Introduction

Water security has been monitored by scientists for a decade owing to decreasing global water supplies [64, 71, 72]. The IPPC (2007, 2014, 2019) aims to promote water resource usage and subsurface water table stability for future generations. Water resource conflicts are linked to border disputes, major dams and reservoirs, environmental issues, and political identities [23, 73]. Background knowledge of a region’s geology and current hydrologic state is also critical for developing effective management techniques. Geophysical studies to evaluate the groundwater potential of confined and unconfined aquifers have become standard practice around the globe [14, 39]. Over the past several decades, rapid advances in electronic technology and numerical modeling have made geophysical research approaches for groundwater exploration and aquifer mapping much more feasible [47, 74, 93, 94].The sustainable management and utilization of groundwater resources are of utmost importance for ensuring the socio-economic development and environmental sustainability of a region [76]. In the context of Southeastern Peshawar, Pakistan, the appraisal of the lacustrine aquifer’s groundwater potentiality and the development of a hydrogeological model hold significant implications for environmental geology and geotechnical engineering [77, 78]. The lacustrine aquifer in southeastern Peshawar is formed by the deposition of sediments in an ancient lake bed [54, 78]. It consists of various layers of sand, silt, clay, and gravel, which act as conduits for the movement and storage of groundwater [54]. The hydrogeological properties of this aquifer, including its recharge mechanisms, hydraulic conductivity, and storage capacity, are crucial factors that determine the groundwater’s potentiality and its sustainable utilization [79, 102]. The appraisal of the lacustrine aquifer's groundwater potential involves a multidisciplinary approach, integrating geological, hydrological, and geophysical investigations [80, 95]. Geological studies help in identifying the lithological characteristics, sedimentary facies, and depositional environment of the aquifer system, providing valuable insights into its storage and hydraulic properties [81, 82, 85, 96, 100, 101]. Hydrological investigations, such as groundwater level monitoring, pumping tests, and water quality analysis, offer a deeper understanding of the aquifer's recharge mechanisms, storage capacity, and vulnerability to contamination. Geophysical techniques, such as electrical resistivity imaging and seismic surveys, contribute to mapping the subsurface structure, identifying potential groundwater pathways, and delineating the extent of the aquifer [83, 86, 87, 99]. Hydrology, environmental geology, and geotechnical engineering all employ surface resistivity methods in various contexts [21, 35, 62, 75, 84]. Resistivity approaches are recommended to provide a high sample rate and high-quality data for precise target characterization in a geometrically constrained region with severe subsurface conditions. Electrical resistivity techniques are among the most widely used geophysical methods for groundwater evaluation due to their low cost, accessibility, and effectiveness in regions with highly diverse underlying lithologies [36, 45, 61]. According to Nag and Ray. [41], GIS and remote sensing techniques are also used for groundwater assessment.

Geophysicists have found that combining drilling data with subsurface resistivity data may be highly advantageous since both hydraulic and electrical aquifer features rely on the pore spaces’ structure [15]. Using geophysical data and the Vertical Electrical Sounding (VES) approach for near-surface measurement, the depth and thickness of an aquifer may be approximated with a degree of uncertainty. Calibration of VES data using borehole logs, lithologies, and groundwater information enhance reliability [42, 97]. Groundwater flow and aquifer potential in saturated situations may be determined using hydraulic characteristics calculated from pumping tests conducted in drilled boreholes [56]. However, if pumping experiments are not possible, it is feasible to get quantitative estimates of hydraulic characteristics by combining them with hydrogeological data [33].

Before drilling a borehole, it is also possible to optimize the site of wells to limit the chance of failure or unexpectedly low pumping rates [49]. The electrical resistivity approach has shown to be effective in groundwater identification and usage [16]. It includes extensive information on hydrogeological conditions and groundwater storage.

A physically significant correlation must be applied theoretically or experimentally to decode the aquifer's resistivity distribution into the aquifer Dar Zarrouk parameters [17, 70]. Aquifers containing fresh and saltwater in various regions can be resolved using longitudinal conductance (S), transverse resistance (TR), longitudinal resistivity (Rs), and coefficients of anisotropy (λ) [46, 55]. Several authors have already assessed Aquifer protection capability using Dar Zarrouk functions [27, 54]. Protective capacity measurements may reveal surface zones where pollutants are being transferred straight into an aquifer [43]. Multiple well-logging and pumping tests in boreholes (Tube wells) are important for estimating aquifer characteristics, including transmissivity (T), hydraulic conductivity (K), storage capacity (S), and the formation factor (F) [70]. The aquifer system is calibrated with the VES data using drill logs, borehole lithologies, groundwater information, and hydro-chemical data, enabling it to be better defined [27, 69].

