Keywords

1 Introduction

Souss-Massa River Basin is one of the most productive agricultural areas in Morocco. Irrigated agriculture produces more than half of Morocco citrus and vegetables [1]. The principal water resource is provided by the groundwater of Souss-Massa aquifer and dams [2, 3].

The diverse geographic, geologic, and climatic characteristics of the Souss-Massa River Basin play an important role in water resource availability, which in turn affects a range of water resource-related activities. The Souss-Massa system is one of the best cases that illustrate the influence of topography, geology, and climate on surface and groundwater flows. Such a large basin area cannot be expected to have uniform climatic and rain patterns; the Souss-Massa shows typical ecosystem zones from Atlas Mountains toward Atlantic Ocean. A combination of human population growth, unsustained water resource use and development, and desertification threatens the Souss-Massa River’s ability to supply crucially needed natural resources to the people of Souss-Massa region and its activities. The geological, structure, and soil characteristics in the basin greatly influence groundwater availability. Significant rainwater deficits and the variable duration of the rainy season result in hydrological shortage that is not necessarily reflected in a direct response of the base flow. This chapter reviews the basin’s physical geography characteristics, the geology, and the water resource availability of the Souss-Massa Basin.

2 Physical Geography

2.1 Geography

The Souss-Massa Basin is located in the middle western of Morocco, occupying a total surface of 27,000 km2 with about 21% of plain area (5,700 km2) and 79% of mountain area (21,300 km2). The Anti-Atlas Mountains in the south, the High Atlas Mountains in the north, the Siroua massif in the east, and the Atlantic Ocean in the west are the natural limits of the Souss-Massa River Basin (Fig. 1).

Fig. 1
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Geographical situation of Souss-Massa River Basin

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Elevations in the basin range from 0 m (Atlantic Ocean) to 4,168 m (Toubkal summit in the High Atlas Mountains). The plain area lying between 0 and 700 m.a.s.l. covers about 5,700 km2 and contains the groundwater reservoir, while the remaining part is mountainous [4–12].

The Souss plain is covered by recent alluvial deposits deposed by Souss River and its tributaries and by Massa River and its tributaries in the Massa plain.

The two hydrographic regions of the Souss-Massa Basin are distinguished by their unique topographic and drainage characteristics. Several studies were carried out in this regard [4, 12–15]. Figure 1 illustrates the hydrographic regions, geographic settings, and characteristics.

The regions are as follows:

  • The Souss River: The headwaters of the Souss Valley have an extensive network of tributaries originating from High Atlas Mountains in the right side and a very light network of tributaries originating from Anti-Atlas Mountains in the southern side. After its confluences with the High and Anti-Atlas tributaries, the Souss Valley flows into a large plain, extending east to west along 182 km toward Atlantic Ocean. The flow of the Souss River and its tributaries is seasonal with irregular and sometimes highly floods between October and February during rainy year. The discharge flow is regulated by four big dams (Mokhtar Soussi, Aoulouz, Imi El Kheng, and Abdelmoumen).

    To summarize the topographic description of the Souss River Basin, we can distinguish three main zones:

    1. (i)

      The upper part of the basin (Souss upstream) between the base of Siroua Mountains and the city of Taroudant where the plain is narrow (1,200 km2).

    2. (ii)

      The middle Souss from the city of Taroudant to the city of Oulad Teima, which extends the central plain of Souss and is wider (1,500 km2), more regular, and less corrugated.

    3. (iii)

      The lower part of the basin from the Oulad Teima to the sea where the cities of Agadir and Ait Melloul take place. The Souss downstream extends over an area of 1,700 km2.

  • The Massa River: It is the second valley that drains the Souss-Massa Basin. It is located 70 km south of the Agadir city, close to the south watershed basin. This fluvial system has only the headwaters from the Anti-Atlas Mountains, which is just the perennial flow to the sea of freshwater southern of Souss-Massa Basin. His course in plain is incised and forms a narrow valley over a distance of around 36 km before flowing into the Atlantic Ocean. The regime of this valley follows annual and interannual climatic irregularities and is characterized by brief flooding, sometimes violent and interrupted by long periods of dryness. The discharge flow is regulated by two dams (Ahl Souss and Youssef Ben Tachfine).

