water
Article
Delineating Groundwater Recharge Potential through Remote
Sensing and Geographical Information Systems
Ahsen Maqsoom 1, * , Bilal Aslam 2 , Nauman Khalid 1 , Fahim Ullah 3 , Hubert Anysz 4, * ,
Abdulrazak H. Almaliki 5 , Abdulrhman A. Almaliki 6 and Enas E. Hussein 7
1
2
3
4
5
6
7
*
Citation: Maqsoom, A.; Aslam, B.;
Khalid, N.; Ullah, F.; Anysz, H.;
Almaliki, A.H.; Almaliki, A.A.;
Hussein, E.E. Delineating
Groundwater Recharge Potential
through Remote Sensing and
Geographical Information Systems.
Water 2022, 14, 1824. https://
doi.org/10.3390/w14111824
Academic Editors: Dengfeng Liu,
Hui Liu and Xianmeng Meng
Received: 19 April 2022
Accepted: 2 June 2022
Published: 6 June 2022
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affiliations.
Department of Civil Engineering, COMSATS University Islamabad, Wah Cantt 47040, Pakistan;
fa17-cve-048@cuiwah.edu.pk
School of Informatics, Computing, and Cyber Systems, Northern Arizona University,
Flagstaff, AZ 86011, USA; ba924@nau.edu
School of Surveying and Built Environment, University of Southern Queensland,
Springfield, QLD 4300, Australia; fahim.ullah@usq.edu.au
Faculty of Civil Engineering, Warsaw University of Technology, 00-637 Warsaw, Poland
Civil Engineering Department, College of Engineering, Taif University, Taif 21944, Saudi Arabia;
a.almaliki@tu.edu.sa
Independent Researcher in Computer Science, Jeddah 12462, Saudi Arabia; a.almaliki1222@gmail.com
National Water Research Center, P.O. Box 74, Shubra El-Kheima 13411, Egypt; enas_el-sayed@nwrc.gov.eg
Correspondence: ahsen.maqsoom@ciitwah.edu.pk (A.M.); hubert.anysz@pw.edu.pl (H.A.)
Abstract: Owing to the extensive global dependency on groundwater and associated increasing
water demand, the global groundwater level is declining rapidly. In the case of Islamabad, Pakistan,
the groundwater level has lowered five times over the past five years due to extensive pumping
by various departments and residents to meet the local water requirements. To address this, water
reservoirs and sources need to be delineated, and potential recharge zones are highlighted to assess
the recharge potential. Therefore, the current study utilizes an integrated approach based on remote
sensing (RS) and GIS using the influence factor (IF) technique to delineate potential groundwater
recharge zones in Islamabad, Pakistan. Soil map of Pakistan, Landsat 8TM satellite data, digital
elevation model (ASTER DEM), and local geological map were used in the study for the preparation
of thematic maps of 15 key contributing factors considered in this study. To generate a combined
groundwater recharge map, rate and weightage values were assigned to each factor representing their
mutual influence and recharge capabilities. To analyze the final combined recharge map, five different
assessment analogies were used in the study: poor, low, medium, high, and best. The final recharge
potential map for Islamabad classifies 15% (136.8 km2 ) of the region as the “best” zone for extracting
groundwater. Furthermore, high, medium, low, and poor ranks were assigned to 21%, 24%, 27%,
and 13% of the region with respective areas of 191.52 km2 , 218.88 km2 , 246.24 km2 , and 118.56 km2 .
Overall, this research outlines the best to least favorable zones in Islamabad regarding groundwater
recharge potentials. This can help the authorities devise mitigation strategies and preserve the natural
terrain in the regions with the best groundwater recharge potential. This is aligned with the aims of
the interior ministry of Pakistan for constructing small reservoirs and ponds in the existing natural
streams and installing recharging wells to maintain the groundwater level in cities. Other countries
can expand upon and adapt this study to delineate local groundwater recharge potentials.
Keywords: geographical information systems; groundwater assessment; groundwater recharge;
remote sensing; Islamabad
Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
1. Introduction and Background
Groundwater is necessary to sustain various forms of life [1]. It is defined as a form
of water occupying all the voids within a geological stratum [2]. It is one of the important
water sources for agriculture, industry, and domestic use worldwide [3]. The groundwater
Water 2022, 14, 1824. https://doi.org/10.3390/w14111824
https://www.mdpi.com/journal/water
Water 2022, 14, 1824
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level is naturally maintained through precipitation that balances the water cycle, which
is crucial for all multicellular life forms. The occurrence of groundwater in a geological
formation and the scope for its exploitation primarily depend on the formation porosity [2].
The aquifers rely upon soil and fissured rocks as the medium of pores for the consistent flow
between them [4]. In these complex networks of interconnected pores, fractures, cracks,
joints, crushed zones (such as faults zones or shear zones), or solution cavities, rainwater
can easily percolate through them and maintain groundwater tables [5].
In the past few decades, the greater reliance on groundwater has decreased groundwater table levels. Globally, more than 60% of agricultural practices depend on groundwater
as a water source [6]. In developing countries in Asia, groundwater-based irrigation has
grown up to 500% [7]. Moreover, due to the rapid increase in population, the demand
for groundwater resources increases due to the inadequate availability of useable surface
water resources. Furthermore, increased industrial and agricultural activities pollute water
resources by directly releasing untreated waste into channels [8]. This eventually results in
the unavailability of clean surface water, causing extreme dependency on the groundwater
table. Therefore, the recharge of groundwater is of extreme importance to meet the global
population’s needs.
Groundwater/aquifer recharge is defined as water entry from the unsaturated zone
to the saturated zone [9]. The degree of the recharge by natural means primarily depends
on the amount of rainfall in a region that is considered a prime element for groundwater
recharge [4]. The relationship between rainfall and the natural groundwater recharge is
mainly governed by the region’s topography, soil moisture content, rock structures, geology,
the extent of fractures, elevation, slope, drainage patterns and density, landform, and landuse/land-cover and climatic conditions [3,4,10]. As a result of climate change, the overall
global precipitation has decreased, resulting in a decrease in groundwater recharge [11,12].
Furthermore, the rapid worldwide urbanization also results in transforming once natural
landscapes into urban water-impervious lands [12]. This limits the availability of freshwater
resources but also causes hindrance in the recharge of the available water resources [13].
This puts tremendous pressure on the groundwater table considering the continuous use of
groundwater to sustain essential life forms [10].
The aforementioned factors are resulting in water scarcity around the globe and are
emerging as a major concern globally [14]. To temporarily maintain the groundwater
levels and meet the ever-increasing water demand, artificial methods for recharging the
aquifers have been employed. These methods are considered a prerequisite for sustainable
groundwater management [3,15]. For this purpose, a new technique called managed
aquifer recharge (MAR) has been gaining popularity lately. It is an efficient means of
recycling storm water or treated sewage effluent for non-potable and indirect potable reuse
in urban and rural areas [16]. Despite these artificial methods, a more sustainable approach
must be adopted, and focus must be put on the natural means of groundwater recharge in
line with the United Nations Sustainable Development Goals (UNSDGs).
In the case of Pakistan, the agriculture sector is the prime contributor to the country’s
GDP, with an overall contribution of 21% [17]. The surface water supplies are sufficient
to irrigate 27% of the cultivable area, whereas the remaining 73% is directly or indirectly
irrigated using groundwater. This is evident since out of Pakistan’s total estimated annual groundwater extraction of 60 billion cubic meters [18,19], more than 85% is used
for agricultural purposes compared to 40% in the rest of the world [20,21]. This makes
Pakistan the third-largest user of groundwater for irrigation in the world [17]. Irrigation
and agricultural usage have caused excessive groundwater abstraction in Pakistan, leading
to water scarcity [7]. This growing deficiency of groundwater and ever-widening consumption for food production could weaken agriculture-dependent economies such as
Pakistan [22,23]. In addition to the great agricultural and industrial demand for water, the
increased urbanization [12] and overpopulation in Pakistan have also led to the overexploitation of ground and underground water. This, in turn, affects the water level/table
and thus its availability [13].
Water 2022, 14, 1824
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Furthermore, the reduction of natural water pervious landscapes due to urbanization [13]
and the natural reduction of precipitation due to climate change also prevent proper
groundwater recharge [12]. Due to these facts, Pakistan is affected by acute groundwater
shortages similarly to most developing countries [24,25]. As a result, the local groundwater
levels are falling, increasing pumping costs and deteriorating groundwater quality. Thus, it
is high time to carry out studies to delineate potential groundwater recharge zones in the
country to use the resulting data to devise mitigation strategies [8].
