The Sahara and Sahel Observatory (OSS) is a North-South-South solidarity partnership platform in the service of sustainable development in Africa

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SAHARA AND SAHEL OBSERVATORY

• The Sahara and Sahel Observatory (OSS) is a
  North-South-South solidarity partnership platform
  in the service of sustainable development in
  Africa

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OSS

• 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
  NGOs.
• The OSS has a rich heritage of experiences and
  actions laboriously acquired and achieved through
  scientific programmes in the service of
  circum-Saharan countries.

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• 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

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• 2- Water resources, in particular shared resources

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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.
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SAHEL-SAHARAN Great Basins Aquifers
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NORTH WESTERN SAHARA AQUIFER SYSTEM SAHARA
AND SAHEL OBSERVATORY
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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.
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Ground flows are manifested at surface
levelunder the form of springs
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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
Picture PNUD 1987
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Photo Ministry of Agriculture, Tunisia
The modernisation of tapping systems has
facilitated the multiplication of drilled wells,
especially artesian
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Total Abstraction in the Saharan Aquifers
Billion of cubic metres/year
and let to a high increase of exploitation
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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
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EXPLOITATION of NWSAS by DRILLED WELLS From
1960 to 2000
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1960
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1970
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1980
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1990
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2000
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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.
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TERMINAL COMPLEXE - MIZDAH
COUPE OUEST_EST MEDIANE à TRAVERS le SASS
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.
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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.
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• 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
• Due to pumping, the risk of increase in salinity
  is considerable
• The water level gradually decreases, and its cost
  is on the rise
• The natural outlets springs and artesian wells,
  are drying up
• Interferences between the various water points
  of the basin are sometimes considerable .

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INTERCALARY CONTINENTAL DRAWDOWNS 1950 ?
2000
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meters
Legend
Legend
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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.
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NWSAS objectives and activities are composed of
three components Hydrogeology
and information system component,  
mathematical model component, and
 consultation mechanism  component
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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.
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The obtained Information system called
 SAGESSE  allows the updating and addition of
new data, statistical queries, graphs, DB GIS
Model connections
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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.
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TERMINAL COMPLEXE ARTESIANISM TO CHOTTS 1950 ?
2050 SCENARIO ZERO
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legend
Aquifer level inferior to Chott
Aquifer level superior to Chott
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Legend
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legend
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legend
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legend
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legend
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legend
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legend
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legend
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legend
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legend
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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
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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 100mthe flow of
the Tunisian Outlet, which contributes in the
recharge of the coastal aquiferof the Djeffara,
must decrease the Ghadames Basin in the
ICpresents drawdown risks.
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²
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.
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NWSAS Risks Map
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Rome Workshop , December 20th, 2002
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.
Picture M.BESBES
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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.
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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.
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SYSTEME AQUIFERE
DU SAHARA SEPTENTRIONAL OSS
May 2003