Le lac Ichkeul : Equilibre naturel et effets anthropiques

The Ichkeul lake: natural equilibrium and anthropic effects

¹ Maître Assistant à l'Ecole Nationale d'Ingénieurs de Sfax, Département de géologie
² Maître de conférence à l'Ecole Nationale d'Ingénieurs de Sfax, Département de géologie
³ Ingénieur à l'Agence Nationale de Protection de l'Environnement, Département de géologie, Ecole Nationale d'Ingénieurs de Sfax

Abstract

In Tunisia, runoff waters mobilisation constitutes a key element for economic activity. Consequently to the recent economic progress and demographic growth, three dams were constructed and three others are projected in the Ichkeul catchment. lchkeul Lake, located at this zone, forms the natural outlet of numerous wadis in the region. With its three international classifications, this lake is found to be faced to a perturbation which may irreversibly affect is biotope equilibrium. The Ichkeul catchment covers a surface of 2080 km² of which 90 to 100 km² are occupied by the lake. It presents a well developed hydrographic system. The continental waters are yielded to the lake by eight main wadis: Morra, Douimis, Sejnane, Ghezala, Melah, Joumine, Mellah and Metrif. The Tinja wadi ensures the marine water supply from Bizerte Lake during the dry period. In the wet season the flow is reversed and waters circulate from Ichkeul lake to Bizerte Lake. The dams controlled area of the catchment is 833 km². It represents 40% of the total catchment surface. The water supply of the three constructed dams is estimated at 250 million m³ representing approximately 70% of the total lake water supply. The second problem which may affect the lake water quality is related to domestic and industrial waste waters that reach the lake through the numerous wadis or by direct discharge. These waters are containing a lot of organic compounds at high concentrations. The cities neighbouring the lake (Menzel Bourguiba, Tinja and Mateur) have a total of 77 000 inhabitants. The waste water generated from these cities is estimated at 24 000 m³/day. These waters are discharged into Bizerte Lake from Menzel Bourguiba city and into Ichkeul Lake from Tinja and Mateur. Up to the end of 1997 no domestic or industrial waste water plant existed in the region.