The conceptual hydrogeological model of the Plitvice Lakes

The Plitvice Lakes National Park, founded in 1949, is located in the central part of the Dinaric karst region in Croatia. Large karst springs and 16 lakes separated by tufa barriers and waterfalls are the fundamental natural phenomenon of the national park, which has a million visitors a year. Lakes are recharged by water from the mountainous region of Lika, and the runoff is directed towards the Black Sea catchment. The whole area of the National park is composed of carbonate rocks with different levels of natural permeability and very complex tectonic relationships, which allowed discharge of groundwater, maintaining the lake and finally partial loss of water to the karst underground after passing through the lake system. Proscansko and Kozjak are the two largest lakes which dominate and by their internal dynamics ensure maintenance of the high water quality of the whole system. A conceptual hydrogeological model of the Plitvice Lakes was the result of complex research in the framework of international cooperation between the University of Zagreb and the Joanneum Research Institute in Graz. The research identified completely new data about the genesis of the water system, the hydrogeological characteristics of the karst water catchment, the dynamics of the water in the lakes, locations of water loss from the Plitvice Lakes system, the hanging position of Lake Kozjak in relation to groundwater and a whole range of other data important for the preservation and protection of water resources in the National Park. Throughout the project were made 3022 measurements of different physicochemical parameters, 7885 of the chemical analysis of water and 1082 analysis of stable isotopes.