Researchers have used different criteria for delineating potential groundwater zones
in previous studies. Examples include the use of lineament and hydro geomorphology [26],
geophysical data with geospatial information [27–33], delineation of artificial recharges sites
using the use of remote sensing (RS) and geographic information system (GIS) [28,34,35],
and the use of RS and GIS for geomorphic features and lineaments [36–42]. These techniques are important tools for enabling the appropriate management of crucial groundwater
resources [43]. They are used to integrate various data to delineate potential groundwater
zone and solve associated groundwater problems. Furthermore, these technologies are
rapid and cost-effective in producing valuable data on geology, geomorphology, lineaments,
slope, etc., which are important parameters for groundwater exploration, exploitation, and
devising management strategy. Therefore, recent studies have used RS, satellite imagery,
and GIS for hydrogeological and hydro-geomorphological investigations.
Several studies have also applied RS and GIS applications to delineate groundwater
resources and potential recharge zones [8,34,44–58]. Some specific examples include a
study by Saraf et al. [59], which used GIS technology to process and interpret groundwater
quality data. In other studies, GIS and RS integrated with multi-criteria decision making
(MCDM) have been successfully used to uncover potential recharge zones [60]. Such
integration has also been used for district groundwater modeling [61], identification of
water zones [62], climatic analysis for groundwater recharge [63], and aquifer analysis
for recharge [64]. Selvam et al. [65] used similar techniques to decipher the groundwater
recharge potential zones in a coastal area of India, which is geographically closer to our
case study area. Other relevant studies using GIS have been described in Table 1 along with
their respective limitations.
Table 1. Studies outlining techniques for groundwater recharge.
Technique Used
Usage and Findings
Key Factors/Parameters
Limitations
Ref
GIS and RS with fuzzy
analytic hierarchy
process (AHP)
Fuzzy AHP was used to
delineate groundwater
recharge zones. Several
parameters were considered,
and GIS and RS techniques
were applied.
Drainage, Geomorphology,
Geology, Land Use/Land
Cover (LULC), Lineament,
Permeability, Slope,
Soil Texture,
Soil Depth, Rainfall.
Fuzzy AHP brings more
complexity and fuzziness
to the decision-making
process, thereby
affecting outcomes.
[66,67]
GIS and
RS with MCDM
MCDM was integrated with
RS and GIS to delineate and
map potential
groundwater zones.
Density, Drainage Geology,
Geomorphology,
Lineament, LULC, Soil,
Slope, Rainfall.
GIS and RS with
frequency ratio (FR)
FR, RS, and GIS were
combined to delineate and
map the potential
groundwater zones.
Drainage Density, Soil
Density, Geomorphology,
Lineament Lithology,
Land-use Pattern, Slope,
Soil Texture, Rainfall.
Thermal
infrared imagery
A thermal infrared
multispectral scanner was
used to delineate potential
groundwater recharge zones.
Hydrogeology, Height,
Thermal Parameters
Various MCDM models
can provide conflicting
rankings of the alternatives
for a common set of
information.
The FR method utilizes
past trends to predict the
future outcome, making
this approach depend on
historical data that may not
always be available.
Thermal activities around
artificial structures such as
power plants and
industrial zones, clouds,
and other distractions can
lead to inaccurate data.
[66,68]
[69–71]
[68,72]
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Table 1 shows various factors considered in respective studies for delineating groundwater resources. In this respect, a more accurate predicting model can be devised by
increasing the number of influencing factors used and improving the data collection procedures. The current study uses an integrated RS and GIS technologies approach to delineate
the potential recharge zones and categorize the study area into regions with high, moderate,
low, and very low recharge potential. These techniques were employed in combination
with the influencing factor (IF) technique, which has been previously used for studies
related to semi-arid areas [10] and coastal areas [65]. However, it has not been employed in
a noncoastal terrain such as the study area in the current research.
Moreover, compared to the previous studies, more factors have been introduced to
increase the accuracy of the predicted results in the current study. The key assessment
factors are overlaid with the spatial analysis tool of ArcGIS 9.3 to produce a combined
thematic map uncovering the zones with their potential recharge. To further improve
the model efficiency, more data were taken for the factors affected by temporal variations
such as rainfall, etc. For other factors, data from a decade were taken and averaged before
being used in the model development to nullify the effect of temporal variations. Further,
thematic maps of larger spatial scales and the digital elevation model (DEM) data of a
smaller resolution were used to study the targeted area comprehensively and accurately.
This study has practical applications for water management in developing and developed countries. For example, the groundwater delineation process paves the way for the
relevant authorities to develop infrastructure and devise critical policies and committees
to better manage the local groundwater sources. Furthermore, it can help policymakers,
town planners, and construction stakeholders to plan future cities with a focus on sustainability and preserving the natural landscape required for proper groundwater recharge.
Moreover, artificial structures could also be constructed to meet the associated groundwater demand and enable groundwater flow towards the region of lower concentration
systematically. Such planned groundwater management will help meet the ever-increasing
and widespread water demand among the country’s residential, commercial, and agricultural zones. Moreover, sophisticated systems such as the one proposed in this study have
lower costs and can easily interpret data to identify and suggest water contributing zones
and factors. Accordingly, the applications in developing countries are numerous, which
are usually concerned about the budgets of such projects. This provides incentives for
developing countries such as Pakistan to use these sophisticated and integrated systems
for groundwater delineation.
Further, this research contributes to the existing literature by providing an efficient
integrated approach of RS and GIS coupled with the IF technique to identify the potential
groundwater zones in a non-coastal study area. A similar approach was used to identify
groundwater recharge zones in the coastal areas [73] and near the watershed [66]. However,
such a study has not been conducted in non-coastal areas in a developing country. This
presents a research gap that has been targeted in the current study. Moreover, a distinguishing element of this study is the introduction of more factors coupled with the use of
more data (of a decade) for the temporal affected factors to nullify the temporal influence
and variations. This was reported as a limitation in multiple similar studies. This study
considers a larger spatial scale and finer resolution compared to other published works.
This study can be extended to other non-coastal cities around the globe.
The main objective of this research is to identify the potential influencing factors that
may impact groundwater recharge. Further, the potential groundwater recharge zones
are determined by incorporating all influencing factors using the IF weightage technique.
This will help the policymakers manage the groundwater resources and help researchers
understand the utilization of remote sensing and GIS for groundwater analysis.
2. Study Area
The case study area of this research is Islamabad, the capital city of Pakistan, located
at the edge of the Potohar plateau. It is located 14 km northeast of Rawalpindi in the
Water 2022, 14, 1824
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province of Punjab. In terms of map reference, it is located at 33◦ 49′ north and 72◦ 24′ east of
Greenwich [74,75]. Islamabad lies at an altitude range of 457–610 m and has 906.50 km2 [76].
The climate of the area is humid and subtropical. May, June, and July are the warmest
months, with average temperatures ranging from 36 ◦ C to 42 ◦ C, with temperatures
sometimes as high as 48 ◦ C. In comparison, the coldest months are December and January,
with mean minimum temperatures ranging from 3 ◦ C to 5.5 ◦ C [77].
In Islamabad, groundwater is mainly used for drinking and agriculture purposes [78].
Since its announcement as the capital on 14 August 1967, the urbanization in and around
Islamabad has been growing rapidly, leading to the development of multiple residential
sectors (Sectors D to I) and more new ones being proposed, such as sectors A to C and
sub-sectors I-14 to I-16 [74]. This is due to the increased migration of people in hopes of
better facilities and high-end, luxurious lifestyles. According to the 2017 census, Islamabad
recorded a population growth rate of 4.91 percent, and its population increased from
0.81 million in 1998 to 2.0 million in 2017 [79]. Such a mass-level migration to Islamabad
increases the demand and reliance on groundwater to sustain life necessities [80].
Moreover, since Islamabad rests on the Potohar Plateau and consists of a hard rock
terrain, its surface does not allow enough permeable surface for groundwater tables to be
properly recharged [70]. As a result, the groundwater levels of Islamabad are depleting
rapidly on an annual basis, as reported by the metropolitan corporation of Islamabad [80].
The Interior Ministry of Pakistan reported a 6 ft decrease in Islamabad groundwater in 2013,
followed by a 10 ft, 16 ft, 23 ft, and 30ft from 2014 to 2017, respectively. It is estimated that
groundwater levels in Islamabad have decreased by five times as of 2018 [80]. Therefore,
it is imperative that new and reliable water sources must be found. Accordingly, it is
necessary to carry out a study to delineate the potential groundwater zones in the city.
