Investigation of Groundwater Potential Using Remote Sensing and Hydro-geophysical Techniques: A Case Study of the Telidjene Basin (Eastern Algeria)

The present study aims to assess groundwater potential in the Telidjene Basin located in the semi-arid part of eastern Algeria, applying an innovative approach combining both remote sensing and hydrogeophysics methods. A re-interpretation of geophysical data and vertical electrical sounding (VES) measurements were applied and calibrated with the borehole data to map the deep structures that may control the presence of groundwater and identify the geological and hydrogeological setting. Morphometric factors affecting recharge were mapped using several types of remote sensing data (SRTM DEM, Landsat-8). Thematic maps were overlaid using the multicriteria method and GIS to detect potential recharge areas. The results show that the main factors influencing recharge are fracturing and drainage density. Four potential recharge areas were identified over a 547 km2 area of the basin. 20% of the area falls in the weakest class, 32% in the weak class, 3% in the moderate, and 16% in the strongest. Furthermore, the study reveals that an alluvial aquifer with a thickness of up to 60m, spreading over the surface, along the Wadi Telijene and the alluvial soil, is deposited unconformably on Cretaceous terrain containing aquifer horizons of varying thickness and different electrical resistivities (10–150 Ωm), drawing an anticlinal structure with lithostratigraphy interrupted by a series of faults and spurs of Aptian and Triassic age. The south-western part of the basin has a high to moderate recharge and storage capacity. Its alluvial cover is directly fed by precipitation and fractured limestones deposited in a syncline outcropping on the edges forming an alluvial and carbonate bilayer aquifer. This study concluded that an integrated approach, involving recent, efficient, and inexpensive technology, such as remote sensing and conventional geophysical method, can be successfully used to identify groundwater potential in the study area.


Introduction
In recent decades, the economic and social development of the municipalities of the Cheria district, which includes the study area, has generated a strong and growing demand for water. In addition, intense agricultural activities have put pressure on various water resources. This overexploitation, in addition to climatic hazards (semi-arid climate), has led to a significant drop in the piezometric levels of the Maastricht and Eocene aquifers. The exploration of other resources is necessary, and the aquifers of the Telidjene Basin constitute potential resources and deserve to be the subject of a more detailed and in-depth study. Thus, a good knowledge of the characteristics of the aquifers of this basin is necessary to better exploit them and preserve them from contamination.
The infrastructures, carried out by the Directorate of Water Resources since the early 1980s, have been insufficient to meet the needs of potable water and irrigation in the region under study. Thus, the lack of hydrogeological studies to examine the existing geoelectric data has led to many problems in the implementation of these infrastructures.
Previous studies conducted on the adjacent basin of Cheria (Baali, 2007) and the aquifer of ''Meskiana'' (Gouaidia, 2008), an ''anticline'' with a hydraulic structure similar to that of the studied basin; have reported the influence of the geological structure on the conditions of recharge of aquifers and storage of groundwater. Baali, in his thesis on the area of Cheria located at 10 km, estimates that the average rainfall is 200 mm/year. All research conducted in the similar semi-arid context reveals that, except in karstic environments, infiltration is minimal or negligible, constituting only a supplement. In this dry climatic context, there is a need to understand and improve the knowledge concerning the conditions of recharge and storage processes and define the influence of factors controlling them, namely, the morphometric characteristics and hydrogeological structure of aquifers in the basin.
The main objectives of this study are to assess the water resource and to improve the knowledge of the aquifer system in the Telidjene Basin using a new efficient, rapid, and low-cost approach to assist the local authorities in decision making and development planning.
To meet these objectives, the present study gives particular importance to the available data and documentation concerning the geophysical campaign (electrical soundings) (CGG, 1976) carried out in the region which has not been exploited in research yet, nor been a subject of study to any hydrogeological synthesis at the Telidjene Basin level. The study also required the execution of (7) VES in the south-western part of the basin where resources are constant, compared with the central and north-eastern part of the basin. Remote sensing data were readily available and of major use to complete the processing and produce a reliable result.
In doing so, two methods were combined: remote sensing and geophysics.
Remote sensing. Applications of remote sensing and GIS for the exploration of potential groundwater areas have been carried out by several studies in different worldwide (Krishnamurthy et al., 1996;Shaban et al., 2006;Haouchine et al., 2010;Chowdary et al., 2009;Oularé et al., 2017;Arulbalaji et al.,2019;Vasileva, 2019;Gonçalves et al.,2019), and it has been found that the factors involved in the determination of potential groundwater areas are different, and therefore the results vary accordingly. The derived results are considered satisfactory based on the field investigations and vary from region to region due to the varied geo-environmental conditions.
