Towards A Sustainable Drainage Solution

transcript

APETT FREE PUBLIC CONSULTATION SERIES

FLOODING AND DRAINAGE

“TOWARDS A SUSTAINABLE DRAINAGE SOLUTION”

Presentation by:

Eng. Vaughn I. Lezama R Eng, FAPE.

Bridging Engineering and the Society

This 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

INTRODUCTION

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.

CURRENT CIRCUMSTANCES AND APPROACH 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

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.

MITIGATION

Extensive erosion in the upstream catchment areas and the resulting sediment and siltation of watercourses has served to reduced channel capacities.

MITIGATION

Honda River

MITIGATION

Marabella River

MITIGATION

Vistabella River

MITIGATION

Gucharan River, Debe

MITIGATION

Mitchell River, Barackpore

MITIGATION

Alley’s Creek

MITIGATION

Cipero River

MITIGATION

Cipero River

MITIGATION

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

OBJECTIVES AND ELEMENTS OF A SUSTAINABLE 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

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.

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.

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.

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

Detention Ponds – Buccarro

Detention Ponds – Mc Bean

Detention Pond - Camden

Detention Pond - Corinth Housing Development

Detention Pond - Golconda

Detention Pond - Tarouba

Detention Ponds - Jerningham

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

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.

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

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

CONCLUSION

Towards A Sustainable Drainage Solution

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