The Sahara and Sahel Observatory (OSS) is a North-South-South solidarity

partnership platform in the service of sustainable development in Africa

SAHARA AND SAHEL OBSERVATORY

Established in 1992, the OSS is an international

organisation composed of 21 African countries, four European countries, four sub-regional African

organisations, as well as United Nations specialised organisations, and NGO’s.

The OSS has a rich heritage of experiences and actions laboriously acquired and achieved through scientific

programmes in the service of circum-Saharan countries.

OSS

OSS action is focused on two major topics that are both strategic and of priority order for its members :

1 – Environmental monitoring, especially of desertification

2- Water resources, in particular shared resources

The North-Western Sahara Aquifer System (NWSAS) project intervenes in

the framework of the programme «Aquifer of the Major Sahel-Saharan Basins» initiated by OSS. The main

objective of the Aquifers Programme is to promote the concept « basin

awareness », facilitating the implementation by the countries of

appropriated strategies and tools for a sustainable management of shared

water resources.

SAHEL-SAHARAN Great Basins Aquifers

NORTH WESTERN SAHARA AQUIFER SYSTEM

SAHARA AND SAHEL OBSERVATORY

The North-Western Sahara Aquifer System or NWSAS refers to the overlapping of two deep aquifer layers: The formation of the Continental Intercalary, being the deeper one, and the formation of the Complexe Terminal, being slightly less in depth. This system overlies an area of onver one Million km2, of which over 60% are in Algeria, a little less than 10% in Tunisia, and 30% in Libya.

Ground flows are manifested at surface levelunder the form of springs …

Picture PNUD 1987

… and foggaras, which have been exploited for quite a long time, and which have given rise to the oases where the modes of living have remained long in perfect symbiosis with the Saharan eco-system.

Timimoun Foggaras Collector

Photo: Ministry of Agriculture, Tunisia

The modernisation of tapping systems has facilitated the multiplication of drilled wells, especially artesian

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0,3

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Fig.2 :Prélèvements Totaux dans les aquifères sahariens en Milliards de m3/an

LIBYE

TUNISIE

ALGERIE

… and let to a high increase of exploitation …

Total Abstraction in the Saharan Aquifers [Billion of cubic metres/year]

The increase in the number of drilled wells and of their exploitation flow

reveals staggering ratesfor the past thirty years :

from 0.6 billion m3/year in 1970,

this exploitation now reaches: 2,5 billion m3/year

EXPLOITATION of NWSAS

by DRILLED WELLS

From 1960 to 2000

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1970

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1980

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1990

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2000

20002000

ALG

TUN

LIB

NWSAS water points

The Saharan Aquifer System is currently surveyed and exploited by about 9.000 water points: drilled wells, springs and foggaras. These water points are distributed

as follows: 6.500 in Algeria, 1.300 in Tunisia and 1.200 in Libya.

TERMINAL COMPLEXE - MIZDAH

INTERCALARY CONTINENTAL - KIKLAH

The NWSAS constitutes a huge water reservoir containing Reserves whose volume is estimated as 30.000 billion m3.

However, not all this water is usable.

RAINFALL on NWSAS [mm/year]

Being mostly of a desert character, this region receives very little rainfall, and the recharge of the aquifer system is only about one billion m3 per year. It is a natural resource that is

not quite renewable.

The issue addressed by the NWSAS is that of ensuring the best possible use of this water reservoir from a sustainability perspective, knowing that a certain number of problems are becoming more and more acute:

1. Due to pumping, the risk of increase in salinity is considerable;

2. The water level gradually decreases, and its cost is on the rise;

3. The natural outlets: springs and artesian wells, are drying up;

4. Interferences between the various water points of the basin are sometimes considerable .

INTERCALARY CONTINENTAL

DRAWDOWNSDRAWDOWNS

1950 2000

metersLegend Legend

The leaders of the three countries are fully aware of these RISKS and have decided to undertake a major joint studies programme, while entrusting the OSS with the project management and with raising the

funds necessary.

In 1998, the OSS obtained assistance by the Swiss Cooperation, IFAD and FAO for a first three-year

phase which started in July 1999. Other cooperation partners, subsequently joined the project.

