The current study aimed to evaluate hydrogeologically the Nubian sandstone aquifer in El-Bahariya Oasis. It represents the main water-bearing horizon in the study area and consists of continental elastic sediments, mainly sandstone alternating with shale and clays. The general flow lines are directed from SW to NE direction, as detected from the constructed potentiometric head contour
map. The piezometric surface reaches 149 m in El-Heiz area at the southern part, while it reaches 90 m at the northern, reflecting higher pressure head of the aquifer in the southern part. The map also illustrates that the southern part is considered as the most promising location for development. The structural elements play an important role in the deposition and distribution of the sedimentary
succession of the Nubian sandstone sediments. Consequently, this sedimentary pattern affects the occurrences and movements of the groundwater within the aquifer system. Along the structurally high areas, in the study area, the piezometric head increases, while the reverse is recorded along the structurally low areas. The stepdrawdown tests data were carried out by calculating the
aquifer loss coefficient (B) and the well loss constant (C).
The B values are smaller compared with C values,indicating that the aquifer under pressure has a behavior of leaky aquifer; therefore, it shows hydraulic connection with surrounding formation. The values of well efficiency range from 78.50% to 87.76%. Analysis of 12 pumping test data (constant discharge tests) was carried out in order to calculate the Nubian aquifer hydraulic parameters (transmissivity, hydraulic conductivity, and storage coefficient). The transmissivity values decrease from 3,045 m2/day in the southern part (El-Heiz area) to 236 m2/day in the northeastern
part (El-Harra area). Accordingly, the aquifer classified as a
high to moderate potentiality. Transmissivity contour map
observes gradual increase of transmissivity values from the
southern to northeastern direction. This may be due to the
increase of shale or clay content in the concerned aquifer in
that direction. The storage coefficient values range between
1.04 × 10−4 and 5.22×10−3, as obtained from the results of
pumping test analysis, which ensure that the Nubian
sandstone aquifer is classified as semi-confined to confined
aquifer type. TheSvalues show a decrease from southwest to
northeast direction as detected from S-map. The hydraulic
conductivity values vary from to 0.46 m/day in the northern
part to 10.88 m/day in the southern part with an average of
5.67 m/day. According to the classification based on K
values, the aquifer is mainly composed of coarse sand.