Enhancing Drought Resilience through Groundwater Engineering by Utilizing GIS and Remote Sensing in Southern Lebanon

Abstract

Countries face challenges of excess, scarcity, pollution, and uneven water distribution. This study highlights the benefits of advances in groundwater engineering that improve the understanding of utilizing local geological characteristics due to their crucial role in resisting drought in southern Lebanon. The type of drought in the region was determined using the Standardized Precipitation Index (SPI), Standardized Vegetation Index (NDVI), Vegetation Condition Index (VCI), and Soil Moisture Anomaly Index (SM). The dry aquifer and its characteristics were analyzed using mathematical equations and established hydrogeological principles, including Darcy’s law. Additionally, a morphometric assessment of the Litani River was performed to evaluate its suitability for artificial recharge, where the optimal placement of the water barrier and recharge tunnels was determined using Spearman’s rank correlation coefficient. This analysis involved excluding certain parameters based on the Shapiro–Wilk test for normality. Accordingly, using the Geographic Information System (GIS), we modeled and simulated the potential water table. The results showed the importance and validity of linking groundwater engineering and morphometric characteristics in combating the drought of groundwater layers. The Eocene layer showed a clearer trend for the possibility of being artificially recharged from the Litani River than any other layer. The results showed that the proposed method can enhance artificial recharge, raise the groundwater level to four levels, and transform it into a large, saturated thickness. On the other hand, it was noted that the groundwater levels near the surface will cover most of the area of the studied region and could potentially store more than one billion cubic meters of water, mitigating the effects of climate change for decades.

1. Introduction

Long-term drought is a significant natural obstacle that harms agricultural and socioeconomic activities. It also adversely affects the ecosystem and jeopardizes the sustainability of various natural environments [1,2,3,4,5,6,7,8,9]. The eastern Mediterranean regions are experiencing record climatic anomalies [10,11,12] and more prolonged and severe droughts in the current decade [13,14,15]; these exceptional droughts are about 98 percent drier than the driest periods of the last 500 years [16]. In the past century, more than 10 million people have lost their lives due to major drought events causing several hundred billion dollars (USD) in economic losses worldwide [17], USD 249 billion of which have been in the U.S. alone since 1980 [18], and the numbers are rising.

National Drought Mitigation Center [19] adopts the classification of drought types into three categories: meteorological, agricultural, and hydrological, with indicators including precipitation, NDVI, soil moisture, and groundwater [20]. Groundwater in karst areas is vulnerable to repeated droughts, as it can lose its storage capacity and take longer to replenish [21,22,23]. Scientists have conducted numerous studies to better understand groundwater droughts in the context of the meteorological drivers and the propagation of droughts through hydrological systems [6,24,25,26,27,28]. Numerous scientific investigations have highlighted that three primary factors predominantly have complex nonlinear interactions that influence groundwater configuration and flow rates: geology, climate, and topography [29,30,31,32,33,34,35,36,37].

The geological strata in the study area, situated in the eastern basin of the Mediterranean Sea and the area shared by the continents of Asia and Africa, has been significantly affected by tectonism. This tectonic activity has resulted in the exposure of geological strata to various events, such as lithostatic, tectonic, and thermal pressures, which can lead to the formation of fractures, cracks, and faults [38,39,40]. As a result, the geological strata in this region have the potential to act as aquifers, making them a subject of interest for researchers and experts in the field.

Numerous theoretical, experimental, and simulation studies have been carried out to better understand the intricate mechanisms underlying groundwater flow in fractured and karstic rocks. These studies have significantly contributed to the advancement of our knowledge on the subject matter [41,42,43,44,45,46,47,48,49], and this knowledge benefits the project proposed here.

In 2017, groundwater accounted for 25% of the global freshwater abstractions, making it a significant source of freshwater worldwide [24,50]. Twenty percent of global groundwater recharge is generated in karst areas [51,52], with renewable groundwater being defined as “any groundwater that can be dynamically captured during pumping that leads to a new dynamically stable equilibrium in groundwater levels within human timescales”. This means that we can transform the depleted Eocene aquifer into a sustainable layer if we can secure sufficient recharge to restore the dynamic balance to its previous state.

Drought is a major driver of crop yield volatility and, in particular, causes low yields that can lead to substantial financial losses [53]. Future predictions of precipitation, temperature, and evapotranspiration are uncertain, where the rapid increase in surface temperature correlates with declining biodiversity, including higher extinction rates [54,55]. Quantifying the spatiotemporal interactions between groundwater and the climate is essential [56]. However, the current understanding of the global-scale sensitivity of groundwater systems to climate change and the resulting variation in feedback from groundwater to the climate system is limited [57,58,59,60]. Therefore, we used remote sensing techniques via Google Earth Engine with several indices that showed no effect of climate factors on groundwater systems between 1981 and 2024 in the study area; these techniques allowed us to identify the type of drought experienced by the region, which is hydrological drought; conversely, groundwater may influence the climate through evapotranspiration and has a climate-cooling and wetting effect [61]. We studied this by exploring the potential artificial recharge of the Eocene aquifer.

This study aims to address the issue of drought by exploring the potential of this region to overcome water scarcity through artificial groundwater flow in geological media. Therefore, we resorted to using a Geographic Information System (GIS), and we used many software programs including ArcGIS Pro 3.3, Global Mapper 22, and AutoCAD 2021 due to their importance in modeling and simulating the supposed water table to be raised to a level close to the surface, developing methods to implement artificial groundwater recharge using sustainable and clean surface resources. In addition, GIS and statistical indicators contributed to the evaluation of the optimal design procedures for dam and tunnel construction, as well as their mechanisms of action during groundwater flow and control. The project’s results are presented in detailed maps.

2. Methods

We relied on the inductive approach, considered one of the most closely related to the reality of such studies [62]. This approach discusses many natural topics that have the same target. The methodologies outlined below served as our guiding framework.

The study focuses on southern Lebanon, which is situated between the Mediterranean coast on the west and the mountain peaks on the east. It encompasses numerous hills and valleys that span from sea level up to 800 m in height. The region extends northward to include the highlands of Al-Tuffah, located on the western slopes of Mount Al-Rayhan. Moving westward from there, the region descends toward the coast and stretches to the borders of Palestine in the south. The study area is located between longitude 35°18′ and 35°50′ east and between latitudes 33°5′ and 33°30′ north, covering 1000 km² (Figure 1); the region is estimated to have a resident population of approximately 200,000.

2.1. Data Sources

We used various satellite data sources, including Landsat 8 and 9, MODIS, Tropical Rainfall Measurement Mission (TRMM), Global Precipitation Measurements (GPMs), Multiple Satellite Constellation (IMERG), and Soil Moisture Active Passive (SMAP) (

Table 1. Satellite and sensor data types and their resolutions [19].

Parameter	Satellite	Sensors	Spatial/Temporal Resolutions and Coverage
Precipitation	Combined TRMM and GPMs With Multiple Satellite Constellation IMERG	Microwave radiometer (TMI, GMI) and RADAR (PR, DPR), microwave imagers and sounders calibrated with GPM sensor data	0.1° × 0.1° 30 min, daily, monthly, 06/2000 to present
Soil Moisture	SMAP	L Band Microwave Radiometer	9 km × 9 km and 36 km × 36 km every 2–3 days, 3/2015 to present
NDVI	Based on MODIS Terra Vegetation Indices 16-Day Global 250 m, long-term mean	MODerate-resolution imaging spectroradiometer (MODIS)	2350 km swath 12/1999–present; generated from the MODIS/061/MOD13Q1
	Landsat 8	Operational land imager (OLI and OLI2)	30 m, 185 km swath, every 16 days, 02/2013–present
	Landsat 9	Thermal infrared sensor (TIRS and TIRS2)	30 m, 185 km swath, every 16 days, 09/2021–present
	Sentinel 2A and 2B	Multi-spectral imager (MSI)	290 km swath; 10 m, 20 m, 60 m; every 5 days, 6/23/2015 and 3/7/2017–present

), as well as field and practical data from studies of dozens of artesian wells drilled in the region. We also used topographic, geological, and water resource data from the National Remote Sensing Centre and Climatic data from the climate department at Beirut Airport and a private weather station.