The Peshawar basin has been the subject of numerous studies exploring groundwater potential assessments in different regions. However, a comprehensive analysis incorporating pumping tests analysis, groundwater characteristics, and identification of highly saturated layers within the saturated zones is noticeably absent. To bridge this gap, it is essential to conduct a detailed study that utilizes borehole data and employs the Dar Zarrouk parameterscomparison. In a recent study, a comprehensive approach for identifying the super-saturated layers within the saturated zones was accomplished by utilizing borehole data and employing Dar Zarrouk parameters. This will not only facilitate groundwater potential delineation but also provide valuable insights into the hydrogeological dynamics of the basin. In this study, the main objectives are to define the groundwater potential and highly saturated zones for fresh groundwater exploration in the area by characterizing the underlying lithologies down to a depth of 170 m. To achieve these objectives, a comprehensive dataset consisting of 13 Vertical Electrical Soundings (VES), five boreholes, hydrologer data, and pumping tests were collected and analyzed. The integration of VES, borehole, and hydrologer data sets was employed to identify the underlying lithology and aquifer system. Additionally, the Dar Zarrouk parameters, which provide insights into the aquifer’s lithological and hydrogeological properties, were determined. Furthermore, the pumping test data was utilized to estimate important aquifer parameters, such as transmissivity, hydraulic conductivity, and storativity, offering valuable information about the aquifer’s ability to transmit and store groundwater. This study aims to provide a comprehensive understanding of the groundwater potential, characterize the subsurface lithologies and its spatial distribution, contributing to effective groundwater and a better understanding of the hydrogeological conditions in the Peshawar basin.

Geology and hydrology of the study area

Because of the Indian-Eurasian plate collision, Pakistan’s northern territory constantly undergoes deformation [25, 26, 66]. In this region, there are many basins and valley systems. Massive amounts of weathering and erosional products have been transported across large distances and deposited in different sedimentary environments, such as talus slopes, alluvial fans, and floodplain deposits [13, 40].

A sedimentary archive in northwest Pakistan’s Peshawar Basin provides a record of the Pleistocene rock-debris supply pattern. The Pliocene–Pleistocene uplift of the Attock–Cherat Range in northern Pakistan prevented the Indus and Kabul rivers from draining, forming the intermountain Peshawar Basin 2.8 Ma ago [6, 8]. Late Pliocene sediment deposition rates ranged from 2 cm/1000 years to 15 cm/1000 years, with accumulations surpassing 300 m thick at the southern boundary. To a large extent, alluvial fans that prograde from the neighbouring Attock–Cherat range along the southern boundary sank the basin. It has subsequently been fragmented by erosion to form the piedmont plains on the lower slopes of the alluvial fans. The inter-basin drainage networks (Kabul, Kalpani, and Indus rivers) ponded from a tectonically controlled drainage threshold (the Khairabad fault) at perhaps near Nizampur (Main Boundary Thrust fault) resulted in interbedded lacustrine and alluvial sediments (Fig. 1a). Ponding created low-energy floodplain and flood-pond sediments in the basin's southwest and center [10, 40]. Late Pleistocene lakes were considered to have deposited lacustrine sediments in the Peshawar basin [3]. However, the geomorphological (origin) properties of these sediments are rhythmically bedded flood deposits, which Cornwell [10] discovered after detailed research covering an area of 8300 km2 in northern Pakistan. Whereas, river mud is covered with thick rhythmic glacial lake boulders in the southern portion of the basin, alluvial fan deposits are abundant, and the top section of the basin is covered with vertical and continuous loess deposits [3, 8, 18]. The Peshawar basin lies on the hanging wall of the Attock-Cherat Range north of the Main Boundary Thrust (Fig. 1a). The basin’s north, northeast, and northwest are meta-sediments with Malakand-Swat-Bunair granitic intrusions.

Fig. 1
figure 1

Base map of the study area a Geological map of the Peshawar Basin and surroundings; b research area map, with circles indicating VES sites and solid red triangles indicating drill positions

Full size image

Furthermore, dolomite and limestone are found in the southwest, while exposed shales are in the southeast. Alluvial deposits are hydrogeological significant because of their inter-layered and diverse lithologies of clays, gravels, sands, and boulders. This alluvial deposit layer displays groundwater systems that are unconfined to semi-unconfined [40]. Several surface streams in the area are most active during the monsoon season, and the terrain of the studied region influences the subsurface water flow [29, 60].

The overburden comprises the top clays, sand, and alternating layers of sand gravel and mixed boulder strata. The research region is part of the Peshawar basin, and the Peshawar basin's stratigraphic sequence is typically occupied by sedimentary to metasedimentary rocks from the Precambrian to the Jurassic period [34, 66]. The Kabul River and the Bara River are the two primary rivers that recharge the aquifer systems. Previous hydrological estimations based on subsurface lithology of borehole data in the Peshawar basin had determined the aquifer systems [60]. This deduced that the Peshawar valley would have plenty of water, which comes from glacier melts in the north and northwest regions and is used for drinking and irrigation [24, 60]. The principal source of recharge for the subsurface aquifer is rain-fed streams.

