# Integrated Geoelectrical and Geological Investigation of a Quaternary Paleo-Depositional Environment in the Haripur Basin, Northern Pakistan: Implications for Groundwater System

Authors: Umair Bin Nisar; Siddique Akhtar Ehsan; Muhammad Farooq; Ramesh Raj Pant; Nangyal Ghani Khan; Faizan Ur Rehman Qaiser; Furqan Mahmud Butt
Journal: Geofluids
 (2023)

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## Abstract

The deposition in Haripur basin not only provides a contemporary insight into old fluvial depositional sequences of the Himalayan foreland but also sheds light on the important continental depositions in a monsoon controlled foreland system. The present study emphasizes the evaluation of the paleo-depositional architecture for sustainable groundwater availability by utilizing a total of four field-based geological observations, eleven boreholes, and fifty-nine vertical electrical sounding (VES) datasets. The acquired surface geological data well correlate with resistivity and borehole data. The derived results of the lithostratigraphic cross-sections and spatial distribution maps reveal three-sided closure depositional. These depositional directions indicate thick successions of coarser sediments near the foothills and interbedded mixture of coarser and finer sediments toward the central and southern parts of the basin. The former conditions provide maximum groundwater yielding capacity for sustainable groundwater supply in the north-eastern and north-western parts of the basin. On the contrary, in the central and southern parts of the basin, the groundwater yielding capacities have drastically decreased due to deposition of finer sediments.


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## Body

## 1. Introduction

Safe water supply and sanitation are among the basic human rights. Ensuring the accessibility of both contributes to the well-being of the citizens. However, the situation gets worse in developing countries, where limited funds are allocated for safe water supply and sanitation [1]. The availability of safe groundwater is an inevitable issue that needs to be addressed. Groundwater resources are not being monitored due to the absence of regulatory authority for water management [2, 3]. The Quaternary paleo-depositional environment plays a vital role in groundwater resources worldwide.The near-surface geological and geophysical techniques are useful for investigating the groundwater resources in the Quaternary depositional environment, as these techniques provide high-resolution subsurface images [4, 5]. The electrical resistivity techniques are widely implemented for geological and hydrogeological studies [6]. Several researchers utilized electrical resistivity survey for various near-surface geological issues including groundwater exploration, mineral exploration, bedrock identification for multistoried buildings, near-surface geological structures such as faults and folds, alluvial fans, basin architecture, and detection of contaminant plumes in groundwater aquifers, respectively [7–15].Total population in the Haripur basin is about four million, most of which reside in small towns [16]. The Haripur basin has a semiarid climate with hot summer and moderate winter. Temperature varies from 21°C to 35°C in summer and from 17°C to 28°C in winter. The surface soil comprises the alluvial and fluvial deposits (Figure 1). The main source of income for local community is agriculture and industries. The southern parts of the basin are irrigated with the water stored in the Khanpur Dam, which also supplies water to Islamabad and Rawalpindi area [17]. Due to rapid urbanization and industrialization across the basin, groundwater aquifers are under stress [17]. In this paper, we focus on integration of vertical electrical sounding (VES), borehole data, and field-based geological data collected across Haripur basin, with the main objectives of (i) investigating the Quaternary paleo-depositional environment and its relation with subsurface groundwater resources and (ii) delineating the dimensions and structures of the aquifer zones in the Quaternary paleo-depositional environment for sustainable groundwater availability.Figure 1
(a) Elevation map; (b) geological units in the study area (modified after [5]). The Haripur basin mainly comprises alluvium bounded by mountains. Tarbella reservoir lies in northwest, whereas dominant streams include Dhotal Kas and Jabbi Kas.
(a)(b)


## 2. Geological Settings

Pakistan has a unique global tectonic framework with the collision of three main tectonic plates: Indian, Eurasian, and Arabian plate [18]. Indian-Eurasian continental-continental collision occurred about 50 million years ago resulting in the formation of Himalayan orogeny [19]. These tectonic plates formulated all kind of geological structure in the entire Pakistan; Haripur basin is one such example. This basin is bounded by Nathia Gali Hissartang in the north, by Margalla Hills in the east, by Gandghar ranges in the west, and by Haripur alluvial/fluvial plain area in the south (Figure 1). The Gandghar ranges comprise Proterozoic, Paleozoic, and Mesozoic Formations. Gandaf formation is the oldest rock formation exposed near the Tarbella dam overlain by Manki formation. The dominating lithologies of Gandaf formation are calcareous phyllitic schist. Manki formation comprises phyllitic, argillitic marble and metasiltstone. Shahkot formation overlies Manki formation and is dominated by limestone [20]. The other major formation comprises Tanawal formation which is dominated by feldspathic sandstone, siltstone, and shale. Tanawal formation, in addition, also contains Sirban dolomite of Abbottabad group.The Nathia Gali Hissartang block comprises rocks from Cambrian, Proterozoic, Mesozoic, and Tertiary age. The oldest rocks of Proterozoic are attributed to Hazara formation. The dominant lithologies include slates and shale [20]. The Cambrian formations in this block include Abbottabad group which is further subdivided into Sirban, Kakul, and Tanawal formations. The lithologies include siltstone, mudstone, and glauconitic and phosphatic shale. Kakul formation comprises Tanaki conglomerate derived from above lying Hazara formation [21, 22]. Data formation of Mesozoic age consists of shale and sandstone lies over Shinwari formation dominated by shale interbedded with limestone. Middle Jurassic Samanasuk formation consists of limestone and lies over Shinwari formation. The Margalla hill block comprises of Paleocene, Cambrian, Cenozoic, and Mesozoic successions. The Paleocene Hangu formation is dominated by grey to reddish brown sandstone along with argillaceous limestone. The Lockhart formation lies conformably over Hangu formation. The dominating lithologies include limestone, shale, and marl at some locations [23].Haripur Plain is drained by Dor River and its tributaries (Figure1). The central, southern, and southeastern parts of the basin are dominated by thick clay deposits which are eroded and deposited by various drains in the area (Figures 1(b) and 2). The clay cover is underlain by sand, gravel, and boulders having variable thicknesses [17]; most of the permeable layers are identified towards the north, east, and west near the foothills which can serve as potential aquifers for the area (Figure 2). Hazara slates act as basement for the overlying clay, sand, and gravel deposits [24].Figure 2
Geological features at four different locations across the Haripur basin. (a) Massive clay identified in the vicinity of Haripur city, (b) interbedded gravel and sand with finer clay and sandy clay identified across upstream areas of Hattar Industrial Estate, (c) thick succession of clay and coarse gravel with sand near khanpur, and (d) interbedded clay and gravel with sand in the Deedan village. The locations of the geological field sites (a–d) are highlighted on the geological map presented in Figure1.
(a)(b)(c)(d)From a hydrogeological perspective, the Quaternary paleo-deposits play a vital role in water storage. The coarser lithologies towards the northern, eastern, and western parts serve as groundwater bearing bodies due to high permeability [17]. These paleo-channels carry most of the aquifer system present in the basin; therefore, demarcation of these paleo-channels is very important. The main tectonic features of the study area include Nathiagali thrust and Khairabad fault. Khairabad fault is a thrust fault striking NNW through the center of the basin and merges into main boundary thrust near Muzaffarabad; due to this thrust, basement rocks are exposed in some localities of Haripur basin, i.e., Hazara slates [24].


## 3. Methodology

### 3.1. Geological Field Data

A geological field trip was conducted to study four sites with various geological and depositional features of the study area (Figure2). The primary objective of the geological field was to identify the depositional pattern of Quaternary deposits. The geological fieldwork involved measurement of geological cross-sections and identification of depositional trends of the stream, which contributed to the distribution of the sediments. The borehole and VES data were also integrated with surface geological features to better understand the volumetric dimension of the basin.


