Resistivity Asam EMA 2012

Hydrostratigraphy and hydrogeology of the western partof Maira area, Khyber Pakhtunkhwa, Pakistan: a case studyby using electrical resistivity

Asam Farid & Khanzaib Jadoon & Gulraiz Akhter &

Muhammad Asim Iqbal

Received: 17 July 2011 /Accepted: 4 June 2012# Springer Science+Business Media B.V. 2012

Abstract Hydrostratigraphy and hydrogeology of theMaira vicinity is important for the characterization ofaquifer system and developing numerical groundwaterflow models to predict the future availability of thewater resource. Conventionally, the aquifer parameters

are obtained by the analysis of pumping tests datawhich provide limited spatial information and turnout to be costly and time consuming. Vertical electricalsoundings and pump testing of boreholes were con-ducted to delineate the aquifer system at the westernpart of the Maira area, Khyber Pakhtun Khwa,Pakistan. Aquifer lithology in the eastern part of thestudy area is dominated by coarse sand and gravelwhereas the western part is characterized by fine sand.An attempt has been made to estimate the hydraulicconductivity of the aquifer system by establishing arelationship between the pumping test results and ver-tical electrical soundings by using regression tech-nique. The relationship is applied to the area alongthe resistivity profiles where boreholes are not drilled.Our findings show a good match between pumpedhydraulic conductivity and estimated hydraulic con-ductivity. In case of sparse borehole data, regressiontechnique is useful in estimating hydraulic propertiesfor aquifers with varying lithology.

Keywords Aquifers . Intermontane basin . Hydraulicconductivity . Hydrostratigraphy . Vertical electricalsounding

Introduction

Spatial distribution of an aquifer's hydraulic propertiessuch as porosity, hydraulic conductivity, transmissivi-ty and specific yield plays a vital role in explaining the

Environ Monit AssessDOI 10.1007/s10661-012-2720-z

A. Farid (*) :M. A. IqbalDepartment of Petroleum Geosciences,The Petroleum Institute,Ruwais Building, P.O Box 2533, Abu Dhabi,United Arab Emiratese-mail: [email protected]

M. A. Iqbale-mail: [email protected]

K. JadoonWater Desalination and Reuse Center,King Abdullah University of Scienceand Technology (KAUST),Thuwal 23955-6900, Saudi Arabiae-mail: [email protected]

K. Jadoone-mail: [email protected]

K. JadoonForschungszentrum Juelich,Institute of Bio- and Geosciences, Agrosphere (IBG3),52425 Juelich, Germany

G. AkhterDepartment of Earth Sciences,Quaid-i-Azam University,Islamabad, Pakistane-mail: [email protected]

groundwater flow system. Transmissivity and hydraulicconductivity are among the most important hydrogeo-logical data needed for managing the groundwaterresources and problems. These parameters also describethe ability of the aquifer to transmit water and thereforehelp in developing models for the groundwater flowregimes (Freeze and Cherry 1979; Fitts 2002). Amongthe most effective ways to calculate hydraulic conduc-tivity are the pump tests that are performed in certainboreholes where hydrogeological information is sought.Sparse location of boreholes gives rise to problems inhydrogeological modeling. Intrusive techniques such asdrilling, logging and pump tests on a large scale canprove to be expensive and time consuming.

Surface geophysical methods can provide efficientservices in terms of spatial coverage. Electrical resis-tivity techniques are considered as the most successfulgeophysical method for the detection of aquifers.These methods are extensively applied to study boththe high and low resistive formations and hence arevaluable tools for studying aquifer vulnerability(Hubbard and Rubin 2002; Sorensen et al. 2005) andsalinity effect on groundwater aquifers (Mondal et al.2010; Baharuddin et al. 2011; Son 2011). Specifically,resistivity techniques are well established and com-monly used to address the solutions for variety ofgeological and environmental problems. Most electri-cal resistivity surveying on the land surface is intendedto probe to depths of a few hundred feet or less. Theseshallow geophysical techniques provide informationabout groundwater reservoirs, construction sites andnear surface ores (Robinson and Coruh 1988; Alile etal. 2008; Ochuko 2011). Resistivity method measuresthe potential differences produced due to the currentflow within the ground on the surface. This is accom-plished by a four-electrode configuration in which twoserve as the potential electrodes and two serve as thecurrent electrodes. The current is injected into theground by current electrodes whereas the potentialdifference is recorded at the potential electrodes. Theflow of electric current through the ground depends oncertain factors, which can vary from site to site anddepends upon the geology of the area. These factorsinclude porosity, grain size, grain shape, lithology,pore geometry and size, packing, sorting, compaction,cementation, depth of sediments, groundwater andgroundwater salinity (Salem 1999). Since the samephysical principles and lithological attributes governthe electric conduction and fluid flow in the ground,

