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Applied Water Science

, Volume 7, Issue 1, pp 349–359 | Cite as

Water wells’ exploitation and its impact on the drying up of foggaras

The case of the foggara of M’ghaer, Timimoune, District of Adrar, Algeria
  • Bensaada MohamedEmail author
  • Boualem Remini
Open Access
Original Article

Abstract

For a long time, man had to explore groundwater by constructing special hydraulic works. Thus, in ancient times, hydraulic civilizations such as the foggaras in Iran, Egypt, China and Latin America were born. In the Algerian Sahara, the foggara has played a leading role in the field of abstraction of groundwater distribution and sharing through formal and strict rules. Today, this technique has been disappearing and drying up. This decline does not only increase year by year, there were over a thousand foggaras in the early 1960s, but today only 915 foggaras have been listed for all those regions. Among the factors favoring the decline of foggara is the exploitation of water by deep holes drilled near the latter. In this article, we try to show the impact of drilling on the foggara.

Keywords

Foggara of Mghaer Timimoune Aquifer Drying up 

Introduction

The space occupied by the population along the Algerian Sahara has been at the origin of the installation of underground tunnels that drain the water table using a regular slope lower than the general slope of the ground, known as the foggaras.

The foggara is a traditional irrigation system used in the oases of Adrar and Timimoune for more than ten centuries. It consists of an underground tunnel draining water from the water reserve to the fields to be irrigated. The foggara has been used in more than 30 countries (Hofman 2007) and given different names: kariz or karez in Iran (Goblot 1979), khettaras in Morocco (Lightfoot 1996 a, b) and kareses in Afghanistan (Hussain et al. 2008).

These concepts and methods have been developed over a long period over the centuries, allowing man to live in these hostile regions by developing and improving these traditional harvesting techniques and management.

The economy of the latter is based mainly on agriculture and this, of course, is conditioned by water. This ancestral hydraulic system gave a peculiar physiognomy to the economic life of the palm; it is a difficult and expensive means of irrigation.

The construction of a foggara is a collective work; the establishment of this system of distribution has led local people to develop through the centuries, organizational, technical and legal water catchment with very elaborate water management and structures.

This management system was strongly influenced by social, cultural and geographical segments of the region. Each individual becomes the owner of one part water, or to financial expenses occasioned, either by participating in the construction or extension of a foggara.

The development of modern agriculture in the region entailed large exploitation, single-crop agriculture and deep well irrigation. This energy- and capital-consuming system has caused a dwindling of the water reserve and thus a decrease in the flow of some foggaras.

The geographical situation of the studied area

The oasis of Timimoune is located in the southwest of Central Algerian Sahara more than 1,000 km off Algiers (Fig. 1). The area is arid and water is rare. That is why the oasis inhabitants exploit underground water without using electric energy by means of the foggara system.
Fig. 1

Geographical situation of the studied area

The region offers a variety of morphological forms. It consists of sandstone plateaus and terraces; the lower areas are occupied by sebkhas and the north and east contain large surfaces covered by dunes (Erg).

The studied area is characterized by a hyperarid climate with high evapotranspiration. Precipitation is rare and usually small with variable quantitative importance from 1 year to another. The average monthly rainfall ranges from 0 mm in July and 3.6 mm in October, and the annual rainfall is 10 mm/year Dubief (1959). The winds are very unpleasant; the maximum number of prevailing winds are from the north east who are responsible for blowing sand. Evaporation greatly exceeds precipitation.

The dry period from June to September has a zero contribution to storm. The coldest month is January (12 °C–16 °C) and the warmest month is July (36 °C–49 °C).

The climatic conditions are harsh including scarcity of rain, intense sunshine, high evaporation, dry air and blowing sand.

