Introduction

In Egypt’s Eastern Desert, Wadi Qena is a significant geological feature that may be found. One of the wadis in the Eastern Desert that has the most considerable length, this valley in Egypt runs from north to south and has a breadth of about 40 km, making it one of the longest wadis in the region. This wadi was developed along an unconformable contact between the Red Sea mountains of Precambrian basement rocks in the east and sedimentary rocks in the west. Wadi Qena encompasses around 18,000 km2 of land. The valley extends south in the opposite direction of the Nile River, eventually joining it at Qena Bend. The Wadi Qena drainage system takes occasional rainfall from numerous catchment regions and runs it till it enters the mainstream. The research region is northeast of Qena Government, between latitudes 28° 00′ and 26° 30′ N and longitudes 32° 15′ and 33° 45′ E.

This area has been the subject of numerous prior studies to understand better the geological, geomorphological, and hydrological settings of Wadi Qena. For example, to identify locations with groundwater resources in the Wadi Qena basin, Hussien et al. (2016) used integrated remote sensing, geophysical, and geological field research, as well as geochemical and isotopic methods. Abdelkareem and El-Baz (2015) evaluated different types of satellite data, including imagery, radar, multi-spectral data, and enhanced thematic mapper to present an overall picture of the Wadi Qena region’s origin.

Many authors have employed remote sensing data signified by the DEM data in groundwater research; for example, Elmahdy and Mohamed (2014) evaluated the influence of geological formations on groundwater accumulation and movement direction in Al Jaaw Plain using DEM data. A similar application was given by Taha et al. (2021), Meneisy and Al Deep (2021), Al Deep et al. (2021), Mohamed et al. (2022), and Meneisy and Al Deep (2021). For groundwater investigation in regions with low rates of precipitation, Khodaei and Nassery (2011) employed the Landsat ETM, IRS (pan), SPOT, and digital elevation model (Southwest of Urmieh, Northwest of Iran). The magnetic data are used for many propose, as represented by Meneisy et al. (2021), which used the aeromagnetic data to determine the Nubian aquifer’s thickness and sedimentary cover. In their 2018 study, Saleh et al. defined the shear zones, basement depth, and geological lineaments at the Barramiya gold mine and the neighboring Eastern Desert of Egypt using gravity and aeromagnetic data. Ghazala et al. (2018) used potential field data to detect subsurface structures in the Sohag Governorate for urban development. Boubaya (2017) also made use of drilling logs, hydrogeological data, magnetic data, vertical electrical sounding (VES), and other methods to identify the existence of groundwater in the western Algerian region known as the Maghnia Plain.

On the other hand, Agyemang (2020) outlined the high groundwater potential zones in the Ghanaian district of Agona East using the magnetotelluric (MT) data. Additionally, Li et al. (2017) evaluated the fracture zones in the Boshan region of Shandong Province, China, that have a low resistivity and may be a water-bearing medium by conducting a controlled source audio-frequency magnetotelluric (CSAMT) survey throughout the river valley. Giroux et al. (1997) used the findings of nine MT-sounding profiles to calculate the effective porosity of the Maastrichtian aquifer and offer a valuable description of the geometry at the bottom of the aquifer.

Geological setting

Sedimentary rocks are observable in the study area’s west. In contrast, basement rocks are noticeable in the area’s east, as illustrated in Fig. 1. The Red Sea mountains, in particular, reveal the earliest units. Sedimentary layers cover these basement rocks from the Nubian and Post-Nubian deposits. The Red Sea mountains, which originate from the Pre-Cambrian era, are located on the eastern side of Wadi Qena, where the igneous and metamorphic basement rocks are exposed. At the same time, the overlaying sedimentary rocks in wadis like Wadi Qena and intramountainous regions are between the Paleozoic and Quaternary. The structural configuration of the Pre-Cenomanian period was the primary factor that determined the distribution of Paleozoic rocks.

Fig. 1
figure 1

Geological map of the study area shows the principal geological formations and the major surface structures, modified after EGSMA (1981)

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These Paleozoic sediments are in the south of Egypt and outcropped in the investigation area’s northern and western parts. In most of Egypt, the Nubian Sandstones serve as the country’s most notable groundwater aquifer, spreading continuously on top of the basement from surface exposures to the deepest subsurface in the north of the western desert. Depending on the geological and structural conditions, the Nubian Sandstone’s thickness frequently changes and rises in the direction to the north. It ranges from about 14 in the south to 403 m thick (El-Shamy 1992). It is worth mentioning that the groundwater of this aquifer occurs under confined conditions (El-Sawy et al. 2011; Moneim 2014).

