Summary:

Size distribution of the river bed material reflects the character and strength of sediment transport and can be used as a variable denoting stability or instability of the channel bed. This paper presents an estimation of grain-size compositions of bed load along the Słomka stream. These size distributions were determined by the photographic method basing on digital analysis of photos of the bed material surface. It is a sufficiently accurate method to analyze the grain size distribution changes. Results of investigations are illustrated by 14 grain-size distributions. It is also showed that variation of characteristic grain diameters and of characteristic parameters along the stream is compatible to the fluvial processes. In some grain-size compositions a percentage gain of fine grains in material corresponds to the local bank erosion, and the others cases are connected with stabilization of the channel sectors.