LULC
Precipitation leaching into the earth is broadly associated with land usage. As a result, it is a highly important requirement for aquifer development. Infiltration is limited in construction zones due to urbanization and industrialization, hence the flow rate on the surface is maximum. Ponds, Marshes, and other waterways are assigned the maximum assessment rating (Table 3). Likewise, alluvium in waterways has a significant infiltration rate. Agricultural lands often encourage higher percolation because of soil pore spaces that absorb and store water in the roots, giving a conduit for water to infiltrate into the ground by weakening up the soils and sediments. Constructed and barren areas, on the other hand, decrease seepage due to lack of porous medium and raised streamflow capability. Consequently, lands with crops and water bodies are referred to as suitable localities for aquifer recharge, whereas residential areas and barren terrain possess aquifer limited recharge ability. The Esri website provides land use and landcover map 2020 with a spatial resolution of 10m (Fig. 5). Trees, waterbodies, flooded vegetation, grass, agricultural land, scrub/shrub, built area, and bare ground are all classified as land-use types (Table 4).
Table 3
Categorization of factors influencing of Groundwater Potential Zone
Influencing factor
|
Classes
|
Weight
|
Influence (%)
|
Rank
|
Land use land cover
|
Waterbodies
|
0.36
|
36
|
5
|
Trees
|
3
|
Grass
|
4
|
Flooded vegetation
|
4
|
Agricultural land
|
5
|
scrub/shrub
|
3
|
Built area
|
1
|
Bare ground
|
2
|
Geology
|
Stream Deposits
|
0.24
|
24
|
5
|
Surficial Deposits
|
5
|
Soan Formation
|
2
|
Dhok Pathan Formation
|
3
|
Nagri Formation
|
1
|
Chinji Formation
|
3
|
Kamlial Formation
|
1
|
Paleocene to Eocene
|
4
|
Mesozoic
|
2
|
Slope
|
0-4.48
|
0.14
|
14
|
5
|
4.48–10.46
|
4
|
10.46–18.83
|
3
|
18.83–28.99
|
2
|
28.99–76.23
|
1
|
Geomorphology
|
High altitude mountains
|
0.11
|
11
|
1
|
High altitude plains
|
4
|
High altitude plateaus
|
2
|
Hills
|
1
|
Low altitude mountains
|
2
|
Low altitude plains
|
5
|
Low altitude plateaus
|
4
|
Mid altitude mountains
|
1
|
Mid altitude plateaus
|
3
|
Rainfall
|
866.04–962.2
|
0.06
|
6
|
1
|
962.2-1005.67
|
2
|
1005.67-1050.46
|
3
|
1050.46–1115
|
4
|
1115-1201.95
|
5
|
Drainage density
|
0.12–0.29
|
0.04
|
4
|
5
|
0.29–0.36
|
4
|
0.36–0.43
|
3
|
0.43–0.5
|
2
|
0.5–0.68
|
1
|
Lineament density
|
0.009–0.13
|
0.03
|
3
|
1
|
0.13–0.23
|
2
|
0.23–0.35
|
3
|
0.35–0.45
|
4
|
0.45–0.58
|
5
|
Soil type
|
Rough broken land
|
0.02
|
2
|
5
|
Non-calcareous silty soils
|
3
|
Non-calcareous loamy soils
|
1
|
Gullied land and bad land
|
5
|
Calcareous silty soils
|
4
|
Calcareous sandy soils
|
4
|
Calcareous loamy soils
|
1
|
Calcareous loamy and clayey soils
|
2
|
Table 4
Land use/land cover of the study are
Land use type
|
Area (km2)
|
Area (%)
|
waterbodies
|
45.96
|
0.76
|
trees
|
1135.56
|
18.72
|
grass
|
8.81
|
0.15
|
flooded vegetation
|
0.49
|
0.008
|
agricultural land
|
2847.70
|
46.95
|
scrub/shrub
|
502.88
|
8.29
|
built area
|
1516.64
|
25
|
bare ground
|
7.93
|
0.13
|
Geology
Aquifer development is influenced by the porosity, permeability, and morphology of subsurface stratigraphic units (Selvarani et al. 2017). As a result, the accessibility and distribution of aquifers in a specific territory are determined by the underlying rock type (Winter 1999). There are nine different types of lithological units in the research region, according to the Geological Survey of Pakistan's 1:1,000,000 scale geological map, ranging in age from Recent to Miocene (Table 5 and Fig. 6).
