Why Port of Spain floods

The rain in Port of Spain fell mainly on the plain. And on the hills. (It fell on the twain.)

When town flooded again and again last month, some of the capital city’s burgesses looked to the hills, blaming deforestation on the elevated regions for the floods in the low-lying areas. Some focused on the drains, pointing fingers at the failure to maintain clear watercourses in the lower Port of Spain area. Others talked of global warming, still others of the end of days. But Ewoud Heesterman sees things a little differently. The Drainage Committee Chairman of the Board of Engineering shared some of his insight with the Sunday Express.

When he spoke, very briefly, about the need for individual citizens to keep the city’s drains clean, Heesterman’s ruminations pretty much echoed the sentiment of the National Emergency Management Agency (NEMA) Director Col Dave Williams, who had told me, “It’s an old cliché: prevention is better than cure. There’s a lot that we do as individual householders that contributes to the problem. While we complain about the government’s responsibility, we must take up our own responsibility.”

While he insisted that the denudation of the hills surrounding Port of Spain did not single-handedly account for the city’s flooding woes, Heesterman did not discount the seriousness of that environmental issue. He did not restrict the problem of deforestation to the issue of unplanned housing, however. Instead, he raised a warning flag for the upcoming dry season.

“If the Maraval and St Ann’s catchments are significantly denuded by bush fires in dry season, floods come faster and harder in Port of Spain in the rainy season,” he said.

So, be careful what you wish for. Trinis, who suffer from chronic short-term memory loss, may think what we need now is lots and lots of sunshine but even that may only cause bush fires, which, in turn only increase and accelerate run-off in the rainy season.

“What it causes is when it rains, the water comes down in greater amounts and faster,” explained Heesterman, adding that the presence of agricultural squatters, who generally cultivate short crops instead of long-term woodland crops on the hills around Port of Spain, also contributes to the chronic floods.

The most revolutionary of Heesterman’s ideas was revealed as he went on to discuss drainage, introducing the concept of “stream regularisation.” Based on the fundamental philosophy that the original model of a meandering and irregular watercourse is the closest to ideal, this cutting edge drainage engineering concept aims to conserve and emulate natural hydrological regimes rather than focusing on drainage alone.

“People make the mistake of thinking that ‘flood management’ is only drainage. If you drain an area that is historically flood prone, you are basically just moving the problem downstream and only making the problem worse,” he said.

He would add, “The present policy of focusing on increasing the channel capacity has created a permanent maintenance nightmare in the lower reaches of the St Ann’s, Malick, Diego Martin and Maraval rivers. Sediment deposit build-up is accelerated and increased by the deforestation and housing development of the upper reaches of the river.”

He continued “A mature forest would generally generate a few tonnes of sediment per hectare per year. Developed land and areas that are denuded of vegetation would produce in the order of 60 or a hundred tonnes of sediment per year. A construction site could go as high as in the thousands. So during construction is when sediment production really soars.”

Hmm. When you think of how much construction is going on in throughout Port of Spain, it is not strange, therefore, that the half-hour flood of late last month created a dust problem in the city which lingers to date.

“What is happening in the United States and in Europe is something called ‘stream regularisation.’ They are actually breaking up concrete drains to regenerate something that more emulates a natural stream, to go back to a situation of a more natural eco-system,” said Heesterman, adding that the standard practice among developers in Port of Spain (as well as the rest of the island) of building narrow, deep drains actually helped to channel the flow of water into downtown Port of Spain.

While his idea of stream regularisation may seem impractical, Heesterman’s outlook was actually quite pragmatic.

“You’re not going to change Maraval River and East Dry River where they run through built up areas. That’s a done deal,” he said, before suggesting one operable solution for the problems he’d identified. “You have to focus on reducing erosion in the upper region and on holding back water instead of letting it come down quickly.”

The first part of his solution, as it pertains to drainage, is the collection of water in the elevated areas. He suggested building check dams and detention basins in the steeper rivers to reduce the rate of water flow. The second part is the redirection of watercourses. To this end, he pointed out the need to intercept and re-direct run off, perhaps in a westerly direction toward the sea, before it got to Independence Square.

“The gradient of north-south streets flattens out in the region of Independence Square,” he observed, indicating that while the city’s parallel streets channeled flood waters down the relatively steep gradient from the surrounding elevations, the reduced force of gravity at the lower gradient of the downtown Port of Spain was insufficient to propel flood waters beyond the region of Independence Square and South Quay.

In fact, that bustling region of the city, which contains both the Port of Spain and Diego Martin transit centres, is the worst of all possible scenarios. Not only is its location on the shoreline an inherent flood risk factor, but it also falls victim to the overflowing East Dry river and serves as a sub-basin for run-off from the surrounding elevated areas.

In short, Heesterman was describing the flooding in Port of Spain as an urban planning failure. Think that’s too harsh? Then you probably haven’t seen the Port of Spain City Engineer, Edwin Yuk Low’s plan to deal with flooding in the city. I did. It’s a three-volume document by Millette Engineering (International) Limited titled “Port of Spain Drainage Study Master Plan Report,” but more commonly called “the Millette plan.” Port of Spain Mayor, Murchison Brown, called it a “very comprehensive” plan. I agree. The document is lucid, thorough, realistic and forward-looking. The authors had the foresight to plan far ahead into the future.

The only snag is that “the Millette plan” is more than 20 years old. Brown said that to the best of his knowledge, there was not any other document being used to deal with the problem of flooding in Port of Spain. He said he was “not aware” of the existence of any more recent plan.

“It’s a good plan,” he said in defence of the Millette plan. “There are parts of it that can still be used.”

Few would disagree that some parts of the 20-year-old document remain relevant, but with more dust on its covers than the streets of Port of Spain the day after an intense downpour, those Millette parchments cannot hold a central place in the City Engineer’s office. And the way Heesterman tells it, the city’s problems with urban planning go way back. He cited the example of the land reclamation projects which pushed back the city waterfront, to create present-day South Quay.

“Every time a little bit of land is reclaimed, the run-off has to go that much further but the driving force to move it along is gravity and the distance from the north of Independence Square to sea level is increasing. So what happens when the floods come [is that] they rush down to Independence Square and then it slows down,” said the engineer. “What you see in places where reclamation is properly planned is that between the old land and the new land you have a relatively wide watercourse that can move out water with a minimal amount of gradient.”

Trinidad and Tobago Meteorological Service Assistant Director, Glendell De Souza, had also indicated the danger of the rapid development of that west coast region of the island, “We are influencing the climate patterns of the western side of the island because of the infrastructure development that has taken place. The development happening along the west coast of Trinidad is affecting the micro-climate of Trinidad. In changing the micro-climate, we are creating disasters…As we continue to develop, the events may produce more torrential rainfall and cause more destruction.”

As the discussion shifted to the wider issue of land use and development planning, Heesterman spoke with even greater authority.

“What you really need is a master plan to be adhered to,” he said, shifting the conversation into a whole other gear.

Next week, we will continue the discussion, looking at the current National Physical Development Plan.

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