## 5 Conclusions  
Our application of the gravity aspects revealed that one aspect, the so-called strike angles, is significantly combed in the localities with known target deposits (_TD_) in Egypt. This discovery allows novel prediction of the localities where there may still be more _TD_ present for further exploitation.  
Additionally, strike angles provide the potential for not only discoveries of oil and gas but also of the groundwater volumes.  
The spatial distribution of the combed strike angles is near the surface. The connection of the gravity disturbance to the stress fields preserved in these geological volumes presents itself a new inexpensive and accessible empirical geophysical tool for the recognition of future resources that include oil, gas and groundwater.  
Our analysis represents the first approximation for the detection of important resources in less accessible regions that may warrant more detailed investigations.  
Groundwater resources were detected for the first time in the form of hypothetical paleolakes in the Great Sand Sea (GSS), North-Western Egypt, and between Kharga and Toshka (TK), Southern Egypt. The boundaries of the detected paleolakes were reconstructed and discussed. It is evident that the water level continued to fluctuate over the course of time.  
Archaeological sites provided a practical constraint (external limiting factor) for the lakes' positions and extents. Specifically: (i) Our detection in the GSS [4] (Section 4.2) allows us to link additional archaeological sites near the groundwater extent expected within the GSS. (ii) Our work focused on TK (Section 4.3) is independent of [56] and others but, however, provides similar results. Here, we estimate lake(s) position(s) and extent including their temporal changes.  
J.K. ([PERSON]): Conceptualization, Methodology, Investigation, Formal analysis, Writing--Original draft preparation, Writing--Reviewing and Editing; J.K. ([PERSON]): Conceptualization, Methodology, Software, Data Curation, Visualization, Formal analysis, Validation; L.V.: Data Curation, Formal analysis, Investigation, Validation, Writing--Original draft preparation, Writing--Reviewing and Editing; G.K.: Methodology, Formal analysis, Investigation, Writing--Original draft preparation, Validation, Writing--Reviewing and Editing; A.B.: Methodology, Software, Data Curation, Investigation, Writing--Reviewing and Editing, Validation, Supervision. All authors have read and agreed to the published version of the manuscript.  
This work has been prepared in the framework of the project RVO #679 858 15 (Czech Aad. of Sciences, Czech Republic, CR) and partly supported by the project LO1506 (PUNTIS) from the Ministry of Education of the CR. G.K.'s support came from the Czech Science Foundation projects 20-08294 S, Ministry of Education LTAUSA 19141. L.V.'s contribution was supported by the Program of the Development of Fields of Study at Charles University, no. Q11: Complexity and Resilience: Ancient Egyptian Civilisation in Multidisciplinary and Multicultural Perspective, and by a non-investment subsidy no. MSMT-40214/2019-12, VEG 2020/1.  
We cordially thank [PERSON] for his work on the model in Section 2.5. The input data--the harmonic geopotential coefficients of the gravity field model EIGEN 6C4--are publicly available; data from our figures (in surfer program) and our figures with high resolution (.png files) can be provided by [PERSON] on request. [PERSON] provided useful geological consultations.  
The authors declare no conflict of interest.