Interaction between a Fresh Groundwater Lens and Saline Lakes in Exuma, Bahamas

Abstract

Holocene sands of Ocean Bight in Exuma, Bahamas, contain a Ghyben-Herzberg freshwater lens, the source of a 39,000 gallons per day water supply. The sands are underlain by Pliestocene limestone, which contains the basement of the aquifer at the salt-water/freshwater interface. The perimeter of the lens is the Atlantic ocean to the east and saline natural ponds to the north, west, and south. These ponds were formed in low-lying areas, where the water table is just below ground and there is direct evaporation from the water table. In Exuma, potential evapotranspirtion exceeds precipitation, and in areas where the water table is above surface, evapotranspiration occurs at the potential rate and ponds become hypersaline. Freshwater lenses become thin to non-existent where these lakes are formed. Three small ponds were excavated into the freshwater part of the lens, as part of a development. Based on the fact that evaporation exceeds rainfall, there is potential for saline intrusion at the site of these ponds. This paper presents the results of the numerical and analytical techniques that were used in assessing the integration of the surface water ponds with the groundwater lens.