Presentation of the foggara of Mghaer

The foggara of Mghaer is located between east longitude (00° 13′ 09″) and north latitude (29° 15′ 34″) (Fig. 2). It consists of a draining tunnel between 70 and 100 cm wide, with the height of a curved man and a series of 380 wells 3–9 m apart.
Fig. 2

Geographical situation of the foggara of Mghaer

It is the biggest foggara in the region of Timimoune, constructed at an unknown time. It might have been developed by Saint Sidi-Othmane and his son who lived in the ninth century of Hegira (Islamic calendar), i.e., 450 years ago (PNUD 1980).

The concept of a foggara

The foggara is a slightly tilted underground tunnel with water flowing downstream due to gravity to a topographic area relatively lower than the piezometric surface.

It consists of a series of wells 3–12 m apart and a tunnel 50–80 cm wide and 90–150 cm high.

The wells have no hydraulic function; they helped in the digging of the foggara and serve presently as air vents (chimneys) and as observation manholes for the tunnel. They help as well in the upkeep, cleansing and removal of sand (Fig. 3).
Fig. 3

A schematic sectional foggara

A foggara may consist of about 500–600 wells; these wells are 3–4 m deep at the start of the village, reaching 30–40 m in the heights of some foggaras, as that of Mghaer whose uppermost well is 40 m deep.

All foggaras are parallel and have almost the same direction; they maintain some distance in between, so as to avoid severe drainage at the expense of neighboring and more ancient foggaras.

The digging out of a foggara is only possible when the ceiling of the water reserve is higher than the areas to be supplied. The upstream part of the foggara penetrates the water reserve, whereas the downstream part supplies water to the palm groves.

The hydraulic works of a foggara

The construction of these works aims at distributing and sharing water according to a traditional social organization. Every beneficiary continually receives his due. The sharing of water is carried out by a system of combs set up in every Kasria according to an ancestral customary rule. Every family canalizes its share of water to their garden by means of a system of canals called séguias.

This ancient system enables a lasting management of the works and a fair distribution of the water resources between all inhabitants of the Ksar.

The main Kasria

At the exit end of the foggara (Photos 1, 2), water is carried to a triangular basin called the main Kasria. It is blocked by a comb-shaped divider made of a soft and easily chiseled stone, serving as a water stabilizer. This comb, also called mocht, is provided with a sufficient number of openings so that water does not flow back.
Photo 1

Exit end of the foggara of Mghaer

Photo 2

Main Kasria

This technique serves to calm the water prior to its distribution; it is a kind of a hydraulic tranquilizer.

The main Kasria distributes the flow of the foggara into three, four or five big channels called majari (plural of majra).

From this basin, the canals stream in all directions toward the tracts of land to be irrigated. At the end of these majari, other secondary Kasria allow water to flow into canals that might be divided anew by another comb toward the gardens of the palm grove also called guemmoun (Photos 3, 4).
Photo 3

Guemoun

Photo 4

Palm grove

The secondary Kasria

It is a new and equally important basin found after the first one and serves to share water between the families and tribes that participated in the construction of the foggara (Photo 5).
Photo 5

Secondary Kasria

At several levels of the palm grove, water is yet again divided by other combs and led toward the tracts by smaller canals (Photos 5, 6). The canals proceed as a very dense distribution network that ends in a collection pond called madjen.
Photo 6

Canal

The madjen

It is a shallow recovery and regulation pond, sometimes rectangular, located in the highest spot of the garden where water is to be collected for 24 h.

The irrigation is generally carried out very early in the morning in summer and at late morning in winter. Every garden has a madjen made of clay or concrete to avoid waste (Photo 7).
Photo 7

Madjen

A geological and hydro-geological overview of the study area

Geologically, the area is formed by a Continental Intercalary just beneath the surface of a large part of the region and represents the main aquifer with interstice porosity. It is characterized by considerable heterogeneity (sandstone, sand and clay) and by a variable power, diminishing from east to west (680 to 240 m). This horizon bevels near Tademait Plateau which is located to the west of the study area.

The hydro-geological study shows that the Sahara is one of the largest deserts in the world, being a sedimentary basin that extends over 780.000 km2.

