The paper presents character and the scope of changes of the flow on the chosen stretch of the river Wilga in Koźmice Wielki province Małopolska. The place of the research above the river near road culvert in the line of the road number 2032K region Wieliczka. In 2014 culvert was reconstructed by administrator. The technical condition of the object didn’t correspond to applicable regulations for engineering objects of this type. Works included total undressing of the existing structure. Two pipes Ø 1.4 m arranged parallel of direction flow were dismantled. They were replaced with the new culvert about rectangular shape 4 × 2 m. Change of the structure culvert’s, his cross sections, different location the current of the river caused increasing speed of flow of the river’s channel before of culvert, causing erosion of river banks. As a result of the high rate of speed on the exit from the culvert, erosion of the channel is also being observed below of structure. Based on geodetic and hydrodynamic measurements possible causes of such a situation were analysed.