Flood Defence Systems(97)


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Flood Defence Systems(97)

  1. 1. Flood Defence Systems Jan T.L. Yap - AguaJaring Integrated Flood Management
  2. 12. Flood Embankment in Action
  3. 13. Flooded Flood Plain
  4. 14. Failed Flood Embankment
  5. 15. Piping through Embankment
  6. 16. Confined Seepage
  7. 17. Strengthening Flood Embankment
  8. 18. Good Performanced Embankment
  9. 19. Failed First-line Embankment
  10. 20. Emergency Intervention - Blow-up
  11. 22. Flood Defence Systems Philosophy of Risk Management Failure Mechanisms Failure Tree Probabilistic Design
  12. 23. Overview design methods of embankments <ul><li>Initialy: pure based on experiences . Crest level established with reference to the highest known water level; </li></ul><ul><li>In the 50s: applying statistical techniques to determine the “Design Water Level” -> Deterministic design method using fixed design values for the various parameters; </li></ul><ul><li>Since the 70s – 80s: Probabilistic Design Method -> using stochastic character of the various load and strength parameters -> based on an analysis of failure mechanism and their probabilities. </li></ul>
  13. 24. Review deterministic design methods <ul><li>Crest level only one of the design parameters of embankment profile. Slope, crest width & berms: stability, maintenance, construction and usage of crest; </li></ul><ul><li>Hydraulic conditions & soil mechanics parameters essential for embankment stability -> limited degree of accuracy -> Safety factors applied based on experience, tradition and intuitive judgement; </li></ul><ul><li>Only determined per embankment stretch or section, while it is in fact part of a flood defence system -> many stretches of different characteristics, and many structures like sluices & water gates and …….. protecting different regions: number of inhabitants, invested capital, strategic utilities, future land use, etc. </li></ul>
  14. 25. Components of a flood defence system
  15. 26. Shortcomings deterministic design methods <ul><li>Various embankment sections in a defence system do not provide same degree of safety; </li></ul><ul><li>It is not known which failure mechanism gives the greatest contribution to the probability of failure of an embankment section; </li></ul><ul><li>The overall length of the embankment system has no influence upon the design of the embankment section; </li></ul><ul><li>Magnitude of damage or loss has no influence on the design; </li></ul><ul><li>The actual probability of inundation (flooding) of the protected area is not known </li></ul>
  16. 27. Principle of Risk Analysis <ul><li>Risk = Probability x Consequence </li></ul><ul><li>Probability of an undesirable event : explosion, inundation, etc. </li></ul><ul><li>Consequence of the occurrence of that event : -> economic loss, damage, loss of life, etc. </li></ul><ul><li>Risk Analysis: the whole set of activities asimed at </li></ul><ul><li>Quantifying </li></ul><ul><li>the probability of an undesirable event ..and .. the consequence of the occurrence of that event . </li></ul>
  17. 28. Advantages of Probabilistic Approaches <ul><li>The flood system is analysed and described as a whole; </li></ul><ul><li>Components of the system can be better inter-related, i.e. less over- and under-designing; </li></ul><ul><li>Various uncertainties are rationally incorporated in the assessment of the safety of the system; </li></ul><ul><li>Better insight into the sensitivity of probability of failure of the system related to the various uncertainties; </li></ul><ul><li>Better insight into the priority for improving the flood defence system (maintenance). </li></ul>
  18. 29. More …..
  19. 30. Failure tree analysis
  20. 31. Probability of Failure
  21. 32. Design Point
  22. 33. Flood Defence Systems Reducing Flood Damages Flood Fighting Flood Proofing Temporary & Demountable Flood Defence Structures
  23. 34. Emergency Measures - Flood Fighting
  24. 35. Controling Under-seepage
  25. 36. Sand Migration due to Underseepage
  26. 37. Road System as Floodway
  27. 38. Temporary Flood Wall
  28. 39. Emergency Flood Wall
  29. 40. Emergency Flood Wall (2)
  30. 41. Local Flood Fighting
  31. 42. Flood Proofing to Reduce Damage
  32. 43. Columns for Emergency Flood Walls
  33. 44. Movable Flood Wall
  34. 45. Floating Houses
  35. 46. Floating Houses (2)
  36. 47. Thank you……