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Application of remote sensing and GIS for delineating groundwater recharge potential zones of Islamabad, Pakistan using IF technique

Introduction

Water scarcity is a major issue of these times. The rapidly growing population, expansion of irrigation areas, and growing urban & Industrialization are putting more stresses on water resources ( Salim et al. 2015 ). The study area is located in the Pothohar Plateau and is a humid subtropical climatic zone with abundant greenery and mountain rich terrain. The groundwater resources in Pakistan are facing a continuous threat of depletion due to many reasons such as reduction in rainfall, increased crop yield, uneven population density distribution ( Asad et al. 2010 ). Groundwater is an important source of water for domestic, agricultural and industrial use. Uneven distribution of water resources and its demand spatially and temporally, economic development, area development and continuous expansion and changing climate, etc. have led to an increase of consumption and thus eventually led to shortages of surface water. Precipitation water also runs of in rivers and streams, a huge percentage of it is lost in the midway, a mediocre percentage of it reaches inwards the groundwater ( Isaac J. et al. 1998 ). Therefore, the reliance on groundwater has increased, leading to its overdraft which resulted in decline of groundwater levels, thus making it difficult for all sort of consumers who rely on fresh water for domestic uses ( MA Sabir et al. 2017 ). Therefore, it is important to thoroughly understand the groundwater resources of this region. Various researchers have used various criteria for delineating groundwater potential zones. For instance, use of lineament and hydrogeomorphology (Nag 2005), geophysical data alongside the geospatial information (Antony Ravindran and Selvam 2014; Kumar et al. 2007; Rodell et al. 2009; Srivastava and Bhattacharya 2006; Selvam 2012; Selvam and Sivasubramanian 2012), delineation of artificial recharge sites using Remote sensing and GIS (Saraf and Choudhary 1998; Jasrotia et al. 2007; Chenini et al. 2010;), use of Remote Sensing and GIS for geomorphic characteristics and lineaments (Kamal and Midorikawa 2004; Gustavsson et al. 2006; Singh et al. 2007; Selvam et al. 2013a, b, c; Singaraja et al. 2015a).Remote sensing (RS) and geographic information system (GIS) is increasingly being used as a tool for a number of applications (Selvam et al. 2014a, b, c, d). The use of Geographic Information System ( GIS ) is becoming increasingly helpful for many sorts of groundwater related problems ( Deepesh et al. 2018 ). Remote Sensing and Geographic Information Software technology is a very effective tool in producing valuable data on geology, geomorphology, lineaments, slope, etc., which are very important factors for groundwater management and exploration ( Rudy et al. 2018 ). This paper utilizes remote sensing and GIS to decipher the groundwater recharge potential zones in the region of Islamabad, Pakistan

Study area

Islamabad is located at 33.43°N 73.04°E at the northern edge of the Pothohar Plateau and at the foot of the Margalla Hills in Islamabad Capital Territory. Its elevation is 540 metres (1,770 ft). To the northeast of the city lies the colonial era hill station of Murree, and to the north lies the Haripur District of Khyber Pakhtunkhwa. Kahuta lies on the southeast, Taxila, Wah Cantt, and Attock District to the northwest, Gujar Khan, Rawat, and Mandrah on the southeast, and the metropolis of Rawalpindi to the south and southwest. Islamabad is located 120 kilometres (75 mi) SSW of Muzaffarabad, 185 kilometres (115 mi) east of Peshawar, 295 kilometres (183 mi) NNW of Lahore, and 300 kilometres (190 mi) WSW of Srinagar, the capital of the Indian territory of Jammu and Kashmir.. The city of Islamabad expanses an area of 906 square kilometres (350 sq mi).

Islamabad has a humid subtropical climate (Köppen: Cwa), with five seasons: Winter (November–February), Spring (March and April), Summer (May and June), Rainy Monsoon (July and August) and Autumn (September and October). The hottest month is June, where average highs routinely exceed 38 °C (100.4 °F). Islamabad’s micro-climate is regulated by three artificial reservoirs: Rawal, Simli, and Khanpur Dam. The latter is located on the Haro River near the town of Khanpur, about 40 kilometres (25 mi) from Islamabad. Simli Dam is 30 kilometres (19 mi) north of Islamabad.

