ABSTRACT

Quantification of natural groundwater recharge in three study sites within the Great Hungarian Plain was performed using environmental tracer techniques, based on utilization of tritium and helium-3 isotopes in groundwater samples taken from multilevel well-nests. Transport models were calibrated by the measured ³H activities at different depths below surface. The 1963 tritium bomb-peak was used to determine the average natural groundwater recharge. Rates of 48 ± 6 mm/yr, 62 ± 8 mm/yr and 27 ± 3 mm/yr, respectively were obtained. The ³H/³He dating technique was also used to determine age profiles at the three sites, giving recharge rates of 48 ± 6 mm/yr, 63 ± 9 mm/yr and 22 ± 4 mm/yr respectively. Although the recharge rates calculated by the two methods agree well with each other, these two approaches to recovering recharge rates are based on different recharge properties. Modelling of the bomb peak distribution is mainly affected by the position of the bomb peak, hence the recharge rate obtained is not necessarily reliable for recent decades. In contrast, the ³H/³He age-depth profile averages the last 4–5 decades, and therefore may provide a better estimation of long term recharge. A third approach to calculating recharge rates using a simple soil moisture—stable isotope approach was found to only be reliable over the most recent few years.