2.2. Remote Sensing

We used remote sensing to assess the three drought types and identify areas of vulnerability using the above satellite data sources. We used the Google Earth Engine (GEE) platform, which provides a comprehensive collection of environmental data sources and relevant satellite imagery to perform this task. This platform also allows for the collection of a large number of multi-temporal images of a single location and enables the generation of drought-specific indices (Standardized Precipitation Index (SPI), Vegetation Condition Index (VCI), Normalized Difference Vegetation Index (NDVI), and Soil Moisture Anomaly Index (SM)) by incorporating available data that best serves the project objectives.

2.3. Geographical Information Systems

We utilized engineering software such as ArcGIS Pro v3.3 (overlay, editing, spatial analyst tools), Arc Map v7.1 (interpolation, conversion, analysis tools), Arc Scene v7.1 (3D tool), Global Mapper v22 (classification, combine/compare tools), AutoCAD 2022, and GEO5 to map and analyze the geological strata and aquifers, examining their spatial distribution, inclinations, curvature, and fractures. To assess their physical and chemical properties, we identified suitable points and locations for horizontal tunnel excavation based on the physical characteristics of the Eocene Strata, and we determined and modeled water table levels to address groundwater drought.

2.4. Modeling and Simulation

We utilized modeling and simulation software such as ArcGIS Pro 3.3 (simulation and modeling tools) to map and simplify the representation of the complex reality in the process of recharging groundwater aquifers and predict the path of the water level, whether surface or groundwater, after building the dam through simulations within the standards available in the study area.

2.5. Geomorphic Indices

We conducted a comprehensive morphometric study of river basins and permanent water courses using mathematical equations and algorithms to determine the optimal dam location based on geological considerations.

2.6. Statistical Techniques

Spearman’s correlation coefficient was relied upon to identify morphometric indicators that were strongly related. Morphometric indices that departed from the correlation values between indices with strong correlations were rejected. The selection was dictated by a non-normal probability distribution of one of the parameters (p < 0.05) [63,64] based on the Shapiro–Wilk test for normality [65].

3. Results

3.1. Climate Elements and Water Resources

Precipitation, Temperatures, and Evaporation in the area

Scientists agree that climate change will have a tangible impact on the supply, demand, and quality of water resources in the Mediterranean basin, which will increase pressure on these resources and on ecosystems in general [66]. The latest statistics from the EEA’s [67] State of Lands and Water report forecasts actually predict that by 2025, draft frequencies will increase by 20 to 60%, and by the end of the century, annual rainfall will decrease by between 8 and 10 mm, with large variations across the region and across different seasons, which will affect agricultural seasons. This region falls under the influence of the Mediterranean climate, which is considered a transitional climate between cold temperate regions and semi-tropical desert regions. In winter, it is exposed to moderate climatic influences; that is, it comes under the direct influence of rainy westerly winds, represented by the upper subtropical jet stream, whose meandering allows cold air masses (cold air valleys) to reach the eastern basin of the Mediterranean [68], accompanied by the emergence of air depressions on the surface caused by the warmth of its waters. This results in an unstable situation that leads to rain, which, in turn, forms snow in the mountain highlands.

The westerly current recedes in the summer toward the upper temperate latitudes, and the subtropical high-pressure centers in the upper strata advance toward the eastern basin of the Mediterranean, resulting in a state of stability that leads to a rise in temperatures.

Precipitation of all kinds is the primary support for water resources [69]. The Standardized Groundwater Level Index (SGI) builds on the Standardized Precipitation Index (SPI) to account for differences in the form and characteristics of the groundwater level and precipitation time series [70]. The study area received annual precipitation between 600 and 1300 mm (Figure 2), especially at higher elevations on the mountain slopes. We used the completely regularized spline, which is one of the radial basic function (RBF) methods for evaluation and mapping the annual rainfall data in ArcMap, which is the optimal method compared to others [71]. It is an exact interpolation technique. The resulting smooth surface passes exactly through the input points, and the greater the value of the number of points, the smoother the surface of the output raster. The average annual volume of precipitation is approximately 650 million m³, and more than half of the study area receives an average yearly precipitation exceeding 700 mm. The general average annual rainfall in the study area is 723 mm, which indicates that the region is not considered an arid or semi-arid region. Still, it is classified as a semi-humid region instead, as it depends on rain-fed agriculture. Spring is the reason for its growth and its continuation during the dry season.

Several decades ago, these quantities of precipitation were sufficient to meet the population’s need for water resources due to the simplicity of life and the reliance on the rainwater provided by nature—collecting and storing it for the summer—in addition to the availability of easily accessible surface water, such as that in canals. The governorate’s residents can quickly reach spring streams and small springs. Because the region’s rivers are far from places of settlement, as they flow through steep gorges with rugged paths, residents cannot benefit from these permanent watercourses. In the current era, with its large increases in population, the development of lifestyles and luxury, and technological progress allowing humans to benefit from groundwater—even depleting it to dangerous levels—there has not been adequate investment into rivers, e.g., by building water projects on them. This situation has placed the study area in the dilemma of having insufficient water resources to meet the population’s needs.

Temperatures directly affect water resources in the study area, as they contribute to increased rates of evaporation from the surface and the upper layer of soil [72]; this also negatively affects water infiltration and, thus, groundwater.

The climatic changes occurring in the eastern Mediterranean basin region have been described in several recent relevant studies [14,73,74,75,76].

In the study area, the average minimum recorded temperatures do not fall below 0 °C, except on very few days of the year, and they are limited to between 0 and 16 °C. The average maximum temperatures recorded are limited to between 15 and 35 °C. This does not prevent the temperature on some days from registering a noticeable increase to approximately 40 °C.

This indicates that the climate of the study area is moderate and that the summer months, which are characterized by high temperatures, are considered relatively moderate, as the temperature rarely exceeds 35 °C.

The temperature averages show an upward trend and are statistically significant with an error rate of 5% according to the Mann–Kendal index, and they reach a threshold of 1% at the Beirut station. In the climatic data available to us for the study area, we detected a shift in temperature with an upward trend; a report prepared by an international team within the framework of the Fifth Assessment of the United Nations (67) indicated that the last three decades have witnessed a gradual increase in temperature on the Earth’s surface. This temperature trend is statistically significantly increasing with a 5% error according to Spearman’s arrangement. At the airport station, it has been shown that the annual temperature rates are rising in an unprecedented manner (

Table 2. Annual average temperature in Beirut, Lebanon.

year	1975	1976	1977	1978	1979	1980	1981	1982	1983	1984	1985	1986	1987	1988	1989	1990	1991	1992	1993	1994	1995	1996	1997
degree	22.5	20.1	25.1	22.3	22.6	22.5	22.4	20.7	23.2	23.2	23.4	23.8	23.2	23.6	23.2	23.1	24.1	22.6	23.2	24.4	24.4	23.3	23.5
year	1998	1999	2000	2001	2002	2003	2004	2005	2006	2007	2008	2009	2010	2011	2012	2013	2014	2015	2016	2017	2018	2019	2020
degree	23.9	24.9	24.1	24.6	24.4	24.4	24.3	25.0	24.1	24.0	24.8	24.8	25.6	25.6	25.3	24.1	24.1	24.3	24.7	23.6	25.9	24.5	25.6

, Figure 3).

We calculated the increase in temperature using the equation shown in Figure 3: y = 0.0381x + 23.231, that is, we multiplied the (variable) slope by the number of years (0.0381 × 46 = 1.75), meaning that the temperature at the Beirut station increased. At 1.75 °C, over approximately four decades, this will negatively affect the water resources in the study area due to the increase in evaporation and transpiration with the increase in the temperature because evaporation is directly linked to the water balance equation.

This increase in temperature will change the patterns of entire ecosystems and will even have a direct impact on many other climatic elements, such as the expansion of the dry season and the dominance of drought over more lands in various parts of the world [77]. The rainy season is limited, as we mentioned previously.

There may also be a direct impact in the form of an increase in consumption rates, which, in turn, will reflect negatively on the water resources in the study area.

Temperature is an essential climatic element and plays a vital role in water balance, as well as other climatic elements and geomorphological processes [69]. Average temperatures in the Middle East increased by 1.5 °C according to the IPCC (2018). This increase is the result of global warming [78]. The Middle East will suffer a 17% drop in available freshwater when temperatures rise by 2 °C [79].

