Significance of validation for karst aquifers' vulnerability assessments: Antalya Travertine Plateau (Turkey) application

Vulnerability maps were generated for Altmova Region within the Antalya Travertine Plateau based on DRASTIC, SINTACS, EPIK, COP and PI methods. Majority of the study area is covered by productive karstic aquifer, which is composed of travertine. Travertine includes typical karstic features such as dolines, springs and caves where groundwater of travertine aquifer is the sole source for irrigation. Areal extends of low, medium, high and very high vulnerability classes and their areal extends were determined for all methods and compared with each other. High and very high vulnerable areas covered > 74% of the study area as investigated by all methods, except PI. Although PI is a specific method for karstic aquifers, this method could not generate a reasonable vulnerability map based on the assigned parameter definitions and scores. Only areal extents were not sufficient to decide about the proper vulnerability method for the study area. Therefore, NO3- concentration based validation method was performed for all generated vulnerability maps. Consequently, the areas which had NO3- concentrations higher than 30 mg/L were matched with high-very high vulnerable areas. According to this validation method, application of SINTACS with "karstic aquifer" weights could validate 95% of the area with NO3- concentrations higher than the selected threshold level of 30 mg/L for Altmova region. This study showed that simulation performance of vulnerability methods was highly related to the defined parameter definitions, score ranges and weights of each method. Similar parameters with variable score ranges could create considerably distinct vulnerability maps. Validation is the essential interpretation step for taking decision on the proper vulnerability method. Additionally, site-specific contaminant observations are critical for validation of vulnerability maps. Validated vulnerability maps could be used as a valuable water resources management tool.