Materials and methods
The linear image self-scanning, abbreviated as “LISS” III is used to uncover the data of Pakistan Remote Sensing Satellite (PRS) 1C, of scale 1:50,000 were used to conduct this particular study. The Survey of Pakistan toposheets 58 H/13, 58 H/14, 58 L/1&5, 58 L/2 with respect to a scale of 1:50,000 were used to prepare thematic maps. The images were interpreted to delineate lithology and land use/ land cover with the help of slandered characteristic image interpretation elements like tone, texture, shape, pattern and size. To easily integrate into GIS platform, the thematic maps were converted into raster form. Shuttle Radar Topography Mission (SRTM) DEM data on a global scale at 90 m horizontal resolution (http://srtm.csi.cgiar.org/) was used for topographic analysis (Fig. 2). A suitable weightage factor has been assigned to each thematic map. The ranking and weightage was assigned to each of the parameter and influencing factor with respect to the features regarding the hydr environment of the area during weightage overlay analysis. The thematic maps were then integrated using “Spatial Analysis tool” in Arc GIS 9.3 (Fig. 3). Preparation of various thematic layers, such as lithology, drainage density, lineament density, rainfall, slope, soil, and land-use with assigned weightage in a spatial domain has been done with remotely sensed data and topographical information from available maps.

Factors affecting groundwater recharges potential
Consisting on four main steps, this methodology is developed to determine ground water potential. The first step involves the identification of the thematic layers which are relevant to groundwater potential. The second incorporates the processing of these thematic layers to ensure uniform projection (projection: UTM, datum: WGS84) and resolution, assigning wightage and scores. The third step integrates all thematic layers alongside scores using the spatial analysis tool from the GIS 9.3 software. The final step categorizes the outputs into four defined classes as 1) poor  2) low  3) moderate and 4 ) high. This data is further compared with processing techniques, including standard color composites, intensity–hue–saturation (IHS) transformation and decorrelation stretch (DS) to map the rock types. Although some studies have ignored this factor by regarding the lineaments and drainage characters as a function of primary and secondary porosity, this study includes geology to reduce uncertainty in determining lineaments and drainage.

Lineament
Lineament is a linear feature in a landscape which is basically an expression of an underlying geological structure such as a fault. Typically a lineament will lookalike as a fault-aligned valley, a series of fault or fold-aligned hills, a straight coastline or indeed a combination of these characteristics. They lookalike as the weaker zone of bed rocks which are usually considered as secondary porosity in hard rock aquifers (Koch and Mather 1997; Selvam et al. 2015a, b). Lineaments, when mapped with the satellite data can correlate with faults, fractures, joints, bedding planes and lithological contacts from ground-check information and available geological data. Major lineaments can be detected in the raw image data, most of the finer details are recognizable in the clear filtered images. In this study, major focused area was to delineate geological lineaments rather than just identification of all linear features. Parameters that were being considered for lineaments include: Lineament-length density (Ld); total length of all the recorded lineaments divided by area under study (Greenbaum 1985):
Ld ¼ Xn
i¼1
Li=A m−1

Lineament frequency (Lf) or lineament count density; the number of visible lineaments per unit area (Greenbaum 1985):
Lf ¼ Xn
i¼1
Ln=A m−2
Where ∑
i¼n
i¼1
Li is length of lineaments in meters and
where A is the area of study in m2

Drainage
The density of drainage network as well as the happening of lineaments, such as faults, fracture, joints, are hydrogeologically very important and have a major influence on the groundwater recharge and movement (Murthy 2000; Kumar et al. 2007). Watershed alongside its parameters were delineated using SRTM data. Drainage densities (DD) were calculated in each of the grid square with the help of the following equation (Murthy 2000): DD ¼ X LWS
AWS
Where,
LWS is total length of streams in watershed
AWS is area of the watershed

Land use/land cover
Land use/Land cover is a major factor affecting the recharge processes. Remote sensing and GIS technique provide a very reliable information for land use/land cover mapping ( A.A. El Baroudy et al. 2016 ). The Factors involve a number of elements including soils, human settlements, vegetation cover, waste lands out of which land-use is the important factor to recharge the ground water in this study area. People settlement such as, concrete embankments, buildings, roads etc., act as impermeable barriers and are the inhibiting factors for water infiltration to the underground. Vegetation has also a major role in groundwater recharge as it affects many processes (Paulo et al. 2016).

Slope
The gradient of slope plays a very important role in infiltration of rainfall as the steeper slopes generate less recharge because water will run down rapidly off the surface during rainfall, allowing insufficient time to infiltrate the surface and recharge the saturated zone under consideration (Magesh et al. 2012). Rainfall is the main source of groundwater recharge in this area as we have previously concluded. The SRTM DEM data was being utilized to derive a slope map in percentage using the SLOPE function in ArcGIS.

Soil
Soil is a product of several factors: the influence of climate, relief (elevation, orientation, and slope of terrain), organisms, and the soil’s parent materials (original minerals) interacting over time that act as a medium for plant growth and as a means of water storage, supply and purification. Soil types of the area are of utmost importance, since it is the main criteria in the recharge of groundwater and agricultural production. Soil characteristics invariably control infiltration of surface water.

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