the hydraulic and electrical conductivities are depen-dent upon each other (Soupios et al. 2007). Severalattempts have been made to estimate aquifer hydraulicparameters from aquifer resistivity (Kelly 1977; Niwasand Singhal 1981, 1985; Huntley 1986; Yadav 1995;Yadav and Abolfazli 1998; MacDonald et al. 1999;Lima and Niwas 2000; Salem 2000; Singh 2005;Shevnin et al. 2006; Soupios et al. 2007; Chandra etal. 2008). These case studies proved to be site specificas lithological and fluid attributes such as pore shapeand size, tortousity, cementation and grain size arehighly variable. Therefore, the estimates of the aquiferparameters from surficial electrical resistivity cannotbe considered as absolute.

Integration of aquifer parameters calculated fromboreholes and resistivity data is highly effective ascorrelation between aquifer hydraulic properties andresistivity is possible because there is a fundamentalrelationship existing between them which dependsupon tortousity and porosity (Bear 1972; Kelly 1977;Mazac et al. 1988; Borner et al. 1996; Rubin andHubbard 2005; Niwas et al. 2006; Akaolisa 2006).Porosity (f) and hydraulic conductivity is a functionof intrinsic formation factor (Fi) whereas aquifer re-sistivity (Rf) is a function of apparent formation factor(Fa). Precise estimation of the Fa is important for theaquifer parameters estimation, and it depends upon thecorrect measurement of aquifer water conductivities(EC) and Rf. The formation factor depends on charac-teristics of the formation such as f, clay content andcementation factor (m) (Helander 1983; Tiab andDonaldson 2004; Ellis and Singer 2007). The forma-tion factor usually decreases with increasing clay con-tent and gets higher with decreasing f and increasingm. Normally, formation factors may be assumed torange from 3 for fine loose sand up to 7 or more forgravel and boulder type lithologies. As clay and siltexert a reducing effect on the formation factor, it maybe around 2 for dirty sands (Kunetz 1966; Zohdy et al.1974; Helander 1983; Bloemendaal and Sadiq 1985).For a homogeneous saturated aquifer, the Fa and Fi

may be similar, but when an aquifer is partially satu-rated and contains clay, the values of Fa and Fi factorsmay deviate (Vinegar and Waxman 1984; Worthington1993; Borner et al. 1996).

The aquifer in the study area consists of varyingamounts of interlayered sand, gravel, clay and occa-sionally boulder beds. The number of boreholes withpump tests in the study area is inadequate to measure

Environ Monit Assess

the hydraulic conductivity of the regional aquifer sys-tem, and drilling more boreholes and conductingpump tests would be expensive. Grain size data forthe lithologies was not available; therefore, a regres-sion technique has been used to estimate the hydraulicconductivities. Average porosity of the aquifer systemis estimated from the modified Archie equation byusing electrical resistivity and conductivity data overthe wells. Since the Maira area is a part of a Peshawarbasin, different types of clay are present in the subsur-face lithologies. In order to obtain good estimates ofaquifer parameters, it is necessary to consider theeffect of clay on the geophysical data. Waxman andSmits (1968) introduced their equations which relateFi to Fa and take into consideration the clay effects.Therefore, the model introduced by Waxman andSmits (1968) is used to calculate the Fi. The Fi wasplotted against the hydraulic conductivities (K)obtained from pumping test analysis, and a best fitregression line was drawn. The resulting regressionequation is used to estimate the values of hydraulicconductivities (K′) initially for wells. The matchingpercentage of K and K′ lies between 66 and 87 %.This regression equation has been applied to all thevertical electrical sounding (VES) points, and K′ isestimated.

