bed sediments, headwater stream, flysch

The ongoing research shows that bedload transport in stepped-bed headwaters underlain by flysch bedrock begins under lower critical conditions, than is usually observed in other environments. A 20- year flood, that occurred in small headwaters (A=0.2-0.4 km2), was able to transport almost all bed material except large boulders with diameters >400 mm. It is the result of a relatively fine sediment supply to the watercourses, significantly decreasing bed roughness in their channels. This fact also leads to frequently observed accelerated incision of mountain streams and larger piedmont rivers flowing on alluvial fans, especially in the case of presence of soft claystone bedrock. We analyzed the coarsest bed fraction in longitudinal profiles of headwater streams with recently prevailing fluvial processes (n=3) and in longitudinal profiles of the streams previously affected by debris flows n=2).