Vol.:(0123456789) 1 3 Environmental Earth Sciences (2019) 78:375 https://doi.org/10.1007/s12665-019-8375-0 ORIGINAL ARTICLE Step‑drawdown test as a tool for the assessment of the Nubia sandstone aquifer in East El‑Oweinat Area, Egypt Bassem S. Nabawy 1 · Ahmed Abdelhalim 2 · Ahmed El-Meselhy 1 Received: 10 October 2018 / Accepted: 17 June 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract 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 coefcients (C and B, respectively), the specifc capacity, and the well efciency 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 efective 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 efciency is mostly afected by the studied parameters, particularly the well loss coefcient, 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 diferent-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. Keywords East El-Oweinat · Transmissivity · Hydraulic conductivity · Aquifer losses · Well efciency · GIS system Introduction East El-Oweinat project, to the East of Gebel El-Oweinat, is one of the most important development agricultural projects in Egypt. It is located at the far southwestern part of Western Desert of Egypt (Fig. 1). The area is bounded by Dakhla and Kharga Oases to the north, the Egyptian-Sudanese borders to the south, Lake Nasser and Toshka Lakes to the east, as well as Gebel El-Oweinat and El-Gilf El-Kebir plateau to the west. The study area is located between latitudes 22°41′12″N and 22°51′12″, and longitudes 28°24′12″ and 28°34′12″E, covering an area of 384 km 2 (about 94,888 feddans, Fig. 1). The Nubia sandstone is among the highly porous and permeable rock sequences in Egypt and is considered the main strategic producing aquifers in North Africa. Its age and classifcation are a matter of controversy due to its bareness of fossils and similarity in the mineral compo- sition (Nabawy et al. 2009, 2010; Nabawy and Géraud 2016). It has been studied in its type sections by many workers, e.g. Said (1962), Issawi (1973), Klitzsch (1979, 1984), Issawi and Jux (1982), Hendriks (1988), Issawi and Osman (1993), Thabit (1994), Nabawy et al. (2009, 2010), etc. In general, it is composed of Cretaceous varicolored fne- to medium-grained sandstone intercalated with some water-bafe to barrier beds (aquitard) of clays, shale and siltstones. These rock sequences have sufered from a long arid periods which increased their fnal porosity and per- meability. Therefore, their storage and fow capacity have * Bassem S. Nabawy bsnabawy@yahoo.co.uk 1 Department of Geophysical Sciences, National Research Centre, Cairo, Egypt 2 Geology Department, Faculty of Science, Cairo University, Giza, Egypt