This can help the policymakers and town planners to preserve such zones with permeable
strata in the city to mitigate this groundwater recharge issue or alternatively better plan the
construction activities around such areas.
Figure 1 shows the Islamabad map that is divided into five zones: zone 1 to zone 5 [74].
These zones are the administrative boundaries of the study area. They can be used as a
reference for policymakers for decision making for each zone with respect to findings of
this research. The city infrastructure has been planned in nine sectors in total, and an
alphabet from A–I represents each sector. Every sector covers an area of approximately
2 km2 and is further subdivided into four sub-sectors, each containing a central shopping
mall, public park, and other amenities [74,81]. These sectors are the gridded divisions of
the city to subdivide the capital into small units. It is similar to municipalities in developed
countries and presents a grid division of the city. Out of the 5, zone 4 has the largest
area, 282.5 km2 [82], while zone 1 has the most developed residential area [83]. Zone 2
has an area of 9804 acres. Since CDA apportioned this zone to a private and cooperative
housing scheme for improvement, zone 2 has become the city’s most alluring space [83].
Zone 3 (203.9 km2 ) is one of the most beautiful areas of Islamabad. Vacation spots such as
Daman-e-Koh and Peer Sohawa are situated in this zone [84]. Zone 5 (157.9 km2 ) is near
the old airport and is one of the most populated zones [85].
Islamabad continues to experience expansion to accommodate the increasing population. The territorial limits of Islamabad have expanded by 87.31 km2 from 1972 to
2009, with a significant reduction in the forest covers and other natural habitats [86]. As a
result, Islamabad has registered the highest population growth rate of 4.91 percent, and the
population has increased from 0.81 million in 1998 to 2.0 million in 2017 [79]. This rapid
urbanization has led to many development projects being initiated within the city, including
the extension of transportation systems, revision of the city master plan, and industrial and
real estate development [12,75] that provide job opportunities to the residents [87,88].
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Figure 1. The study area (Islamabad) and its zones.
‐
Due to this rapid increase in population, Islamabad has undergone many predicted
and unpredictable changes [74]. One such change is the higher water demand in the
region [80]. The main water resources for Islamabad are surface- and groundwater. Simli
‐
Dam and Khanpur Dam are major water resources for Islamabad. Along with the surface
‐
water, the Capital Development Authority (CDA) supplies groundwater extracted from
180 tube wells to Islamabad. Private and municipal wells are also used to fulfill the local
water requirements [79]. Despite the aforementioned resources, the increased population
has heightened the reliance on groundwater since it is one of the primary sources for
domestic use [89]. The resulting extensive use of groundwater in the region leads to the
‐
depletion of natural groundwater resources [80].
‐
Moreover, considering that the study area is situated in the Potohar Plateau, where the
terrain is geologically composed of tertiary sandstone, limestone, and alluvial deposits [77],
the recharge capacity of the region is not good. Thus, groundwater does not recharge
properly, resulting in the depletion and unavailability of clean drinking water. The areas
facing severe water shortage include sectors G6, G7, H8, G13, I-10, [90], and I-8/1 [91]. Thus,
‐
it is important to manage the regional groundwater resources [78]. For this purpose,‐ the
current study delineates Islamabad’s potential groundwater recharge zones. The obtained
potential recharge map provides the information to help improve the local management
of groundwater resources. Such an assessment is important for future planning and
development policies in the area and devising strategies for efficiently utilizing natural
resources such as groundwater.
3. Factors Affecting Groundwater Recharge Potential
‐
‐
Groundwater is affected by multiple factors such as land use, slope, and lineament [92].
In addition, the study area’s rainfall, soil conditions, and soil types also influence the
Water 2022, 14, 1824
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groundwater [93]. In this study, 15 influencing factors (Ifs) were identified and used to
develop potential zones to produce an error-free diverse outcome instead of a single influencing factor outcome, which provides a limited outcome in terms of accuracy [65]. Broadly,
these factors can be grouped into four key groups: (1) elevation and slope, (2) rainfall and
drainage, (3) land-use/land-cover and soil characteristics, and (4) faults, as listed in Table 2.
The influencing factors (IFs) are the factors that can affect some features of the target object,
system, or phenomenon [94]. IFs can be used as control variables to determine the key
influencing factors of an object, system, or phenomenon. These have been used in various
studies. In water-related studies, IFs have been used to assess the seasonal changes in water
quality [95], water transport through cracks in concrete [96], distribution characteristics of
microplastics in urban tap water [97], comprehensive evaluation and urban agglomeration
water resources carrying capacity [98], and others. Accordingly, in the current study, IFs
are used to delineate potential groundwater recharge zones in Islamabad, Pakistan. These
15 key factors are listed in Table 2 and discussed subsequently.
Table 2. Factors influencing groundwater recharge classified criteria.
Group
Elevation and slope
Rainfall and drainage
Land use/land cover
and soil characteristics
Faults
Key Factors
Source of Categorization
Selected Ref
Elevation
Slope
Slope length
Aspect
Total wetness index
Rainfall
Drainage distance
Drainage density
Land use/land cover
Soil
Lithology
Plan curvature
Profile curvature
Distance to faults
Fault density
Height value
Slope gradient
Measurement of slope lengthwise
Aspects of area
Runoff collection and infiltration
Zones with rainfall recement
Distance to drainage networks
Density values for drainage
Satellite imageries
Textures
Rock type details
Detailed area curvature
Flow categorization
Lineament distance
Density for lineaments
[99]
[100]
[100]
[70]
[101]
[93]
[102]
[103]
[104]
[72]
[105]
[70]
[61]
[106]
[107]
3.1. Elevation
Surface elevation plays an important part in groundwater recharge. It is the primary
source for triggering the water flow under gravity [99]. Elevation studies highlight the
regions contributing to the groundwater flow; i.e., higher slopes allow less water infiltration.
Islamabad has variable elevation, as it is composed of both mountainous regions and flat
surfaces. The mountainous regions have higher slopes that transfer water from higher
elevation to lower elevation. A similar study found designated slope as a very important
factor in groundwater recharge [108]. Previous research has indicated that gentle slopes
and flat surfaces have higher recharge potential compared to inclined surfaces and higher
slopes [100]. Therefore, the inclusion of surface elevation signifies the groundwater flow
and determines the flow direction as it induces the flow under gravity [108–110]. A major
part of the current study area consists of mountainous regions with high surface elevations.
Therefore, it is used as a key factor in the current study.
3.2. Slope
Slope defines the extent to which groundwater can be recharged with the precipitated
water [100]. The regions with higher slopes experience rapid water running over the surface,
hindering the absorption of precipitated water into the groundwater [65]. Conversely,
in areas involving lower slopes and vegetation, the water cannot run off the surface
rapidly, and thus, more of it is absorbed in between the pores and adds to the groundwater
table [100]. In relevant studies, it has been established that the topographical feature of the
slope impacts the directional flow of water and indicates its accumulation. Further, the
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flat surfaces with gentle slopes displayed the highest infiltration capacity [109,111], thus
contributing to an increase in the groundwater table. Our study area, Islamabad, comprises
high-slope areas, as the northern outskirt is predominant with the mountain region, making
the slope one of the important factors for the current study. Accordingly, the slope has been
included as one of the key factors in this study.
3.3. Slope Length
Slope length indicates the physical characteristic of the slope in terms of its extension
and magnitude. It helps determine the flow and highlight possible regions of groundwater
retention [100]. Being a primary factor for groundwater contribution, slope length determines runoff strength and the groundwater flow direction. Slope length also indicates the
amount of rainfall that would reach the groundwater table through infiltration [100,108,109].
Gentle slopes have greater infiltration capacity, displaying greater groundwater recharge
potential and vice versa [100]. Slope lengths help understand the flow of precipitation as
the water runs off from higher elevation towards the lower elevation. Considering that our
study area is predominantly sloped in the northern parts due to mountain ranges, this is an
important factor in this research.
3.4. Aspect
The front-facing side of a slope, or generally the face of the slope, is defined as
the aspect [109]. When combined with the slope and slope length maps, the aspect can
indicate the extension of a particular slope in a specified direction to unveil the potential
flow of groundwater [70]. The aspect proceeded by flat surfaces or gentle slopes allows
the precipitated water to flow smoothly and streamlined, thereby maximizing the area’s
infiltration capacity, leading to greater recharge [70,109]. Islamabad is composed of higher
elevations at the northern outskirt that stretches predominantly towards the east. The aspect
is proceeded by the gentle and flat surfaces containing the residential zone of Islamabad.
