## 2 Materials and Methodology  
Location of the study area: Indus Basin of Pakistan is subdivided into Upper and Lower Indus Basin. Upper Indus Basin consists of four hydrological units, locally known as Thal, Chaj, Rachna, and Bari Doab (Figure 1). Doab is the tract of land between two rives. Upper Indus Basin is a well-transmissive and continuous unconfined aquifer where lithology varies from coarse sand to sandy loam with clay lenses [26]. The study area Lower Bari Doab (LBD) is bounded by Ravi and Chenab rivers in the northwest and west, respectively, and by the Sutlej River in the southeast. On the eastern side, it shares a border of nearly 80.5 km with India. The total area of the doab is nearly 19,600 km\({}^{2}\). It is about 402 km in length from the border to the confluence of Chenab and Sutlej Rivers and the average width is nearly 96.5 km [27]. LBD is located between latitude 29\({}^{\circ}\)30\({}^{\prime}\) to 31\({}^{\circ}\)45\({}^{\prime}\) N and longitude 71\({}^{\circ}\) to 74\({}^{\circ}\)45\({}^{\prime}\) E (Figure 1). The northeastern boundary of Bari Doab lies near  
Figure 1: Hydrogeological map along with location Of ERS sites of Bari Doab (after [10]). the foothills of the Himalayan range and almost coincides with the Lahore district. LBD is a part of the Indus Basin Irrigation System and comprises a network of canals [28]. Climate: Agriculture is the principal occupation in Lower Bari Doab. There are two seasons termed Kharif and Rabi. The Kharif season includes the monsoon months starting from 15 July to 15 September and the Rabi season is the relatively dry winter season from 15 October to 15 April. The climate is arid to semi-arid, and the mean annual precipitation ranges from 102 mm in the south to 508 mm in the north. Two-thirds of this precipitation occurs in the four summer months. Maximum temperature ranges from about 20 \({}^{\circ}\)C in December and January to about 41 \({}^{\circ}\)C in May and June. Hydrogeology: Lower Bari Doab is a part of the Indo-Gangetic Plain and is covered by Quaternary alluvium, which presumably overlies semi-consolidated tertiary rocks or metamorphic and igneous rocks of Precambrian age [29]. Several deep test holes ranging from 243.83 to 396.22 m depth were drilled to determine the thickness of the alluvium and the depth of the bedrock. In these test drills, the bedrock was encountered in only three holes at 381.59, 311.19, and 282.84 m in the northeastern part of the Bari Doab [29]. Therefore, in the Lower Bari Doab area, the total thickness of the Quaternary alluvium and the distribution of tertiary and older rocks were not found [30]. The subsurface lithology consists of mainly sand encountered in test holes and water wells showed the water-bearing characteristic of the alluvial deposits, that form the aquifer of the Bari Doab. A comparative study of the lithological logs provided a fairly good idea about the texture and structure of the heterogeneous alluvium to the depth of 183 m. The subsurface lithologies inferred in the Quaternary alluvial complex consisted of clay, sandy silt, fine sand, fine-to-medium sand, medium-to-coarse sand, coarse sand, and gravel. The alluvial material covering the study area formed part of the extensive heterogeneous and isotropic unconfined aquifer underlying the Indus Basin and was believed to be more than 304.79 m thick. Geological evidence also indicated that the aquifer is unconfined [31]. The aquifer yield varies from 100 to 300 m/h in Bari Doab [10] (Figure 1). Electrical Resistivity Survey: The geoelectrical method measures the distribution of the subsurface resistivity which is a physical property depending on the characteristics of the materials [32]. The principle of the electrical resistivity method is based upon injection/passage of electric currents into the ground for the discovery of electrical features of the materials buried in the ground [33].