Investigating the Interaction Between the High Aswan Dam Reservoir and Nubian Aquifer Under Increasing Nile Upstream Damming

Nile downstream countries, particularly Egypt, which depend on the Nile as their primary water resource, face a water budget deficit due to increasing consumption, hydroclimatic changes, and upstream damming (i.e., the Grand Ethiopian Renaissance Dam (GERD)). To address these challenges, Egyptian authorities introduced new management strategies for the High Aswan Dam Reservoir (HADR), the third largest artificial reservoir globally, is proposed to develop new agricultural areas. However, the interconnectivity between the HADR and the fossil Nubian aquifer, Africa's largest transboundary aquifer, remains speculative due to a lack of in situ investigations. To address this gap, we constructed a hydrogeological flow model to simulate HADR-Nubian Aquifer interaction under various upstream damming operation and flow condition scenarios, using the Moldflow model, incorporating geological, geophysical, and hydrogeological data. Our results indicate that the water-saturated normal faults serve as preferential flow pathways connecting the HADR to the Nubian Aquifer, potentially facilitating bidirectional water exchange depending on relative hydraulic head gradients. Our findings underscore forthcoming challenges for this linkage if the level of the HADR falls below approximately 160 m above mean sea level due to unmanaged upstream damming operations during the Nile’s extended drought periods. Under these conditions, the Nubian Aquifer's pressure head could surpass the HADR's reservoir head, resulting in aquifer discharge back into the HADR. This would alter the aquifer's water budget and compromise the planned agricultural developments in the adjacent areas, which constitute approximately 10% of Egypt's total arable land. These findings support a cooperative transboundary water management agreement that considers maintaining HADR water levels above critical thresholds to ensure both agricultural development and long-term aquifer sustainability across the Eastern Nile Basin.