Summary:

In May and June 2010 two extreme floodwaves inuduced by heavy rainfall in Carpathians Mts. have resulted in four levée breachs in mid-Vistula reach and one levée breach in lower reach of the Vistula valley. The basic outline of the flood was presented on the basis of data collected by Institute of Meteorology and Water Management - National Research Institute (IMWM-NRI): total precipitation, stage hydrograms from three water gauges with telemetric system and discharge. The field research was conducted on: all levée breaches were mapped by GPS. Morphology of sub-alluvial basement in the low-Vistula reach was mapped by drilling in the river channel (in the islands, sandy bars and river banks). The data obtained from our field research were compared to results of geological mapping of the river channel carried out in mid-Vistula reach before 2007 by other author. Using GIS-data base we juxtaposed all these data what has revealed adjacent location of all levée breachs to protrusions of sub-alluvial basement. The model of levée breachs process caused by piping in the low-Vistula reach was presented. The influence of the sub-alluvial basements on the underseepage process was discussed with emphasis on geological setting and geomorphology of the floodplain.