Materials and methods

Electrical resistivity data

A total of 13 VES sites were reported in the study region, ranging from 71.2–71.8 °E to 33.75–33.9°N (Fig. 1). The ABEM Terameter SAS-4000 instrument was used to collect data. For the VES survey, we employed a Schlumberger electrode arrangement with a maximum distance between current electrodes of 180–200 m [27, 54]. A regular profiles orientation N-S to E-W was maintained and the data for apparent resistivity (a) gathered across the study region comprised half of the current electrode spacing (AB/2), voltage (V), current (I), and geometrical factor (K). The c field data were evaluated using computer software (IPI2win), which provides an automated evaluation of the apparent resistivity. The interpretation of the data into a model is based on the thickness of the geo-electric layers (Fig. 2). In order to assign resistivity data to lithological units, we relied on existing borehole lithology records and standardized resistivity measurements in the research region. This approach allowed us to accurately analyze the resistivity data and incorporate it into our model. By considering the thickness of the geo-electric layers and incorporating information from the borehole records, we were able to derive meaningful insights from the data and create a comprehensive model for further analysis.

Fig. 2
figure 2figure 2

(a–c) represent the VES data inversion and forward model results comparison with electro-stratigraphic model

Full size image

Dar Zarrouk parameters are described in electrical prospecting as the product of transverse unit resistance (T) and longitudinal conductance (S), as well as the coefficient of anisotropy (λ). These qualities are essential for data interpretation as well as stratified conductor modeling. The subsurface electro-stratigraphic model (Fig. 2), demonstrates that the identified units are determined quantitatively based on their apparent resistivity and thickness as explained by Zohdy et al. [70]. This model provides a valuable means of understanding the subsurface geological structure by analyzing these two parameters. The hydraulic Dar Zarrouk is as follows:

$$Si= \sum_{i=1}^{n}\frac{hi}{pi} \left(Siemens\right)$$
(1)
$$\mathbf{T}\mathbf{i}=\sum_{\mathbf{i}=1}^{\mathbf{n}}\mathbf{p}\mathbf{i}.\mathbf{h}\mathbf{i}\left(\mathbf{O}\mathbf{h}\mathbf{m}.{\mathbf{m}}^{2}\right)$$
(2)
$$\lambda \, = \,\sqrt {\rho _{T} /\rho _{L} } \, = \,\sqrt {\frac{{\left( {\sum\nolimits_{i}^{n} {\rho _{i} h_{i} } } \right)\left( {\sum\nolimits_{i}^{n} {\frac{{h_{i} }}{{\rho _{i} }}} } \right)}}{{\left( {\sum\nolimits_{i}^{n} {h_{i} } } \right)^{2} }}}$$
(3)

whereas PT and PL represent the transverse apparent and longitudinal apparent resistivity respectively, the equation for the coefficient of anisotropy may be easily obtained using a one-square-meter block of earth cut out of a set of layers of the infinite lateral extent of particular resistivity p and variable thickness of depth h, with the subscript i signifying the position of a layer of earth. Integrating VES data with borehole data sets for both confined and unconfined aquifer systems produced the thickness maps (Fig. 2).

Tube well data and pumping test analysis

In a recent investigation, five tube wells (PS-01, PS-02, PS-03, PS-04, and PS-05) were bored, each with a depth of 160–170 m and several borehole analyses were also performed (Figs. 1b, 3, 4, 5, Additional file 1: Fig. S1). Drilling findings reveal alluvial sediments as well as lacustrine mud as underlying lithologies in a few boreholes. The lithology, geometry, resistivity, formation factor, and specific yield of water-bearing rocks were determined using geophysical well logs, as well as the source, transport, and chemical and physical properties of groundwater [68]. This information was then shown to identify the saturated zone and the tube well design. Each well was pumped for more than 800 minutes, with the decline of the water level in the tube well and the discharge rate being measured (Table 1), [49, 57]. Field measurements were plotted on semi-logarithmic coordinate paper, with the drawdown (h) plotted on the linear y-axis scale and the time (t) after pumping began shown on the logarithmic x-axis scale (Fig. 3, a1). Transmissivity and hydraulic conductivity were calculated using the Cooper–Jacob method (single-well pumping test) [50]. The following is the equation that was used to calculate the Transmissivity:

Fig. 3
figure 3

(a–d) The pumping test analysis approach was used to estimate the transmissivity in the borehole (i.e. PS-01, PS-02, PS-03, and PS-04).

Full size image
Fig. 4
figure 4

Borehole data (PS-01 to PS-04) (a–d) Shows the depth logs, such as the resistivity log (SPR), spontaneous potential log (SP), lithological chart, aquifer types, and the transmissivity of each borehole, in relation to the tube well design

Full size image
Fig. 5
figure 5

Relief map of the Dar Zarrouk parameters. a Estimated transverse resistance map for the region’s layer overlain aquifer. b map of Longitudinal conductance, c anisotropy relief map of this study aquifer region

Full size image
Table 1 Data from pumping tests and parameters of the groundwater aquifer
Full size table
$$T\, = \,\frac{{2.3\,Q}}{{4\pi \Delta \left( {h0 - h} \right)}}$$
(4)

While T (h0-h) is the drawdown per log cycle of time, Q is the constant pumping rat. Based on the pumping test analysis of the following formula, the hydraulic conductivity of stratified aquifer layers was determined [1].

$${\text{K}} = {\text{ T}}/{\text{d}}$$
(5)

Where K stands for hydraulic conductivity, T for transmissivity, and d for saturated layer thickness (pumped depth). The resistivity and grain size of borehole lithologies were used to classify them. The studied depth and expected resistivity values were plotted against AB/2 until the depth and anticipated resistivity values were achieved. Drilling data from the VES transects were utilized to calibrate the anticipated resistivity and lithologies, as well as to identify prospective zones. The anticipated resistivity and lithologies were calibrated using existing drilling data from the VES transects’ area (Figs. 2, 4, Additional file 1: Fig. S1). Using resistivity modeled curves and borehole lithology, a standard strata correlation was produced separately for lithologies above and below the water table (Table 2). The resulting standard correlation was applied to every one of the field curves generated from all of the VES data points [54]. Most geophysical methodologies are difficult to comprehend because the response curves generated by resistivity data may be matched with various realistic resistivity distributions.