2.2 Geomorphology

As a geomorphological point of view, the Souss-Massa plain is shaped as a gutter at very small bending radius, adjusted to the mountainous foothills and in the axis of Souss River which traced its bed. Headed and branched off in the upstream portion, it is relatively cashed in the downstream part. From east to west, the slope is 1% to Aoulouz; it decreases to 0.5% near Taroudant and 0.3% in the downstream part of the plain. From Aoulouz to the Atlantic Ocean, the elevation of the plain is range from 700 to 0 m over a distance of 150 km [12].

The plain has no notable reliefs except some remains of a Cretaceous cuesta in the form of hills and buttes split and almost completely hidden in the Pliocene–Quaternary formations filling the plain [4, 7, 14, 16, 17].

The actual course of the Souss and Massa is due to erosion processes caused by floods [9, 17–20]. Floods in Souss-Massa are very scarce and occur irregularly: after 10 mm of rain, rill wash occurs over the area and concentrated flow begins in some valleys; when the flood is effective in the main valley, its effects, except for rill incision on the slopes, are mainly the construction of inner fans at the mouths of the tributaries, a widening of the braided channel reach, and a delivery of the suspended load to the ocean [15]. Consequently, occurrence of vertical and lateral channel erosion in the whole catchment, colluvial deposition on slopes, widening of the braided channels in the median zone, and silt deposition in the distal zone collectively characterize the predominant processes in present-day conditions. Two other noteworthy characteristics are the various types of calcareous indurations and links with eolian deposits.

2.3 Climate

The Souss-Massa area has a typical semiarid to arid climate. The variation of rainfall is very important in time and space showing a clear decrease from the mountains to the plains. The average rainfall is 250–300 mm/year in the plain (Fig. 2) and around 500–600 mm/year in the mountain [21].

Fig. 2
figure 2

Annual variation of precipitation in three main meteorological stations (Agadir, Taroudant, and Aoulouz) in the Souss-Massa Basin

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The annual mean temperature ranges between 14 and 18°C in the High Atlas and Anti-Atlas. The average temperature in the plain is higher and can reach up to 20°C [22]. The rainfall period extends from November to March, and the dry season can extend up to 7 months (April to October). Although the potential evaporation is very high in the plain and can reach up 2,000 mm/year [12], the rainfall exceeds the evaporation during winter in the mountain areas that become the main recharge areas.

3 Geology and Tectonic Setting

The Souss-Massa Basin (Fig. 3) is a part of the Pre-African trench. It is a narrow fainting zone with recent sedimentary deposits, embedded between the High Atlas in the north and the Anti-Atlas in the south. Both Atlasic domains are connected at depth beneath the Souss Valley in a complex manner and are covered with thick detritic formations and calcareous marls of Plio-Quaternary deposits. These overlie a Cretaceous–Eocene syncline [6, 7, 16]. The northern flank of this syncline largely, but only partly, outcrops the side of the High Atlas. The southern flank is seen as an alignment of hills in the middle of the valley.

Fig. 3
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Geological map of Souss-Massa Basin in [6] modified

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3.1 Geological Formations

In addition to monumental works on the Souss Basin [16, 23–25], several studies were carried in this area [4–7, 9, 10, 12, 14, 26]. The age of the geological formations ranges from Paleozoic to Quaternary. The plain is composed of Plio-Quaternary sediments (sands, gravels, and lacustrine limestone), which covers a Cretaceous syncline in the north of the basin and a Paleozoic schistose basement in the south (Fig. 3).

The Plio-Quaternary strata in the plain are locally heterogeneous both in vertical and lateral directions (Fig. 13). The syncline axis is oriented on east–west direction (Fig. 4). Its northern flank outcrops vertically in the High Atlas and marks a vertical fault, which is known as the South Atlas fault. Its southern short flank outcrops slightly in the center of the basin.

Fig. 4
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Logs of deep oil and hydrogeologic boreholes showing the stratigraphy of the subsurface of Souss-Massa plain

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The High Atlas shows an alternation of permeable and impermeable Mesozoic formations. Some layers contain evaporate minerals (gypsum in Jurassic and Cretaceous and halite in Triassic formations).

