Implications of groundwater development and seawater intrusion for sustainability of a Mediterranean coastal aquifer in Tunisia.

Tunisia relies extensively on coastal groundwater resources that are pumped at unsustainable rates to support irrigated agriculture, causing groundwater drawdown and water quality problems due to seawater intrusion. It is imperative for the country to regulate future groundwater allocations and implement conservation strategies based on robust hydrogeological assessments to alleviate the adverse impacts of groundwater depletion. We developed a 3D transient density-dependent groundwater model by coupling MODFLOW-2000 and MT3DMS to improve understanding of seawater intrusion into the Korba aquifer in Tunisia. Results indicate that groundwater overexploitation since 1965 induced 5.15 Mm3/year of seawater inflow while reducing submarine discharge into the sea by about 9.74 Mm3/year as compared to the steady state water budget in 1965. Projecting withdrawals from 2014 up to 2050 results in a slow but extensive groundwater table decline forming a cone of depression 15 m below sea level. The seawater wedge under this business-as-usual scenario is expected to reach 1.8 km from the shoreline, causing significant mixing of the TDS-rich seawater in the aquifer system. The cone of depression under a 25% increase in groundwater withdrawal drops to about 20 m below sea level while the saltwater front reaches 2.5 km inland. Countering the seawater intrusion problem requires reducing groundwater pumping by 17 Mm3/year to push back the saltwater front along the coastline by about 25% over a 43-year period. Application of the presented generic groundwater simulation framework guides developing management strategies to mitigate seawater intrusion in the Korba coastal aquifer and similar areas.