Delineating potential sites for arti ﬁ cial groundwater recharge using a mathematical approach to remote sensing and GIS techniques

The management of the available groundwater resources is vital in arid and semi-arid regions. Arti ﬁ cial recharging should be integrated with the groundwater resources to maintain long-term water sustainability. This study applied the cost-effective and time-saving techniques of remote sensing and GIS to delineate the groundwater recharge potential in the Al-Sarhan Basin, located in arid and semiarid regions of Jordan, by following the weighted linear combination method. The results revealed three distinct groundwater potential recharge zones (low, moderate, and high potential zones). High to moderate groundwater recharge potential zones occupied 75% of the Al-Sarhan area with considerable arti ﬁ cial recharge capacity because of the suitable geology, soil texture, drainage density, and ﬂ at terrain conditions. The map also depicted that 25% of the Al-Sarhan area possesses low groundwater recharging potential. The model further revealed the presence of 93% wells in potential groundwater recharge zones. analysis and hydrogeological analysis of the study area. The integration of remote sensing and GIS techniques with environmental data produced satisfactory results.

GRAPHICAL ABSTRACT INTRODUCTION geomorphology, soil texture, slope, lineament density, and land use/cover of an area (Satpathy & Kanungo 2006;Das & Pardeshi 2018). Each of these factors exerts individual or combined effects during the artificial groundwater recharging process. Therefore, a comprehensive understanding of these factors is crucial for the accurate assessment of the groundwater recharge potential (PR) of an area.
Different methods can be adopted to investigate the potential and distribution of groundwater resources. Remote sensing and GIS techniques have been widely used to determine the spatial distribution of groundwater potential zones through logistic regression model (Ozdemir 2011), frequency ratio model (Moghaddam et al. 2015;Naghibi et al. 2015), multi-criteria decision-making model (Mukherjee et al. 2012;Kumar et al. 2014;Machiwal & Singh 2015;Das et al. 2017;Das & Pardeshi 2018;Arulbalaji et al. 2019;Haque et al. 2020;Khan et al. 2020), mathematical models, and other geostatistical and geospatial techniques (Mallick et al. 2015;Singh et al. 2017;Jasrotia et al. 2019;Sarkar et al. 2020). Several studies have also explored other groundwater exploration methods such as drilling, geophysical, and geological methods. However, these methods are costly, time-consuming, and require more human resources (Park et al. 2017;Arabameri et al. 2019). GIS and RS (remote sensing) methods can effectively prepare a groundwater potential map (GPM) and improve the accuracy and speed of groundwater studies (Naghibi & Dashtpagerdi 2017). Recently, these techniques have become important tools to efficiently analyse spatiotemporal data and predict outcomes of freshwater resources (Ghayoumian et al. 2007;Nagarajan & Singh 2009;Subagunasekar & Sashikkumarb 2012;Senanayake et al. 2016).
In this study, we used time-saving and cost-effective remote sensing and GIS techniques to delineate groundwater recharge potential zones. Suitable sites were evaluated for their groundwater recharge capacity through knowledge-based variable Uncorrected Proof analysis and hydrogeological analysis of the study area. The integration of remote sensing and GIS techniques with environmental data produced satisfactory results.

Study area
The Wadi Sarhan Basin lies between Jordan and Saudi Arabia. These areas are classified as arid or semiarid based on the traditional classification of Mediterranean climatic zones (Figure 1). The study area in the basin region within Jordan consists of 15,572 km² whereas the elevation ranges from 1,037 m in the southwest of Jordan to about 555 m along the Jordan-Saudi Arabia border (NR 1986). The major geological formations of the aquifers are sedimentary and crystalline rocks-basalt, limestone, sandstone, and alluvium with some marl (TWAP 2015). Two fault systems affect the study area (the West-East Siwaqa and Salawan faults and the North-East Sarhan fault).

