THE CATCHMENT-AREA OF THE SV-IVAN-KARST SPRING IN ISTRIA (CROATIA)

This paper discusses the results of a geological, hydrogeological, and hydrological analysis of the catchment boundaries and area of the Sv. Ivan karst spring. The underground watershed has been determined by geological and hydrogeological methods. The control used was the hydrologic water budget analysis appropriate for karst basins with limited data (Turc, 1954). The Sv. Ivan spring includes one main spring and several intermittent springs. The water in the main spring penetrates the flysch layers which limit the spring's discharge; therefore, the discharge of the main spring is fairly uniform. The ratio between minimum and maximum yearly discharges ranges from 1:3.3 to 1:12.8. Only a part of the water flows through the main spring while the other springs in the zone are overflows. The catchment area of Sv. Ivan spring zone is defined as 65 km2.