Geophysics. Because remote sensing data are relevant to the hydro-morphometric characteristics of the aquifer, it is necessary to incorporate other data sources such as geophysics, especially the electrical method. The use of geophysical methods provides valuable information to identity the nature as well as the geometry of the valuable information and to monitor the hydrogeological process (Zitouni et al., 2017;Moreira et al., 2021;Breusse, 1963) This integrated methodology, combining remote sensing and geophysics, has been used by several authors and studies worldwide (Gyeltshen et al.,2020;Mohamaden et al., 2017;Ogungbade et al., 2021;Nicaise et al.,2019;MogajiandOmobude, 2017); moreover, the new technology based on remote sensing is considered as an effective, fast and less costly tool that provides data on factors controlling the presence and water movement.
This study would be a reliable reference to help decision-makers establish their future development plans, recalling that the commune of Telidjene is counted among the most unfavorable communes and has not benefited from any budget allocated for water search actions since the 1970s.
However, the available data do not allow the evaluation of the hydrodynamic characteristics of the existing aquifers nor their geometry in-depth, which does not allow integrating them in the management tools of the water resource that require precise quantitative results.

Study area
This study focuses on the Telidjene Basin, which is geographically located at the eastern end of the Saharan Atlas with an area of 547 km 2 . Administratively, it belongs to the commune of Telidjene, located about 70 km south-west of the wilaya of Tébessa (Fig. 1). The region is located in the topographic map of Telidjene and the map of Cheria at 1/50.000, a part of the sheet of Bir Sbeikia. The region is characterized by a semi-arid climate with a relatively cold and rainy winter and a very hot and dry summer.

Geology and hydrogeology
The basin of Telidjene is located in the south of Tébessa district, and corresponds to an anticline structure limited in the north by the reliefs of Djebel Bou Kammech, in the north-east by Djebel Krima, in the south by Djebels Debibir and Ouassif, and in the west by Djebel Aghour el Kifene (Fig. 3). The lithologic units in the study area are dominated by Tertiary, and Quaternary soils were filled during this period by sediments of continental facies from the limestone massifs that limited it. Indeed, the Wadi Telidjene and its tributaries, draining this basin from north-east to south-west, have deposited fill material such as alluvium-forming fluvial terraces that are well developed over the entire basin, where they record very accurately the erosion activity near the NW and SO offsets (Vila, 1994a).
Available lithologic logs of wells drilled in the study area indicate the coexistence of two types of aquifers, namely, superficial alluvial deposits and 'deep tertiary formations underlying the alluvial deposits,' which could have a hydraulic potential more favorable to exploitation.
The alluvial aquifer reaches a maximum of 60 m and disappears at the edges of the basin, while the carbonate aquifers could be exploited at varying depths and their thickness depending on their location in the basin and the geological structure.
As the basin is located in the atlasic domain, its structure is dominated by a vast atlasic fold with a diapiric core (Dubourdieu, 1950). This has caused several faults, giving rise to strong fracturing of the Cretaceous edge formations, which would facilitate water infiltration.

Materials
For this study, a multi-spectral image from the Landsat 8 satellite and a digital elevation model extracted from the SRTM 30 were used to extract the lineaments using the QGIS and GEOMATICA programs. The DEM digital elevation model was used to produce the thematic maps used in this work, except for the land use map, which was digitized from the map produced by the Bureau National des Etudes pour le Développement Rural (INSID, 2011). In addition, geological maps (ENERGOPROJECT-ENHYD, 2002;Vila, 1994a;Vila, 1997), at scales of 1/200 000 and 1/50 000 were processed. Geo-electrical sections of the Compagnie Générale de Géophysique (CGG, 1976) were used to produce geological and hydrogeological sections, and geological and hydrogeological data of wells and boreholes with information on geology, static water levels, flow rates, and deep lithology were used. This information was provided by the Directorate of Water Resources (DRE) and Agricultural Services (DSA) of the Tébessa district, the National Office of Geological Research (ORGM), and the National Company for Research, Production, Transport, Processing, and Marketing of Hydrocarbons (SONATRACH). Finally, with a field GPS, the coordinates of the wells were recorded with water level measurements using a manual piezometric probe (capacitive sound). Geoelectrical data were collected with an ABEM TERRAMETER SAS 300 instrument using the Schlumberger disposition. duplicated, which is closed in the north-east by Djebel Boudjelal and Djebel Doukkane, and the south-west by Djebel Dehar and Ahrour el Kifène. The vast plain of Ain Telidjene limited by this ridge and drained to the south by the Wadi Telidjene is rugged by two derived mountains: in the west, the Hamimat-Meskouta mainly consisting of Triassic formations, and in the east, the Hamimat Souda formed of Aptian limestone. This is the region where the erosion has been the strongest and almost all the Maastrichtian and Campanian have been eroded and only appear in the summits.
