Introduction

Cheria plain which covers an area of 720 km2 is located about 45 km south west of Tebessa city and in the north east of Algiers between 7°30′–8°E, and 35°–35°30′N (Fig. 1). It is a wide triangular plateau. The altitudes vary from 985 to 1700 m. The development of the urban population and the agriculture provokes an increasing strain of the quantity and the quality of water resources. Cheria basin constitutes an individualized hydrogeological basin and is formed by different geological formations. It is limited by synclines folds initiated during Eocene and Miocene compressive phases. It can be subdivided into three hydrogeological units, namely porous and two fissured formations. The porous formations consist of mio-plio-quaternary, whereas the fissured formations are constituted by karstic limestone, and they are subdivided into two different units. They form the most interesting reservoir, while the Eocene limestone aquifer forms the permanent water available in the study area.

Fig. 1
figure 1

Geological and geographical map of the studied region (Chamekh 2016)

Full size image

Geological and climatological context

The studied area is located in a semi-arid region. The annual precipitation and temperature average successively are 280 mm/year 15 °C (Chamekh 2014). The remarkable precipitation, the presence of fractures and fissures and cold–dry climate facilitate the appropriate conditions for karstification. The great part of annual precipitation comes from snow, which falls in winter and melts with increasing temperature in early spring.

The Eocene limestone aquifer is intensively fractured and karstified. The major sub surface karst cavities is located in the northern and the centre part of Cheria syncline. They are widespread in the Eocene forming the upper formation under the Quaternary cover in the Cheria syncline.

On the geological plan, the basin is synclinal structures with a stratigraphic succession (Fig. 2) ranging from Cretaceous to Eocene constitute the main formations. The later constitute the upper formations which occupy more than 80% and it is under the quaternary cover, the 20% are composed from the mio-plio quaternary filling deposits in the Cheria syncline. Evidently enough, geological climate factors will have an influence on the groundwater flow field. Eocene limestone formations are overlain by mio-plio-quaternary alluvial (Chaffai et al. 2006; Baali 2007; Fehdi et al. 2010; Chamekh 2014). Eocene limestone is intensively fractured and covered by varying thickness layer constituted by gravel, sand, silt and clay (Fehdi et al. 2010).

Fig. 2
figure 2

Geological cross section of the studied region (Gaud 1977)

Full size image

The basin is affected by many different tectonic phases and neotectonic movements (Hammimad 2005). Fractures orientations are dominantly found in NE–SW and NW–SE, and they are sliced by a sub-orthogonal third set of N–S. Generally, fractures are underlain by zones of localized weathering and increased permeability and porosity.

Hydrogeological setting

Eocene limestone constitutes thick, densely fractured carbonate succession, and it is characterized by a high permeability (Chamekh et al. 2015), and the presence of many karst landforms (Gaud 1977; Chaffai et al. 2006). It constitutes the most extensive aquifer in Cheria plain which covers an area about 100 km2 at the centre of the basin. The depth of the aquifer roof ranges from 100 to 250 m. The perennial water availability is related to the great potential of Eocene limestone aquifer. The alluvial aquifer is not appreciably used for drinking water as it used to be. From a hydrochemical point, both the amount of dissolved limestone and the enlargement of fractures depend obviously on the chemical composition of the rock and the water (Kiraly 1971). The chemical analysis results of this study are listed in Tables 1 and 2.

Table 1 Chemical composition (in mg/l) of groundwater (September 2013)
Full size table
Table 2 Chemical composition (in mg/l) of groundwater (April 2014)
Full size table

Karst is a unique hydrogeologic terrain in which the surface and ground water regimes are highly interconnected and often constitute a single and dynamic flow system (White 1993). In the Cheria plain, the karst is a landscape which is formed from the dissolution of soluble rocks including Eocene limestone. It is characterized by sinkholes, caves and underground drainage system. Nearly all the surface karst features are formed by internal drainage and the collapse which trigged by the development of underlying caves. This process of dissolution leads to the development of the caves, sinkholes, springs and streams that are typical of a karst landscape. In Cheria syncline, the karst sinkholes are simulated out using Flac 2 D software (Aziz et al. 2014). The diameters of the underground cavities vary from 1 m to more than 40 m.

The karst aquifer can be conceptualized as an open hydrologic system having a variety of surface and subsurface input, throughput, output flows and boundaries. They are defined by the catchment limits and geometry of conduits (Ford and Williams 1989).

According to the Piper and Schoeller–Berkaloff diagram (Figs. 3, 4), two types of water facies are found depending on the traversed formations lithology, where wells, springs and streams are located in. From one hand, wells and rivers in karstified rocks have low salinity water with conductivity values between 300 and 700 µS/m, Calcium Ca > 170 mg/l and bicarbonate Hco3 > 130 mg/l.

Fig. 3
figure 3

Piper diagrams of September 2013 and April 2014 (Chamekh 2016)

Full size image
Fig. 4
figure 4

Schoeller–Barkaloff diagrams of September 2013 and April 2014 (Chamekh 2016)

Full size image

On the other hand, the conductivity values vary between 1000 and 2000 µS/m, Calcium Ca > 60 mg/l and bicarbonate Hco3 > 90 mg/l in springs and wells on the alluvial aquifer.

