Surface–groundwater alteration under GERD operations: implications for recharge and groundwater sustainability in the eastern Nile Delta aquifer

ABSTRACT

Infographic showing the potential impacts of rapid GERD reservoir filling on Egypt’s Eastern Nile Delta aquifer, including a 12%–14% decline in canal water levels, up to 53% reduction in aquifer recharge, and groundwater declines of up to 7.7m, leading to seawater intrusion, groundwater depletion, and water shortages. Integrated Nile Basin management is highlighted as a mitigation strategy.

Egypt relies on the Nile River for about 97% of its freshwater, with groundwater acting as a critical supplementary resource in its arid environment. The construction and operation of the Grand Ethiopian Renaissance Dam (GERD) pose substantial risks to downstream water availability, particularly in the eastern Nile Delta aquifer (ENDA), where recharge is strongly dependent on Nile flows and irrigation canals. This study employs the MODFLOW model to assess the impacts of four GERD filling scenarios (reservoir levels of 616, 628, 637, and 646 m a.m.s.l.) on groundwater dynamics. Results show that GERD operations reduce the active storage of the Aswan High Dam, leading to declines of 12%–14% in river discharge and canal water levels. Consequently, aquifer recharge decreases by 12%, 25%, 39%, and 53%, while groundwater heads drop by 7.70, 6.37, 3.79, and 2.35 m, respectively. These changes reveal a strong linkage between reduced surface water availability, diminished irrigation return flows, and groundwater depletion, increasing the risk of seawater intrusion. The findings underscore the need for integrated water management, adaptive canal operations, and strengthened transboundary cooperation to ensure Egypt's long-term water security.