Table 2 Subsurface lithology and VES data are compared
Full size table

To develop a comprehensive and reliable geological model, it is crucial to calibrate the collected data against a separate set of data obtained independently. In recent tudy area, various sources of information were utilized, including lithostratigraphic logs (which provide details about the layers of rock or sediment), surface geological observations, measurements of water table depths, and recordings of electrical conductivities from existing tube wells. By incorporating these multiple data sources, researchers aimed to enhance the accuracy and validity of their geological model, ensuring a more robust understanding of the subsurface conditions in the study area. [59] (Figs. 2, 4).

Aquifer model

The VES data, tube well data (usually the lithology), and hydrologic data sets were used to develop a complete three-dimensional model of the aquifer system in the research region [28, 54]. The study utilized three sets of data: surface resistivity values, lithological information, and well logs from tube wells. These datasets were compared with the surface topography, as shown in Fig. 6. The lithologies identified helped classify aquifers as either unconfined (freely receiving and discharging water) or confined (water is under pressure in an impermeable layer). Additionally, the development environment of the aquifers was determined. By comparing the lithostratigraphic models derived from thirteen vertical electrical sounding (VES) values and five tube wells, we were able to match them and identify the types of aquifer systems present in the study area. This approach allowed for a comprehensive understanding of the aquifer characteristics and their distribution based on the integration of multiple data sources.

Fig. 6
figure 6

Borehole and VES data sets were used to create a 3D surface elevation and subsurface lithological model of the research region. a Aquifer resistivity layers and surface elevation about subsurface depth; b aquifer hydrogeological model; c subsurface lithological face from unsaturated to the saturated zone of the aquifer system and aquifer types

Full size image

Results

Electro-stratigraphic variation

Previous studies have used quantitative analysis of vertical electrical soundings to classify geo-electric data according to resistivity and layer thickness. These geo-electrical units were used to develop the electro-stratigraphic model. As a result, five to six geoelectric subsurface layered assemblages were identified. For this research work, geophysical and geological data were collected, along with lithological data from tube wells, to construct an accurate hydrogeological model by correlating and establishing specific links between all variables [28, 38]. The groundwater subsurface model shows a series of consecutively low and high resistivity differences. Therefore, it is possible to determine the depth of the groundwater table and distinguish between unsaturated and saturated sediments in the study area.

Although clay layers interlocked in the lithology of saturated sediments, many subsurface resistivity faces (21 ohm-m) have been identified, and resistivity values fluctuate significantly (15–85 ohm-m) in unsaturated zones (Table 2, Fig. 2). VES sounding such as VES-1, VES-4, and VES-7 illustrate interpreted preliminary findings employing the subsurface layers’ thickness, resistivity, and lithology. The underlying groundwater distribution for each stratum is shown by compiling an electro-stratigraphic column (Fig. 2).

Aquifer parameters analysis

Characteristics of Dar-Zarrouk, such as transverse resistance (TR), longitudinal conductance (S), and coefficient of anisotropy (λ), was estimated for the layer overlaying the aquifer system (Table 3, Fig. 5). longitudinal conductance is one of the geo-electrical measurements used to identify areas of potential groundwater [44]. By Hasan et al. [20], aquifer system longitudinal conductance refers to the protective capacity of layers above the aquifer that may operate as a filter/barrier for percolating fluid. According to the results, S values ranged from 0.14 to 1.2 mhos (Table 3). The S concentrations of 0.7–1.2 mhos have been found in the southeastern half of the study area. The high findings might be explained by the existence of clay beds, which are classified as having “Good” defensive properties (Table 4, Fig. 5b). There is a decent level of protective capacity in the study area’s central and northeastern regions with values between 0.29 and 0.65 mhos. Despite having a weak to poor protective capacity of 0.07–0.14 mhos, the area's Northwestern and Southwestern sides are nevertheless classified as having a weak to bad protective capacity (Table 4).

Table 3 Shows the Dar Zarrouk parameters and aquifer thickness based on VES data
Full size table
Table 4 Depicts the aquifer's protective capacity in terms of longitudinal conductance (modified after [91])
Full size table

The values of transverse resistance range from 2300 to 22948 Ωm2 (Table 3, Fig. 5a). High TR values (10000–22000 Ωm2) may be found from the northwest to the southwest. The research area’s low TR values (7000 Ωm2) are calculated in the middle southwestern section. Low TR values, on the other hand, are associated with low-resistivity formations (such as clayed soil) and a shallow foundation, while higher TR values are associated with high-resistivity formations and occurrences of deeper groundwater potential [44].