The average volume of evaporation in this region (private weather station) is estimated at 43–51% of the volume of precipitation [68]. This percentage of evaporation has a significant and negative impact on the region’s water resources and, particularly, groundwater. As high daily evaporation rates lead to the impoverishment of the soil and the water in the upper rocky Strata, when the soil is dry, water will not flow for a significant distance until the water content in the soil becomes sufficient and the pressure head becomes less harmful. The specific discharge is measured with an equation from Cushman and Tartakovsky [80]:

q = −K (θ) ∂h/∂l

(1)

where q is the discharge and θ is the water content of the soil (θ volumetric soil water content (m³/m³).

The maximum infiltration capacity is not reached because the unsaturated hydraulic conductivity is not at its maximum (Equation (1)). When the daily volume of precipitation is low, the rock strata do not benefit from precipitation because of their rapid evaporation.

We thus conclude that the temperatures in the region are a natural obstacle to facilitating the infiltration of precipitation to the underground strata. Conditions tend to become more dangerous with the advancement of time due to climate change because the annual rainfall amounts are expected to decrease, in addition to the decrease in the rainy season in the eastern Mediterranean basin.

Evaporation rates vary depending on various natural conditions; the evaporation rate is considered the engine of the general hydrological cycle and is its first element.

Drought in the Mediterranean basin is expected to increase by 10% if temperatures rise by 1 °C. This would contribute to taking the region toward desertification, exacerbating the current conditions of the water problem, and increasing pressure on water resources [74]. This affects the production of wheat, olives, vines, and all kinds of vegetables, and the population in the study area depends on these crops for their livelihood. The probability of fires occurring will increase, in addition to the effects resulting from human pressure on natural resources [81].

The impact of climate change on the Mediterranean basin may affect the groundwater reserves of freshwater. Climate change has direct and indirect negative effects on the economy. We should not ignore the anomalous weather conditions that may occur due to these changes and fluctuations in climatic elements around the world—especially waves of intense heat or extreme cold in which temperatures are noticeably higher or lower than their annual average in a particular region.

3.2. Tectonic Influence on Water Resources

Tectonic activity is the predominant source for the formation of geological features [82]. Tectonism determines the inclination of these strata and produces faults, fractures, cracks, and torsions, which are considered one of the quickest and easiest ways to move and direct groundwater [83]. Rainwater that infiltrates through the cracks created by these movements and the joints between the rocks is held there and becomes a factor contributing to the karst process and the formation of groundwater. Tectonic pressure resulting from the formation of the Red Sea between the African and Asian continents in the Miocene era led to the continental break-up between Africa and the Sinai Peninsula on one end and the Arabian Peninsula on the other [84]. A group of longitudinal strike-slip faults appear to the south, starting from Aqaba and passing through the Wadi Araba Depression, the Jordan Valley, the Dead Sea, and Lake Tiberias, all the way to Lebanon, Syria, and the Anatolian Mountains of Turkey, with a length of approximately 1200 km [84,85].

These tectonic forces have led to major faults in the study area with large dimensions in terms of lateral (several kilometers) and vertical (several hundreds of meters) displacement and the appearance of fractured and collapsed zones. In addition, the extension of significant faults has resulted in the fracturing of Cretaceous and Tertiary limestone [83]. This has resulted in several transverse fractures and longitudinal ripples, including the Bint Jbeil syncline and Jabal Amel anticline, which are adjacent to each other. Fractures and ripples aid in forming underground reservoirs that store infiltrated water, where fractures play a positive role in accelerating the passage of this water to the depths.

The southern Lebanese region has experienced relative tectonic stability since the Late Cretaceous–Eocene period, but it was later subjected to a series of minor movements [86].

The deformation that resulted from the pressure exerted on the strata in the study area created many convex and concave ripples (syncline, anticline) that were interrupted by some fractures. Some of this deformation contributed to the formation of important underground reservoirs in the region.

-

Nabatieh–Bint Jbeil Concave: This concave takes the shape of a rectangle from the south, at the Lebanese–Palestinian border, to the north, in the Iqlim al-Tuffah area (Figure 4 and Figure 5). Its surface is covered by continental Neogene limestone rocks (Mcg), followed by Eocene rocks (E2) in the center of its axis, and on the edges, Cretaceous rocks (C4) appear. Moreover, due to the high horizontal pressure on the sides, the rock masses thinned in the middle and formed a concave ripple, or what is referred to as a syncline. The main factor in its formation was the presence of resilient and soft rock strata that tectonic movements could not break (Senonian C6 and Albian C3), which allowed it to form the rocky undulations that contributed to its formation. The axis of this concave inclines from the north and from the south toward the center at the stream of the Litani River [87], while its sides are unequal and incline toward Al-Hula in Palestine (Figure 4).

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The convex of Jebel Amel: This convex is complementary to the concave of Nabatieh–Bint Jbeil from its western side. It begins to slope toward the sea from its axis at the town of Ansar in the district of Nabatieh and the city of Bint Jbeil (Figure 4 and Figure 5), and it contributes to groundwater flow to the sea, causing springs to discharge several kilometers from the shore, opposite the city of Tyr and the town of Khaizran.

Fractures can develop and evolve due to various factors, such as tectonic activity, heightened fluid pressure, and fluid erosion. Researchers have extensively studied these factors [88,89].

Fractures are well developed in carbonate rocks, which are consolidated rocks [90], such as those found in the study area, and they have secondary porosity that allows water to be filtered and stored in these multi-set voids.

During the search for groundwater, we use fractures as the most important clues, as they create voids and separations in rocks and, thus, increase their porosity and permeability.

Most of the fractures in the study area are of a type involving a thrust fault and a lean-slip fault in which the upper block, above the fault plane, moves up and over the lower block, and there are also secondary faults that appear to be semi-parallel. The general direction of these faults is northeast–southwest. Moreover, there are occasional minor fractures (lineaments) in all directions (Figure 6).

The fractures reach deep underground strata (Figure 6), that is, more than 400 m below the surface of the Earth, but the presence of an impervious and soft rock layer (Senonian) between two hard strata (Eocene and Cenomanian) prevented water from leaking from the upper stratum toward the lower one and contributed to the exacerbation of karst processes within it. This made the Eocene layer an ideal layer for groundwater storage and flow.

3.3. Stratigraphy and Lithology in the Study Area

The lithological characteristics of exposed rocks play a major role in the groundwater recharge rate. They act in two ways: first, they percolate surface water to the stratum underneath, and second, they store water in rock voids, fissures, and bedding planes [91].

The lithology was identified using the available geological maps [92]. The lithological distribution in the form of classes was obtained according to formations attributed to Quaternary, Neogene, Paleogene, Cretaceous, and Jurassic deposits (Figure 4 and Figure 6).

Each rock formation mentioned in the study area has similar depositional and stratigraphic sequences from top to bottom, with few diverse rock beds intervening. The main rock components, including the stratigraphic sequence, the interbedded rock strata, and the thickness of exposed rocks in the total sequence, were determined for each rock formation.

In addition to the Cretaceous and the Paleogene, which are separated by the Senonian insulating layer (C₆), the study area has a small area with other strata (bc, c3, c2b, c1, J, and Mcg), as well as a small area with Quaternary sediments (Q) (

Table 3. Lithological characteristics of strata in the study area.

Time	Age	Code	Name and Nature of Rocks	Area/km2	Permeability % from Annual Precipitation Amount
Secondary	Jurassic	J7	Portlandian oolitic limestone	13	15–35
	Cretaceous	bc	Neocomian–Barremian basalt	6.7	0
		C1	Neocomian–Barremian sandstone	31.4	10–20
		C2b	Abtian dolomite	16.7	30–35
		C3	Albian marly limestone and marl	15	1–3
		C4	Cenomanian dolomitic limestone	388.6	34–41
		C6	Senonian marl	119	2–3
Tertiary	Paleogene	E2	Upper Eocene marly and chalky limestone	307.5	20–35
	Neogene	Mcg	Miocene conglomeritic limestone	16.4	9–20
Quaternary		Q	Quaternary deposits	11.6	5–10
Total				926

).

The calcareous strata make up 95% of the area (Table 3). These limestone formations have high porosity (30–40%), suggesting high permeability [91,93,94] due to their physical properties. This is firstly due to the presence of small intergranular voids, allowing it to retain quantities of water. Moreover, a connection between these spaces enables the water to pass through them to form vast stores of freshwater inside the depths of the ground, referred to as aquifers. The geological formations located in the study area are considered suitable for storing vast amounts of water and have favorable conditions for the karstification process within their rocks [21].

