engleski

Origin and dynamics of aquifer recharge in Zagreb area

The Zagreb aquifer system is located in the NW part of the Republic of Croatia, in the urban area of the Croatian capital, along the Sava River. Numerous well fields are accommodated within this aquifer system, which are crucial for the water supply of the City of Zagreb and its greater region. The aquifer is unconfined and connected to the Sava River. It covers area of approximately 350 km2. The aquifer system is built of two Quaternary aquifers deposited during the Middle and Upper Pleistocene (lacustrine-marshy deposits) and Holocene (alluvial deposits). Considering hydrogeological aspects, the Quaternary deposits are divided into three basic units: aquifer system overburden built of clay and silt ; shallow Holocene aquifer built of medium-grain gravel mixed with sands ; and deeper aquifers from Middle and Upper Pleistocene, with frequent lateral and vertical alterations of gravel, sand and clay. The Sava river, which is the main source of groundwater recharge within aquifer system, is in direct hydraulic connection with the shallow aquifer, which has extremely high values of hydraulic conductivity (up to 3000 m/day). Recharge of the aquifer also occurs through the precipitation, but the changes in the Sava river water levels dominantly influence the changes in the groundwater levels across the whole aquifer. The estimation of the origin and dynamics of aquifer recharge with reference to interactions between the surface waters (precipitation, Sava river) and groundwater was supported by the European Community 7th Framework Project GENESIS (226536). The project was conducted by sampling of groundwater at three piezometers located on the right bank of the Sava river and surface water of lake Bundek. To reach the goals samples were analyzed for stable oxygen and hydrogen isotopes. At the same time environmental tracer data (δ18O, δD) were collected continuously from precipitation and Sava river. All isotope analyses were accompanied by the chemical properties measurements of the water samples. Samplings were performed on monthly basis (δ18O, δD) during the period from January 2011 to January 2012. Stable isotope analyses indicated different infiltration times of surface water of the Sava River to different wells.

Zagreb aquifer; Groundwater; Stable isotopes

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