Sector III is an area of subtabular fractured limestone plateaus with the typical bare landscape of the Nememcha (Vila, 1994b), which opens up to the north from the outskirts of Reliai and Kef Zora, where the limestone plunges from 50° to 30° toward the center of the basin and closes in the south.

Structure of the Telidjene Basin.
A geoelectrical section (CGG,1976, pl. 5, profile C) that passes the axis of the anticline and the Hamimat Souda spur, made on the electrical profile C (Fig. 4), totaling 20 vertical electrical soundings in AB 2000 was reinterpreted. Stratigraphic logs from different sources (Table  1) were used to calibrate the superficial horizons, whereas the DDN-101 and Bdj-2 oil drillings were used to correlate the deeper formations highlighted by the CGG geophysical survey.
The geological section (Fig. 5) shows that the anticline structure is occupied by formations ranging in age from the Maastrichtian to the Triassic (older formation), which is in abnormal contact with younger formations. The geological formations of the Telidjene   Basin are composed of intercalations of marls and limestone interrupted by the spur of Hamimat Souda built by the formation of the Aptian age. The Albian is the thickest formation; it can be seen on the surface at the level of a point abutting Hamimat Souda and on the southern slope of Hamimat Meskhouta.
Borehole and well inventory. The number of boreholes and wells inventoried in the basin is 32, the most representative of which are those intended for drinking water supply (DWS) with 4 boreholes located in the region of Bir Said (III) and next to the Telidjene city (Sector II). In addition to the mentioned boreholes, 26 wells exploited by the farmers for domestic and irrigation use that capture the alluvial groundwater were used to draw the piezometric map.
The north-eastern part of the basin (zone I), on the other hand, is supplied with potable water from the Elmalabiod basin located at the northeast limit of the perimeter. We did not find any boreholes or wells in this zone, probably due to the limited or even non-existent aquifer possibilities in this part of the basin. Table 1 shows the distribution of the boreholes/wells by type of use and their characteristics including   Piezometry. Observation of the morphology of the piezometric map of December 1991 (Charef et al.,1991), shows that the groundwater flow generally follows a north-east to a south-east direction (Fig. 7a).
The groundwater drainage axis coincides with the course of the Wadi Telidjene, which drains surface water. Locally, two flow directions can be observed, one parallel to the axis of the wadi and the other almost perpendicular, which comes from the slopes towards the wadi, this suggests that the groundwater is fed from the slopes. The piezometric map for November 2018 (Fig. 7b) shows that the flows are directed from north-east to south-west, a significant change in the flow direction appears at the level of Bir Said (sector III) following the change in the direction of Wadi Telidjene with also a flow direction coming from the massifs and perpendicular to the axis of the wadi. This orientation also suggests that the water table is fed by water from the peripheral massifs.
(a) (b) Geophysics. To determine the geometry of the existing aquifers, a geophysical survey by the Compagnie Générale de Géophysique (CGG, 1976) ( Fig. 4) covering the sector (II) was used. An electrical profile of 7 vertical electrical soundings (VES) in AB 1000 was carried out in sector III of Bir Said, aiming to highlight the geometry of the superimposed aquifers of the Quaternary and Eocene-Maastrichtian, captured by the BS1 and BS2 boreholes. No investigation program has been carried out in sector I, it is due to the lack of water points to validate the results. The hydraulic and geological borehole data shown in Table 2 were used to calibrate and reinterpret the geo-electric sections (Figs. 8 and 10) and to determine the age of the geological aquifer formations, thickness, and resistivity of the various formations.
Interpretation. Profile C' was used to trace the geological section on the axis of the anticline, as discussed in the geology section (Fig. 5).

