The main problem related to the karst system in Slovenia is its complex and deep structure. In most cases, the karst spring catchment area, recharge and conduit system are unknown. For this reason, the Težka Voda spring was chosen where the size of the catchment area is known and one conduit can be predicted on the basis of tracer tests (Habič, Kogovšek, 1992). The main goal of this master research work is to develop a calibrated groundwater flow model of a karst aquifer drained by the Težka Voda karst spring (SE Slovenia). This will provide the quantification of the system and dynamics of the karst aquifer.
Thus, this work aims to improve the understanding of the Težka Voda spring and to calibrate the model so that it adequately simulates the observed discharge while the hydraulic heads (for which no observation exists) vary within reasonable ranges.
Methods used for defining the parameters for the karst spring of Težka Voda are:
• Numerical calibrated model of the obtained aquifer based on the measured discharge rates of the Težka Voda spring. The model employed is based on the assumption of Darcy flow,
• Groundwater recharge calculation based on the equation soil-water balance approach,
• Sensitivity tests of individual hydraulic parameters,
• Master recession curve computed by the method developed by Posavec, et al. 2017.
The model is used with three representative years, a year with the average precipitation rate, a maximum precipitation year and a minimum precipitation year. The calibrated model will finally be used to assess the impact of changes in the temporal and spatial distribution of recharge on the spring discharge and the hydraulic heads within the aquifer.
The main conclusion of the calibrated model is that the year with the average precipitation rate gives the best estimation and simulation of the measured discharge rates at the Težka Voda spring. Years with extreme precipitation rates do not describe the measured discharge rates. This indicates more complex system conditions than the ones described with the model. Therefore, the model works well for the year with the average precipitation; however, in the case of years with extreme amounts the model fails to simulate these more complex conditions because of the model simplification. Based on the model results the connection between the matrix and conduit flow is well expressed in the karst aquifer.