Table 5
Stratigraphic Units
|
Area (km2)
|
Area (%)
|
Age
|
Lithological Description
|
Stream Deposits
|
74.323
|
1.23
|
Recent
|
Poorly sorted and uncemented silt, sand, and gravel.
|
Surficial Deposits
|
2935.684
|
48.40
|
Holocene
|
Loose and unstratified erosional clay, silt, sand, gravels, pebbles sediments. Early Sub-recent to Recent age ancient stream alluvium including boulders, cobbles, pebbles of limestone and sandstone.
|
Soan Formation
|
355.026
|
5.85
|
Late Pliocene-Early Pleistocene
|
Claystone, soft siltstone, and subordinate conglomerate interbed of coarse-grained sandstone.
|
Dhok Pathan Formation
|
540.135
|
8.90
|
Early to Middle Pliocene
|
Compact, hard, and orange-red claystone comprise the horizons of the conglomerate in the top section. cross-bedded, medium bedded, and fine to medium-grained sandstone in the lower section.
|
Nagri Formation
|
498.617
|
8.23
|
Pliocene
|
Conglomerate, silty or sandy claystone, Cross-bedded and calcareous sandstone having medium to coarse-grained texture.
|
Chinji Formation
|
222.232
|
3.66
|
Late Miocene
|
Friable and hard claystone with intercalations of cross-bedded, medium to thick-bedded, soft sandstone.
|
Kamlial Formation
|
1331.026
|
21.94
|
Middle to late Miocene
|
Thick bedded, jointed, calcareous, and medium to coarse-grained sandstone with interbeds of weathered and speckled claystone.
|
Paleocene to Eocene
|
91.758
|
1.51
|
|
Hangu, Lockhart, and Patala Formations of Makarwal Group are mainly composed of clay, siltstone, sandstone, limestone with interbeds of shale and marl.
Margala Hill Limestone, Chorgali, Kuldana, and Kohat Formations of Cherat Group are predominantly comprised of limestone and calcareous shale.
|
Mesozoic
|
17.199
|
0.28
|
|
Sumana Suk Formation of Baroch Group and Chichali, Lumshiwal Formations of Surgar Group are found in Islamabad and Rawalpindi area. Compositionally Limestone with subordinate marl, glauconitic sandy shale, glauconitic and calcareous sandstone.
|
Slope
The slope has an important role in influencing aquifer availability and recharge settings in a given geographic region. The slope is calculated in degrees using spatial analyst tool in arc toolbox (Keane et al. 2001; Dawoud et al. 2005; Solomon and Quiel 2006; Lee et al. 2012; Misi et al. 2018). Slope affects both groundwater percolation and potential. A sharper inclination is represented by a higher slope value. The gradient or inclination is computed by dividing the variation in height by the lateral separation between any two places on the line. In general, plain and slightly inclined topography support penetration and subsurface water recharging, whereas steeply undulating terrain stimulate outflow with little or no permeation (Magesh et al. 2012). The potentiality of groundwater is estimated to be higher in the smooth and moderately tilting landscapes (Rao 2006). Higher freshwater storage will be possible with flatter terrain. The use of topographical maps in estimating groundwater level heights is critical (Sener et al. 2005). The best groundwater horizon is a mixture of discontinuities (lineament) and morphologically depressed landforms (Rao 1992). The slope of the specified research region is developed in ArcGIS 10.5 spatial analyst using the DEM of the SRTM with 12.5m spatial resolution acquired from the Alaska Satellite Facility (ASF) website. The region's slope ranges from 0 to 76.2 degrees and is reclassified into five categories, with each class retrieving a grade based on its usefulness in underground water recharging (Fig. 7).
Geomorphology
Hydrological research and the determination of aquifer supplies rely critically on geomorphic features. Surface water infiltration into the earth's interior is favorably impacted by morphological aspects. Tectonic processes and depositional activities are primarily responsible for the landform development of a hard rock topography. Global landform classification data obtained from the European Soil Data Centre (ESDAC) is digitized because of the raster's large cell size. This data source provides worldwide hydro-morphological categorization computed by the JRC (Joint Research Centre), indicating relief categories depending on relief curvature and elevation segmentation depending on a DEM (Meybeck et al. 2001). The mentioned geomorphological parameters can be identified in Islamabad and Rawalpindi districts: High altitude, mid-altitude, and low altitude mountains, high altitude, mid-altitude, and low altitude plateaus, high altitude and low altitude plains, and hills (Table 6). The area's extreme north and northeast have high, medium, and low mountains, as well as high and medium altitude plateaus (Fig. 8). Vast high and low altitude plains, as well as low altitude plateaus consisting mainly of eroded alluvial deposits (silt, sand, and gravel) in the northwest, southeast, and southern parts of the catchment region, contribute as a potential aquifer recharge source in the research region.
