MODERN CONTRIBUTIONS TO THE NUBIAN AQUIER, SINAI PENINSULA: GEOCHEMICAL, GEOPHYSICAL, AND MODELING CONSTRAINTS

The deserts of Egypt, namely the Eastern Desert (ED), the Western Desert (WD), and the deserts of the Sinai Peninsula (SP) are amongst the most arid deserts in the world (WD, receiving <5 mm/yr; ED: 30 mm/yr; SP: 60 mm/yr); however, the geologic evidence indicates that climate alternated between arid and wet periods throughout the Quaternary, and the last of the major wet periods occurred during the Holocene (9500 to 4500 yr BP). It is believed that the Nubian Aquifer in the WD, ED, and SP was recharged in the previous wet climatic periods. While this statement is true for the WD, it is not for the ED and Sinai. In dry climatic periods similar to the ones we are witnessing today, the Nubian Sandstone (NSS) Aquifer in the Western Desert of Egypt is receiving no local recharge because negligible rain is precipitating. That is not apparently the case in the ED and more so in the Sinai Peninsula. In both areas, precipitation over the mountains is channeled downstream over the NSS cropping out at the foothills of the Red Sea hills providing ample opportunities for groundwater recharge. The conceptual model outlined above has been successfully tested in the SP using geophysical, isotopic, and rainfall-runoff modeling. Interpretations of conventional Electrical Resistivity (ER) profiles is consistent with the presence of unconfined Nubian Sandstone saturated aquifers flooring recharge areas at the foothills of the crystalline basement in Sinai at the Baraga (thickness: 65-100m; resistivity: 100-125 ohm.m) and Zalaga (thickness: 20-166.7-m; resistivity: 25-130 ohm.m) locations. The isotopic composition of groundwater samples from wells tapping Nubian aquifer underlying recharge areas (δD: -22.7 to -32.8‰) is consistent with these waters being mixtures of two end members: (1) fossil Nubian groundwater with compositions similar to the WD Nubian samples (δD -72 to -81‰) and, (2) modern meteoric precipitation (δD -19.9 to -22.5‰) now residing in fractured basement in the SP. The average annual modern recharge over the Nubian aquifer was assessed at 3.2 x 10⁵ m³/yr applying the SWAT (Soil Water Assessment Tool) Hydrologic Model.