The three components of

NWSAS project

HYDROGEOLOGY &

INFORMATION SYSTEM

MATHEMATICAL MODEL

CONSULTATION

MECANISM

NWSAS objectives and activities are composed of three components :

« Hydrogeology and information system » component, «  mathematical model » component, and « consultation mechanism » component

DATA BASE ARCHITECTURE

The development of the Information System has included a review of the current situation, the construction of the conceptual model, the

establishment and the operating of a common data base. The scope of the task may be appreciated in view of the diversity and multiplicity of the operations carried out with regard to the 9.000 water points inventioried :

collection and homogenisation of the classification and identification systems, critical review, detection of erratic data, correction and

validation.

Topographical mapWater points layerhydrogeological layersThematic layersGrid cells

Grid cellsDigital data by grid cellsResults by grid cell

BD GIS

Numerical model

Information System « SAGESSE »

Factual InformationDescriptive GIS dataTime SeriesSocio-economic dataWater points coordinatesWater points relation Grid

The obtained Information system called « SAGESSE » allows the updating and addition of new data, statistical queries,

graphs, DB – GIS – Model connections

Besides, the calculations made on the Model reveal that a mere continuation of the current abstractions,

called « Scenario zero » would result in additional drawdowns in the two aquifers, in particular the

Chotts basin.

Such a situation would be unacceptable for the Complexe Terminal: any risk of percolation from the

Chott to the aquifer would be fatal for the latter in terms of salinity. Here, it is necessary to envision a reduction of abstractions as a plausible scenario.

TERMINAL COMPLEXE

ARTESIANISM TO CHOTTSARTESIANISM TO CHOTTS

1950 2050

SCENARIO ZERO

Aquifer level inferior to Chott

Aquifer level superior to

Chott

legend

Legend

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IC Drawdowns , High Hypothesis

Both the High Hypothesis and the Low Hypothesis would lead, in view of the obtained results, to unacceptable impacts

on the future of the NWSAS

The simulations made based on the Model have highlighted the more vulnerable zones and allowed the establishment of

the NWSAS RISKS MAP:

In the Artesian basin, the expected additional drawdowns exceed 100m;

the flow of the Tunisian Outlet, which contributes in the recharge of the coastal aquifer

of the Djeffara, must decrease;

the Ghadames Basin in the ICpresents drawdown risks.

The most exposed sector is the Chotts Basin.

Along the Syrte coastline, the risk of marine intrusion would be seriously prejudicial to the Terminal Complexe and in

Ferjan, major drawdowns are expected.

There are possibilities of increasing the exploitation of the NWSAS, especially in the « new » and remote regions:

Western Basin in the IC, Wadi Mya in the TC. However, there are still some uncertainties in this regard, which require

further investigations.

²

GhadamesJufrah

Western Basin

Oued Mya

Artesian Basin

Syrte

Tunisian OutletChotts

NWSAS Risks Map

What is the future outlook for NWSAS at the end of this investigation phase? The problems faced by the three NWSAS countries naturally induce to address these issues jointly: The practice of partnership conducted under the NWSAS project has built mutual confidence and trust, as well as the conviction that information sharing, which is the cornerstone for any solidarity, has become an activity that is not only possible, but also indispensable.

Rome Workshop , December 20th, 2002

Picture M.BESBES

Consultation Mechanism in its First Phase

The three NWSAS countries decided to set up a permanent tripartite consultation mechanism for a joint management of the NWSAS.

The Mechanism has assigned many missions that are focused on the production of monitoring indicators, the development of data bases and of models, the promoting of studies, research and training, as well as a

consideration of the future of the mechanism itself.

CHOTTS BASIN

VALIDATION of ABSTRACTION by USERS GHADAMES BASIN

SAHARA WATER BANK

NWSAS SURVEY NETWORK

PROCESS and OPTION of IRRIGATION

IC WESTERN BASIN

DJEFFARA PARTICULAR STUDY

TC SUB MODEL BISKRA

MODELES REGIONAUX

SOCIO ECONOMICASPECTS

CONSULTATION MECHANISM

NWSAS PHREATIC AQUIFER

WATER QUALITY PROTECTION

HUMID AREAS

NWSAS RECHARGE

ASPECTS ENVIRONNEMENTAUX

SALTED SOILS

NWSAS MODEL

NWSAS : ACTIVITIES of PHASE II

The implementation of the consultation mechanism has already started, in an experimental phase, within the OSS, as requested by the countries. The mechanism is sustained by a programme of in-depth studies and of sub-models. These studies take into consideration the socio-economic aspects and the environmental impacts; they should bring appropriate solutions to the problems and to multiple risks highlighted by the first phase of the SASS.

SYSTEME AQUIFERE DU SAHARA

SEPTENTRIONAL

OSS – May 2003