Karst groundwater source protection based on the time-dependent vulnerability assessment model: Crnica springs case study, Eastern Serbia

The implementation of sanitary protection zones is one of the most widely used approaches for preventive groundwater protection. Current regulations are usually based on the determination of the horizontal groundwater travel time component, while the vertical component is commonly neglected. Karst aquifers are especially sensitive to contamination through the unsaturated zone, and consequently numerous methods for determining intrinsic vulnerability have been developed. Many of these methods take into account the effects in the unsaturated zone, but mostly by indirect means. Vulnerability assessment methods do not fully reflect the component of groundwater residence time, making groundwater delineation zoning more difficult, with possible ambiguous and subjective results. Therefore, a method that incorporates the two equally important components (horizontal and vertical) is needed to facilitate groundwater protection zoning. The time-dependent model represents a redesigned vulnerability assessment method, created for karst aquifers, to incorporate the travel time component. This model incudes horizontal and vertical groundwater flow components and also considers a surface component toward ponor zones. The baseline for groundwater travel time through the unsaturated zone was adopted from the Time–input method. The estimation of the horizontal travel time component was based on the conceptual duality of flow in karst aquifers, which has fast and slow components. For the allogenic part of the karst aquifer catchment area (subcatchments of the ponor zone) travel time components were estimated according to different influencing factors e.g. slope, soil type, vegetation, and rainfall intensity. This methodology was tested on the case example of the Crnica karst source located at the western part of the Kučaj anticline in Eastern Serbia. The methodology was shown to be more accurate and appropriate for the delineation of the groundwater protection zones than existing approaches.