HYDROLOGIC IMPACTS OF LAKE NASSER AND THE TUSHKA LAKES ON THE NUBIAN AQUIFER IN SW EGYPT

Water shortage in the Middle East could affect human welfare, economic activities, and stability in the region. Egypt and other arid and semi-arid countries have adopted aggressive policies to capture surface water resources for reclamation of desert land. The Aswan High Dam, constructed in Egypt in 1964-1968, created the world's second largest artificial lake, Lake Nasser. Recently, as the reservoir has approached maximum storage capacity, several new lake reservoirs (Tushka Lakes) have developed in the lowlands west of Lake Nasser. Using a groundwater flow model, we investigated the dynamic change of the Nubian aquifer related to the development of Lake Nasser and the Tushka Lakes.

To fully capture interactions between the surface and groundwater in the study area, the model domain included the area covered by the entire Lake Nasser in Egypt and Sudan, the Tushka Lakes, and their surroundings. The stages and the temporal variations (1967-2002) in the areal extent of the lakes under investigation were extracted from CORONA, Landsat TM, and DTED data and from recorded (1967-2000) surface water levels for Lake Nasser. The topography of the area now covered by water in Lake Nasser was estimated from (1) the areal extent of Lake Nasser in 1967 (CORONA) and 1972 (MSS), (2) DTED acquired in 1989, and (3) historic lake levels.

Transient simulations suggest that the Nubian aquifer, a fossil groundwater reservoir, is significantly affected by recharge from Lake Nasser and the Tushka Lakes. To date, the recharge from Lake Nasser to the aquifer amounts to 10⁹ m³. After the lake reached maximum storage capacity, annual recharge decreased from 10⁷ m³/yr in 1996 to 10⁶ m³/yr in 2002. The trend of decreasing recharge is consistent with the gradual reduction of hydraulic gradient between the lake stage and the groundwater level in the Nubian aquifer. Since 1998 excess water in Lake Nasser has been routed through existing flood diversion to the Tushka Lakes. The recharge from these lakes to the Nubian aquifer has been rising (10⁵ m³/yr in 1998 to 10⁶ m³/yr in 2002); currently, recharge from the Tushka Lakes approximates recharge from Lake Nasser. Continuous encroachment of Lake Nasser water onto the lowlands could increase opportunities for sustainable use of fossil water of the Nubian aquifer, now being replenished by Lake Nasser.