### 3.2. Borehole Data

A total of eleven boreholes were drilled to constrain various lithologies (Figure3). Borehole data were acquired in the form of driller’s log. The driller’s log contained lithological information of subsurface at different depths. The driller’s log requires minor adjustments for rock samples encountered at deeper levels. This minor adjustments in depth were made considering the delay factor for rocks samples encountered at greater depths that tend to reach at the surface with relatively delayed time. These boreholes were utilized as a scale for the calibration of VES points in order to increase the reliability of the subsurface model.Figure 3
Location of the boreholes, VES points, and subsurface cross-sections are highlighted on the base map of the study area. A total of six subsurface cross-sections (A-A’, B-B’, C-C’, D-D’, E-E’, and F-F’) were generated utilizing these datasets and presented in Figure7.


### 3.3. Vertical Electrical Sounding Data

An ABEM SAS 1000 Terrameter with Schlumberger electrode configuration is utilized to acquire VES dataset across the Haripur basin (Figures4(a) and 4(b)). The system consists of four electrodes placed in a straight line and plugged into the earth. The two outer electrodes, A and B, are current electrodes, and the two inner electrodes, M and N, are potential electrodes (Figures 4(a) and 4(b)). The current electrodes are used to inject current into the ground (Figure 4(a)) and two potential electrodes reading the potential difference values after the current passes through the stratified rocks (Figure 4(b)). The depth of current penetration into the ground is proportional to electrodes spacing [25]. The longer distance between the current electrodes will cause the flow of electric current to penetrate deeper rock layers (Figure 4(a)). The electric current flowing through the subsurface rock layers causes electrical voltage that can be measured using a multimeter connected through the voltage electrodes. The distance among the potential electrodes is kept smaller than the current electrodes (Figures 4(a) and 4(b)). For this survey, the maximum current electrode (AB/2) and potential electrode (MN/2) spacing ranges were 1 to 1000 m and 0.5 to 200 m, respectively. The electrode spacing were modified at places due to topographical constraints in the northern portion of the study area (Table 1).Figure 4
(a) Schematic illustration of the basic measurements using electrical resistivity method. Solid black lines represent current flow through layered subsurface structure. Dashed red line contours electrical potential, and (b) the Schlumberger electrode configuration is utilized for this study. AB represents spacing between current electrodes, and MN represents spacing between potential electrodes (modified after [29–31]).
(a)(b)Table 1
Resistivity ranges associated with different lithological units across the study area (modified after Yadav et al. [28]).
Resistivity (Ωm)Lithological interpretation15-20Clay10-20Silty clay and silty sand25-70Fine to medium grain sand45-220Medium to coarse grain sand with gravels650-1300Unsaturated gravel≥800TopsoilFor qualitative processing and interpretation of the raw VES field data, 1X1D Interprex(™) and IPI2WIN were utilized [26, 27]. The sounding curve (Figure 5(a)) represents a reliable relationship between electrode spacing (AB/2) and apparent resistivity (ρa). The field data from each sounding curve was plotted on bilogarithmic scale, with the current electrode spacing flow through layered subsurface structure. Dashed red line contours electrical potential. (AB/2) was plotted along abscissa and the acquired apparent resistivity (ρa) values along ordinate (Figure 5(a)). The curve formed by such plotting is called field curve. The acquired field curve was then correlated with the characteristic curve; by this process, thickness and true resistivity of each layer were computed. The default RMS error for each VES point was set as 2.5%. This error was high at some localities due to inclusion of noisy points which were corrected thus reducing the RMS error (Figure 5). Table 1 shows the resistivity ranges of various lithological units derived by correlating VES and borehole datasets [28].Figure 5
(a) The VES point (E5) acquired in the northeastern part of the study area. The best fit characteristic inversion curve (black line) is drawn on the acquired subsurface resistivity data points highlighted with red dots. (b) Brehole (BH-10) drilled nearby the E5 shows three main lithologies in the subsurface. The blue curve is the inversion of the resistivity points that also indicate generalized subsurface layers with thicknesses.


## 3.1. Geological Field Data

A geological field trip was conducted to study four sites with various geological and depositional features of the study area (Figure2). The primary objective of the geological field was to identify the depositional pattern of Quaternary deposits. The geological fieldwork involved measurement of geological cross-sections and identification of depositional trends of the stream, which contributed to the distribution of the sediments. The borehole and VES data were also integrated with surface geological features to better understand the volumetric dimension of the basin.


## 3.2. Borehole Data

A total of eleven boreholes were drilled to constrain various lithologies (Figure3). Borehole data were acquired in the form of driller’s log. The driller’s log contained lithological information of subsurface at different depths. The driller’s log requires minor adjustments for rock samples encountered at deeper levels. This minor adjustments in depth were made considering the delay factor for rocks samples encountered at greater depths that tend to reach at the surface with relatively delayed time. These boreholes were utilized as a scale for the calibration of VES points in order to increase the reliability of the subsurface model.Figure 3
Location of the boreholes, VES points, and subsurface cross-sections are highlighted on the base map of the study area. A total of six subsurface cross-sections (A-A’, B-B’, C-C’, D-D’, E-E’, and F-F’) were generated utilizing these datasets and presented in Figure7.


## 3.3. Vertical Electrical Sounding Data

An ABEM SAS 1000 Terrameter with Schlumberger electrode configuration is utilized to acquire VES dataset across the Haripur basin (Figures4(a) and 4(b)). The system consists of four electrodes placed in a straight line and plugged into the earth. The two outer electrodes, A and B, are current electrodes, and the two inner electrodes, M and N, are potential electrodes (Figures 4(a) and 4(b)). The current electrodes are used to inject current into the ground (Figure 4(a)) and two potential electrodes reading the potential difference values after the current passes through the stratified rocks (Figure 4(b)). The depth of current penetration into the ground is proportional to electrodes spacing [25]. The longer distance between the current electrodes will cause the flow of electric current to penetrate deeper rock layers (Figure 4(a)). The electric current flowing through the subsurface rock layers causes electrical voltage that can be measured using a multimeter connected through the voltage electrodes. The distance among the potential electrodes is kept smaller than the current electrodes (Figures 4(a) and 4(b)). For this survey, the maximum current electrode (AB/2) and potential electrode (MN/2) spacing ranges were 1 to 1000 m and 0.5 to 200 m, respectively. The electrode spacing were modified at places due to topographical constraints in the northern portion of the study area (Table 1).Figure 4
(a) Schematic illustration of the basic measurements using electrical resistivity method. Solid black lines represent current flow through layered subsurface structure. Dashed red line contours electrical potential, and (b) the Schlumberger electrode configuration is utilized for this study. AB represents spacing between current electrodes, and MN represents spacing between potential electrodes (modified after [29–31]).
(a)(b)Table 1
Resistivity ranges associated with different lithological units across the study area (modified after Yadav et al. [28]).
Resistivity (Ωm)Lithological interpretation15-20Clay10-20Silty clay and silty sand25-70Fine to medium grain sand45-220Medium to coarse grain sand with gravels650-1300Unsaturated gravel≥800TopsoilFor qualitative processing and interpretation of the raw VES field data, 1X1D Interprex(™) and IPI2WIN were utilized [26, 27]. The sounding curve (Figure 5(a)) represents a reliable relationship between electrode spacing (AB/2) and apparent resistivity (ρa). The field data from each sounding curve was plotted on bilogarithmic scale, with the current electrode spacing flow through layered subsurface structure. Dashed red line contours electrical potential. (AB/2) was plotted along abscissa and the acquired apparent resistivity (ρa) values along ordinate (Figure 5(a)). The curve formed by such plotting is called field curve. The acquired field curve was then correlated with the characteristic curve; by this process, thickness and true resistivity of each layer were computed. The default RMS error for each VES point was set as 2.5%. This error was high at some localities due to inclusion of noisy points which were corrected thus reducing the RMS error (Figure 5). Table 1 shows the resistivity ranges of various lithological units derived by correlating VES and borehole datasets [28].Figure 5
(a) The VES point (E5) acquired in the northeastern part of the study area. The best fit characteristic inversion curve (black line) is drawn on the acquired subsurface resistivity data points highlighted with red dots. (b) Brehole (BH-10) drilled nearby the E5 shows three main lithologies in the subsurface. The blue curve is the inversion of the resistivity points that also indicate generalized subsurface layers with thicknesses.


