The use of remote sensing and GIS for the estimation of water loss from Tushka lakes, southwestern desert, Egypt

As a result of the spill-over of the excess water from lake Nasser, the great reservoir formed by the Aswan High Dam on the Nile, the Tushka lakes came into being within natural geological depressions in the southeastern part of the western desert of Egypt. By the end of 1998, the water of river Nile had entered Tushka depressions for the first time, once lake Nasser's water level had exceeded 178 m above the mean sea level. Intermittently, water continued to discharge into the depressions until the end of 2001 forming four lakes; however, the lakes began to shrink because of the inconsistency of flooding levels. The behavior of hydrological regime of these lakes during the period 2002-2006 was assessed using an integration of remote sensing and GIS techniques, which found that the total surface area of the lakes had diminished from 1591 km(2) to 937 km(2), and their water volumes reduced from 25.26 billion m(3) to 12.67 billion m(3). The study further revealed that the levels of the lakes surfaces had lowered by approximately 10 m over the course of those four years. This significant rate and volume of water loss can be attributed to both evaporation and infiltration. A comparison between the average annual evaporation rate at Tushka lakes and the calculated water loss revealed that most of Tushka lakes' water is lost through evaporation with a very limited amount being percolated to the ground water. Assuming that no further over flooding of the Nile will occur, these lakes will start to vanish in 2012 and disappear completely by 2020, which will result in significant environmental impacts. (c) 2008 Elsevier Ltd. All rights reserved.