Addressing water resource challenges on Vis island, Croatia: an integrated approach to karst aquifer management

Vis is a small, remote island in the eastern Adriatic Sea predominantly composed of karstified carbonate rocks. The unique geological and hydrogeological context results in an autonomous water supply from its karst aquifer. The primary extraction site, the Korita well field in the central part of the island, benefits from natural protection against seawater intrusion via two hydrogeological barriers: (i) an impermeable volcanic-sedimentary-evaporite rock complex connected to a diapir structure to the west, and (ii) a zone of reduced permeability beneath karst poljes to the south. The current pumping capacity (up to 42 l/s) meets the local population demand. However, peak summer tourism and changes in precipitation patterns attributed to climate change impose significant stress on the groundwater resource during dry periods, leading to occasional supply reductions in the recent past. To address this issue, interdisciplinary research has been conducted over the past two decades to ensure the sustainable utilization of this primary resource under changing climatic conditions.

This research incorporates detailed aquifer and catchment characterization through a combination of methods: hydrogeological (pumping and tracer tests, continuous groundwater level, electrical conductivity, and temperature monitoring), hydrochemical (groundwater ion composition and isotope analyses), geophysical (electrical resistivity tomography, seismic refraction, and magnetotellurics), structural (fault and fracture analysis), and hydrological (water balance calculations and climate modeling). These investigations are complemented by socio-economic analyses of future water demand and the feasibility of managed aquifer recharge solutions.

Results indicate long-term stability in groundwater quality and quantity despite variable precipitation (the sole recharge source), suggesting substantial groundwater reserves and resilience to seasonal pumping peaks and periodic droughts. However, increasing water demand, climate change, and the risk of seawater intrusion pose potential threats. Ongoing and future researches aim to develop a comprehensive sustainable water management strategy, encompassing: (i) identification of potential new extraction zones and well development, (ii) an early warning system for seawater intrusion, (iii) optimized pumping rates at Korita, (iv) revitalization of rainwater harvesting for agricultural irrigation, (v) managed aquifer recharge, and/or (vi) implementation of small-scale desalination.

Acknowledgment: This research was conducted in the scope of the internal research project SIS-VIS at the Croatian Geological Survey, funded by the National Recovery and Resilience Plan 2021–2026 of the European Union – NextGenerationEU and monitored by the Ministry of Science, Education and Youth of the Republic of Croatia.