Table 6
Geomorphology of the study are
Geomorphic landforms
|
Area (km2)
|
Area (%)
|
High Altitude Mountains
|
27.26
|
0.45
|
High Altitude Plains
|
1146.96
|
18.89
|
High Altitude Plateaus
|
1.63
|
0.02
|
Hills
|
34.60
|
0.57
|
Low Altitude Mountains
|
569.69
|
9.38
|
Low Altitude Plains
|
1974.10
|
32.51
|
Low Altitude Plateaus
|
920.38
|
15.16
|
Mid Altitude Mountains
|
553.55
|
9.12
|
Mid Altitude Plateaus
|
843.32
|
13.89
|
Rainfall
One of the most important primary sources of aquifer recharge is rainfall (Ghayoumian et al. 2007; Magesh et al. 2012; Omid et al. 2014; Shekhar and Pandey 2014). Rainwater permeates into the earth, refilling aquifers. As a result, the frequency and intensity of precipitation received by a locality are valuable aspects to consider while determining and interpreting hydrogeological basins and aquifer potential, which are influenced by the region's climatic variations (Minh et al. 2019; Shao et al. 2020). Potential for groundwater is generally high in regions with significant precipitation and vice versa. This study's rainfall map 2011–2020 is generated utilizing datasets from the Climatic Research Unit (University of East Anglia) and NCAS. The data is then imported into a GIS platform, used the Raster Processing tool to combine all the bands in ArcGIS 10.5 and the rainfall map was prepared using the spatial interpolation technique IDW. Cell statistics have been used to compute average annual rainfall from 2011 to 2020, which is then reclassified into five classes with values ranging from 866 to 1202 mm/year (Fig. 9). It has been observed that the northeastern part of the research area acquires the maximum rainfall, whereas the southwest section obtains the least. Heavy rainfall increases groundwater recharge, therefore it is given more weight.
Drainage Density
The total length of all stream orders per unit area is known as drainage density (Shekhar and Pandey 2015). This is shown by the following expression:
$$\text{D}\text{r}\text{a}\text{i}\text{n}\text{a}\text{g}\text{e} \text{D}\text{e}\text{n}\text{s}\text{i}\text{t}\text{y}= \sum _{i=1}^{i=m}\frac{{S}_{i}}{A}$$
4
Where ∑Si indicates the whole length of the stream's drainage pattern and A represents the unit area. In groundwater recharge, drainage density is an essential geomorphological variable. The fill function of the hydrology tool included in ArcGIS software is implemented for the watershed or drainage pattern to minimize the DEM distortion. This fill operation optimizes the grid cells by reducing unwanted high terrain pixels and filling in sinks. The upgraded DEM is used to identify the orientation of water accumulation and surface flow applying the hydrology tool in ArcGIS 10.5. Since aquifer recharge is proportional to surface runoff and permeability, drainage density is linked to aquifer recharge (Magesh et al. 2012; Selvam et al. 2013a; Huang et al. 2013). If the drainage density value is high, the surface runoff will be high and water infiltration to the subsurface is low. However, because of the minimal surface water runoff zone, surface water is extensively penetrated. Rivers and other water bodies are often regarded as prominent variables of the hydrological cycle and groundwater recharge. Conversely, if a region has too many streams, the drainage density increases, leading to an increase in surface runoff, decreased infiltration, and poorer aquifer recharge (Nag 2005; Kumar et al. 2007; Jha et al. 2010; Magesh et al. 2012). It ranges from 0.12 km/km2 to 0.68 km/km2 in this area under study and then reclassified into five divisions, namely, very high (0.5–0.68), high (0.43–0.5), medium (0.36–0.43), low (0.29–0.36), and very low ( 0.12–0.29) km/km2 (Fig. 10).
Lineament Density
Lineaments are continuous structures in the earth's crust that represent subsurface tectonic and geologic features in stratigraphic formations. Lineaments are hydrogeologic features (faults, cracks, curvature, blocks, joint sets, and other topographic discontinuities) that can be extracted using satellite imagery (Leary et al. 1976). They are secondary permeability parameters that indicate rainwater, groundwater circulation, and accumulation (Rao et al. 2001). As a result, these earth's features are crucial for hydrological modeling and watershed management (Sener et al. 2005). Groundwater exploratory research initiatives in many regions have reportedly achieved better productivity levels when drilling locations were led by lineament analysis (Teeuw 1995). The lineaments are extracted from the tectonic map of Pakistan compiled by Ali H. Kazmi and Riaz A. Rana in 1982 to transform the structural pattern into a numerical value. The grid cells algorithm is adopted to evaluate the lineament density for this objective (Nag and Ghosh 2012; Rahmati et al. 2014; Kumar and Chandra 2017).