The Cretaceous layers resulting from the major transgression in the area, underlain the plain (Fig. 4). This is confirmed by data revealed from boreholes that penetrated rocks from surface alluvium through Turonian-age rocks. The deep boreholes and geophysical measurements have shown a large variability in the substratum (Figs. 6, 7 and 8).

The Anti-Atlas Mountains are characterized by carbonate and crystalline formations [16, 24, 26].

3.2 Structural Evolution

Several authors [7, 14, 16, 28–31] describe the Souss Basin as a tertiary synclinorium structure including two depocenters located in the western and eastern parts of Souss Basin. The Souss plain, which acted as the High Atlas foreland basin during the Cenozoic, constitutes an E–W-oriented depression separated from the Ouarzazate Basin by the Siroua high plateau.

Many studies have emphasized the role of the inversion tectonics in the evolution of High Atlas system and its foreland [29, 32–37].

Thrust and fold structures would have resulted from the reactivation (inversion), caused by the Cenozoic compressional events, of the preexisting extensional faults associated with the Triassic–Liassic Atlasic rifting.

The beginning of tectonic inversion is not synchronous; the western border has been lifted in the first, as suggested by the absence of Eocene deposits and unconformity of Aquitanian conglomerate on Maastrichtian levels [28].

The northern edge of Souss Basin is bounded by 150 km long in the South Atlas Front. This WSW–ENE striking fault zone is structurally formed from west to east by four main fault tracts [38]: the WNW striking, 30-km-long Agadir–Tagragra fault tract; the WSW striking, 3-km-long Oued Issen fault tract; the east–west striking, 45-km-long North Taroudant fault tract; and the E–W to WNW striking, 40-km-long Oulad Berhil fault tract.

The deformations visible within the basin are recent (Quaternary age); and, in the western part, Ambroggi [16] distinguished from surface observations, several folds, and flexures affecting quaternary levels. These structures are, from north to south, (1) the Mesguina syncline, with an axis east–west; (2) the Aknibiche anticline with an axis E–W to ENE–WSW; (3) El Klea and Chrarda flexures; (4) Haffaia–Ouled Bou Rbia anticline (NE–SW to E–W) which appears outcrops of Cretaceous layers.

3.3 Geometry and Structure of Subsurface

The exploration of the subsurface structure of the Souss-Massa plain is based on the determination of electrical discontinuities from the quantitative interpretation of electrical sounding and the correlation between the geoelectrical cross sections [27, 39]. These discontinuities probably correspond to faults or flexures affecting the basement of the plain; they are divided into three main families’ directions: NE–SW, WSW–ENE, and N–S.

The first family is represented by the F1 discontinuity (F1a and F1b) traversing El Klea region, north of Oulad Teima, and El Gouna region, orientated NE–SW. It corresponds to the fault of El Klea [6, 7] initially described like a subsurface flexure by [16].

This fault has been identified in oil borehole El Klea II and HB1 (Fig. 4), and from the analysis of seismic profiles (Fig. 5), the fault of El Klea (F1) affects, with an average dip about 50–60° toward the NN, the Mesozoic and Paleozoic basement formations, defining a half-graben collapsed SSE with an approximate initial dip of 10 [35, 36, 40, 41]. It is extended to the ocean, separating the coastal area of Souss downstream of western plain of Chtouka and middle Souss, thereby defining the first compartment of Souss-Massa plain.

Fig. 5
figure 5

The interpreted seismic reflection image across El Klea (KF) and Biougra (BF) faults. P-Q Plio-Quaternary, C Cretaceous, J Jurassic, T Triassic, P Precambrian and Paleozoic, in [36], modified

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The second family oriented ENE–WSW is indicated by the F2 discontinuity passing at Biougra and the south of Cretaceous outcrops, and F3 discontinuity parallel to F2 appears on the eastern hill El Haffaia from the Cretaceous outcrops of Sidi Borja and Tagtrannt and then joined the F2 discontinuity at the Cretaceous El Madida hill. This discontinuity family divides between the second and the third compartment, the one located beyond the Cretaceous outcrops of the Souss Valley toward the Anti-Atlas and the other located beyond the Cretaceous outcrops toward the High Atlas.