Methods of field investigation

In the karstified Eocene limestone, lineaments tend to be less detected in discharge areas (lowland, wide and flat valleys) in contrast to the high density in recharge areas (highland narrow-mountainous ravines). In addition, the presence of a stream network in the former can be considered as a recharge source to the underlain karstic groundwater system.

Aerial photographs (1:2000), topographic maps, geological maps and satellite images are part of the remote sensing analysis. The lineament frequency and the lineament intersection maps are based on the aerial photographs. The grid files were located and contoured in Surfer software, which also produces the lineament frequency and the lineament intersection maps. These maps identify areas of high fracture frequency and of highest fracture intersections.

The piezometric survey was undertaken in six parts. From May 2010 to April 2014, sixty points of piezometric measurements were performed (wells and drilling). The initial phase of the survey starts from site visits to all properties within the respective field areas. Then, landowners were contacted regarding the location of bores, wells and springs on their property. Next, relevant details were recorded and permission were sought to revisit the sites to survey the wellhead elevation and groundwater level during the main survey.

During the sites visits, details of bores, wells, springs and water hole were recorded using a standard field sheet. The spatial location of relevant features was fixed using a handheld GPS unit.

Results and discussion

The piezometric map (Fig. 5) of different periods showed a flow converges to the center. In the northern part of the basin, the flow direction is north–south while in the southern part the flow converging towards a drainage axis, which coincides clearly with the Wadi Cheria that has west direction (close to the mountain of Allouchat). Two zones were identified according to hydrodynamic and hydrochemical properties. The map indicates the existence of a depression cone in Cheria village where the flow converges; the latter is apparently due to an overexploitation of groundwater; this zone is characterized by the presence of a great number of wells. All karstic areas are prone to subsidence because of natural or induced fluctuations in the local groundwater levels. Both local groundwater recharge and abstraction can lead to this subsidence.

Fig. 5
figure 5

Piezometric map of September 2013 (left) and April 2014 (right) (Chamekh 2016)

Full size image

The hydrochemical study is based on the water sampling from May 2010 to April 2014. This performance showed a remarkable dominance of magnesium chloride facies or calcium chloride facies (Chamekh et al. 2015), which hides the bicarbonate facies due to the circulation of ground water in the carbonate rock existing in the studied areas (Baali et al. 2014).

The presence of high nitrate concentrations in the groundwater samples which are collected from shallow aquifer is resulted from the contamination of Cheria Wadi not from the massive usage of artificial fertilizers.

Broadly speaking, the water shows a very high salinity with conductivity 9000 µS/m in the south basin, and 800 µS/m in north basin and with pH values around 6–8 (Chamekh 2014).

The effective management of karstic aquifers should include controls on the rate and range of the fluctuations in the piezometric surface and the distribution of infiltration. Large-scale abstraction for industry or irrigation can cause subsidence. Irrigation of fields is confirmed as cause in the increase of the subsidence features in geologically susceptible areas (Gutiérrez et al. 2008). The effect of underground water fluctuation has also a paramount importance (Sowers 1975), which describes the occurrence of two large sinkholes after 3 days of pumping. Catastrophic collapses can be happened, as an example the problems that appeared by abstraction and irrigation in Cheria. The general direction of principle stress can be obtained from the rose diagram trends according to the classical interpretation (Chamekh 2011). A relation is proposed between tectonic episodes of faulting style and preferential directions of karstification and flow direction (Fig. 6).

Fig. 6
figure 6

Relationships of fractures mapped from the area (Chamekh 2011)

Full size image

There are four groups obtained from the results gathered from the rose diagram (Fig. 7); they are classified according to their order of importance: the 1st group is 130°–140°E; the 2nd groups is 100°–110°E; the 3rd group is 40°–50°E and the 4th group is 0°E. They are caused by the tangential movements compression (Baali 2007). The direction N40–50 is the result of post-Miocene fault which creates the rift of El Hamammet (Hammimad 2005). In this case, the movement of the karst groundwater is closely controlled by the regional tectonic structure. Many cavern conduits have been found in the basin and their development coincides with the direction of geological fault and fractured zone (November 1999). A lot of sinkhole and dolines are covered with a layer of Quaternary alluvium consisting of clay, sand and gravel debris of Eocene limestone rocks, like dolines of Draa Douamis in north of the basin (Fig. 8).

Fig. 7
figure 7

Lineament mapping and cross diagram of fracture distribution

Full size image
Fig. 8
figure 8

Geomorphological map of the area surrounding the Cheria karst system (Chamekh 2016)

Full size image

Conclusion

Based on the results of the previous maps, the predominate flow converges from the periphery to the centre. The most important directions of flows are NW, NNE–SSW and they move into the centre. The recharge zones can be identified with the subsurface aquifers. The natural discharge zones are reproduced in the subsurface; the pattern of the major drainage axis is created by the watercourse along the piezometric surface of the subsurface aquifers. The southern part of the basin is often converging towards a drainage axis which coincides clearly with the Wadi Cheria (EW direction). The application of remote sensing technique and the aerial photographs leads to identify and understand the fracture system which is the result of structural deformation. Flow pattern of the Eocene limestone aquifer system reveals that the groundwater direction flows are toward the south and south eastern parts and is guided by the fractures and the preferential directions of the karst cavities.