• The Cretaceous period:

The formations of this period are considered the most widespread in the study area (Figure 4), with an area of approximately 580 km². This is a positive indicator regarding groundwater reservoirs [95]. This era is divided into the Lower and Upper Cretaceous. Lower Cretaceous, consisting of the base of Cretaceous (C1) and Albian (C3), includes rocks that are distributed in relatively small areas on the outskirts of the study area.

The Upper Cretaceous, consisting of C4–C6, includes Cenomanian rocks (C4), which are considered the most widespread and important, covering approximately 389 km² of the general area. They are groups of dense, pale yellow dolomitic rocks at the top with gray and white limestone rocks at the bottom (C4c), and the limestone rocks are interspersed with some marly sections (C4b and C4a). Their thickness reaches more than 600 m, and they are frequently fractured. These units contain quartz nodules and a large number of burials within them such as marine and terrestrial fossils. Senonian rocks (C6) are gray marly rocks, chalky limestone, and impervious marly rocks that often contain siliceous sections. They are considered the ceiling of the Cretaceous period. These are often exposed in isolated low-lying areas. Their thickness reaches 150 m, and they contain some solid black phosphate and petroleum rock conglomerates.

The Eocene (E2) formations are located over a large area of approximately 307 km² (Figure 6). The rocks of this period are sedimentary and are marly limestone rocks with siliceous sections, dolomitic limestone, soft limestone, and hard coastal limestone. The thickness of this layer in the study area is estimated to be between 300 and 400 m [87].

3.4. Geomorphological Features

Groundwater fluxes are most strongly driven by topographic gradients [96]; the regions where changes influence the movement of groundwater in the elevation of the land surface are highly consistent with water tables that are regulated by topography [97].

The study area contains a large number of plateaus and hills [98] and is divided by the Litani River into two natural parts; the first is the northern part, represented by the Nabatieh region, and the other is the southern part, represented by the areas of Marjayoun and Bint Jbeil (Figure 7).

The northern section is a plateau with an average height between 450 and 500 m above sea level, with the exception of its northern area, represented by the Iqlim al-Tuffah region, which reaches a height of 1400 m at the town of Jbaa. This plateau generally slopes toward the west with an average slope of 5%. The southern section is similar to the northern section in terms of its topography, but its height above sea level varies between 550 and 950 m (Figure 7). The highest part is on the outskirts of the town of Maroun al-Ras. Then, the elevation decreases by 350 m toward the north on the banks of the Litani River. On its east, it is 550 m above sea level, and on the western side, it is 450 m. The general slope of this section is from the south toward the north and west.

The study area is approximately 50 km long and 15 to 17 km wide. It contains a large population, exceeding 200,000, which leads to great pressure on the water resources in this region.

3.5. Karst and Rock Permeability Are Positive Indicators of Groundwater

Geological media are classified into three categories based on their pore structures: porous, cracks, fractured, and karst [99].

The Middle Cretaceous period rocks, especially the Cenomanian (C4) and Eocene (E2) rocks, are characterized by a very high permeability that occupies a large part of the study area. This positive indicator is addressed later, as this very high permeability allows water to penetrate the rock to great depths. When it reaches insulating strata, it forms vast underground reservoirs, especially since the permeable strata in the region are thick.

Senonian Cretaceous roof rocks (C6) are considered impervious rocks. These rocks lie between Cretaceous and Eocene rocks, making the Eocene layer a phreatic subterranean reservoir (free aquifer or saturated thickness).

In Lebanon, carbonate rocks are considered ideal for karstification and the resulting manifestations, such as sinkholes and caves [83]. Many extensive studies have been conducted on karst phenomena in Lebanon [100,101,102,103], where karst geomorphology, such as sinkholes, doline, tunnels, grottoes, and underground rivers, is present.

Karstification is the process of dissolving calcite, CaCO₃, the main component of limestone rocks. As water passes through the soil into the ground, it carries monoxide carbon gas with it, which begins the process of dissolving the internal parent rock and leads to the formation of internal gaps, passages, and caves due to the high acidity of the water.

Karstification is a significant and very influential factor in our study in terms of finding solutions, such as when choosing a location for a project (surface or underground).

3.6. Assessing Drought Conditions on the Surface and in the Subsurface Using Remote Sensing

Remote sensing technology is crucial for assessing surface and subsurface drought conditions [98,104]. This technology provides valuable information on various drought types and indicators that are mathematical representations of water deficit (and excess) compared to historical data, such as the Standardized Precipitation Index (SPI), Normalized Difference Vegetation Index (NDVI), Vegetation Condition Index (VCI), Soil Moisture Anomaly Index (SM), and unconfined groundwater levels, which can help experts understand the severity and extent of drought conditions according to NASA and National Drought Mitigation Center criteria [19,20].

By analyzing remote sensing imagery based on the reflectance and/or emission of electromagnetic radiation, passive (Sentinel 2) [105,106,107,108], active (Sentinel 1) [109,110,111,112], thermal (Landsat 8) [113,114,115,116], and optical (most satellites) [116,117,118,119] data can be obtained. Experts can develop effective drought and groundwater management strategies and take timely action to mitigate the impacts of drought on the environment and human activities.

The Standardized Precipitation Index (SPI) (Figure 8) is primarily defined to characterize meteorological drought, whereas historical rainfall data at any location fitted with gamma distribution represent cumulative probability function; therefore, if a rainfall event carries a low probability on the cumulative probability function, it is indicative of a drought event.

The SPI values can be interpreted as the number of standard deviations by which the observed rainfall anomaly deviates from the long-term mean, and its average over different periods (3, 6, 9, and 12 months) indicates the severity and duration of drought [120].

Figure 8 from the Google Earth Engine (GEE) shows the SPI resulting from the combination of the satellite Tropical Rainfall Measurement Mission (TRMM) and Global Precipitation Measurements (GPMs) with multiple satellite constellation (like Sentinel 2A, 2B, etc.), The observed period of the study area for the SPI begins on 1 January 1981 and ends on 25 July 2024; it shows that the region is near level 1, meaning that the study area is not exposed to meteorological drought.

VCI: MODIS data are used to calculate the Vegetation Condition Index (VCI) (Figure 9) for a specific time and location. The VCI is expressed as a percentage and is an indicator of the status of vegetation cover as a function of NDVI minima and maxima encountered for a given ecosystem over many years. It is a better indicator of the water stress condition than the NDVI [19]. The deviation of the vegetation condition is an indicator of the intensity of the impact of drought on vegetation growth.

The Normalized Difference Vegetation Index (NDVI) normalizes green-leaf scattering in near-infrared wavelengths with chlorophyll absorption in red wavelengths. It measures the greenness and density of vegetation captured by a satellite image. By calculating the difference between two bands, visible red and near-infrared, we can determine that healthy vegetation has a very characteristic spectral reflectance curve.

To obtain the VCI in GEE, we define a variable that selects the NDVI band from the MODIS 16-day image collection and map the function across the collection, then we define variables that derive the minimum and maximum NDVI values across the image collection at the pixel level; we then define variables for differencing NDVI images, minima, and maxima encountered. Then, we export the image to Arc-GIS for mapping it.

Figure 9 shows the study area un-exposed to agriculture drought according the NDVI and VCI indices.

The Soil Moisture Anomaly Index (SM) (Figure 10) uses the SMAP satellite, whereas the NASA Land Information System (LIS) provides a framework for the comprehensive characterization of the land surface and hydrological extremes such as drought [121]. The SPoRTLIS provides real-time surface fields and soil moisture percentiles to determine drought. This indicator is considered one of the most accurate indicators of surface and subsurface hydrological drought, as the exploration range reaches 2 m under the soil and at successive and distant periods.

We create this index using GEE by defining a variable for the SMAP 9 km Surface and Root Zone Soil Moisture product.

Figure 10 shows that the region has been extremely exposed to hydrological drought, due to many natural and human reasons, as the recharge of the groundwater layers was affected by the reduction in the rainy season and the abnormal amounts of rainfall in a short period, in addition to the excessive extraction of groundwater in this region.

3.7. Hydrogeological Concept and Groundwater in the Study Area

Seepage is the transfer of precipitation or surface water through the pores and small cracks of rocks into the ground.

