Causes of Flooding

Flooding occurs across various areas of Trinidad and Tobago for several reasons, usually a combination of both natural and man-made causes.

Natural Causes

Human Causes

Natural Causes

Intense/Heavy Rainfall

During heavy or intense rainfall, as large drops hit the ground with force, drops may bounce off the ground instead of being absorbed by the soil. Rainwater then runs off across the surface, increasing the runoff and water levels in watercourses. Intense or heavy rainfall can occur anytime throughout the year, but these events typically occur during the rainy season, where conditions for intense convective activity are favorable.

Prolonged Rainfall

Heavy rainfall on October 17th 2018, part of a multi-day heavy rainfall event that contributed to unprecedented flooding across parts of Trinidad

After several hours to several days of rainfall, soils become saturated. At this point, the land is unable to hold any additional water, and rainfall become surface runoff. This runoff will raise already swollen watercourses and trigger flash flooding and/or riverine flooding. Trinidad and Tobago typically has the highest threat for prolonged rainfall during the rainy season, where the Inter-Tropical Convergence Zone, or tropical systems, can cause multi-day rain events.

Relief (Topography)

Relief is the difference in height between the lowest and highest point on land. In mountainous or hilly areas, surface runoff can move quickly down steep slopes and into low-lying areas. The surrounding low-lying areas in Trinidad and Tobago, such as much of Northwestern Trinidad and the East-West corridor, south of the Northern Range, typically experience flash floods as streams and rivers become overwhelmed with surface runoff during a heavy rainfall event.

Human Causes

Deforestation


An aerial shot, provided by Fishermen and Friends of the Sea, showing an area that had been cleared to make way for the new Manzanilla highway near southern boundary of the Aripo Savannah.

Deforestation is the removal of a forest or forested area, where the land is then converted into a non-forest use. The clearing of trees and brush reduces the volume of water soils can absorb and retain. This leads to increased surface runoff, which then leads to increased flow into watercourses.

Note that wild or bush fires, where the forest and surrounding vegetation is burnt, is can be considered both a natural or man-made cause depending on the ignition source as it a similar effect of deforestation on the land.

Poor Land Use Practices

Across Trinidad and Tobago, slash and burn agriculture, over cultivation and over-grazing reduces the viability of the soil for vegetative growth. This leads to a result similar to deforestation where the volume of water the soils can absorb and retain is reduced and the surface runoff is increased.

Urbanization

Development across Trinidad and Tobago, over the last several decades, occurred at a rapid pace. This urbanization of already flood prone areas led to the replacement of permeable soil with impervious layer of asphalt and concrete – both impervious surfaces. This leads to pluvial flooding, which encompasses both street/urban flooding and flash flooding due to increased surface runoff.

Improper Waste Disposal

Illegal dumping in Trinidad. Photo: Ministry of Rural Development & Local Government

This is the most preventable cause of flooding across Trinidad and Tobago. Waste that has been improperly disposed, such as dumping in or around watercourses to as simply littering ultimately find their way into drains, streams and rivers during rainfall, blocking or impeding water flow. This obstruction causes water to back up or overflow watercourses and lead to flooding.

Quarrying

Quarrying is the process of removing rock, sand, gravel or any other minerals from the ground in order to use them to produce materials for construction or other uses. Quarrying itself leads to deforestation and leaves the land unable to support vegetative growth. This increases surface runoff and leads to flooding.

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