3D geological modeling for complex aquifer system conception and groundwater storage assessment: Case of Sisseb El Alem Nadhour Saouaf basin, northeastern Tunisia

With water table drop, managers got extremely concerned about the future of the groundwater resources sustainability of the Sisseb El Alem Nadhour Saouaf aquifer (SANS). In order to understand the groundwater flow dynamic and to assess the functioning of the aquifer system, a three-dimensional (3D) regional geological model of the SANS basin was carried on. The 3D geological model was developed by the combination of 2D seismic reflection profiles, calibrated by wireline logging data of oil wells, hydraulic wells and geological field sections. The 3D geological model shows that the Oligo-Neogene and Eocene aquifers in the study area represent important geometric variations and cumulated thickness affected by intensive fractures. The modeled stratigraphic units were combined with the hydraulic properties to estimate the groundwater storage. The estimated storage in 2016 was around 11 × 109 m3 and in 1971, it was 16 × 109 m3, so, 30% of the groundwater stored previously was consumed in 45 years. Yet, a variable spatial distribution of storativity was demonstrated, ranging from 1 to 3.4 × 106 m3/km2. These results prove the importance of hydro-geophysical investigation and numerical modeling to depicting hydrostratigraphic trends and suggest, that the fate of groundwater resources in the SANS aquifer seems though to be more a matter of the disparity of the groundwater storage than a matter of quantity.