The third family consists of the F5, F6, F8, and F11 discontinuities oriented N–S to NNE–SSW. The F5 and F11 discontinuities pass in the NW of Oulad Berhil. F6 discontinuity is located in NW of Arazan region. The F8 discontinuity is detected between Oulad Teima and Sebt El Guerdane towns.

The geoelectrical cross sections show a deepening of Cenomanian–Turonian resistive strata from the south toward the north and the interpretation of this structure as a horst and graben system (Figs. 6, 7, and 8).

Fig. 6
figure 6

Geoelectrical cross sections along three profiles E, F, and D realized in Souss downstream [27]

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Fig. 7
figure 7

Geoelectrical cross sections along three profiles A, B, and C realized in middle Souss [27]

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Fig. 8
figure 8

Geoelectrical cross section along Souss upstream area [27]

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The correlations made on these geoelectrical cross sections made it possible to highlight electrical discontinuities and to elaborate the structure map (Fig. 9). The latter most likely corresponds to major faults, which affect the underground strata in the area.

Fig. 9
figure 9

Structural map of subsurface of Souss-Massa plain showing the syncline axis, faults, and compartments [27, 39]

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The correlation of these faults, was carried out taking into account the structural directions already described in the region by [30, 31, 35–38, 40–45].

The faults have divided the Souss-Massa plain underground into four compartments (Fig. 7). The first compartment (I) corresponds to a collapsed area between the El Klea fault (F1) crossing and the Atlantic coast forming the coastal aquifer of Souss. The second compartment (II) corresponds to a depression, limited in the south by Cretaceous hills in the plain and to the north by the South Atlas foothills. The third compartment (III) is located between the Cretaceous outcrop in the center of the Souss Valley and Paleozoic outcrops of the Anti-Atlas. The fourth compartment (IV) is located between Oulad Berhil and Aoulouz in the Souss upstream (Fig. 9).

4 Water Resource Availability

4.1 Surface Water Availability

The surface water availability may vary a lot over the year or even between 1 year and another and depend on climate change.

4.1.1 Renewable Surface Water

The renewable resources are estimated to be 131 and 418 million cubic meters in the Massa and Souss Basin, respectively (Table 1).

Table 1 Average monthly and annual renewable surface water in the Souss-Massa Basin on million cubic meters [46]
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4.1.2 Drainage Network and Runoff

The Souss-Massa River Basin has a very dense hydrographical network, where the larger sides are the High Atlas range and the Anti-Atlas, the two converging in the east. In between, a depression, with a triangular shape, increases in width from the west to the east.

At the Souss River, the main tributaries coming from the High Atlas Mountains are larger and with higher discharge than the tributaries from the left margin (Fig. 11). The left margin tributaries are perpendicular to the main channel. The tributaries from the right margin are tangential to the main river and have a dendritic network in the mountains. The main tributaries from the east to west in the right margin are the Oued Lemdad, Oued Talkjount, Oued El Ouaar, Oued Mhannd, and Oued Issen, while those from the left margin are the Oued Tidnass, Assif n’Oulil, Oued Sdas, and Oued Merkh (Fig. 11).

The Souss headwaters collect waters from the High and the Anti-Atlas system and after crossing the Souss plain flow to the Atlantic Ocean in the Souss mouth at the Ait Melloul city.

The hydrological regime of the Souss and Massa Rivers is characterized by strong seasonal and interannual irregularity. The average discharge of Souss Basin is estimated to 394 million m3/year. In Aoulouz at the dam, the average discharge is 170 million m3/year, depending on water availability of water year. The Souss river bed is dry in Taroudant for 8 months per year on average, because the water discharge is diverted from the main channel to the irrigation channels and seeps into the groundwater. At its mouth in Ait Melloul, water discharge observed is about 200 million m3/year that is lost at sea.

The rest is taken, seeped into groundwater, evapo-transpired by vegetation cover, or lost through evaporation.

The flows have high interannual irregularity and depend on precipitation [12] and regulated by dams. In the downstream of Aoulouz dam at the entrance to the Souss River in the plain, the annual average flow is 4.87 m3/s with a maximum of 28.05 m3/s and a minimum of 0.001 m3/s. In the Taroudant station the annual average flow is 0.92 m3/s with a maximum of 6 m3/s and a minimum of 0.001 m3/s. In the mouth of Souss River, the annual average flow is 4 m3/s with a maximum of 25.4 m3/s and a minimum of 0.002 m3/s (Table 2 and Fig. 10).

