Summary:

The aim of the paper is to predict a morphological changes of the riverbed on a section of the Skawa River within back-water reach of Świnna Poręba water reservoir. The increasing bed level which is a result of deposition of bed material, have influence on water surface elevation during flood and can threaten surrounding areas. Between spring 2003 and summer 2006 carried out measurements which consist of: survey measurements of a section of Skawa River, granulometric composition of the bed material, velocity profiles and measurements of the water surface elevation during flood events. Prediction of the morphological changes was possible using twodimension CCHE2D model developed by the University of Mississippi. The numerical modeling focused on the simulation of historical flood events, t-year discharges with probability between p=50% and 0.1% under different water levels in the reservoir ranged between 304.56 m a.s.l - without back-water effect and 309.60 m a.s.l. - normal water surface level. The simulation runs included bedload and suspended load transport which caused of bed elevation changes. Back-water reach, where deposition take place, depends on reservoir water surface level can extend up to a distance about 1.5 km. Numerical results of forecasting of fluvial processes on the studied reach yields that exploitation of water reservoir should take into consideration morphological changes within back-water reach of the water reservoir.