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The internal renewable water resources (IRWR) are estimated at 241 km3/year. Surface water resources are estimated at 241 km3/year, groundwater resources at 103 km3/year and the overlap between surface water and groundwater is estimated to be 100 percent (Table 2).
Surface water resources
Guyana is an Amerindian word meaning “Land of many waters”. Numerous rivers flow into the Atlantic Ocean, generally in a northward direction. Of these, fourteen river basins were monitored during the period 1965-1974: Waini, Pomeroon, Essequibo, Potaro (tributary of Essequibo), Mazaruni, Cuyuni, Supenaam, Demerara, Berbice, Canje (tributary of Berbice), Boerasirie, Mahaica, Mahaicony and Abary. Table 3 shows the monitoring of seven river basins, representing about three quarter of the total area of the country: Essequibo, Cuyuni, Potaro, Mazaruni, Demerara, Berbice and Canje. The Essequibo, the country’s major river, runs from the Brazilian border in the south to a wide delta west of Georgetown. The rivers of eastern Guyana cut across the coastal zone, making east-west travel difficult, but they also provide limited water access to the interior. Waterfalls generally limit water transport to the lower reaches of each river.
The Corantyne river is the border river with Suriname, from its source till the sea. The total flow is estimated at 50 km3/year. It is considered that the entire flow of this river is generated both in Guyana (50 percent) and in Suriname (50 percent) and therefore is part of the IRWR of each country and is not considered to be a border river. Incoming flow from Bolivarian Republic of Venezuela through the Cuyuni river basin is estimated at 30 km3/year. This brings the total renewable water resources (TRWR) to 271 km3/year. Possible exchanges with Brazil through the Takatu river basin are not known.
The groundwater system comprises three aquifers beneath Georgetown and the coastal plain. The “upper” sand is the shallowest of the three aquifers and its depth varies from 30 to 60 m, with thickness ranging from 15 to 120 m. It is not used as a source of water because of its high iron content (>5 mg/l) and salinity (up to 1 200 mg/l). Most potable water is obtained from the two deep aquifers. The “A” sand is typically encountered between 200 and 300 m below the surface with thickness ranging from 15 to 60 m. Water from the “A” aquifer requires treatment for the removal of iron. The “B” sand is found at about 300 to 400 m with thickness of between 350 and 800 m. Water from this aquifer has very little iron, a high temperature and a trace of hydrogen sulphide which can be treated with aeration.
Lakes and dams
A small amount of the surface water resources is trapped by a long low earth embankment to form large shallow dams locally known as “conservancies”. The conservancies are located in the “backland” or upper stream catchment areas and comprise water-retaining embankments and structures. There are four large human-made conservancies:
- The Abary conservancy on the Abary river, also called Mahaica Mahaicony Abary (MMA), has a total capacity of 609 million m3 and has been designed to provide irrigation to about 17 500 ha.
- The East Demerara Water conservancy (EDWC), which dams the Maduni river and Lama creek, has a capacity of 16 million m3 and has been designed to provide irrigation to about 34 500 ha. It also supplies potable water to Georgetown, to augment the groundwater supply. Ten percent surface water is used for potable water supply against 90 percent groundwater.
- The Boerasirie conservancy collects the flow from the Boerasirie river, Warimia creek, Jumbi creek and finally the South Durabana creek. It has a total capacity of 166 million m3 and has been designed to provide irrigation to about 36 000 ha.
- The Tapakuma conservancy dams the water from three inland lakes on the Essequibo coast and releases it as needed for irrigation. It has a total capacity of 18 million m3 and has been designed to provide irrigation to about 12 000 ha.
All the conservancies store water at higher elevations than the surrounding fields, thus irrigation can take place by gravity flow to these areas.
Abary, Demerara and Boerasirie conservancies are entirely covered by weeds. While in most years water supply is ensured throughout the year, if droughts occur during the secondary November-January wet season, these conservancies may have water shortages. Water shortages may also occur in the Tapakuma conservancy, which is partly supplied by pumping from the Pomeroon river, to release water or to take in water if needed to supplement irrigation needs in Region II.
The hydropower technical exploitable capability is 37 000 GWh in 2008. Despite the country’s large potential, only 1 GWh/year is actually generated (World Energy Council, 2008).