Floods, Flooding And Management


Published on

Floods, Flooding And Management - As Geography

Published in: Education, Technology
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Floods, Flooding And Management

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