The Cretaceous rocks enclosed two assembles; the first is the formations that belong to the Lower Cretaceous, which belongs to the Nubian aquifer. The second is the Upper Cretaceous rocks intercalated with the Nubian Sandstone strata, primarily limestone, chalk, and shale. In Wadi Qena, marine and near-shore sediments were submerged by sea transgression from the late Cretaceous to the Tertiary (Klitzsch et al. 1990). This period was sporadic by an erosional phase that removed most limestone and chalks from the wadi. After that and during the Tertiary, the marly chalk and limestone of Paleocene and Eocene time were deposited before the regression associated with the closure of the Neo Tethys.

Quaternary deposits covered a large area of Wadi Qena. During the Pleistocene epoch, Egypt was marked by numerous dramatic events, where it prevailed by an aridity climate with some fluctuations. Laterally, the conglomerates and sands were deposited in a short pluvial time. This period was sporadic by a hyper-arid phase during which the Nile deposited silts (Said 1990; Abdalla et al. 2009).

The research area is in Egypt’s stable shelf regions, which are somewhat flexure and where folding slightly affects the region’s structure (Said 1962). The limestone plateau is highly affected by the Wadi Qena structures. Wadi Qena structures are considered an anticline fold by many authors, i.e., Hume (1929), Billings (1954), Stern and Hedge (1985), El Gaby et al. (1988), Abdel Ghany (2011), El-Sawy et al. (2011), Moneim (2014), and Abdel Moneim et al. (2015). It is one of the oldest geological formations on Egypt’s stable tectonic shelf. This anticline fold is disturbed by a different fault system, especially those bounded by the depression of Wadi Qena from the west (Aggur 1997). In the study region, several surface structural lineaments representing surface faults that have been geologically mapped are illustrated in Fig. 2a.

Fig. 2
figure 2

a Surface structural lineaments of the study area as traced from the geological map of Egypt (EGSMA 1981). b Rose diagram of the surface structural lineaments illustrates the azimuth frequency (bearing %) and the percent of total lineation lengths (length %)

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These faults are identified using the scaled geological map of Egypt shown in Fig. 1 (1:2,000,000), which was released in 1981 by the Egyptian Geological Survey and Mining Authority (EGSMA). A graphic depicts these surface faults’ azimuth and frequency relationships. According to the rose diagram, the NNW-SSE, NE-SW, and ENE-WSW tendencies are grouped in the main surface structural lineaments according to their abundance, as shown in Fig. 2b.

Methodology

In order to give high-resolution spatial data for the topography of the earth’s surface, the digital elevation model (DEM), as measured by the Shuttle Radar Topography Mission (SRTM), is employed. The research region’s terrain, morphology, drainage system, and stream order have been extracted and mapped using DEM data NASA JPL (2013).

We employ the ArcGIS Hydro tool to create a drainage network system from the DEM data. In this tool, the D-8 algorithm introduced by O'Callaghan and Mark (1984) is applied to the data. Moreover, the drainage pattern can be analyzed to calculate the stream order, which numerically represents each stream’s size. In order to collect the aeromagnetic data for the Egyptian General Petroleum Corporation, the Western Geophysical Company of America used an aircraft proton-free precision magnetometer with a sensor that had a very high sensitivity at the time of approximately 0.01 nT (AerService 1983). The sensor was attached to the tail stinger of the aircraft (sheets 1A and 1B) with a scale (1:50,000) are used. These aeromagnetic maps represent the total magnetic intensity (TMI) field data at an altitude of 120 m above the ground surface, with a contour interval of 10 nT. The TMI data was digitized using ArcMap software for further processing and interpretation. The TMI data were transformed to the north magnetic pole after being corrected for the international geomagnetic reference field (IGRF) with the following geomagnetic parameters (total field strength of 42,425 nT; the inclination of 38.89°; and declination of 2.0°). The RTP reduction aims to eliminate the bias in the locations of the magnetized sources in the areas of intermediate latitudes like the study area. The magnetic data may then be used to identify the layout of the subsurface structures and the main geological directions, as well as determine the depth of the basement rocks, which will allow one to have a comprehensive grasp of the hydrogeological environment under the surface.

In order to accomplish the structural interpretation of the RTP data, two essential methods are used. First, the structural analysis of the constructed first vertical derivative map to detect the fault’s locations and directions. This method is crucial for investigating groundwater because it may be able to identify the primary subsurface water flow pathways.

