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Floods, Flooding And Management
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Floods, Flooding And Management



Floods, Flooding And Management - As Geography

Floods, Flooding And Management - As Geography



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    Floods, Flooding And Management Floods, Flooding And Management Presentation Transcript

    • Floods, Flooding and Management
      AS Geography
    • Plenary
      Why did the Mississippi floods of 1993 occur?
      How do waterfall’s form?
      What do we mean by competence and capacity?
    • Learning Objectives
      For students to understand the principle of flood frequency and how to calculate this
      Students to appreciate and demonstrate that there are both human and physical causes of flooding
      That there are various strategies that can help alleviate the effects of flooding
    • The Story so far...
      Students have already provided an in-depth analysis of the Mississippi floods of 1993.
      Have some knowledge of why Bangladesh floods
      We understand the principles of flooding
      So why does it happen and what can we do?
    • Why do Rivers Flood?
      Rivers flood naturally
      People live near rivers from both a historical as well as a cultural perspective
      Floods are a natural hazard
      Many rivers flood consistently
      Humans alter natural landscapes flood risk can increase.
    • Flood Frequency
      How to calculate flood frequency:
      Size of largest flood for each year is ranked with 1 being the largest for all available records for any given year
      T = n+1
      T = Recurrence intervals
      n = The number of years of observation
      m = The rank Order
    • What does this tell us?
      It indicates the number of years within which a flood of this size can be expected
      What problems can you see in this equation?
      It’s based on historical data
      It doesn’t mean floods can’t occur less or more frequently
      The EA recommend that that flood defences should be built to withstand a 1 in 50 year flood
      The EA however build flood defences for a 1 in a 100yr flood
    • Activity
      Complete the flood frequency activity handed out
    • Physical
      Causes of Flooding
    • Physical Causes
      Flooding occurs when a river’s discharge exceeds the capacity of it’s channel to carry the discharge
      Excessive levels of precipitation over a prolonged period of time. Leads to soil saturation when water table reaches ground surface there is an increase in overland flow.
      Intensive Precipitation over a short period of time especially on hard sun baked ground.
    • Physical Causes
      Snowmeltespecially when subsoil is still frozen as there is limited infiltration capacity.
      Climatic Hazards – Cyclones in Bangladesh, Hurricanes in Gulf of Mexico. Deep low pressure systems in mid latitude climates
      Relief– The slope of the river Basin
      Vegetation – Can help increase infiltration and thus reduce surface run off
    • Physical Causes
      Geology – Rock type both pervious and porous
      Soil Type – Sand to clay type soils and changes in infiltration
      Drainage Density – Amount of surface streams within the basin
    • Example of Floods
      Physical causes of floods have caused floods such as:
      Boscastle August 2004
      Bangladesh 1998
    • What factors Increased the risks of floods in Boscastle?Watch the video and you decide.
    • Boscastle Floods
    • Human
      Causes of Flooding
    • Human Causes
      Urbanisation – Reduces infiltration and increases runoff
      Deforestation – Reduces interception
      River Management – Dams can cause issues along with other techniques
      Climate Change – Heavier storms, more frequent, melting of ice caps
    • Activity
      Complete the table activity on your sheets
    • Homework
      Complete the exam paper for Monday.