Quaternary Deposits as the Hydrogeological System of Eastern Slavonia

The area of eastern Slavonia, situated between the Drava and Sava rivers, comprises three geotectonic units: the eastern part of the Drava depression in the north, part of the Slavonia-Srijem depression in the south and the central Djakovo-Vinkovci plateau together with the Vukovar plateau. These units are separated by deep faults that reach the base of the Tertiary sediments. The first 200 m of Quaternary deposits are saturated with fresh water. The aim of this study was to find out whether the faults form impermeable boundaries separating the waterbearing deposits into independent hydraulic systems, or if a singular hydraulic entity exists. Results of the analysis indicate that lithological continuity of the aquifers exists along the fault zones on the margins of the Djakovo-Vinkovci and the Vukovar plateaux, which means that there is no impermeable hydraulic boundary on the watershed between the Sava and Drava river valley. The part of eastern Slavonia between the Sava and Drava rivers is one hydraulic system consisting of zones with different transmissivity values. In the zones of reduced transmissivity, the hydraulic connections are weakened, but not broken. Such zones exist not only along the fault zones of the Djakovo-Vinkovci plateau and the Vukovar plateau, but also within the Sava and Drava depressions. The terrain morphology influenced formation of both the surface and the underground watershed, parallel to the extension of the Djakovo-Vinkovci and Vukovar plateau. Therefore, within this single hydraulic entity, when the draw-down reaches the watershed due to excessive pumping, the watershed will be displaced from its natural position