The hydrological cycle for Barbados starts with the evaporation of the ocean water. As the moist warm air rises, it cools and water vapour condenses to form clouds. Moisture is transported by winds and ultimately returns to the surface as precipitation (rainfall). When the rainfall reaches the ground, some of it evaporates back into the atmosphere, while some seeps into (infiltrates) the ground to become part of the groundwater system. When rainfall intensity exceeds the rate of infiltration, or when the ground becomes saturated, the balance of the water runs off overland as stormwater.
The topography of Barbados slopes downward from Mount Hillaby in the Scotland District, to the coast. Moving westward from the Scotland District, there are three distinct “terraces” and numerous gullies (or channels) that transmit rainwater from the higher elevations towards the coast.
Barbados Topography, Geological Sub-Regions (Stantec), and Example of Terraces and Gullies.
The geology of Barbados typically consists of a coral limestone “cap” overlying oceanic rock, which is made up of sandstones, clays and marls. The limestone is highly “karstified”, meaning it contains many holes, tunnels and sinkholes through which rainwater can flow.
Water infiltrating the coral limestone at higher elevations flows downwards until it encounters the much less permeable rock of the Oceanic Group. The groundwater then flows along the interface between the two rock groups towards the coastline. It eventually encounters a large lens of freshwater, which saturates the limestone cap, and sits above the salt water from the ocean. The existing Barbados Water Authority (BWA) drinking water supply wells are located above the first coral ridge, and draw from the large lens of freshwater.
Approximately 90% of the water that is supplied to consumers is returned to the groundwater system as wastewater.
The chemicals in limestone, and the length of time it takes for the water to infiltrate the rock and become part of the water supply, assists in purifying the wastewater. The BWA has established “zones” that place restrictions on the way land can be used at various locations, which protects the groundwater quality near our public water supply wells. In addition, the BWA and the Environmental Protection Department run regular tests on the water quality to ensure that it meets World Health Organisation standards for drinking. However, we should always be mindful of what we discard in our wastewater.
Influences on water supply
Water resources are important to both society and ecosystems. We not only depend on a reliable, clean supply of drinking water to sustain our health, we also need water for agriculture, energy production, recreation, manufacturing, etc., many of which put pressure on water resources.
Land development (e.g., housing, hotels, golf courses, etc.) has increased the demand for water resources. At the same time, the increase in hard structures or impervious surfaces, i.e., pavements, roads, etc., means that instead of rainwater infiltrating and recharging the groundwater supplies, it becomes runoff and flows into the sea. Therefore, land development increases the need for water, but and can also be a major cause of the loss of water resources. In addition, surface water (runoff) is connected to both groundwater and coastal waters, which has implications for the potential pollution of water resources in general.
During heavy rainfall, “runoff” flows over the land surface and into the gullies. Inland, the gullies have steep slopes, but begin to flatten as they reach the coastal areas. Prior to development along the coastline of Barbados, the runoff would flow through the gullies and into the ocean, or seep into the ground. However, over many years, the introduction of buildings, roads, bridges and culverts (many that are undersized) have restricted the flow of water, which contributes to flooding in the coastal area. Dumping of waste into the gullies impacts water resources as well as compounding the effects of flooding.
Beach berms naturally occur across the mouth of some of the drainage outlets at the coast. These berms contribute to flooding, as they block the flow of water to the ocean. Water builds up behind the berms before finally overtopping or causing the berm to break (or “breach”), releasing the flood water, and any potential contaminants, to the ocean.
There is the potential for flood waters to intrude into wastewater systems, which may overwhelm the systems, causing overflow and damage. In addition, inundation of wastewater systems may result in direct mixing of wastewater with stormwater, thereby contaminating the stormwater. This has other potential effects on the quality of the receiving waters (i.e., groundwater and coastal nearshore), as well as associated environmental and public health concerns. Despite their importance, the health risks are not readily identifiable to the public.
Climate Change Impacts on Water Supply
As temperatures increase, humans and animals need more water to thrive and maintain their health. Activities such as raising livestock, growing crops, and producing energy also require water. Agriculture - fisheries, livestock and crops - are highly dependent on specific climate conditions. Heavy downpours can increase the amount of runoff that goes into water bodies, thereby transporting sediment, nutrients, chemicals, and garbage into water supplies. With increased temperatures, waterborne bacteria and harmful algal toxins may be present in freshwater sources at different times of the year, or in places where they were not previously threats.
Coral bleaching due to temperature increase and other stressors, such as pollution
Increases in sea level, when combined with the projected decrease in rainfall, will cause saltwater (i.e., seawater) intrusion into coastal and groundwater aquifers, reducing the availability of freshwater (i.e., drinking water). Sea level rise can result in erosion and a decrease in the width of beaches. However, an increase in height of the beach berm at certain locations (e.g., Holetown) is also feasible, which may trap floodwaters.
Climate change has important implications with respect to water resource and flood management in Barbados. A reduction in annual rainfall leads to the potential for increased frequency and duration of drought conditions, which would reduce groundwater recharge, thus impacting our water supply. Increased rainfall intensity may lead to more runoff and less infiltration (i.e., less groundwater recharge), resulting in increased flooding near the coast.