Table 2 Interannual variation of average flows in the Souss Basin [22]
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Fig. 10
figure 10

Interannual average flows of Oued Souss in the three main stations from 1954 to 2010

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The first conclusion we have drawn from these figures is that in Taroudant, the flows are much less abundant than Aoulouz despite the contributions of tributaries between the two stations. We must therefore admit that a quantity of water at least equal to the difference of rates observed in Taroudant and in Aoulouz evaporated, diverted from the main channel to the irrigation channels by local residents to irrigate cultivated area and seeps into the groundwater. The volume of water, disappeared either to the atmosphere or to groundwater, can be of the order of 90 hm3 per year, a continuous flow of 3 m3/s (Table 2).

We also noticed the huge quantities of water lost in the ocean, highlighted by the flows observed in Aït Melloul. These volumes are estimated to average 240 hm3 per year; these are very significant amounts that could be recovered, at least partially, if they were retained behind dams located on tributaries of the High Atlas and the upstream basin.

The Massa River has its headwaters only in the Anti-Atlas and flows to the northwest collecting waters from tributaries such as the Oued Assaka.

In the Massa Basin, the annual average flow is 4.16 m3/s with a maximum of 20.06 m3/s and a minimum of 0.83 m3/s (Table 3).

Table 3 Interannual variation of average flows in the Massa Basin [46]
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4.1.3 Dams

The Souss and Massa Rivers are under the influence of the system of reservoirs of Mokhtar Soussi, Aoulouz, Imi El Kheng, Abdelmoumen, Dkhila, Ahl Souss, and Youssef Ben Tachfine with the total capacity of 639.99 mm3 (Fig. 11). These reservoirs regulate the downstream flow of the river, with the purpose of avoiding floods and artificial groundwater recharge and assuring the necessary flow for the main water concessions in the lower course of the Souss and Massa: the drinking water concession and that of the channels for the irrigation of the Aoulouz area, Sebt El Guerdane area, and Massa plain. The characteristics of the reservoirs of Souss-Massa Basin are shown in Table 4.

Fig. 11
figure 11

Main tributaries of Souss-Massa River and location of dams in Souss-Massa Basin

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Table 4 Capacity of the man dam of the Souss-Massa Basin (Source: ABHSMD 2015)
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The dam of Aoulouz is located in the Souss Valley, between the reservoir of Mokhtar Soussi and city of Aoulouz. The dam was commissioned in 1991. Its storage capacity is 89 mm3; its main use is artificial recharge groundwater and irrigation. The reservoir of Aoulouz receives contributions of water from the reservoir of Mokhtar Soussi (overflow) and from the valleys Ouzioua, N’ait Oughelli, and Imirguene.

Youssef Ben Tachfine is a big dam with 298.2 mm3 of storage capacity and is located in the Massa Valley. The dam is a nonrigid dam. It was finished in 1972. The main tributary of the reservoir is the Assif n’Assaka, Oued Boutergui, Assif n’Boukoura, and Oued Massa.

The reservoir of Abdelmoumen is the second big dam, after Youssef Ben Tachfine, in the Souss-Massa Basin and is located 45 km northeast of Agadir in the Issen Valley; its storage capacity is around 198.4 mm3. The main tributary of the reservoir is the Oued Issen.

Mean discharge at the Souss River is 400 m3/s, with the tributaries from the right margin showing a higher discharge than those from the left margin.

4.2 Groundwater Availability

Groundwater availability in the Souss-Massa is heavily influenced, with dry season contributions. In general, groundwater tables are affected by annual rainfall and soil permeability. Groundwater is extremely important for drinking, industrial, and irrigation water supply (which is of excellent quality in most cases) for both urban and rural settlements.

