Karst Water. Resources (Proceedings of the Ankara - Antalya Symposium, July 1985). IAHSPubl.no. 161 -

THOUGHTS ON KARST WATER RESOURCES IN THE MOUNTAINS ^

Abdel kader Latati Directorate of Water Research and Planification Hydraulic Administration, Rabat, Morocco

Abstract

The Central Middle Atlas is a chain of mountains stretching from the Southwest to the Northeast between the Central Massif at the West, the Eastern Middle Atlas at the Northeast and the plains of upper Moulouya at the Southeast.

Plateaus of less than 2000 m in altitude called Middle Atlas causses dominate the West and North. An anticlinal structure is situated SE and oriented SW—NE enclosing large synclinal structures.

The dolomitic and calcareous formations of the lower and middle Lias landscape outcrop on the causses. Series of layers from Dogger to Pliocene cover these formations that are found in the folded chain.

Up North, the calcaro - dolomitic layers of the Lias sink under Neogene basin of Fes - .

The Central Middle Atlas is drained by the two largest rivers of Morocco :

The Sebou to the North and Northeast and the Oum Er Rbia to the Southwest.

The causses offer an abundant and varied sampling of karstic dissolution hill - shading ranging from minute forms to poljes and large dry valleys. But it is mostly just a superficial karst where lateral corrosion is no more active.

The classical procedures for karstological studies are very limited for the following reasons : Lack of accessible subterranean galleries; springs are generally located far away from the karstic areas. The sires and discharges variabilities of the springs are very diverse.

The subterranean flow occurs through a multitude of elemantary channels rather than through wide subterranean galleries. In addition to systematic observations of springs and rivers discharges, the emphasis is placed on the evaluation of the regularized flow of water by karstic aquifers, especially by the use of simulation models.

Water resources mobilization undertaken at earlier time on the Oum Er Rbia basin will be reinforced by multiple purpose project dams for the upper Sebou basin.

633 634 A.Latati,

Introduction to the domain

The Middle Atlas is a mass of high grounds stretching along 400 kms from the Upper Atlas at its Southwest to the Guercif plain at its Northeast, forming.an orographic barrier between the Atlantic: and oriental parts of Morocco. The Middle Atlas is subdivided into three structural domains. :

The Meridianal Middle Atlas which overhangs the Tadla plain at the South up to the gap of Srou river, from which point a sub - tabular structure of layered plateaus of 800 to 2000 m normally called "The causses of the Middle Atlas" is found to the North. At the East and Southeast, we find the "folded Middle Atlas".

The Central Middle Atlas takes place between the Srou valley at the South, the Central Plateau at the West and the Fes - Meknes plain up North. Its limit with the Oriental Middle Atlas is a hollow limit NE-SW passing by the East of causse up to the antic­ linal of Tichkout mountain, at the East of which, the folded chain that started at the Bekrite - synclinal as small basins and thin valleys, presents large folded sets.

The Central Middle Atlas covers about 8000 km2. The Middle Atlas causses that show the most important karstie forms are the area where the dolomitic and calcareous formations of the lower and middle Lias outcrop. Layers of the Trias rock salt separate these formations from the Paleozoic substratum. In the folded Middle Atlas, these formations sink under thick layers of Dogger to Pliocene, but outcrop in almost all over the anticlinal ripples.

At the Northern limit of the causses, the calcareous and dolomitic formations sink toward the North, under the Meknes - Fes Neogene basin and rest on the Southern Rrf Substratum.

Under the Meknes - Fes basin, the structure of the Lias is very upportioned by faults and flexures some of which appear at the surface. The superficial layer is marly Miocene series (Om South to many hundred m thick up North)keeping the Lias nappe under pressure. Resting over these series, we find a complex of lacustrine limestone, sandstone and conglo­ merates that hold the supperfical nappe. The two nappes communicate through the faults and flexures or through the semi - permeable marly layers.