Geology and geomorphology of the area

The geographical location of the Peshawar basin is inthe northwestern region of Pakistan as shown inFig. 1a. The study area lies in the southeastern partof the Peshawar basin as highlighted in the Fig. 1b.The northern Pakistan region is undergoing subduc-tion of the Indian continental plate below the Eurasianplate (Kazmi and Jan 1997; Shahzad et al. 2009,2010). The folding of the relatively soft top layershas created the mountain ranges. Peshawar basin isknown as one of the best agricultural lands in thecountry. The land is fertile and suitable for the culti-vation of sugarcane, wheat and tobacco. Water ispresent in abundance in the Peshawar valley, comingfrom glacial melts in the north and northwest, and isused for drinking and irrigation purposes (Bundschuh1992). Various stream channels and rivers as shown inFig. 1c drain the basin and eventually join Indus andKabul rivers. The Peshawar basin is irrigated bothwith surface water by various canals originating from

Kabul, Swat and Indus Rivers and by groundwater aswell where access to canal water is difficult.

The study area is a part of a large intermontane basinwhere sedimentation has taken place from weatheringand erosion from the surrounding mountain belts(Burbank 1983; Tahirkheli 1985; Bloemendaal andSadiq 1985). Figure 2 shows the location of boundaries,canals, exploratory boreholes and VES points. The areais situated between Latitude 33° 56′ to 34° 18′ N andLongitude 72° 01′ to 72° 48′ E. The average altitude ofthe area is 350m above mean sea level (AMSL)with thehighest point reaching 404 m AMSL. The alluvial plaincovers an area of 379 km2. The area has a semi-aridclimate with hot summers and mild winters. The winterrains are generally of long duration and low intensity,whereas the summer rains come in short showerswith high intensity due to their monsoon character(Government of Pakistan 1998). The area is surroundedby the Maira branch canal in the north, Badri Khwarnala towards the east, Kalpani nala to the west, Kabulriver towards the southwest and Pehur main canal to-wards the southeast, collectively acting as the bound-aries of the study area. The mountain ranges towards thenorth and the northeast are composed of granites, seyen-ites, gneiss and schists whereas towards the south andsouthwest, sandstones, shales and limestones are com-mon (Martin et al. 1962; Sajjad 1988; Rafiq and Jan1989). Due to this intensive tectonic movement, thebedrock has steep dips, and strata from different geo-logic ages appear in outcrops. In the catchment area ofMaira, strata of the so-called Swabi Chamla Metasedi-mentary group are exposed at the surface. The stratigra-phy of these rocks is difficult to establish, since theyonly occur as isolated patches in the alluvial plain. Afew isolated outcrops are visible in the project area.Locally some clay mounds are found in the area andhave been formed by the shifting of the river beds andtransformation of the basin into a lake during theMiddlePleistocene when outflow of the Indus was blocked(Nizami 1973). The bedrock of the area is overlain withan alluvial fill of Quaternary age with a thickness ofseveral hundred meters. Along the mountain ranges,piedmont deposits are found consisting of weatheredbedrock which has been transported for a relatively shortdistance (Bloemendaal and Sadiq 1985; Akhter et al.2012). Figure 3 shows the surface geology of the area.

The study area consists of a sandy plain with un-dulating relief. There are no major hills or mountainsinside the area or along its boundaries, except for a few


scattered outcrops. In addition, 13 boreholes (WA-1,WA-2, …, WA-13) were drilled in the area in order toget the information about the subsurface lithology.

Figure 4 shows the lithologs of some of the boreholesdrilled in the area. It is observed that the aquifer consistsof alternating sand and clay layers. The sand grades in

Fig. 1 a Geographical location of the study area. b Digital elevation model Peshawar basin (data source: Geosoft 2012). cPhysiography of the Peshawar basin (Kruseman and Naqavi 1988). Study area is highlighted by the red box


grain size between coarse and fine. Mostly coarse tomedium sand is found in the eastern part of the studyarea whereas it grades to fine sand towards the west.

Methodology

Electrical resistivity survey

A geo-electrical survey carried out by Water and PowerDevelopment Authority (WAPDA) under the Pak-Dutchprogram for groundwater investigations on the alluvialplains provides information on the lithological setup ofthe sub-soil and groundwater quality. In total, 51 VESwere performed in the western part of theMaira area. Thesurvey was intended to furnish information regarding theoccurrence of fresh water aquifer zones in the area.Soundings were obtained by employing a Schlumbergerconfiguration with a half current electrode spacing(AB/2) ranging from 1.5 to 1000 m. The soundingswere run at successive distances of about 1.6 km.The resistivity data was modeled by using IPI2WINsoftware (IPI2WIN-1D computer programme. 2000;Zananiri et al. 2006; Sultan et al. 2009) consideringinformation derived from lithologic logs and geologicmaps, and data on subsurface water levels and elec-trical conductivities. The measured apparent resistivitycurve and interpreted (modeled) curves are shown inFig. 5a–d. The resistivity values plotted against depth

are schematized to a resistivity layer model: a sequence ofhorizontal layers according to different resistivities.Calibration between lithologies and resistivities was doneat the borehole locations to get a unified layer modelapplicable to all field curves. General calibration is shownin Table 1. The information detailed in Table 1 has beenused to interpret all the resistivity soundings and devel-oping layer models.

