headwater streams, fluvial accumulations, grain-size parameters, wet sieving, Digital Gravelometer, macrogranulometric analysis, Outer Western Carpathians

Mountain headwater streams are narrow and relatively steep channels with stream gradient higher than 0.01 m/m (Thompson et al. 2006). Headwater streams are characterised by coarse sediments with variable share of gravel and boulder fraction (Montgomery, Buffington 1997) and, in the area of Outer Western Carpathians, by strong fluctuation of the bed sediments size distribution in the longitudinal profile (Škarpich et al. 2010). Granulometric analysis is a standard tool in the research of fluvial system dynamics and transformation of channel forms. Quantitative grain-size parameters are one of the fundamental information about sediment source, transport history and conditions during accumulation. Resulting grain-size parameter values can be influenced by selected method of granulometric measurement. For the variability determination of the coarse-sediment grain-size parameters in the longitudinal profile of 4 selected headwater streams in flysch Outer Western Carpathians we performed granulometric analysis of channel bars and bed sediments by 3 different methods: wet sieving, optical granulometry (digital photoanalysis) and pebble counts using Wolman (1954) sampling method. Moreover, on 2 of the studied streams, method of 5 largest boulders (Galia, Škarpich 2013) was applied to verify ability of this tool to assess the channel-forming processes and to detect the (dis)connectivity in coarse sediment transport.As compared with results from wet sieving and Wolman (1954) sampling, results obtained by optical granulometry are not variable enough to correctly identify the influence of particular factors (e.g. influence of claystone ratio in bed sediments, character of sediment inputs or human interventions) on the fluctuation of the sediment grain-size parameters in the longitudinal profile. Thus, optical granulometry is not a proper tool for the grain-size analysis of the fluvial sediments in the flysch mountain headwater streams.