The Middle Atlas is considered as the "water tower of Morocco". This expression applies better to the Central Middle Atlas that represents the origin of the two major rivers of the country. The most important one is the Sebou and its tributaries : Beht, R'Dom and Mikkes that drain 2/3 of the area. The Oum Er Rbia river and its tributaries of the left side, particularly the Srou river, drain about 1600 km2. However, surface and subsurface basins are different. The dividing line of the subterranean water basins goes approximately through the plateau at Central West, around de Tizi - Ntratten accident and separates the Amekla and Guigou causses. Large amount of infiltrated water in the Southern causses converges to Oum Er Rbia springs (Fig. 2). Up North, the infiltrated water returnes directly or indirectly to the Sebou river at the East and NE, or supplies either the Ribaa - Bittit springs located between causse and Meknes - Fes basin or the aquifers of this basin. Thoughts on karst water resources 635

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Karstic Forms

On the causses, karstic forms are very noticeable from tiny holes to very wide depressions that give the landscape its identity. But it is mostly just a superficial karst. The thin layer of the limestone and the porous dolomite do not allow the development of caves, natural wells and subterranean galleries. The areas with the most karst area totaly dry while springs emerge on borders where different conditions exist. Possibilities for research on karst in these areas are then very limited.

Specific Conditions and Karstification Process

Lithological conditions — Karstic rocks are limestone, dolomite, gypsum or rock salt:

— In spite of the importance of outcropping Carixien and Domerian limestones, they are usually thin layers (dm to m) alternating with clay and marly layers unfavorable for their karstification. In areas where the marl and the clay are absent, the limestone offers however an excellent field of minute dissolution forms as grikes. That is the case of the Carixien calcaro -dolomitic "metrical banks" which present a good fissure permeability and offer the best field of rock - shelters and dolines.

— The lower Lias dolomitic series are less karstified because of their porosity. Even though the large space they occupy, the density of the dolines is relatively low.

— The outcropping of the gypsum and the rock salt is usually rare, the water that washes out these formations is briny (Oum Er Rbia springs). When outcropping, the clays of the Trias are impermeable and the dissolution forms are limited. On the other hand, high density of dolines is found in places where clay is covered with dolomitic thin layers or an old solifluxion flow. In the karstification process, the covering porous formations seem to be a compress that undertakes the dissolution of the underlying clay. But in such case, it is often difficult to identify the karst of the dolomitic formations from the repercussion of a deep karstification of the Trias that appears on the surface.

Tectonic conditions — The layer dips in the Middle Atlas causses are seldom very high. The density of dolines is higher on the low dip layers, beyond certain limit (15—17°) we find less dolines. The karstification process is also developed on synclinal dispositions and on the accident lines that may be the origin of a "karst barre" (Afriroua in El Hammam causse). The lateral corrosion is more active where water table is maintained near the surface.

Karstic forms

The Middle Atlas causses present a very rich and varied samples of karstic forms : minute carving, dolines, poljes... In addition to the lithological and the tectonic conditions, the distribution of karstic forms depends on the altitude and the continentality.

Minute forms — The minute karstic forms and nivokarstic shelfs ar located at high altitude or occupy the croups summits of the causses. Thoughts on karst water resources 537

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J ( J bel } Mountain 0 ( Oued) River Lacustrine limestone of the Pliocene Marl and sandstone of the upper Miocene j j Post lias formations fciri."-) Limestone of middle lias Dolomite of tower lias Trias and Paleozoic

Fig. 2 - Central Middle Atlas structural sketch . 638 A.Latati

Blind, dry valleys- They are very developed in the porous and alterated dolomite when outcropping in absence of collapse bowels. The larges form is locally called "I ssiane" and means a deep shakehole cultivated especially in the Imouzzer causse^

The dolines - Their density and size are variable with karstified rocks. According to their size, we consider two "types:

- Collapse dolines are developed by the squeezing of subterranean galleries following the attitude of the calcaro - dolomitic layers or by drawing off the terra - rossa.

- Giant Dolines and Uvalas are developed on the dolomite less soluble by superficial dissolution but are sometime occupied by collapse dolines resulting probably from the underlying Trias karstified formations.

Poljes — They are found in certain areas of Amekla, El Hammam and Ajdir causses at mean altitude of 1450—1650 m and are always digged out by superficial dissolution in a hollow structure (faults, synclinal dispositions..). Their shape is very tied to the groundwater table fluctuations. Several poljes are occupied by lakes (dayete) that are broken up but kept in shape in opposition to the warping poljes with no ponor and that are fossil poljes. Now, there is no functional polje, some ones are however sub - functional but the subsiding of the groundwater and the absence of flood do not allow lateral corrosion actions.

