Statistical and analytical study of the propagation of flood-induced groundwater rise in an alluvial aquifer

The propagation of stage rises of the river Danube in an adjoining alluvial aquifer (Kisalföld, NW Hungary) has been studied by preparing a map which shows the lag times corresponding to maximum correlation values between the hydrographs of groundwater observation wells and the river stages. As expected, the lag times for the unconfined aquifer generally exceed those for the semi-confined part. The complex pattern suggests that other rivers in the area also play a role and that transmissivities and resistances of a cover layer are not sufficiently well known, despite the presence of a relatively dense network of bore holes. A systematic increase of the lag times with the distance from the river was noted at two sections. Nine flood events have been selected to study how well observed head rises could be predicted using equations for the calculation of the propagation of the head for phreatic and for confined conditions. The results suggest that the water levels in the complex flood plain and the river bed conductance of silted up branches during the rise of the flood play an important role.