Morphological patterns of headwater streams based in flysch bedrock: Examples from the Outer Western Carpathians

• We evaluated a large dataset of channel-reaches coming out from flysch midmountains.
• Bedrock-cascades and step-rapids were added to the employed reach-scale system.
• Channel gradient, bankfull width and an amount of LWD are dependent on the basin area.
• Bankfull depth was recognized as an independent variable in the basin area.
• Downstream coarsening was only observed in alluvial stepped-bed morphologies.

A channel-reach morphology of mountain headwater streams results from the balance between fluvial and hillslope processes. A large dataset (n = 102) of channel-reaches coming out from flysch mid-mountains was evaluated and compared with streams occurring in other environments. Two new channel-reach morphologies were distinguished with respect to their differences in the ratio of sediment supply to transport capacity: bedrock-cascades and step-rapids. The chaining of channel-reach morphologies by gradient criteria and the parameters of channel gradient and bankfull width related to the basin area show similar trends, when compared to other recent studies. By contrast, bankfull depth indicates its independence on increasing basin area. Significant downstream coarsening of bed material occurs only in alluvial stepped-bed morphologies (cascades, step-pools and step-rapids) mainly due to strong slope–channel coupling processes. Moreover, the specific ratio of bankfull width and d90 predicts the interlocking of boulder steps as well as well-developed step-pool morphology. An amount of large woody debris is closely related to the activity of strict local forest management in evaluated channels, as a significant decrease in large woody debris pieces is observed with increasing basin area.