Ksecstk Springs

Beside the area of Imouzzer causse where springs are located along the synclinal axes, the infiltrated water reappears generally at the borders of the area in springs, rivers or supplies the aquifers of Fes - Meknes basin at North. The biggest spring is that of Oum Er Rbia at constant discharge that goes rarely below 11 m3/s. The second big spring is Ain Sebou that emerges at the border of the Sebou river at its entrance to the causse at NE. Its mean discharge is estimated at 6*4 m3/s. There is also springs of the Ribaa - Bittit complex (11 springs) that overflow at contact line of El Hajeb causse and Fes - Meknes basin at North. Their total mean discharge is 5,2 m3/s.

Springs Flow Regime

In general, the principal springs are perennial. An intermittent (temporary) spring results often as an out - flow of an other more regular spring situated at lower level.

The discharge variability analysis shows that each spring is a different case. Their behaviour ranges from very stable to very instable irrespective of their discharge amount or their altitude. Even springs that were once assumed to be supplied by the same karstic network showed different variability (see below).

Particular Flow Regimes Three cases are underlined Thoughts on karst water resources 639

— The stopping of the flow of two springs and the lowering in considerable manner of the discharge of three other ones, all situated in the outflowing area of Ribaa - Bittit, were observed during 26 hours June 6,1981.

This event could have been the result of partial but brutal wrapping of the major karstic network that supplies these 5 springs due to a collapse of a weller roof. This interpretation was called into question later after the drought phenomenon that persists since 1980. In fact, between the two springs that ran dry on. June 6, 1981, there is A. Atrous (880 m) and A. Aguemguem (908 m), A. Atrous running dry again since 1983, however A. Aguemguem located at higher altitude still discharging. This testifies the com­ plexity of the subterranean flow.

— The flow inversion phenomenon during the siphoning of the A. Sebou spring : This vauclisian spring of Sebou river (S.E of ) comes out from a gulf 12 m deep and 215 m2 at surface, centred with a subvertical conduit more than 33 m. in depth and about 4 m2 in section. During certain conditions of low flow period and when storm runoff occurs it submerges the spring, and causes an inversion of the flow. This inversion often lasts for a few days before the spring starts discharging again.

— Losses, appearances and loss - reappearances along the river channels : Discharge of the Aggai river is re - infillrated in the through the limestone on the way to Sefrou and re - appears at the gorges of Sebou river.

— Losses - reappearances and non point contribution of the Sebou river bed, in particular, between Ait Youb and Pount Portugais etc...

Research and Water Mobilization Groundwater research and water resources studies

Limited industrial activities and the low availability of cultivated land did not require a regional research. Actually, the irrigated area in the Sebou basin causses is estimated at 6000 ha (, El Hajeb, , Imouzzer, Sefrou and Amekla). Springs discharges are the main sources of irrigation, also the use of groundwater is in increasing development.

Potable water supply is satisfied through groundwater works. Groundwater research is based on geophysical and aerial photo - interpretation studies that are not always con­ clusive in this areas.

The studies concentrated in the Northern causses show a diversified behaviour of the Lias formations. Non crocked limestones are impermeable; in some area we find two super­ posed nappes. In a word, the porous dolomites with thin diaclases are more likely to develop a diffused nappe than subterranean galleries network. But according to the pumped discharges from wells, the two cases may be separately or simultaneously found without being able to predict that in advance.

On the other hand, chemical analysis of springs water are not helpful because it indicates calcic and magnesian bicarbonate faciès characterizing the dominant dolomitic 640 A.Latati

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Fig. 3 - Major works of the Upper Sebou Projects. Thoughts on karst water resources 641 formations. However they could give information on the washing - out of the halites of the Trias. Isotopic and traces analyses are not usual in Morocco.

For the tracers, they are not used in the Middle Atlas because of the lack of possible sites (no accessible galleries).

In addition to the reappearances studies (stage and discharge measurements) the infiltration capacities of the calcareous and dolomitic formations are still a big problem. In fact, overflow is negligible, water infiltrated represents the effective precipitation. Evapotranspiration is estimated from classical formulas using climatological data. In the Ifrane causse, and using a long observation series, the amount of infiltration was estimated to represent 53% of the total precipitation. The hydrological global model of Ribaa -Bittit springs gives different estimation (37%).

