- The Tlemcen Mountains are a real water tower in western Algeria, a region with limited water resources and which is hit several times a century by intense multi-year droughts (more than 3 following years). To cope with these periods of drought, one of the region's best assets is the existence of large karst aquifers. Their renewable reserves (the flux) are significant, but are already largely used. On the other hand, permanent reserves (the stock) are not subject to any strategic management,

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... lthough they would cover water demand during multi-annual drought episodes. We will show that more intensive exploitation of permanent reserves would make it possible to cover demand during 50-year and even 100-year droughts, through the construction of additional well fields, which would not be exploited in a "usual" year (when dams are the most cost effective water resource), but only during periods of severe rainfall deficit. This is the strategy that made it possible to cope with the serious 1979-1999 drought episode, at an economic and environmental cost much lower than seawater desalination. In the longer term, the high storage capacity of these aquifers would also make it possible to store valuable resources that are presently lost at sea (the overflow of dams during rainy years and the outflow from wastewater treatment plants in winter).