Seepage is the displacement of precipitation or surface water through rock pores and cracks into the ground. This water typically originates from precipitation and minor seepage from rivers and lakes, though riverbeds and lake bottoms often have clay layers that limit this process. Without such layers, water seeps through and is halted by an impermeable layer. The hydraulic properties of rocks affect how water seeps; porous rocks have uniform properties, while karst and fractured limestone are more variable due to localized karst formations [122].

In the study area, 90% of rocks are prone to karst processes, affecting groundwater estimations. Surface water-bearing strata in the area include the Eocene Strata, which is an unconfined aquifer or saturated thickness and is influenced by atmospheric pressure and gravity. The Senonian (C6) layer blocks seepage, leading to impermeable strata. An aquifer can be described as a physiographic unit containing a single large aquifer or several interconnected aquifers [123]. There are two water-bearing strata in the study area: the Eocene layer (E2) and the Cenomanian layer (C4) (Figure 4 and Figure 6).

3.7.1. Eocene Aquifers

Physical Characteristics

The Eocene aquifer is a free aquifer with a saturated thickness, extending from the Triassic period and largely exposed in the study area, except for a small portion covered by recent Quaternary strata. It drains non-artesian, flowing into karst springs or where it meets insulating strata, particularly the Senonian, which separates it from the Cretaceous strata. Composed of highly cracked limestone, dolomite, siliceous, and marl sections, it stretches from the northern Iqlim al-Tuffah area to the southern Aitaroun, near the Palestinian border (Figure 4 and Figure 6). Its thickness ranges from 300 to 400 m [87] and is subject to significant karst processes due to precipitation and other factors, allowing rainwater to penetrate through cracks and fissures.

The Direction of Groundwater Flow

Groundwater moves through rock pores, cracks, and fissures according to Darcy’s Law, influenced by permeability and hydraulic gradient [123]. This movement can be tracked using non-toxic tracers [124]. Water velocity in limestone ranges from 0.6 to 6 m per day. The Eocene aquifer’s flow extends into the Nabatieh–Bint Jbeil ripple from both east and west, with some springs appearing along the Litani River.

Natural Recharge Eocene Aquifers

Water balance equation:

GWr = [P − (ET + R)] × S

(2)

GWr = the average volume of precipitation recharge;

P = the average annual volume of precipitation over the area of the underground reservoir;

ET = the average evapotranspiration, direct evaporation from bodies of water and precipitation, and evaporation through plants;

R = the average surface runoff volume over the exposed area of the underground storage;

S = the exposed area of the rock Strata.

Thus,

The surface of the Eocene aquifer receives abundant amounts of precipitation, estimated at approximately 745 mm.

Surface runoff from precipitation: The percentage of surface runoff from precipitation in the Eocene layer averages approximately 7.5% of the annual precipitation rate, so the surface runoff value becomes approximately 56 mm. Therefore, the equation becomes the following:

GWr/Eocene according to Equation (2) = [745 − (341 + 56)] × 3⁻¹⁰ × 307 ×10⁶ = 106,000,000 m³.

Darcy’s law [125] of laminar flow is as follows:

Re = ρvd/µ

(3)

where Re is Reynold’s number, ρ is the water density, v is the average pore velocity, d is the average pore diameter, and µ is the dynamic viscosity of water at a given temperature.

Hydrogeologists generally accept the assumption of laminar flow throughout granular porous media with Re < 100 for the sake of simplifying the mathematics of flow Equation (3) [126].

Transmissivity is the rate at which water is transmitted through a unit width of an aquifer under a unit hydraulic gradient. It is expressed as the product of the average hydraulic conductivity and thickness of the saturated portion of an aquifer (

Table 4. Characteristics of the Eocene Strata.

Rock Formation	Average Thickness (b)	Area	Hydraulic Properties
			Porosity (Ø)	Permeability (P) % from Annual Precipitation	Moisture Content (ɱ)	Hydraulic Conductivity (k)	Transmissivity T = k×b
	(m)	km2	%	%	%	m/s	m2/s
Eocene	300	330	35–41	38	7–9	10−4	3 × 10−3

).

Darcy’s Law (Equation (4)) describes the flow of groundwater through a porous medium.

$$\mathrm{Q}=-\mathrm{K}\mathrm{A}{\displaystyle \frac{\mathrm{d}\mathrm{h}}{\mathrm{d}\mathrm{l}}}$$

(4)

Q is the volumetric flow rate. K is the hydraulic conductivity of the aquifer. A is the cross-sectional area perpendicular to the direction of flow. dh/dl is the hydraulic gradient. To simplify Darcy’s Law, we can use the Dupuit–Forchheimer assumption:

$$\mathrm{Q}=-\mathrm{K}\mathrm{A}{\displaystyle \frac{\mathrm{d}\mathrm{H}}{\mathrm{d}\mathrm{l}}}$$

(5)

where dH/dl is the slope of the water table. This is often applied to steady-state horizontal flow in free aquifers.

Geometry of the Eocene Aquifer

The Eocene aquifer extends from north to south for a length of approximately 50 km and is geometrically divided into two parts: the northern and southern parts (Figure 11).

The engineering study of this aquifer using geographic information systems and engineering software (Figure 12) showed that the northern section has a general lean of approximately 0.3% from the north toward the center at the Litani River.

The maximum elevation above sea level is approximately 620 m in the area of Iqlim al-Tuffah, and the lowest elevation is approximately 132 m at the Litani River (Figure 13).

The thickness of this layer ranges between 400 m in the northern region and 370 m at the river’s edge, decreasing to approximately 30 m in the river’s downstream area. This is the smallest thickness of this layer in the study area. The southern part of the concave layer of the Eocene layer leans from the south toward the center at the Litani River, with a lean of approximately 0.3% (Figure 11).

The highest elevation of this section above sea level in the southern region is 935 m; it then descends toward the north at the edge of the Litani River by 350 m.

The thickness of this part is approximately 540 m in the south and 400 m in the middle. That is, this part is approximately 140 m thicker than the northern part of the Eocene Strata. The width of this layer that is exposed on the surface ranges from 8 km in the south to 12 km in the center, reaching 3 km in the extreme north.

3.8. Support for the Eocene Aquifer with Clean Water Resources from the Litani River

3.8.1. Morphometric Characteristics of the Litani River Basin in the Study Area

Drainage basin engineering is used to determine watershed surface flow and the drainage mechanism in their basins through indicators based on mathematical relationships, through which one can form a quantitative value for qualitative aspects to help in a more realistic understanding of the aspects of a river basin.

These indicators are numerical indications that provide for the concept and type of flow in waterways during their permanent flow; as a result, one can determine whether a river is suitable for constructing dams or has a great capacity for sedimentation in its stream.

The Litani River is the focus point of these studies, as its annual volume discharge is up to 350 million cubic meters [94].

All values associated with the study area used in the analysis of morphometric indicators were extracted (

Table 5. Morphometric parameters obtained from ArcGIS and global mapper software.

Basin area	400 km2	Total number of streams (permanent and intermittent)	506	Average stream length	0.77 km
Basin perimeter	125.2 km	Shorter stream	0.02 km	H max	1181 m
Main channel length	32 km	Longer stream	3.2 km	H min	30 m
Stream axial length	25 km	Length of all streams	387 km	Basin length	40 km

) through the use of remote sensing (RS) and geographic information systems (GISs) (Figure 14 and Figure 15).

• Form factor (F_f)

The shape factor of a basin (F_f) (Equation (6)) is a parameter that makes it possible to determine its geometry and is related to the flows of the drainage network.

F_f = A/L_c² = 0.25

(6)

A: Basin Area; L_c: Basin length

2.

Circularity ratio (Rc)

This parameter is the ratio between the area of a basin and the area of a circle that has a circumference equal to the length of the basin’s perimeter (Equation (7)); therefore, when values are not close to unity, this indicates that the shape of the basin does not resemble a circle.

Rc = A/P²/^4π = 0.32

(7)

P: Basin Perimeter

3.

Elongation ratio (Re)

This parameter takes a maximum value of 1 for perfectly round basins (Equation (8)). This is the ratio between the diameter of a circle with the same area as that of the basin (D_c) and the maximum basin length (L_c). Furthermore, these values can be grouped into the following forms: a circular form when Re > 0.9, an oval form when 0.9 > Re > 0.8, and a less elongated form when Re < 0.7; this is the form in the study area.

Re = D_c/L_c = 0.57

(8)

4.

