Modern and fossil groundwater in an arid environment: A look at the hydrogeology of Southern Oman

The Sultanate of Oman has, in recent years, made substantial advances in its agricultural sector, with an increasing reliance on groundwater resources for irrigation. The Public Authority for Water Resources (PAWR) has developed considerable understanding of groundwater availability and quality through comprehensive exploration programmes, including a nationwide survey of enivronmental isotopes in groundwaters, surface waters, and precipitation. The aim of the isotope study was to provide estimates of mean residence times of groundwaters and define their recharge sources. This paper discusses the results of our studies of the extensive and relatively undeveloped aquifers in the southern 'Dhofar' region of Oman. Precipitation systems are discussed as potential groundwater recharge sources. Groundwaters within the interior desert or 'Najd' Region were intensively studied with additional focus on groundwaters in the Salalah Plain and Dhofar Mountains. The shallow, phreatic aquifers in the Najd were found to contain modern, tritiated waters recharged by infrequent storms. The deeper aquifers, which outcrop in the mountains to the south, contain groundwaters under flowing artesian pressure, which without exception were found to be fossil (mean residence times from 4000 to 30,000 years BP). The older age estimates were found in the northern Najd, further from the recharge area. Stable isotope data indicate that the recharge source was unlike the current monsoon which occurs today in the Dhofar Mountains. More likely, rainstorms during pluvial periods in the past were the recharge source to these aquifers. (author). 11 refs, 9 figs, 2 tabs