## 4. Results and Discussion

The geological field observations were useful to identify and categorize the subsurface units. Sediment size has direct relationship with the transporting agents and their velocities. Coarser sediments dominate the foothills or depositional mouths, and finer sediments indicate calm conditions and low stream velocity [32]. On the basis of geological field data patterns of sand, silt and clay were divided into several geomorphic units in Peshawar basin, Pakistan [33]. Kevin [33] also identified several rhythmic depositional cycles of sediments including sand silt and clay in the west of study area. This suggested that stacked sequences are periodic breakout flood deposits. These Quaternary deposits are associated with Kabul and Indus rivers flowing in the region [33]. The lithologs generated by field measurements indicate the variations in river energy over the time [33]. Similar approach was adopted for current work in which lithologs are generated based on the geophysical and borehole datasets in the Haripur basin drained by the Dor River.The outcrops indicate progressive decrease in the sediment size across the central and southern parts of the Haripur basin (Figures2(a) and 2(b)). In the eastern, northern, and western parts, coarser and large grain size lithologies are present. This may indicate high stream energy [34]. The fining upward grain size is indicative of progressive loss of river energy, through time, within the river channel as the flow velocity decreases [34].


### 4.1. VES Calibration with Borehole Logs

The computation of true formation resistivity is essential for a reliable interpretation of electrical resistivity data. Thicknesses of individual subsurface layers are derived from the true formation resistivity. The layer parameters identified in several VES are calibrated with the nearest available boreholes across the basin (Figure5(b)). The borehole data reveals that subsurface lithologies consist of Hazara slate acting as a basement rock overlain by the Quaternary alluvial deposits. These Quaternary deposits are represented by clay, silty clay, sand, gravel, boulder, and mixture of these lithologies. These deposits are important due to their ability to store a quantity of water of economic interest. The sandy material is considered a proven groundwater aquifer as these bodies have good porosity and permeability to store and transmit the groundwater [28]. Resistivity method among other geophysical techniques is highly sensitive to lithological and pore fluid variations. It is essential to calibrate VES results with the borehole lithologies to place strong constraints on its reliability [28].The VES data shows six subsurface layers well-constrained by borehole data across different locations in the basin (Table1). The topsoil reveals the highest resistivity value about 800 Ωm. It reveals variable thickness ranging from 1 m to 5 m in the north, south, and central regions. Massive clay succession with interbedded sand and gravel packages encountered during the borehole drilling shows relatively low resistivity values [17, 28]. The resistivity values range from 15 to 20 Ωm for the clay. The resistivity values range from 10 to 50 Ωm for silty clay. In case of saturated silty clay resistivity of the material drastically reduces. On the contrary, dry silty clay reveals relatively high resistivity values. The resistivity values range from 25 to 70 Ωm for sandy material. Gravel packages encountered during drilling show a resistivity value of 65-1300 Ωm (Table 1). The borehole and VES reveals the presence of gravel packages and silty clay in the central and southern parts of the basin. Based on the integrated results, the Haripur basin can be classified into two distinct geomorphic units: (i) massive clay units with interbedded coarse clasts mainly in the south and central regions and (ii) the dominant gravel and sand units interbedded with minor clays in the northeast and west.


#### 4.1.1. Northern Part of the Basin

The calibration of VES dataset with borehole stratigraphy is carried for the interpretation of the resistivity curves in the proximity of Havelian and adjoining areas (Figure1(b)). A 100 m drill-hole (BH-10) dominated by stream deposits in the proximity of Havelian was selected for calibration with the VES point (E5) (Figures 3 and 6(a)). The Havelian area consists of two dominating lithological units’ boulder and clay with gravel of nonuniform thicknesses of about 15-20 m separated by finer sediments such as silty clay and clayey beds (Figure 6(a)). The area is located within paleo-meanders of the Dor River, where intermittent flooding events in the Quaternary age indicate high energy conditions [17].Figure 6
(a–c) VES curves (E5, D6, and D3) showing well-correlation with the lithological units, thicknesses, and depths, encountered in the boreholes (BH-10, BH-09, and BH-02) in the northern, central, and southern regions across the Haripur basin.The VES curve correlated well with the stratigraphic units derived from the borehole data (Figure6(a)). VES result provided high resolution for the upper unsaturated soil layer of relatively high resistivity about 800 Ωm. The upper clay with gravel is reflected well with resistivity values between 100-180 Ωm. The lower boulder body of 20 m is separated from the clay with gravel body by intervening silty clay which reflects a sharp change in electrical resistivity values of 20 Ωm. The resistivity values of clay with gravel are much higher (80 Ωm) than the clayey body, suggesting a dry coarser texture. These lithologies correlate well with the borehole stratigraphy. The massive boulder body ranging from 45 to 100 m is saturated by groundwater, which is evident from decreasing resistivity values in VES dataset.


#### 4.1.2. Central Part of the Basin

A 120 m drilled borehole (BH 09) in the proximity of Nathiagali/Haripur area was selected for the calibration with VES point B7 (Figure6(b)). The adjoining areas of Haripur are underlain by deposits of multilithological units such as massive gravel and silty clay along with interbedded clay units [24]. BH-09 (Figure 6(b)) shows the first gravel unit with a thickness of 22 m followed by clay with gravel units having a thickness of 20 m. The second gravel unit starting at depth of 40 m has a total thickness of 42 m with interbedded clay units of variable thicknesses. This gravel unit is underlain by a massive silty unit of 30 m thickness followed by a boulder unit. The area is located in the proximity of the Dor River and represents a high-energy condition indicating seasonal streams progressing further west towards Tarbella reservoir [17]. The result of VES data shows good correlation with the borehole data (Figure 6(b)). After the very high resistive topsoil about 900 Ωm, the upper gravel layer of high resistivity is well-resolved by the resistivity data. The high resistivity values about 80 Ωm of the upper gravel layer may suggest presence of unsaturated body. The second unit is indicated by a change in resistivity values due to the presence of moist clay with gravel about 60 Ωm. At a depth of about 40 m, a decrease in resistivity values about 50 Ωm indicates the presence of another saturated gravel body which is followed by saturated clays having a resistivity range of 19-30 Ωm. This second gravel body at depth of 40 m can serve as saturated zone of a confined aquifer. Subsurface layers of sand and gravel encountered at about 40 m depth can yield economic quantities of water pertaining to high porosity and permeability, lateral extent, and sufficient thickness. This refers to quantity of groundwater that can be delivered to increasing population and industry. However, no pumping test is carried out in the region to identify aquifer characteristics and to describe quantitative information of groundwater.