The aspect can indicate the flow of precipitation and groundwater accumulation towards
the inner zones in Islamabad. Therefore, it is used as a key factor in the current study.
3.5. Topographic Wetness Index (TWI)
The topographic wetness index (TWI) is a steady-state wetness index used to quantify
topographic control on hydrological processes [101]. TWI indicates control over the groundwater processes, such as flow and retention in a specified zone. Several studies have been
published explaining the process to calculate the TWI [101,111]. TWI provides detail about
the flow of groundwater considering the effect of the slope. TWI can impact groundwater
flow and its occurrence in a varied elevation areas such as Islamabad. Numerous studies
have linked TWI, slope, and elevation effects to the water recharge potential [65,100,109].
TWI gives an indirect indication of water moisture availability and potential recharge zones.
Therefore, this has been used as a key factor in the current study.
3.6. Rainfall
Rainfall or precipitation positively affects the groundwater table because of larger
water infiltration [93]. Rainfall has always been a reliable source of freshwater [65]. Previous
research has linked both the movement and occurrence of ground and surface water to
mainly depend upon rainfall [108,111]. Considering that the rainfall quantities of the study
area can indicate the movement of groundwater and can depict the flow and accumulation
of water bodies, it is important to include this factor while investigating groundwater
recharge zones [109]. Therefore, it is considered significant for Islamabad as well and used
in the current study as a key factor. Further, since Islamabad is a rainy area, and some
mountainous regions in the area receive more rainfall than other parts of Pakistan, rainfall
is a key factor dictating the local climate and recharging the water sources.
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3.7. Drainage Distance
Drainage distance is crucial for water studies, such as its occurrence and flow assessments. Drainage distance highlights the geological distance between successful drainage
zones. The drainage density indicates the drainage condition of the water shed [109].
Groundwater movement beneath the surface can be unfolded by uncovering the drainage
networks according to lineaments such as underground fractures and faults. Lineaments
impact groundwater movement within the surface [65,102]. For studies relating to groundwater recharge, the inclusion of drainage distance is crucial because of its relationship
with permeability which is the property that describes the flow of water bodies beneath
the earth’s surface [108]. A similar study prioritized areas comprising more considerable
drainage distances for the groundwater recharge potential and vice versa [109]. Accordingly, drainage distance has been shortlisted as a key factor in the current study for the
study area of Islamabad.
3.8. Drainage Density
Drainage density is the ratio of all the streams over the area to the total area [65]. It
indicates the drainage capacity and measures the drainage over a particular watershed [103].
A higher drainage density region indicates a well-distributed water flow area with multiple
streams contributing to the flow and recharge and vice versa. A similar study has linked
higher drainage density to greater groundwater recharge potential [108]. According to the
previous research, the drainage density contributes toward the groundwater recharge as
it describes the flow pattern and the occurrence of water beneath the surface [65,109]. As
Islamabad receives higher rainfall towards the northern outskirts, and the density of the
drainage network would greatly influence the flow and occurrence of groundwater in the
region, drainage density is selected as a key factor for this study.
3.9. Land Use/Land Cover
Land use/land cover involves several elements, including soils, human settlements,
vegetation cover, waste lands, etc. [112]. The settlement in an area affects the groundwater
due to the human-made structures. The land vegetation covering is one of the major
groundwater factors used for retaining water [65]. Depending upon the porosity and
permeability, the soil conditions of an area also control groundwater seepage through the
surface. RS and GIS usage for land mapping has gained popularity recently [6,104]. With
the help of land use/land cover, a similar study has linked the best and most abundant
agricultural practices with groundwater availability over the study region [109]. For
Islamabad, the regions should be studied based on their demand for groundwater, thereby
necessitating the inclusion of land use/land cover in this study.
3.10. Soil
Soil is one of the most important factors for groundwater recharge since groundwater
movement through the surface is controlled by soil type and properties [65]. Accordingly,
parameters such as porosity and permeability are of utmost importance and are crucial to
groundwater flow [72]. Moreover, the soil is also responsible for the filtering or buffering
activities between the atmosphere and the groundwater in the biosphere [65]. Therefore,
it is considered one of the prime influencing factors in groundwater recharge analysis.
Considering that soil properties vary in each region, large-scale test data of the soil type
might be required. In previous research consisting of a variable soil type for groundwater recharge, higher weightage has been allocated to the soil as a contributing factor.
Accordingly, it has been declared as one of the high IF [109,111]. Furthermore, greater
variations of the soil types were seen influencing the groundwater recharge potential in
relevant studies [108]. In the current study area, the terrain has high soil variation; the
northern outskirts are predominant with mountainous soil, and the southern outskirts are
predominant with loamy soils. Thus, soil type is selected as a key factor in this study.
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3.11. Lithology
Lithology refers to the physical appearance of rocks. Rock characteristics impact
the movement of water beneath the surface [105]. In smaller rocks, the water finds more
passage for movement and vice versa. If the grains are arranged in a well-graded manner, there is no passageway for water and vice versa [65]. Lithology plays an important
part in dictating groundwater flow via channels, permeability, and occurrence [104]. This
factor has been considered in a similar groundwater recharge study outlining the influence of rock type, soil type, and the higher permeability on groundwater movement and
occurrence [105,109]. Several other factors may influence the lithological characterization
and its impact on groundwater recharge. However, this research is limited to lithological
information and does not have permeability, porosity, or grain size information. Further,
it is based on a literature review for assigning weightages of lithologies. The terrain is
composed of various rock types in our study area, including tertiary sandstone, limestone,
and alluvial deposits [84]. Lithology contributes to groundwater flow and is included in
the current study [105].
3.12. Plan Curvature
Plan curvature explains the geometry of a particular region. It helps understand the
way contours intersect the horizontal region and their impact on the slope inclination of a
particular zone [70]. It explains the flow of groundwater and helps establish a generalized
flow pattern. Plan curvature approximates the inclination of various zones that impacts
groundwater recharge through topographical influence [111]. The inclination of the area
is marked with a slope that runs from the region of higher inclination towards the lower
inclination, thus indicating groundwater flow [100,109]. The region of Islamabad is higher
in inclination towards the northern region that goes down towards the southern zones.
This is because the northern area is comprised of mountainous regions, and the southern
zone consists of high-populous flat regions, establishing a generalized pattern of inclination
decrease [111]. The inclination and gentle slopes and the presence of flat surfaces greatly
influence groundwater recharge [108]. Therefore, plan curvature has been included as a
key factor in this study.
3.13. Profile Curvature
Profile curvatures define the nature of the ground zones under study: linear, concave,
and convex. It is defined as the line parallel to the direction of the maximum slope. Patterns
might indicate a general linear formation with a defined value approaching zero. A positive
value indicates an upward concave profile, while the negative region represents an upward
convex profile [70]. The profile curvature helps classify the area into lower or higher waterretention zones depending upon its convexity and concavity. Accordingly, the regions
comprising elevated convex profiles within center zones are regarded as less water holding
and vice versa [110]. The curvature of the study area is included in this study to assess
its effect on the water-retention capability of the zone following related studies [109,110].
Considering the variability of Islamabad’s surface in terms of slope and elevation, it is
important to consider the influence of profile curvature on groundwater recharge in this
region. Therefore, this factor has been used in the current study.
3.14. Distance to Fault
Faults describe the change in geological composition in a particular zone [106]. These
indicate the movement and change a particular rock surface has undergone in a specified
period. For example, earthquake-induced faults can indicate rapid geological movement beneath the surface. The parameters of faults can have vast ranges. Distance to faults impacts
the flow and occurrence of groundwater [108]. It is important, as it indicates groundwater
flow and can highlight the zones contributing to underground-water flow [106,109]. In our
study area, Islamabad and nearby regions have more faults that influence the groundwater
recharge. Thus, this factor is included in the current study.
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3.15. Fault Density
The magnitude of faults (density) indicates the potential groundwater regions. In
a similar study, lineaments such as faults have been reported to impact the groundwater recharge potential zones and are considered key IF [108]. Fault density helps determine the occurrence and movement of groundwater beneath the surface. Many relevant
studies have included fault density as a key factor in assessing groundwater recharge
potentials [60,65,66]. As previously discussed, Islamabad has higher faults than the rest of
the country. Therefore, fault density is included as a key factor in the study.
