1. Introduction
The rapid evolution of water needs for economic and social activities indicates that the kingdom of Morocco is currently in a transitional phase between a period when these resources were inexhaustible and the actual state where the current shortage continues to worsen, especially in the southern regions of the kingdom [
1]. This situation is due to the increasing demand for water, the overexploitation of resources, and the shortage of natural supply due to repeated periods of drought that characterize its arid to semi-arid climate [
2]. Moreover, all scientific studies show that Mediterranean countries, including Morocco, are affected by global climate change, including rising temperatures and falling rainfall [
3]. A vast and deplorable waste is noticed also. On a total of 16 billion m
3/year of surface water, 9 billion m
3 are lost by evaporation, flowing to the sea or by existing leaks in the distribution networks [
4]. As a result, and to be able to meet the expressed needs, the country’s natural water resources must be enhanced, according to a coherent overall plan, taking into account the requirements for conservation, prevention, and protection, both in quantity and quality [
5]. The cohesion of any project proposed in the past shows specific weaknesses due to the involvement of various natural parameters, which are generally difficult to assess and, above all, very dependent on climatic hazards and geological conditions [
5]. This fact often complicates any attempt at an effective and appropriate management approach. These weaknesses are felt mainly in the watersheds of the southern regions, characterized by a high climatic contrast compared to those in the north [
6].
In these regions, which are generally densely populated and whose economy depends mainly on agricultural activities, the overexploitation of groundwater leads to a secular decline in the groundwater level [
7]. In addition, the continuous need to increase crop production and the introduction of more water-intensive crops puts increased pressure on these resources, leading to their decline in quantity [
8] and quality. In Morocco, water consumption from irrigation is about 90% [
9]. Understanding its impact on the hydrological cycle is necessary for efficiently managing groundwater resources and promoting more sustainable agriculture [
10,
11]. The high demand for food has shifted the practice of irrigation from surface water to deep groundwater irrigation, leading to its rapid decline [
8,
12,
13]. Morocco’s current total renewable water resources (surface and groundwater) are estimated at 29 billion cubic meters (BCM) per year [
4]. The usable component is 20 billion cubic meters, of which 16 billion cubic meters is surface water and 4 billion cubic meters is groundwater. Approximately 70% of this potential is currently exploited (i.e., 11 billion cubic meters of surface water and 2.7 billion cubic meters of groundwater) [
4]. The depletion of groundwater by these agricultural activities is of increasing concern to groundwater resource managers in Morocco [
1,
5,
14].
The Tata region, located in southeastern Morocco, is currently facing the challenge of excessive exploitation of its deepwater resources, particularly those from the alluvial aquifer, due to the region’s recent agricultural expansion. Agricultural activities in this region require approximately 82 million cubic meters of water (15,000 cubic meters per hectare) [
15]. The annual volume of water used is 69.3 million cubic meters [
15], with 8.3 million cubic meters per year (12%) from surface water and 61 million cubic meters per year (88%) from groundwater. Water balance calculations reveal a relatively significant deficit (15%) for agricultural perimeters. Furthermore, this deficit is expected to increase as agricultural space expands and will undoubtedly hinder the economic development of the region, which has already been weakened by climate change in recent decades. This deficit will be particularly noticeable in alluvial aquifers due to their easy access and high productivity [
16,
17,
18,
19].
Hence, it is of great significance to conduct hydrogeological investigations in this region, which is considered a representative example, where severe climatic conditions and water shortage are increasingly becoming prominent. These factors, in turn, impose a certain level of stringency on the living standards of the populace residing in this area. Young et al. [
20] and Shishaye et al. [
21] have shown the importance of these studies in the characterization of alluvial aquifers.
This research fits this perspective to characterize and update the knowledge on the productivity of alluvial aquifers of the Tata basin and to evaluate the factors that influence it. In addition, this study proposes solutions to cope with the overexploitation of water resources of the alluvial aquifer, which is currently under strong pressure due to the increase in irrigated areas in recent years. To achieve this, an integrated approach was used, combining geological, hydrogeological, and geophysical methods to characterize the aquifer. As part of a wider effort to manage groundwater resources, this study proposes the construction of a recharge dam to replenish the Tata alluvial aquifer. The proposed recharge dam would not only help in mitigating the effects of water scarcity but also contribute to the sustainable development of the region.
