Development of a Protocol for the Karst Water Source Protection Zoning: Application to the Classical Karst Region (NE Italy and SW Slovenia)

Although karst aquifers are highly vulnerable and represent an important water resource, they are often inadequately protected. Furthermore, national water resource protection policies lack precision regarding the criteria for delimitation of source protection zones in karst. Usually either vulnerability assessment or travel time is considered. The proposed integrated protocol considers both. It is specifically designed for large karst aquifers where i) an additional distinction between areas of different liability to contamination within the aquifer, and ii) a certain generalisation of protection classes should be made for practical reasons. The protocol includes a detailed description of the separate steps of the protection zoning procedure. Information obtained from both artificial and natural tracers is used to account for the variability of groundwater flow under different hydrologic conditions. Analysis of groundwater physico-chemical parameters time series is better employed under high flow regimes and analysis of artificial tracers breakthrough curves under low flow conditions. Source protection zones are divided into three levels of protection, which should be further generalised, validated and adjusted to land use plans. The protocol has been applied to the Classical Karst Region transboundary aquifer (NE Italy and SW Slovenia). The results enable a uniform delineation of protection zones encompassing water sources that have not been protected to date, and improve the understanding and management of transboundary aquifers. The proposed protocol can be used in other karst aquifers, and adjusted to national protection legislation and spatial planning frameworks.