The coefficient of anisotropy can be used to determine the aquifer's type and storage capacity [47, 48]. Electrical anisotropy in rocks is produced in multilayered aquifers via alternating layers of thin-bedded sandstones and shales with apparent lamination [5]. Between 0.27 and 1.35 was shown to be the optimum value of “λ” in recent research (Table 3). In the Northwestern section, the high “λ” values (>1) are indicating the subsurface clay with minor sand dominating layers. There is a noticeable trend toward the northeastern part of the country in terms of low to intermediate “λ” (0.22–0.5) values (Fig. 5c). The mixed lithologies of sand gravels and boulders, as well as the low coefficient of anisotropy associated with the fractured bed rock material, are represented by intermediate anisotropy [58]. The low anisotropy also suggests high-density water-filled fractures in basement rocks [44], and although this research did not represent a particular basement complex, it was thought to be important for understanding groundwater potential.

The aquifer transmissivity, hydraulic conductivity, and formation resistivity are shown by Borehole Tube or well data (PS-01, PS-02, PS-03, PS-04, PS-05) (Table 1, Fig. 4, Additional file 1: Fig. S1). By comparing geophysical logs, a correlation between surface electrical resistivity and borehole data was developed, and resistivities derived from VES were connected to borehole lithologies [22]. TR and aquifer transmissivity have a direct connection, with the greatest TR values correlating to the highest aquifer transmissivity values, and vice versa [51, 52]. The aquifers’ transmissivity (T) varies from 19.52 to 41.56 m2/day, whereas hydraulic conductivity (K) values vary from (0.152 to 0.34 m/day) (Table 1). The aquifer's specific capacities have a significant role in the yield and discharge of the saturated aquifer, which varies from 2.33 to 8.0 gpm/ft (Table 1). The rate at which specific capacity increases or decreases reflects lithological change as well as groundwater flow. The abrupt lithological change might indicate a low-capacity aquifer system [7].

Aquifer system

Groundwater potential zones and the aquifer system’s behavior were determined using hydrogeological features such as the thickness of subsurface lithology, geo-electrical layer, saturation zone thickness, and the types of aquifers compared with borehole data. It is possible to use pumping test results to distinguish between various types of aquifers [4]. Clay layers serve as hydraulic barriers that separate aquifers because of their poor hydraulic conductivities [30]. During our research, we found that the aquifer was comprised of a mixture of unconsolidated material (clay, sand, and intermixed gravels and boulders) and bedrock (lacustrine mudstone) (Figs. 2, 4, Additional file 1: Fig. S1). This interpretation is based on Borehole data (PS-01, PS-02, PS-03, PS-04, PS-05), such as lithology, resistivity, and Spontaneous Potential (SP) well logs. Clay layers at a given depth serve as aquitards. Similarly, in PS-01, the aquitards, which consist of compacted clay layers, are found at depths ranging from 115 to 118 m. In PS-02, these aquitards extend from depths of 118–125 m. At PS-03, the aquitards start at a depth of 128–130 m. As for PS-04, the aquitards are present within a depth range of 119–123 m, while in PS-05, they vary between 127 and 132 m. Notably, in PS-04, the aquitards comprise a mixture of clay and sand layers, effectively acting as barriers for the confined aquifer zones. The saturated confined layer, characterized by highly saturated zones, initiates at a depth of approximately 119 m and extends down to the lower boundary of the aquifer. Barriers between unconfined and constrained aquifers are formed by the low-permeability formation or layer [4, 30]. The two types of aquifers exhibit contrasting storativity values, providing a useful means of distinguishing between them. Storativity refers to the capacity of an aquifer to store and release water [4]. In this context, the range of storativity values observed is between 0.000113 and 0.000213 (Table 1). These values suggest that the aquifers possess distinct storativity characteristics, enabling us to differentiate between them based on their ability to store and transmit water.

Discussion

Groundwater storage zone

The extremely impermeable clayey overburden protects the subterranean aquifer from contamination by surface runoff because of its high longitudinal conductivity. The research area’s central and northeastern sections provide good protective capacity with values between 0.29 and 0.65 mhos. The area’s Northwestern and Southwestern sides have a weak-to-poor protective capacity of 0.07–0.14 mhos (Table 4). Gravel, sand, and boulders are intermixed in low S levels, whereas mixed clay with gravel and sand is present in intermediate values. Protective layers may be formed when clay and silt are present in the stratum layer that lies under the aquifer. When present in high amounts, they form a protective cover [2]. The longitudinal conductance of low-resistivity materials varied from one VES point to the next, implying that the overall thickness of the materials changed [12, 67].

