Prądnik is a stream characterized by a deep cut, narrow valley, poorly developed as an effect of permanent danger coming from a flood. Longitudinal profile of the valley shows gradually decreased bottom fall and in the mean time much slower diminishing hight of the surrounding hills which leads to the particular situation of floods heaving good access to the bottom of the valley. Huge irregularities in the both stream and valley directions as well as in the cross-sections water flow capacities are caused by the difference in the amount of material delivered from slopes and tributaries combined with changing valley bed composition. Dynamic changes in the Prądnik structure are shown by the hydraulical modeling results composed from values of critical and calculated shear stresses, floods capacities calculated for cross-sections of the valley and the stream, water level width, water velocities and valley slopes. Prądnik might be considered as a testing ground for learning the impact of processes capable of making great morphological changes in the structure of the valley and doing it in the short time. Particularly in front of possible intensification of flood events observed currently in Poland it might be useful to track the development of hydrological events of this valley and their impact on the Prądnik’s morphological structure.