Figure 6a–d shows the modeled resistivity cross sec-tions along AA′, BB′, CC′ and DD′, respectively. Gen-erally the resistivity cross sections show a three-layermodel, the top clay and unsaturated sand/gravel layer,the middle saturated sand layer which comprises theaquifer, and the bottom clay and bedrock layer. Thetop clay layer is present in patches, and its resistivityranges between 5 and 30Ω m. The highest resistivitiesare associated with the dry and unsaturated sand/gravelbeds and fall in the range of 200–1000Ω m. Aquiferresistivities fall in the intermediate resistivity range of40–150Ω m. The aquifer is heterogeneous and consistsof various layers of coarse, medium and fine sands withinterbedded clays. In the section AA′, low resistivityvalues at VES 13, 14 and 15 are interpreted as a claymound. The presence of a clay mound can be confirmedfrom the borehole WA-13 where increased amount ofclay can be seen. Bedrock is encountered in cross sec-tion (b) between VES points 34 and 28. The zone offresh water aquifer strata along this section appears to bethinner, up to maximum depth of 60 m only.

Fig. 2 Location of exploratory boreholes, resistivity points, study area boundaries and cross sections profiles


The EC values of the water samples collected fromdifferent wells in the area range between 300 and600 μs/cm which indicate that the groundwater is gen-erally fresh. In case of water-saturated porous medium,the Rf is considered the product of Fa and the resistivity ofgroundwater (Rw) and can be expressed with the formula:

Rf ¼ Fa � Rw

Fa ¼ Rfð Þ Rwð Þ:=ð1Þ

Rf andRw aremeasured in ohmmeter. In this methodRf isobtained from resistivity sounding curves (Orellana andMooney 1966), and Rw is the resistivity of water being

the reciprocal value of EC, which is determined onwater samples taken from boreholes and wells by ap-plying the formula:

Rw ¼ 10000 EC:=

Pumping test analysis

Jacob’s method has been applied for the calculation ofthe aquifer parameters as it is one of the most frequentlyused methods in pumping test analysis (Chapuls 1992;

Fig. 3 Regional geology of the study area (Searle et al. 1996). Study area is highlighted by blue box


Fetter 1988; Kruseman and de Ridder 1991; Ratej andBrenčič 2005). Jacob’s method during pumping phaseassumes that well is pumped at a constant rate resultingin drawdown of groundwater in the well. The draw-down is plotted against time on a semi-log paper andnoted usually in a log cycle. Later this drawdown valueis used to calculate the transmissivity and hydraulicconductivity. Jacob’s method during recovery phaseassumes that water table will rise in the well once thepumping has ceased. The rise in the water level isplotted on a semi-log paper, and the recovery is notedusually in a log cycle. This value is later used tocalculate the transmissivity and hydraulic conductivity.A pumping test with constant discharge has been car-ried out by WAPDA on each test well. The duration ofthe pumping period was generally 1000 min. Thedepths to the water level in the pumped test well weremeasured during both the pumping period as well asduring the recovery. Interpretation of the drawdowncurves gives information about the hydraulic propertiessuch as transmissivity and hydraulic conductivity ofthe pumped aquifer. The results are summarized inTable 2.

Hydraulic conductivity estimation

The resistivities derived from modeling are averagedover the thickness of the aquifer for wells and the VESpoints. The average resistivity of the aquifer is termedas Rf and is calculated from modelled resistivitycurves whereas Rw is obtained directly from site meas-urements at wells. For fully water-saturated aquifer, Fa

has been calculated for the wells by using the relationas shown in Eq. (1).

