ABSTRACT. How the floodplain vegetation raises the floodrisk on the river Tisza.With the following article more attention should be drawn to the fact that the impact of the floodplain roughness on the water level is decisive. Some Hungarian studies dealing with this issue are summarised and the most significant statements are lined out. Beside the channel-geometry the hydraulic aproximations play also an important role when modeling a compound channel. With a 2D numerical model a sensitivity analysis was made to study how the floodplain vegetation raises the flood risk. Some general statements were made on how the water level can be decreased with e.g. interventions along the river banks or developing a ‘hydraulic corridor’, a cutoff through the meander.
Key-words: floodplain, risk, Tisza, vegetation, impact