Karst aquifers can be quite complex regarding structure and water flow. To characterize them properly and to better understand their functioning, one needs to monitor them continuously in various points, such as springs, ponors, water-active caves and surface streams.
The Malenščica karst spring is one of the most important water sources in Slovenia, and provides water for more than 22.000 people. The catchment covers almost 800 km2 large binary karst aquifer recharged by both an allogenic and autogenic component that can vary depending on the hydrological conditions. The allogenic inflow coming from upstream located poljes makes the water resource quite vulnerable to contamination during medium to high flow conditions. On the other hand, an assessment of volume of autogenic water available during low flow is crucial for the local water supply.
A dense monitoring network was set up in autumn 2016. Autonomous data loggers measuring water pressure, temperature and electrical conductivity in 30-minute intervals were installed at six springs, four ponors, three surface streams and seven water-active caves. In addition, two rain-gauges are measuring precipitation at the same time interval. The data collected in the period from October 2016 to September 2018 were then sorted out and combined with hydrological data of the Slovenian Environment Agency and manual measurements of water discharges to elaborate several rating curves. This allowed quantification of discharge components, constructing a water balance of the whole aquifer depending on the hydrogeological conditions, in order to determine the influence of different types of recharge, and to assess recharge-discharge relations.
The results improve the current understanding of the investigated aquifer, and show the importance of considering temporal variations of drainage area in hydrogeological studies. The results can further be used for risk assessment of the karst aquifer and protection strategies of drinking water source.
Key words: karst aquifer, autonomous measurement, water balance, hydrologic variability.