The identified subsurface resistivity variations in the unsaturated zones indicate the presence of potential groundwater reservoirs with varying permeability. The interlocking clay layers in the lithology of the saturated sediments suggest a relatively impermeable barrier that can retain water within certain zones [4]. The resistivity values ranging from 15 to 85 ohm-m in the unsaturated zones indicate variations in the porosity and moisture content of the sediments. Lower resistivity values (15 ohm-m) suggest higher porosity and increased moisture content, while higher resistivity values (85 ohm-m) indicate lower porosity and decreased moisture content [88], Table 2, Fig. 2. These variations can be attributed to differences in the composition and arrangement of sediments, as well as the degree of saturation. The VES soundings, specifically VES-1, VES-4, and VES-7, have provided preliminary interpretations based on the thickness of subsurface layers, resistivity values, and lithology. By analyzing these factors, an electro-stratigraphic column was compiled, illustrating the distribution of groundwater within each distinct subsurface layers (Fig. 2). These columns combine the results from the VES soundings and provide valuable insights into the potential locations and characteristics of groundwater reservoirs at different depths. These findings emphasize the complexity of the subsurface hydrogeological system, highlighting the interplay between lithological composition, resistivity values, and groundwater distribution. The identified interlocked clay layers contribute to the overall heterogeneity of the aquifer system, affecting its storage and transmission properties [89]. The high resistivity values are produced by intermixed sand, gravels, and boulders (23–120 ohm-m) [37]. Bedrock is exposed at higher altitudes, which may restrict currents from penetrating deeper (Fig. 1). According to Hodlur et al. [22], the low resistivity values are due to the presence of saturated sand and clay beneath the surface (Fig. 2).

In saturated conditions, the transverse resistance represents a hindrance to the lateral movement of groundwater within an aquifer. It is determined by several factors, including the hydraulic conductivity of the aquifer material, the thickness of the aquifer, and the presence of confining layers. The concept of transverse resistance was initially introduced by Dupuit. [90] as part of his work on groundwater flow in confined aquifers. Dupuit recognized that the lateral flow of groundwater is constrained by the presence of impermeable boundaries, resulting in resistance to transverse flow. In the recent study, the high TR values, ranging from 10000 to 22000 Ωm2, are predominant in the northwest to the southwest region. On the other hand, the middle southwestern section exhibits lower TR values of around 7000 Ωm2, while (TR) in this study ranges from 2300 to 22948 Ωm2 (Table 3, Fig. 5a). The presence of different geological formations and their respective resistivity characteristics play a crucial role in determining TR. The High TR values are associated with high-resistivity formations, indicating the presence of more resistive materials such as consolidated rocks, gravels, boulders and sandy soils (Figs. 2, 4, 5a). Higher TR values are generally associated with occurrences of deeper groundwater potential. Deeper groundwater potential implies a greater vertical distance between the water table and the surface, indicating more resistive subsurface layers [103]. These layers restrict the lateral flow of groundwater, resulting in higher transverse resistance. The total transverse resistance is one of the geo-electric properties used to define the major location of groundwater potential. The hydraulic conductivity values estimated from the borehole analysis at PS-01 and PS-02 exhibit intermediate to high values [104]. The hydraulic conductivity at PS-01 is estimated to be 0.152 m/day, while at PS-02, it is determined to be 0.34 m/day. As the TR is also dependent on the hydraulic conductivity, at the PS-01 and PS-02, the TR values are around 5000–7000 Ωm2, this indicates that the aquifer materials present at these locations have relatively high permeability. These values fall within the range of intermediate to high hydraulic conductivity, suggesting that the subsurface materials are conducive to groundwater flow. Higher hydraulic conductivity values generally indicate areas with greater groundwater recharge potential and faster rates of groundwater movement. Exceptionally high transverse resistance values relate to subsurface deposits that are very resistant [62]. Conversely, low TR values are found in areas with low-resistivity formations, such as clayed soils. Clayey soils typically have higher hydraulic conductivity but lower resistivity compared to other formations. As a result, they exhibit lower transverse resistance [92]. Transverse resistance values may also be used to estimate the flow direction of groundwater in an aquifer. The transverse resistance associated with the unsaturated aquifer thickness is often greater than the transverse resistance associated with the saturated aquifer thickness in the absence of or with exceptionally low clay concentration [51]. The boreholes PS-03 (36.3 m2/day) and PS-04 (41.56 m2/day) have the highest transmissivity values. However, the hydraulic conductivity (K) values at PS-03 and PS-04 are relatively high, measuring around 0.34 and 0.32 m/day, respectively (Fig. 5, Table 1). The high ratio of T and K in the study area represents the coarser lithological material or the fractured zones [27, 28, 54]. In the subsurface groundwater potential zones, medium to fine intermixed clay, sand, and gravel material with moderate to low T values could be suggested. The various thickness differences of the groundwater potential zones might be determined from low to high T and K values [9]. The variations in lithological composition and the presence of different materials in the subsurface can have significant implications for groundwater resource management. Coarser lithological materials, such as sands, gravels, and boulders typically reveal higher hydraulic conductivity due to their larger pore spaces, allowing water to flow more easily [105]. Fractured zones can create preferential pathways for groundwater flow, leading to increased transmissivity despite relatively high hydraulic conductivity. In contrast, the subsurface groundwater potential zones within the study area are characterized by medium to fine intermixed clay, sand, and gravel materials. These materials exhibit moderate to low transmissivity values. The moderate transmissivity values suggest that groundwater movement in these zones may be relatively slower compared to the areas with higher transmissivity.