The geological features significantly influence the geometry, direction, and severity of the subsurface faults (Hall 1964). Many researchers have used the same technique, i.e., Ghazala (1994), Saleh and Saleh (2012), Khattach et al. (2013), Bakheit et al. (2014), and Araffa et al. (2018). The primary purpose of doing a trend analysis is to sketch out the primary structural trends that are responsible for regulating the flow of groundwater.

The second approach makes use of the analytical signal methodology, which is derived from the data on the total magnetic field, in order to ascertain the location of the causal bodies, which are, for the most part, basement rocks and their depth. Such a technique is recently used as it is useful to detect the base of the groundwater aquifer (Nubian aquifer), which delineates the area of greater depth and has a greater water reserve.

We used the analytical signal approach to conduct a quantitative analysis of the TMI data. The amplitude A of the analytical signal may be determined with the assistance of the equation provided by Nabighian (1972, 1974):

$$=\sqrt{{\left(\frac{\partial M}{\partial x}\right)}^{2}+{\left(\frac{\partial M}{\partial y}\right)}^{2}+{\left(\frac{\partial M}{\partial z}\right)}^{2}}$$
(1)

where M is the magnetic field and \(x\), y, and \(z\) are the unit vectors of the two horizontal and vertical directions.

Following the lead of Roest et al. (1992), the following equation may be used to determine, based on the analytical signal, the depth (d) to the magnetized source bodies:

$$\left.\left|A(x)\right.\right|\propto \frac{1}{{x}^{2}+{d}^{2}}$$
(2)

where A is the magnetic field at point x.

Direct and inverse modeling are two reversed operations typically performed sequentially in two-dimensional modeling. Geosoft Oasis Montaj was used for the 2-D modeling. During the inverse modeling process, a comparison is made between the observed potential effect and the estimated potential impact generated by the inferred potential models. However, using computer software, magnetic and gravitational effects for models with complicated forms have been predicted for every two-dimensional polygon in the model. These predictions were made for models with various configurations (Talwani et al. 1959). Every one of the predicted magnetic profile’s orientations extends westerly to the eastern ward direction. The figure displays the locations of the modeled profiles in their respective environments (Fig. 8). In the investigated region, the geological succession comprises two primary rock types: sedimentary cover, which primarily consists of wadi deposits, and basement rocks. In this particular instance, the most simplistic way to model this succession was to assume a two-layer earth model, in which the basement is the magnetized source layer. The magnetic susceptibility of the non-magnetized sediments is assumed to be 0.0001 CGS units, whereas the magnetic susceptibility of the highly magnetized basement is given to be 0.027 CGS units.

Collecting magnetotelluric (MT) data, the natural variations of the electric and magnetic natural fields are recorded simultaneously. The magnetic field is captured entirely, including its horizontal and vertical components. On the other hand, the only electric field components recorded are the horizontal ones. There are several kinds of devices available for use in the process of measuring MT data. A technological advance in the MT recording system is required for simultaneous multi-channel data acquisition. The ADU-07e system is characterized by a high sampling rate from 128 to 4096 Hz.

The configuration of the equipment used to record the MT data consists of two geoelectric dipoles oriented north–south (Ey) and east–west (Ex)with 50-m separation and three magnetic sensors buried in the ground, which alignment to the north–south and east–west for the two horizontal sensors, and the third one is buried vertically in the ground. The magnetic sensors (Hx, Hy, Hz) are buried in the ground to protect them from human and animal disturbance, avoid any movement that may cause by the wind or other reasons, and protect them from rising the temperature.

The formulation of the Maxwell equation to give the mathematical description of magnetotelluric principles was given by Vozoff (1972) as follows: the propagation of electromagnetic waves inside the rocks depends on many variables, i.e., conductivity and frequency. The depth where the strength of the field is reduced to \({e}^{-1}\) is known as the skin depth \(\delta\):

$$\delta =\sqrt{\frac{2}{{\mu }_{0}\sigma \omega }}$$
(3)

where \({\mu }_{0}\) is the magnetic permeability of the vacuum space, \(\sigma\) is the earth conductivity, and \(\omega\) is the angular frequency.

