English abstract
Nejd area is the driest region of Oman and is underlain by the aquifers of Tertiary age. The water resources of this vast area have until recently been largely ignored and poorly understood. This water is an important resource and its careful development could sustain a significant amount of irrigated agriculture over an extended period of time. A detailed hydrogeologic evaluation based on potentiometric, hydrochemical, and well hydrograph data was made.
Three principal aquifers appear to exist within the Nejd area. They are located within the Dammam and Rus Formations (Aquifer A), the Upper Umm Er Rhaduma Formation (Aquifer B), and the Lower Umm Er Rhaduma Formation (Aquifer C), at depths ranging between 16 to 280 m below ground surface. The major aquifer horizons are normally associated with limestone units. In most cases their permeability is enhanced in varying amounts by solution channelling thus making them anisotropic. Aquifer transmissivities as a result vary greatly, ranging between 10 m/day to 8,300 m2/day.
The findings based on the geologic and hydrologic data collected such as stratigraphic, hydraulic parameters, and well construction detailed show that Aquifer A is an unconfined aquifer, Aquifer B is generally a confined aquifer although it is semi-confined in some areas and Aquifer C is confined over the entire Nejd, with flowing artesian conditions prevailing in the north and north-west portions. Water quality in the Nejd varies substantially, but the general trend for all aquifers display an increase in salinity towards the north and northeast. The trend corresponds to the groundwater flow direction and probably reflects increasing residence time and dissolution of salts into the groundwater. There is no distinct chemical type associated with the different Nejd aquifers. However, more saline waters tend towards the Nat- Cl" type and several waters from Aquifers A and B, north of Thumrait, are of the Na-S04" type.