#### 4.1.3. Southern Part of the Basin

The VES point D9 and borehole stratigraphy (BH 02) of 130 m depth located in the proximity of Hattar and Haripur area were selected for calibration (Figure6(c)). The geological fieldwork (Figure 2) carried out in these areas revealed multiepisodes of stream deposits dominated by low-energy conditions. Furthermore, the area comprises two lithological units: a massive clay unit with minor interbedded sand bodies and a second unit comprised of massive sand with gravel body with variable sediment size.Figure6(c) shows that the borehole (BH-02) consists of two major lithologies, i.e., clay and fine to coarse sand. Beneath the surface soil layer, a massive silty clay body of 50 m thickness exists which is underlain by coarser sand body of approximately 7 m thickness followed by another massive silty clay body with a thickness of approximately 55 m. These massive silty clay units are underlain by sand and fine sand beds with a thickness of approximately 20 m. The area is located at a proximal distance about 13 km from the Dor River, and dominating lithologies are fine-grained indicating low energy conditions (Figure 2(a)). The VES curve acquired at the Hattar area shows resistivity values ranging from 19 to 920 Ωm. Relatively higher resistivity values are encountered in the upper part that suggest presence of the unsaturated silty clay deposits, whereas the intermediate resistivity values that occur beneath the low resistivity values, ranging from 40 to 50 Ωm, may indicate sand beds. This sand layer could act as an aquifer with high yielding capacity. A very low resistivity zone ranging from 19 to 20 Ωm is identified by VES curve as massive saturated silty clay. This massive silty clay may suggest low-energy conditions associated with the Dor River and its tributaries. The VES curve shows an increase in the resistivity values linked with the sand body lying at a depth of about 115 m having a resistivity value ranging from 40 to 50 Ωm. The presence of massive sand at this depth indicates high-energy channel deposition and can act as a confined aquifer that can produce sustainable groundwater for local population and industry [30].


### 4.2. Reconstruction of Quaternary Architecture

The VES data is well-correlated with surface geological observations and borehole logs. This integrated approach shows remarkable results in estimating Quaternary paleo-depositional environment of the basin. The electrical resistivity values established by [28] were utilized to infer electro-stratigraphy for the development of alluvial architecture (Table 1). The alluvial architecture is produced by integrating sixty VES curves, eleven boreholes, and exposed surface geological sections. The Haripur basin lies in the monotonously flat plains; however, there are gradual variations in the elevation from east to west (Figure 1(a)). The results derived from the datasets are used to develop six lithostratigraphic cross-sections (A-A/, B-B/, C-C/, D-D/, E-E/, and F-F/), each about 100 m deep across the basin (Figures 7(a)–7(f)).Figure 7
(a–f) Cross-sections based on well-calibrated electrical resistivity values with borehole dataset. Lithological variations across the cross-sections are associated with stream fluctuations. The orientation of the cross-sections is also represented on this map and also in Figure3.The cross-section A-A/ (Figure 7(a)) is about 20 km long and developed from the northwest to southeast by using twelve VES points and two deep boreholes drilled close to the Dor River. It begins from Nathiagali towards the Tarbella reservoir (Figure 3). The cross-section A-A/ reveals a deposition sequence that is indicative of mainly three episodes (Figure 7(a)). From surface down to 50 m depth, rock layers are predominated by the coarser sediments. The second episode is characterized by patches of clay sediments that lies at about 50 m to 80 m depth at different locations (Figure 7(a)). A massive gravel and boulder layer about 20 m thick is identified at 80 m depth (Figure 7(a)). The deposition sequence across A-A/ represents coarser sedimentary layer and a thin layer of finer sediment and then a massive gravel and boulder layer. This suggests fluctuations in stream velocities from high stream to low stream energy and flood dominated period. The channel activity indicted by clay lenses present at about 20 m and 75 m depths also suggests variable stream activity and sediment influx. This cross-section A-A/ well dominated by coarser sedimentary layers may act as aquifer bodies at various depths that can yield water quantities at a higher rate.The cross-section B-B/ is constructed using fifteen VES points and four boreholes (Figures 3 and 7(b)). It is about 18 km long and runs from the north to south (Figure 7(b)). The cross-section B-B/ can be divided into two main lithological units: (i) from surface down to 80 m depth finer material consisting of clay and silt and (ii) bottom part from 80 to 110 m comprising coarser lithologies dominated by gravel (Figure 7(b)). The presence of gravel lenses at about 25 m depth indicates the transition locations of JabiKas and JariKas streams across the cross-section B-B/. A progressive loss in stream energy may deposit finer sediments [35]. This region contains mainly fine grain sediments that are impermeable and may contribute very low-yield groundwater.The cross-section C-C/ run from north to south parallel to cross-section B-B/ (Figure 7(c)). It is about 14 km long and generated by using seven VES points and three boreholes (Figure 3). The cross-section also reveals two main lithological units (Figure 7(c)). The first lithological layer consists of finer particles having a thickness of about 50 m. The second lithological unit is dominated by coarser lithologies ranging from 50 m to 100 m depth. The cross-section also reveals two coarse grain lenses about 20 m deep and two thin lenses of fine sediments at about 70 m depth. This deposition of coarser sediments within finer lithological layers pertains to a loss in the stream energy resulting in deposition of lightweight coarser sediments. The two lenses consisting of finer sediments suggest variation in sediment influx during deposition. The shallower lithologies may yield less water due to impermeability, whereas, the deeper layers can safely yield groundwater. The lenses identified in the north and south of cross-section can act as perched aquifers with low yield due to less spatial extent and clay domination above and below.The cross-section D-D/ (Figures 3 and 7(d)) is about 10 km long and oriented in north south direction. It is constructed using nine VES points and nine boreholes. The cross-section mainly reveals two major depositional sequences (Figure 7(d)). The first deposition comprises finer sediments ranging from the surface down to 60 m depth. This deposition sequence suggests a loss in stream energy depositing lighter weight sediments. A considerable increase in the stream energy might result in deposition of coarser layer about 20 m thick. Two coarser grain lenses at about 25 m depth are also observed in the north and south of cross-section indicating variation in stream load periodically (Figure 7(d)). The coarser layer at about 60 m depth capped at top and bottom by finer sedimentary sequences can transmit groundwater of economic interest to the local community.The cross-section E-E/ (Figures 3 and 7(e)) is formulated using eight VES points and three boreholes having depth of about 100 m along a north-south profile. The top surface layer consists of variable grades of clay mixed with gravel and boulder throughout the section due to which electrical resistivity ranges from 20 to 60 Ωm. The gravel and boulder facies dominate in the steep narrow valley from Havelian towards the center of the basin. Around Havelian area, the upper gravel and boulder body appears to be quite extensive (spatially and vertically) consisting of medium-size gravel deposits, whereas near Haripur, the upper gravel and boulder body is comparatively thin, and lower sand mixed with clay is approximately 30-40 m thick. The upper gravel and boulder body corresponds to subsurface deposition of the present-day Dor River [24]. The coarser lithologies encountered across this cross-section can provide water storage capacities with high yield.The cross-section F-F/ (Figures 3 and 7(f)) lies in an east-west direction and comprises four VES points and three boreholes. The total depth of this cross-section is 105 m; part of this cross-section lies near the foothills while the remaining part lies in the center of the basin. Bedrock is exposed along this cross-section. Towards the east of the bedrock, a coarse sediment deposition is observed, which is attributed to the Margalla hills. This coarse sediment deposit is encountered at shallower depths in the eastern side; however, as the distance from foothills increases, deposition of finer sediments arises that indicate a decrease in the stream velocity over time. To the west of the bedrock, finer sediments having a thickness of 40 m are deposited; this package also contains two coarse lenses at shallow depths which can store water. Beneath this succession, a large coarse body with a thickness of 40-105 m exists which contains massive clay lenses attributed to decrease in the stream velocity for a certain time. In terms of aquifer yield, the eastern part contains shallow aquifer systems but this surficial system is also prone to surface contamination due to its exposure and no soil cover. The second aquifer system lies deeper in the center of the basin which can yield less water due to the presence of finer sediments.The results of cross-section depict that northern part is dominated by coarser sediments contrary to the southern part of the cross-section that is mainly dominated by finer sediments. Additionally, the results suggested that due to progressive loss of stream energy, fining upward sequence developed in the central and southern parts of the basin. The electrical resistivity values, borehole lithology, and overall depositional environment suggest that clay/silty clay material dominates the central and southern part. Similar findings are revealed by geological fieldwork (Figures2(a) and 2(c)). In terms of yielding capacity, the northern, eastern, and western parts of the basin contain lithologies associated with high water yield due to the presence of coarser lithologies, whereas towards the central and southern part, water yield decreases considerably due to the presence of finer lithologies.A fence diagram is constructed to show the six cross-sections in three-dimensions to better understand the depositional pattern of the basin. The fence diagram reveals an overall depositional system; from east to west, the coarser sediments are distributed, whereas center and southern part is dominantly occupied by the finer sediments (Figure8). The northern part experiences coarser sediment deposition due to high stream energy condition near Havelian and thins out in the central and south part across the Haripur basin. A similar condition is observed in the east-west direction. Therefore, coarser sediments are shallower and thicken in the eastern corner as compared to the western part near Tarbella Lake, where finer sediments are observed in the VES and borehole data (Figure 8). The Gandghar ranges in the western part also contribute to the depositional architecture of the basin by providing coarse sediment for deposition in the foothills and finer sediments in the central part of the basin [24].Figure 8
The alluvial architecture of the Haripur basin is represented by fence diagram. Relatively, coarser sediments dominate in the north and west; however, finer clays and silt are present in the center. The basemap represents generalized location of profiles that are integrated to generate the fence diagram.The Quaternary depositional pattern based on the stream energy conditions can be divided into three levels: first, depositional episode deposited coarser material (boulder, gravel, and sand), indicating high stream energy conditions in the north, east, and western side of the study area; second, depositional episode indicating a progressive loss in streams energy resulting in the deposition of finer sediments (such as a mixture of sand/shale); and third, depositional episode is marked by the deposition of the finest material, justifying the overbanked conditions associated with seasonal precipitation events.


