Step-drawdown test as a tool for the assessment of the Nubia sandstone aquifer in East El-Oweinat Area, Egypt

The Cretaceous Nubia sandstone aquifer is the main aquifer in East El-Oweinat area along the Egyptian–Sudanese borders and in NE Africa. East El-Oweinat project has been recently considered one of the main agricultural projects in the southwest of the Egyptian Western Desert. So, the hydrogeological assessment for the Nubia aquifer in East El-Oweinat area has been done through studying and characterising the hydraulic parameters and step-drawdown test. The well and aquifer losses coefficients (C and B, respectively), the specific capacity, and the well efficiency as well as the aquifer and aquitard thickness have been estimated and traced through a total of 46 wells that have been distributed through the study area in two sectors, southern and northern. For the purpose of further exploration, the effective porosity (∅), hydraulic conductivity (K), and transmissivity (T) have been estimated for the wells in the northern sector. In addition, an aquifer assessment quality index has been introduced to assess and to rank the studied aquifer. Therefore, it is concluded that the hydraulic and the step-draw down parameters as well as the aquifer and aquitard thicknesses are prospective for further exploration to the north and the east of the northern sector in the study area. The well efficiency is mostly affected by the studied parameters, particularly the well loss coefficient, the hydraulic parameters and the well design as well. GIS approach and ArcGIS software have been applied to delineate the spatial distribution of the well performance characteristics, in order to compare between the studied groundwater wells and to integrate the different-acquired data. A set of isocontour maps have been introduced to match the lateral variation of the studied parameters and the aquifer potential to refer to the best direction for further underground water exploration.