Floods, Flooding And Management

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Floods, Flooding And Management - As Geography

Floods, Flooding And Management - As Geography

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  • 1. Floods, Flooding and Management
    AS Geography
  • 2. Plenary
    Why did the Mississippi floods of 1993 occur?
    How do waterfall’s form?
    What do we mean by competence and capacity?
  • 3. 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
  • 4. 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?
  • 5. 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.
  • 6. 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
    m
    T = Recurrence intervals
    n = The number of years of observation
    m = The rank Order
  • 7. 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
  • 8. Activity
    Complete the flood frequency activity handed out
  • 9. Physical
    Causes of Flooding
  • 10. 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.
  • 11. 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
  • 12. 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
  • 13. Example of Floods
    Physical causes of floods have caused floods such as:
    Boscastle August 2004
    Bangladesh 1998
  • 14. What factors Increased the risks of floods in Boscastle?Watch the video and you decide.
  • 15. Boscastle Floods
  • 16. Human
    Causes of Flooding
  • 17. 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
  • 18. Activity
    Complete the table activity on your sheets
  • 19. Homework
    Complete the exam paper for Monday.