The underground water flows mainly from NE to SW and generally converges toward the foggaras of Timimoune, Adrar and Reggan (Fig. 4).
Fig. 4

Hydro-geological map of Algerian Sahara

In the region of Timimoune and Adrar, water starts to flow from East to West.

The aquifer is mainly supplied by the infiltration of streaming water from the southern side of the Saharan Atlas and from the edges of the Tademait Plateau.

The geology of Timimoune is basically made up by shales overcome by soft sandstone, sometimes harsh conglomeratic level. Into surface the sandstones have a stratification cross bedding, by going to the airport, into the upstream of foggaras Mghaer the rock consists of a quartzitic slab (Fig. 5).
Fig. 5

Lithostratigraphics formations of the studied sector

The establishment of a hydrogeological section passing through the foggaras of Mghaer shows that the geology is constituted by the intercalary Continental (Fig. 6).
Fig. 6

Hydrogeological section of the foggara of Mghaer

Establishment of a hydrogeological section passing through the foggaras of Mghaer show that the geology is constituted by the intercalary Continental, lithostratigraphy is formed by a heterogeneous sandstone facies, sands, clays and gravels.

The Hydraulics of the wells neighboring the foggara of Mghaer

In order to determine the interference between the wells and the foggaras, we refer to the data collected from the well (F4), (c.f Table 1).
Table 1

Lithostratigraphic and technical log of drilling F4

The interpretation of the results of the test sheet by one level of long-term led us to calculate the radius of influence or the range of the well by applying the Law of Dupuit and the law of log–log approximation by C.E. Jacob.

The graphic interpretation of trial pumping

The execution and interpretation of the measured data (c.f Table 2), reduction and time have been based on Dupuit’s formula and that of C.E. Jacob on the expression of underground hydrodynamics.
Table 2

Pumping well test F4

t (s)

Δ (m)

t (s)

Δ (m)

t (s)

Δ (m)

t (s)

Δ (m)

0

0

1500

11.61

18000

13.35

68400

13.85

30

6.26

1800

11.86

19800

13.36

72000

13.94

60

7.36

2100

12.03

21600

13.46

75600

13.98

90

7.90

2400

11.99

23400

13.51

79200

14.00

120

8.31

2700

12.15

25200

13.56

82800

14.02

150

9.30

3000

12.21

27000

13.60

86400

14.04

180

9.56

3300

12.27

28800

13.64

93600

14.06

210

9.64

4200

12.33

30600

13.65

100800

14.07

240

9.70

4800

12.36

32400

13.67

108000

14.07

270

7.76

5400

12.41

34200

13.68

115200

14.08

300

9.80

6000

12.46

36000

13.69

122400

14.08

360

9.86

6600

12.52

37800

13.70

129600

14.08

420

10.11

7200

12.61

39600

13.70

136800

14.10

480

10.23

8100

12.81

41400

13.70

144000

14.09

540

10.34

9000

12.86

43200

13.71

151200

14.08

600

10.45

9900

12.96

46800

13.72

158400

14.08

720

10.49

10800

13.06

50400

13.73

165600

14.08

840

10.64

12000

13.11

54000

13.74

172800

14.08

960

10.70

13200

13.16

57600

13.75

ANRH ADRAR

1080

10.82

14400

13.25

61200

13.78

1200

11.13

16200

13.28

64800

13.82

Data obtained through experimentation pumping descent constant; flow rate: 50 l/s. Well diameter: 12 inch. Pumping time is 48 h

Supposing that the system is permanent, the drawdown of a well with r 0 radius is given by Dupuit formula:
$$\Delta_{{r_{ 0} }} = \frac{Q}{2\pi T}\;\; \times \;\;{\text{Log}}\;\;\frac{R}{{r_{0}^{2} }}$$

Given that:

\(\Delta_{{r_{ 0} }}\): The drawdown measured in the pumping work in meters

Q: The constant pumping rate in (m3/s)

