engleski

THE INFLUENCE OF THE RIVER DAM TE-TO ON THE GROUNDWATER LEVELS OF ZAGREB AQUIFER

Zagreb aquifer consists of gravel-sand sediments saturated with water, which is located in the area of City of Zagreb. It spreads along the Sava River in northwest direction approximately 30 km long, with average width of 10 to 15 km, and thickness of 5 to 10 meters in the western parts, all the way to about a hundred meters in the eastern parts of the system. The groundwater of the aquifer is the basis of City’s water supply, and is currently abstracted at six well fields. The groundwater levels have been permanently decreasing since 1950 in the whole area of the aquifer, and the reasons are mostly attributed to lowering of the Sava River bed, which results in lowering of Sava River water level, to the construction of flood defense banks along Sava River, which prevented potential infiltration of water from flooded areas into the aquifer, and rising exploitation of groundwater for the purpose of water supply. The purpose of this paper is evaluating the influence of river dam TE-TO, constructed at the beginning of 1990’s, on the groundwater level of Zagreb aquifer. For that purpose time sequences of groundwater levels were analyzed in 325 piezometers in Zagreb aquifer in the period from the start of measuring of each piezometer until 2009. Based on the analysis performed, it can generally be concluded that the trend of level decrease has been stopped with construction of river dam, and after construction it continued decreasing in similar intensity, which means the levels are higher today than they would have been if there weren’t river dam. The influence of river dam is the largest in the area of aquifer west from the river dam, and it amounts from 0.2 to 4.9 m while the mean value is 2.3 m, but it can also be identified in parts of the aquifer immediately to the east from the river dam. The influence of river dam is more distinct in the area of the left bank of Sava River, where a significant influence can be followed almost all the way to the west border of the aquifer in the area of Podsused hight, and it is more distinct in the part of the aquifer that is closer to the Sava River. On the other side of Sava River, on its right bank, the influence of dam significantly decreases moving towards western parts of the aquifer. The influence of the dam, on the largest part of the aquifer, does not manifest itself in the increase of the groundwater levels, but in the decreasing of their negative trend, and this process is most distinct in the areas of well fields. Thanks to dam, one of the largest Zagreb’s well field Mala Mlaka is today still active and the leading well field of the City of Zagreb. The received results show that even small dams can significantly decrease the negative trend of groundwater levels in well field areas, therefore when designing new dams on the Sava River, the effect that should be achieved in certain parts of the aquifer should primarily be considered.

Zagreb aquifer ; groundwater level ; impact of river dam

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