In order to calculate the hydraulic conductivity (K′)from surface resistivity soundings, we need informationregarding the porosity of the aquifer. The porosity of theaquifer has been estimated by using the Archie equation.Archie (1942) equation can be reformulated (Soupios etal. 2007) to the form as given in the equation:

ϕ ¼ e1 mln= að Þþ1 mln= 1 Fi=ð Þ ð2Þ

where f is the porosity, m is the cementation factor andα is the coefficient of lithology. The values of m and αshould be determined for the site under investigation. Inthis study due to the lack of borehole information, this

Fig. 4 Lithologs for theboreholes WA-1, WA-2,WA-3, WA-5, WA-7, WA-11and WA-13. Vertical blacklines represent the locationof screen installed in thewell. Lithologs describe thevariable nature of aquiferlithology


was not possible, so theoretical values in accordancewith lithology have been assumed as 1 and 1.3, respec-tively, for the aquifer system.

The crossplot between inverse ofFa i.e. (1/Fa) and Rwfor the wells is shown in Fig. 7. The intercept of theregression line determines the value of 1/Fi i.e. 0.25.The inverse of 1/Fi gives the Fi which is 4. The slope ofthe straight line (0.0156) as shown in Eq. (3) determinesthe inverse of the matrix resistivity (Huntley 1986). TheFi obtained by this method is the average Fi for theaquifer system. The Fi obtained by the intercept of thestraight line in Fig. 7 is put in Eq. (2) to get the value of ffor the aquifer. The f of the aquifer is calculated to be0.34, which represents the average value for the aquifer.

Y ¼ 0:0156xþ 0:0434 ð3ÞThe aquifer has a significant amount of clay; there-

fore, Fa, Fi and Rw are related by the equation according

to Worthington (1993) taking into consideration clayeffects:

1 Fa= ¼ 1 Fi= þ BQv Fi=ð ÞRw ð4Þ

where Qv represents the cation exchange capacity perunit volume, and B is the parameter describing theaverage mobility of the cations near the grain surfacesand is related to f according to Worthington (1993) bythe equation:

LogQv ¼ �3:56� 2:74logϕ: ð5Þ

The parameter B varies with resistivity according toWorthington (1993) by the equation:

B ¼ 3:83 1� 0:83exp �0:5=Rwð Þð Þ: ð6ÞThe parameter BQv is obtained by using Eqs. (5)

and (6). Equation (4) is used to calculate the individual

Fig. 5 a–d Apparent resistivity data are marked by smallcircles. Solid black curve represents the apparent resistivitycurve. Red curve is the best fitted curve to the apparent resistiv-ity data. Solid blue block line is the modelled resistivity

(synthetic resistivity). Horizontal axis is the current electrodespacing (AB/2) in meters, and the vertical axis is the resistivityin ohm meter


Fi for all the wells and the VES points. The Fi forwells and K are plotted in Fig. 8.

The K and Fi are related by the equation:

y ¼ 1:4127x1:6493 ð7Þ

Table 1 Calibration between different lithologies and resistivity

Resistivity range(Ω m)

Lithology

200–1000 Dry sand and gravel

5–30 Clay formations with minor sand layers

40–150 Sand/gravel aquifers

100–250 Bedrock

Fig. 6 Modeled resistivity cross section of the profiles AA′, BB′, CC′ and DD′ is shown, respectively, in a, b, c and d

Table 2 Transmissivity (T), hydraulic conductivity (K) and theaquifer thickness of the well drilled in the study area

Well name Pumping thickness (m) T (m2/day) K (m/day)

WA-1 37 1190 32.16

WA-2 34 360 10.58

WA-3 16.5 980 59.39

WA-4 23 55 2.39

WA-5 22 1330 60.45

WA-6 19 890 46.84

WA-7 23 610 26.52

WA-8 30 2000 66.66

WA-9 30 1240 41.33

WA-10 16.5 1080 65.45

WA-11 30 860 28.66


where x is the Fi, and y is theK. K′ is obtained by Eq. (7)for the wells. Fi, K and K′ are summarized in Table 3 forwells. Equation (7) is then used to calculate K′ on all theVES by using the Fi, and the results are summarized inTable 4.

