Lumped-parameter models as a tool for determining the hydrological parameters of some groundwater systems based on isotope data.

The use of lumped-parameter models for interpreting environmental tracer data is based on the assumption that the transit time distribution function of the tracer particles through the groundwater system under consideration is known or can be assumed. These functions describe the whole spectrum of the transit times of single tracer particles transported through the system between the entrance (recharge area) and the exit (spring, stream, pumping well). The main parameter of each model is the mean transit time of water through the system. This parameter is determined by calibrating the model using the environmental tracer concentrations measured in the output. Additional useful hydrological information can be derived from the model parameters. The paper presents the transit time distribution functions of some commonly used lumped-parameter models and shows examples of their application for solving bank filtration problems (drinking water supply for Passau, Germany), and determining the water dynamics and water balance in a heterogeneous karstic aquifer (Schneealpe, Austria).