Les barrages de Cheffia Et de Mexa Dans le bassin versant de l’Oued Mafragh (Extrême Nord-Est algérien)

Abstract

The Mafragh river basin is located in the extreme North-East of Algeria, one of the most watered regions of Algeria. Faced with climate changes and growing competition between users, the challenge of mobilization, management and protection of water is of great concern. The two Algerian-Tunisian transboundary hydrosystems, equipped with dams, wadi Bounamoussa at the Cheffia dam in the west (575 km2) and wadi Kébir-Est at the Mexa dam in the east (651 km2), are the essence of this research. After describing the physical contexts (mountain-plain duality), the exploitation of monthly and daily data series from the ANBT allowed to analyze the variability of the terms of the dams water balance (inflows, outflows and reserves). Precipitation plays a decisive role in the abundance and irregularity of flow. The Cheffia dam ensures since 1965 an average regulated volume of 74.25 hm3 per year (series 1970-2017). The Mexa dam (receptacle of the releases of the Bougous dam and that of Barbara in Tunisian territory) has allowed to regulate an annual volume of 65.59 hm3 (series 2003-2020). The examples of the floods of March 1973, April 2003 and February 2012 have shown the risks incurred by the plain downstream. During the exceptional floods of 2012, the plain of El Tarf was the receptacle of the cumulative flows and excess volumes (417 hm3) discharged in the emergency by the two dams (Mexa and Cheffia). The protection of agricultural land in the valley of Kebir-East has shown their effectiveness and their limits following the damage caused by the floods of 2012 and those occurring in January 2015. The vulnerability of flood-prone areas is accentuated by an extension of the agglomerations, which requires an urban planning taking closely into account the stakes related to this hazard. These events have led to ask questions about the possibilities of adapting management instructions to reduce damage. The interconnection of existing dams (Mexa, Cheffia and Bougous) and those under construction (Boukhroufa) and planned (Boulathane dam, Bounamoussa II dam and water intake on Oued Kébir-Est), is expected to contribute to a large control of surface water in the Mafragh basin but also to reduce the flood hazard for the downstream territories.