Author: Laura Bačani, mag.ing.geol.
Spring Rakovac is located on the Mt Žumberačka gora in the Poklek area, about 1.5 km NW of the village Koretići and about 1 km NW from Eko Selo Žumberak (Figure 1). This research has been carried out in order to determine the possibility of water usage from the spring Rakovac as an additional source of drinking water for the needs of the public water supply of the City of Samobor. The first step was to design and build a rectangular sharp-crested weir situated directly downstream from the spring (Figure 2). A metal pipe with a cover and a padlock was installed next to the weir, in which automatic data loggers were installed. The logers measure the water level (head) over the weir (Figure 3). Water levels are then calculated into discharges using the flow curve. The flow curve of the spring shows the connection between water levels and discharges. Monitoring of the spring discharge has begun in 2019 and is still ongoing. The Rakovac spring hydrograph (discharge – time graph) shows that most of the monitored time discharges are low, i.e. less than 10 l/s, whereas the discharges greater than 50 l/s appear in less than 10 % of monitored time. On several occasions the discharge was greater than 300 l/s, but such great discharges are of very short duration. Great differences in minimum and maximum discharges, and rapid changes in discharge from a few l/s to several hundred l/s are typical characteristics of karst springs. This youtube link shows the Rakovac spring discharge at 30 l/s (https://www.youtube.com/watch?v=8T99jAE85Xg).
Figure 1 Location of the spring Rakovac
Figure 2 Rectangular sharp-crested weir at the Rakovac spring
Figure 3 Automatic data loggers installed inside the metal pipe
Laura Bačani, mag.ing.geol. is research asistant at Department of Geology and Geological engineering, Faculty of Mining, Geology and Petroleum Engineering, Zagreb University. She is enrolled in Doctoral study Applied Geosciencies, Mining and Petroleum Engineering. Her PhD topic is modeling the water flow in the unsaturated part of Zagreb aquifer.
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