Prospective assessment of the water balance of the Northern Gafsa Aquifer, South-western Tunisia

Abstract

The United Nations (UN) annual report on water resources released in 2015 announced that the world will face a global water deficit of about 40% by the year 2030. Around half of the world’s population depends on groundwater for fulfilling the daily consumption (drinking; domestic use). As humans require a water supply for their survival, it seems important to establish an adequate strategy for water resources management and for predicting the water balance which in their turn enable the estimation of groundwater recharge. Such a task has been the focus of the present study. This study intends to estimate the average recharge and predict the water situation under different scenarios up to 2050 for the Northern Gafsa aquifer (South-Western Tunisia), characterized by an arid climate. The estimation of the recharge rate and water balance depends on the piezometric data (recorded by 16 piezometers during 18 years (2001–2018)) which was used in the balance sheet method and in the interpolation by Arcgis software. The spatial study of the piezometric variation during the period between 2011 and 2018 has revealed that the southern part of the aquifer is the most vulnerable to depletion. The prediction of the water situation of the studied aquifer is established on three scenarios, corresponding to exploitation growth rates of 2.2, 4.8 and 8.5% for scenarios 1, 2 and 3, respectively. The average recharge rate in the Northern Gafsa aquifer was estimated of 25.6 mm/year. Simulations of the examined aquifer depict a negative water balance and a continuous drawdown. The 8.5% growth rate (Scenario 3) is expected to cause the total depletion of Northern Gafsa groundwater in 2045. Indeed, this serious situation requires the establishment of an adequate strategy to mitigate the current overexploitation (limiting illicit drilling…) and to satisfy the growth in water needs (finding other water resources…).