Lecturer, Department of Civil
and Environmental Engineering,
The University of the West Indies,
St Augustine Campus
Several weeks ago, we were astonished by the scenes of utter devastation from floods, not so much because of what we saw, but more because they were from Western Europe. The question on many lips was how could such have happened, so many lives lost, considering all their resources, including sophisticated engineering works to withstand floods. More than that, such countries certainly would have had well devised systems that would not have made them so vulnerable to a hazard that is, after all, very predictable.
The next two questions we should now be asking are:
1. Can such floods occur here in Trinidad and Tobago?
2. What would be the scale of damage if such floods occur?
The answer to the first question is a resounding yes. The two main factors for that flood, namely extreme rainfall coupled with intense urbanization, are very likely to occur here. In many of our catchments, urbanisation has already happened apace, without the requisite expansion of flood control works. Additionally, over the last decade, we have been experiencing more extreme rainfall than any time period in recent memory. Many of these events have not as yet occurred in these heavily urbanised areas. However, local meteorologists think that it is just a matter of time before we do have rainfall events such as the one in October 2018 in Greenvale, or in December 2019 in South Oropouche, falling on these areas.
As to the second question—what would be the scale of disaster should such flooding occur—a realistic answer is “widespread and heartrending losses.” As far as I know, we have not really done the planning for such extreme, but likely, scenarios. And by planning, I do not mean figuring out how we are to respond to the consequences of such flooding. Rather, I mean, what do we do to avoid such losses, knowing that such can occur.
If we are to ensure that losses are limited and no lives are lost from a very extreme rainfall event falling on a heavily urbanised catchment, say, like Diego Martin, then we must first begin by looking at the effectiveness of our current system for tackling floods. When we do so, we would realise that our dependence on engineering works alone would not be sufficient. These works are river alignment, widening and paving, the installation of detention basins, flood gates and pumps.
They are the attempts by engineers at controlling nature by changing the features of floods, by reducing water velocities and by containing water in defined places. We have to admit that we do not have the capability to control future floods and begin broadening our toolkit to include other measures as well.
Measures for Flood Risk Management
Measures available for managing flood risk can be placed into five categories, namely, flood defence, prevention, mitigation, preparation and recovery.
Flood defence
This measure can be described as keeping the water away from people. It is the measure that is most popular and almost the one expected by our population to take us through our changing climate.
The Drainage Division has been the lead agency in implementing such measures. Over the last fifty years, they have performed numerous studies with a view to identifying appropriate engineering works to solve our flooding problems. These studies have identified major engineering works for solving widespread flooding. Almost invariably, their recommendations have not been implemented because of their high price tag, with low returns on investment.
Flood prevention
This measure is best described as keeping people away from the water, for high water levels are only of concern if it occurs in human communities and/or interests. This necessarily implies that we are able to identify, with an acceptable level of certainty, the zones that are to be classified as floodplains and hence for which occupancy would not be allowed; or if allowed, then with compliance to enforceable restrictions. This would not prove easy to implement, for firstly, it requires a large amount of data for doing flood analyses to define the zones. If that is not challenging enough, the next step is getting the population to accept and to stay away from the identified no-build zones.
Flood mitigation
Flood mitigation defined here is an acknowledgement that it is not always feasible to keep people away from the water, nor is it possible to keep the water away from people. That is to say, it admits that households will be surrounded by water from time to time. Its aim, however, is in minimizing the ensuing damage. In days of old, many homes were built on stilts so that the ground floor was above the expected flood levels. Flood mitigation is about how we develop our land. It may mean, for example, that in our spatial planning of communities, playing fields and structures that are temporarily occupied are placed on the low lands, and that homes and institutions are placed on elevated lands.
Flood preparation
Given the very likely occurrence of extreme rainfall such that even mitigative measures may lead to flooding of ground floor levels, there are steps that flood victims can take to prevent loss of life and to minimize loss of property. This would involve providing households early warning for them to take action, including evacuation, for preservation of life, limb and belongings.
Flood recovery
This measure is about how approaches are modified from the lessons of past floods. It involves having a method by which previous floods can be comprehensively examined, including the causes—excess rainfall, or a blocked bridge, for example—the nature and the extent of the damage, how well did the infrastructure function, a re-creation of the event to determine what could have been done differently to reduce damage from future floods.
These five measures should all be part of the national flood-risk management strategy.
Clearly, they can’t be managed by any one agency, but some agency is needed to ensure that the right mix of these has been established, and that there is constant review to ensure that maximum effectiveness is achieved.
There are particular weaknesses in our current system that must be addressed in order for us to effectively implement these measures. Suffice it to say that unless certain actions are taken then no meaningful improvement can be achieved.
These actions are as follows:
• Improvement of our data collection capabilities, in terms of the physical features of our lands, rainfall, streamflow and flood levels, and the social, economic and environmental costs associated with floods;
• The appropriate application of modern techniques for predicting flood water levels and velocities so that flood prone areas can be clearly demarcated, and that correct information is available for designing engineering works;
• The streamlining and improved coordination among the agencies involved in flood-risk management so that all the measures can be properly implemented;
• A guaranteed source of funding and resources for building flood management capacity, taking into account the consequences of delayed action in developing this national strategy; and
• The involvement of public sector, private sector and population acting together to reduce flood damage;
• A sensitised, involved and interested population that would ensure that flood-risk reduction remains a central national issue, not just one for the wet season; a population that would continue to remind decision makers of consequences for leaving our flood-risk management system up to the vagaries of the weather.
The images we have seen recently of communities across T&T struggling to cope with clean up after flooding are disturbing, especially when we know that with some effort, they can be avoided.
The scenes in Western Europe should remain in our minds for if we do not act quickly enough to improve our flood risk management system, then these could be the images we witness.
Over the next few articles,
each of the actions listed
above will be discussed.