2. Study Area
The Tata watershed, with an area of 2567 km
2, is a well-individualized hydrographical system of the Anti-Atlas mountain chain. It is situated in the province of Tata in the southeastern part of Morocco, between Lambert coordinates X (200,000 and 280,000) and Y (290,000 and 360,000) (
Figure 1).
The climate of the basin is continental and semi-arid, with low rainfall (<150 mm/year) and high average summer temperatures (>32 °C) [
22,
23]. The analysis of 70-year monitoring rainfall period data shows alternate humid periods, with a duration of 8 years, followed by more extended dry periods. The range of daily and seasonal temperatures is high (19 °C in winter and 30 °C in summer). The wet period is between October and March, and the dry one can extend from April to September. The average relative moisture values show significant monthly variations, exceeding 40% in summer. They are over 40% in November, December, January, and February, when low temperatures (<16 °C) are registered.
The Tata watershed is compact, with a Gravelius Index of 1.84, and is characterized by a dense drainage network [
24]. About 18 tributaries from the mountain ranges on either side of the valley contribute significantly to the flow of the Wadi Tata. The contribution from springs is very low (<1 m
3/s). The monthly discharge of Wadi Tata is highly variable, because of the large variability in rainfall in the basin.
In economic terms, agriculture is the main activity in the region, with 5500 hectares of irrigated land [
15]. It is developed at the oases where traditional palm groves are irrigated from alluvial aquifers by khettaras, wells, and resurgences [
24,
25] (
Figure 2).
Geologically, the basin is occupied by Precambrian formations composed of granite, gabbro, and schist at the Ighrem, Tagragra, and Agouliz inliers (
Figure 3a). The Paleozoic cover occupies a large part of the basin, including volcano-sedimentary deposits progressing to carbonate deposits of “Lower limestones” topped with pelites of a purplish-red color “Lie-de-vin” followed by carbonate deposits of “Upper limestones” and schists–calcareous series [
26,
27,
28,
29,
30,
31,
32,
33,
34]. Sandstones and quartzites of the Ordovician age occupy the southern part of the basin, followed by Devonian shale and limestone [
35,
36]. Alluvial deposits fill the valleys and form alluvial aquifers [
23] (
Figure 3b and
Figure 4). Structurally, three major fault directions exist in the basin: NNE–SSW, NE–SW, and E–W [
27] (
Figure 3a). NE–SW sills and doleritic dykes related to the opening of the Atlantic Ocean in the Triassic/Lias period traverse all these terrains [
37].
From a hydrogeological perspective, the Tata watershed can be described as a series of parallel ridges intersected by two significant cluses, Tagmout in the north and Tata in the south, which are separated by plains known as Feijas. The Quaternary alluvial filling overlays the Hercynian bedrock in these Feijas (
Figure 5), containing water tables that are primarily utilized for irrigating palm groves. Recharge of the alluvial aquifer occurs mainly through flooding, precipitation, and underground contributions from adjacent plain filling formations, in direct contact with the Adoudounian limestone formations. The marginal limestone formations upstream of the cluses represent ideal recharge zones for the alluvial groundwater due to their highly extensive, fractured, and fissured characteristics. These formations infiltrate precipitation to supply the underflow of the deep valleys.
Apart from the alluvial formations, the basin is dominated by discontinuous aquifers, as illustrated in
Figure 3b, which possess nearly identical hydrogeological parameters. In comparison with the alluvial aquifer, the groundwater storage of these formations is insignificant. In these discontinuous aquifers, groundwater is primarily stored in fractures and crushed zones and circulates within a network of high hydraulic conductivity zones. Discharge of groundwater takes place in river valleys and depressions.
