Located in the heart of Tobago, the Main Ridge Forest Reserve encompasses 4,000 hectares of tropical rainforest, reaching heights of 604 metres.
Since 1776, it has been a crown reserve, making it the oldest protected forest reserve in the western hemisphere, home to a number of flora and fauna, including the rare white-tailed Sabrewing Hummingbird, which is endemic to the island of Tobago.
Besides having a unique biodiversity and being described as the literal backbone of Tobago, the Main Ridge also acts as a watershed, playing a vital role in our water cycle and groundwater recharge.
A watershed is a region of land where water drains into a waterbody and can exist in all shapes and sizes.
Every waterbody is a part of a watershed and will play an important role in the water cycle.
In the context of the Main Ridge of Tobago, the watershed drains rainfall from high points into surrounding streams and rivers under the influence of gravity and has an eventual location into the fifteen watersheds on the island. Some of this rainfall ends up on surfaces such as trees, rocks, buildings and other hard surfaces, while some rainfall may seep into underground reservoirs known as aquifers.
In Tobago, groundwater is produced mainly from deep-set metamorphic and igneous bedrock aquifers.
The fault and fracture systems in these rocks facilitate flow paths for groundwater.
Water wells are then used to produce the groundwater from these fractured bedrock aquifers.
[caption id="attachment_1063950" align="alignnone" width="505"] Geologic map of Tobago showing the different lithologic units and major faults. - Map courtesy GSTT[/caption]
A water well contains a submersible pump, which pumps water from the surrounding aquifer into the borehole of the well and then to the surface, where it is transported to a water treatment facility.
So, what makes the Main Ridge a good watershed for aquifers? The reserve consists of higher regions and then gradually becomes flatter towards the coast, giving the area a suitable angle of elevation for precipitation to run off and collect both at the surface and below.
Tobago also consists of three main lithological belts, which run roughly east to west. They are: North Coast Schist, Tobago Volcanic Group and Plutonic Suite.
All three groups are intruded by a series of dykes and are overlain by younger sedimentary rocks. The island is located along the boundary of the Caribbean and South American Plates.
Tectonic activity along these plate boundaries produces fault systems in the rocks. Linear features are formed on the surface and within the subsurface because of these fault systems and are called lineaments. It is along these lineaments that flow paths are created and feed the watersheds. Once water runoff passes through these lineaments, they flow to the aquifer.
Tobago's aquifer systems expand across the Main Ridge and are often referred to as a mega watershed. More than 90 per cent of the island's groundwater supply comes from this mega watershed.
The highly diverse