Fig. 8. Geo-electrical cross-section along profile D-G (modified)
The geoelectric section following the D-G profiles shows the alternation, from top to bottom, of 8 geoelectric levels, of which the most important are the Mio-Plio-Quaternary, represented by recent alluvium, moderately resistant (50-150Ωm) and discordant with the Cretaceous and Triassic formations covering the dome area. The Maastrichtian limestones highlighted in the northeastern part are characterized by the highest resistivity (200-800Ωm). This horizon is of no hydrogeological interest because of the weak fracturing affecting this zone; the lowest resistivity is attributed to the Triassic formations (2-10 Ωm). Between these two levels, there are horizons of hydrogeological interest, such as the Albo-Aptian, Cenomanian, and Turonian, with resistivities close to each other and ranging between 5 and 100 Ohm, which is due to the presence of the conductive component materialized by clays and marls in addition to carbonate formations.
Profile H' (Fig. 10) is run in Sector III. Field data were obtained from the execution of 7 vertical electrical sounding VESs that were processed by the IPI2WIN software ( Fig. 9). This software allows an interactive semi-automatic interpretation that takes into account  The geo-electrical section on profile H (Fig. 10) was established based on the calibrations at boreholes BS-1 and BS-2, which correspond to the following lithostratigraphy: _ 'Quaternary' built by recent and ancient alluvium marked by a resistivity between 10 and 150 Ωm;

Remote Sensing Data
Remote sensing imagery and GIS analysis techniques were used to delineate the different potential recharge areas in the Telidjene Basin by identifying and mapping the different surface factors believed to control the infiltration of surface runoff to recharge the underlying unconfined aquifers.
Processing of satellite images. For this work, the geological maps were digitized, imported into QGIS, and georeferenced. We used a multispectral Landsat 8 image. The M.N.T. digital terrain model (Fig. 11) was also used to extract the lineaments, watershed map, slope map, drainage density map, TWI map, roughness map, and curvature map.
Lineament extraction. To achieve good results, the extraction was carried out both by semi-automatic and automatic extraction of the lineaments, and their identification was performed in three steps. First, the faults were digitized using QGIS on a geological map (Fig.  12a), and automatic extraction was performed using the PCI GEOMATICA program through its Line module (Fig. 12b). Finally, the lineaments were extracted semi-automatically using the visual interpretation and the Hill-shade function of the QGIS software of the images generated from the SRTM DEM (Fig. 12c).
Artificial features, such as roads and other linear structures, were excluded from the interpreted lineaments. The extracted lineaments were superimposed on the satellite image for verification, and some of these lineaments were confirmed in the field. Finally, the QGIS and Rockworks software were used to merge the 3 lineament maps extracted from the different methods into a single global map (Fig. 12d), and to extract the statistical parameters of the lineaments (number and lengths) to realize the rosacea diagram by an angular fraction of 10°.
Recharge mappings criteria and weighting. The methodology adopted was based on the use of multi-criteria analysis techniques. It consists of the delimitation of favorable groundwater recharge areas by considering the factors affecting the recharge process (Krishnamurthy, 1996;Shaban, 2020;Singh et al., 2013;Ta et al.,2011). The thematic maps were produced in two stages: the first stage was devoted to the description of the factors controlling aquifer recharge, and the second is devoted to the acquisition and classification of these factors, followed by the assignment of weights and their integration (Oularé et al., 2017).
Identification of decision criteria. The identification of the criteria determines the quality of the information generated during decision-making. Many important criteria are identified, selected, and evaluated for the establishment of different thematic maps (Jourda et al., 2006), namely slope (%), drainage density (km/km ²), lineament density (km/km ²), permeability (m/s) derived from the lithological map, land use, terrain roughness index (TRI), topographic wetness index (TWI), and curvature. It is important to point out that we did not take into account the piezometric map, which shows poor distribution of the wells inventoried in the region, nor the rainfall map because of the lack of variability of this parameter over the whole basin.
Classification, evaluation, and standardization of decision criteria. According to previous works, each decision criterion is divided into classes representing either a particular environment or an interval of values of 5 classes qualified as very weak, weak, moderate, strong, and very strong; they have been determined for this work for each criterion. To provide the most appropriate conditions for interpretation, the different classes for each criterion are standardized according to their particular influence on reservoir formation. A rating scale ranging from 1 to 10 was used (Table 2). A relationship was then established between these factors, taking into account the degree of influence of each factor on the recharge process (Shaban et al., 2006;Chowdary et al., 2009).   The total coefficient assigned to each factor was determined based on the relationship between the first and second factors. For a major-type relationship, a coefficient of 1 is assigned to the first factor, while a factor of 0.5 is assigned to it when the relationship is of the minor type (Fig. 13).
