March 14, 2021
Last week a persistent trough of low pressure stretching from the Bahamas to Honduras brought several days of heavy rain that soaked most of the North Coast. The Meteorological Service Division issued flash flood warnings for Portland, St. Ann, St. Mary, Trelawny and St. James. Montego Bay seems to have taken the worst of it. There was at least one death when a car was swept into the Barnett River near Westgate, and parts of the nearby Fairview Shopping Centre had a couple of feet of water running down the roads.
Since the beginning of the year, the Caribbean Institute for Meteorology and Hydrology has been forecasting a more or less normal shift from dry season to wet. That suggests increasingly frequent heavy showers from late April through June. However, the forecasters note that “A persistent weak La Nina pattern is expected to persist during the upcoming season, which may drive increasing uncertainty into the seasonal rainfall forecast.”
In fact, flooding has been reported across Jamaica in the last few months. From Kingston to Negril, most parishes have had at least one stretch of undermined or washed-out road that needed repairing. Port Maria still hasn’t fully recovered from the drowning it got in February. Power lines went down, buildings collapsed, a landslide took two lives in St. Andrew and there was a near-miss at Sandy Gully.
Drains that had already been cleaned were blocked with silt and debris and need cleaning again. The Bog Walk Gorge, as usual, was impassible. A bridge in Hanover has been closed because a large amount of bamboo, apparently uprooted from the river bank, washed down and got stuck, turning the bridge into a dam. The same thing may have happened with the Barnet River. When temporary blockages from fallen trees or big stones give way, all the water that was trapped behind them comes down in a rush and sweeps everything in its path.
This is a grim illustration of some fundamental facts that a lot of planners don’t seem to grasp. First, water runs downhill, following the path of least resistance to the lowest point – usually sea level. It will go over, under, around or through any barrier put in its way. That’s why sooner or later everything ends up in the sea.
Second, water is heavy. Your 2-litre carton of milk or juice (mostly water) weighs nearly 4.5 pounds. Fill a 2-gallon household bucket and it’s a 20-pound load. Moving water exerts a powerful force – enough to carry big stones and trees, or toss cars around.
Jamaica generally has done a poor job of managing its watersheds. Much of their efficiency as natural flood preventers, water purifiers and reservoirs has been lost in the name of growth and progress. Uphill, brush and trees have been cleared for logging, quarrying, agriculture and housing estates. Rain can’t soak in so it rushes downhill and becomes somebody else’s problem, carrying the neighbourhood’s litter with it.
At the bottom, flood plains and coastal wetlands have been drained, dumped up and paved over to make room for commercial development. The higher volume of runoff coming downhill now has nowhere to slow down, spread out and lose its trash. As long as the drainage system – storm sewers, stream beds, gullies and ditches -- stays within its banks, the trash goes straight into the sea.
Poor development planning makes flooding almost a sure thing. When there is a heavy rain or something gets blocked, the overflow has nowhere to go but the streets and parking lots of neighbouring communities. If you build houses on a riverbank, sooner or later they’ll be in the river. And if you put a large mostly concrete shopping centre at the very bottom of the system, on a fragile piece of sea-level land that should have been the watershed’s final outflow, a flooded parking lot should not be much of a surprise.