The cumulative length of all observed lineaments has been divided by the area under investigation to quantify the lineament density (Edet et al. 1998). The following relationship demonstrates this:
$$\text{L}\text{i}\text{n}\text{e}\text{a}\text{m}\text{e}\text{n}\text{t} \text{D}\text{e}\text{n}\text{s}\text{i}\text{t}\text{y}= \sum _{i=1}^{i=n} \frac{{L}_{i}}{A}$$
5
where ∑Li is the entire length of all lineaments in kilometers and A is the grid's area in square kilometers.
Islamabad and Rawalpindi districts are occupied with secondary and influential lineaments ranging in length from 0.008 km/km2 to 0.58 km/km2, according to the analysis. After that, the calculated lineament density was categorized into five classes. Due to its suitability in aquifer recharge capability, the zone with the maximum lineament density (0.45–0.58) received a high ranking (very good), while the zone with the minimum lineament density (0.008–0.13) is regarded to have a very poor groundwater potential and received the lowest ranking. The density map of lineaments is shown in (Fig. 11).
Soil
While determining an area's groundwater potential zone, the soil is a primary geomorphic key element. Infiltration rate, the grain size of the soils, the moisture content in the soils, composition of the soils, and permeability of the soils are all parameters that influence groundwater recharge (Cosby et al. 1984; Harini et al. 2018). The effective porosity and hydraulic conductivity of the soil control its permeability, which is affected by geometry, porosity, and wetness index. The rate of flow and infiltration is considerably impacted by the soil (Bera et al. 2020). In the GIS platform, a soil map of Punjab (1978) generated from the Soil Survey of Pakistan was georeferenced, digitized, and reclassified in eight soil classes (Fig. 12). The non-calcareous loamy soil, which has low porosity, minimal absorption, and poor groundwater potential, is the prominent soil type with geographical distribution in the research region. Calcareous sandy soils, rough broken land, calcareous and non-calcareous silty soils are integrated as medium-coarse grained, well-drained soils with relatively high weights, reflecting a high groundwater potential. Whereas calcareous loamy-clayey soils, gullied land, calcareous, and non-calcareous loamy soils have a moderate-low permeability and limited groundwater recharge suitability (Table 7).
Table 7
Soil classification of the study are
Soil classification
|
Area (km2)
|
Area (%)
|
Rough broken land
|
870.88
|
14.36
|
Non-calcareous silty soils
|
453.78
|
7.48
|
Non-calcareous loamy soils
|
1627.73
|
26.83
|
Gullied land and bad land
|
130.94
|
2.16
|
Calcareous silty soils
|
1302.03
|
21.46
|
Calcareous sandy soils
|
50.77
|
0.84
|
Calcareous loamy soils
|
556.90
|
9.18
|
Calcareous loamy and clayey soils
|
1072.97
|
17.69
|
Ground Water Potential Zone (Gwpz)
Using RS/GIS techniques, the GWPZ for the research area are developed by overlaying multiple thematic layers such as LULC, geology, slope, geomorphology, rainfall, drainage density, lineament density, and soil type. Groundwater potential zones are delineated using AHP multi-decision making analysis and then giving various suitable sites. The weights of multiple parameters vary from 0.36 to 0.02, with LULC and soil receiving the maximum and minimum ranking. Geology 0.24, slope 0.14, geomorphology 0.11, rainfall 0.06, drainage density 0.04, and Lineament density 0.03 are the other six thematic layers derived weights. The rating of thematic maps is determined on the viewpoints of several professionals and referred to the different available literature. The on going research area's GWPZ is classified into five zones: very poor, poor, moderate, good, and very good (Table 8). Due to the distribution of surficial, stream deposits and agricultural area with high water penetration capacity, the very good GWPZ is dominated in the south and north-western regions of the research area, as shown by the GWPZ map (Fig. 13). This suggests that the geology, LULC, and slope are important factors in groundwater recharge. Furthermore, the capability for infiltration of the groundwater system is impacted by the distribution of geomorphic landforms, rainfall, lineament density, drainage density, and soil.
Table 8
Ground Water Potential Zone
|
Area (km2)
|
Area (%)
|
Very Good
|
1090.56
|
18.04
|
Good
|
1972.05
|
32.63
|
Moderate
|
1801.73
|
29.81
|
Poor
|
1153.78
|
19.09
|
Very poor
|
26.05
|
0.43
|