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SAHARA AND SAHEL OBSERVATORY

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. OSS.

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SAHARA AND SAHEL OBSERVATORY

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  1. 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

  2. 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 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.

  3. 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

  4. 2- Water resources, in particular shared resources

  5. 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.

  6. SAHEL-SAHARAN Great Basins Aquifers

  7. NORTH WESTERN SAHARAAQUIFER SYSTEM SAHARA AND SAHEL OBSERVATORY

  8. COMPLEXE TERMINAL TUNISIE LIBYE ALGERIE CONTINENTAL INTERCALAIRE 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.

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

  10. … 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

  11. Photo: Ministry of Agriculture, Tunisia The modernisation of tapping systems has facilitated the multiplication of drilled wells, especially artesian

  12. Total Abstraction in the Saharan Aquifers [Billion of cubic metres/year] … and let to a high increase of exploitation …

  13. 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

  14. EXPLOITATION of NWSAS by DRILLED WELLS From 1960 to 2000

  15. 1960

  16. 1970 1970

  17. 1980 1980

  18. 1990 1990

  19. 2000 2000

  20. 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.

  21. 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.

  22. 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.

  23. 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 waterlevel 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 .

  24. INTERCALARY CONTINENTAL DRAWDOWNS 1950  2000

  25. Legend Legend meters

  26. 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.

  27. 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

  28. 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.

  29. Information System « SAGESSE » Factual Information Descriptive GIS data Time Series Socio-economic data Water points coordinates Water points relation Grid BD GIS Topographical map Water points layer hydrogeological layers Thematic layers Grid cells Grid cells Digital data by grid cells Results by grid cell Numerical model The obtainedInformation system called « SAGESSE » allows the updating and addition of new data, statistical queries, graphs, DB – GIS – Model connections

  30. 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.

  31. TERMINAL COMPLEXE ARTESIANISM TO CHOTTS 1950  2050 SCENARIO ZERO

  32. legend Aquifer level inferior to Chott Aquifer level superior to Chott

  33. Legend

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  44. 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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