### 4.3. Aquifer Assessment

Boreholes and VES datasets suggest aquifer lithologies at about 40 m, 60 m, 80 m, and 100 m depths across the Haripur basin (Figures5–8). The horizontal slices of isoresistivity suggest distribution of subsurface lithologies in a region [5]. The isoresistivity horizontal maps are generated using VES data at 40 m, 60 m, 80 m, and 100 m depths across the Haripur basin (Figures 9(a)–9(d)). The thickness and depths of the subsurface layers are estimated by the inversion of the acquired apparent resistivity values across each sounding point (Figure 5). Different resistivity values are contoured to generate an isoresistivity map at a certain depth. The apparent resistivity values range from 20 to 210 Ωm (Figures 9(a)–9(d)). The trend of the resistivity values across the four depths reveals two distinct zones: (i) resistivity values ranging from 20 to 40 Ωm mainly concentrated in the south center and west and (ii) resistivity values ranging from 40 to 210 Ωm identified in the northwest, north, and east of the basin.Figure 9
Spatial distribution resistivity maps generated at (a) 40 m, (b) 60 m, (c) 80 m, and (d) 100 m depths. The maps represent distribution of resistivity at certain depths. The high resistivity values are encountered in the north that may suggest presence of saturated/unsaturated fine lithologies. In the center and southwest, lowest resistivity values are present that suggests relatively coarser lithologies such as gravel, boulders, and sand.The lithological interpretation of the subsurface layers carried out by the resistivity dataset is well-constrained by the boreholes drilled across the region (Figure6). The interpretation of the resistivity values shows that low resistivity values corresponds to finer sediments including clay, silty clay, and mix lithologies of clay and sand in the southern and central regions of the basin (Table 1). Mainly fine grain sediments were encountered across the boreholes drilled in the south (Figure 6(c)). The domination of fine grain lithologies suggests considerable decrease in subsurface layer’s permeability that are not suitable for safe yield of groundwater. The distal distribution of finer sediments in the southern, central, and western regions suggests paleo-depositional direction towards southwest. The depositional environment for the finer sediments in the basin is characterized by low stream energy [34].The isoresistivity depth maps (Figures9(a)–9(d)) reveal high resistivity values mainly in the northern, eastern, and northwestern parts of the basin. The coarse sediments including sand, gravels, and boulders are favorable aquifer lithologies corresponding to comparatively high resistivity values (Table 1). The boreholes also encountered thick layers of coarser sediments in the north and east of the basin (Figure 6(c)). The coarser lithologies are indicative of a paleo-depositional mouth comprising sediments mainly deposited by the Dor River and its tributaries (Figure 1(b)). Surface geological data (Figure 2) reveal that coarse sediments are also distributed along the Dor River extending from the northeast of the basin towards the Tarbella reservoir (Figures 1(b) and 2). The depositional environment for the coarse sediments in this part of the basin is characterized as high stream energy [34]. The northern part of the basin contains freshwater supplied by the snow melting from the surrounding mountain ranges [17].Thickness of finer sediments increases towards the center and south, whereas coarser sediments are encountered near the foothills toward north, east, and northwest (Figures6–8). The boreholes, field-based geological observations, and VES data show that confined aquifer may exist at shallow level about 20 m depths near foothill slopes. The groundwater table also fluctuates from the foothills to the center and south of the basin [5]. The groundwater level range between 15 and 25 m near the foothills, whereas towards the center of the basin, it drops down to 40-80 m. In the south, the groundwater level drops down to 90 m.


## 4.1. VES Calibration with Borehole Logs

The computation of true formation resistivity is essential for a reliable interpretation of electrical resistivity data. Thicknesses of individual subsurface layers are derived from the true formation resistivity. The layer parameters identified in several VES are calibrated with the nearest available boreholes across the basin (Figure5(b)). The borehole data reveals that subsurface lithologies consist of Hazara slate acting as a basement rock overlain by the Quaternary alluvial deposits. These Quaternary deposits are represented by clay, silty clay, sand, gravel, boulder, and mixture of these lithologies. These deposits are important due to their ability to store a quantity of water of economic interest. The sandy material is considered a proven groundwater aquifer as these bodies have good porosity and permeability to store and transmit the groundwater [28]. Resistivity method among other geophysical techniques is highly sensitive to lithological and pore fluid variations. It is essential to calibrate VES results with the borehole lithologies to place strong constraints on its reliability [28].The VES data shows six subsurface layers well-constrained by borehole data across different locations in the basin (Table1). The topsoil reveals the highest resistivity value about 800 Ωm. It reveals variable thickness ranging from 1 m to 5 m in the north, south, and central regions. Massive clay succession with interbedded sand and gravel packages encountered during the borehole drilling shows relatively low resistivity values [17, 28]. The resistivity values range from 15 to 20 Ωm for the clay. The resistivity values range from 10 to 50 Ωm for silty clay. In case of saturated silty clay resistivity of the material drastically reduces. On the contrary, dry silty clay reveals relatively high resistivity values. The resistivity values range from 25 to 70 Ωm for sandy material. Gravel packages encountered during drilling show a resistivity value of 65-1300 Ωm (Table 1). The borehole and VES reveals the presence of gravel packages and silty clay in the central and southern parts of the basin. Based on the integrated results, the Haripur basin can be classified into two distinct geomorphic units: (i) massive clay units with interbedded coarse clasts mainly in the south and central regions and (ii) the dominant gravel and sand units interbedded with minor clays in the northeast and west.


