Discussion
Discussion on "Influence of structures on drainage patterns in the Tushka region, SW Egypt. Journal of African Earth Sciences 136, 262–271" by C.A. Robinson, H. El-Kaliouby, E. Ghoneim

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Abstract

The publication entitled Influence of structures on drainage patterns in the Tushka region, SW Egypt, Journal of African Earth Sciences 136 (2017) 262–271, introduced a preliminary geophysical study to delineate the hydrogeological potential of Tushka basin in south Egypt (Robinson et al., 2017). However, that study omitted some important topics that can greatly affect its final achievements in Tushka area, e.g. 1) The dominant meteorological conditions, 2) Geomorphological features, 3) Structural setting, 4) Petrophysical potential of the studied sequences, 5) Hydrothermal activities, 6) Hydrogeological system and connectivity with Lake Nasser, and 7) Quality control for the geophysical results.

Introduction

The Paleozoic-Cretaceous Nubia sandstone is regional aquifer/reservoir sequences extends in northeast Africa, in Egypt, northwest Sudan, northeast Chad and southeast Libya. It is highly porous and permeable strategic sequences producing water and oil. Its age stills matter of controversy due to bareness of fossils and similarity in its mineral composition. In its outcrops and subsurface extensions in south and central parts of Egypt, it mostly discriminated into siliceous sandstone, in addition to slightly and highly and ferruginated siliceous sandstone.

Due to the strategic importance of the Nubia sandstone as a source of underground water and oil production, its geologic and structural settings, its mineral composition and diagenesis, as well as its petrophysical and pore fabrics have been extensively studied by many authors in south Egypt (Issawi, 1973, 1978; Issawi and Jux, 1982; Klitzsch, 1984; Hendriks, 1988; Issawi and Osman, 1993; Thabit, 1994; Nabawy et al., 2009a, 2009b; 2010; Nabawy and Géraud, 2016).

Tushka Lakes and canals are one of the important agricultural projects in south Egypt where majority of the Egyptian population lives on 6% of the land in the Nile Valley and its Delta. Tushka Lakes will be supplied with the water overflow coming from water flooding from Lake Nasser during flooding season. The area is entirely underlain by the Nubian aquifer. Structurally, the study area had been subjected to some tensional E-W forces which lead to creating some regional E-W normal fault, e.g. Kalabsha fault (Abdeen, 2001). Huge reserves of underground water/hydrocarbons are accumulated in the porous to highly porous and permeable rock sequences of the Nubia sandstones. The distribution and migration of these economic fluids accumulations are mostly controlled by the structural and geologic settings of the Nubia sandstone in the different localities. So, the storage and flow capacities of the Nubia sandstones in south Egypt, central and north Eastern Desert, Sinai, and the Gulf of Suez were studied by many authors (e.g., Temraz and Elnaggar, 2016; Nabawy and David, 2016; Kassab et al., 2017; El-Gendy et al., 2017; Nabawy et al., 2019a, 2019b; El Sharawy and Nabawy, 2018, 2019; Elgendy et al., 2019; Sarhan and Basal, 2019). Therefore, the main target of the present discussion is to throw the light on the hydrological regime of the Nubia aquifer in Tushka Egypt and in particular the achievements by Robinson et al. (2017) who studied impacts of the structural patterns in Tushka area on the Nubia aquifer. They concluded that the underground aquifer is recharged by some normal surface fractures and that some seepage is established from the Lake Nasser to the underground aquifer.

Section snippets

Methodology

In the disused paper (Robinson et al., 2017), the authors studied the palaeo-drainage patterns in Tushka area based on some enhanced satellite images constructed from two DEM products; 1) ASTER DEM (made from VIS wavelengths) that were applied to image surface topography, and 2) NASA's Shuttle Radar Topography Mission (SRTM) dataset to image the palaeo-topography. Then the obtained drainage network from the ASTER-DEM and SRTM DEMs were retrieved and compared based the same hydrologic routine.

Discussion

In the following section, a detailed discussion will be introduced to declare the main topics that have been omitted from the mentioned study of Robinson et al. (2017). Each topic will be discussed in details, indicating its misleading achievement, with a list of supported literatures.

Conclusions

From the present discussion it is achieved that, recharging the Nubian aquifer in south Egypt through fault planes and drainage pattern is localized to some local areas around the Lake Nasser as the northern parts of Khor Tushka as mentioned by some authors. In general, impacts of fault planes and drainage pattern on the Nubian aquifer are limited or absent due to; 1) Rarity of rainfall and dryness of Tushka area as a part of the great Sahara in north Africa, 2) The highly porous and permeable

Acknowledgements

The author would like to express his deep thanks to the anonymous reviewers for their constructive comments that improved and reconstructed the present manuscript. A special acknowledgment is also extended to the editors of AES, Prof Dr. Damien Delvaux and Prof Dr. Mamdouh Abdeen, whose insightful suggestions and patience have led to a concise discussion.

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