Application of geophysical techniques for shallow groundwater investigation using 1D-lateral constrained and 2D inversions in Ras Gara area, southwestern Sinai, Egypt

Environmental Earth Sciences (2023) 82:120 https://doi.org/10.1007/s12665-023-10796-4 ORIGINAL ARTICLE Application of geophysical techniques for shallow groundwater investigation using 1D‑lateral constrained and 2D inversions in Ras Gara area, southwestern Sinai, Egypt Mohamed A. Genedi1 · Mohamed A. S. Youssef2 Received: 7 July 2022 / Accepted: 5 February 2023 © The Author(s) 2023 Abstract There is an urgent need for greater water resources to support sustainable development in Ras Gara area of southwestern Sinai. Determining the water-bearing zones of the shallow Quaternary aquifer of the Araba Formation in the study region is therefore the main objective of the research. This will be done by using a variety of geophysical techniques, such as DC resistivity sounding and shallow seismic refraction surveys. Using the Schlumberger array (max. AB = 1200 m), the DC data were gathered at 27 VES locations along five primary profiles. At the same locations, 27 spreads totaling 115 m in length of seismic data were also performed. One-dimensional laterally constrained (1D-LCI) inversion is only applied to the DC data in order to generate a best-fit model, whereas 2D inversion is applied to other datasets. The area is divided up into five geo-electrical layers based on the results of 1D-LCI inversion of DC data, and the aquifer is classified into fresh (third layer) and saline bearing-zones (fourth layer). The resistivity values of the fresh-zone range from 8.7 to 26.7 Ω.m, with only low values (5–7.5 Ω.m) found at some VES sites, while the resistivity values of the saline-zone range between 0.9 and 3 Ω.m, except for (14.4 Ω.m) at VES-04. At depths of (2.4–15.6 m) and (8.7–28.5 m) for the fresh and saline zones, respectively. In this region, the shallow low resistive (about 10–100 Ω.m) and intermediate high conductive (< 10 Ω.m) layers of the 2D-DC inverted model represent the fresh and saline zones of the aquifer, respectively. The basement rocks were represented by a deep, extremely high resistive layer that can reach 40,000 Ω.m. Three subsurface layers are identified from the results of the 2D inversion of seismic data (VP1 = 400–1100 m.s−1, VP2 = 1200–1900 m.s−1 and VP3 = 2400–5400 m.s−1). The saturated zone of this aquifer is represented by the second layer (depth, 3.7–20.5 m). The basement rocks are also reflected in the last layer of high velocity. The inversion results and the previously available hydro-geological map data show a good degree of concordance. In the eastern portion of the study area, additional water wells could be drilled for additional water resources. Keywords DC electrical resistivity (DCER) · Shallow seismic refraction (SSR) · One-dimensional lateral constrained inversion (1D-LCI) · 2D inversion · Hydro-geophysics · Southwestern Sinai Introduction * Mohamed A. Genedi Mohamed A. S. Youssef 1 Department of Geology, Faculty of Science, Mansoura University, 35516 Mansoura, Egypt 2 Exploration Division, Nuclear Materials Authority, Po. Box 530, Maadi, Cairo, Egypt Due to the scarcity of water, the desert, which makes up the majority of Egypt, offers significant difficulty for the government. The population of Sinai has recently improved their living conditions, which has resulted in excessive demand for water. In order to irrigate a desert area and thereafter establish significant agricultural zones for sustainable development, particularly in the south Sinai Peninsula, shallow groundwater excavation is urgently required. Groundwater resources are essential for urban growth and attract investment to the Sinai Peninsula. Many others have examined these resources in Sinai, particularly in the southern section (Elewa and Qaddah 2011; Arnous and Omar 2018; Yousif 13 Vol.:(0123456789) 120 Page 2 of 17 and Hussien 2020; El-Badrawy et al. 2021; Ibrahim et al. 2021; Zarif et al. 2021; Elshalkany et al. 2022; Soliman et al. 2022). Geophysical research is necessary and productive in the investigation of shallow groundwater. Several authors investigated geophysical groundwater in Sinai's west-central, south, southeastern, and southwest regions (Nigm et al. 2001; Rabeh 2003; Youssef 2006; Aboelkhair et al. 2020; Basheer and Alezabawy 2020; Zarif et al. 2021; Shebl et al. 2022). Furthermore, near the study area, other studies were Environmental Earth Sciences (2023) 82:120 conducted by many authors including Youssef (2010, 2016), Ghoneimi et al. (2020), and Zarif et al. (2021). Ras Gara is located in Egypt's Sinai Peninsula (Fig. 1a), between latitudes 28°08′38″ and 28°09′20′ N and longitudes 33°45′37″ and 33°46′36′ E (Fig. 1b). It is bounded to the northwest by El-Tor City, and to the west and south by the Gulf of Suez. When using a single geophysical technique in regions with complicated geology, such as the Sinai Peninsula, it is difficult to determine the precise hydrogeological Fig. 1  (a) Google map of Sinai Peninsula. (b) Location map of the study area including the vertical electrical sounding (VES) sites along five main profiles in the study area. (c, d) Geologic and hydro-geologic map of Sinai Peninsula (Elewa and Qaddah 2011) 13 Environmental Earth Sciences Page 3 of 17 (2023) 82:120 condition. The goal of integrating two or more geophysical techniques is to resolve ambiguities in the interpreted data, obtain a more reliable final model, and offer a more precise representation of the subsurface distribution (Yusoh et al. 2018; Daniel et al. 2019). Therefore, by merging the inversion data from the two methods, the subsurface interpretation can be improved. To determine the subsurface profile without affecting the environment, electrical resistivity and seismic refraction methods have become popular site investigation techniques (Razak et al. 2015). In the present study, vertical electrical sounding (VES) of DC resistivity and shallow seismic refraction surveys were used to measure the depth and thickness of subsurface layers holding the shallow Quaternary groundwater aquifer in Ras Gara, southwestern Sinai. The primary goals of our study are to (1) define shallow structural features, such as subsurface composition, the depth of basement rocks, and faults found, (2) examine shallow aquifer characteristics in the studied area, such as its depth, thickness, and extension depending on the use of various geophysical techniques, and (3) apply one-dimensional lateral constrained (1D-LCI) inversion on VES data to improve resolution for output models with slow lateral variations, (4) apply two-dimensional (2D) inversion to DC and seismic data to obtain better images of the subsurface layers, and (5) prepare true resistivity, velocity, and top depth image maps for the water-bearing horizons of the Araba Formation to determine the lateral extension and top depth of this aquifer. Many authors (Auken et al. 2005; Wisén et al. 2005; Schmalz and Tezkan 2007; Lin et al. 2019; Ourania 2021; Genedi et al. 2021) have applied the 1D-LCI inversion t (...truncated)