### 4.1.1. Northern Part of the Basin

The calibration of VES dataset with borehole stratigraphy is carried for the interpretation of the resistivity curves in the proximity of Havelian and adjoining areas (Figure1(b)). A 100 m drill-hole (BH-10) dominated by stream deposits in the proximity of Havelian was selected for calibration with the VES point (E5) (Figures 3 and 6(a)). The Havelian area consists of two dominating lithological units’ boulder and clay with gravel of nonuniform thicknesses of about 15-20 m separated by finer sediments such as silty clay and clayey beds (Figure 6(a)). The area is located within paleo-meanders of the Dor River, where intermittent flooding events in the Quaternary age indicate high energy conditions [17].Figure 6
(a–c) VES curves (E5, D6, and D3) showing well-correlation with the lithological units, thicknesses, and depths, encountered in the boreholes (BH-10, BH-09, and BH-02) in the northern, central, and southern regions across the Haripur basin.The VES curve correlated well with the stratigraphic units derived from the borehole data (Figure6(a)). VES result provided high resolution for the upper unsaturated soil layer of relatively high resistivity about 800 Ωm. The upper clay with gravel is reflected well with resistivity values between 100-180 Ωm. The lower boulder body of 20 m is separated from the clay with gravel body by intervening silty clay which reflects a sharp change in electrical resistivity values of 20 Ωm. The resistivity values of clay with gravel are much higher (80 Ωm) than the clayey body, suggesting a dry coarser texture. These lithologies correlate well with the borehole stratigraphy. The massive boulder body ranging from 45 to 100 m is saturated by groundwater, which is evident from decreasing resistivity values in VES dataset.


### 4.1.2. Central Part of the Basin

A 120 m drilled borehole (BH 09) in the proximity of Nathiagali/Haripur area was selected for the calibration with VES point B7 (Figure6(b)). The adjoining areas of Haripur are underlain by deposits of multilithological units such as massive gravel and silty clay along with interbedded clay units [24]. BH-09 (Figure 6(b)) shows the first gravel unit with a thickness of 22 m followed by clay with gravel units having a thickness of 20 m. The second gravel unit starting at depth of 40 m has a total thickness of 42 m with interbedded clay units of variable thicknesses. This gravel unit is underlain by a massive silty unit of 30 m thickness followed by a boulder unit. The area is located in the proximity of the Dor River and represents a high-energy condition indicating seasonal streams progressing further west towards Tarbella reservoir [17]. The result of VES data shows good correlation with the borehole data (Figure 6(b)). After the very high resistive topsoil about 900 Ωm, the upper gravel layer of high resistivity is well-resolved by the resistivity data. The high resistivity values about 80 Ωm of the upper gravel layer may suggest presence of unsaturated body. The second unit is indicated by a change in resistivity values due to the presence of moist clay with gravel about 60 Ωm. At a depth of about 40 m, a decrease in resistivity values about 50 Ωm indicates the presence of another saturated gravel body which is followed by saturated clays having a resistivity range of 19-30 Ωm. This second gravel body at depth of 40 m can serve as saturated zone of a confined aquifer. Subsurface layers of sand and gravel encountered at about 40 m depth can yield economic quantities of water pertaining to high porosity and permeability, lateral extent, and sufficient thickness. This refers to quantity of groundwater that can be delivered to increasing population and industry. However, no pumping test is carried out in the region to identify aquifer characteristics and to describe quantitative information of groundwater.


### 4.1.3. Southern Part of the Basin

The VES point D9 and borehole stratigraphy (BH 02) of 130 m depth located in the proximity of Hattar and Haripur area were selected for calibration (Figure6(c)). The geological fieldwork (Figure 2) carried out in these areas revealed multiepisodes of stream deposits dominated by low-energy conditions. Furthermore, the area comprises two lithological units: a massive clay unit with minor interbedded sand bodies and a second unit comprised of massive sand with gravel body with variable sediment size.Figure6(c) shows that the borehole (BH-02) consists of two major lithologies, i.e., clay and fine to coarse sand. Beneath the surface soil layer, a massive silty clay body of 50 m thickness exists which is underlain by coarser sand body of approximately 7 m thickness followed by another massive silty clay body with a thickness of approximately 55 m. These massive silty clay units are underlain by sand and fine sand beds with a thickness of approximately 20 m. The area is located at a proximal distance about 13 km from the Dor River, and dominating lithologies are fine-grained indicating low energy conditions (Figure 2(a)). The VES curve acquired at the Hattar area shows resistivity values ranging from 19 to 920 Ωm. Relatively higher resistivity values are encountered in the upper part that suggest presence of the unsaturated silty clay deposits, whereas the intermediate resistivity values that occur beneath the low resistivity values, ranging from 40 to 50 Ωm, may indicate sand beds. This sand layer could act as an aquifer with high yielding capacity. A very low resistivity zone ranging from 19 to 20 Ωm is identified by VES curve as massive saturated silty clay. This massive silty clay may suggest low-energy conditions associated with the Dor River and its tributaries. The VES curve shows an increase in the resistivity values linked with the sand body lying at a depth of about 115 m having a resistivity value ranging from 40 to 50 Ωm. The presence of massive sand at this depth indicates high-energy channel deposition and can act as a confined aquifer that can produce sustainable groundwater for local population and industry [30].


## 4.1.1. Northern Part of the Basin

The calibration of VES dataset with borehole stratigraphy is carried for the interpretation of the resistivity curves in the proximity of Havelian and adjoining areas (Figure1(b)). A 100 m drill-hole (BH-10) dominated by stream deposits in the proximity of Havelian was selected for calibration with the VES point (E5) (Figures 3 and 6(a)). The Havelian area consists of two dominating lithological units’ boulder and clay with gravel of nonuniform thicknesses of about 15-20 m separated by finer sediments such as silty clay and clayey beds (Figure 6(a)). The area is located within paleo-meanders of the Dor River, where intermittent flooding events in the Quaternary age indicate high energy conditions [17].Figure 6
(a–c) VES curves (E5, D6, and D3) showing well-correlation with the lithological units, thicknesses, and depths, encountered in the boreholes (BH-10, BH-09, and BH-02) in the northern, central, and southern regions across the Haripur basin.The VES curve correlated well with the stratigraphic units derived from the borehole data (Figure6(a)). VES result provided high resolution for the upper unsaturated soil layer of relatively high resistivity about 800 Ωm. The upper clay with gravel is reflected well with resistivity values between 100-180 Ωm. The lower boulder body of 20 m is separated from the clay with gravel body by intervening silty clay which reflects a sharp change in electrical resistivity values of 20 Ωm. The resistivity values of clay with gravel are much higher (80 Ωm) than the clayey body, suggesting a dry coarser texture. These lithologies correlate well with the borehole stratigraphy. The massive boulder body ranging from 45 to 100 m is saturated by groundwater, which is evident from decreasing resistivity values in VES dataset.


## 4.1.2. Central Part of the Basin

A 120 m drilled borehole (BH 09) in the proximity of Nathiagali/Haripur area was selected for the calibration with VES point B7 (Figure6(b)). The adjoining areas of Haripur are underlain by deposits of multilithological units such as massive gravel and silty clay along with interbedded clay units [24]. BH-09 (Figure 6(b)) shows the first gravel unit with a thickness of 22 m followed by clay with gravel units having a thickness of 20 m. The second gravel unit starting at depth of 40 m has a total thickness of 42 m with interbedded clay units of variable thicknesses. This gravel unit is underlain by a massive silty unit of 30 m thickness followed by a boulder unit. The area is located in the proximity of the Dor River and represents a high-energy condition indicating seasonal streams progressing further west towards Tarbella reservoir [17]. The result of VES data shows good correlation with the borehole data (Figure 6(b)). After the very high resistive topsoil about 900 Ωm, the upper gravel layer of high resistivity is well-resolved by the resistivity data. The high resistivity values about 80 Ωm of the upper gravel layer may suggest presence of unsaturated body. The second unit is indicated by a change in resistivity values due to the presence of moist clay with gravel about 60 Ωm. At a depth of about 40 m, a decrease in resistivity values about 50 Ωm indicates the presence of another saturated gravel body which is followed by saturated clays having a resistivity range of 19-30 Ωm. This second gravel body at depth of 40 m can serve as saturated zone of a confined aquifer. Subsurface layers of sand and gravel encountered at about 40 m depth can yield economic quantities of water pertaining to high porosity and permeability, lateral extent, and sufficient thickness. This refers to quantity of groundwater that can be delivered to increasing population and industry. However, no pumping test is carried out in the region to identify aquifer characteristics and to describe quantitative information of groundwater.


