engleski

Groundwater quantity in the Zagreb aquifer

The Zagreb aquifer is built of gravel and sand deposits stretching along the Sava River at the City of Zagreb territory. The municipal water supply relies on the groundwater from the aquifer. The aquifer is of unconfined type and its upper margin of saturation is a phreatic line exposed to the atmospheric pressure. The aquifer is generally replenished by infiltration from the Sava River, infiltration of precipitation, and underground inflows from both west and south. The analysis of the groundwater table data collected for the City of Zagreb area indicates an average groundwater table decrease of 1-2 m every 10 years. Reasons for the groundwater table decrease include: (1) deepening of the Sava riverbed caused mostly by construction of the power plant reservoirs on the Sava upstream from Zagreb, training of tributaries, and gravel mining in the riverbed, (2) increase in groundwater abstraction for the City of Zagreb water supply, and (3) construction of dikes along the Sava River to prevent occasional flooding of the floodplain, and consequently potential infiltration of water from the flooded areas into the aquifer. Total annual pumping rates for all Zagreb well fields exceed the annual groundwater replenishment rates, which mean that the Zagreb aquifer is "overpumped". That part of the quantity pumped that exceeds the replenishable reserves is made up from permanent unreplenishable reserves. The permanent reserve volume was 3.88 km3 in 1976, and 3.72 km3 in 2006, therefore it decreased by 4% in thirty years. To conclude: total groundwater quantity in the Zagreb aquifer is comparatively abundant, however presence of a negative groundwater table trends and excessive pumping from the aquifer ask for caution, which means quality monitoring and systematic analysis and interpretation of the monitoring results. This ensures realistic inputs for an optimum management of water as a strategic Croatian resource.

Zagreb aquifer; groundwater quantity; overpumping

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