Environmental Isotopes as a Tool in Hydrogeological Research in an Arid Basin

Stable and radioactive isotopes (deuterium, tritium, ¹⁸O, ¹⁴C) were used as an aid for better understanding the regime of recharge and flow in ground water in the Wadi Feiran basin in the southern Sinai. The annual average precipitation in the Sinai basin is between 80 mm in its upper reaches and 15 mm in the lower regions. In the upper part, underlain by crystalline rocks, ground water was found in shallow and deep fractures as in shallow alluvial deposits. The quality of water in the shallow fractures showed little effect of evaporation in relation to precipitation, which shows that recharge occurs directly and quickly through the open fractures. In the middle part of the basin, water in the riverbed alluvium was found to be recharged mainly by flood water and discharged also through deep fractures. In the lower part of the basin, the ground water was found to flow into the alluvial plain at A‐Tor. Part of it mixes with paleo‐water and emerges as thermal springs.