aquifer

Estimating recharge thresholds in tropical karst island aquifers: Barbados, Puerto Rico and Guam

Jones, IC, and JL Banner. 2003. Estimating recharge thresholds in tropical karst island aquifers: Barbados, puerto rico and guam RID C-8676-2011. Journal of Hydrology 278 (1-4) (JUL 25): 131-43.

Abstract: 
The hydrology and geochemistry of groundwater in tropical island aquifers, such as Barbados, Guam and Puerto Rico, are significantly influenced by tropical climatic conditions. Recharge to these aquifers is the product of regional and local climate patterns that control rainfall. Oxygen isotopes can be used to estimate the amount and timing of recharge on these islands because seasonal fluctuations of rainwater oxygen isotopic compositions are related to the amount of rainfall. The karst aquifers on Barbados, Guam and Puerto Rico have similar rainwater and groundwater oxygen isotopic compositions. Comparison of groundwater and rainwater oxygen isotopic compositions in the three aquifers indicates that: (1) recharge occurs by rapid infiltration with little evaporation prior to recharge; and (2) recharge is associated with similar monthly rainfall thresholds of 190–200 mm. These rainfall thresholds are remarkably similar for three aquifers in different geographic locations. Differences between the spatial variations of groundwater oxygen isotopic compositions on Barbados and Puerto Rico can be attributed to the more complex groundwater flow system on Puerto Rico. The surprising similarities of hydrologic conditions under which recharge will take place can be attributed to similarities in climate and geologic conditions, such as soils and limestone bedrock, that exist on the three islands. We therefore speculate that similar recharge-rainfall thresholds may be observed in other tropical karst aquifers.

GROUND WATER OPERATIONAL MODEL YAUCO, PUERTO RICO

Abstract: 
A numerical groundwater model was constructed to simulate groundwater flow in the Yauco Alluvial Valley aquifer. The groundwater flow model was constructed to evaluate future management options, including the potential to increase aquifer firm yield through a conjunctive management of ground and surface water. The aquifer within the Yauco Valley consists of river alluvium deposited over the incised Juana Díaz formation and Ponce limestone. A finite-difference, numerical model was developed to simulate ground water flow in the Yauco Valley. The single-layer model encompasses the entire alluvial deposits of the valley which extends from the Yauco town to the Caribbean Sea. The model was calibrated to October 1960 and 1970 to 1974 water levels. Different management scenarios were modeled to analyze and determine how much water can be extracted from the aquifer and evaluate the conjunctive use potential. Results demonstrate that the aquifer could be subjected to a total extraction in the order of 4.6 to 4.8 mgd (1-1.25 mgd above current extractions) without reducing the water levels to a point that could produce saltwater intrusion. Simulations showed that groundwater extractions could be increased by 5 mgd to 6 mgd during the dry season (March-August) if artificial recharge is provided in the range of 1.3 mgd to 1.95 mgd on a year-around basis. This demonstrates that the potential exists to conjunctively use ground and surface water to increase aquifer yield
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