4. Methodology
The current study follows a four-step approach. In the first step, the relevant thematic
layers are identified. First, the thematic layers used for the study were extracted that
act as input data for the eventual delineation of recharge zones. These thematic maps
present the geographical map of the study region in accordance with the subject matter. The current study utilizes thematic maps for 15 hydrological factors. These include
distance to faults, land use, lithology, drainage density, slope, soil, rainfall, plan curvature, fault density, profile curvature, TWI, elevation, aspect (the front-facing direction of a
slope), drainage distance, and slope length. These factors were extracted from previous
literature [60,66,87,103,113] considering the geological properties of the study area as listed
and are discussed in Section 3 of the study.
The thematic maps used in the research were generated at a 1:200,000 scale considering
that this would eventually increase accuracy. In addition, the majority of the data sets were
available at this scale. The differing scales were later normalized for the sake of uniformity.
The digital elevation model (DEM) data are used on a global scale at 30 m × 30 m resolution
for topographic analysis. This resolution is highly important, as it contributes to how
sharply the objects can be seen in an image. It represents the size of the tiniest feature
captured by a satellite sensor or portrayed in a satellite photo. It is commonly expressed
as a single number representing the length of one of the sides of a square (grid) [12]. In
addition to the normalization of the input data, uniformity is ensured in their format
for easy integration of these thematic maps into the GIS platform. For this purpose, the
acquired maps are converted into raster form before integration with the GIS.
In the second step, the pre-processing of the thematic layers was performed to ensure
uniform projection and resolution. This is followed by the assignment of scores and suitable
weightage to each factor. During weightage overlay analysis, the ranking was given for each
parameter of each thematic map, and weights were assigned according to the influences
(following IF technique) of the feature on the hydrogeological environment of the area
coupled with that parameter’s contribution toward the groundwater recharge as shown in
previous researches [65,108,109].
The IF technique was used to assign scores and get a diverse and error-free outcome. A diversely produced thematic map considers the input from multiple hydrological
procedures, thus not relying on a single hydrological process where the outcome can be
manipulated and is prone to error. Moreover, due to finer resolution, any errors in the
weighted overlay analysis within the ArcGIS were eliminated since such resolutions result
in finer interpretation.
The third step involves using ArcGIS to deploy the thematic layers to get the processed
images containing the potential zones. In this step, all the scored thematic maps along
are integrated by employing the “Spatial Analysis tool” in ArcGIS 9.3, whereby rankings
are assigned to all the thematic maps. Then, these weighted thematic maps are overlaid
using ArcGIS to highlight the potential recharge zones. In the fourth (last) step, the study
area was categorized based on the potential groundwater rechargeability into five different
classes: poor, low, medium, high, and best in terms of their capability for the groundwater
recharge potential.
Figure 2 shows a flowchart summarizing the methodology used in this study. The
associated steps include acquiring the data, converting to raster, preprocessing (confirming
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projection and resolution coupled with assigning
scores and weights), integrating GIS for
‐
final output, and categorizing the study area based on groundwater recharge capability.
Figure 2 also shows the source of the acquired data. Accordingly, the thematic maps are
acquired from Landsat-8 TM Satellite, Aster DEM, and soil and geological maps of Pakistan.
The following sections explain the IFs used in this study in detail, their sources, and the
procedure for assigning weights to each of these factors.
Figure 2. Flowchart for potential groundwater assessment using integrated remote sensing and
GIS techniques.
4.1. Acquisition of Thematic Maps for Contributing Factors
Table 3 below enlists the sources for acquiring thematic maps for all the contributing
factors. The soil thematic map was generated using the Soil Map of Pakistan [114]. Land use,
rainfall, and TWI thematic maps were generated using Landsat 8TM satellite data. Drainage
distance, slope, plan curvature, profile curvature, slope length, elevation, drainage density,
and aspect thematic maps were generated using ASTER global DEM. Finally, distance
to faults, lithology, and fault density thematic maps were generated using data from the
geological map of Pakistan on a scale of 1:200,000 [115].
Table 3. Acquisition of Thematic Maps for Contributing Factors.
Factors (units)
Sources of Acquisition for Thematic Maps
Soil
Land use, TWI, Rainfall (mm/y)
Drainage distance (m), Slope (degree), Plan
curvature, Profile curvature, Slope length (m),
Elevation (m), Drainage density, Aspect
Distance to faults (m), Lithology, Fault density
Soil map of Pakistan
Landsat-8 TM satellite data
ASTER GDEM
Geological map of Pakistan
These thematic map data were cross-checked using ground surveys for cross-validation.
The imagery was visually interpreted to delineate rainfall, land use, and other factors with
the help of slandered characteristic image-interpretation elements such as tone, texture,
shape, size, pattern, and association using the Landsat 8 satellite data products. These data
sets are used for assessing groundwater recharge potential [65,109,111].
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4.2. Weightage Assignment via IF Technique
Weights and rates were assigned to the factors to obtain a final combined recharge
potential map. Using the IF technique, the influence of various factors was taken into
account, and the level of impact they have on the hydrological aspect of groundwater flow
and its occurrence was assessed. A weightage approach was included as used by [65] to
assign weightage to the factors that would ultimately define the control they can assert over
the groundwater recharge of the study area. The current study follows a similar approach.
In assigning weights to the considered factors, five major descriptive levels were plotted for
each factor ranging from very high to very low, including some interrelated levels. These
weightage values range from 10 to 1 point, i.e., a very high range is assigned a score of
10, and the minimum level is 1 following relevant groundwater studies [113,116]. These
weights for each factor were assigned based on their degree of impact on groundwater
recharge as extracted from relevant literature [6,10,63,113].
5. Results and Discussions
This section presents the results and discussions in line with the adopted method.
5.1. Spatial Analysis of Considered Key Factors
Figure 3 represent the resulting thematic maps of the 15 considered factors for the
current study area. Figure 3a highlights the wells or water extraction points in the study
area. These are primarily located in the residential zones and plain areas of Islamabad.
Figure 3b shows the thematic map of rainfall for Islamabad. The resulting map highlights
that Islamabad receives ample rainfall. Further, it shows a rhythmic increase in rainfall
volume from south to north. The northeast outskirts receive the highest rainfall, consisting
of regions from Rawat to Crore Village. Low-rainfall regions are evident in the southwest.
Considering the high rainfall in the northeastern regions, there are more chances for more
groundwater recharge and high groundwater levels in alluvial plains [64], thus displaying
a higher potential for groundwater recharge. Moreover, the map shows that around
44% of the area receives less than 882 mm of rainfall, 16% area receives rainfall between
882–999 mm, 10% area receives rainfall between 999–1116 mm, 9% area receives rainfall
between 1116–1233 mm, while 21% of the area receives most rainfall ranging between
1233–1350 mm. This shows that around 40% of Islamabad receives good rainfall. This
assessment can help policymakers preserve the natural terrain in the region receiving more
rainfall and utilize it for groundwater recharge.
Figure 3c shows Islamabad’s thematic layer of plan curvature data. The figure categorizes the regions based on concavity and convexity. The map shows that the northeast
region of Islamabad is composed of higher convexity, whereas a systematic decrease in
convexity is observed from north to south. This indicates a higher surface and altitude
in the north and a gradual decrease towards the south. This heavily contributes to the
groundwater flow from north to south, where a gentler slope and plain area can accumulate
this water and get recharged. A similar study accounted for alluvial plain and gentle slopes
to be more promising for groundwater potential due to large infiltration rates, high porosity,
and permeability [116].
Figure 3d shows the thematic layer of soil data for Islamabad, where the region is
classified based on soil composition. Soil types impact groundwater flow directly, but they
also impact other important phenomena, such as infiltration [117], which ultimately impact
groundwater recharge. The soil conditions define permeability, which impacts groundwater
infiltration and soil porosity. For example, the calcareous loamy soil is abundant in arid and
densely populated areas. Figure 3d shows that the mountainous soil forms the northern
edge of Islamabad that receive a decent amount of rainfall. Such soil helps infiltration,
enabling the groundwater to flow towards the inner zones. While no definite pattern exists
throughout the study area, calcareous soils are mostly reported for various regions.
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Figure 3. Cont.
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Figure 3. Thematic layers of selected factors for Islamabad’s data (part 1), (a) well data, (b) rainfall
data, (c) plan curvature, (d) soil data, (e) distance to fault, (f) drainage distance, (g) profile curvature, (h) TWI, (i) slope, (j) elevation, (k) slope length, (l) lithology, (m) land use, (n) fault density,
(o) drainage density, (p) aspect.