3D model of an aquifer system

For the study area, a three-dimensional model of the subsurface aquifer system was developed (Fig. 6). The elevation and lithology variations on the surface and under the earth are shown in this geographical distribution model (Fig. 6a, b). The highest elevation more than 670 m, is found in the south and southeast, while the eastern and northern regions are at a lower level, less than 380 m (Figs. 1b, 6a, b). Aquifer parameters were compared with five boreholes (BH-02, BH-02, BH-03, BH-04, and BH-05) drilled in typically elevated regions using the hydrological model and their finding were matched with Zarrzok parameters (Fig. 6a, b). The resistivity profiles obtained from the Vertical Electrical Sounding (VES) technique provide valuable insights into the lithology and resistivity characteristics of the subsurface layers (Fig. 6a). The variation in resistivity observed across these layers reflects the differences in their composition and geological properties, shedding light on the subsurface strata (Fig. 6a). The shallow alluvial deposits have substantial lateral and vertical differences. Clay layers’ act as aquitards between the saturated layers in the well-developed aquifer system (Fig. 6c). When encountering a compacted clay layer, the resistivity values tend to increase significantly due to the limited conductivity and decreased water saturation. This high resistivity indicates that the clay layer acts as a barrier, preventing the vertical flow of water and confining the underlying aquifer [106]. An unconfined aquifer lacks an impermeable layer on top, allowing water to freely recharge and discharge through the aquifer. Resistivity values in unconfined aquifers can vary depending on the composition and saturation of the sediments. Higher resistivity values may indicate lower water content and higher porosity, suggesting the presence of unsaturated or partially saturated zones within the aquifer. A confined aquifer is characterized by an impermeable layer above and below the aquifer, which restricts the vertical movement of water. The resistivity values in confined aquifers tend to be higher due to the presence of compacted sediments or low-permeability layers, such as clay or shale [106, 107]. These layers act as barriers and impede the flow of groundwater, resulting in higher resistivity readings.

The presence of dry gravel and sands is associated with high resistivity levels in the borehole data and the VES subsurface resistivities of five hydrological layers used as an indicator to estimate the groundwater potential zones (Fig. 6b) [37]. A similar condition was discovered in the Peshawar Basin (Fig. 6b, c), where thick clay layers divide unconfined and confined aquifer zones [40].

Olatunji and Musa. [47] and Olayinka and Oyedele. [48] demonstrated the usefulness of the coefficient of anisotropy in determining aquifer type and storage capacity. By considering the anisotropic nature of the aquifer, these studies provided valuable insights into the aquifer's ability to transmit water and its storage potential. In addition to its relationship with lithology and hydraulic properties, electrical anisotropy has been linked to the inhomogeneity of underlying materials. Olasehinde and Bayewu. [46] investigated the connection between inhomogeneity and water development. They found that the parameter λ provides information on the inhomogeneity of underlying materials like topsoil and aquifer layers. Recent research has identified an optimal range of λ values between 0.27 and 1.35, which is suitable for characterizing inhomogeneity and spatial variations (Table 3). Furthermore, regional variations in electrical anisotropy have been observed. In the northwestern section of the study area, high λ values (>1) indicate the dominance of subsurface clay layers with minor sandy layers. Conversely, the northeastern part of the country exhibits low to intermediate λ values (0.22–0.5) (Fig. 5c). These variations in electrical anisotropy across different regions provide insights into subsurface geological heterogeneity and can be useful for understanding aquifer architecture and groundwater flow patterns [107]. Similarly, storatvity is one of the important factor for differentiating aquifer types. According to Atangana. [4], two kinds of aquifers have differing storativity values, which may be used to differentiate between them in a recent study we observed the storativity values of 0.000113–0.000213 (Table1). From 0.01% to less than 1% of aquifer capacity may be attributed to confined wells. Although the specific yield (also known as storativity) of an unconfined aquifer is more than 0.01, this suggests that confined aquifers store water by extending their matrix and compressing water, both of which are often small in quantity [65]. In the PS-04 the specific capacity is highest up to 8.0 gpm/ft and the discharge rate 654.119 m3/day, while the drawdown is almost 4.57 m, moreover the transmissivity and storativity exceed 41.56 m2/day and 0.000281, respectively (Table 1). A combination of high values for aquifer parameters, including specific capacity, discharge rate, and low drawdown, transmissivity, and storativity, suggests a highly productive and efficient groundwater system [109]. High specific capacity indicates the aquifer’s ability to deliver water to wells, while a high discharge rate implies a substantial release of water. Low drawdown indicates a minimal decline in water levels during pumping, highlighting the aquifer’s responsiveness. High transmissivity signifies efficient horizontal water flow, and high storativity reflects the aquifer's substantial water storage capacity. Together, these characteristics suggest a well-connected aquifer with ample water supply, conducive to sustainable water resource development and various water-dependent activities [108, 110]. Recent studies suggest that the aquifer system is comprised of three types of aquifers: unconfined, semi-confined, and confined. Alluvial to fluvial deposits in our study area are hydrogeological significant because of their inter-layered and diverse lithologies of clays, gravels, sands, and boulders [40]. Cornwell [10] reposted that the Peshawar basin is composed of thin, horizontally bedded sand, silt, and clay layers that are flooded in nature. Late Pleistocene lakes over the Peshawar basin were originally thought to have deposited these sediments [19, 32]. Because the sediments were accumulated by weathering and erosion in situ, they have a limited ability to be sorted by their composition [40]. The analysis of borehole data provides valuable insights into the characteristics of the aquifer system. The data indicates the presence of an alluvial overburden aquifer system (Figs. 4, 6bc). Within this system, the initial depth of the confined aquifer varies across different boreholes, ranging from 112 meters to 130 meters. In the unconfined to semi-confined region, aquifers with a thickness ranging from 24 meters to 110 meters can be observed (Figs. 4, 6bc, Additional file 1: Fig. S1). These findings highlight the variability in aquifer depth and thickness within the study area. These aquifers were formed by the rapid deposition of coarser materials at high speeds, while the slower deposition of finer sediments was caused by variations in rainfall, topography, and streamflow [63].