## 4.1.3. Southern Part of the Basin

The VES point D9 and borehole stratigraphy (BH 02) of 130 m depth located in the proximity of Hattar and Haripur area were selected for calibration (Figure6(c)). The geological fieldwork (Figure 2) carried out in these areas revealed multiepisodes of stream deposits dominated by low-energy conditions. Furthermore, the area comprises two lithological units: a massive clay unit with minor interbedded sand bodies and a second unit comprised of massive sand with gravel body with variable sediment size.Figure6(c) shows that the borehole (BH-02) consists of two major lithologies, i.e., clay and fine to coarse sand. Beneath the surface soil layer, a massive silty clay body of 50 m thickness exists which is underlain by coarser sand body of approximately 7 m thickness followed by another massive silty clay body with a thickness of approximately 55 m. These massive silty clay units are underlain by sand and fine sand beds with a thickness of approximately 20 m. The area is located at a proximal distance about 13 km from the Dor River, and dominating lithologies are fine-grained indicating low energy conditions (Figure 2(a)). The VES curve acquired at the Hattar area shows resistivity values ranging from 19 to 920 Ωm. Relatively higher resistivity values are encountered in the upper part that suggest presence of the unsaturated silty clay deposits, whereas the intermediate resistivity values that occur beneath the low resistivity values, ranging from 40 to 50 Ωm, may indicate sand beds. This sand layer could act as an aquifer with high yielding capacity. A very low resistivity zone ranging from 19 to 20 Ωm is identified by VES curve as massive saturated silty clay. This massive silty clay may suggest low-energy conditions associated with the Dor River and its tributaries. The VES curve shows an increase in the resistivity values linked with the sand body lying at a depth of about 115 m having a resistivity value ranging from 40 to 50 Ωm. The presence of massive sand at this depth indicates high-energy channel deposition and can act as a confined aquifer that can produce sustainable groundwater for local population and industry [30].


## 4.2. Reconstruction of Quaternary Architecture

The VES data is well-correlated with surface geological observations and borehole logs. This integrated approach shows remarkable results in estimating Quaternary paleo-depositional environment of the basin. The electrical resistivity values established by [28] were utilized to infer electro-stratigraphy for the development of alluvial architecture (Table 1). The alluvial architecture is produced by integrating sixty VES curves, eleven boreholes, and exposed surface geological sections. The Haripur basin lies in the monotonously flat plains; however, there are gradual variations in the elevation from east to west (Figure 1(a)). The results derived from the datasets are used to develop six lithostratigraphic cross-sections (A-A/, B-B/, C-C/, D-D/, E-E/, and F-F/), each about 100 m deep across the basin (Figures 7(a)–7(f)).Figure 7
(a–f) Cross-sections based on well-calibrated electrical resistivity values with borehole dataset. Lithological variations across the cross-sections are associated with stream fluctuations. The orientation of the cross-sections is also represented on this map and also in Figure3.The cross-section A-A/ (Figure 7(a)) is about 20 km long and developed from the northwest to southeast by using twelve VES points and two deep boreholes drilled close to the Dor River. It begins from Nathiagali towards the Tarbella reservoir (Figure 3). The cross-section A-A/ reveals a deposition sequence that is indicative of mainly three episodes (Figure 7(a)). From surface down to 50 m depth, rock layers are predominated by the coarser sediments. The second episode is characterized by patches of clay sediments that lies at about 50 m to 80 m depth at different locations (Figure 7(a)). A massive gravel and boulder layer about 20 m thick is identified at 80 m depth (Figure 7(a)). The deposition sequence across A-A/ represents coarser sedimentary layer and a thin layer of finer sediment and then a massive gravel and boulder layer. This suggests fluctuations in stream velocities from high stream to low stream energy and flood dominated period. The channel activity indicted by clay lenses present at about 20 m and 75 m depths also suggests variable stream activity and sediment influx. This cross-section A-A/ well dominated by coarser sedimentary layers may act as aquifer bodies at various depths that can yield water quantities at a higher rate.The cross-section B-B/ is constructed using fifteen VES points and four boreholes (Figures 3 and 7(b)). It is about 18 km long and runs from the north to south (Figure 7(b)). The cross-section B-B/ can be divided into two main lithological units: (i) from surface down to 80 m depth finer material consisting of clay and silt and (ii) bottom part from 80 to 110 m comprising coarser lithologies dominated by gravel (Figure 7(b)). The presence of gravel lenses at about 25 m depth indicates the transition locations of JabiKas and JariKas streams across the cross-section B-B/. A progressive loss in stream energy may deposit finer sediments [35]. This region contains mainly fine grain sediments that are impermeable and may contribute very low-yield groundwater.The cross-section C-C/ run from north to south parallel to cross-section B-B/ (Figure 7(c)). It is about 14 km long and generated by using seven VES points and three boreholes (Figure 3). The cross-section also reveals two main lithological units (Figure 7(c)). The first lithological layer consists of finer particles having a thickness of about 50 m. The second lithological unit is dominated by coarser lithologies ranging from 50 m to 100 m depth. The cross-section also reveals two coarse grain lenses about 20 m deep and two thin lenses of fine sediments at about 70 m depth. This deposition of coarser sediments within finer lithological layers pertains to a loss in the stream energy resulting in deposition of lightweight coarser sediments. The two lenses consisting of finer sediments suggest variation in sediment influx during deposition. The shallower lithologies may yield less water due to impermeability, whereas, the deeper layers can safely yield groundwater. The lenses identified in the north and south of cross-section can act as perched aquifers with low yield due to less spatial extent and clay domination above and below.The cross-section D-D/ (Figures 3 and 7(d)) is about 10 km long and oriented in north south direction. It is constructed using nine VES points and nine boreholes. The cross-section mainly reveals two major depositional sequences (Figure 7(d)). The first deposition comprises finer sediments ranging from the surface down to 60 m depth. This deposition sequence suggests a loss in stream energy depositing lighter weight sediments. A considerable increase in the stream energy might result in deposition of coarser layer about 20 m thick. Two coarser grain lenses at about 25 m depth are also observed in the north and south of cross-section indicating variation in stream load periodically (Figure 7(d)). The coarser layer at about 60 m depth capped at top and bottom by finer sedimentary sequences can transmit groundwater of economic interest to the local community.The cross-section E-E/ (Figures 3 and 7(e)) is formulated using eight VES points and three boreholes having depth of about 100 m along a north-south profile. The top surface layer consists of variable grades of clay mixed with gravel and boulder throughout the section due to which electrical resistivity ranges from 20 to 60 Ωm. The gravel and boulder facies dominate in the steep narrow valley from Havelian towards the center of the basin. Around Havelian area, the upper gravel and boulder body appears to be quite extensive (spatially and vertically) consisting of medium-size gravel deposits, whereas near Haripur, the upper gravel and boulder body is comparatively thin, and lower sand mixed with clay is approximately 30-40 m thick. The upper gravel and boulder body corresponds to subsurface deposition of the present-day Dor River [24]. The coarser lithologies encountered across this cross-section can provide water storage capacities with high yield.The cross-section F-F/ (Figures 3 and 7(f)) lies in an east-west direction and comprises four VES points and three boreholes. The total depth of this cross-section is 105 m; part of this cross-section lies near the foothills while the remaining part lies in the center of the basin. Bedrock is exposed along this cross-section. Towards the east of the bedrock, a coarse sediment deposition is observed, which is attributed to the Margalla hills. This coarse sediment deposit is encountered at shallower depths in the eastern side; however, as the distance from foothills increases, deposition of finer sediments arises that indicate a decrease in the stream velocity over time. To the west of the bedrock, finer sediments having a thickness of 40 m are deposited; this package also contains two coarse lenses at shallow depths which can store water. Beneath this succession, a large coarse body with a thickness of 40-105 m exists which contains massive clay lenses attributed to decrease in the stream velocity for a certain time. In terms of aquifer yield, the eastern part contains shallow aquifer systems but this surficial system is also prone to surface contamination due to its exposure and no soil cover. The second aquifer system lies deeper in the center of the basin which can yield less water due to the presence of finer sediments.The results of cross-section depict that northern part is dominated by coarser sediments contrary to the southern part of the cross-section that is mainly dominated by finer sediments. Additionally, the results suggested that due to progressive loss of stream energy, fining upward sequence developed in the central and southern parts of the basin. The electrical resistivity values, borehole lithology, and overall depositional environment suggest that clay/silty clay material dominates the central and southern part. Similar findings are revealed by geological fieldwork (Figures2(a) and 2(c)). In terms of yielding capacity, the northern, eastern, and western parts of the basin contain lithologies associated with high water yield due to the presence of coarser lithologies, whereas towards the central and southern part, water yield decreases considerably due to the presence of finer lithologies.A fence diagram is constructed to show the six cross-sections in three-dimensions to better understand the depositional pattern of the basin. The fence diagram reveals an overall depositional system; from east to west, the coarser sediments are distributed, whereas center and southern part is dominantly occupied by the finer sediments (Figure8). The northern part experiences coarser sediment deposition due to high stream energy condition near Havelian and thins out in the central and south part across the Haripur basin. A similar condition is observed in the east-west direction. Therefore, coarser sediments are shallower and thicken in the eastern corner as compared to the western part near Tarbella Lake, where finer sediments are observed in the VES and borehole data (Figure 8). The Gandghar ranges in the western part also contribute to the depositional architecture of the basin by providing coarse sediment for deposition in the foothills and finer sediments in the central part of the basin [24].Figure 8
The alluvial architecture of the Haripur basin is represented by fence diagram. Relatively, coarser sediments dominate in the north and west; however, finer clays and silt are present in the center. The basemap represents generalized location of profiles that are integrated to generate the fence diagram.The Quaternary depositional pattern based on the stream energy conditions can be divided into three levels: first, depositional episode deposited coarser material (boulder, gravel, and sand), indicating high stream energy conditions in the north, east, and western side of the study area; second, depositional episode indicating a progressive loss in streams energy resulting in the deposition of finer sediments (such as a mixture of sand/shale); and third, depositional episode is marked by the deposition of the finest material, justifying the overbanked conditions associated with seasonal precipitation events.