Figure 3e shows the thematic layer map of distance to fault for Islamabad. This map
categorizes regions with respect to distances to faults. Considering that the faults act
as points with more recharge capability, more distance from faults implies less recharge
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capability and vice versa. In this respect, Figure 3e shows that the major faults are all
located on the outskirts of Islamabad. The zones comprising convex geological features and
landscapes have nearby faults, whereas the southern regions comprising more land use and
less geological convexity comprise low distances to faults. This aligns with several studies
that have established patterns with lineaments and groundwater recharge potential [10,118].
Overall, the southern regions with less distance to faults display more recharge potential in
the current study area.
Figure 3f shows the thematic layer of drainage distance for Islamabad. It categorizes
the study area based on the distance of various zones from the drainage networks. Figure 3f
shows that the study area comprises abundant and closely located drainage networks.
However, there is no defined pattern for the drainage distances in the study area. Considering that a lesser distance from the drainage pathway displays higher groundwater recharge
potential [119], the drainage distance thematic map suggests that the study area has a larger
potential for groundwater recharge. Further, there is a well-distributed groundwater flow
throughout the region. Figure 3g shows the thematic layer of profile curvature for Islamabad. It highlights the geological characteristics of Islamabad and depicts the concavity and
convexity of the region. It is indicated that the outskirts of the northern region are higher
in altitude and contribute to the groundwater flow under gravity. A higher profile value
indicates a rising elevation, ensuring a systematic flow towards the inner edges with the
highest and densest land use in Islamabad. This is in line with a previous study’s findings
that suggest a higher potential of gentle slopes for groundwater recharge [116].
Figure 3h shows the thematic layer of TWI for Islamabad. The TWI map shows
the impact of geology on the hydrological aspects. The outskirts, shaded in deep blue
in Figure 3h, show the zones with geological makeup that impact regional hydrology.
Following our thematic maps for the land use, well data, and rainfall, the TWI highlights
Islamabad’s northern outskirts as the areas directly reaching the groundwater. The inner
edges with lower index value contribute little to the groundwater flow, while the geological
makeup of the outermost skirts contributes greatly to the groundwater flow towards the
center, housing the area with the highest and densest land use. A direct relationship
between the higher TWI value was also established by another study [120]. Following
our findings, a higher TWI value suggests a better groundwater recharge potential in the
Islamabad region.
Figure 3i shows the thematic layer of slope data for Islamabad, showing that the
northern outskirts of Islamabad have the highest slope. The slope plays an important part
in determining the runoff direction of groundwater. The thematic map indicates that 23%
of the region has a slope greater than 48 degrees, 38% has a slope ranging from 36 to 48,
16% has a slope ranging from 24 to 36, 9% has a slope ranging from 12 to 24, and 4% of the
region has a slope less than 12 degrees. The figure shows that the outskirts of Islamabad in
the northern region comprise the highest slopes due to mountains that promote a rapid
runoff towards the south. While some water is lost during the runoff, infiltration takes
water to the deep soil layers, contributing to recharging the local groundwater table.
Islamabad’s outskirts comprise Attock, Wah Cantt, and Taxila in the west; Murree
in the northeast; Haripur in the north; Gujar Khan, Rawat, Mandrah, and Kahuta in the
southeast; Rawalpindi to the south and southwest; and other Punjab regions in the east.
The greater slope in the northern region ensures a flow of water towards the south with the
highest settlement and greatest water recharge potential.
Figure 3j shows the thematic layer of elevation data for Islamabad. Islamabad is high
on the northern edge due to the mountains that decrease towards the south. The area with
residential zones, i.e., the inner edges, and that towards Rawalpindi has higher population
density and low elevation. This systematic decrease of elevation contributes directly to the
groundwater flow as the water flows under the action of gravity. The higher elevation area
also receives greater rainfall, as shown in our rainfall thematic map, ensuring infiltration
and surface runoff towards the inner edge. Thus, the area with higher elevation retains
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rainwater for a lesser time duration and generates more runoff towards the residential
areas in Islamabad, in line with published studies [64].
Figure 3k shows the thematic layer of slope length data for Islamabad that highlights
the lengths of slopes in the region. Longer slope lengths are evident on the northern
outskirts, while a rhythmic slope length decrease can be observed towards the south. The
area with the highest land use comprises regions with lower slope length values. The
groundwater flows from the northern sides with the highest slope lengths promoting
recharge potentials and infiltration. The gradually decreasing slopes towards the center
help with groundwater recharge to meet the requirements of the local population.
Figure 3l shows the thematic layer of lithology data for Islamabad that shows regions
with limestone and unconsolidated deposits to be abundant in the area. However, there
is no defined pattern, and the data are scattered throughout the region. The concentrated
regions are highlighted in red, green, and purple colors in Figure 3l. There is a presence of
sandstone in the northeastern region along the dense mountainous regions that continues
towards the northwestern region.
Further sandstone and unconsolidated deposits are seen within the areas of highest
land use towards the southwest. Past glacial activity has contributed to the unconsolidated
deposits in the region due to the weathering of rocks. A previous study also established a
pattern between the weathering of rocks towards the increased groundwater recharge potential [121]. An increased recharge was also observed in the area of higher unconsolidated
deposits in another study [120]. Accordingly, there is a greater potential for groundwater
recharge in the study area.
Figure 3m shows the thematic layer of land-use data for Islamabad, showing areas
such as bare land, water bodies, built up, and vegetative regions. Such a map displays
the variation of population density and associated water demand throughout the study
area [10]. The thematic map for Islamabad indicates that 4% of the region comprises bare
land, 36% is built-up region, 51% is vegetative, while 9% of the study area is composed of
water bodies. Further, it can be observed that most of the built-up region is around the
inner region of Islamabad. This region falls towards the city of Rawalpindi, which has a far
greater population density than Islamabad. The runoff from the northern region infiltrates
into the groundwater table around these internal regions, where there is a greater need
for water.
Figure 3n shows the thematic layer of fault density for Islamabad that highlights geological features induced by the movement of rock bodies. These faults govern groundwater
flow following their complex and favorable topography. Accordingly, the fault densities
for the area include 43 % area with less than 15 fault density, 6% area ranging from 15 to 41,
35% ranging from 41 to 65, 7% ranging from 65–91, while 9% of the study area has fault
density greater than 91. The map indicates that the northeastern edges of Islamabad consist
of lower-density faults than the northwestern region, where there are more mountains. The
maximum land use is towards the internal regions with no major geological faults. Previous
studies have linked fault-dense regions with higher groundwater recharge potential [10].
Thus, there is a higher recharge potential in the northwestern areas of Islamabad.
Figure 3o shows the thematic layer of drainage density for Islamabad that highlights
the northeastern regions to have streams or rivers with relatively long lengths. This ensures
a deep-water flow towards the inner edges of Islamabad. Thus, the northeastern region
contributes majorly towards the groundwater flow in the areas of highest land use. Further,
a flow from the northern to the southern edge is seen with the major contribution from the
northeastern region. A previous study showed that high-density drainage regions have
greater groundwater recharge potential [122]. This is in line with the current study where
major water sources contribute to the water recharge. The same has been highlighted by
the rainfall thematic map, where the northeastern region receives most of the rainfall and
has a high drainage density, thus contributing to the groundwater flow and recharge.
Figure 3p shows the thematic layer of aspect data for Islamabad that categorizes
regions based on their compass directions. The aspect map lists out the front-facing
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direction of regions along with the compass. For example, the major constituting region
in the northeast contains southeastern front-facing regions that align with thematic maps
of land use and wells in the study region. The dense regions with most residential and
commercial zones are in the southeast. The flow from the north region is ensured towards
the southeast region. The southeastern compass front directions of the geological regions
act as a gentle slope that promotes groundwater recharge in Islamabad [116].
These influencing factors were considered based on a literature review and classified
based on their impact on groundwater recharge contribution, i.e., the class at which lesser
the groundwater recharge potential would rank lower and vice versa. For example, a
higher slope would have lesser groundwater potential, or a lower TWI would mean low
water moisture and low groundwater recharge potential; hence, these classes would have
lesser weightage.
5.2. Weightage Calculation for Influence Factor (IF) Techniques
After obtaining the individual thematic maps for each of the contributing factors, these
factors were integrated to obtain a potential holistic map that highlights the recharge potential of Islamabad. Accordingly, weights and rates were assigned to the 15 key factors. For
incorporating the mutual influence of the factors, rate values were assigned to them. Two
points were given for every major effect, while one point was given to the corresponding
factor for each minor effect. The cumulative weightage of both major and minor effects was
considered for calculating the relative rate, as shown in Table 4. Table 4 shows that factors
such as lithology influence six of its fellow factors majorly. It has a noticeable impact on the
lineament, drainage, land/use, slope, and soil types. Thus, it has been assigned a value of
2 six times (2 × 6 factors).
