No abstract

Abstract. Discrete fracture network (DFN) models generally require solution of flow and transport equations in three-dimensional networks of either disc, polygonal, or pipe elements. Pipe network elements have significant advantages in computation for both flow and transport. However, there is a need to develop an efficient procedure for derivation of the properties of these pipes to ensure that they are hydraulically equivalent to the DFN network of polygonal elements. In this study a boundary element procedure for derivation of pipe properties is developed and demonstrated. The results show that the hydraulic behavior of pipe networks can be equivalent to that of polygonal-element DFN models. IntroductionThree-dimensional discrete fracture network (DFN) models are becoming accepted as a tool for modeling heterogeneously connected rock masses [Dershowitz and Einstein, 1988; Reeves et al., 1994]. DFN models provide a useful alternative to continuum approaches where discrete feature geometry and connectivity play a major role.Recent research has focused on ways to improve the efficiency of DFN models, which can be constituted by of the order of 105 or even 10 6 polygonal or disk-shaped fractures. In the proposed approach the conductance is estimated by means of the boundary element method (BEM) as an influence factor between each trace. This provides a better approximation than the qualitative relationship, because the BEM can be formulated to produce conductance values that are consistent with the flow pattern within each fracture.As a first approximation, conductances might be calculated 2685

The water level of the Dead Sea, a terminal hypersaline lake (total dissolved solids, approximately 340 g/L) has decreased at an average rate of 0.5 m/yr since 1960 and by 0.8 m/yr between 1981 and 1989. The dramatic long-term water level variation of the Dead Sea and the seasonal short-term fluctuations are accompanied by parallel variations of groundwater levels in an adjacent aquifer. A general methodology based on a simplified yet reliable one-dimensional flow model, together with continuous measurements of groundwater levels in observation wells, enables analysis of aquifer structural and hydraulic properties. Furthermore, this analysis enables prediction of future groundwater levels in unconfined and confined aquifers due to future changes in lake levels. Introduction Closed basin-terminal lakes are special types of lakes known to exist in many arid parts of the world including, for example, Great Salt Lake in the United States [Spencer et al., 1985], Lake Magadi in Africa [Eugster, 1970], and the Dead Sea in Israel [Neev and Emery, 1967]. (A closed basin lake is generally defined as a lake without any surface outlet. A terminal lake is defined in this work as a closed basin lake which is a sink for both surface water and groundwater. A flow-through lake is generally defined as a lake containing inlets and outlets.) The volumes and water levels of these lakes have varied throughout their history, mainly due to climatic effects. The hydraulic response of the adjacent groundwater to these changes has been studied for flow-through lakes [e.g., Winter, 1978, 1983; Cherkauer and Zager, 1989; Krabbenhofi et al., 1990; Evans et al., 1991; Sacks et al., 1992; Anderson and Cheng, 1993] and for river flows and streamflows [e.g., Hall, 1968; Pinder et al., 1969; Hall and Moench, 1972; Moench et al., 1974; Reynolds, 1987] but rarely analyzed for the case of a terminal lake [Almeno dinger, 1990]. For a terminal lake, Almendinger [1990] proposed a simple theoretical model that considers a circular closed basin lake, which operates as a large pumping well due to evaporation. Another relevant work, though conducted in a coastal aquifer near the ocean, was completed in Australia [Love, 1991] where changes in groundwater level are assumed to be the result of changes in sea levels, on a timescale of thousands of years. The water level of the Dead Sea, a terminal hypersaline lake, has decreased at an average rate of 0.5 m/yr since 1960. The long-term water level variation of the Dead Sea and the seasonal short-term fluctuations are accompanied by parallel variations of groundwater levels in an adjacent aquifer which is an •Geological Survey of Israel, Jerusalem. 2Department of Environmental Sciences and Energy Research, Paper number 94WR03154. 0043-1397/95/94 WR-03154505.00 ET AL.: WATER LEVELS OF DEAD SEA AND AN ADJACENT AQUIFER Yechieli, Y., The effects of water level changes in closed lakes (Dead Sea) on the surrounding groundwater and country rocks, Ph.D. thesis, Weizmann Inst. of Sci., Rehovot, Israel, 1993.

No abstract

No abstract