These coefficients were therefore assigned at the level of each factor according to their importance in relation to the others, applying the methodology described above. The total weights calculated for each factor are listed in Table 3.  Shaban et al., 2006)

Thematic maps
Lineament density map. The presence and importance of a network of lineaments are potential indicators of water recharge (Bruel et al., 1999;Yao, 2012) since highly fractured areas have permeable locations through which water infiltrates and travels several tens of kilometers. The fracture density maps (Fig.  14a) are derived from the superimposition of 3 lineament maps produced by the QGIS and GEOMATICA programs, geological maps at scales of 1/200 000 and 1/50 000, an ASTER DEM map with a resolution of 30m, and a Landsat 8 image with a resolution of 30m. The global lineament map was processed by the QGIS program to determine fracture density; Rockworks was used to derive lineament directions.
Five classes are identified, concentrated essentially on the edges and towards the west of the watershed, very strong fracturing density, strong fracturing density, moderate fracturing density, weak fracturing density, and very weak fracturing density.
Permeability map. The permeability map was derived from existing lithological maps at scales of 1/200 000 and 1/500 000. These were digitized and then reclassified, according to the hydrogeological characteristics and nature of the natural formations of the cover (Banton and Bangoy, 1997;Castany,1982). According to the permeability power of the rock formations (Table 4), the permeability map was reclassified into 3 main categories: moderate, weak, and very weak (Fig. 14c).
This parameter allowed us to identify 5 classes concentrated essentially on the edges and towards the west of the watershed, very strong fracturing density, strong fracturing density, moderate fracturing density, weak fracturing density, and very weak fracturing density.
Slope. The slope map was created using a digital elevation model (DEM). The examination of the slope values led to the identification of 4 classes: steep, medium, shallow, and very shallow slopes (Fig. 14d). On the mountains, the slope is very steep, which favors high surface runoff and less water infiltration, which results in a lower groundwater recharge capacity (MachiwaL et al., 2011), and in the foothills, we found a medium to the low slope. The lowest values were recorded in the areas between the mountain foothills and plains, which are the areas that favor infiltration into the soil (reduce runoff) and have a higher groundwater recharge capacity due to high rainwater retention. The lowest values were recorded in the areas between the mountain foothills and plains, which promote infiltration into the soil (reduce runoff) and have a higher groundwater recharge capacity due to high rainwater retention.   Banton and Bangoy, 1997) Drainage density map. In the study of the erosion processes established by Horton1945, drainage density is lower as the infiltration capacity is risen and varies in the same direction as the stream and the opposite direction of the underground flow. According to Greenbaum (1985), the transmissibility of the terrain appears to be the dominant factor in drainage density, which is one of the most important indicators of hydrogeological characteristics. The drainage network for the study area was created from the SRTM global elevation data, and the drainage density values were grouped into four drainage density classes (Fig. 14e): very low, low, medium, and high Land use map. The land-use map (Fig. 14f) was obtained by digitizing the land use map of Tébessa edited by the National Institute of Soil, Irrigation, and Drainage (INSID, 2011). The original map has 8 classes: forests, roads, wadi, built, dry crops, non-irrigated crops, market gardening, irrigated eye cultivation, bare soil area with rocky ground, and pastures. Several studies have shown that changes in land use strongly influence groundwater recharge (Roose, 1973;Owuor et al., 2016). According to the influence of the nature of the occupant on the recharge, the land-use map
Terrain roughness index TRI. The calculation of the roughness index allows us to characterize the different types of relief. Roughness characterizes the aspect of the surface, which can be smooth or modeled in multiform micro-relief. It acts as a surface holding agent on gentle slopes; it favors water storage and slows down runoff (Magunda, 1997;Onstad et al., 1984;Kamphorst, 2000). Fig. 14g shows the terrain roughness map of the Telidjene Basin with values ranging from 0.11 to 0.87. The values were reclassified into 5 categories: high weights assigned to low roughness values, and vice versa.
Topographic wetness index TWI map. This index combines the local upstream contribution area and the slope. It is generally used to measure the effect of topography on hydrological processes (Beven and Kirkby, 1979;Nair et al., 2017) (Fig. 14h). It is commonly used to measure and evaluate the spatial distribution of moisture conditions and requires only the elevation data to be well distributed over the study area. The calculated model is independent of time and is a static representation of the landscape.
