Abstract
This study examines historically measured groundwater levels on observation wells of Zagreb and Samobor-Zapresic aquifers since the 70-ies of the 20th century until today. The analysis also entails older groundwater level maps dating from the 60-ies of the previous century, which offer additional insights into the historical groundwater levels. The analysis of the existing groundwater levels and historical groundwater levels has identified changes of those levels in certain areas of the aquifer, special reference being taken to developments which, with time, led to deceleration of negative trends of groundwater levels in certain parts of the aquifer. The most significant such developments in the past 50 years or so are the construction of the weir of the Zagreb cogeneration plant (TE-TO) in the Sava river and occurrence of hydrologically above-average favourable years like 2013/2014, which have been separately analysed. The analysis has found that today's groundwater levels in Zagreb and Samobor-Zapresic aquifers are generally lower by approximately 3 to 6 m in comparison with the historical levels from the 60-ies of the last century.
Highlights
Groundwater is an important freshwater resource used for irrigation, industrial needs, and public water supply in many countries of the world, the same is true for the Republic of Croatia, where 90% of the needs for public water supply is satisfied by groundwater exploitation
The analyses have shown that, on average, groundwater levels declined by 1-2 meters every 10 years, and the main causes of continuous decline of groundwater levels in the Zagreb and Samobor-Zaprešić aquifers are to be found in the lowering of the river bed of the Sava River, the construction of levees for protection from flooding which disabled occasional flooding of the hinterland and infiltration of water from flooded areas into the aquifer, as well as groundwater exploitation for the needs of public water supply of households and industry
As far as the wellfields used for public water supply are concerned, the medium groundwater level amounted to approximately 128.5 m a.s.l. in the area of the Bregana wellfield, approximately 123.5 m a.s.l. in the area of the Šibice wellfield, and approximately 122.5 m a.s.l. in the area of the Strmec wellfield
Summary
Considering the importance of groundwater, numerous authors have examined the main causes of groundwater level decline. The analyses have shown that, on average, groundwater levels declined by 1-2 meters every 10 years, and the main causes of continuous decline of groundwater levels in the Zagreb and Samobor-Zaprešić aquifers are to be found in the lowering of the river bed of the Sava River, the construction of levees for protection from flooding which disabled occasional flooding of the hinterland and infiltration of water from flooded areas into the aquifer, as well as groundwater exploitation for the needs of public water supply of households and industry. Considering the engineering interventions in the Sava River in the form of construction of the weir of the Zagreb cogeneration plant TE-TO (Biondić, 1995), as well as the occurrence of hydrologically above-average favourable years such as 2013/2014, the author has analysed the developments which have temporarily slowed down the negative trends of groundwater levels, but haven’t halted them
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