A sand boil at the toe of a river embankment is the surface manifestation of the occurrence of backward erosion piping in the aquifer underlying the flood protection structure. The risk of river embankment failure, and thus flood, greatly increases in sites affected by sand boils, therefore the phenomenon must be prevented as much as possible. Sand boils are routinely detected along many river embankment systems during high water events. The sand boils catalogued in the middle-lower stretch of the Po river are more than 130. A large number of sand boils have been also observed in Hungary, along the Danube river and its tributaries.