Significant seasonal population spikes, a lack of permanent surface water resources, and increasing groundwater pumping for domestic water supply and agricultural irrigation threaten freshwater security on small Mediterranean islands due to saltwater intrusion. On the island of Bozcaada, Western Türkiye, a substantial population increase from tourism during the summer months creates major water demand, exacerbating water management challenges. Despite a mainland-supplied water system serving the island’s main residential area, local wells are still used to meet the needs of remote areas where public water supply is unavailable. Private wells drilled for isolated water supply and agricultural irrigation are overexploiting the island’s coastal aquifers, leading to saltwater intrusion. To simulate the complex variable-density flow and mass transport dynamics within the island's unconfined aquifer, this study develops a three dimensional numerical model using the MODFLOW2005–SEAWAT framework. The model quantifies the freshwater lens geometry and identifies key salinization pathways, such as saltwater upconing and lateral encroachment, through a mathematical modeling approach that integrates geological drill logs with field-monitored hydraulic data. Calibration was performed using a multi-depth approach against observed hydraulic heads and specific conductance data to ensure process accuracy. The model was then validated using data from a 2.5 year field monitoring campaign and online data loggers installed at five locations in the island aquifers. Model results indicate elevated chloride concentrations and electrical conductivity (EC) along the coastal area, particularly in the north, west, and east of the island, where most agricultural activities and tourism facilities are located. The study found that the north and east of the island are especially vulnerable to saltwater intrusion, with upconing primarily resulting from excessive groundwater abstraction for irrigation and domestic use. After establishing the baseline status, the model was used to predict and assess the individual and combined effects of sea-level rise and reduced climatic recharge. The findings show that, in regulating the saltwater wedge position, the spatial distribution of pumping is as important as the total extraction volume. By linking physical process evaluations with water-user stresses, this study provides a robust foundation for decision support that extends beyond conventional modeling. These results offer essential guidance for improving recharge management and well placement to ensure fresh groundwater resilience in highly challenged Mediterranean island environments.
ZULAL et al. (Tue,) studied this question.