In order to understand the hydrological functioning of the aquifer system, several studies have been carried out during the last years [5, 6, 8–11, 21, 27, 39, 47–55] using different approaches and tools. The more pertinent information from these was used here in summarizing the groundwater resources of the area. According to these authors, groundwater resources in the Souss River Basin area are developed from two aquifer systems:

4.2.1 Deep Aquifers

Two types of deep groundwater have been recognized in the Souss-Massa Valley. They correspond to the Cenomanian–Turonian limestones and conglomerates of the continental Neogene. Both have provided conditions for drilling artesian at Oulad Teima, Ain Chaib, El Klea, El Gouna, and recently Ait Igas with low flow on the ground (13 l/s). In some places, Cenomanian–Turonian aquifer communicates closely with a shallow aquifer. Their deep aquifers have a similar facies; they are Ca-Mg-HCO3.

The recharge area for the deep confined aquifer is in the northern part of the region, meaning come from lateral water flow from the water tables of border of High Atlas Mountains (outcrop areas). Some recharge also occurs from infiltration from the rivers in the foothills where deep and superficial layers are combined and vertical leakage [5, 7].

The deep limestone aquifer of the Cenomanian–Turonian is encountered at an average depth of about 250 m below ground surface (Fig. 12). It has an average thickness of 50 m and is composed chiefly of limestone flint and dolomite (karstified upstream). The Cenomanian–Turonian bed represents an available confined aquifer that can be important in water resource management in the Souss area.

Fig. 12
figure 12

Roof isohypse map of Turonian aquifer established after electric sounding and deep borehole data

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4.2.2 Shallow Aquifer

Despite the interest shown by the deep aquifers, the shallow aquifer is considered the most important hydrogeological unit in the Souss-Massa Valley because, firstly, it is the easiest to use both extensively as intensively and, secondly, it contains most of the groundwater resources in the basin.

This groundwater flows through sedimentary rocks that accumulated during the Neogene and Quaternary orogenic phases. These sediments are recognized by drilling and sounding consisting of sandy marl and sandstone in the Gulf of Agadir; conglomerates, calcareous marl, limestone, sandstone, silt, and alluvium across the plain; and conglomeratic formations mainly from alluvial fans on the mountainous borders. Continental Neogene formed by powerful conglomerate deposits at the foot of the High Atlas mountains. Further to the south, it is fluviolacustrine formations mainly calcareous clay, clay, and sandstone interbedded with conglomerates. This is the famous formation of Souss [23] assigned to the Pliocene–Quaternary. Other older formations that are permeable, such as Cenomanian–Turonian limestone, are identified in the valley and are the islets of Haffaia, Ouled Bou Rbia, Aaricha, Sidi Borja, and Tagtrannt. The lithology of shallow aquifer is very complex in detail (Fig. 13).

Fig. 13
figure 13

Geological cross section established after hydrogeologic borehole data in the Souss downstream, showing the very complex lithology. (1) pebbles; (2) sand; (3), alluvium; (4) sandstone; (5) marls with pebbles; (6) clay; (7), clay and pebbles; (8) sandy clay; (9) clayey sand; (10) sandy limestone; (11) shelly limestone; (12) clayey limestone; (13) calcareous marls; (14) sandy marl; (15) alternance marl and calcareous marls; (16) clay and marl; (17) limestone, (18) dolomite, (19) marl, (20) borehole code

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However, it seems possible to distinguish four aquifers communicating with each other:

  • Souss formation: the most widespread in the plain. Its lithology is very complex; we can distinguish, nevertheless, three predominant facies [7] (lacustrine, clayey limestone, and mainly calcareous marls) overlying a fluviolacustrine facies (sandy–sandstony and clayey) in its lower part. The third facies is formed by more or less solidified conglomerates which constitute the near total of the formation, at the foothills of the High Atlas and toward the eastern part of the plain. They appear as interbeddings reaching sometimes 10–15 m in calcareous marl and clayey sandstone series.

    The Souss formation is widely in the plain, with different characteristics; the center transmissivity T is good (in the order of 1.5 · 0−2 m2/s) and a coefficient of 3 · 10−2 emmagasinement S whereas border, formation is poor aquifer except alluvial fans (T varies between 7 · 10−3 and 8 · 10−4 m2/s). The thickness varies from 200 to 400 m zones [6, 7].

  • Fossil beds of the Souss Valley: formed by sands, sandstones, and gravels from old alluvium dating from the Quaternary. The average transmissivity is in the range of 50 · 10−2 m2/s with a storage coefficient ranging between 5 · 10−2 and 1 · 10−1. The thickness of this formation is between 20 and 40 m and can reach more than 50 m upstream.