Compactness coefficient (Kc)

The compactness coefficient describes the relationship between a basin’s perimeter and a circle with the same area (Equation (9)); the more circular the basin is, the closer the result is to unity; however, this is not the case in the study area.

(Kc) = P/√ πA = 3.53

(9)

5.

Basin relief (H)

The basin relief (H) is defined as the difference between the maximum and minimum height (Equation (10)). It plays an important role in the superficial flow and development of the drainage network, permeability, and susceptibility to soil erosion.

H = H_max − H_min = 1151 m

(10)

6.

Hypsometric Curve of the Basin

The hypsometric curve is the area in km² between two levels. It provides a graphic representation of the basin relief, where the ordinate represents the elevation above sea level in meters and its abscissa.

7.

Rainwater Harvesting Potential Index (RWHPI)

The planning of water harvesting projects is a multi-criterion problem because it depends on several factors. Rainwater harvesting (RWH) is one of the most common practices for mitigating water scarcity.

8.

Drainage density (D_d)

(D_d) = L/A = 0.08

(11)

L: Main channel length of the stream

Drainage density (D): The ratio that defines the drainage density represents the number of rivers in the catchment needed to drain a basin [127] (Equation (11)), and it describes the drainage distribution and spacing in a watershed or the total length of channels per unit area [128].

9.

Constant of channel maintenance (C_m)

(C_m) = 1/D_d = 12.5

(12)

The constant of channel maintenance (C_m) is the ratio between the area of a drainage basin and the total length of all channels (Equation (12)); it is equal to the drainage density [129].

10.

Stream frequency (F)

(F) = N/A_d = 1.26

(13)

N: Total stream number of the Basin

The stream frequency (F) is the number of stream segments per unit drainage area (usually per square kilometer) (Equation (13)). Dense networks have high stream frequencies.

11.

Stream length ratio (R_l)

(R_l) = L_u¯/L_u¯−1 = 3.34

(14)

The stream length ratio (R₁) (Equation (14)) is the ratio between the mean length of streams of a particular order and that of the next-lowest order.

12.

Bifurcation ratio (B_r)

(B_r) = N_u/N_u+1 = 0.998

(15)

This indicates an understanding of the runoff behavior and the shape of the basin (Equation (15)), and it is measured for flooding-prone areas. The probability of flooding is high when a short period of concentration is indicated.

13.

Sinuosity (S)

(S) = L/L_a = 1.28

(16)

Sinuosity is a consequence of channel migration processes in meandering rivers (Equation (16)), where flow through a channel sets up instabilities that drive bank erosion and accretion, which change the planform curvature [130].

14.

Mean stream length (L_m)

(L_m) = L_u/N_u = 0.76

(17)

Average stream length (L_m) (Equation (17)): This is defined as the ratio of the length of a stream to the number of streams [131].

15.

Relief gradient (R_g)

(Rg) = Mean Elevation − Mini elevation/Maxi Elevation − Mini elevation = 0.5

(18)

The selection was dictated by a non-normal probability distribution of one of the parameters according to Equations (18) and (19) (p < 0.05) [63,64], based on the Shapiro–Wilk test for normality [65].

$$\mathrm{W}={\displaystyle \frac{({\sum }_{\mathrm{i}=1}^{\mathrm{n}}\mathrm{a}\mathrm{i}\mathrm{x}\mathrm{i})^2}{\sum _{\mathrm{i}=1}^{\mathrm{n}}(\mathrm{x}\mathrm{i}-\overline{\mathrm{x}})^2}}=0.160<0.850 \mathrm{so} p<0.05$$

(19)

The results for the morphometric parameters of the drainage network allowed us to understand the basin’s hydrological behavior. This would make the Litani River’s course suitable for establishing a dam with which one could reserve a huge amount of water, which we will estimate.

3.8.2. Artificial Recharge

Subsurface fluid flow is a complex and interdisciplinary topic involving various scientific and engineering fields, such as hydrogeology, rock mechanics, geotechnical engineering, and earth resource engineering [132,133,134].

This area of study requires a comprehensive understanding of the dynamics of fluid flow through rocks and the associated geological properties.

The artificial recharge of groundwater with available natural resources involves an increase in the volume of infiltration of rainfall or surface water into geological formations carrying groundwater [135]; this can occur via the injection of water through wells or the mitigation of runoff [136], provided that this process is adapted to the topographical and geological conditions and soil type, in addition to the quality of the water with which the recharging will occur, so as not to lead to the destruction of the underground storage and its exclusion from service [137].

Establishing obstacles or dams to inject aquifers using horizontal wells (or trenches perpendicular to the riverbed) from surface watercourses for transport over long distances allows for subsequent leakage [138], especially in the fractured and cracked Eocene rocks, which are characterized by multi-scale heterogeneity due to their geometrical features, which exhibit variations in surface roughness, fracture apertures, fracture density, and connectivity [118,139]. The hydraulic and geomechanical properties of fractured rocks are strongly dependent on these spatially varying geometrical parameters [140,141,142].

This method aims to increase the area of contact between water and soil and extend the time taken for seepage into the aquifer strata [143]. Accurately estimating the pore size and geomorphological features of the rock strata is crucial for ensuring the successful artificial recharge of underground aquifers; for example, karst processes, which are dependent on the injection of water, carry carbon dioxide (CO₂), and this prevents several adverse effects in the process of artificial recharging underground aquifers [144]. Moreover, groundwater flow mainly induces the deformation of fractured and cracked media [145]. This increases the capacity of the aquifer according to an extension of Biot’s poroelasticity theory [146] with the equation of continuum mechanics for coupled hydromechanical processes [145,147,148].

Based on what we studied through the use of geographical information systems and remote sensing of a number of morphometric parameters of the river courses, the characteristics of the Eocene aquifer, and its geometry, as well as the use of several algorithms and mathematical equations associated with them, we confirmed the possibility of establishing a dam on the Litani River to support and recharge the Eocene aquifer.

3.8.3. Dam Properties

Dams are built on river courses based on the functions that are assigned to them.

In addition to natural characteristics, the intended role also has an impact on the specifications for building dams. The study area suffers from water scarcity and a lack of sustainable electricity supply, in addition to slow economic growth and a lack of job opportunities in light of the high unemployment rate and the migration and displacement of a large number of residents of this region [68].

Locating the dam

The first goal of building this dam is to support the Eocene aquifer during the dry season. Accordingly, the location of the dam must be on the rocks of this layer that are visible on the ground due to the geometric characteristics of this Strata, which we discussed previously, especially in terms of its presence within a tectonic concave. Then, we must take advantage of the largest area of water in contact with this Strata, which necessitates the presence of this dam at the furthest point on either end of the boundaries of this Strata.

The topographical factor also has an impact on the determination of the location for building the dam, as it has become clear through data obtained from geographic information systems that the optimal place is where the two edges of the valley converge with each other.

Geologically, the rocks on which the dam is based must be hard and thick so that they are not exposed to natural accidents.

This approach provides opportunities to explore the geological, geomorphological, and morphodynamic controls on the position of the dam.

The distinctive hydromorphological attributes of the Litani River make it a spatial unit that is of interest for dam construction (Figure 16).

3.8.4. Geomorphic Indices for Dam Construction

W_c is the channel width: 11 m. W_v is the valley width: 50 m. L_v is the length along the axis of the valley: 528 m. L_c is the channel length: 1010 m. A is the amplitude of sinuosity: 252 m. λ is the wavelength of sinuosity: 314 m. R_c is the radius of curvature of a meandering river: 54 m. D is the maximum depth of the valley: 190 m.

SI is the wavelength of the sinuosity of the meandering reaches; SI > 1.25 corresponds to highly sinuous or meandering rivers (Equation (20)), whilst values of SI < 1.1 represent straight rivers.

SI = L_c/L_v = 1.9

(20)

Variations in the SI index are mainly controlled by changes in water discharge and sediment load in response to tectonic, climatic, and anthropogenic factors [129,149].

The R_c/W_c ratio is an indicator of meander maturity [150] (Equation (21)). When this ratio is between 2 and 3, the lateral erosion rate is high.

R_c/W_c = 4.9

(21)

This means that the lateral erosion rate is low, and this is the optimal condition for dam construction.

Next, we calculate the river incision factor (If) (Equation (22)), which quantifies the incision in a valley, by comparing the difference between the valley width (W_v) and channel width (W_c) with the valley depth (D) at a specific location.

