Human impact


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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