Curvature map. Curvature is the quantitative expression of the nature of the surface profile and can be concave or convex. Water tends to decelerate and accumulate in convex and concave profiles (Reiffsteck, 2003). The curvature ranges in the study area vary from 4.33 to -2.46. The values are reclassified into 5 classes such as -2.46 to -1.10, -1.10 to 0.25, 0.25 to 1.61, 1.61 to 2.97 and 2.97 to 4.33. High weight is assigned for a high curvature value and vice versa. Fig.  14i shows the curvature map of the Telidjene Basin.

Results
Lineaments. Analysis results are presented in the form of a lineament map, a lineament density, and a rosacea diagram. The lineament map shows a heterogeneous lineament distribution (Fig. 4).
As shown in (Fig. 14b), the main predominant directional families are ''NW-SE'' and ''E-W'', respectively. The ''NW-SE'' family is marked throughout the region and is subparallel to the major Tébessa-Morsott ditch accidents, followed by the ''E-W'' direction, which is predominant mainly in the south-western part of the watershed. The latter comes from two other sets of lineaments, although to a lesser degree than the first two directions, with a ''NE-SW'' orientation and ''NNW-SSE'' to N-S orientation.
Aquifers. The identification of the aquifer systems was elaborated based on the lithological data of the outcropping geological formations, and the results of the existing drilling works, allowing the definition of the main aquifer systems. The geophysical study carried out by the Compagnie Générale de Géophysique was been used to highlight the extent of the alluvial aquifer of the part of the eroded dome with a diapiric core (the Telidjene Anticline). The aquifer systems we defined in the Telidjene watershed are shown in Fig. 8 and Fig. 10 and are numbered as follows: (1) The aquifer of the Plio-Quaternary. Consisting mainly of alluvium, gravel, and pebbles, it is generally located along the Wadi of Telidjene, the plains, and the dejection cones, it is most exploited by farmers. This aquifer, located in the dome area, was studied in detail by CGG (1976). The bedrock of this layer is composed of marls, hard limestones, and sometimes clays, which is due to the lateral heterogeneity of the geological structure with varied nature.
(2) The two-layer aquifer of the Bir Said region III. It is the result of the superposition of Quaternary formations built by ancient and recent alluvial deposits and Maastrichtian limestones, with more or less dense fissured and karstic networks. The Maastrichtian aquifer is confined; it has a hard roof without cracking, with a thickness varying from 20 to 40m. According to the boreholes DDNS-101, DDN-1, and BDJ-2; the thickness of the Maastrichtian limestones is approximately200m; water inflows are observed between 41 and 85 m deep, which shows that the water of these aquifers circulates under pressure.
(3) Turonian aquifer. This zone presents a confined karstic aquifer in fissured and karstified limestones made up of hard limestones intercepted by borehole T2.
(4) Cenomanian Aquifer. This aquifer is exploited by drilling BT2, it is a confined aquifer approximately 30 m thick in fissured marly limestones, with a roof built by marly formations.
(5) Albo-Aptian Aquifer. The diversity of hydrogeological conditions, essentially related to the geological structure and properties of the Albo-Aptian rocks, shows a change in the water resources in this area. T3 intersecting this zone shows saturated horizons in limestones, and marly limestones form a confined aquifer system. However, information on the deposit of this aquifer and its hydraulic link is insufficient and often confused to allow an estimation of the exploitation of the zone. At a distance of 3,000 m towards the southwest, drill T4 intercepting the marly and marly limestone formations has proven to be unproductive for pumping, which indicates that these limestone intercalations are impermeable and sterile. It should be recalled that borehole T3 has been stopped for several years due to a drop in the flow rate, and at the time of drilling, the flow rate of this borehole was 2.6 L/s.

Comparison of piezometric maps for the period 1991-2018.
In general, the current flow direction was unchanged compared with that in 1991. The orientation is still from the north-east to the south-west, the extension of the isopiezes of November 2018 on sector III of Bir Said confirms that the direction of the flow follows that of the main wadi.
A decrease in the piezometric level was observed between 1991 and 2018 on the entire plain. Hamimat Meskhouta and Hamimat Souda are the sectors where the greatest drop in the piezometric level can be observed at 59.5 and 58 m, respectively. In the remaining sectors, the average variation value between 1991 and 2018 varies between 30 and 44 m. Generally speaking, the piezometric level has decreased significantly, which has led to the cessation of most of the wells inventoried in the 1991 period (Charef et al., 1991).
Groundwater potential recharge zones map. The weighted overlay of the different thematic maps made it possible to construct a synthesis map showing the locations of areas potentially favorable to groundwater recharge (Fig. 15).