MATERIAL AND METHODS
Water availability in semiarid areas depends on total annual precipitation, evaporation, rock composition, fluctuations in precipitation and distribution, and physical properties of the soil. Therefore, knowing the groundwater PR index is crucial, especially in semiarid areas, to monitor and identify potential groundwater recharge sites. The calculation of groundwater PR depends on the water table depth, permeability towards aquifer, soil type, and net recharge equation. All these factors are useful for identifying groundwater PR sites. The methodology used in this study for determining the groundwater recharge potential of the Al-Sarhan Basin is illustrated in Figure 2.
The geological map (1:25,000) of the study area was prepared by the Natural Resources Authority (NRA) under a national geology mapping project containing tectonic lineaments of the area (MO 1986). Remote sensing data were used to demarcate other geological lineaments in the study area using satellite image processing techniques. Satellite images were obtained from the Landsat 8 Operational Land Imager (OLI) and thermal infrared sensors (TIRs) from the U.S. Geological Survey (USGS). Finally, a lineament density map was prepared using GIS techniques and a lineament layer (Figure 3(a)) Geomorphological data from the digital elevation model (DEM) of the Shuttle Radar Topography Mission (SRTM) of the National Aeronautics and Space Administration (NASA) did not show any features of a river plane. These data were also used to extract geomorphologies, slopes, and streams networks . The most notable area consists of a low plantation surface with a small mountain that rises gently sloping from the surroundings. The DEM of the study area was further used to create the slope map of the area using the ArcGIS 10.4 software (Figure 3(b)). The DEM data from the USGS showed that about 74% of the study area consists of flat terrain characterized by slopes between 0 and 6, while, 26% of the study area has different terrain characteristics, that affect the water runoff.
The drainage network layer was extracted using the hydrology tool in the GIS environment and DEM data from the USGS were used to generate the drainage density map of the study area (Figure 3(c)). A land use/land cover map of the study area was built using four satellite images captured by Landsat 8 OLI/TIR from the USGS, where land use and land cover were classified using the maximum likelihood method in the supervised classification technique. About two-thirds of the study area consists of an equally covered limestone desert. A saline transition zone was identified as another land-use class in the area (Figure 3(d)). Generally, GIS technology was used in this study to digitize the hydrologic and geographic information for constructing a fundamental database by adjusting appropriate scores of different factors (Yeh et al. 2016). Finally, the spatial analysis function was used to demonstrate the potential groundwater recharge zones in the study area. The GIS techniques efficiently identified the groundwater.
A lithological map of the study area was prepared by scanning, geo-rectifying, and digitizing the 1:50,000 geology map produced by the NRA, Jordan (MO 1986) (Figure 4(a)). Different types of rocks, such as igneous, sedimentary, and metamorphic, were identified in the study area. Limestone, chalky limestone, and chalk marl limestone cover most of the study area. The  . north-eastern part of the study area is mostly made of basalt rock, whereas the southern part is made of fluvial sandstone, indicating a Kurnub formation. Identifying rock types and their distribution is essential to determine the permeability of the ground. Thus, the permeability of each rock type was used to assign respective weights to rock types in the study area based on the textural properties that allow water to pass through aquifers. The presence of highly permeable rock types with a large proportion of fractures in an area makes it suitable for groundwater recharging (Krishnamurthy et al. 2000). The soil cover map was provided by the Ministry of Agriculture in Jordan (NSMLUP 1996) (Figure 4(b)). The most prominent soil types in the study area are those with loamy, silty, clay, and clay loam textures. Other soil textures, such as sand loamy and sandy, are distributed to varying degrees in specific zones across the study area. Knowing soil texture is crucial for understanding the degree of water infiltration in aquifers of the study area. Therefore, weights were assigned to different soil texture types according to their permeability, which is directly related to the infiltration and percolation rates of the aquifers.
The Al-Sarhan Basin stands in the semiarid zone of the Mediterranean climate. Generally, the precipitation in the Al-Sarhan Basin increases during the winter season from the southern to northern parts of the area. Monthly total precipitation  Uncorrected Proof data were obtained from the Meteorological Department of Jordan (MDJ) to calculate the average annual rainfall in the Al-Sarhan Basin. Subsequently, the same value of the average annual rainfall (less than 50 mm) was distributed throughout the Al-Sarhan Basin area (TWAP 2015). Finally, all layers, which were used to calculate the groundwater PR index, were converted into the raster format from the vector format. Jordan Transverse Mercator (JTM) projection, created by the Royal Jordan Geographic Center (RJGC), was used to prepare the map. The conversion process was an important part of the linear combination method adopted in this study.
The rating of these variables depends on their importance for determining groundwater PR sites (Table 1). The PR index, given by the equation below, is an indicator of groundwater potential. The PR ratings and weightings were modified to suit the particular conditions of semiarid areas, particularly those of the study area. The PR index was calculated using Equation (1) as follows: where PR is the groundwater potential recharge index. The subscripts 'w' and 'r' refer to the weight and the rank of an individual parameter, respectively. A weight value, assigned to each parameter, ranged from one to eight based on the direct effect of each parameter on groundwater occurrence. Each parameter was also ranked from one to ten based on the hydrogeological significance of each class. The weights and ranks assigned to each parameter that influences groundwater potential are presented in Table 1. The factors used in the calculation of the PR index were the rainfall index (RF), lithology index (LG), geomorphology index (GG), slope gradient index (SG), lineament density index (LD), drainage density index (DD), land cover/land use index (LC), and soil cover index (SC). After using the general equation to calculate the PR index (Shahid et al. 2000), we validated it by comparing the results with the water table level of wells in the area.

