engleski

Protection of the Miljacka karst spring: an underground connection between the rivers Zrmanja and Krka

Miljacka is a karst spring situated in the Krka River canyon, in Dalmatia, Croatia. Its catchment is mostly built of karstified carbonate rocks and it is a part of well known Dinaric karst. During the last few years a bulk research program was performed in the Miljacka spring catchment area. Achieved results comprise all previous conclusions, together with some new aspects. The main reason for this research was establishment of sanitary protection for this strategically important karst spring. Sanitary protection zones were proposed, but because of some new understandings of this complex karst system, they will have to be extended in the future with parts of the Krka River catchment area. Although the Miljacka spring is situated in the Krka River canyon, majority of its water flows from quite distant Zrmanja River, which was proven by dye tracer tests in the past. During the recent research, hydrochemical investigation of the Miljacka proven that it is only partially true, and some portion of the spring water originate from the Krka River as well. Therefore, significant parts of the terrain will have to be added to the Miljacka spring catchment area and to sanitary zones as well. The most of the investigated area is built of karstified carbonate rocks, of Eocene-Oligocene (Promina rock mass), Cretaceous, Jurassic and Triassic. Complexity of this karst system is especially presented with the main characteristics of the Zrmanja River, which usually dries out in the swallow-hole zones during the summer dry season. These swallow-hole zones are active throughout the year and water that infiltrates the karst underground in that area discharges mostly at the Miljacka spring. This “hanging” part of the Zrmanja River was proven with boreholes in the past years, but that phenomenon should be investigated in detail. The main problem for any hydro-researcher of the Miljacka spring is shortage of the measured discharge data. This can be avoided in the future either by construction of the direct measuring place, or by measurements on the Krka River profile, but very close to the Miljacka (up and down stream), because the possibility of existence of swallow holes in river bed is quite high.

karst spring, hydrogeology, sanitary protection zones, Dalmatia, Croatia

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