3. Materials and Methods
The methodology employed in this study was based on assessing the correlation between well yield and well depth with the underlying geological formations. To achieve this, a geological map of Morocco was edited in a Geographic Information System (GIS) at a scale of 1:500,000, obtained from the Moroccan Ministry of Energy and Mines. Topographic maps were generated from a Digital Elevation Model (DEM) with a spatial resolution of 30 m, downloaded from the United States Geological Survey (USGS) website (
http://earthexplorer.usgs.gov/, accessed on 14 December 2022). The drainage network was also derived from the DEM data (
Table 1).
Hydrogeological data, including well flows, the resistivity of geological formations, and groundwater piezometric levels, were extracted from borehole logs of 64 wells, obtained from the Drâa-Oued Noun Hydraulic Basin Agency, and tracked from 1970 up to the present time. Furthermore, flood data were used to estimate extreme flows for sizing the future recharge dam to promote water infiltration in the alluvial aquifer.
In addition, a geophysical survey was conducted in the northern part of Tata city to evaluate the recharge capacity of the alluvial deposits by the recharge dam. The survey was conducted in November 2017 using the Schlumberger configuration with a maximum current electrode spacing of 250 m, which yielded the apparent electrical resistivity (ρa, Ω m) at different depths of the soil. Fifteen Vertical Electrical Soundings (VES) were executed and distributed across three profiles. The Schlumberger configuration was selected due to its better resolution, greater probing depth, and less time-consuming field deployment compared to other configurations [
38]. The VES electrode array recorded the electrical current I applied to the outer A and B electrodes, and the potential difference ∆V was measured between the inner M and N electrodes [
39,
40,
41]. The apparent resistivity ρa recorded by the VES can be defined as per Flathe and Leibold [
41], Telford et al. [
42], and Niculescu and Andrei [
43]:
where: ρa = Apparent resistivity (Ohm.m); ∆V = Potential difference (mV); I = Current intensity (mA); K = Geometrical electrode factor (Equation (2)).
The quantitative interpretation of the measurements, previously plotted on a bi-logarithmic diagram, begins with smoothing the curves. Automatic processing is then utilized to perform data inversion, allowing the geophysicist to obtain the correct model through successive approximations until the identification of geological layers. The comparison of these results with well data enables a reasonable estimation of the true resistivities. It is important to note, however, that the theoretical interpretation presented in this scheme assumes that the geological formations explored are tabular, isotropic, and have sufficient resistivity contrast between them [
43].
5. Conclusions
The Tata watershed is a region that contains localized alluvial groundwater in two areas, Tagmout to the north and Tata to the south. The study evaluated the factors that influence the productivity of wells by integrating geological, hydrogeological, and geophysical data in the study area.
Analysis of 64 wells showed that geological formations, such as alluvium and limestone, topography, such as being located in a valley, type of aquifer, and proximity to rivers can all affect well productivity. The most productive wells were found to be associated with shallow alluvial aquifers, with depths of less than 43 m. The study also analyzed piezometric maps to understand groundwater flows. The results indicated that the direction of groundwater flows follows that of surface water, with most of the recharge occurring during flood events. However, the study found that the groundwater level has significantly declined in recent years due to the increase in irrigated surfaces in the area. The government of Morocco has provided financial incentives to the agricultural sector, which has led to increased irrigation, resulting in the overexploitation of the alluvial groundwater.
To address the overexploitation of the alluvial groundwater, the study proposes a recharge dam north of Tata city. The results of the application of the Ecret model show the benefit of this kind of dam for the recharge of the alluvial water table of Wadi Tata. The rate of increase in underground reserves has been multiplied by 10. Additionally, a more detailed analysis of other hydrogeological units such as the basement complex, composed of Precambrian igneous and metamorphic rocks, is necessary to help locate high-yielding wells. The exploration of this type of aquifer will help alleviate the pressure on alluvial aquifers. Future studies should collect additional data and examine the relative influence of each factor on well productivity.
Overall, the study provides decision-makers with an appropriate solution to address the overexploitation of the alluvial groundwater in the Tata watershed, which includes a thorough understanding of the hydrogeological system and further exploration of groundwater using various scientific methods.