T: Transmissivity in m2/s

t: The pumping time, in seconds

r o: The radius of the pumping well in meters

R: The well range in meters

In the case of a non-re-fed underground water reserve by drainance or by a boundary, one can express the range of the wells depending on pumping time, by applying Jacob’s logarithmic approximation to the well itself:
$$\Delta_{{r_{ 0} }} \;\; = \;\;\frac{Q}{4\pi T}\;\;{\text{Log}}\;\;\frac{2.25Tt}{{r_{0}^{2} S}}\;\; = \;\;\frac{Q}{2\pi T}\;\;{\text{Log}}\;\;\frac{{\sqrt {Tt/S} }}{{r_{0} }}$$
And comparing this expression to the Dupuit formula, one draws:
$$R = 1.5\;\sqrt {\frac{T\;\; \times \;\;t}{S}}$$

Given that S: is the storage coefficient, without unit of measurement

The tracing of the descent of the water drilling (F4)

By putting the well level drawdown values on (y) axis in meters and pumping time values in seconds on the (x) axis, the graph result gives a representative straight line of which we determine the slope C [\(C = \Delta_{2} - \Delta_{1}\)] and the storage coefficient is obtained by numerical calculation in the second term of the expression of Jacob:
$$T = \frac{0.079Q}{C}\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;S = \frac{{2.25Tt_{0} }}{{r_{0}^{2} }}$$
The value of the range shows a clear influence on the foggara of Ouled Nouh, which is now dried, and a decrease in the flow of the foggara of Mghaer (Fig. 7).
Fig. 7

Well’s Descent Curve (F4)

T = 1.79.10−3 m2/s et S = 0.008

Or \(R = 1.5\;\;\sqrt {\frac{T\;\; \times \;\;t}{S}}\) = 295.5 m

The well’s impact on the foggara

The obtained values for the influence radius for well (F4) can be applied on well (F13) due to the fact that we are dealing with the same aquifer (continental intercalary), and that shows the direct impact of the latter on the foggara of Mghaer (Fig. 8), i.e., a clear decrease of the flow and wasting away of vegetation because of the lack of water (Photo 8a, b).
Fig. 8

Interference between wells and foggaras

Photo 8

Gardens withering due to the drying up of some seguias

The follow-up of the difference in the foggaras flow between 1998 and 2009 shows a slow death of vegetation (Table 3).
Table 3

History of the flow of foggara of Mghaer

Years

1998

1999

2000

2001

2002

203

2004

2005

2006

2007

2008

2009

Q. l/s

23

18

13

9

7

6.3

6

5

4.5

1

1

0.5

It is noticeable that the sealing of the fields (proximity to the airport), the lack of maintenance and of skilled workforce have also contributed to the decrease of flow. A foggara needs a periodical maintenance and at least a yearly cleansing, but the cost thereof is considerably high and the know-how has not been handed down from generation to generation (Fig. 9).
Fig. 9

Evolution of the flow of the foggara of Mghaer

Conclusions and recommendations

As has been shown above, drilling deep water wells near the foggara has a direct impact on it (due to the lowering of the piezometric level of the underground water reserve): the decrease of flow.

The construction of the foggara has taken a long time and thousands of unknown individuals in order to provide water to the inhabitants of this extremely arid area. The foggaras have been essential to the prosperity of some civilizations. In Iran for instance, they constituted the main water supply system. Water is a real property which requires a delicate way of distribution.

In order to save this hydraulic patrimony, we need to find a way that combines both old and modern techniques of underground water channeling.

In order to save this universal patrimony, the exploitation of the wells must be efficiently carried out so as to avoid interference with the foggaras. To do this, it is essential to diminish the pump flow, to cleanse the foggara regularly, and not to waterproof the areas surrounding the centuries old tunnels.

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© The Author(s) 2014

Open AccessThis article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.

Authors and Affiliations

  1. 1.Branch from the Post-graduation and Scientific ResearchSuperior National Agricultural SchoolAlgiersAlgeria
  2. 2.Department of Water Sciences and of EnvironmentUniversity of BlidaBlida DistrictAlgeria

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