Abstract
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.
Highlights
Laboratory of Water Science and Technology, National Agronomic Institute of Tunisia, 43, Avenue, Abstract: 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
The recharge process is limited to El Houareb dam leakage and Ain El Beitha flow infiltration through the karst formation [8,11,12]; and the Kairouan plain aquifer has started experiencing a net groundwater depletion [13,14]
To detect the impact of the two dams’ impoundment on the groundwater level trends and what the situation would be if the two Sidi Saad and El Houareb dams were not and what the situation would be if the two Sidi Saad and El Houareb dams were not conconstructed beside the impact of the raise in pumping rates on this decline, two scenarios structed beside the impact of the raise in pumping rates on this decline, two scenarios were defined based on existing data on dams and aquifer withdrawals
Summary
The Kairouan plain basin (Central Tunisia) has faced a serious issue of groundwater resources degradation, a problem that is emblematic in semi-arid and arid regions (e.g., Ethiopia [1], Egypt [2]). Since the 1980s, to protect the Kairouan city from hazardous floods and to mobilize groundwater resources essentially for irrigations purposes, two dams have been erected, namely Sidi Saad and El Houareb These dams have deeply modified the groundwater cycle both in terms of fluxes and processes [8,9] and the floodwater hardly reaches the aquifer [6,10], “erection of large dams and erosion control structures moved and reduced the recharge fluxes [11]. In a first step, it is essential to develop a conceptual and groundwater flow model, starting from borehole data, well-pumping tests, and well monitoring, so as to investigate the general groundwater flow behavior and the main flow budget components as well as to simulate the groundwater head from 1969 to 2017 This needs a straightforward model, which should be able to capture the general groundwater flow behavior within the Kairouan plain aquifer, without introducing complex fine-resolution even though the real system is heterogeneous. To satisfy the requirement of simplicity and robustness, a multi-dimensional approach is proposed and illustrated for the Mio-Plio-Quaternary aquifer
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