Development and Distribution of Permeability in Carbonate Aquifers

Abstract

Unlike aquifers in nonsoluble rocks in which the permeability tends to be both inherent and fairly even in local distribution, aquifers in carbonate rocks tend to have their permeability developed through circulation of water and solution of the rock and to have an uneven distribution of permeability. The extent to which near‐surface carbonate rocks have permeability developed in them depends on the degree to which water that is high in dissolved carbon dioxide has moved through joints and other openings to places of discharge.The following well‐established generalizations indicate that the geometry of carbonate aquifers is commonly different from that of other aquifers. (1) The circulation of water and solution activity tend to be greatest in the upper part of the zone of saturation and tend to lessen with increased depth. (2) The moderately large openings in the path of bulk flow of groundwater tend to enlarge by solution action; contrastingly, the small openings not in the path of bulk flow enlarge only slightly. The texture of permeability in a few carbonate aquifers is fine and even but in most carbonate aquifers is more commonly coarse and uneven. Where the texture of permeability is fine and fairly even, as in the Biscayne aquifer of southeastern Florida, the aquifer may be riddled with a close network of solution channels or interstitial openings. Where the texture of permeability is coarse and uneven, ramifying solution channels are bounded by a large volume of relatively dense impermeable carbonate rocks. The channel network system is especially prominent in the upper part of the zone of saturation. In many cases the gross permeability seemingly decreases exponentially with increasing depth. The dynamic water table, becoming flatter and moving lower as permeability increases, is bounded above by a cavernous unsaturated zone that is a relic of the former permeable zone of saturation. With passing geologic time, the solution channel network loses its aquifer characteristics when (1) the water table moves downward to the base of the aquifer, (2) the cavernous rocks are destroyed by erosion, or (3) the aquifer becomes buried under later deposits and lies below the groundwater circulation system. The history of some carbonate aquifers includes early development under water table conditions, burial and preservation under later deposits, resurrection, and reactivation in the modern groundwater circulation system. Observable or discernible recognition can be made of (1) aquifers having fine textured permeability, (2) aquifers having coarse textured permeability, and (3) aquifers that have been resurrected and are now reactivated; each type of aquifer has distinctive characteristics that help in hydrologic evaluations of carbonate rock systems.

Fluid flow in the Chalk of England

“…Other workers (Swinnerton 1949;Legrand & Stringfield 1971) have agreed with this mechanism of development, in which it is assumed that the aquifer is initially homogeneous and isotropic. Uniformly fractured chalk approximates tolerably well to this ideal and possesses many of the characteristics of the 'fine-textured carbonate aquifer' of Legrand & Stringfield (1971).…”

“…Uniformly fractured chalk approximates tolerably well to this ideal and possesses many of the characteristics of the 'fine-textured carbonate aquifer' of Legrand & Stringfield (1971). Clearly, however, minor natural variations in the initial primary fissure spacings and apertures--including any variations related to the presence of the valley--will cause departures from the ideal case of Fig.…”

“…As permeability increases, the water table becomes flatter and moves downwards (Legrand & Stringfield 1971). Progressive erosion and lowering of the valley floor will similarly lead to a lowering of the water table.…”

Fluctuation of NO3-N in groundwater of the reservoir of the Sunagawa Subsurface Dam, Miyako Island, Japan

“…Moderately large openings serving as inlets for the infiltration of rain into the unsaturated zone tend to enlarge by solution; in contrast, small openings not connected to the infiltration pathway enlarge only slightly (Legrand and Stringfield 1971). Consequently, the unsaturated zone of limestone has both micropores and macropores.…”

Simulation of the development of karst aquifers: role of the epikarst

“…During the past decades a large number of publications have dealt with the elucidation of these processes. Until 1980, conceptual models for the development of karst aquifers were presented, e.g., by Mandel (1966), White (1969), LeGrand and Stringfield (1971), Palmer (1975), and Ford and Ewers (1978). After the dissolution kinetics of calcite had been quantified (Berner and Morse 1974;Plummer et al 1978;Buhmann and Dreybrodt 1985a, b), one-dimensional numerical models were developed in order to simulate the enlargement of a single fracture (Dreybrodt 1990, Palmer 1991.…”