Dear Editor,
Why do parts of Guyana flood during the two known annual rainy seasons? Simple. Those flood-prone areas are reclaimed natural swamplands or seasonal natural flood zones with insufficient natural and artificial drainage. Many areas on the coast (except the high sand reefs that rarely flood whereon coastal Indigenous Guyanese used to live and move and have their being before the other Guyanese arrived), parts of the Rupununi and other places in this land of many waters are like that.
The other Guyanese who arrived later built gravity drainage systems that were designed at maximum best to drain 2.5 to 3.0 inches of daily rainfall, provided the rainfall was evenly distributed during 24 hours. If that amount falls in a few short hours (known as “short duration high intensity rainfall,” Ramraj, R. 1990), the water will back up and flooding will occur before the water is drained off in 24-48 hours. If this type of rainfall occurs for several days, or if the daily rainfall exceeds the maximum drainage capacity of the area, say, 9.6 inches (Strathaven, ECD, November 19, 2014) or 7.5 inches (Bush Lot, WCB, June 9, 2017) or 7.4 inches (John’s Village, June 22, 2017) then the flooding will be prolonged for several days or even a week or more (figures from Hydromet daily weather briefs).
The Black Bush Polder area was built from reclaimed swamp and was designed to have a best daily drainage capacity of 1.5 inches by gravity drainage, but due to siltation in the mile-long outfall channels, is about 1 inch daily (Rowe, W. D. 1970). The fossil-fueled pump stations were installed to aid gravity drainage when the sluices cannot be opened at high tides, but these alone cannot achieve 1.5 inches daily, as nothing beats a koker door at draining flood waters. On May 24, 2021, Johanna BBP received 2.8 inches of rainfall, the highest reported for that day.
The maximum designed drainage capacity of an area is reduced by vegetation-filled canals silted-up canals, garbage-filled canals, filled-in canals and human inefficiencies in operating and maintaining the drainage infrastructure and protective back-dams, sideline dams and sea-dams. So, an area might be draining at a reduced daily capacity of 1.5 inches or even less, resulting in longer drain-off times for backed-up floodwaters. It is in the interest of all that the drainage system be maintained in top-class condition, so that the shortest possible drain-off times can be achieved in the face of excessive rainfall and areas spend minimum time under floodwaters.
I have a suspicion that the authorities from inception leave inefficiencies in the system so as to have to something to blame when flooding occurs, as it would astound people that flooding can still happen in a perfect system, but that is just the evil part of my mind thinking. Bear in mind that even in top-class drainage efficiency condition, once rainfall exceeds the maximum drainage capacity, flooding will occur, as it takes time even for the best system to drain off excessive flood waters. But with a highly efficient system, we can at least be satisfied that we have done our best and leave nature to do the rest, until we invent new as-yet-undiscovered ways of manipulating nature to do our will to keep our collective feet dry.
Sincerely,
M. Xiuquan-Balgobind-Hackett
