Groundwater Conditions and the Geoenvironmental Impacts of the Recent Development in the South Eastern Part of the Western Desert of Egypt

摘要

The area to the southeast of the Western Desert of Egypt has been subjected to considerable development activities over the last few years. The development includes the cultivation of about 2260 km2 of the desert lands "the well-known Toshka Project". The hydrogeological conditions of the area are subjected to detailed investigation based upon the construction of the water table maps, hydrologeologic cross-sections, pumping tests, aquifer geometry, and recharge-discharge relationship. The study revealed that the Quaternary and the Nubia sediments are the main water bearing layers in the area. The Quaternary aquifer is of limited potential and made of mixed sand with clay deposit ranges in thickness between 5 to 10 m. The Nubia aquifer is the oldest sedimentary formation and the main groundwater resources in the area. It is represented by multilayered of sand and silt exists generally under artesian conditions. It is composed of three water bearing horizons partially separated by two confining horizons and extends in thickness ranges between 70 and 230 meters. The thickness increases away from the high dam lake. The analysis of pumping tests of the aquifer indicated that its potentiality is increasing north of the High Dam Lake (HDL) whereas it decreases in the other direction. This is due to high hydraulic conductivity and aquifer thickness in the area northeast of Khor Toshka and at west of Garf Hussein. The hydraulic conductivity of the aquifer ranges between 12.73 and 0.9 m/day. The review of the changes in groundwater levels in the area showed that there is a drop in ranges between 1 and 14 meters in the last few years indicating that the extraction from the groundwater is much more higher that the replacement rate. Also, the analysis of the fluctuation of water levels of the HDL and the groundwater level indicated that the influence of water on groundwater level in the area is observed only at a distance less than 10 km from the lake shore line. Seepage from the HDL is estimated as 238.13 × 10~6 m~3/year. The geo-environmental impacts of the development on the surface water and ground-water in the area are evaluated.