IS THE NUBIAN SANDSTONE AQUIFER SYSTEM BEING DEPLETED?

The Nubian Sandstone Aquifer System (NSAS) covers large territories (area: 2 × 10⁶ km²) in four countries: Sudan (17%), Libya (34%), Chad (11%), and Egypt (38%). The NSAS comprises two interconnected major basins: the Kufra Basin in Libya, Sudan, and Chad and Dakhla Basin in Egypt. In this study, we are developing and applying an integrated cost-effective approach to understand the hydrologic setting of the NSAS and the factors (i.e., natural and/or anthropogenic) controlling it evolution. In this understanding we are trying to answer these questions: (1) is the NSAS used in a sustainable manner, or it is being depleted? (2) if the latter is true, how long could it be used and what would the optimum extraction rates be?

Analysis of the Gravity Recovery and Climate Experiment (GRACE)-derived Terrestrial Water Storage (TWS) inter-annual trends over the NSAS revealed an area of significant TWS depletion (1.3 ± 0.66 × 10⁹ m³/yr) that is correlated with the Dakhla Basin in Egypt. Findings include (1) excessive groundwater extraction, not climatic changes, is responsible for the observed TWS depletion; (2) we estimate that the Dakhla Basin in Egypt, if mined at present extraction rates, could last for a period approaching 4000 years. If, instead, we were to adopt the projected rates of artificial extraction in 2070 (2.8 × 10⁹ m³/yr) and the present natural discharge rates (0.506 × 10⁹ m³/yr), it will be consumed in less than half this period (1500 years), and in an even shorter time period (350 years) if the extraction rates continue to double every 50 years; and (3) observed depletions over the Dakhla Basin and their absence across the remaining segments of the NSAS suggest that the aquifer is at near-steady conditions except for the Dakhla Basin that is witnessing unsteady transient conditions. Implications for applying the methodologies advocated for assessment and optimum management of a large suite of fossil aquifers worldwide are clear.