Environmental Study of the Underground Dam on the Recharge of Om Lagsab's Underflow

The objective of this study is to develop a numerical groundwater model for the Om Lagsab system, localized in the area of Gafsa in the Tunisian Southwest, to bring out the impact of the underground dam on the groundwater resources and on the artificial recharge.

In a first stage, we started by collecting the data relative to the different variables as the climate and the hydrogeologic and physical characteristics of the Om Lagsab system; then we proceeded to the development of the hydrogeologic model of this aquifer.

In a second stage, the developed numerical model has been calibrated in steady conditions. The hydrodynamic parameters, which were obtained from the calibrated model, were later used in the simulations of various scenarios. We began with two scenarios: with and without the dam to determine its impact on the recharge of the groundwater system. The obtained results were not also satisfactory; the measured piezometric values and those calculated present important gaps.

Then a third scenario, with new hypotheses based on the geology, was essential to explain these gaps and estimate the role of the dam. The main conclusion stemming from these works is that the underground dam of Om Lagsab had no effective role in the recharge of the groundwater system. This dysfunction was due to the existence of permeable zones which engendered leaks in our reservoir.