Application of Methods for Resource and Source Vulnerability Mapping in the Orehek Karst Aquifer, SW Slovenia

Abstract

In a shallow karst aquifer in SW Slovenia assessment of groundwater and drinking water source vulnerability has been performed using different methods. The small, but well defined, Orehek karst is mainly drained by the no longer exploited Korentan spring. The recharge area of the spring is well karstified, densely wooded, and covered by thin soils. Besides precipitation, the spring is additionally recharged by temporally active sinking streams. To assess the vulnerability, two methods, COP+K and Slovene approach, have been applied. Both methods provide tools for assessing vulnerability in carbonate rocks. They both rank among very sophisticated methods that require vast amounts of data, time, and financial and technical resources. Both methods share the same methodological procedure and consider the same type of information, categorized by the same factors. On the other hand, the scoring, classification and weighting of individual parameters between the methods are different. Consequently, the resulting maps differ significantly. Major differences between the results are identified and discussed. In addition, sensitivity analysis of individual factors have been performed and compared to cross-correlation, autocorrelation and water budget calculations. The results show high dependence of the COP+K method to the parameters characterizing the infiltration conditions (the so-called C factor) and distance to water source. The Slovene approach vulnerability classes are mainly influenced by thickness of the soil cover, presence of morphological features and the temporal hydrological variability that is justified by the performed statistical analysis.