Hydrogeological and isotope mapping of the karstic River Savica in NW Slovenia

Hydrogeological mapping comprises a group of methods with which the area of interest is carefully inspected for the appearance of groundwater related phenomena. During the mapping of groundwater and surface water, samples can be collected for further analysis. On the karstic River Savica (NW Slovenia) the methodology of detailed hydrogeological mapping was tested by which, every 100 m along the river course, samples of water were collected for stable isotopic composition of oxygen (delta O-18). River Savica results from two main tributaries (Velika Savica and Mala Savica) recharging on a high mountain karstified plateau with an average discharge of 5.08 m(3)/s. Application of hydrogeological mapping methodology to the riverbed resulted in a conceptual model of the groundwater components entering the river. Based on the end member mixing models and with the application of isotope and electrical conductivity data as conservative tracers, it was possible to estimate the contribution of different karstic groundwater components to the river outflow. For the first time it was estimated that, under low and average water conditions, Mala Savica contributes from 12 to 17 % and Velika Savica from 78 to 82 % of the total River Savica discharge, there being only minor inflow from the other sources.