If = [(W_v − W_c)/D] = 0.2

(22)

Measuring the If index allows for the quantification of the narrowing or widening of a river valley along its course, and a low If value (<10) typically indicates the “V” shape of mountainous valleys.

Since its value is very low (0.2), this indicates that the two edges of the river are very close together; this helps in the construction of a dam with the smallest amount of building materials due to the close distance between the two edges in this location.

Through the intersection of these indicators and relevant natural, ecological, and social data, the specific location for building a dam on the Litani River was determined: “Arid el Ajrad” between the villages of Alman and Zawtar El Gharbiyeh (33.3105°; 35.4500°).

3.8.5. Characteristics of the Dam

To determine the dam’s dimensions, we characterized the dam in relation to the topography of the area and the purpose of its construction. The height of the dam body above the base is the most important factor, as it can contribute to the understanding and study of the quantities of water retained behind the dam, as well as the quantities of water that can feed the Eocene aquifer.

Based on the previous data, morphometric equations, and determination of the optimal location for this dam, we determined the width of the dam at the crest between the two edges of the valley to be approximately 559 m at an altitude of 290 m above sea level. That is, the height of the dam body above the base was 160 m. This was the maximum height of the dam body, and, accordingly, the areas that will benefit from the height of its water table are determined. However, it is possible to benefit from the lower heights of the dam, as the mere presence of the dam in this area will lead to the flooding of the river basin and, thus, support the Eocene aquifer. However, the greater the height, the more the recharging of this layer extends north and south toward areas that are farther away and in need of water sources.

The maximum area of the dam body or the wall facing the river (Equation (23)) was calculated using geographic information systems to determine the dimensions of the trapezoid-shaped dam:

A = (a + b) × h/2 = 47,000 m²

(23)

A is the area, a is the smallest base, b is the largest base, and h is the height.

Worldwide, there are many types of dams, as the type is determined by some natural factors, such as topography, geology, and soil, while other factors are human and economic, such as the goal of constructing the dam. There are also political and military considerations. The aggregate or rock type is the most suitable for the study area because longitudinal tunnels need to be excavated to facilitate the passage of water toward the aquifer. From these excavation materials, we can backfill the dam over a long distance.

For this dam to be safe, the area behind the dam must be backfilled for a distance of more than 100 m, most of which can be secured from tunnels that must be excavated into the rock mass of the Eocene Strata. Then, it is expected that the total volume of the dam in its maximum state will reach about 4 million cubic meters.

3.8.6. Artificial Recharge by Tunnel

The construction of this dam is accompanied by the construction of two main tunnels. The first tunnel extends from the dam lake toward the south for a distance of up to 16 km; spatial analysis of data from the geographic information system showed that when the water level in the dam rises to a level of 290 m above sea level, artificial springs can be created for a distance of 6 km in Wadi Al-Hujair and Wadi Al-Saluki. The height of these two valleys above sea level is approximately 290 m.

Then, several cross-tunnels branch out from the tunnel, with each tunnel not exceeding 2 km in length. They can be used in two cases: either direct artificial springs or a lower water tank very close to the surface. From this idea, we support the reason for the extension of this first main tunnel to a distance of 16 km, as the water in this tunnel will come very close to the surface. Then, the residents of these areas (Shakra, Mays al-Jabal, Aitaroun, Bint Jbeil, etc.) will be able to install wells to depths of 100, 150, and 250 m (maximum) to reach the permanent water source provided by the dam on the course of the Litani River. Note that the region has wells at a depth of 700 m and often suffers from the loss of water sources or the inability to obtain sufficient energy to draw water from these overwhelming depths.

The Eocene aquifer will remain saturated with water that seeped into it from precipitation in the winter because the drainage process was carried out through small springs in the course of the Litani River, and since the dam contains a water level that is approximately 200 m higher than the base of the Eocene Strata, water will be unable to seep out due to counter pressure; this will facilitate the planned artificial refeeding.

This applies to the second main tunnel that extends north toward the Nabatieh area, where the water source will come close to the surface.

The capacity of the Eocene aquifer will be enhanced after filling the proposed dam. On the one hand, it will retain the water seeping into it from 45% of the annual precipitation; this is the percentage of the Eocene rocks’ ability to pass precipitation into the aquifer storage. On the other hand, additional quantities will leak into this layer from the reservoir behind the dam, which holds water, reaching a height of approximately 160 m.

Areas shown in blue indicate where the groundwater level corresponds to the surface of the Earth and where there may be artificial springs or small dams from which to benefit in the summer. Areas in yellow indicate where the water table is within 150 m from the surface. Areas in olive indicate where the water table is within 250 m from the surface (Figure 17), while dark green indicates where the water table is lies between 250 and 540 m from the surface. This is the maximum depth of the Eocene Strata.

The first horizontal tunnel proposed for excavation into the Eocene layer in the study area is shown in Figure 18. This tunnel is supposed to be at an altitude of 200 m above sea level, that is, 70 m above the base of the dam, which would lead to the emergence of several springs in some of the neighboring valleys; these would be considered subsidiary streams of the main river. The streams will flow in these valleys throughout the year because the river will feed them after the dam is built. More importantly, we can build small dams on these streams to reserve larger quantities of water for use later in the summer and to supply the surrounding towns with water for domestic, agricultural, and industrial use.

The groundwater level will rise above the tunnel level. That is, it will rise to 290 m above sea level due to the hydraulic head in the reservoir, where it will be equal to the upper level in the dam. This will allow water to flow rapidly into the rocky voids whose level is less than 290 m, forming several seasonal springs that are likely to cease flowing when the water level in the dam drops below this height. The Saluki and Al-Hojair valleys are among the most significant valleys that will benefit from this process because of their long paths; in these valleys, we can also build small dams with which we can reserve large quantities of water to recharge the Eocene aquifer in the summer.

3.9. Using GISs to Determine Areas Benefiting from Groundwater According to Their Proximity to the Surface

To determine the areas benefiting from groundwater based on their proximity to the surface, after the simulation of the building of the dam, we analyzed the geospatial data using GISs to identify the locations where the water table was closest to the surface. We achieved this by using various GIS tools, such as elevation models, hydrological models, and ArcScene 10.7 software, to create a 3D map that showed the areas closest to the recharged groundwater. By analyzing this map, we identified the areas that were likely to benefit from groundwater according to the depth and accordingly planned four depth levels: 0, 150, 250, and deeper than 250 m (Figure 19).

The quantities of water that can be retained within the Eocene aquifer after artificially recharging using the water of the dam located on the course of the Litani River are determined by the ability of the rock to retain water, which, in turn, is linked to the percentage of voids present in these rocks (porosity), which was estimated to be about 5% (Table 4).

3.9.1. The 0 m Depth of the Water Table

This area extends about 6 km beyond the reservoir; it is located below the towns of Qantara, Toulin, and Burj Qalawiyah. It is situated between 130 and 290 m above sea level, covering an area of approximately 15.5 km². This area is the lower part of Wadi Al-Hujayr, and it is connected at its end with the course of the Litani River (Figure 20).

To ensure sufficient water storage until the end of the summer, it is recommended to establish a small dam in the middle of this valley near the town of Froun. This dam will be able to store more than one million cubic meters of water. The reason for this is the presence of the impervious Sinonian rock layer at the bottom of this valley, which will help to prevent the leakage of water into underlying permeable strata, such as the Cenomanian Strata.

3.9.2. The 150 m Depth of the Water Table

This is regarded as a key region of the water table due to the dam’s construction along the Litani River. The groundwater level will be found at depths between 0 and 150 m for considerable distances to both the north and south of the dam (Figure 21). The altitude in this area ranges from 290 to 440 m above sea level. In the north, water within the Eocene aquifer will reach the towns of Nabatieh, such as Kfarsir, Aba, Ansar, and Harouf, which are among the towns that suffer most from severe shortages of water resources during the summer.

More importantly, the southern regions will benefit from the surface waters being close to 150 m. Because these towns are currently required to drill to depths of more than 750 m to obtain water, this in itself is a major challenge to economic investment in the region.

This level extends away from the course of the Litani River by about 14 km south, reaching the middle of Wadi Saluki, which is located between the towns of Mays al-Jabal, Shaqra, Hula, Majdal Salam, and Bani Hayyan. The residents of these towns will be able to easily benefit from the sustainable groundwater in the Eocene layer due to its proximity to the surface; thus, it does not require excessive investment in drilling operations.