  • Sandstones and limestones: it is about conglomerates and sandstony and shaly limestones from the Pliocene Agadir marine and sandstone and dunes in the south of Agadir. These sediments are often intercalated clay and a transmissivity of between 2 · 10−3 and 20 · 10−3 m2/s.

  • Cretaceous outcrops in the plain: in the middle of the plain, in the Southern flank, hills of the Cretaceous syncline, the Turonian outcrops or under a thin cover, communicates laterally with the Plio-Quaternary aquifer. This formation, karstified on the surface, is very transmissive, with T ranging between 5 · 10−2 and 20 · 10−2 m2/s; deep karst is not developed and T is 2.5 · 10−4 m2/s. The power of this series range from 10 to 30 m thick.

4.3 Water Use

4.3.1 Water Resource Demands

During the 4 last decades (1970–2010), Souss region has had a significant socio-economic development. Therefore, the constant economy’s growth and social development has produced increasing demands of both, surface and groundwater resources.

The volume of water used in the Souss-Massa amounts to about 1,100 million m3, 68% of this volume is pumping from groundwater. Irrigated agriculture uses more than 95% water resources mobilized in the basin.

The volume of water allocated to the drinking and industrial water is around 50 million m3 mainly provided from groundwater (about 76%). The major urban centers are supplied with as follows:

  • The greater Agadir is supplied from surface water (Abdelmoumen–Dkhila and Moulay Abdellah dams) and groundwater (Souss–Chtouka water table).

  • The water supply for the Biougra city is assured from Chtouka shallow aquifer.

  • Taroudant province is supplied from Souss shallow aquifer.

The volume of water allocated to agriculture amounts to almost 1,050 million m3 for irrigation of over 134,000 ha, of which 68% comes from ground water.

  • Drinking and industrial water:

    The evolution of drinking and industrial water requirement is based on the evolution of the population that would reach close of 2,637,000 inhabitants in 2020. According to the Hydraulic Agency of Souss-Massa-Draa Basin (ABHSMD) the drinking and industrial water is growth from 52 mm3 in 2005 to 70 mm3 in 2020 (Table 4).

  • Irrigation water:

    The hydro-agricultural development experienced since the area 1970 was also reflected in a significant increase in water demand irrigation currently valued at nearly 1,100 million m3. The irrigated area should evolve from 149,000 ha in 2003 to nearly 150,000 ha in 2020. The water requirements are estimated at nearly 1,030 million m3 (Table 5).

    Table 5 Water requirement in the Souss-Massa region [46]
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4.3.2 Wells and Groundwater Abstraction

As a consequence of decrease in precipitation and demographic pressures, groundwater pumping has been accelerated and the exploitation of the aquifers has intensified (Table 6).

Table 6 History of groundwater exploitation for irrigation, drinking and industrial water in Souss-Massa [46]
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A number of problems associated with increasing water scarcity and recurrent and extended droughts have been noticed in the Souss area particularly in the past few decades [21, 48, 54]. Manifestations of water scarcity include, among others, an alarming decline of both surface and groundwater resources, which resulted in the introduction of strict water control by the hydraulic agency (Fig. 14).

Fig. 14
figure 14

Decrease in water table during the last 4 decades in [21]

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A large number of active boreholes (more than 25,000) have been drilled in the Souss area with depths varying from a few meters to 300 m (Fig. 15). Most of them penetrate the Plio-Quaternary sands and gravels of the Souss-Massa aquifer. Although some of the wells are used for industrial or drinking water, most of water up to 94%, is used for irrigation. Local authorities estimate the total water abstraction in 650 million cubic meters per year [46]. On average groundwater abstraction exceeds recharge by an estimated 260 million cubic meters annually [46]. This overpumping has led to a decrease in the water levels in a range of 0.5–2.5 m/year (Fig. 14) in the past 4 decades.

Fig. 15
figure 15

Wells and boreholes pumping water in Souss-Massa plain aquifer [56]

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There are concerns that the recurrent droughts will further deplete the available water resources.