Simulation models are not yet perfected in this field. Indeed, the use of conclusive precipitation - discharge models are limited because of the short period of observation data available up to now and also because of the problem of ground water basin delimitation. The use of hydrogeological global models are limited also because of the poor and inadequate piezometric observations.

The problem is very crucial while the uncertainty of evaluating the supply of Fes - Meknes basin from the causses is still formulated.

Water Resources Mobilization — Even though the technics for water prospection in karstic massifs are not well developed, efforts are deployed in water resources evaluation and mobilization studies. Springs water of Oum Er Rbia is used in irrigation in the Tadla plain. At its origin this water is of a good quality (DR less than 700 mg/l),. until it mixes with salty water of the Triasic substratum, then its salinity increases up to 1200—1400 mg/1 and limits its utilisation in water supply and irrigation, especially during low flow period. This salt content decreases with the contribution of Srou, Ouamana and Derna rivers as well as Bin El Ouidane - Afourer diversion channel during high flow.

In the Sebou watershed, an example of multiple purpose project could illustrate water resources mobilization in this basin (Fig. 3).

Upper Sebou Complex (projected) — Supplied totally or partially with the causses of , Amekla, Sefrou and Imouzzer as well as surface water of its upper tributaries (Fuigou, MTJez, Zloul, etc.), the upper Sebou project includes the following structures:

MT>ez Dam - With the capacity of 525 Mm3, it will allow the discharge to be transfered in Matmata gallery to Idriss 1st dam on the Inaouene river. It will also allow to operate a power plant of 49 GWh mean productivity and 36 MW pick power.

El Menzel - Ain Timedrine Complex — Mainly designed for power production. Its caract- eristics are :

Pick power 145 MW4 Guaranteed power 17 MW, Mean productivity 318 GWh. 642 A.Latati

Ait Youb - Matmata Complex - This project should allow both an increase of the regular­ ized volume of Idriss Premier dam, and to operate a power plant designed because of the altitude difference between the transfer point and Inaouene river. The main characteristics of this project are :

Pick power 404 MW,;$ Guaranteed power 17 MW, Mean productivity 579 GWh plus 48 GWh at Idriss premier dam.

Once finishing the diversion of the railroad and the highway of Fes -Oujda that limit the capacity of Idriss Premier dam, the regularized volume intended to irrigation will be 829 Mm3 (72,300 ha). The upper Sebou project will increase this volume to 1480 Mm (132^000 ha). In both cases the wild drift to the Sebou between Idriss Premier and irrigated area are taken into account.

Potable water supply from Ait Youb dam will amount to 209 Mm3.

REFERENCES Couvreur, G., 1974, Le role de la neige dans l'évolution des formes karstiques de haute montagne du Haut Atlas - Marac : Memories et Documents, Phénomènes karstiques (II), C.N.R.S, France, V. 15, p. 135-138.

Ek, Camille, and Mathieu, Leon., 1964. La Daya de Chiker - Etude Geomorphologique: Ann. Soc. Géologique de la Belgique, extraits.

Latati, Abdelkader., 1985. Etude Hydrogeologique du Bassin de Meknes - Fes : Plans Directeurs Intègres d'Aménagement des Eaux des Bassins du Sebou, Bou Regreg et Oum Er Rbia, Maroc, edition provisoire, 142 p.

Martin, Jacques., 1981. Le Moyen Atlas Central - Etude Geomorphologique : Notes et Mémoires, Serv. Geol. Maroc, no 258.

, 1983. Classification des Sources Karstiques : Direction de la Resherche et de la Planification de l'Eau, Maroc,

, 1981. Inventaire Speleologique de Maroc : Direction de l'Hydraulique, Division des Ressources en Eau, Maroc,

, 1984. Hydrologie des Sources de Fes - Meknes - Situation au Premier Semestre 1984 : Direction de la Recherche et de la Planification de l'Eau, Maroc,

, 1984. Fluctuations Piezometriques et Debimetriques dans le Panneau de Haj Kaddour depuis 1981 : Direction de la Recherche et de la Planification de l'Eau, Maroc.