Three run-off hydropower plants (HPP) with storage are planned to be built in the Central Sava River area, namely the Renke HPP, the Trbovlje HPP and the Suhadol HPP. The construction of the dams will result in river accumulation behind each dam. Changes in surface water levels will consequently also have an impact on the rise in groundwater head. More extensive field research of the area was carried out in 2009, when piezometers were installed, and pumping tests were carried out to determine the hydraulic properties of the geological formations. Groundwater levels have since been monitored manually and, in some piezometers, continuously using pressure probes. Data from previous research was collected and consolidated. The hydrogeological situation was analysed from borehole data, pumping tests, geological and hydrogeological maps. The analysis was carried out using QGIS software, a Geographic Information System (GIS) tool for processing and analysing spatial data. Based on the analysis, the situation has been unified into hydrogeological classes. The goal was to assess the extent to which the rise of water in the reservoir has an impact on the groundwater levels in the immediate vicinity of the stream, based on the data collected. Analytical methods for one-dimensional groundwater flow were used to assist in the impact assessment. The calculations were made in MS Excel and the results were exported as graphs. Due to uneven distribution of the available borehole data, the calculations were made for selected characteristic profiles, named after the piezometers, they cross, and for each barrier of the hydropower plants. Considering the hydrogeological situation, the calculated impacts are shown on a map generated in QGIS. The results show that the permeability of the geological formation has the greatest impact on groundwater, followed by the elevation difference between accumulation head and groundwater head. In addition to the calculations, the hydrogeological situation and local topography are taken into account in the impact assessment.
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