of Basin areas. The law a stream numbers states that the higher the a drainage basin increases from one There is of fairly fixed regularity with which the area of stream order the fewer the number of tributaries e.g. the will this is be more the law of basin areas. The in a regularity is 4,7 stream order totherenext alwaysknown as stream order ones than [two’s fixedgiven drainage basin. times] 47 of 29 © Boardworks Ltd 2005
  • 48. Calculation of area according to the squares method Count the number of WHOLE squares that fall within the outline 1 cm 1cm Number of squares fully covered = 18 Count the number of squares covered by + half Number of squares covered by +half = 7 Total number of square covered =25 Area of one square = LXB = 1cm x 1cm = ,5 km X ,5 Km = ,25 square Km Area of 25 squares = ,25 X ,25 = 6,25 square Km 48 of 29 © Boardworks Ltd 2005
  • 49. Calculation of Drainage Density Stream order at X = 4 1 cm 1 cm Number of squares fully covered = 42 Number of squares cove by more than half = 13 Total number of Squares = 55 Area of 1 square =LXB = 1cm X 1cm = ,5 km X ,5 km = ,25 square km Area of 55 squares = 55 x ,25 sq. km = 14 sq. km 49 of 29 © Boardworks Ltd 2005
  • 50. Learning objectives What is a drainage basin? How does the drainage basin system operate? Factors affecting run-off and infiltration in a drainage basin. Drainage Basin Management. Stream Ordering. Laminar and Turbulent Flow. 50 of 29 © Boardworks Ltd 2005
  • 51. Laminar Flow  River-bed is level and even Turbulent Flow  Water flows in layers  Water in contact with the bed and banks flows slowly due to friction  Successive layers achieve greater speeds. Fastest speeds occur in the middle just below the surface  Water travels faster, but there is less erosion since the lower layers protect the river channel.  River-bed is uneven and steep  Water continually changes levels and flows with a ‘bubbling’ action  Lots of erosion takes place, because the sand particles are lifted by water. 51 of 29 © Boardworks Ltd 2005
  • 52. 52 of 29 © Boardworks Ltd 2005
  • 53. What do you know about drainage basins? Source: http://www.boardworks.co.uk/ Source: http://www.boardworks.co.uk/ 53 of 29 © Boardworks Ltd 2005