Integrated Groundwater Flow Modeling for Managing a Complex Alluvial Aquifer Case of Study Mio-Plio-Quaternary Plain of Kairouan (Central Tunisia)

In central Tunisia, anthropic activities, such as groundwater abstraction for irrigation, have resulted in excessive groundwater level declines of the Mio-Plio-Quaternary aquifer hosted in Kairouan Plain. Besides, the two dams El Houareb and Sidi Saad's impoundment since the 1980s has deeply modified the natural process of aquifer recharge. Hence, some studies claim the dam's instauration of this groundwater depletion; however, some other studies attribute this critical situation to an issue of groundwater management. A multidisciplinary study was carried out to retrace the groundwater flow dynamics for 48 years before and after the dams' erection and to understand the main factors causing the groundwater depletion. Hence, a conceptual model was developed based on gathering all available data from 114 borehole logs, 10 seismic lines, and 08 petroleum wells. Based on this reconstructed geometry, the groundwater head was simulated using the numerical code Modflow. The model was calibrated in steady-state with reference to the piezometric levels measured in 1969 and in the transient state for the period 1970-2017 and validated for the period 2007-2017. The outputs of the calibrated model show a relevant finding of the decrease of the inflows coming from the rivers' beds (Zeroud and Marguellil) from 1990 to 2017 by 48%; yet, the pumping rate has increased by 119%. The simulated scenario without dams and maintaining the same withdrawals has shown a groundwater level rise downstream of the plain; yet, in its upstream, the depletion was less intense compared to the current model. However, the case of doing without dams and raising withdrawals from the aquifer has generated a huge decline reaching 22 m near Draa Affane.