Towards A Sustainable Drainage Solution

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This presentation notes that in economic terms flooding is the major natural disaster experience in Trinidad and discusses the lack of sustainability of the current approach to drainage and flood mitigation and proposes some solutions such as storm water management at source as a possible solution to flooding

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Towards A Sustainable Drainage Solution

  1. 1. APETT FREE PUBLICCONSULTATIONSERIES Bridging Engineering and the Society FLOODING AND DRAINAGE “TOWARDS A SUSTAINABLE DRAINAGE SOLUTION”Presentation by:Eng. Vaughn I. Lezama R Eng, FAPE.
  2. 2. INTRODUCTIONThis discussion will address the following issues: Current circumstances and approach to drainage and flood mitigation and whether the current approach is a sustainable solution. Objectives and Elements of a Sustainable Drainage System Some recent approaches which need to be further expanded and explored Conclusions/Recommendations
  3. 3. CURRENT CIRCUMSTANCES ANDAPPROACH TO DRAINAGE AND FLOOD MITIGATION Flooding in economic terms is by far the major natural disaster experienced in Trinidad & Tobago. This is so since we have little experience of devastating hurricanes and earthquakes and none of volcanoes or other such natural phenomena. Given the increasing frequency and magnitude of flooding and the resulting social dislocation and devastation, the economic losses over time could have a serious negative impact on the country’s development and economy.
  4. 4. CURRENT CIRCUMSTANCES ANDAPPROACH TO DRAINAGE AND FLOOD MITIGATION To date the major attempt to eliminate or mitigate flooding has been in trying to improve the carrying capacity of existing watercourses by:  Construction of river embankment  Dredging, paving, lining and widening of water courses
  5. 5. CURRENT CIRCUMSTANCES ANDAPPROACH TO DRAINAGE AND FLOOD MITIGATION Notwithstanding these efforts the improved capacities of many of the newly lined and paved channels are soon exceeded and there is no further opportunity for increasing channel capacity Over the last twenty years or more several million dollars have been spent on dredging, widening and embankment construction along the Caroni River. Recently there was a bulletin warning that this river was likely to burst its banks.
  6. 6. CURRENT CIRCUMSTANCES ANDAPPROACH TO DRAINAGE AND FLOOD MITIGATION Extensive erosion in the upstream catchment areas and the resulting sediment and siltation of watercourses has served to reduced channel capacities.
  7. 7. CURRENT CIRCUMSTANCES ANDAPPROACH TO DRAINAGE AND FLOOD MITIGATION Honda River
  8. 8. CURRENT CIRCUMSTANCES ANDAPPROACH TO DRAINAGE AND FLOOD MITIGATION Marabella River
  9. 9. CURRENT CIRCUMSTANCES ANDAPPROACH TO DRAINAGE AND FLOOD MITIGATION Vistabella River
  10. 10. CURRENT CIRCUMSTANCES ANDAPPROACH TO DRAINAGE AND FLOOD MITIGATION Gucharan River, Debe
  11. 11. CURRENT CIRCUMSTANCES ANDAPPROACH TO DRAINAGE AND FLOOD MITIGATION Mitchell River, Barackpore
  12. 12. CURRENT CIRCUMSTANCES ANDAPPROACH TO DRAINAGE AND FLOOD MITIGATION Alley’s Creek
  13. 13. CURRENT CIRCUMSTANCES ANDAPPROACH TO DRAINAGE AND FLOOD MITIGATION Cipero River
  14. 14. CURRENT CIRCUMSTANCES ANDAPPROACH TO DRAINAGE AND FLOOD MITIGATION Cipero River
  15. 15. OBJECTIVES AND ELEMENTS OF ASUSTAINABLE DRAINAGE SYSTEM (SDS) Surface water drainage systems developed in line with the ideals of sustainable development are collectively referred to as Sustainable Drainage Systems The objective of a SDS design would be to reduce runoff by integrating storm water controls throughout the drainage catchment area in small, discrete units. Through effective control of runoff at source, the need for continuous drain capacity improvement is minimized
  16. 16. OBJECTIVES AND ELEMENTS OF ASUSTAINABLE DRAINAGE SYSTEM (SDS) Because of our limited land space and to a lesser extent lack of land use control we do not have the advantages of a large land mass with expansive and varied topographic and geological which can easily facilitate the various components of a SDS. Some of the components of a SDS include:  large constructed wetland ponds with wetland vegetation to which storm water can be directed for storage  Filter strips or wide densely vegetated areas that can treat runoff from adjacent impermeable areas
