Rivers, flood and management CASE STUDIES

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  • RIVERS - CASE STUDIES
    • Flooding
      • South Asia flooding, 2007
        • Facts
          • Flood most years due to:
            • Monsoon climate
            • 90% of the land is low-lying
            • Increased discharge from Brahmaputra river from molten snow and ice from Himalayas
          • July+August 2007 - sever flooding especially in Bangladesh and India
        • Factors
          • Physical factors
            • Heavy rainfall
            • Sudden monsoon after dry and early summer
            • Saturated soil and so increased runoff and discharge
            • Peak discharge of Brahmaputra+Ganges coincided; greater discharge downstream
          • Human factors
            • Deforestation in Nepal + Himalayas
              • less interception + increased discharge
            • Growth of urban areas
              • increased surface runoff
            • Collapse of old dams
        • Impacts
          • SOCIAL
            • >2000 people died due to slow evacuation, drowning and reluctant to leave
            • Lack of drinking water
            • 25mil homeless
            • Houses destroyed due to saturated porous rock
            • Dhaka inundated
            • 44 schools destroyed - loss of education
          • ECONOMIC
            • US$ 1bil damage to crops+property
            • Loss of raw materials and livestock
            • 10k km of roads destroyed
          • ENVIRONMENTAL
            • Polluted rivers
            • Fertile silt deposited on floodplains
      • Carlisle flooding, Cumbria, 2005
        • Facts
          • Large drainage basin - high discharge
          • Steep sides
          • Short lag time due to many streams
          • 8 Jan 2005, flooding of Carlisle by river Eden
        • Factors
          • Physical
            • 36 hrs of heavy rainfall
            • surface runoff on saturated ground
            • 52 cumecs of peak discharge
          • Human
            • surface runoff from impermeable concrete
            • Overflowed sewerage systems causing 25% of flooding problems
        • Impacts
          • SOCIAL
            • 3 people died and 3k homeless
            • Loss on education
            • problems with travel+ receiving post
          • ECONOMIC
            • £100mil in repairs
            • 350 businesses shut down due to no electricity/transport/telephone
            • Sewage, police station, council offices flooded
            • 80 buses destroyed
            • Roads and bridges damaged, e.g. Warwick Road
          • ENVIRONMENTAL
            • Increased river bank erosion is some areas
            • Polluted rivers
    • Flood management
      • Hard engineering - Three Gorges Dam (China)
        • Facts
          • Yangtze River 6380km
          • Rainy season (flooding) June-August
          • Reservoir that stores 22km3 of water
          • 26 turbines - largest hydroelectric power station in the world
          • 3600km of levees on lower and middle part
        • Positive effects
          • Frequency of flooding reduced to every 100yrs
          • The turbines produce 3% of China's electricity demand
          • Safer to navigate the river
          • Increase in river shipping (for bigger ships)
        • Negative effects
          • 13 cities submerged once reservoir is full
          • Farmland and 657 factories will be flooded by reservoir
          • Entrapment of sediment from the dam - severe flooding
          • Endangered species + destroyed habitats, e.g. 100 baiji dolphins left
          • The dam can increase flooding in tributaries
      • Soft engineering - Abingdon
        • Facts
          • Town in SE on Thams and Ock flood plains
          • Houses have 1% flooding chance a year
          • Hard engineering rejected due to costs and flood risk downstream
        • Defences
          • Gravel soakways on A34
          • Flood storage area allowed to flood, e.g. Tilsley Park
          • New houses on Ock flood plain to have better drainage systems
          • Tesco to have permeable tarmac
          • EA 24hrs Floodline
          • Afforestation
          • Flood wardens for warnings and advice
          • Restrictions on land use
        • Successfullness
          • Many floods warnings by EA since 2008
          • No flood on Ock floodplain but flood on Thames floodplain due to planning restrictions and land management
          • 2008 flood: less damage, less cost, less injuries but flooding still occurs

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