Reconstruction of natural groundwater flow paths in the multiple aquifer system of the northern Negev (Israel), based on lithological and structural evidence

 The Judea Group, a limestone and dolomite karstic aquifer of late Albian–Turonian age, is one of the most important sources of water in Israel. In the western part of the country, the Judea Group aquifer is also known as the Yarkon–Taninim basin. In the northern Negev, the Judea Group is a recipient for fresh water flowing southward from the Hebron Mountains and of brackish paleowater flowing northward from Sinai. Very little is known of the hydraulic properties of this aquifer. In order to outline assumed natural flow paths that existed in this karstic environment prior to groundwater exploitation, use was made of lithological, structural, and paleomorphological features. A detailed hydrogeological conceptual model of the Judea Group aquifer in northern Negev was established by the geological interpretation of high-resolution seismic reflection and by analysis of lithological evidence from boreholes. Isopach, isolith-contour, and isolith-ratio maps were compiled for the main lithological components. Increase in transmissivity values is inversely proportional with the cumulative thickness of argillaceous components. The lithological and hydraulic evidence provides the basis for subdividing the subsurface into distinctive permeability zones for the upper and lower sections of the aquifer; for outlining possible preferential groundwater flow paths for both subaquifers; and for improving understanding of groundwater-salinty variations that result from lithological variability, direction of groundwater flow paths, groundwater flow rates, and the duration of rock/water interactions. In an earlier conceptual model of the basin, the Judea Group aquifer was regarded as a continuous and undisturbed entity. The present study reveals an intricate groundwater flow pattern that is controlled by lithological and structural factors that create zones of preferential flow. This interpretation bears on the overall evaluation of groundwater resources and their management and exploitation. Received, December 1996 · Revised, October 1997, June 1998 · Accepted, July 1998