This map, which was classified into 4 categories, shows the following: The high potential class represents 16% of the basin surface; it is dominated by very strong fracturing and carbonate formations, which are mainly located in inaccessible areas and are impacted by very strong fracturing.
The class with moderate potential represents 32% of the total surface area of the basin and meets well to moderate drainage conditions.
The low and the very low potential classes represent 32% and 20% of the occupied proportion, respectively. These zones are located in areas with high and moderate drainage density, in the north-eastern part, as well as in the south-western parts of the landforms, which are underlain by weakly fractured limestone.
According to these statistics, the most favorable zone is mainly located in inaccessible areas and is impacted by very strong fracturing. The area with moderate potential occupied 32% of the land. It can be concluded that the region of Telidjene offers strong to moderate potentialities in groundwater and that this zone covers approximately 48% of the territory.
Validation of the results of the groundwater potential recharge zones map. Based on the results of the hydrogeophysical study, we were able to obtain information on the distribution and structure of the Quaternary water table as well as the carbonate formations (Maastrichtian and Eocene). This information allows measuring the coherence of the remote sensing results and the hydrogeophysical study, as the water table presents unconfined horizons controlled by recharge.

Fig. 15. Groundwater potential recharge zones map
The hydrogeophysical study showed that the Bir Said (sector III) is the most promising area for the presence of groundwater. This area is characterized by a high groundwater potential, confirmed by the presence of a large saturated thickness of the Quaternary aquifer. According to the synthesis map, this area is marked by a strong to moderate potential, as well as the most productive wells and boreholes, which confirms that the area benefits from a recharge coming from the alluvial formations as well from the edges materialized by fractured limestone.
Therefore, to validate the map of potential recharge areas, it was overlaid on the 26 existing boreholes and wells in the basin. It was found that wells with a flow rate of 3 l/s or less were superimposed on the low to very low class. The water points with a flow rate greater than 4 l/s are superimposed on the moderate to high classes, suggesting that this increase in flow rate, particularly in this part, is due to direct infiltration of the alluvial cover and a supply from the carbonate edges, revealing a high potentiality according to the summary map (Fig. 16). responsible for improved permeability and enhanced groundwater localization (Mpofu et al., 2020); the study confirmed a strong relationship between faulting and potential recharge areas. In general, the majority of the productive wells were located in a corridor marked by a high density of fractures (Figs. 12d and 14a) that extends from the Draa Foum Debbane passing through Kef Zora, Reliai, up to the outlet of the Basin. This fracturing constitutes a zone of weakness where erosion is more active and constitutes a privileged place for the development of ravines constituting the axes of gathering and channeling rainwater. It is the only zone (sector III) where the dip direction of the Eocene and Maastrichtian calcareous layers follows the water table flow direction and is favorable for feeding the alluvial water table. This process helps explain the stability of the piezometric level in Sector III. It should be noted that the BS1 borehole drilled in 1995 intercepts the alluvial formations and Maastrichtian limestone (Table 1). Its current piezometric level is 41.60 m with an insignificant drawdown of 0.60m compared with the initial level; this information confirms the result of the groundwater potential recharge map. In fact, there is a good response of the recharge to precipitation by direct infiltration from the alluvial cover and the fractured limestone outcrops in this sector.
Aquifers. Influenced by the network of lineaments and fractures, the aquifer system in the Telidjene Basin is compartmentalized into two structures: an anticlinal structure occupying the dome region and a synclinal that is positioned south-west of the basin. These structures control the groundwater flow (Chelih et al., 2018) by the presence of lateral discontinuities due to the change of the geological facies as well as the series of faults of ''NW-SE'' and ''E-W'' directions which appear perpendicularly to the direction of the flow in the dome region. The same fault family acts as a drain and promotes infiltration when parallel to the flow direction.
Although this study presents an effective means of initiating the aquifer geometry of the Telidjene Basin, it is insufficient to lead to a hydrodynamic characterization of the aquifer infrastructure. Future research will need to deepen the knowledge around this issue.
Groundwater potential recharge zones. Based on the methodology presented, the study area was classified

Discussion
Lineament. The presence of lineaments could indicate the location of brittle deformation that could also be into 4 potential recharge zones, namely strong, moderate, weak, and very weak, covering 16%, 32%, 32%, and 20% of the study area, respectively. Although a large part of the study area (48%) has a high to moderate recharge capacity, it can be seen that groundwater resources are somewhat limited in the study area, since that the most favorable class is located in inaccessible limestone outcrops where extension and dip are not favorable for flow towards the water table but rather towards the adjacent basins.
