The shallow aquifer of Jerba Island is particularly sensitive to sea level rise (SLR) because the island's relief is very moderate and the altitude of the piezometric surface is close to zero. Seawater intrusion is widespread along the coast, but its amplitude varies from one area to another, depending on the groundwater abstraction rate induced by different economic patterns. The freshwater lens found in the eastern part of the island is likely protected by infiltration from the return of irrigation water and some wastewater.
To meet the expected growth in demand, integrated management of all water resources will be essential (irrigation quotas, infiltration of treated wastewater, import of water from the continent and desalination of seawater).
In this study, we are digitally studying the impact of sea level rise (SLR) through the implementation of a 3D-FEFLOW salinity transport model for the shallow aquifer on Jerba Island. The model was calibrated and validated using data from 1992-2018 and allowed the water balance to be reconstructed.
Changes in groundwater and sea water intrusion have been estimated under various climate change scenarios (RCP 8.5 and 4.5). Recharge, abstraction, discharge into the aquifer, precipitation and groundwater requirements were projected under the same scenarios. For each scenario, piezometric and salinity maps were simulated for the years 2030, 2050 and 2100.
Simulations in the model show that the Jerba aquifer is sensitive to SLR and intensive groundwater abstraction. With the increase in population and economic activity, the long-term sustainability of the shallow aquifer is highly dependent on water balance, which can only be achieved with limited groundwater abstraction and significant imports of water from land or sea (desalination). Increasing agricultural production through irrigation is no longer an option. Nevertheless, sustainable management of the shallow aquifer is still possible, with the aim of preserving orchards (palm and olive trees) and tourist activities that form the basis of the island's economy.