Insights into riverbank filtration hydraulics through high temporal resolution analysis of transit time distributions

Abstract In the current study transit time distributions (TTDs) and mixing ratios (MR) are determined and analyzed in the riverbank filtration (RBF) systems of two operating waterworks along the Danube River. Particle tracking method was used based on a calibrated and validated numerical groundwater flow model of both groundwater resources. TTDs and MRs are showing temporal variation and are highly dependent on the instantaneous river stage and pumping rate. The validity of the obtained TTDs is verified by applying a weighted temporal mean method and comparing its result to observed stable isotope data. The water production at the two RBF systems is dominated by water of river origin. The median mixing ratio is above 90% for each studied well. Median transit times can range from around 10 days to 6 months. High temporal resolution analysis of TTDs is used to improve our understanding of the transient flow patterns of RBF systems.