Characterisation of karst aquifers on regional and local scales: the recharge area of the Malni water source

The global challenges of drinking water supply will further increase in light of projected social and environmental changes. Karst aquifers are important sources of drinking water, supplying a quarter of the world's population and a good half of Slovenia’s. In karst, the flow is focused into conduits that drain water toward abundant springs. Because the position and size of conduits are known only to a very limited extent, the spatial and temporal distribution of water flow is unpredictable, making protection of karst aquifers difficult. This fact is especially true for aquifers in a tectonically active and structurally complex environment, such as the Dinaric Karst. Characterization of an aquifer aims to determine the structural, hydraulic, transport and geochemical properties of the aquifer. Due to the high heterogeneity of karst aquifers, extrapolation of local aquifer characteristics to a regional scale is practically impossible. On the other hand, for the same reason, processes at the local level (e.g. constriction or breakdown in an important conduit) may affect a wide area, including the abundance of and potential risks to springs. The project will address the hydrological system of springs at the southern edge of Planinsko polje, which receive water from the Notranjska poljes, the Pivka Basin and the Javorniki aquifer. The Malni Spring is a water source for 21,000 inhabitants of the Postojna and Pivka municipalities. Increasing demand for the water and various risks due to human activities call for better understanding of the entire hydrological system, from the point of view of water supply and from the point of view of understanding and protection of the karst natural heritage. It is known the past research that the regime of Malni and Unica springs is largely determined by the situation in the Mysterious Lake in the cave Planinska Jama. There waters from the Notranjska poljes and from Javorniki aquifer merge and then further diverge to the Unica and Malni Springs. We will apply and develop a method, which combines speleological research, hydrological measurements and hydraulic models, to explore the dynamics and mechanisms of the local temporal and spatial flow distribution. This will allow us to assess and propose the possibilities of direct capture of the autogenic water of the Javorniki aquifer, which is less exposed to pollution. Similar research will be continued at the eastern edge of the Pivka basin, where access to the groundwater of the Javorniki aquifer is possible in the caves Matijeva Jama and Jama v Ždinku, which have been identified as potential water sources in a previous project. Research on a regional scale will focus on water budget, quantity, quality and risk. Distributed recharge models will be applied, taking into account the characteristics of the soil, epikarst and vadose zone. A regional model of the Javorniki aquifer will be built in the MODFLOW-USG environment, which accounts for flow in conduits. The model will be iteratively adapted to fit regional flow patterns and water level dynamics. The model will also be combined with the recharge model to assess the water balance and determine the boundaries of the aquifer. The research will also focus on better determination and understanding of solute and particle transport in the catchment of the investigated water sources. Models will be used to simulate different scenarios of transport and will be compared to field results of the measurement network and results of dye tracing experiments. Another goal is to evaluate current quantitative and qualitative status of the selected water sources and to suggest their optimal use. In assessing the possibilities and conditions of their use in the future, we will predict the risks of pollution due to different human activities, as well as the quantitative availability due to changes in land use and climate change. We will develop an early warning system for pollution and a proposal for quality monitoring.