Characterising scale-dependence of hydraulic conductivity in carbonates: evidence from the Bahamas

Aquifer and core test data for the calcitic Pleistocene Lucayan Limestone a quifer of the Bahamas exhibit a strong dependence of hydraulic conductivity on test scale, to length scales of 10(2)-10(3) m. In contrast, the scale-d ependence of hydraulic conductivity in the poorly consolidated Holocene aqu ifer is much less marked, being independent of scale above 10(0) m. Core sc ale conductivities of the Pleistocene aquifer are much less than those in t he Holocene because of pore occlusion by cementation, but the development o f linked vug porosity, fissure and cavernous porosity along paleo-exposure horizons gives higher hydraulic conductivities at larger scales. We suggest that the observed scale dependence is related to the existence of a range of void types (termed characteristic conductive elements) with aperture and connectivity increasing, and abundance decreasing with sample scale. (C) 2 000 Elsevier Science B.V. All rights reserved.