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IB Geography: Drainage Basins: Channelisation

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IB Geography: Drainage Basins: Channelisation

  1. 1. Channelisation
  2. 2. Channelisation:
  3. 3. Channelisation: A deliberate attempt to alter the natural geometry of a water course. It is an example of hard engineering.
  4. 4. Channelisation: A deliberate attempt to alter the natural geometry of a water course. It is an example of hard engineering. The reasons for using channelisation can include:
  5. 5. Channelisation: A deliberate attempt to alter the natural geometry of a water course. It is an example of hard engineering. The reasons for using channelisation can include: • Increasing the capacity of a channel to prevent flooding.
  6. 6. Channelisation: A deliberate attempt to alter the natural geometry of a water course. It is an example of hard engineering. The reasons for using channelisation can include: • Increasing the capacity of a channel to prevent flooding. • Providing a straighter and deeper channel for navigation.
  7. 7. Channelisation: A deliberate attempt to alter the natural geometry of a water course. It is an example of hard engineering. The reasons for using channelisation can include: • Increasing the capacity of a channel to prevent flooding. • Providing a straighter and deeper channel for navigation. • Preventing bed or bank erosion.
  8. 8. Channelisation: A deliberate attempt to alter the natural geometry of a water course. It is an example of hard engineering. The reasons for using channelisation can include: • Increasing the capacity of a channel to prevent flooding. • Providing a straighter and deeper channel for navigation. • Preventing bed or bank erosion. • Reclamation of wetland by lowering the water table.
  9. 9. Channelisation: A deliberate attempt to alter the natural geometry of a water course. It is an example of hard engineering. The reasons for using channelisation can include: • Increasing the capacity of a channel to prevent flooding. • Providing a straighter and deeper channel for navigation. • Preventing bed or bank erosion. • Reclamation of wetland by lowering the water table. • Straightening rivers to make farm land more manageable, or to allow bridges or highways to be built more easily.
  10. 10. 1. Resectioning or enlarging
  11. 11. 1. Resectioning or enlarging 2. Realignment or straightening
  12. 12. 1. Resectioning or enlarging 2. Realignment or straightening 3. Bank protection
  13. 13. 1. Resectioning or enlarging 2. Realignment or straightening 3. Bank protection 4. Lined channels
  14. 14. 1. Resectioning or enlarging 2. Realignment or straightening 3. Bank protection 4. Lined channels 5. Containment
  15. 15. 1. Resectioning or enlarging 2. Realignment or straightening 3. Bank protection 4. Lined channels 5. Containment 6. Vegetation Clearance
  16. 16. 1. Resectioning or enlarging 2. Realignment or straightening 3. Bank protection 4. Lined channels 5. Containment 6. Vegetation Clearance 7. Dredging
  17. 17. 1. Resectioning or enlarging
  18. 18. 1. Resectioning or enlarging • Involves enlarging the cross-section of the channel.
  19. 19. 1. Resectioning or enlarging • Involves enlarging the cross-section of the channel. • The channel is deepened and / or widened to increase its hydraulic efficiency, and to allow a larger discharge to be contained within the channel.
  20. 20. 1. Resectioning or enlarging • Involves enlarging the cross-section of the channel. • The channel is deepened and / or widened to increase its hydraulic efficiency, and to allow a larger discharge to be contained within the channel. • Can also be used to lower the water table on the floodplain, therefore allowing wetlands to be reclaimed for agriculture.
  21. 21. 2. Realignment or straightening
  22. 22. 2. Realignment or straightening • A meandering river can be straightened by means of artificial cut-offs.
  23. 23. 2. Realignment or straightening • A meandering river can be straightened by means of artificial cut-offs. • The aim is to increase the long profile gradient so that there is an increase in velocity and flood waters can be removed more quickly.
  24. 24. 2. Realignment or straightening • A meandering river can be straightened by means of artificial cut-offs. • The aim is to increase the long profile gradient so that there is an increase in velocity and flood waters can be removed more quickly. • Can also have an economic impact on river transport.
  25. 25. 3. Bank Protection