Results and discussion

Since the aquifer consists of variable lithologies andthe borehole information is sparse with no information

regarding the grain size, a unified relation had to beestablished between hydraulic conductivity and theintrinsic formation factor. For this reason K is plottedagainst the Fi in Fig. 8, and the relationship obtainedby this method will determine the K’ for any value ofFi. Table 3 shows percentage matching between K andK′. K′ obtained by this method matched 66–87%withK.The results are summarized in Table 4. Figure 9a showsnearly constant K′ (between 20 and 23 m/day) towardsthe eastern side between points AA8 and AA2. Towardsthe western side between points AA20 and AA9, K′ is

Fig. 7 Crossplot between1/Fa and formation waterresistivity. Inverse of the in-tercept of the straight linedetermines the intrinsic for-mation factor which is 0.25for the present study

Fig. 8 Crossplot betweenintrinsic formation factorFi and pumped hydraulicconductivity K


variable and lies between 7.8 and 38.7 m/day. A claymound can be interpreted at point AA14 which results inlow K′ of the sediments. Figure 9b shows the variation ofK′ along the profile BB′. Low K′ is interpreted to existbetween points BB25 and BB23. The profiles CC′ andDD′ in Fig. 9c, d represent variation of K′ in the north-south direction.

Hydrostratigraphy

Cross section AA′A″ is shown in Fig. 10 and has twoparts, i.e. between A-A′ and A′-A″. The portion be-tween A and A′ is developed by using resistivity andborehole calibration, whereas that between A′ and A″is derived from correlation of borehole logs. Threedistinct layers can be interpreted from the cross sec-tion: top clay layer mainly in the northeastern part, thesand/gravel layers which comprise the fresh wateraquifers, and the bottom clay layer with minor sand.The cross section suggests that the eastern portion ofthe study area is dominated by coarse sediments in-cluding coarse to medium sand and gravels whereasthe western portion is dominated by finer sedimentsincluding fine sand and clays. The collected resistivitydata mainly represent an alluvial cover with a promi-nent zone of unsaturated sand deposits below theground surface. Below these deposits fresh water aqui-fer beds are located to a depth of 120 m. These aquiferbeds are interpreted to be associated with the resistiv-ity ranging between 40 and 150Ω m in the saturatedzone. At depths greater than 120 m, clay formations andaquifer beds with less fresh groundwater seem to bedominant as expressed by the interpretation of layerswith resistivity of 25Ωm. Cross section BB′B″ also hastwo parts, B-B′ and B′-B″, and is shown in Fig. 11. Theportion between B and B′ is developed by using

Table 3 Comparison of pumped hydraulic conductivity (K) andestimated hydraulic conductivity (K′) in terms of percentage,where Fi is the intrinsic formation factor for the boreholes

Borehole K (m/day) K′ (m/day) Fi % matching

WA-1 32.16 22.9 7.8 71.4

WA-3 59.39 44.7 5.9 75.2

WA-4 2.39 2.9 2.9 82.1

WA-5 60.45 82.4 12.0 73.3

WA-6 46.84 53.9 4.4 87

WA-11 28.66 42.9 6.2 66.8

Table 4 Interpreted aquifer resistivity (Rf), intrinsic formationfactor (Fi) and estimated hydraulic conductivity (K′) on the VESpoints

VES point Rf (Ω m) Fi K′ (m/day)

AA2 51.0 5.2 21.4

AA1 50.4 5.2 21.4

AA3 51.5 5.2 21.6

AA4 50.9 5.2 21.2

AA5 49.0 5.3 21.8

AA6 50.3 5.4 22.7

AA7 49.2 5.3 21.9

AA8 49.3 5.2 21.6

AA9 38.0 4.0 14.1

AA10 40.1 4.3 15.4

AA11 63.5 6.7 32.8

AA12 59.4 6.6 31.6

AA13 45.6 5.1 20.4

AA14 25.4 2.8 7.8

AA15 55.3 6.1 28.0

AA16 55.6 6.2 28.3

AA17 52.9 7.2 36.7

AA18 47.2 6.4 30.4

AA19 41.0 5.6 24.1

AA20 54.6 7.4 38.7

BB21 68.0 7.3 37.4

BB22 59.0 6.3 29.6

BB23 50.8 5.4 23.1

BB24 39.3 4.2 15.2

BB25 40.1 4.3 15.7

BB26 54.5 5.8 26.0

BB27 53.0 5.7 24.8

BB28 50.2 7.0 34.6

BB29 49.9 6.9 34.3

BB30 60.6 8.4 47.2

BB31 61.3 8.5 48.2

BB32 51.8 7.2 36.5

BB33 35.1 6.1 27.7

BB34 47.8 8.3 46.2

BB35 59.9 8.2 45.6

CCC 65.7 7.0 35.4

CC2 65.0 6.8 33.4

CC3 65.0 6.8 33.4

CC4 63.4 6.4 30.4

CC5 61.7 6.4 30.2

CC6 69.2 7.2 36.5

CC7 68.8 7.1 36.1

DD36 50.7 5.4 23.0


resistivity and borehole calibration whereas that be-tween B′ and B″ is derived from correlation of boreholelogs. Apart from bedrock, three distinct layers can berecognized: top coarse sand layer, middle coarse tomedium sand and fine sand layer, and bottom clay layer.The top sand layer is characterized by coarse sand in theeast and fine sand in the west. Themiddle fine sedimentslayer is more sandy towards east and more clayey to-wards the west as depicted by the boreholes. Bedrock isencountered in some soundings and belongs to Now-shera Reef Complex. In general the study area is

