WATER RESOURCES

Fresh water resources are likely to be threatened in two main ways by climate change. Firstly, by sea level rise, which is likely to increase salt-water intrusion within freshwater aquifers. Secondly, by increased frequency and severity of droughts, as has been experienced in recent decades; and many climate models suggest this may intensify in the future in the Caribbean region. Barbados is almost entirely dependant on groundwater supplies.

With available per capita natural water resources estimated at 350 m3 _{per person per year,}

Barbados is classified as a water scarce country (Reid, 1994). The total annual water resources of Barbados are estimated at 59.0 million m3 _{per year in an average year and approximately 45 m}3

million per year in a 1:15 year drought. This is based on an annual average rainfall of 1450 mm per year (Klohn Crippen, 1997). Up until February 2000 fresh groundwater accounted for 96.8% of Barbados’ potable water supply; while fresh water springs accounted for 3.2% of the water supply. Two desalination plants have been recently built in Barbados. One plant is capable of supplying up to 10 % of the island’s drinking water needs. An additional small plant has been built by a local hotel to produce irrigation water. Together these plants are capable of relieving approximately 12% of the stress on the nations water reserves. Therefore Barbados is still 88% dependent on rain-feed groundwater resources.

Under present conditions the Barbados Water Authority utilizes 34 millions of gallons per day (MGD) of the national water resources for drinking water. The desalination plant produces 10.8%, the St. Michael catchment 52.8%, the St.Philip catchment 20.2%, the Westcoast catchment 13.4%, and the Springs produce 2.8% of the national drinking water supply. Figure 2.7 shows the groundwater catchments in Barbados.

32 V uner ability and Ada ptation

Figure 2.7: Distribution of groundwater catchments and wells in Barbados.

The major aquifers are found in the coralline areas; and Barbados’ aquifers are unconfined aquifers, hydraulically connected to the sea. Thus sea level rise, and the resultant saline intrusion, could have a significant impact on the water supply in Barbados.

2.2.2.1. Saline Intrusion in Barbados

Saline intrusion has both a horizontal and a vertical component, with the salt water moving horizontally into the aquifer and vertically upward due to the influence of pumping on the dual density relationship between fresh water and salt water. Through component 6 of the CPACC project an analysis of the effect of sea level rise on the freshwater supplies of Barbados was performed.

Water levels in the St.Michael catchment have been measured at 0.45 to 0.60m above sea level with fluctuations of up to 1.35m. The water wells in the St.Michael catchment area are also located a good distance inland. The water levels in the St. Philip catchment have been measured at 0.3 to 0.6m above sea level with fluctuations up to 1.2m. Many of the wells in the St.Philp catchment are also located inland. At the West Coast, the water levels are on average 0.3m above sea level. Traditionally many West Coast Wells were a few hundred metres inland. However, due to saline intrusion in the 1940s, pumping of these wells was stopped. At present, wells in use are further inland, on the first land terrace inland from the coast.

33 V uner ability and Ada ptation

Table 2.3: Mean distance of catchments from the sea (m).

Catchment Mean Distance from Sea

St. Michael 4539.18 m

St.Philip 4750.50 m

Westcoast 992.80 m

The wells in the west coast catchment are those more likely to suffer from saline intrusion. Barbados Water Authority (BWA) pumping data for June 2000 shows that the West coast catchments provide 13.4% or 4.93 MGD of the national potable water budget. According to the BWA statistics, however (WRMWLS, 1997), this figure provides water for approximately 51,000 persons along the western coast and the northern parishes of Barbados. Additionally these catchments are licensed to provide an additional 6.93 MGD to private users. This includes significant parts of St. James, and all of St. Peter and St. Lucy.

The area serviced includes the island’s luxury tourism sector, the shopping areas of Speightstown and Holetown, and the island’s largest sugar factory. The parish of St. Lucy has one garment manufacturing factory, which employs about seventy (70) persons, and a cement plant, which employs about one hundred persons. Therefore the West coast wells are extremely important for much of the island’s population and economic activity.

An analysis of the effect of a 0.2m, 0.5m and a 0.9m rise in the sea level, on the west coast catchment was performed. The west coast catchment already suffers from saline problems as a result of overpumping, which causes the chloride value in the water to be above the WHO limit of 250 ppm of Chloride (Cl). Analysis of water quality and rainfall data collected by the BWA shows that there is a seasonal element to the present chloride problems in this catchment. The highest probability of exceedence of 250 ppm chloride occurs in July and December, which corresponds to the end and beginning of the dry season respectively.

The effect of this seasonality is that during the dry season, under a scenario of sea level rise and reduced rainfall the catchment will be significantly more vulnerable to saline intrusion. This is due to the fact that the general elevation of the saline interface will be raised and with less recharge the freshwater lens will be significantly thinner and more subject to upconing.

Equations used by Mahesha (1995) were used to track the movement of the toe of the freshwater saltwater interface. Analysis showed that under the sea level rise scenarios suggested, the wells in the west coast catchment could not be used for drinking water purposes.

It has already been noted that these wells provide water to the 51,000 people and much of the hotel industry on the luxurious west coast. Thus it is clear that under certain conditions Barbados will have to look to augment its water supply for certain areas of the country as potable water will be lost as a result of sea level rise.

34 V uner ability and Ada ptation

Changes in precipitation and temperature for the Caribbean region as outlined by the IPCC in the third assessment report, will also have a devastating effect on Barbados’s freshwater supply. The amount of freshwater available will decrease dramatically under these conditions, and Barbados will have to examine alternatives (eg. expansion of the desalination sector) in order to provide enough freshwater for local use.