Table 4. Relative rates and scores for each potential factor.
Factors
Major Effect (A)
Minor Effect (B)
Distance to Faults
Land use/Land cover
Lithology
Drainage Density
Slope
Soil
Rainfall
Plan Curvature
Fault Density
Profile Curvature
TWI
Elevation
Aspect
Drainage Distance
Slope Length
2+2+2+2
2+2+2+2+2+2
2+2+2+2+2+2
2+2+2+2+2+2
2+2+2+2+2
2+2+2+2+2
2+2+2+2+2
2+2
2+2+2+2
2+2
2+2+2
2+2+2+2
2+2+2
2+2+2+2
2+2
1+1+1
1+1+1+1
1+1+1+1
1+1+1
1+1+1
1+1+1
1+1+1
1
1+1
1
1+1
1+1+1
1+1
1+1
1+1
Proposed Relative
Rates (A + B)
Normalized Relative
Rates (Y) in %
11
16
16
15
13
13
13
5
10
5
8
11
8
10
6
Σ = 160
6.875
10.000
10.000
9.375
8.125
8.125
8.125
3.125
6.250
3.125
5.000
6.875
5.000
6.250
3.750
Σ = 100
160
100
Similarly, other factors have also been assigned their respective rate values using the
same approach. Overall, the major effect (A) and minor effect (B) are summed for all factors,
and their cumulative sums are calculated for each factor to get the proposed relative rates.
The cumulative proposed relative rates sum up to 160. Using this value, the normalized
relative rates are calculated, where the proposed relative rate of each factor is divided by
the cumulative proposed related rates and multiplied by 100 using Equation (1). The values
are rounded off to the nearest integer.
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Normalized relative rates (Y ) =
Proposed relative rates ( A + B)
× 100
Commulative Proposed relative rates (Σ( A + B))
(1)
After the assignment of rate values, the next step is to assign weights. In this process,
five major descriptive levels are plotted for each factor ranging from very high to very low,
including some interrelated levels as shown in Table 5. Factors contributing majorly, such
as rainfall, can be seen as very dominant in relevant studies [108,109] and in abundance
in the southeastern regions of the study area and thus were assigned higher weights. In
contrast, factors such as profile curvature were assigned a lower weightage, as the area
followed a rhythmic curvature, and the influence of curvature was not dominant in terms
of groundwater flow, as evident from Figure 3 (previously shown).
With a weightage of 8.1%, rainfall is a dominant factor in the southeastern parts of
the study area. Plan curvature data indicate a slight shift in curvature as seen from the
thematic map and thus were assigned a weightage of 3.1%. The higher curvature would
result in a greater flow of water beneath the surface [66]. Soil is the primary factor that
controls seepage and the associated groundwater recharge [117]. Thereby, it was assigned
the highest weightage (8.1%). Likewise, faults being the primary indicator of geographical
movement (earthquakes or tectonic) over the years indicate a weaker and vulnerable
zone suspectable to the greater flow of groundwater channels beneath the surface. It
adds greatly to the groundwater recharge and was hence assigned a weightage of 6.8%.
Drainage distance, profile curvature, and TWI were assigned weights of 6.2%, 3.1%, and
5%, respectively.
The data obtained from thematic maps do not indicate an abrupt or dominant effect of
these considered geographical features (key factors) over the study area, thus acquiring a
lower weightage in our study area. The slope indicating the natural flow of water towards
the lower altitude area was assigned a weightage of 8.1%. Elevation and slope length
were assigned the weightage of 6.8% and 3.7%, indicating the flow towards lower-elevated
areas and the flow speed. Accordingly, the lower the speed, the greater the infiltration
and vice versa [122]. Lithology has been assigned a weightage of 10%. It indicates the
rock characteristics that dictate the water flow beneath the surface in channels and streams.
Land use is another primary factor that was assigned 10% weightage. It has been utilized
by several related studies [60,66]. Finally, fault and drainage densities and aspects indicated
the magnitude of faults, drainage networks, and front-facing direction of slopes signifying
the flow of groundwater beneath the surface and were assigned weights of 6.2%, 9.3%, and
5%, respectively, in this study.
After the assignment of rates and weights, the % influencing score was calculated
using Equation (2). The % influencing score is defined as the percentage of factor effect on
recharge potential (%) and is shown in Table 5 for each factor, where X is the normalized
weight from 1 to 10, and Y is the rate from 1 to 10.
% in f luencing score =
Total Weightage Σ( X × Y )
× 100
Grand Total Weight ( GTW )
(2)
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Table 5. Weight evaluations of factors influencing potential recharge capacity.
Factors
Rainfall
Plan curvature
Soil
Distance to fault
Categories
<882
882–999
999–1116
1116–1233
1233–1350
<−2.34
−1.74
−1.2
0.6–2.6
>2.6
Calcareous Loamy
Soil Piedmont
Calcareous Silty Soil
Gullied Land
Complex
Rough Broken Land
Mountainous land
with nearly
continuous soil
Mountainous land
with patchy soil
Urban
Calcareous Loamy
Soil
<100
100–200
200–500
500–1000
1000–2000
2000–5000
>5000
Effect
Normalized Weight (X)
Normalized
Relative Rates (Y)
Based on Table 4
Weighted Rating
(1–10)
(1–10)
(X × Y)
Very Low
Low
Medium
High
Very High
Very Low
Low
Medium
High
Very High
2
4
6
8
10
2
4
6
8
10
Very High
10
High
8
High
8
65.00
Medium
6
48.75
Medium
6
48.75
Very Low
4
32.50
Low
2
16.25
Very High
High
High
Medium
Medium
Very Low
Low
10
8
8
6
6
4
2
68.75
55.00
55.00
41.25
41.25
27.50
13.75
8.125
3.125
16.25
32.50
48.75
65.00
81.25
6.25
12.50
18.75
25.00
31.25
Total Weightage
max(X) × Y
MAX Effect on
Recharge Potential (%)
81.25
8.125
31.25
3.125
81.25
8.125
68.75
6.875
81.25
8.125
6.875
65.00
Water 2022, 14, 1824
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Table 5. Cont.
Factors
Drainage distance
Profile Curvature
TWI
Categories
<100
100–200
200–500
>500
<−3.14
−2.24
−1.8
0.7–2.9
>2.9
<2
2–4
4–6
>6
Slope
Elevation
Slope length
Lithology
<12
12–24
24–36
36–48
>48
<531
531–617
617–756
756–994
>994
<10
10–20
20–30
30–40
>40
Limestone
Sandstone
Unconsolidated
deposit
Effect
Normalized Weight (X)
Normalized
Relative Rates (Y)
Based on Table 4
Weighted Rating
(1–10)
(1–10)
(X × Y)
Very High
High
Medium
Low
Very Low
Low
Medium
High
Very High
Very Low
Low
Medium
High or very
high
Very High
High
Medium
Low
Very Low
Very High
High
Medium
Low
Very Low
Very High
High
Medium
Low
Very Low
High
Medium
10
8
6
4
2
4
6
8
10
2
4
6
10
50.00
10
8
6
4
2
10
8
6
4
2
10
8
6
4
2
10
6
81.25
65.00
48.75
32.50
16.25
68.75
55.00
41.25
27.50
13.75
37.50
30.00
22.50
15.00
7.50
100.00
60.00
Low
4
6.250
3.125
5.000
8.125
6.875
3.750
10.000
62.50
50.00
37.50
25.00
6.25
12.50
18.75
25.00
31.25
10.00
20.00
30.00
40.00
Total Weightage
max(X) × Y
MAX Effect on
Recharge Potential (%)
62.50
6.250
31.25
3.125
50.00
5.000
81.25
8.125
68.75
6.875
37.50
3.750
100.00
10.000
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Table 5. Cont.