  26. 26. 3. Bank Protection • Erosion of banks and meander migration causes loss of land and may undermine structures such as building and bridges.
  27. 27. 3. Bank Protection • Erosion of banks and meander migration causes loss of land and may undermine structures such as building and bridges. • Concrete blocks.
  28. 28. 3. Bank Protection • Erosion of banks and meander migration causes loss of land and may undermine structures such as building and bridges. • Concrete blocks. • Steel revetments.
  29. 29. 3. Bank Protection • Erosion of banks and meander migration causes loss of land and may undermine structures such as building and bridges. • Concrete blocks. • Steel revetments. • Gabion boxes.
  30. 30. 3. Bank Protection • Erosion of banks and meander migration causes loss of land and may undermine structures such as building and bridges. • Concrete blocks. • Steel revetments. • Gabion boxes. • Wing dykes (groynes).
  31. 31. 4. Lined channels
  32. 32. 4. Lined channels • Resectioned lengths of river are often lined with concrete to improve channel efficiency.
  33. 33. 4. Lined channels • Resectioned lengths of river are often lined with concrete to improve channel efficiency. • There is a reduction in the energy lost through friction so flow velocity increases.
  34. 34. 4. Lined channels • Resectioned lengths of river are often lined with concrete to improve channel efficiency. • There is a reduction in the energy lost through friction so flow velocity increases. • Flood risk is decreased as water is moved away quicker.
  35. 35. 4. Lined channels • Resectioned lengths of river are often lined with concrete to improve channel efficiency. • There is a reduction in the energy lost through friction so flow velocity increases. • Flood risk is decreased as water is moved away quicker. • Lined channels are often used in urban areas where access for maintenance is limited or other forms of management are not possible.
  36. 36. 5. Containment
  37. 37. 5. Containment • An extreme form of channelisation.
  38. 38. 5. Containment • An extreme form of channelisation. • The channel is contained within concrete arches or pipes.
  39. 39. 5. Containment • An extreme form of channelisation. • The channel is contained within concrete arches or pipes. • Used where rivers flow under roads or built-up areas.
  40. 40. 5. Containment • An extreme form of channelisation. • The channel is contained within concrete arches or pipes. • Used where rivers flow under roads or built-up areas. • Can be difficult to maintain because of access problems.
  41. 41. 5. Containment • An extreme form of channelisation. • The channel is contained within concrete arches or pipes. • Used where rivers flow under roads or built-up areas. • Can be difficult to maintain because of access problems. • They have a flood design level, above which they may cause ponding.
  42. 42. 6. Vegetation Clearance
  43. 43. 6. Vegetation Clearance • A smooth, regular channel can carry three times the discharge of a channel of similar size and gradient, which has its banks covered with extensive weeds, reeds and other plants.
  44. 44. 6. Vegetation Clearance • A smooth, regular channel can carry three times the discharge of a channel of similar size and gradient, which has its banks covered with extensive weeds, reeds and other plants. • Plants reduce the size of the channel and aid silt deposition.
  45. 45. 6. Vegetation Clearance • A smooth, regular channel can carry three times the discharge of a channel of similar size and gradient, which has its banks covered with extensive weeds, reeds and other plants. • Plants reduce the size of the channel and aid silt deposition. • Seasonal cutting can be ecologically beneficial.
  46. 46. 6. Vegetation Clearance • A smooth, regular channel can carry three times the discharge of a channel of similar size and gradient, which has its banks covered with extensive weeds, reeds and other plants. • Plants reduce the size of the channel and aid silt deposition. • Seasonal cutting can be ecologically beneficial. • Removal of vegetation is normally achieved with great ecological damage.
  47. 47. 7. Dredging
  48. 48. 7. Dredging • Involves the removal of sediment from the channel to enlarge its capacity.
  49. 49. 7. Dredging • Involves the removal of sediment from the channel to enlarge its capacity. • The dredged material can be removed from the channel or just loosened and the channel flow utilised to remove it.

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