Hydrogeology of Fresh-Water Lens Beneath a Holocene Strandplain, Great Exuma, Bahamas

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The beach-ridge strandplain at Ocean Bight, Great Exuma, partially fills a large embayment bordered by the Lucayan Formation (Pleistocene limestone), the bedrock of Great Exuma Island. Seismic refraction profiles indicate that the Holocene sand body rests in an amphitheater-like bedrock bowl beneath the strandplain. Direct current resistivity and electromagnetic surveys show that the lens extends downward into the Lucayan bedrock below much of the strandplain. The lens is thickest along the central, shore-parallel axis of the strandplain; therefore, flow is not only shoreward but also inland. The reason for the inland groundwater flow is a large net water loss (− 0.5 m year−1 according to earlier studies) at inland ponds near the Holocene/Pleistocene contact bounding the strandplain. Dupuit-Ghyben-Herzberg (DGH) modeling using negative recharge at the ponds confirms the explanation for the landward flow and the corollary isolation of the Ocean Bight lens. For the purpose of DGH modeling, the aquifer at the Ocean Bight strandplain can be considered a two-layer (Holocene on Pleistocene) island that conforms to the outline of the strandplain. The buried high-conductivity layer (the Lucayan) reduces the thickness of the lens.

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Journal of Hydrology, v. 125, issues 1-2, p. 93-109

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