Factors
Land use
Fault density
Drainage density
Aspect
Categories
Bare area
Vegetation
Water
Built-up
<15
15–41
41–65
65–91
>91
<1
01/01/1984
1.84–2.68
2.68–3.53
>3.53
Flat
North
Northeast
East
Southwest
Southeast
South
West
Northwest
Effect
Low
High
Very High
Medium
Very Low
Low
Medium
High
Very High
Very Low
Low
Medium
High
Very High
Very High
Very High
High
High
Medium
Medium
Low
Low
Very Low
Normalized Weight (X)
Normalized
Relative Rates (Y)
Based on Table 4
Weighted Rating
(1–10)
(1–10)
(X × Y)
4
8
10
6
2
4
6
8
10
2
4
6
8
10
10
10
8
8
6
6
4
4
2
10.000
6.250
9.375
5.000
40.00
80.00
100.00
60.00
12.50
25.00
37.50
50.00
62.50
18.75
37.50
56.25
75.00
93.75
50.00
50.00
40.00
40.00
30.00
30.00
20.00
20.00
10.00
Total Weightage
max(X) × Y
MAX Effect on
Recharge Potential (%)
100.00
10.000
62.50
6.250
93.75
9.375
50.00
5.000
GTW:
Σ = 3118
Σ = 100
Water 2022, 14, 1824
𝑖𝑛𝑓𝑙𝑢𝑒𝑛𝑐𝑖𝑛𝑔 𝑠𝑐𝑜𝑟𝑒
𝑇𝑜𝑡𝑎𝑙 𝑊𝑒𝑖𝑔ℎ𝑡𝑎𝑔𝑒 𝛴 𝑋
𝑌
𝑥
𝐺𝑟𝑎𝑛𝑑 𝑇𝑜𝑡𝑎𝑙 𝑊𝑒𝑖𝑔ℎ𝑡 𝐺𝑇𝑊
23 of 30
5.3. Final Combined Recharge Potential Map
After considering rate assessment, different layers of recharge potential were ‐superimposed in the ArcGIS tool. As a result of the integration of the 15 contributing factors,
the final combined potential map was generated, which highlights the overall recharge
potential of Islamabad, as shown in Figure 4. The resulting map generated with the help of
influencing factors’ relative rates categorizes the region into five descriptive levels based
on the rechargeability. These descriptive levels include “best”, “high”, “medium”, “low”,
and “poor”, each with a distinctive color.
Figure 4. Potential groundwater recharge zones in the study area.
From the output thematic map (Figure 4), it is evident that the eastern region of the
study area is the most suitable for groundwater recharge. Accordingly, it is highlighted
‐
to be the “best” region. This region received the highest rainfall as per the previously
presented maps. This is in line with previous studies that argued that the higher the
rainfall, the greater the groundwater recharge and vice versa [116,123]. Moreover,‐ it can
be observed from Figure 4 that the groundwater recharge potential decreases as we‐ head
towards the western side of Islamabad. A decreasing pattern for groundwater recharge
is seen as we move from east to west in the study area. Most of the mountainous region
is located towards the northeast of Islamabad, receiving the highest rainfall and having
higher slopes, inducing rapid runoff. Towards the center and to the west, the slope length
decreases, thus indicating a higher recharge potential, as gentle slopes were attributed to
higher recharge potential [122].
Table 6 presents the data of each category shown in graphical form in Figure 4 and
gives the exact portions of the study area having best to worst recharge capability. It shows
that the area labeled under the “best” comprises 136.8 km2 , covering 15% of the study
area. Similarly, an area of 191.52 km2 falls under our map’s “high” classification, covering
21% of the study area. Another 35% of the region collectively serves as a competent
region (preferred) for groundwater recharge. The moderate zone covers 218.88 km2 of area,
covering 24% of the study area. In contrast, the potentially poor and low zones make up
13% and 27% of the area, i.e., 118.56 km2 and 246.24 km2 , respectively.
Water 2022, 14, 1824
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Table 6. Classification of potential recharge areas.
Recharge Potential Category
Average %
Area Extant (km2 )
Very High
High
Medium
Low
Poor
15%
21%
24%
27%
13%
136.8
191.52
218.88
246.24
118.56
The results show that around more than half (51%) of the total area of Islamabad does
not have sufficient recharge capability, and the city is dependent on only 35% of the total
area to fulfill the city’s demand for groundwater for daily life usage. This can be taken into
consideration by local authorities when planning to meet the local water requirements and
groundwater recharge. The city planners and policymakers should take mitigation steps
and devise strategies to preserve most of this 35% of the land to avoid any further damage
to the already fragile water condition of the city. The information devised from this final
groundwater potential zones map can help resolve the long due water shortage issues in
various sectors of Islamabad and nearby areas through efficient management and preservation of groundwater resources in the area. Compared to the previous studies [36–42],
this study addresses the research gap of applying this methodology in a non-coastal region and modifies it by using thematic maps of larger spatial scale and the DEM data
of smaller resolution to refine the accuracy of the process. All the previous published
research used the one-time dataset and map the output. However, these do not depict the
true representation of the groundwater recharge. This is because the considered datasets
may change temporally, needing more datasets to overcome this limitation. Hence, this
study used the annual mean for all datasets, which change with respect to season or time.
Secondly, previously published research used limitedly influencing datasets that might not
present the actual situation of the study. In the current research, all the contributing factors
were analyzed and used to consider the entire situation. Accordingly, the model gives
reliable actual output. Moreover, the study also considers more contributing factors than
the previous studies to further enhance the accuracy of the output. The research presents a
holistic approach that gives comparatively improved results and can be applied to other
regions as and when required.
6. Conclusions
Considering the constant increase in groundwater demand in Islamabad with increasing population growth, the decreasing groundwater level has become a matter of concern
for the local authorities. This study attempts to develop a groundwater potential recharge
zone map of the study area of Islamabad, Pakistan, to help the policymakers devise efficient
policies for mitigating this problem.
The methodology involves the integration of RS and GIS to develop a map that
highlights the groundwater recharge potential in the study area. In our scenario, 15 key
factors were selected based on their contribution to the recharge. These include soil, land
use/land cover, drainage distance, slope, rainfall, plan curvature, distance to faults, profile
curvature, TWI, elevation, slope length, lithology, fault density, drainage density, and aspect.
Thematic maps were generated and overlayed using GIS. A holistic map was devised at
the end, comprising input from 15 of the influencing factors and their weights to produce
a weighted map. The resulting map categorizes the region into five different descriptive
levels, namely poor, low, medium, high, and best, based on the groundwater recharge
potential. The results showed that 13% of the area falls in the poor-recharge-potential
category, 27% area has a low potential, 24% has medium potential, 21% has high potential,
and 15% has the best chance of recharging the groundwater table. Overall, around 35% of
the study area is suitable for groundwater recharge, and more than half is unsuitable for
such purposes.
Water 2022, 14, 1824
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This study provides a holistic model with more accurate results than the previous
studies by introducing a comparatively greater number of factors and employing the
thematic maps of larger spatial scale and DEM data of a smaller resolution. The current
study paves the way for future infrastructure development by the concerned authorities to
meet the water demand of Islamabad and preserve the precious natural terrain with high
recharge potential.
The study is limited in terms of the factors considered. Further, it is restricted to a
single region in a developing country for testing purposes. Moreover, considering that
this study was limited in terms of the unavailability of geophysical data for the case study
area, future researchers can conduct further research by including the geophysical and
field data from multiple regions. This can help in carrying out the subsurface groundwater
modeling as well as 3D modeling of the targeted study area. Further, similar studies can be
conducted for larger nearby regions and developed countries to help move toward global
sustainability goals and tackle climate change effects. The effects of vegetation on recharge
can also be investigated in the future.
Author Contributions: Conceptualization, A.M., B.A. and F.U.; methodology, A.M., B.A., N.K. and
F.U.; software, A.M., B.A., N.K. and F.U; validation, A.M., B.A., N.K., F.U., H.A., E.E.H. and A.H.A.;
formal analysis, A.M., B.A. and N.K.; investigation, A.M., B.A., N.K. and F.U.; resources, A.M., B.A.,
N.K., H.A., E.E.H. and A.H.A.; data curation, A.M., B.A., N.K. and F.U.; writing—original draft
preparation, A.M., N.K., B.A. and F.U; writing—review and editing, F.U., H.A., E.E.H., A.A.A. and
A.H.A.; visualization, A.M., B.A., N.K., F.U. and A.A.A.; supervision, A.M., B.A., F.U. and A.H.A.;
project administration, A.M., B.A., F.U. and A.H.A.; funding acquisition, A.H.A. and H.A. All authors
have read and agreed to the published version of the manuscript.
Funding: This research was funded by Taif University Researchers Supporting Project number
TURSP 2020/252, Taif University, Taif, Saudi Arabia.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Data can be shared upon reasonable request.
Acknowledgments: The authors appreciate Taif University Researchers Supporting Project number
TURSP 2020/252, Taif University, Taif, Saudi Arabia for supporting this work.
Conflicts of Interest: The authors declare no conflict of interest.
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