The area covered by this level of groundwater in the Eocene layer is approximately 89 km², and the height of the water there, as we mentioned previously, is 150 m.

3.9.3. The 250 m Depth of the Water Table

Naturally, the greater the height above sea level, the greater the depth from the surface to the water table. This can be applied to our third Strata, in which the groundwater level lies at a depth of between 150 and 250 m (Figure 22). This area includes the towns located next to the city of Nabatieh, such as Kfar Rumman, Habbouch, Al-Duwair, Deir Al-Zahrani, Romain, and Houmin.

Many of these towns experience a significant shortage of water resources during the summer. Thus, the shallower groundwater levels, at depths of 150 to 250 m, represent a notable advantage for easier water extraction. In the southern region, water continues to flow towards the far south, reaching about 18 km from the Litani River. It extends to the borders of the towns of Blida and Aitaroun in the far south, as well as the towns of Al-Suwanah, Khirbet Selm, and Tulin in the west.

The quantities that this level of the Eocene aquifer can store depend on the area of this Strata, which is estimated to be 97 km² based on data from geographic information systems.

3.9.4. The Layer of the Water Table at a Depth of up to 250 m

This layer is concentrated in the far south due to the region’s elevation above sea level, which is more than 900 m. This means that it is normal for the depth of the water table to increase. However, of course, the situation is much better than it was before, as drilling previously reached 800 m to obtain small amounts of water at a high financial cost. However, if this project is implemented, these areas will be able to obtain sustainable groundwater with a maximum depth of only 400 m (Figure 23).

This area is approximately 121 km², and it includes the city of Bint Jbeil and its neighboring villages and towns.

4. Discussion

4.1. Water Projects and Proposed Recommendations to Confront Drought

The Cenomanian aquifer in the region has ample groundwater, but it is located at a depth of over 800 m (Figure 13). The high cost of extraction, coupled with the water often being mineralized and of low natural quality, makes it less favorable to access. On the other hand, the Eocene aquifer near the surface is experiencing a groundwater drought. Therefore, extracting water from the Cenomanian aquifer requires considerable financial investment and the use of high-capacity submersible pumps powered by energy sources that require maintenance throughout the year.

To achieve maximum efficiency in the artificial recharge process, careful hydrological, hydrogeological, and engineering investigations are necessary to select suitable sites for recharge structures [151,152,153,154,155]. By augmenting the natural water supply through increased infiltration of rainwater and surface water into saturated geological formations, we can overcome some of the challenges and dilemmas associated with water resource management [139] by using several methods and techniques, such as injecting water through wells, mitigating runoff, or creating watersheds over hollows, sinkholes, shafts, and some natural geomorphological features [136,156,157,158,159,160,161]; moreover, the quantification of subsurface discharges in highly heterogeneous areas such as alluvial surficial aquifers is ruled by several uncertainty sources [162]

During summer, the water table of the Eocene aquifer drops below 4 m, and its rock thickness can reach up to 540 m (as reported by the Artesian Well Technical Report in Chakra). The aquifer’s southern part, situated in the Bint Jbeil District, leans from the south to the north, while its northern part, situated in the Nabatieh District, leans from the north to the south, with the Litani River separating the two parts. This means that groundwater generally does not flow beyond the study area. Consequently, the thickness of this aquifer increases in the south and is limited at the center (as shown in Figure 11). Based on our analysis, we estimate that the general inclination of these strata is approximately 0.3% from the south and north toward the center at the Litani River.

4.2. Potential Environmental and Ecological Issues

Sustainable water management is a significant challenge in the basin. Thus, the Litani River Basin represents a representative hydrological system for setting water-related SDGs (especially Goal 6).

The Litani River contributes to meeting the social, industrial, energy, and ecosystem functions of more than a million people living in its water basin. It is essential to the national economy.

The lower basin of the Litani River is still untouched by what the upper basin in the Bekaa region is suffering from, where the most significant part of the basin is located where the quality and quantity of water are deteriorating, affecting food safety, threatening sustainable agricultural practices and affecting the functions of ecosystems. The Lower Litani benefits from multiple springs with good water quality [83].

This proposal contributes to meeting the expected outputs from the invested resources and efforts and implementing Sustainable Development Goal 6, specifically Goals 6.1, 6.3, 6.4, and 6.5. These objectives apply to integrated river basin management, considering critical components of river basins, including water, ecosystems, socio-economic development, capacity, and data [163]. Therefore, future missions and programs dealing with environmental management of the Litani River do not need much work to bridge the gap between research and policy and improve water governance, legislation, and institutional capacities.

4.3. Future Research

Groundwater Modeling and Simulation

A model of a ground-water system can be described as a simplified representation of a real-world system that closely approximates its relevant excitation–response relationships. Models are typically simplified compared to reality, which is inherently complex, proposing a set of assumptions that capture the essence of the system and the features of its behavior that are pertinent to the specific problem being studied. Because of this simplification, there is no single model that fits every groundwater system.

The maps presented in Figure 24 describe the modeling of groundwater flow in the free Eocene aquifer (saturated thickness), which was completed using geographic information systems in the Darcy Flow and Darcy Velocity tools, where we obtained raster data to calculate head height from data from artesian wells drilled in the area (Figure 24).

The assumptions made in the model are those through which we can predict the movement of water within the Eocene layer and its directions, in addition to simulating the water table and its levels after the implementation of the dam project.

Although less complex than others, this modeling shows that the groundwater level will rise with the rise in the water level behind the dam to be completed, as these are considered preliminary simulations of what could become. The maps in Figure 24, each of which indicates a distinctive feature and hypothesis that contributes to understanding the movement of water and what the results of the project may lead to from a natural and operational perspective, support improvement of the vision for decision makers. These models confirm, from a scientific perspective and based on hydrogeological data and characteristics, that if this project is completed, the groundwater level will rise significantly, through which we can secure the community’s requirements of clean and sustainable water resources.

Groundwater flow assessment in rock masses is a key issue in the resolution of many engineering, geotechnical, and hydrogeological problems to reconstruct the flow path induced by tunneling and forecast the water inflow location, discharge rate, and water table drawdown [164].

The results of the modeling and simulation confirmed that the groundwater level will rise by the height of the dam on the Litani River, meaning that if we build a dam 100 m high from the base, the groundwater level will rise by 100 m from the bottom of the Eocene layer and over several kilometers to the south and north.

The modeling hypotheses also show that the stakeholders’ benefit from groundwater will be available at low economic costs due to the rise in the water table to areas close to the surface, which will secure large quantities of sustainable water resources for most of the towns located above the Eocene layer, which extends over a length of fifty kilometers.

5. Conclusions

This study created a practical scientific foundation for managing the issue of drought in the southern Lebanon region by utilizing groundwater engineering to address this transboundary problem.

It has been shown that there is a positive connection between groundwater drought and drought in general and that treating the former will have consequences for the latter.

According to the natural study, remote sensing, geographic information systems, and advanced mathematical algorithms were crucial in determining the optimal approach to recharging and supporting the Eocene aquifer for drought resistance and sustainable groundwater management. The research findings indicate that the successful implementation of geological engineering techniques to combat groundwater drought relies heavily on the distribution and structure of geological units. It was demonstrated that morphometric studies and the remote sensing of surface water resources effectively contributed to the identification of the best locations for constructing structures that artificially recharge groundwater. As noted, a dam that is between 30 and 160 m high should be built on the Litani River. This dam will help retain the abundant river water, which gravity can then direct into the Eocene aquifer through horizontal tunnels.

Through this process, we anticipate that the water table in the region will rise toward the surface, leading to the emergence of new springs in the valleys’ depths, which can then be contained through the construction of small dams. We categorized the water table into four distinct levels:

• Level zero: This pertains to areas where the water table reaches the surface, forming sustainable streams, rivers, and swamps.
• The 150 m level: These areas encompass locations where the water table is situated at a depth of 0 to 150 m below the ground surface.
• The 250 m level: This level corresponds to areas where the water table is 150 to 250 m below the ground surface.
• Depths exceeding 250 m: This level encompasses the remaining areas situated above the Eocene Strata, with the water table depth ranging from 250 to 540 m, extending to the base of the Eocene Strata.

This project aims to deliver over one billion cubic meters of clean and sustainable groundwater, meeting the domestic, agricultural, and industrial water demands in the study area.