WATER- Human and Physical causes of flooding

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  • Natural and anthropogenic causes of flooding
    • ANTHRO-POGENIC
      • Deforestation- destroys interception and transpiration. roots give good soil structure. (INDIRECT).
      • Channelisation - smoothing out river bed to increase speed of flow. may have impacts further downstream which may be overwhelmed with increased discharge.
      • grazing animals and ploughing machinery trample soil which cannot then infiltrate as much water so overland flow (runoff) increases.
      • Dams - block the flow of sediment so there is increased river bed erosion downstream.
      • HARD ENGINEERING - Dams, Channelisation and River embankments.
        • Dams - block the flow of sediment so there is increased river bed erosion downstream.
        • Channelisation - smoothing out river bed to increase speed of flow. may have impacts further downstream which may be overwhelmed with increased discharge.
      • SOFT ENGINEERING - making greater use of flood plains (temporary stores of flood water) and using them for conservation and potentially agriculture/ recreation.
      • Sewage systems reduce infiltration by 4%, increasing surface runoff. Debenhams,Guildford; little flood prevention schemes, football pitch and car park by river.
    • NATURAL
      • depressions (low pressure systems) causing storm surges (leading to flooding) and flash flooding (from intense storms).
      • rapid snowmelt in the plains of SIBERIA.
      • Bangladesh
        • flood prone due to many flood plains and deltas from GANGES, PADMA and MEGHNA.
      • Impervious surfaces (towns and cities), and where ground surface is underlain by impermeable rocks
      • Where volcanoes melts water beneath ice sheets that is suddenly released (Jokullhlaups), and when volcanoes generate land or dam failure.
      • STORM DESMOND: 03/12/15
        • Hit CUMBRIA, caused by deep Atlantic low-pressure system.
        • Localised flooding in North West England (North Wales, Scotland, Northern Ireland).
        • Had more than a month's rainfall in one day.
        • Honister received 341.1mm of rain on 24 hours.
        • Orographic and convectional rainfall combines and already saturated ground caused extreme flooding.
        • 40 schools closed, 5,200 homes evacuated.
        • Lancaster uni closed early due to power cuts.
        • £50 million paid to cumbria and Lancashire CC;s

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