Comparative application of four methods of groundwater vulnerability mapping in a Slovene karst catchment

Abstract

Four methods of groundwater vulnerability mapping have been applied in a Slovene karst catchment and validated by tracer tests. The test site is characterised by high water table fluctuations, manifested in intermittent lakes and variable drainage divides. A first multi-tracer test (two injections) allowed subdivision of the catchment into zones of different degrees of contribution ('inner zone' and 'outer zone'). For vulnerability mapping, only methods that consider the specific nature of karst aquifers such as heterogeneity and duality of infiltration processes, were selected: EPIK, PI, the 'Simplified Method' and the 'Slovene Approach'. For validation, a second multi-tracer test (four injections) was carried out. The time of first detection and the normalised recovery were used as validation criteria. The results suggest that EPIK and the Simplified Method sometimes overestimate vulnerability, while PI and the Slovene Approach tend to deliver more realistic results, at least during low-flow conditions. The Slovene Approach gives the clearest guidance on how to deal with hydrologic variability, for example by assigning lower vulnerability to occasionally active sinking surface waters than to permanent ones. As a conclusion, commonly accepted validation techniques are needed and should be applied by default to evaluate different vulnerability mapping methods and the resulting maps.

Karst spring catchment: an example from Dinaric karst

“…As a consequence of fast GWL rising, numerous temporary karst springs as well as overflow of groundwater from one to the other (not only neighbouring) can emerge in karst spring catchment. This can be a reason for quick changes of karst spring catchments (Andreo et al 2009;Binet et al 2006;Birk et al 2014;Bonacci 1999;Bonacci et al 2013;Fabre and Perrineau 2001;Finger et al 2014;Ravbar and Goldscheider 2009;Terzić et al 2014). …”

“…Parts of karst springs' catchments (drainage basins) were divided into inner and outer zones by some authors (for example Ravbar and Goldscheider 2009). In some cases inner zone represents autogenic (Ravbar and Goldscheider 2009), while outer zone is allogenic (BaillyComte et al 2012;Ravbar et al 2012;Birk et al 2014) part of the karst spring catchment.…”

Recent advances in karst research: from theory to fieldwork and applications

“…Nevertheless, vulnerability maps may be of no help, or even provide questionable/wrong information, if they are not accompanied by the correct interpretation of the hydrogeological setting. This requires the validation of karst vulnerability maps, which may be pursued by applying several different techniques (Ravbar & Goldscheider 2009), such as tracer tests, isotope analyses and hydrograph studies.…”

Groundwater vulnerability based on four different assessment methods and their quantitative comparison in a typical North European Lowland river catchment (the Pliszka River catchment, western Poland)

“…Vias et al (2005) com pared re sults ob tained from four in dex meth ods for dif fuse flow in a car bon ate aqui fer and no ticed that they gen erated maps that were dif fer ent but shared gen er ally sim i lar spatial dis tri bu tions of vul ner a bil ity. How ever, in cer tain ar eas, differ ent meth ods may also pro vide thor oughly dif fer ent re sults, ren der ing the re sults un re li able (Ravbar and Goldscheider, 2009).…”