River Case Studies

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  • Case Studies- Rivers
    • Flooding of South Asia, 2007
      • Factors
        • Physical
          • Monsoon, suddenly after very dry early summer
          • Heavy rainfall- Assam 169.5 mm in 24 hours n 22nd July
          • Long duration of heavy rainfall completely saturated soil, increasing runoff
        • Human
          • Deforestation in Nepal and the Himalayas, less rainfall intercepted
          • Growth of urban areas, due to migration
          • Collapse of earth dams in India causing further flooding
          • No flood defences or warning system (poor country)
          • Low incomes so little money to recover after the flood
      • Impacts
        • Social Impacts
          • Over 2000 people died, as people where reluctant to evacuate
          • Lack of clean drinking water, wells were polluted
          • 25 million made homeless
          • 112000 houses destroyed, porous mud bricks saturated
          • Children lost out of education 44 schools destroyed
        • Economic Impacts
          • Estimated $billion, damage to crops and property
          • Factories closed around Dhaka. Many poorest workers became unemployed
          • Loss of livestock, 80% of Bangladesh rely on agriculture for livelihood
          • Debt increased individually and nationally
          • 10,000 km of roads destroyed
        • Environmental Impacts
          • Flood deposited fertile silt on flood plain
          • Rivers polluted with sewage
    • Flooding of Carlisle, Cumbria 2005
      • Factors
        • Physical
          • Heavy rainfall on 6th January 36 hours, 200 mm rainfall
          • Rainfall on already saturated ground
        • Human
          • Large built-up area, lots of tarmac so little infiltration
          • Drains and sewage system overflowed becoming a source of flooding in some areas
      • Impacts
        • Social Impacts
          • 3 died
          • 3000 made homeless
          • Children missed out on education, 4 schools serverely flooded
          • Increase in stressed related conditions after the floods
        • Economic Impacts
          • Year to repair damage, over £100 million in damage
          • 350 businesses shut down- no electricity, telephone service or transport
          • 70,000 addresses no power
          • 80 buses destroyed, as well as roads and bridgges
        • Environmental Impacts
          • Flooding increased river bank ersoion
          • Rivers were polluted with rubbish and sewage
    • Hard Engineering, Yangtze
      • Runs through China, 6380 km long
        • Seasonal flooding common- has rainy seasons June-August
        • 5 major floods over last 100 years
      • Defences- 3 Gorges Dam
        • Multiple dams on the Yangtze to reduce flooding- biggest is 3 Gorges Dam
        • 101 km high, work began in1994
        • Reservoir built up behind the dam to catch flood water can store 22 km3
        • Largest hydroelectric power station in world
      • Effects
        • Positive
          • Major flooding reduced from every 10 years to every 100 years
          • 3% of China's energy provided by hydroelectric on dam
          • Safer to navigate the Yangtze, river shipping increased as bigger ships can travel up it as reservoir is deeper
        • Negative
          • People had to relocate, as water level in reservoir risen
          • Reservoir flooded farmland, over 600 factories and 1300 sites of cultural intrest
          • Sediment usually carried by the river getting trapped by the dam causing it to fail
          • Dam could destroy habitats
          • Dam doesn't protect everyone- increased flooding of tributaries leading to the dam
    • Soft Engineering, Abingdon
      • Defences
        • Gravel soakaways on the A34 road
        • Low-value lands allowed to flood
        • Planning restrictions on new housing development built on Ock flood plain
        • Tesco's forced to revise extension plans, had to add drainage improvements
        • Flood warning plans and 24 hour floodline
        • Local voluntary flood wardens- advice/ warnings
        • Restrictions on land use
      • Reduces damage, but floods still occur
        • Difficult to measure success of defences- as less flooding could be less serve weather or successful defences
        • Several warnings issued by Environment Agency, 2008
        • 2008 floods made less damage

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