The high potential class also occupies the areas of slope breaks, from which we observe the abundance of alluvial fans that present privileged places for infiltration due to their coarse granulometry (Amelot et al., 2003).
It should be remembered that the 1991 piezometric map showed a flow direction perpendicular to the axis of the main talweg, which confirms that recharge occurs through direct infiltration of the alluvial fans and not from the limestone outcrops where dip and extension of the layers are opposite to the direction of flow of the water table. The presence of marl-clay intercalations in the edge formations in contact with the water table aquifer also makes its feed difficult.
In the present study, the 8 parameters that were retained are the most important in determining the recharge zones based on the experience of previous work. However, topographic wetness index and curvature maps show similar zoning; as per Table 3, the weight assigned to each factor according to its hydrogeological characteristics is the same, which means that these indicators are equal. Overestimation of factor weights could also be done if there is a dependency relationship between the parameters. These observations lead to the suggestion of statistical correlation analysis to measure the degree of dependency of the factors, avoiding redundancy and finding the most discriminatory factors for predicting the recharge phenomenon by the multi-criteria method (Pinson and Stollsteiner, 2016).
Piezometry. The piezometric levels of the boreholes capturing the aquifer horizons under the Quaternary cover in the dome and Bir Said regions show stability over time (Table 1). However, it was not possible to establish a mapping for these deep horizons due to the insufficient number of monitoring wells. This missing information did not provide better knowledge of the interactions of these deep horizons with surface waters nor did it provide information on understanding their behavior and capabilities.

Conclusions
The present study demonstrates the effectiveness of integrating remote sensing with hydrogeophysics to identify the most favorable areas for groundwater exploitation in the Telidjene region. The study showed that the alluvial aquifer extends over the entire basin plain and benefits from a weak to moderate recharge in the dome region where an anticlinal structure with complex geology is encountered; in the south-west, it benefits from a recharge by the edges of the calcareous formations of Maastrichtian and Eocene age and deposits in normal contact, thus forming a two-layer aquifer.
The exploitation of geoelectrical data also shows that this water table is deposited in an unconformity on aquifer horizons of Cretaceous age in the dome region. These are the Turonian, Cenomanian, and Albo-Aptian aquifers, where resources can change within the same aquifer due to the existence of a marly component alternating with the limestones, as well as the complexity of their geological properties and structure. These aquifers require detailed geophysical and hydrogeological investigations to determine their geometry, especially their lateral extension, recharge conditions, and hydrodynamic characteristics.
A multidisciplinary methodology was also used to delineate potential groundwater recharge areas, which is a GIS-based multi-criteria decision-making technique. The proposed technique, which is widely used, uses several parameters depending on the hydrogeological context. These parameters made it possible to evaluate the potential for groundwater recharge. The study used satellite data (SRTM data), geological, and land use mapping to prepare 8 thematic maps, namely, slope, drainage density, permeability, fracturing, land use, roughness, topographic wetness index, and curvature.
The map of potential recharge areas was made based on the mapping of the 8 thematic layers that were reclassified to achieve the best result. A weight is assigned to them according to the influence of each factor on the recharge capacity of the land and its relative importance to groundwater. Weights were assigned to the thematic layers according to their influence on recharge as well as the relationship In summary, the results of this study demonstrated the efficacy of combining remote sensing techniques and hydrogeophysics to produce a reliable decision tool on groundwater potential based on geoelectrical parameters, accessible morphometric measurements, and induced by subsurface datasets. The study made it possible, for the first time, to shed light on the hydrogeological context of the Telidjene Basin and to improve knowledge about the aquifer system as well as its recharge conditions. Remote sensing work made it possible to update the geological map of the region by creating a new lineament map, while the processing of hydrogeophysical data facilitated the establishment of new geological and hydrogeological sections. The maps obtained through this technique can be used by local authorities and managers to select suitable sites for drilling new wells, and it can also help in formulating effective groundwater development strategies for the study area to ensure the long-term sustainability of this vital resource.
The obtained results deserve to be refined by other studies, in particular by integrating the "geophysical" parameter in the multi-criteria analysis and treating it in a GIS environment to allocate potential groundwater areas by moving from a qualitative approach to a quantitative approach. Knowledge of the geometry of the deep aquifers in the dome area needs to be improved to better control the exploitation of the locations.
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