Assuming that the magnetic permeability \({\mu }_{0}\) does not differ significantly in the earth, then the skin depth equation can be approximated as in Eq. (4):

$$\delta \left(T\right)\approx 500\sqrt{T{\rho }_{a}}$$
(4)

where \({\rho }_{a}=1/{\sigma }_{a}\) (Ω m) is the apparent resistivity of the uniform half-space, and \(T=\frac{2\pi }{\omega }\) (s) is the period of electromagnetic waves. The impedance of the magnetotelluric Z (m/s), which is represented by a ratio between the electric and magnetic fields recorded at the surface, may be found by solving the following equations:

$$z\left(\omega \right)=\frac{{E}_{{y}_{0}}}{{B}_{{x}_{0}}}$$
(5)
$$z\left(\omega \right)=-\frac{i\omega }{k}$$
(6)
$$z\left(\omega \right)=-\frac{i\omega }{\sqrt{i\omega \mu \sigma }}$$
(7)
$$z\left(\omega \right)=-\sqrt{\frac{\omega }{{\mu }_{\sigma }}}\sqrt{i}$$
(8)

The impedance equation was rearranged to produce the apparent resistivity of medium \({\rho }_{a}\) (Ωm) (Eq. 9):

$${\rho }_{a}=\frac{\mu }{\omega }{\left|z\right|}^{2}$$
(9)

Results and discussion

The primary objective of this research is to establish the nature of the connection that exists between the waterways on the surface and the geological features on the surface that are relevant to the Wadi Qena area using satellite (DEM) data as well as the subsurface structures using geophysical techniques, mainly aeromagnetic and magnetotelluric data.

First, a look at the figure that determines the drainage pattern (Fig. 3a, b) demonstrates that surface water flow, which is produced by rainfall, drains downhill to the Nile Valley from steep limestone escarpments and the Red Sea Hills in the western and eastern areas, respectively. This movement of water takes place in both of these locations. The use of aeromagnetic data has the benefit of allowing for the delineation of the key underlying structural trends, which, as can be shown in figure, may affect the direction that the drainage pattern and the stream order take in the region (Fig. 3b). The most important findings that came out of this research point to the existence of a sizable surface water basin, which is highlighted by the drainage patterns. The overall length of the streams in the region under investigation is 15,453.7 km, and the length of the mainline is 79.4 km. The majority of the flow of surface water travels in a direction that is generally north to south. The catchment area covers around 15,568.3 km2 on its whole.

Fig. 3
figure 3

a Drainage system map of Wadi Qena and surrounded wadis, plotted over the surface topography map of the study area. b Stream order of Wadi Qena with MT station locations

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The anomalies have a magnetic field with a strength ranging from 1204 nT. According to the entire magnetic intensity map, up to 947 nT (Fig. 4a). Lower magnitudes are clustered in the western half of the region, whereas larger magnitudes are concentrated in the eastern and southern areas, indicating highly magnetic sources (basement rocks). Generally, the most dominant long-extended magnetic anomalies are seen in the north–south, northeast-southwest, and northwest-southeast directions.

Fig. 4
figure 4

a The shaded color map of the total magnetic field intensity of the study area after AerService (1983). b The shaded color reduced to the north magnetic pole (RTP) map

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The geographical position of the important anomalies varies somewhat from that of the TMI map on the reduced-to-the-pole map (Fig. 4b). The RTP map demonstrates a slight difference in the magnitude of the anomaly’s values that reaches up to 1802 nT. The majority of the small to medium amplitude anomalies are dispersed on the map, while the highest anomalies of high values are concentrated in the northeast and the middle of the map. This gives an impression about the location of the shallow magnetic sources and/or basement uplift.

The first vertical derivative is depicted in Fig. 5a, which illustrates the locations and extensions of the positive and negative closures reflected from shallow magnetic sources and their faults and/or contacts. The results vary in magnitude from 3.53 to − 2.31 nT/m.

Fig. 5
figure 5

a The first vertical derivative map illustrated with the faults plotted on the primary trend. b The Rose diagram represented the main subsurface trends; the red petals display the azimuth frequency (bearing %), and the blue petals represent the percent of total lineation lengths (length %)

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These anomalies extend mainly in the northwest-southeast direction, and there is another anomaly trending in the northeast-southwest direction and finally to the east–west direction. The rose diagram represents the structural lineaments of the subsurface faults as they were realized from the first vertical derivative map and shown in Fig. 5b. This technique identifies fault trends based on the percentage of all measurements or the percentage of total lineation lengths. According to the findings, the main fault trends affecting the study area are, in descending order, the NE-SW, NW–SE, and ENE-WSW. Comparing Figs. 3 and 5, we notice the similarity between the main structural trends and the main direction of Wadi Qena and its branches.

