The respective roles of modern and paleo recharge to alluvium aquifers in continental rift basins: A case study from El Qaa plain, Sinai, Egypt

Even though assessment of aquifer characterization and recharge mechanisms in rift-related basins, especially in arid environments, is essential for developing sustainable management strategies and food security assurance, a little attention has been paid to understand these parameters. In this manuscript, we utilize an integrated remote sensing, hydrological and isotopic approach together with previously published data to better understand the aquifer characteristics and the respective roles of modern and paleo recharge to the post-Miocene alluvium aquifer in El Qaa plain, which represents the eastern margin of the Gulf of Suez continental rift basin. Our findings indicate that: (1) the alluvium aquifer is largely formed of sand and gravels intercalated with silt and clay lenses and exceeds 500 m thick, (2) the groundwater salinity gradually increases towards the Gulf of Suez (from 402 to 5613 mg/l) with increasing the distance from the crystalline rocks bounding the alluvium-dominated plain, (3) isotopic analysis reveals that all of the groundwater samples show mixed isotopic signature between modern and paleo waters (δ 18 O: −6.79 to −4.433‰, and δ 2 H: −46.36 to −21.99‰). Basin-scale hydrological parameters show that the aquifer receives an annual modern recharge of 39 × 10 6  m 3 and isotopic mass balance calculations indicate that the modern water ranges between 20 and 70% of the total volume of water in the aquifer. We suggest three dam locations along the southernmost basins in El Qaa plain to enhance the modern recharge to the aquifer and to harvest surface runoff of an annual volume of 737 × 10 3  m 3 sufficient to supply freshwater to 13 thousands of the residents of south Sinai. The present study suggests that topographically-driven modern recharge to rift-related basins is taking place with significant amounts even under hyper-arid conditions and calls for paying special attention to investigate the response of these aquifers to climate variability.