Abstract: Despite that fractured coastal aquifers are widespread, the influence of fracture characteristics on seawater intrusion (SWI) has not been explored in previous studies. This research uses numerical modelling in a first step towards understanding the influence of fracture orientation, location and density on the extent of seawater and accompanying patterns of groundwater discharge in an idealised coastal aquifer. Specifically, aquifers containing single fractures or networks of regularly spaced fractures are studied using modified forms of the Henry SWI benchmark problem. The applicability of equivalent porous media (EPM) models for representing simple fracture networks in steady-state simulations of SWI is tested. The results indicate that the influence of fractures on SWI is likely to be mixed, ranging from enhancement to reduction in seawater extent and the width of the mixing zone. For the conceptual models considered here, vertical fractures in contact with the seawater wedge increase the width of the mixing zone, whereas vertical fractures inland of the wedge have minimal impact on the seawater distribution. Horizontal fractures in the lower part of the aquifer force the wedge seaward, whereas horizontal fractures located within the zone of freshwater discharge enhance the wedge. Inclined fractures roughly parallel to the seawater-freshwater interface increase the landward extent of seawater and fractures perpendicular to the interface inhibit the wedge. The results show that EPM models are likely inadequate for inferring salinity distributions in most of the fractured cases, although the EPM approach may be suitable for orthogonal fracture networks if fracture density is high and appropriate dispersivity values can be determined.

Abstract: One of the major causes for the deterioration of water quality bearing heavily on the water crisis in Israel is the ongoing contamination of its water resources by saline water bodies. The present paper reviews the geochemical processes forming saline water, lists and explains certain chemical and isotopic parameters which enable understanding these processes and describes the saline groundwater bodies and various salinization phenomena occurring in the country’s various aquifers. Deterioration of groundwater in Israel is caused by numerous natural processes such as encroachment of sea water, migration of connate, highly pressurized brines penetrating into fresh groundwater, by subsurface dissolution of soluble salts originating in surrounding country rocks and by water-rock interaction. In addition to sea water, two saline water bodies were identified as the main factors causing salinization of fresh groundwater: (a) Ca-chloride brines encountered in the Jordan-Dead Sea Rift Valley, in various parts of the Negev and of the Coastal Plain, and (b) Na-chloride saline water identified in the subsurface of the Negev and in the southern part of the Coastal Plain. Intensive exploitation of groundwater in Israel has disturbed the natural equilibrium which prevailed between fresh and saline water. The newly established groundwater flow regimes have facilitated the migration of saline water bodies, their participation in the active hydrological cycle and the progressive contamination of fresh groundwater. These processes which were not anticipated by planners and water resources managers emphasize that large-scale groundwater exploitation was undertaken without giving sufficient consideration to the occurrence and subsurface migration of saline water and brines.

Abstract: The southern Coastal Plain in Israel incorportates a transitional fringe of the desert in which three different chemical types of groundwater are found: (1) near-surface waters from springs along the Besor River course: (2) shallow- to moderate-depth waters from the slightly westward-dipping Pleistocene coastal aquifer (this aquifer, which consists of sandstone layers of the Kurkar Group, is recharged in the Coastal Plain); and (3) deep waters of the westward-dipping Upper Cretaceous Judea Group carbonates, which are recharged in the mountains in the east. A thick aquiclude of Upper Cretaceous-Tertiary rocks separates the Judea Group aquifer from the overlying coastal aquifer in the southern Coastal Plain. Isotopically light oxygen and depleted deuterium characterize the Judea Group waters, as expected from high-altitude recharge. The isotopic composition of the Coastal Plain waters is variable, but for the most part enriched in 18O and D. Within the southern Coastal Plain aquifer a southern subgroup comprises waters more depleted in heavy isotopes than those of either the northern or eastern subgroups. The Besor waters are isotopically similar to the Judea Group waters, reflecting their origin in the mountain region, and flow through the surficial river gravels and sands. It is suggested that leakage of the Besor waters into the underlying southern Coastal Plain aquifer results in mixing of the two water types. The most prominent chemical feature characterizing the groundwater of the southern Coastal Plain is Na+Cl− \textgreater 1. This Na+Cl− ratio can be maintained only by a continuous input from a non-marine source of Na. The most plausible source of this Na is the dissolution of feldspar derived from the windblown loess deposits which cover the area and/or leaching of trona minerals found in the unsaturated zone, combined with base-exchange processes.