Saturated aquifer system range from semi-confined to confined zones, and the boreholes (PS-01 to 05) has a saturated thickness of more than 130 m. The hydrogeological characterization of aquitards in multiple borehole stations reveals significant variations in depth, composition, and potential implications for groundwater dynamics and resource vulnerability. At PS-01, aquitards consisting of compacted clay layers are found at depths ranging from 115 to 118 m, acting as barriers to prevent vertical water movement between aquifer zones. This suggests relatively good protection of the confined aquifer zone against potential contamination from overlying layers. In contrast, at PS-02, aquitards extend from depths of 118–125 m, indicating potential differences in the local geological setting and influencing groundwater connectivity and vulnerability (Figs. 4, 6bc). The significance of aquitard continuity in controlling groundwater flow patterns and recharge rates has been emphasized in previous studies [111]. PS-03 exhibits aquitards starting at a deeper depth of 128–130 m, suggesting distinct hydrogeological conditions that need to be understood to assess groundwater dynamics and resource vulnerability. PS-04 features aquitards within a depth range of 119–123 m, comprising a heterogeneous mixture of clay and sand layers. This unique composition raises concerns about permeability, hydraulic conductivity, preferential flow paths, and increased vulnerability to contaminant migration (Figs. 4, 6bc). Further investigations are required to comprehend the implications of this heterogeneous aquitard. Similarly, in PS-05, aquitards vary in depth between 127 and 132 m, indicating distinct hydrogeological conditions that may influence groundwater movement, recharge rates, and the availability and quality of the confined aquifer resource. Understanding the specific characteristics of aquitards in each borehole site is crucial for effective groundwater management and protection of this vital resource [98, 108, 111, 112]. The recent study findings regarding the starting depths of confined layers in each borehole location provide valuable insights into the hydrogeological characteristics of the study area. The data suggests a consistent pattern where the highly saturated zones originate at an approximate depth of 119 m and extend downward until reaching the lower boundary of the aquifer. This observation indicates the presence of a significant water-bearing zone within the confined aquifer, emphasizing its potential as a vital water resource. These findings highlight the importance of understanding the depth and extent of the confined layers in order to effectively manage and utilize the highly saturated zones within the aquifer for sustainable water supply.

According to this study, which confirms previous findings, the Bara River and rain feeds are the major sources of recharge for subsurface groundwater aquifers [11]. Freshwater is concentrated in the Peshawar basin’s aquifer system. An ancient stream may have been submerged under more recent sediments, as suggested by these aquifer systems, according to Seong et al. [53].

Conclusions

This research was focused on groundwater potentiality and aquifer features from the Southern Peshawar region, which revealed fascinating geoelectrical and hydrogeological approaches. Hydrogeological potentially of the study was delineated by implementing the vertical electrical resistivity (VES), tube well data, and pumping test analysis. During this study, 13 VES and five Borehole data were used to assess the groundwater potential zone. Dar-Zarrouk parameters usually transverse resistance (TR), longitudinal conductance (S), and coefficient of Anisotropy (λ) show a variation in the distribution of the aquifer system. These findings shed light on the complex nature of the subsurface aquifers. The Pumping test results elucidated the profound influence of transmissivity (T) and hydraulic conductivity (K) on the rate of discharge and the type and characteristics of the aquifers. This valuable information provides crucial insights for understanding and managing the groundwater resources in the region Aquifer system constitutes an unconfined, semi-confined, and confined nature with the beginning depth of the confined aquifer ranging from 118 m to 130 m, depending on the borehole. While the thickness of unconfined to semi-confined aquifers ranges from 24 to 110 m, these aquifers are formed by the deposition of fine to coarser materials (clay, sand, gravel and boulders). Importantly, the presence of low-permeability clay layers acted as aquitards, exhibiting very low hydraulic conductivity. These clay layers play a significant role in confining and separating the aquifer units within the system. The Aquifer in the Southern Peshawar region proved to be a valuable storage reservoir, containing a substantial amount of groundwater at considerable depths. The transmissivity and conductivity of the aquifers ranged from low to intermediate values, indicating the potential for groundwater utilization in the study area.