Uncorrected Proof
The GIS environment was used to conduct the required operations for the identification of potential groundwater sites within the study area (Table 2). First, LC was generated using the maximum likelihood method under the supervised classification in ERDAS IMAGINE software, which was imported to ArcGIS and then reclassified based on Table 1. LC values varied from12 to 42 after reclassification (Figure 5(a)). Second, GG and SG were extracted from SRTM DEM. Table 1 was used to classify pixel values of geomorphology and slope. A single GG value of 28 indicated a flat land with a plantation surface, while SG values varied between 5 and 40 ( Figure 5(b)). Third, maps for LG, RF, and SC were edited by accounting for the ratings described in Table 1 (the outputs of editing were converted from the vector format into the raster format).
LG values varied between 16 and 48 after reclassification ( Figure 5(c)). A single RF value of 4 indicated annual precipitation of less than 600 mm, whereas SC values varied between 12 and 48 ( Figure 5(d)). Finally, LD and DD were calculated using the line density function tool in the GIS environment and considering the classification described in Table 1.

RESULTS AND DISCUSSION
The resulting map of groundwater potential recharging indicates the artificial recharging capacity and was divided into three classification zones: high (PR 172-227), moderate (PR 154-171), and low (PR 103-153) (Figure 7). The map depicts that 25% of the Al-Sarhan area consists of zones with low groundwater recharging potential, whereas 48% of the area possesses the moderate potential of artificial recharging. The statistical data revealed that 27% of the total area can be categorized as a high potential artificial recharging area. The Al-Sarhan area has a considerable artificial recharging capacity mainly because of the suitable geology, soil texture, drainage density, and flat terrain. The observation that the southern part of the study area has a high recharging potential might be due to the existence of fluvial sandstone, high infiltration rates triggered by lineaments, and a high drainage density. Figure 8 shows the potential groundwater recharge zones in the Al-Sarhan Basin.
The model was validated using data from 82 groundwater wells located in the study area. Six of these wells were located in the low zone, 17 in the moderate zone, and 59 in the high zone (Table 3). The model revealed that 93% of the wells in the study area were located in potential groundwater recharge zones (moderate/high zones).
The direction of groundwater flow in the southern part of Jordan, according to the static water level in the monitored wells, indicates the natural recharging potential throughout the study area (Figure 9). To enhance the existing groundwater resources in the Al-Sarhan area, artificial recharging strategies, such as trenches, check dams, percolation pits, recharge basins, land flooding, and recharge wells, could be built-in ridges and furrows (Board-India 2007). However, recharging wells is more likely to be successful because of the high evapotranspiration rate in the Al-Sarhan area.
The use of data with increased accuracy and spatial resolution can further improve the results of the approach followed in this study. Moreover, this method can be applied to the whole territory of Jordan after adjusting parameters, ranks, and weights. The method can also be extended to other arid and semiarid regions, with appropriate modifications, to identify the potential groundwater recharging zones. In situ field verification of the existing terrain conditions (land use/land cover and drainage systems) is useful to identify the most suitable artificial recharging strategy for replenishing groundwater in the study area. Overall, this technique provides valuable information for choosing and implementing suitable groundwater management activities.
Different studies around the globe have used geospatial tools to delineate the potential zones for artificial groundwater recharge in arid and semiarid areas. Jothiprakash et al. (2003) and Krishnamurthy et al. (2000) have applied these methodologies for identifying artificially rechargeable zones. The accuracy of the final results significantly depends on the thematic  layers and resultant weighting factors used in the study. Magesh et al. (2012) and Manikandan et al. (2014) have used the multi-influencing factor (MIF) technique to identify the zones with groundwater recharging potential. Kumar et al. (2007), Krishnamurthy et al. (2000), and Prasad et al. (2008) have also used geospatial technologies to delineate the zones with groundwater potential in hard rock terrains with variable geological settings. Several researchers have carried out the integration of influential factor layers using the weighted overlay method on a GIS platform for delineating the zones with artificial recharging potential. Shaban et al. (2006), Yeh et al. (2009), andShashikkumar &Metilda (2012) have applied a similar approach to identify artificial recharging sites in hard rock terrain.

CONCLUSIONS
Groundwater is the main water resource in Jordan, however, limited annual precipitation negatively affects the amount of surface and groundwater. This study applied cost-effective and time-saving remote sensing and GIS techniques to delineate the groundwater PR zones in the Al-Sarhan Basin. The study categorized the groundwater potential zones as low, moderate, and high potential zones. The high-to-moderate groundwater recharging potential extended to approximately 75% of the Al-Sarhan area, whereas 25% of the area was classified as a low groundwater potential zone. The study also revealed that approximately 7% of the groundwater wells were located in the regions with a low PR, 21% in the regions with moderate groundwater potential, and 72% in the regions with high groundwater potential. This study provides insights for developing prospective guidelines that decision-makers can follow to propose, design, and implement sustainable recharging projects within the concerned areas. Furthermore, this groundwater potential zone map could facilitate proper planning and management of groundwater usage in arid and semiarid regions.