4.4 Water Balance and Water Level of Souss-Massa Aquifer

4.4.1 Water Balance

The major trend indicates an overall decrease in water resources, due to the combination of the natural decreased recharge and human activities (pumping). The demand for water in the Souss-Massa Basin exceeds the sustainable supply and the deficit is made up by mining groundwater. A groundwater balance from 1972 to 2007 is presented in Tables 7 and 8.

Table 7 Water balance of the shallow aquifer of Souss (million cubic meters) [46]
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Table 8 Water balance of the shallow aquifer of Massa-Chtouka (million cubic meters) [46]
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4.4.2 Groundwater Level

The reduction in piezometric level of water table of Souss and Chtouka aquifer due to overpumping and drought exhibited by a decreasing of water deficit varies from 100 to 370 mm3/year for Souss aquifer and 60 mm3 for Chtouka aquifer [46].

The piezometric level analysis in the Souss-Massa aquifer between 1996 and 2010 (Fig. 16) shows a reduction in water table level of about 15 m in the Souss upstream, more than 30 m in the middle Souss, between 12 to 20 m in the Souss downstream, while in the Chtouka-Massa area, the piezometric level was reduced between 10 and 15 m.

Fig. 16
figure 16

Piezometric-level evolution of water table of Souss and Chtouka aquifer between 1996 and 2010

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We can see that the decline of the water table has a general trend in Souss-Massa Basin which is variable in time and space due to several factors as the quantity of recharge and inflow to the groundwater system, the amount of groundwater pumping, and the distribution and intensity of the operated wells.

In 2003 the Hydraulic Agency of Souss-Massa produced a piezometric map of Souss-Massa unconfined aquifer (Fig. 17). The shallow piezometric contours show a general eastern–western groundwater flow. The recharge is mainly coming from the Atlas Mountains.

Fig. 17
figure 17

Piezometric surface contour map of the Souss-Massa shallow aquifer [2]

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4.5 Artificial Recharge

In some parts of Souss-Massa, due to over-exploitation of groundwater, decline in groundwater levels resulting in shortage of supply of water, and intrusion of saline water in coastal area have been observed. In such areas (e.g., Sebt El Guerdane and Oulad Teima), there is need for artificial recharge to improve the groundwater situation.

For the first time the artificial recharge of the groundwater was made by ABHSMD at 1991 until now, from the Aoulouz and Imi El Kheng dams, with an average released volume of 64 mm3/year [56]. The artificial recharge scheme in Souss area makes use of the direct recharge technique which typically employs retention dykes (3–4 m of high of the wall), in the bed of Souss and Talkjount River, to enhance the natural percolation of water into the subsurface [56].

The use of artificial recharge from Aoulouz and Imi El Kheng dams in the upstream part of the basin is due to geological conditions, high permeability and good water quality in this part of the watershed. The aim is to strengthen a share of the natural recharge, and thus to cope with continuing declines in water level and the risk of sea intrusion, and secondly to give effect to the dilution, waters being more mineralized in the medium and in the downstream parts of the watershed. Generally the artificial recharge is low compared to the reservoir volume and can reach 30–40 m3/m2 for an average released flow of 70 m3/s from dam, due to which the renewal rate is also low [3, 49].

5 Conclusion

This chapter has summarized the main synthesis results of physical geography, geology, and water resource availability of Souss-Massa River Basin.

From the geomorphology and geology point of view the Souss-Massa Basin is a southern foreland of the western High Atlas. The Souss-Massa plain occupies a depression between two major structural domains: the Anti-Atlas in the south and the High Atlas in the north. That depression is filled with Mesozoic to Quaternary sedimentary deposits overlying the Paleozoic basement.

Water resources for the area consist of surface water, dams and groundwater resources. The renewable surface resources are estimated at 131 and 418 million cubic meters in the Massa and Souss Basin, respectively. Seven reservoirs are installed in the basin with the total capacity of 639.99 million cubic meters, these reservoirs produces a number of economic and social benefits in the region. About 645 million cubic meters per year of groundwater (renewable and non-renewable aquifers) are currently used in the region. Most of the groundwater resources in the region are fully exploited (decrease in the water levels in a range of 0.5–2.5 m/year in the past 4 decades), and some aquifers are overexploited, particularly in Sebt El Guerdane area.

Therefore, the information provided in this synthesis would be useful for the subsequent elaboration of strategies for current and future water management in the region.