Table 4 (continued)

VES point Rf (Ω m) Fi K′ (m/day)

DD37 23.5 2.5 6.5

DD38 21.4 2.3 5.6

DD39 33.4 3.5 11.4

DD40 34.9 5.8 25.8

DD41 35.4 3.8 12.5

DD42 51.1 5.4 22.9

DD43 51.4 5.5 23.2

Fig. 9 Estimated hydraulic conductivity K′ versus the ERS points along profiles a AA′, b BB′, c CC′ and d DD′


characterized by different kinds of sediments. Thecoarse sediments are concentrated towards the north-eastern part of the study area whereas fine sedimentsare found in the south and the southwest. Due to fre-quent changes in the location of the river and streambeds, the lithological composition is heterogeneous inboth horizontal and vertical sense. The Kabul and Indus

rivers have also deposited sediments in the area andhave reworked local available material.

Hydrogeology

Water from Swat River is diverted and transportedthrough a tunnel under the Malakand pass towards

Fig. 10 Stratigraphic cross section AA′A″ established by cali-brated resistivity and borehole data. Three layers are marked as topclay layer, intermediate sand/gravel layers and bottom clay layers.

The sand/gravel layers act as the aquifer in the area. It is clear fromthe figure that the subsurface towards the eastern side of thesection is more sandy and is dominated by coarse sediments

Fig. 11 Stratigraphic cross section BB′B″ established by cali-brated resistivity and borehole data. Apart from bedrock, threelayers can be seen: top coarse sand layer, coarse to medium sandlayer and fine sand–clay layer. The coarse and intermediate fine

sand layers act as the aquifer in the area. The eastern part of thecross section is more sandy and is dominated by alternate coarseand fine sand whereas western side is clay dominated


the Mardan Plain. Part of this water reaches the studyarea through the Maira Branch. The Maira Branch dis-tributes this water in the study area by means of variousdistributary canals. On the eastern and western sides ofthe study area, various streams flow and the water isdischarged into the Indus and Kabul Rivers, respective-ly. The groundwater from tube wells in the study area isof good quality throughout the area with electrical con-ductivity values between 300 and 600 μs/cm. The elec-trical conductivity of water originating from MairaBranch is 300 μs/cm, which suggests it is fresh innature. Depth of the water table is generally less than5 m near the nallas/rivers, whereas in the centre of thearea, it is more than 30 m deep. The fresh water aquiferstrata are thick in the north eastern part of the study areaand are associated with resistivity layers of 40–150 m,having transmissivity values ranging from 90 to1800 m2/day. Higher transmissivity values 600–1800 m2/day are found near the northeastern part ofthe area between wells WA-8, WA-9 and WA-10. How-ever, transmissivities 150–600 m2/day are found nearthe Kabul River and the southeastern boundary of theproject area. The hydraulic conductivity of the bedrockis very low as compared to the alluvial fill strata.

Conclusions

An integrated approach of estimating aquifer parametersfrom electrical resistivity and pumping test is a goodalternative to drilling more wells and conducting pumptests. The above study has shown a useful relationshipbetween hydraulic conductivity and electrical parametersin alluvial aquifers with varying layers of sand, graveland clay. A relationship has been established betweenelectrical and hydraulic parameters for the area whereborehole information is very sparse and grain size data isnot available. The method can predict the hydraulicconductivity with approximately 60–90 % confidence.This approach is helpful for site recommendations byanalyzing the possibility of finding hydraulically con-ductive strata and fresh water. The study area has thickbeds of coarse sand with sufficient transmissivities to actas good aquifer in the eastern part, whereas the westernpart is dominated by variable lithologies and hydraulicconductivities. Thick alluvial strata with high hydraulicconductivity qualify for drilling a production well in thewestern part of the study area.

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Resistivity Asam EMA 2012