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   Human attempts to modify drainage systems    to prevent flooding   But sometimes these efforts have adverse    effect...
Direct                        Indirect• River regulation e.g R. Nile     • Deforestation e.g Amazon• Channelisation e.g R....
   The water in the basin is used for a variety of    purposes:    › Irrigation – there is a vast network of canals helpi...
 Water   quality is low Biochemical Oxygen Demand (BOD)levels are very high Riverquality decreases during periods of lo...
 Excessive          extraction of groundwater has caused the water table to drop rapidly Three     sectors consuming the...
   Land subsidence – Bangkok is sinking by 10cm    per year – lead to major structural damage to    buildings and roads ...
 It   is estimated that many parts of the city  will be under water all-year round in 17  years’ time. To alleviate its ...
Modify   the river channelUse engineering structures to control floodsHard engineering to carry large discharge quickly...
   Protect the whole basin   Use methods that work with nature rather than    against it   Soft engineering   To reduc...
 Straightening Resectioning Building levees Bank stabilisationEffects: Reduce friction Increased velocity Increased...
   Increased flood defense – additional flood    storage provided by the enlarged floodplain   More opportunities for re...
Human impact
Human impact
Human impact
Human impact
Human impact
Human impact
Human impact
Human impact
Human impact
Human impact
Human impact
Human impact
Human impact
Human impact
Human impact
Human impact
Human impact
Human impact
Human impact
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Human impact

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Transcript of "Human impact"

  1. 1.  Human attempts to modify drainage systems to prevent flooding But sometimes these efforts have adverse effects and actually helps to cause flooding at other areas Any modification has the potential to cause changes in the drainage system and these changes have severe consequences
  2. 2. Direct Indirect• River regulation e.g R. Nile • Deforestation e.g Amazon• Channelisation e.g R. Thames • Afforestation – a problem in the early period when• Water abstraction e.g R. much of the ground is bare Colorado egTennessee Valley• Irrigation e.g Syr Darya, Aral • Urbanisation e.g floodplain sea development in Oxford• Dam Construction e.g Three • Mining – impact of water Gorges Dam quality• Waste disposal e.g R. Ganges • Agricultural practice e.g New Bedford River22• Drainage
  3. 3.  The water in the basin is used for a variety of purposes: › Irrigation – there is a vast network of canals helping to irrigate India’s rice crop › Domestic use – for drinking water and sewage disposal › Industrial use – there is a large concentration of tanneries, petrochemical and fertiliser complexes, rubber, jute and textile industries › Disposal of waste water – from industrial, residentials and agricultural areas › Navigation › Religious practices – disposal of dead bodies
  4. 4.  Water quality is low Biochemical Oxygen Demand (BOD)levels are very high Riverquality decreases during periods of low flow because there is less water to dilute the polluting materials
  5. 5.  Excessive extraction of groundwater has caused the water table to drop rapidly Three sectors consuming the largest amount of water are: › Agriculture › Industry › Domestic use
  6. 6.  Land subsidence – Bangkok is sinking by 10cm per year – lead to major structural damage to buildings and roads Shortage of safe drinking water – the shallow aquifers in Bangkok have become contaminated with salt water from the nearby ocean Increased risk of flooding – aggravated by land subsidence
  7. 7.  It is estimated that many parts of the city will be under water all-year round in 17 years’ time. To alleviate its problem, Bangkok would have to reduce its groundwater extraction rate by at least one-half – a formidable challenge, because water demand is expected to grow rapidly in the coming decades
  8. 8. Modify the river channelUse engineering structures to control floodsHard engineering to carry large discharge quickly downstream
  9. 9.  Protect the whole basin Use methods that work with nature rather than against it Soft engineering To reduce overland flow hence river discharge
  10. 10.  Straightening Resectioning Building levees Bank stabilisationEffects: Reduce friction Increased velocity Increased water temperatures: › No shading, no cover for fish life, rapid daily & seasonal fluctuations in temperatures – reduced leaf material input
  11. 11.  Increased flood defense – additional flood storage provided by the enlarged floodplain More opportunities for recreation – public perception is largely favour of natural landscape Improved water quality – due to natural settling of sediments on the floodplain and river bed, increased interception of pollutants by vegetation Greater nature conservation of wildlife in the riverine environment
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