Long series of groynes are built from both river sides to narrow river channels and prevent bank erosion with the aim to improve the conditions for inland navigation and prevent lateral channel migration. Single groynes or short series of groynes are built to impede local bank erosion, deviate the water flow, free an intake or fix the position of migrating bars at certain locations. These structures divert the flow towards the opposite river side where channel bed erosion increases the risk of bank failure. Flow and river bed adaptation have been extensively studied, especially for long series of groynes. Instead, studies dealing with opposite bank erosion caused by single or short series of groynes are still lacking. We investigated this phenomenon in the laboratory and using 2D numerical models with LES. This paper shows some preliminary results.