mountain stream, grain-size analysis, bed sediments, Wolman method, the Kněhyně Torrent, Moravskoslezské Beskydy Mts

The study deals with relationships between bed sediments of the Kněhyně Torrent and local geometric parameters in selected cross-sections. Downstream grain-size trends are also described. Wolman (1954) methodology was used for the grain-size analysis at 10 locations of 3.9 km long studied longitudinal profile. Additional geomorphic mapping provided information about spatial distribution of sediment sources (i.e., bank failures, gullies and landslides). The grain-size percentiles (D16, D50, D84) were calculated, which were later used as a key factor to identify a change of sediment calibre. In general, these changes of bed grain sizes were caused by anthropogenic impacts, namely by a check dam construction, and a river restoration of downstream part of the studied channel, and by activity of channel-hillslope processes (gullies development, landslides). The results indicated a significant dependence between the parameters of local channel geometry (i.e., bankfull width and channel slope) and bed grain-size. We found out that the anthropogenic factors had a larger effect on resulted bed grain-sizes than natural character of sediment supply.