Karst aquifer average catchment area assessment through monthly water balance equation with limited meteorological data set: Application to Grza spring in Eastern Serbia

In the absence of detailed exploration of karstic catchments, the calculation of available reserves and elements of the water balance equation frequently reflect the topographic size of the catchment area, and not the actual, active (underground) size. The two differ largely where karst is concerned. The paper deals with the problem of average catchment area size estimation in the situation when meteorological data are limited to precipitation and temperature, but discharge records are available for long period. Proposed methodology was applied to, calibrated, and validated on 15 karst springs in Serbia. Results obtained with the model differ up to 20% from hydrogeological exploration results. One of investigated springs is Grza karst spring, which belongs to the karstic formation of Kučaj and Beljanica (the Carpatho-Balkanide Arch of Eastern Serbia). In this paper, we used the Grza Spring to show model application and necessary improvements to progress from graphoanalytical to analytical model. The average catchment area is linked to the model parameter that reduces potential to real evapotranspiration on monthly bases. The model potential lies in the possibility to determine not only catchment area, but real evapotranspiration and dynamic volume of the porous - karst groundwater storage as well