Streszczenie:

The analysis of variability of riverbed elevation recorded at three selected gauging cross-sections: Czchów on the Dunajec River and Olchowice and Rzuchów on the San River is presented in the paper. The studies concern the period of more than one hundred years. The focus is on the analysis of the river course maintenance at selected gauging stations. The research shows that the river course may change spacially and temporally with varying intensity. In the period of 50 - 100 years, these changes can be slight, but permanent changes in the direction of the river channel development can be also observed. The paper presents the trends of riverbed changes during the long period of time of the selected mountain tributaries of the upper Vistula River, which were studied on the basis on the variability of observed mean annual water stages. In the paper there are given the reasons for the observed changes in the river course and channel geometry. These changes were caused by river regulation consisted of the shortening and narrowing of the river channel and the sediment exploitation as well. The method of assessment of the variability of the river channels level in the long period of time presented in the article may be the first step to future research on trends in the river channel and river valleys development.