## 4.3. Aquifer Assessment

Boreholes and VES datasets suggest aquifer lithologies at about 40 m, 60 m, 80 m, and 100 m depths across the Haripur basin (Figures5–8). The horizontal slices of isoresistivity suggest distribution of subsurface lithologies in a region [5]. The isoresistivity horizontal maps are generated using VES data at 40 m, 60 m, 80 m, and 100 m depths across the Haripur basin (Figures 9(a)–9(d)). The thickness and depths of the subsurface layers are estimated by the inversion of the acquired apparent resistivity values across each sounding point (Figure 5). Different resistivity values are contoured to generate an isoresistivity map at a certain depth. The apparent resistivity values range from 20 to 210 Ωm (Figures 9(a)–9(d)). The trend of the resistivity values across the four depths reveals two distinct zones: (i) resistivity values ranging from 20 to 40 Ωm mainly concentrated in the south center and west and (ii) resistivity values ranging from 40 to 210 Ωm identified in the northwest, north, and east of the basin.Figure 9
Spatial distribution resistivity maps generated at (a) 40 m, (b) 60 m, (c) 80 m, and (d) 100 m depths. The maps represent distribution of resistivity at certain depths. The high resistivity values are encountered in the north that may suggest presence of saturated/unsaturated fine lithologies. In the center and southwest, lowest resistivity values are present that suggests relatively coarser lithologies such as gravel, boulders, and sand.The lithological interpretation of the subsurface layers carried out by the resistivity dataset is well-constrained by the boreholes drilled across the region (Figure6). The interpretation of the resistivity values shows that low resistivity values corresponds to finer sediments including clay, silty clay, and mix lithologies of clay and sand in the southern and central regions of the basin (Table 1). Mainly fine grain sediments were encountered across the boreholes drilled in the south (Figure 6(c)). The domination of fine grain lithologies suggests considerable decrease in subsurface layer’s permeability that are not suitable for safe yield of groundwater. The distal distribution of finer sediments in the southern, central, and western regions suggests paleo-depositional direction towards southwest. The depositional environment for the finer sediments in the basin is characterized by low stream energy [34].The isoresistivity depth maps (Figures9(a)–9(d)) reveal high resistivity values mainly in the northern, eastern, and northwestern parts of the basin. The coarse sediments including sand, gravels, and boulders are favorable aquifer lithologies corresponding to comparatively high resistivity values (Table 1). The boreholes also encountered thick layers of coarser sediments in the north and east of the basin (Figure 6(c)). The coarser lithologies are indicative of a paleo-depositional mouth comprising sediments mainly deposited by the Dor River and its tributaries (Figure 1(b)). Surface geological data (Figure 2) reveal that coarse sediments are also distributed along the Dor River extending from the northeast of the basin towards the Tarbella reservoir (Figures 1(b) and 2). The depositional environment for the coarse sediments in this part of the basin is characterized as high stream energy [34]. The northern part of the basin contains freshwater supplied by the snow melting from the surrounding mountain ranges [17].Thickness of finer sediments increases towards the center and south, whereas coarser sediments are encountered near the foothills toward north, east, and northwest (Figures6–8). The boreholes, field-based geological observations, and VES data show that confined aquifer may exist at shallow level about 20 m depths near foothill slopes. The groundwater table also fluctuates from the foothills to the center and south of the basin [5]. The groundwater level range between 15 and 25 m near the foothills, whereas towards the center of the basin, it drops down to 40-80 m. In the south, the groundwater level drops down to 90 m.


## 5. Conclusions

An integrated geological and geophysical approach is utilized to characterize the Quaternary paleo-depositional architecture of the Haripur basin. A large number of drilled boreholes, VES points, and surface geological datasets were used to evaluate the paleo-depositional environment and potential aquifer distribution in it. The geological studies indicate that the study area is dominated by fluvial depositional environment with three possible depositional directions from the north, the east, and the west. The well-dominated finer lithologies of outcrops indicate fining upward trend due to progressive loss of stream energy in the center and south. Coarser grain size outcrops indicate coarsening upward trend due to high stream energy condition in the north, east, and west. The subsurface lithologies are clay dominated in the central and southern parts. This suggests low-energy conditions in these regions of the Haripur basin. The surface and subsurface interpretation show episodic deposition in the basin. This suggests seasonal stream avulsion resulting in the deposition of coarser lithologies in the proximity of foothills and finer lithologies in the center and south of the basin.The occurrence of groundwater has a strong relationship with the distribution of paleo-channels in this Quaternary paleo-depositional environment. The shallow paleo-channels are mainly encountered in the vicinity of foothills. This may result in presence of groundwater at shallow depth about 15~40 m. Deeper paleo-channels are identified in the central and southern parts which suggest presence of groundwater at greater depth about 80~115 m. The reconstruction of the paleo-depositional environment from the VES, borehole, and surface geological observations well-correlates with the yielding capacity of aquifers in all parts of the basin. The studies suggest occurrence of high-yielding aquifers in eastern, western, and northern parts of the basin and the occurrence of low-yielding aquifers in the central and southern parts of the basin.



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*Source: 1057457-2023-03-06.xml*