PLEISTOCENE LOW SEA LEVEL STANDS AND A CONCEPTUAL MODEL FOR THE EVOLUTION OF THE KARST AQUIFER ON THE NORTH COAST OF PUERTO RICO

A series of dye tracing experiments supports a previous theoretical model for the evolution of strike-oriented discharge from a sequence of seaward dipping carbonates on the north coast of Puerto Rico. Groundwater inputs located along strike, drain in the dip direction, and are collected along strike by master conduits which discharge to dip-oriented streams. This pattern is consistent with the probable evolution of head-loss within the aquifer.

The lowest conduits were formed during low sea-level stands, and, at present, these appear to be partially blocked by Post-Pleistocene backfilling of the stream valleys. The gravel and sand sediments, now in series with the karst conduits, deprived these low resistance dissolution pathways of part of their hydraulic advantage. This caused the portions of the karst aquifer so affected to have properties superficially like those of a granular aquifer. Higher conduits, following this same pattern, drain normally. The effects of low sea-level stands upon karst aquifers are not restricted to island and coastal environments. Inland areas, as remote from the coast as Mammoth Cave, are similarly affected.