  17. 17. OBJECTIVES AND ELEMENTS OF ASUSTAINABLE DRAINAGE SYSTEM (SDS) SDS Components CONT’D  Wet ponds which are basins with a permanent pool of water and which provide temporary storage for additional runoff above the permanent water level. Wet Ponds could provide amenities for recreational and aesthetic benefit provided that water quality can be enhanced.  Extended Detention Ponds. These are normally dry and are designed to detain a certain volume of runoff as well as provide water quality treatment.
  18. 18. OBJECTIVES AND ELEMENTS OF ASUSTAINABLE DRAINAGE SYSTEM (SDS) Detentions Ponds represent the one element of a SDS which may be most suitable and applicable to our local circumstance and to the extent that this may be so these should become a mandatory part of our drainage system design.
  19. 19. SOME RECENT APPROACHES TO FLOOD MITIGATION In recent years with the advent of the EMA that agency has established a requirement that in any new development for which a CEC is required the drainage system must be so designed as to ensure that the pre-development runoff from the site must not be exceeded after the development is completed.
  20. 20. SOME RECENT APPROACHES TO FLOOD MITIGATION Invariable this has resulted in the need for some form of detention structure and as a consequence a number of new land developments have incorporated the use of detention ponds. As of now there are no known locally established design criteria with respect to the required storage volume of these ponds so that design and performance of detention ponds is currently a work in progress
  21. 21. SOME RECENT APPROACHES TO FLOOD MITIGATION Detention Ponds – Buccarro
  22. 22. SOME RECENT APPROACHES TO FLOOD MITIGATION Detention Ponds – Mc Bean
  23. 23. SOME RECENT APPROACHES TO FLOOD MITIGATION Detention Ponds – Mc Bean
  24. 24. SOME RECENT APPROACHES TO FLOOD MITIGATION Detention Pond - Camden
  25. 25. SOME RECENT APPROACHES TO FLOOD MITIGATION Detention Pond - Corinth Housing Development
  26. 26. SOME RECENT APPROACHES TO FLOOD MITIGATION Detention Pond - Golconda
  27. 27. SOME RECENT APPROACHES TO FLOOD MITIGATION Detention Pond - Golconda
  28. 28. SOME RECENT APPROACHES TO FLOOD MITIGATION Detention Pond - Golconda
  29. 29. SOME RECENT APPROACHES TO FLOOD MITIGATION Detention Pond - Golconda
  30. 30. SOME RECENT APPROACHES TO FLOOD MITIGATION Detention Pond - Tarouba
  31. 31. SOME RECENT APPROACHES TO FLOOD MITIGATION Detention Pond - Tarouba
  32. 32. SOME RECENT APPROACHES TO FLOOD MITIGATION Detention Ponds - Jerningham
  33. 33. SOME RECENT APPROACHES TO FLOOD MITIGATION Detention Ponds - Jerningham
  34. 34. CONCLUSION The traditional hydraulic engineering approach to solving the drainage problem has provided some relief in some instances but has not resulted in any long term solution to the flooding problem The financial allocation budgeted for drainage works on a yearly basis is essentially for improving existing drainage channels and cleaning of watercourses. Much has been talked about but little else have been seriously attempted over the years
  35. 35. CONCLUSION The current drainage regime throughout the country is in crisis and a reversal of the present situation is the only feasible solution. As such all new land development should be required to produce a post-development runoff that is not more than 80% of the pre-development runoff. Managing storm water at source with more emphasis on short term storage and attenuation of discharge into downstream watercourses could provide a more sustainable solution to flood mitigation.
  36. 36. CONCLUSION The use of Detention Ponds as a means of managing storm water discharge should become mandatory for all land developments In any land development the provision of an appropriate plot should be required for storm water management in the same way that there is a current requirement to set aside plots for recreational and communal use as part of the land use planning
  37. 37. CONCLUSION Consideration should be given to offering an incentive to urban townhouse developers to provide a certain volume of storage for roof water which can be used for purposes which do not required potable water. THANK YOU

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