Sensitivity analysis of the oasis system and safeguard measures for the Metouia Oasis (Tunisia)
The Métouia oasis is situated in south-eastern Tunisia near the coast of Gabès City. The climate is arid with rare and irregular precipitation events. The oasis originated from a confined subsurface that was hydraulically connected to surface springs that had already been exhausted by human activities. The soil features are presently dominated by the evolution of salinization and water-saturation processes either partially or totally affecting the soil profile. The visible salt deposits and soil salinization processes are generated by the salinity of irrigation water and the shallow water table as well as the rising capillarity head. These processes are strongly influenced by the weak soil leaching mechanisms, on the one hand, and the poor drainage schemes, on the other hand. The four-year monitoring programme (2001 – 2004) focussed on important abiotic water and soil parameters and showed a close relationship between water quality and the generated geochemical processes parallel to the degradation of the non-saturated zone, in which gypsum accumulation processes are taking place. In addition to the above mentioned factors, the poor land exploitation system and the lack of integrated management of the oasis system are also important. Due to the high sensitivity of the oasis and in order to overcome the problems, several recommendations were proposed concerning the optimization of the irrigation scheme, the water supply network and drainage schemes. The recommended hydraulic infrastructure, combined with the proposed management rules for the oasis, would lead to better control of ground-water fluctuations and improvement of leaching and aeration processes in the unsaturated zone.