The analytic signal map (Fig. 6) shows a contour line of 0.1 nT/m. The high analytical signal represents the dimensions of the magnetized sources, while the studied area’s calculated basement depth values are shown in Fig. 7b. This depth ranges from 101 to − 1165 m relative to sea level; the location of the selected profiles for 2-D analytic signal depth calculation is shown in Fig. 7a. For the quantitative calculation, we select profiles out of the areas where the basement complex is presented to avoid errors in calculation. To demonstrate the geometry of the Wadi Qena basin, a 3D plot is shown in Fig. 7c with a general decrease in basement depth to the west and center. This occurs at the same time as the existence of the step faults in the center and the crystalline hills of the Red Sea in the eastern section of the region. The depth of the magnetized rocks, as seen in Fig. 7, demonstrates that the region is capable of being divided into subbasins that are kept apart by discontinuous basement uplifts.

Fig. 6
figure 6

The shaded color relief map of the analytical signal with contour line 0 nT/m delineating high magnetized igneous rocks

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Fig. 7
figure 7

a The selected profiles for analytic signal depth calculations. b Depth map generated from the 2D analytic signal. c 3D plot of Wadi Qena area surface topography and calculated depth

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The surface and subsurface structural characteristics that have been interpreted show that the surface faults that are cutting through the mountains made of Precambrian crystalline rocks and the superimposing strata of the Phanerozoic extend extensively into the subterranean succession. The existence of the structure trend, which extends in the NW–SE direction and runs parallel to the Red Sea, may be interpreted as the reactivation of a previous structure trend. The axial plane of the Wadi Qena anticline is connected to the structural weakness that was present in the basement rocks at the time of the emergence of the Red Sea. In addition to this, there is a plethora of other buildings that exhibit the Gulf of Suez (NW–SE) and Gulf of Aqaba trends (NE-SW). The depth values were calculated from the level of observation (flight height) of the magnetic data and then corrected by subtracting the flight height elevation from the calculated values.

Wadi Qena originated in the structural weakness area on the axial plane of the Wadi Qena anticline. The area contains a set of normal faults and a step of faults that developed during the weathering process. The drainage pattern of Wadi Qena may be seen to match with the depth of the basement map in Fig. 7b. The models that were created by 2-D magnetic modeling demonstrate that there is fluctuation in the basement relief surface, with the greatest thickness of sedimentary cover being around 500 m. This is especially true under the Wadi Qena mainstream. The position of the magnetic profiles (Figs. 8 and 9 displays the 2-D models, whereas Fig. 10 displays the position of the magnetic profiles.

Fig. 8
figure 8

Topographic map shows the study area with modeled 2-D magnetic profiles location, drainage network, MT stations, well logging data, and boundary of the basement rocks outcrops

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Fig. 9
figure 9figure 9

Part 1: modeled magnetic profiles from 1 to 3. Part 2: modeled magnetic profiles from 4 to 6

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Fig. 10
figure 10

a, b, c, and d are the electrical resistivity model calculated from magnetotelluric station no. 1, 2, 3, and 4

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The gathered drilling information includes two well logs: gamma-ray, resistivity, density, and caliper logs. The location and depth information is provided in Table 1. The location of these two wells is shown in Fig. 8. Two well logs are available. According to the well logging data gathered (REGWA 2009), the depth to the basement was found to increase to the south as a general trend.

Table 1 Measured water table and basement depth from well-logging data (after REGWA 2009)
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The geoelectric models generated by the MT inversion (Fig. 10a to d) show that in most soundings, the low resistivity layer reaches a depth of more than 400 m. Most of the data models show four layers. In the first layer in most of the models, the apparent resistivity is low in general. However, the resistivity values that are often the greatest are typically associated with the basement surface, which is the base of the groundwater aquifer. On the other hand, a low resistivity suggests that the sediments are entirely saturated with water.

Conclusion

This study aims to highlight the relationship between streamlines generated along surface structures and the deep-seated structures related to groundwater aquifers. The drainage pattern reveals that the direction of the surface water flow is produced by rainfall and drains westward to the Nile Valley. The surface water is collected from the high limestone escarpment, and the Red Sea mountains are located in western and eastern areas. The findings of the magnetic data interpretation effectively delineate the principal subsurface structural trends and their influence on the direction of the drainage pattern. The conventional order, with values (6 and 7) being the highest in order, may be found in the boundary between highly magnetic basement rocks to the east and less magnetized sediments to the west, as illustrated in figure. This order is the highest in order (7b). The data collected from drilling indicates that the depth to the basement in Wadi Qena ranges from 400 to 525 m, which makes sense considering its location close to the Red Sea mountains. According to the geoelectric models, the average depth to the aquifer base while moving southward and downstream of Wadi Qena. Finally, integrating geological and geophysical approaches using structural settings could be beneficial in studying groundwater occurrences and sources of recharge.